RIKEN
Accelerator
Progress Report
Vol.

国立研究開発法人理化学研究所

仁科加速器科学研究センター

RIKEN Nishina Center for Accelerator-Based Science

54

RIKEN Accelerator Progress Report
Vol.

国立研究開発法人理化学研究所

54

仁科加速器科学研究センター

RIKEN Nishina Center for Accelerator-Based Science
Wako, Saitama, 351-0198 JAPANRIKEN Accelerator Progress Report 2020 Vol. 54
This is an unabridged version of the 54th volume of RIKEN Accelerator Progress Report(hereinafter referred to as APR), the official annual report of the Nishina Center for
Accelerator-Based Science.
A PDF version of APR can be downloaded from our website.
http://www.nishina.riken.jp/researcher/APR/index_e.html

Published by
RIKEN Nishina Center for Accelerator-Based Science
2-1 Hirosawa, Wako-shi, Saitama 351-0198 JAPANDirector of RIKEN Nishina Center for Acclerator-Based Science
Hiroyoshi Sakurai
Editorial Board
H. Ueno (Editor-in-Chief), S. Naimi, D. Suzuki, H. Yamazaki, A. Kohama, E. Hiyama, T. Matsuzaki, R. Seidle, T. Doi,
T. Tada, T. Tamagawa, K. Takahashi, Y. Higurashi, K. Ozeki, T. Sumikama, K. Morimoto, H. Sato, M. Watanabe, T. Ikeda,
I. Watanabe, H. Haba, K. Tsuneizumi, K. Tanaka, Y. Watanabe, H. Nagahama, M. Wada, E. Sugisaki, and I. Yoshida
Contact
Progress@ribf.riken.jp
All rights reserved. This report or any portion thereof may not be reproduced or used in any form, including photostatic
print or microfilm, without written permission from the Publisher.
Contents of the manuscripts are the authors' responsibility. The Editors are not liable for the content of the report.
RIKEN Nishina Center for Accelerator-Based Science, September 2021

PREFACE
The RIKEN Accelerator Progress Report isthe annual report of all the research activities conducted at the RIKEN Nishina Center for Accelerator-Based Science (RNC). This
volume, No. 54, covers the activities conducted during the Japanese ﬁscal year of 2020
(i.e., April 2020 to March 2021).
Last December, the news of the sad demise ofProf. Dr. Akito Arima, who passed away on
December 6, 2020, became widespread worldwide. As many people know, he was a distinguished physicist of the nuclear structure theory. As one of the top administrators of universities and institutes, he contributed toward thepromotion of academic activities in the ﬁeld of
science and technology; he was also a politicianof the House of Councilors and ministers of the government. He was the President of RIKEN from 1993 to 1998;
during this period, he launched three major research activities at the current RNC: realizing the RI Beam Factory(RIBF) project, and establishing the RAL branch oﬃce for muon sciences and the RIKEN BNL Research Center(RBRC) for high-energy nuclear physics. Following the commencement of its operation in 2007, the RIBF has
become one of the best facilities worldwide for low-energy nuclear physics. I was incredibly happy to present him
with the achievements of the RIBF at the conference in Shanghai in 2018, as a celebration of his 88th birthday.
Furthermore, he also encouraged international relationships with Asian countries, especially China and Vietnam,
and signiﬁcantly improved research collaboration. At the RNC Monthly Meeting held on December 9, 2020, all
the RNC members oﬀered a silent prayer in view of his considerable achievements and contributions. As a person,
he was known for his ﬁrm philosophy and humanity; he loved nature, physics, and the youth. At this occasion,
I would like to oﬀer my deepest condolences and also express my sincere respect for his guidance across a wide
range of ﬁelds.
In 2020, the world was aﬀected by the COVID-19 pandemic. Consequently, given that the coronavirus is carried and spread by people, people’s activities have been severely restricted. Nevertheless, personal relationships
remained intact owing to advances in the Internet. As a result, many discoveries pertaining to human communication through various online/virtual activities have been reported. For instance, all the PAC meetings in
FY2020 were organized remotely. Furthermore, certain symposia and workshops were conducted in a hybrid stylecombining in-person and online communications.
Onsite activities, where people and things/facilities interact, form the essence of technological development andexperimental research. It is, therefore, considerably important to implement measures for preventing the spreadof the coronavirus. At the RIBF, we were able to avoid a divide between people and things/facilities, while
sustaining the research activities. Local and domestic staﬀ members realized achievements in terms of developing
facilities and conducting experiments. One such achievement is the upgrade of the RILAC (SRILAC) and thecomplete installation of GARIS-III; this represents the completion of the preparation for moving forward withnovel research. Furthermore, we succeeded in increasing the 70 Zn and 238 U beam intensities at the SRC, thus
realizing a high-intensity beam for the HiCARI campaign using “tracking” germanium detectors and the massmeasurement of many unknown nuclei during the MR-TOF experiment performed in parallel.
However, onsite research activities were still stagnant, given the restrictions on people traveling across borders
and overseas. This resulted in a divide between people and things/facilities at the overseas research facilities of
the RHIC and RAL and the joint international research at the RIBF.
Seventeen press releases were issued in FY2020, and selected achievements of 2020 are compiled in the “Highlightsof the Year” section of this volume. These indicate the growing multi-disciplinary activities at the RNC for
science, technology, and innovation. It should be noted that these achievements were made not only by in-house researchers and engineers at the RNC but also by collaborating users at the RIBF, RBRC, and RAL. The
paper titled “Surface localization of the dineutron in 11 Li,” which was published in Physical Review Letters, is a
result of the first spectroscopy with fully completed kinematics measurements conducted at SAMURAI in orderto demonstrate the dineutron component in 11 Li. With regard to heavy-ion beam breading, the paper titled“Improvement of rotifer as the new food item in larviculture” had a significant impact on the society, and theresults were featured as “Godzilla the rotifer” in the Economist magazine issued January 23, 2021.
Awards were also presented to the colleagues of the RNC. Takahiro Nishi was presented with the 17th Annual
Meeting Award of the Particle Accelerator Society of Japan, and Takashi Ichihara was presented with the 2020
JPCERT/CC Certificate of Gratitude, JPCERT Coordination Center. Furthermore, the Nishina Memorial Prize
was awarded to Kazuma Nakazawa, a visiting scientist at the Strangeness Nuclear Physics Laboratory.
With regard to the organization of the RNC, Hiroyuki Ichida and Masanori Kidera were appointed as the Team
Leaders of the Plant Genome Evolution Research Team and the Infrastructure Management Team, respectively,
as of October 2020.
The coronavirus crisis is expected to continue even after 2021. Nevertheless, we are extremely grateful to be
blessed with an environment that allows us to continue with our research. Hence, it is vital that we acknowledge
the mission of RIKEN and aggressively accept new challenges in research and development activities.

Hiroyoshi Sakurai
Director
RIKEN Nishina Center for Accelerator-Based Science

CONTENTS

RIKEN Accel. Prog. Rep. 54 (2021)

C O N T E N T S
PagePREFACEGRAVUREFEATURE ARTICLEFirst Beam from SRILAC ··················································································································S1

Ⅰ. HIGHLIGHTS OF THE YEAR
Oblate shapes and metastable states of 92, 94Se ···························································································
P. -A. Söderström et al.

S13

Properties of 187Ta revealed through isomeric decay ···················································································P. M. Walker, Y. Hirayama, et al.

S14In-gas-cell laser resonance ionization spectroscopy of 196, 197, 198Ir ····································································
M. Mukai et al.

S15

Fragmentation of single-particle strength around the doubly-magic nucleus 132Sn and the position of the 0f5/2 proton-holestate in 131In ····························································································································
V. Vaquero et al.

S16

Experimental studies of the two-step scheme with an intense radioactive 132Sn beam for next-generation production ofvery neutron-rich nuclei ·············································································································
H. Suzuki et al.

S17

On-line commissioning of the new SLOWRI/ZD-MRTOF system ··································································
M. Rosenbusch et al.

S18

Mapping of a new deformation region around 62Ti ·····················································································
S. Michimasa et al.

S19

Surface localization of the dineutron in 11Li ·····························································································
Y. Kubota et al.

S20

Probing alpha clusters in the low-density region of the nuclear surface ·····························································J. Tanaka, Z. H. Yang, et al.

S21

Reaction cross sections on a deuteron as a probe of nuclear radii ····································································
W. Horiuchi et al.

S22

Mean-square radius of the neutron distribution and skin thickness derived from electron scattering ···························
H. Kurasawa et al.

S23

Isotopic production of high-radiotoxic nuclide 90Sr via proton- and deuteron-induced reactions ································
R. Matsumura et al.

S24

CP-odd gluonic operators in QCD spin physics ························································································
Y. Hatta

S25

Start the operation of AVF-BIS and its performance evaluation as a successor system to BIS···································
M. Komiyama et al.

S26

HiCARI: High-resolution Cluster Array at RIBF ·······················································································
K. Wimmer et al.

S27

Removing non-isobaric ions from an MRTOF-MS by periodic electric pulses ····················································S. X. Yan, M. Rosenbusch, et al.

S28

Development of the gaseous Xe scintillation detector for heavy RI beams ·························································
Y. Hijikata et al.

S29

μSR study of slightly pressurized organic superconductor κ-(ET)4Hg2.89Br8 ························································
D. P. Sari et al.

S30

Targeted alpha therapy of cancer: Evaluation of [211At] AAMT targeting LAT1 ···················································
K. Kaneda-Nakashima et al.

S31

Influence of antibody stabilization with sodium ascorbate on radioimmunotherapy with an 211At-conjugatedanti-tissue factor antibody ···········································································································
H. Takashima et al.

-5-

S32

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RIKEN Accel. Prog. Rep. 54 (2021)

Kinetics of Rad51 foci in G2 phase after heavy-ion irradiation in mammalian cells···············································
M. Izumi and T. Abe

S33

Improvement of rotifer as the new food item in larviculture···········································································
K. Tsuneizumi et al.

S34

Ⅱ. RESEARCH ACTIVITIES I (Nuclear, Particle and Astro-Physics)
1. Nuclear Physics
RI beam production at BigRIPS in 2020··································································································
H. Takeda et al.
Production cross-section measurement and new-isotope search for very-neutron-rich RIs produced from 70Zn beamat 345 MeV/nucleaon by BigRIPS separator······················································································
H. Suzuki et al.

1

2

N = 32 shell closure below calcium: Low-lying structure of 50Ar·····································································
M. L. Cortés et al.

3

Proton removal and lifetimes in the Ca isotopes: Spectroscopy and reaction studies··············································
H. L. Crawford et al.

4

Evolution of collectivity in Ti isotopes towards the N = 40 island of inversion·····················································
T. Koiwai, K. Wimmer, et al.

5

RIBF190: Exploring collectivity beyond 78Ni····························································································
F. Browne, V. Werner, et al.

6

Neutron intruder states and collectivity beyond N = 50 towards 78Ni·································································
F. Flavigny et al.

7

High-resolution spectroscopy and lifetime measurements in neutron-rich Zr and Mo isotopes···································
W. Korten et al.

8Single particle structure of semi-magic 129Ag82··························································································
T. Parry et al.

9Characterization of a strongly Coulomb-excited state at an excitation energy above 4 MeV in 136Te····························
A. Jungclaus et al.

10

Study of the 9C proton breakup reaction··································································································
A. I. Chilug et al.

11

Gamow-Teller giant resonance in 11Li neutron drip-line nucleus······································································
L. Stuhl et al.

12

One proton removal cross section of 25F with a carbon target··········································································
Y. Yoshitome et al.

13

Particle identification of SAMURAI11 experiment·····················································································
J. Gao et al.

14

Symmetry energy investigation with pion production from Sn + Sn systems························································
G. Jhang et al.

15

Proton efficiency function for high-multiplicity events in the SπRIT-TPC investigated by the embedding technique········
M. Kaneko et al.

16

Observation of anisotropic collective flow of charged particles and neutrons in heavy-ion collisions at beam energies
of 400 MeV/nucleon··················································································································
S. Yamamura et al.

17

Measurement of proton elastic scattering from 132Sn at 300 MeV/nucleon in inverse kinematics································
T. Harada et al.

18

Results on the β decay of 60Ge and 62Ge measured at RIBF············································································
S. E. A. Orrigo et al.

19

On the β-decay of 70Kr·······················································································································
A. Vitéz-Sveiczer et al.

20

Measuring β-decay strength distribution in the 78Ni region using VANDLE························································
M. Singh et al.

21

Constraining multi-neutron emission models with spectroscopy of neutron-rich Ga isotopes using BRIKEN array··········
R. Yokoyama et al.

22

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RIKEN Accel. Prog. Rep. 54 (2021)

Spectroscopy of 99Cd and 101In from β decays of 99In and 101Sn········································································
J. Park et al.

23

Total absorption γ-spectroscopy study of the beta decay of 100Sn·····································································J. A. Victoria et al.

24

Shape evolution of 106, 108, 110Mo in the triaxial degree of freedom·····································································
J. Ha et al.

25

Evolution of proton single-particle states in neutron-rich Sb isotopes beyond N = 82·············································
A. Jungclaus et al.

26

BRIKEN measurements of Pn-values and half-lives for understanding the formation of the r-process rare-earth peak:
progress on the Ce to Nd region·····································································································
A. Tarifeño-Saldivia et al.

27

Precision measurement of ground-state electric quardrupole moment for neutron-rich 21O·······································
A. Gladkov et al.

28

Investigations of magnetic moments in Coulomb fission···············································································
G. Häfner et al.

29

Re-measurement of the 4He(8He, 8Be) reaction··························································································
S. Masuoka et al.

30

Alpha-decay correlated mass measurement of 206, 207Ra using an MRTOF-MS system equipped with an α-TOF
detector ·································································································································
T. Niwase et al.

31

First high-precision direct determination of the atomic mass of a superheavy nuclide·············································
P. Schury, T. Niwase, et al.

32

β-decay spectroscopy of 187Ta··············································································································
M. Mukai et al.

33

β-γ Spectroscopy of 192Re···················································································································
H. Watanabe et al.

34

Insight into the reaction dynamics of proton drip-line nuclear system 17F + 58Ni at near-barrier energies·······················
L. Yang et al.

35

2. Nuclear Physics (Theory)
Dineutron and effective pairing forces in momentum space···········································································
M. Yamagami

37

Structure of 12C studied by the no-core Monte-Carlo shell model·····································································
T. Abe et al.

38

Double charge-exchange phonon states···································································································
X. Roca-Maza et al.

39

Exotic nuclear shape due to cluster formation at high angular momentum··························································
B. Dey et al.

40

Probing dilute nuclear density by antiproton-nucleus scattering······································································
K. Makiguchi et al.

41

Nuclear charge radii with a trained feed-forward neural network·····································································
Di Wu, C. L. Bai, et al.

42

Effects of finite nucleon size, vacuum polarization, and electromagnetic spin-orbit interaction on nuclear binding
energies and radii in spherical nuclei·······························································································
T. Naito, X. Roca-Maza, et al.

43

Trajectory in 2D plot of IS and IV densities of 48Ca and 208Pb·········································································
S. Yoshida, H. Sagawa, et al.

44

Energy-weighted sum rule for Gamow-Teller giant resonances in high-spin isomeric states of N = Z nuclei··················
M. Sasano et al.

45

A fully microscopic model of total level density in spherical nuclei··································································
N. Quang Hung et al.

46

Isobaric analog state energy in deformed nuclei: A toy model ········································································
X. Roca-Maza et al.

47

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RIKEN Accel. Prog. Rep. 54 (2021)

Parity-conserved self-consistent CHFB solution························································································
K. Sugawara-Tanabe and K. Tanabe

48

Role of exact treatment of thermal pairing in radiative strength functions of 161, 163Dy nuclei·····································
L. Tan Phuc et al.

49

Non-relativistic expansion of Dirac equation by the reconstituted Foldy-Wouthuysen transformation··························Y. X. Guo and H. Z. Liang

50

On the role of three-particle interactions in nuclear matter·············································································
W. Bentz and I. C. Cloët

51

A3-Foresight theory collaboration for nuclear data library: A3LIB···································································
K. Yoshida52

3. Nuclear Data
EXFOR compilation of RIBF data in 2020·······························································································
T. Tada et al.

53

4. Hadron Physics
Transverse momentum dependence of forward neutron single spin asymmetries in polarized p↑ + p collisionsat √ s = 200 GeV······················································································································
B. Mulilo et al.

55

Transverse single-spin asymmetry for very forward neutral pion production in polarized p + p collisionsat √ s = 510 GeV······················································································································M. H. Kim et al.

56

Transverse single spin asymmetry in charged pion production at midrapidity in polarized p + p collisions at 200 GeV······J. H. Yoo et al.

57

Improvement of the DCA resolution for PHENIX······················································································
G. Nukazuka et al.

58

Recent progress of polarized Drell–Yan experiment at Fermilab,SpinQuest (E1039)··············································
K. Nagai et al.

59

Measurement of J/ψ productions in p + d and p + p at SeaQuest······································································
K. Nakano et al.

60

Expression of interest for EIC-Japan······································································································
Y. Goto et al.

61

Semi-inclusive deep inelastic scattering at the Electron Ion Collider·································································
R. Seidl

62

Bus-extender development for sPHENIX INTT detector···············································································
T. Hachiya et al.

63

5. Hadron Physics (Theory)
Non-global logarithms in hadron collisions at Nc = 3···················································································
Y. Hatta and T. Ueda

65

Veriﬁcation of the QED tenth-order electron g − 2:Diagrams without a fermion loop··············································
A. Hirayama and M. Nio

66

6. Particle Physics
Time development of conformal ﬁeld theories associated with L1 and L−1 operators···············································
T. Tada67

Study of Lorentzian sine-square deformed CFT·························································································
X. Liu and T. Tada

68

Empirical formulas for the standard-model parameters·················································································
Y. Akiba

69

Quarternion-spin-isospin model for the standard-model parameters··································································
Y. Akiba

70

R = 12H02 and its implications to gravity and cosmology··············································································
Y. Akiba

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7. Astrophysics and Astro-Glaciology
A novel high-resolution laser-melting sampler for discrete analyses of ion concentrations and stablewater isotopic compositions in firn and ice cores·················································································
Y. Motizuki et al.
Annually resolved d-excess record from a shallow ice core (DFS10) near Dome Fuji station, East Antarctica················
Y. V. Sahoo et al.

73
74

8. Accelerator
High-intensity vanadium-beam production to search for a new super-heavy element with Z = 119·····························
T. Nagatomo et al.

75

R&D in AVF cyclotron······················································································································
J. Ohnishi et al.

76

Charge stripper ring for RIKEN RI beam factory·······················································································
H. Imao77

2020 operational report for the Nishina RIBF water-cooling system·································································
T. Maie, E. Ikezawa, et al.

78

Status of vacuum pumping systems in accelerator facilities···········································································
Y. Watanabe et al.

79

9. Instrumentation
Development of 216Th and 220Th beams at the BigRIPS separator·····································································
N. Fukuda et al.
BYACO ecosystem for innovative online operation of BigRIPS experiments with seamless connection tocomprehensive analysis···············································································································
T. Sumikama et al.

81

82

Development of auto-focusing and auto-centering system for the BigRIPS separator·············································
Y. Shimizu et al.

83

Thermo-mechanical simulation of high-power rotating target for BigRIPS separator·············································
K. Yoshida and Y. Yanagisawa

84

Incidents involving the DMT3 magnet in the beam transport line from SRC to BigRIPS·········································
K. Kusaka et al.

85

Trace-back method for dispersion matching conditions of primary beams at RIBF················································
A. Sakaue et al.

86

Conceptual design of a heavy ion storage ring RUNBA················································································
M. Wakasugi et al.

87

Development of Resonant-Extraction Charge Breeder (RECB)·······································································R. Ogawara et al.

88

Development of a forward detector for the measurement of the mean square radius of the neutron distributionof unstable nuclei by electron scattering···························································································
H. Wauke et al.

89

Ion-beam-profile monitor using MCP at the SCRIT electron scattering facility····················································
T. Ohnishi et al.

90

Extraction test of stopped Bi isotopes in PALIS gas cell···············································································
T. Sonoda et al.

91

Improvement of evacuation time of RI from argon gas cell············································································
T. Sonoda et al.

92

Fourth report on offline tests for RF carpet transportation in RF ion guide gas cell at the SLOWRI facility···················
A. Takamine et al.

93

High mass resolving power and isomeric state separation at SLOWRI/ZD-MRTOF system·····································
W. Xian, M. Rosenbusch, et al.

94

Offline ion source for laser spectroscopy of RI at SLOWRI···········································································
M. Tajima et al.

95

Temperature and pressure dependence of ion extraction from RF gas cell···························································
D. Hou, A. Takamine, et al.

96

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Degrader optimization for ZeroDegree gas cell··························································································
S. Chen et al.

97

Online extraction efficiency from RF ion guide gas cell at SLOWRI·································································
S. Iimura et al.

98

Development of MCP timing detector for low-energy heavy ions····································································
T. T. Yeung et al.

99

Improvement of kicker system for rare-RI ring··························································································
Y. Yamaguchi et al.

100

Improved position resolution of the beam diagnostics detector for the Rare-RI Ring··············································
G. Hudson-Chang, S. Naimi, et al.

101

Computer server and network for HiCARI experiments················································································
H. Baba et al.

102

Development of a high-bandwidth waveform processing system using RFSoC····················································S. Takeshige et al.

103

GPU acceleration of SAMURAI particle tracking simulation·········································································
J. Gao104

Observation of Rb D1 fluorescence in superfluid helium using picosecond time-resolved detection····························Y. Takeuchi et al.

105

Development of ion trap system for the neutralizer toward production of spin-polarized RI beam using atomic
beam magnetic resonance method···································································································
K. Imamura et al.

106

Status of the J-PARC E16 experiment in 2020···························································································
S. Yokkaichi et al.

107

Construction of GEM Tracker for J-PARC E16 experiment Run0-a··································································T. N. Murakami et al.

108

Performance evaluation of the electron identification system for the J-PARC E16 experiment···································S. Nakasuga et al.

109

Intermediate silicon tracker for sPHENIX experiment at RHIC·······································································
I. Nakagawa et al.

110

Detection efficiency of the INTT test bench for sPHENIX·············································································
G. Nukazuka et al.

111

Radiation resistance of bus extender cable for sPHENIX-INTT······································································
H. Imai et al.

112

Electrical and mechanical properties of the bus-extender··············································································
M. Morita, Y. Akiba, et al.

113

Upgrade of the Si-CsI array TiNA for transfer reactions at OEDO···································································
B. Mauss, J. W. Hwang, et al.

114

Heat durability test of molybdenum foil for the new CRIB cryogenic gas target···················································
S. Hayakawa et al.

115

Radiation resistivity test of an optical fiber for laser cooling of francium atoms····················································
T. Hayamizu et al.

116

Development of novel detection system for francium ions extracted from online surface ionizer································
N. Ozawa et al.

117

Experiment on hydrogen removal apparatus for helium supply and recovery system··············································
M. Nakamura et al.

118

Safety interlock system for LINAC building·····························································································
A. Akashio et al.

119Computing and network environment at the RIKEN Nishina Center·································································
T. Ichihara et al.

120

CCJ operations in 2020······················································································································
S. Yokkaichi et al.

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Ⅲ. RESEARCH ACTIVITIES II (Material Science and Biology)
1. Atomic and Solid State Physics (Ion)
Control of electrical conductivity in diamond by boron-implantation using an ECR ion source—application ofhigh-temperature and high-pressure annealing····················································································
H. Yamazaki et al.

123

Single-event effects in SiC planar and trench power MOSFETs······································································
M. Iwata et al.

124

Profile measurements of dual-microbeams generated by glass capillaries···························································
M. Mori et al.

125

2. Atomic and Solid State Physics (Muon)
Partial order of conduction electrons in Mn3CoSi·······················································································
S. Shamoto, D. P. Sari, et al.

127

Magnetism and superconductivity in underdoped region of T*-type La1−x/2Eu1−x/2SrxCuO4−yFy····································
M. Takahama et al.

128

Spin dynamics in Pyrochlore Nd2Mo2O7··································································································
L. J. Chang et al.

129

Possible multipolar ordering in spin-orbital-entangled d 2 system on a face-centered-cubic lattice·······························
T. Takayama et al.

130

Successive Transitions in Spin-dimer Compound Cs3V2Cl9············································································
H. Kikuchi et al.

131

Magnetism of novel heavy fermion compound YbCu4Ni investigated by μSR······················································
T. Taniguchi et al.

132

ZF-μSR measurement to investigate thermal hysteresis of MgTi2O4 at low temperature··········································
U. Widyaiswari et al.

133

Observation of Cu spin fluctuations in over-doped regime La2-xSrxCuO4 nanoparticles············································
S. Winarsih et al.

134

The electron transfer channel in the sugar recognition system assembled on gold nano particles································
T. Goto et al.

135

Antiferromagnetic ordering of λ-(BEST)2FeCl4 observed by µSR measurement···················································
T. Kobayashi et al.

136

Zero-ﬁeld µSR on the out-of-plane superconductivity of λ-(BETS)2GaCl4··························································
D. P. Sari et al.

137

Li-ion di usion in LiFeSixP1−xO4/C with x =0 and 0.03··················································································
F. Astuti et al.

138

Measurement of muon spin rotation in muonic hydrogen atom·······································································
S. Kanda and K. Ishida

139

A LYSO calorimeter prototype for muonic X-ray detection···········································································
S. Kanda and K. Ishida140

3. Radiochemistry and Nuclear Chemistry
Production of 266Bh in the 248Cm(23Na, 5n)266Bh reaction and its decay properties··················································
H. Haba et al.
Measurement of the isotopic ratio of Np-236 to Np-237 in Th-232 + Li-7 reaction products by accelerator mass
spectrometry··································································································································
A. Nakajima et al.
Production and photon measurement of 229Pa toward the observation of radiative decay of 229mTh······························
Y. Shigekawa et al.
Measurement of extraction time and e ciency of 220Rn ions using a cryogenic RF-carpet gas cell for the chemistryof superheavy elements···············································································································
Y. Shigekawa et al.
Anion-exchange behavior of Db in HF/HNO3 solution·················································································
M. Kato et al.

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143

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Anion exchange of Rf in H2SO4 using the batch-type solid-liquid extraction apparatus AMBER································
T. Yokokita et al.

148

Online anion-exchange experiment of Zr in H2SO4 for the chemical study of Rf in H2SO4·······································
T. Yokokita et al.

149

Solvent extraction of Zr and Hf from HCl by Aliquat 336 using a ﬂow-type extraction apparatus toward online
chemical studies of element 104, rutherfordium··················································································
Y. Kasamatsu et al.

150

Cation- and anion-exchange behavior and UV-vis spectroscopy of Zr in HBr for chemical characterization ofbromide complexes of Rf·············································································································
T. Yokokita and H. Haba

151

Solvent extraction of Fr and Cs with calix[4]arene-bis(benzocrown-6)······························································
Y. Komori and H. Haba

152

Solvent extraction and speciation of astatine species via thin layer chromatography··············································
S. Maruyama et al.

153

Ru and 57Fe Mössbauer spectroscopic studies of Na2Ru1−xFexO3 of sodium-ion battery electrode (2)·························
K. Hamano et al.

154

Targeted alpha therapy for thyroid cancer: Radiation-induced toxicity of [211At]NaAt in mice···································
Y. Liu et al.

155

Quality conﬁrmation of RIKEN 186Re using bifunctional chelating agents and derivatives·······································S. Oshikiri et al.

156

Complex formation of Rhenium-186 with lipophilic ligands —Comparison with technetium-99m—··························I. O. Umeda et al.

157

Simultaneous imaging of Na+/K+ by semiconductor Compton camera GREI·······················································S. Motomura et al.

159

Development of image reconstruction method for a multiple-isotope PET using 44mSc············································
T. Fukuchi et al.

160

Double photon emission nuclides for double photon coincidence imaging··························································
H. Takahashi et al.

161

Production cross sections of 225Ac in the 232Th(14N, xnyp) reactions at 116 and 132 MeV/nucleon·······························
X. Yin et al.

162

Cross sections of alpha-particle-induced reactions on natNi: Production of 67Cu····················································S. Takács et al.

164

Production cross sections of 68Ga and radioactive by-products in deuteron-induced reactions on natural zinc·················
Ts. Zolbadral et al.

165

Activation cross section measurement of the deuteron-induced reaction on yttrium-89 for zirconium-89 production········
M. Sakaguchi et al.

166

Excitation functions of deuteron-induced reactions on 141Pr for medical radioisotope production·······························
M. Aikawa et al.

167

Production cross sections of medical radioisotope 153Sm in alpha-particle-induced reaction on natural neodymium··········
M. Sakaguchi et al.

168

Production cross sections of 155Tb in deuteron-induced reactions on natural gadolinium··········································
D. Ichinkhorloo et al.

169

Production cross sections of natEr(d, x)171Er reactions on natural erbium·····························································
M. U. Khandaker and H. Haba

170

Measurement of production cross sections of 175Hf in the natLu(p, x) and natLu(d, x) reactions····································
Y. Komori et al.

171

99

4. Radiation Chemistry and Biology
Selection of high-yield rice mutant induced by heavy-ion beam irradiation ························································
Y. Hayashi et al.
Whole genome sequencing analysis for detecting mutations induced by carbon- and argon-ion irradiations ofrice (Oryza sativa L.)·················································································································
R. Morita et al.

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Detection of structural variations in three responsible genes induced by relatively high-LET ion beams in rice··············
Y. Shirakawa et al.

175

Dose-dependent mutagenic effects of 160-MeV/nucleon-argon beam in Arabidopsis thaliana··································
K. Ishii et al.

176

Argon-ion-induced mutant of Arabidopsis thaliana exhibiting accelerated leaf chlorosis·········································
A. Sanjaya et al.

178

Effect of heavy-ion irradiation on survival rate of Torenia fournieri··································································
A. Matsuta et al.

179

Behaviors of the Saprophytic Tricholoma matsutake Mutants G1 and Ar 59 In Vitro Substrate Cultivation: the former
exhibited Morphological Changes while the latter did not·······································································
H. Murata et al.

180

Ⅳ. OPERATION RECORDS
Program Advisory Committee meetings for nuclear physics and for materials and life sciences·································
H. Ueno et al.

181

Electric power status of RIKEN Nishina Center in 2020···············································································
E. Ikezawa et al.

182

RILAC operation·····························································································································
K. Oyamada, E. Ikewaza, et al.

183

Operation report on the ring cyclotrons in the RIBF accelerator complex···························································
S. Ishikawa et al.

184

Operation report on the RIKEN AVF cyclotron for 2020···············································································
M. Nishida et al.

185

Present status of liquid-helium supply and recovery system···········································································
T. Dantsuka et al.

186

Operation of the BigRIPS cryogenic plant·······························································································
K. Kusaka et al.

187

Radiation safety management at RIBF····································································································
K. Tanaka et al.

188

Operation of the Pelletron tandem accelerator···························································································
T. Ikeda et al.

190

Fee-based activities of the Industrial Application Research Team····································································
A. Yoshida et al.

191

Activity report of the second-term (2014–2021) RIBF Theory Forum·······························································
T. Abe et al.

192

Ⅴ. EVENTS
Symposium on Nuclear Data 2020········································································································
H. Otsu et al.

195

The 8th Asia-Pacific Conference on Few-Body Problems in Physics (APFB2020)················································
E. Hiyama et al.

196

Domestic Workshop on Spin Physics······································································································
Y. Goto et al.

197

Ⅵ. ORGANIZATION AND ACTIVITIES OF RIKEN NISHINA CENTER(Activities, Members, Publications & Presentations)
Organization
1. Organization Chart ·················································································································

199

2. Finances······························································································································

200

3. Staffing·······························································································································

200

4. Research publication···············································································································

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5. Management·························································································································

202

6. International Collaboration········································································································

206

7. Awards·······························································································································

207

8. Brief overview of the RI Beam Factory·························································································

209

Center Director·······························································································································

211

Laboratories
Nuclear Science and Transmutation Research Division
Radioactive Isotope Physics Laboratory···························································································

213

Spin isospin Laboratory··············································································································

220

Nuclear Spectroscopy Laborarory···································································································

227

High Energy Astrophysics Laborarory·····························································································

232

Superheavy Element Research Group······························································································

238

Superheavy Element Production Team·······················································································

240

Superheavy Element Device Development Team··········································································

243

Astro-Glaciology Research Group··································································································

245

Nuclear Transmutation Data Research Group·····················································································

247

Fast RI Data Team··············································································································

248

Slow RI Data Team·············································································································

250

Muon Data Team················································································································

252

High-Intensity Accelerator R&D Group····························································································

254

High-Gradient Cavity R&D Team····························································································

255

High-Power Target R&D Team·······························································································

256

Research Facility Development Division
Accelerator Group·····················································································································

257

Accelerator R&D Team········································································································

259

Ion Source Team················································································································

260

RILAC Team····················································································································

261

Cyclotron Team·················································································································

262

Beam Dynamics & Diagnostics Team·······················································································

263

Cryogenic Technology Team··································································································

265

Infrastructure Management Team·····························································································

266

Instrumentation Development Group·······························································································

268

SLOWRI Team··················································································································

270

Rare RI-ring Team··············································································································

273

SCRIT Team·····················································································································

275

Research Instruments Group·········································································································

277

BigRIPS Team···················································································································

278

SAMURAI Team················································································································

281

Computing and Network Team································································································

283

Detector Team···················································································································

285

Accelerator Applications Research Division
Beam Mutagenesis Group············································································································

287

Ion Beam Breeding Team······································································································

288

Plant Genome Evolution Research Team····················································································

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RIKEN Accel. Prog. Rep. 54 (2021)

RI Application Research Group·····································································································

293

Nuclear Chemistry Research Team···························································································

294

Industrial Application Research Team·······················································································

300

Subnuclear System Research Division
Quantum Hadron Physics Laboratory······························································································

301

Strangeness Nuclear Physics Laboratory···························································································

306

Radiation Laboratory··················································································································

309

Meson Science Laboratory···········································································································314

RIKEN BNL Research Center·······································································································

319

Theory Group····················································································································

320

Experimental Group············································································································

324

Computing Group···············································································································329

RIKEN Facility Offce at RAL·······································································································

334

Safety Management Group···········································································································

338

User Liaison Group···················································································································

340

RIBF User Liaison Team·······································································································

341

Outreach Team··················································································································

342

Office of the Center Director·········································································································

343

Partner Institutions···························································································································

347

Center for Nuclear Study, Graduate School of Science, The University of Tokyo···········································

348

Wako Nuclear Science Center, IPNS (Institute of Particle and Nuclear Studies),
KEK (High Energy Accelerator Research Organization)··································································

358

Ⅶ. APPENDICES
Symposia & Workshops·····················································································································

361

Seminars·······································································································································

362

Events··········································································································································

367

Press Releases ································································································································

368

Preprints ······································································································································

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CONTENTS

RIKEN Accel. Prog. Rep. 54 (2021)- 16 -

FEATURE ARTICLE

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

First Beam from SRILAC

RILAC upgrade
overview

project—Background

and

RILAC and beam intensity to initiate the project ofsynthesizing the new element.
Large accelerator facilities have contributed to society in the recent year in addition to promoting basic
science such as research on super heavy element (SHE).
At RIBF, several eﬀorts have been invested in producing and distributing radioisotopes for research. Oneof the most popular isotopes is 211 At, and its production using AVF cyclotrons is being actively pursued for
future medical applications.10) 211 At has a short halflife of approximately 7 h, and a high-intensity beamof particles is essential for mass production. However,
the technology for the mass production of 211 At has
not been established. Therefore, the establishment ofa technology for the mass production of useful isotopes
has been added to the objectives of the RILAC upgrade
plan.
The RILAC upgrade project (Fig. 1), which aims tosynthesize new elements and develop technology for themass production of useful radioisotopes, was approved
with a supplementary budget in FY2016. Indeed, thisenhancement plan will lead to a considerably higher
intensity of the beam to the RRC, especially the metal
ion beam, compared to that before.
The target performance expected in this upgrade
program is to accelerate ions with M/q = 6 to E =6.5 MeV/nucleon at more than 2.5 particle µA. To
achieve this goal, we ﬁrst built a new ion source. The
structure of the ion source is almost identical to the

The synthesis and naming of the 113th element, nihonium, is one of RIKEN’s most noteworthy achievements; further, it has had a social impact in that the
new element from Japan was added to the periodic
table of elements.1–3) This element was produced by
the RIKEN heavy-ion linac (RILAC),4) which has beenin operation since 1980 as an injector to the RIKEN
ring cyclotron (RRC) and for stand-alone applications
such as those in atomic physics. In 1996, RILAC was
upgraded to increase the beam intensity in RRC,5–7)
and in 2001, a booster linac 8) was installed as part of
the RI Beam Factory (RIBF) project 9) under ﬁnancial support from CNS, the University of Tokyo. Thisﬁnal step allowed nuclear physics experiments to be
conducted in the RILAC facility.
Following the success of nihonium, research collaborations led by RIKEN scientists have set the next
project of synthesizing new elements of atomic numbers greater than 118. To this end, metal ion beams
such as vanadium and chromium need to be accelerated. However, the production cross section is expected to drop to less than a quarter of that for producing nihonium, and therefore, beam intensities need
to be increased. In addition, it was estimated that theacceleration energy will need to be increased. Therefore, we need to increase the acceleration voltage of

Fig. 1. Overview of RILAC upgrade project. 18-GHz ECRIS was replaced by R28G-K, and a downstream
part of RILAC was replaced by SRILAC.

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FEATURE ARTICLE

RIKEN Accel. Prog. Rep. 54 (2021)

28-GHz superconducting electron cyclotron resonanceion source (SC-ECRIS) that has been operational since2010.11) There is a risk of damage to SC cavities inthe downstream caused by the high-intensity beams.
Therefore, we decided to limit the emittance in the
low energy beam transport (LEBT) section up to theradio frequency quadrupole (RFQ) by measuring thebeam emittance eﬀectively.
Second, we replaced the last four normal conducting
cavities in the RILAC booster with ten SC cavities toincrease acceleration energy. Quarter-wavelength resonators (QWRs) were used as the SC cavities. A frequency of 73.0 MHz, which is four times the fundamental frequency of the RIBF, was selected for the SC cavities. This frequency is selected considering its futureapplication as an RIBF injector. For the SC-QWR,
we developed a 75.5 MHz QWR that cooperates with
KEK under the ImPACT program since FY2014.12)
This experience has been of great help in the upgrade
project.
In addition to the ion source, SC cavities, and refrigerator, test facilities of the cavities and a new hotlaboratory building for processing radioisotopes wereconstructed. Further, a gas-ﬁlled recoil ion separator(GARIS) -II was moved from the RILAC facility to theE6 room in the Nishina Memorial Building to start theSHE experiments as soon as possible.13) Meanwhile,
the RRC resonator was modiﬁed to solve the problem
of insuﬃcient voltage at the RRC,14) which had beena bottleneck in increasing beam intensity. This modiﬁcation greatly contributed to the large increase in theuranium beam intensity for the BigRIPS experiments.
The construction of the ion source completed in
March 2018 and the installation of the SC cavity in
March 2019; this was followed by the construction of
the control system of the SC cavities and the com-

Fig. 3. Schematic cross section of the R28G-K. The large
volume plasma chamber is surrounded by six SC
solenoidal and one SC hexapole magnets. Both the 18and 28-GHz microwaves are injected from the right sideof the plasma chamber. The HTO is mounted on theinjection side of the plasma chamber.

missioning of the refrigerator in September 2019. The
ﬁrst beam was delivered on January 28, 2020 and thefacility inspection was conducted on March 30, 2020,
which marked the completion of the construction planon schedule and within budget. This project could
not have been accomplished without the help of therelated manufacturers, KEK for the collaborative research, administrative staﬀ for the many orders, andthe management of the Nishina Center. We thank everyone who supported this project.
28-GHz Superconducting ECR Ion Source for
RILAC
We constructed a 28-GHz SC-ECRIS as an essential
part of the RILAC upgrade that began in FY2016. An
ECRIS conﬁnes a hot electron plasma in which electrons are heated by microwaves through the ECR in a“magnetic ﬁeld well.” That is, a “magnetic mirror ﬁeld”
created by a combination of solenoidal and hexapole
magnets known as the minimum-B conﬁguration.15)
Multiple charged heavy ions are created by countlesscollisions of ions with suﬃciently high-energy electronsin plasma. In the next projects at RILAC such as
the search for new SHE with atomic number Z > 118
and RI production, it is necessary to provide unprecedented high-intensity ion beams. This means that itis necessary to conﬁne the electron plasma, which hasa higher density and a higher temperature than theplasma generated in the ECRIS used in RILAC, ina stable manner. Therefore, as shown in Fig. 2, new
SC-ECRIS named RIKEN 28-GHz SC-ECRIS “KURENAI” (R28G-K) equipped with fully SC magnets and ahigh-power microwave generator system was launchedin 2018.

Fig. 2. Photograph of R28G-K and microwave generators(18-GHz klystron amplifier and 28-GHz gyrotron system). Extracted ion beams are analyzed by the dipole
magnet and transported to the accelerator cavities of
RILAC.

2- S2 -

FEATURE ARTICLE

RIKEN Accel. Prog. Rep. 54 (2021)

R28G-K is equipped with six SC solenoidal magnets
and a SC hexapole magnet as shown in Fig. 3. The arrangement of the SC magnets was set by the Ion source
team of RIKEN Nishina center 11,16) based on previous
research.17–19) The SC coils are fabricated from Nb-Ti
alloy and immersed in liquid He (more than 300 L)
maintained in a high-power cryostat system combinedwith two 10-K GM (RDK-408S, SHI ltd.) and one 4-K
GM (RDK-408D2, SHI ltd.) cryocoolers. Further, a
GM-JT cryocooler (4 W at 4 K, SHI ltd.) is used to remove the excess heat induced by the large amounts ofhighly energetic X-ray radiation from the plasma. The
maximum magnetic ﬁeld of microwave injection side
(Binj ), beam extraction side (Bext ), and radial magnetic ﬁeld at the plasma chamber surface (Br ) are 3.8,
2.4, and 2.1 T, respectively. Otherwise, the bottomof the “ﬁeld well” Bmin changes from 0.5 T to 1.0 T,

Fig. 4.

which makes the microwaves with both frequencies of
18 GHz and 28 GHz available to induce ECR with suitable mirror ratios such as Binj /Bmin ∼ 4, Bext /Bmin∼ 2–3, and Br /Bmin ∼ 2–3. Further, the shape of themirror ﬁeld around the Bmin area can be changed arbitrarily by using the six solenoidal magnets. In otherwords, the ﬁeld gradient and size of the ECR region can
be changed to study the eﬀects on the ECR plasma
to optimize the beam intensity with a higher charge
state. Since the SC magnets can generate a strong
and large mirror ﬁeld, the plasma chamber is a largecapacity cylinder with an inner diameter of 150 mm
and a length of 575 mm. A total of 10 L/min or moreof cooling water ﬂows through the chamber wall. The
large volume of the plasma chamber increases not only
the volume of plasma but also the conﬁnement time of
the ions in the plasma to achieve a higher charge state.

Side and top views of the layout of SRILAC. Apparatuses described in the text are labeled.

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FEATURE ARTICLE

RIKEN Accel. Prog. Rep. 54 (2021)

The high-power microwave system contains a 1.5-kW
klystron ampliﬁer and 5-kW gyrotron for microwaves
with frequencies of 18 GHz and 28 GHz, respectively.
The high-power microwaves heat the electron in theplasma to remove the electrons bound deep inside theatoms or ions.
Recently, we have been developing a method to evaporate a solid material with a high melting point suchas vanadium or calcium oxide using the high temperature oven (HTO).20) The tungsten crucible of the HTO
is heated to 2,000 K by the Joule heat caused by thehigh DC current of 700 A. For supplying the vanadium
beam to search for the new SHE, the experiment lasted
for about a month; therefore, we modiﬁed R28G-K
so that two ovens could be used as described in the
progress report this year.

Fig. 5. Photographs of DPS (Left) and gas-jet curtain(Right).

Overview of SRILAC

Figs. 4 and 5) was completed in December 2019. In
operations during the past year, we conﬁrmed thatthe DPSs achieved the desired pressure reductions ina stable manner without serious problems such as ﬁeld
emission problems.
During operations with GARIS-III for SHE research,
He leakages to the SRILAC became an issue although afour-stage large DPS upstream of the GARIS (DPSG)
was used for the windowless accumulation of He gas
up to ∼70 Pa. The pressure of DDPS is increased to∼10−7 Pa with the gas-ﬁlled GARIS-III when we use
the narrow oriﬁces of ϕ15 mm in the DPSG, whichmakes it diﬃcult to transport high-intensity heavy-ion
beams.
We introduced a N2 gas-jet curtain downstream of
DPSG (Figs. 4 and 5). The gas-jet curtain method is
a new method introduced in the DPS of the He gas
stripper.22) This method suppresses the leakage of Hegas by hitting a N2 -gas jet perpendicular to the He gas
ﬂow, and it converts the leaked gas into N2 gas, which
can be evacuated eﬀectively with the DPS.
The gas-jet curtain system has a beam aperture
with the diameter of ϕ25 mm. The nozzle is a twodimensional Laval nozzle designed to generate an N2 gas jet with a Mach number of 3.5 by optimizing with
CFD calculations (Fig. 5).
In the tests with the GARIS team, we conﬁrmedthat there was no serious backﬂow of N2 gas to the
GARIS-III when the gas-jet curtain was under our operating conditions using a quadrupole mass analyzer.
The eﬀect of charge exchanges and energy losses of
the injected beams by N2 gas jet were conﬁrmed to be
negligible.
The installation of the gas-jet curtain was ﬁnishedin September 2020. The leakage of He gas was signiﬁcantly reduced with the N2 gas-jet curtain and thepressure of the DDPS was ∼10−8 Pa even with larger
oriﬁces greater than ϕ25 mm in DPSG, which reduced
the diﬃculties with high-intensity beam transport to
the GARIS-III.

The superconducting-RILAC (SRILAC) comprises
three cryomodules (CM1, CM2, and CM3, see “SRILAC cryomodule” for detail), with room-temperature
medium energy beam transport (MEBT) between
them as shown in Fig. 4. The CMs contain neither SC magnets nor cold diagnostic devices. For
the beam transport line connecting the CMs, the socalled MEBT, a newly designed beam energy position monitor (BEPM) is employed instead of traditional wire scanners and Faraday cups to avoid thegeneration of particulates that cause the degradationof the cavity performance (See “Beam energy position
monitoring system for SRILAC ” for detail). Further,to prevent the contamination of the SC parts wherethe vacuum pressure level is 1 × 10−8 Pa, it is important to have an isolation system between the existing room-temperature part where the vacuum pressurelevel is several 10−5 Pa and the SRILAC (See “Compact particle-removal diﬀerential-pumping system andN2 gas-jet curtain for SRILAC ” for detail).
Compact particle-removal diﬀerential-pumping
system and N2 gas-jet curtain for SRILAC
A compact non-evaporable getter-based diﬀerential pumping system (DPS) with electrostatic particle
suppressors 21) has been developed to mitigate the large
diﬀerence in the vacuum and clean conditions between
the SRILAC and existing old RILAC with beamlines
built almost four decades ago. The three-stage DPS
was designed to achieve a pressure reduction from theexisting beamline vacuum (10−6 –10−5 Pa) to an ultrahigh vacuum of less than 10−8 Pa in SC cavities withina very limited length of only 75 cm, which ensures abeam aperture greater than 40 mm. All components(chambers, pumps, valves, vacuum gauges, etc.) werecleaned and assembled in an ISO class-1 clean room.
The installation of the DPSs (UDPS and DDPS, See4- S4 -

FEATURE ARTICLE

RIKEN Accel. Prog. Rep. 54 (2021)

Table 1. Design parameters of SC-QWRs for SRILAC.
The surface resistance is conservatively assumed to be
22.4 nΩ in the calculation.
Item
Operating temperature
Frequency at 4.5 K
Duty
Einj
Eout
Maximum gap voltage
Cavity typeNo. of SC cavities
Synchronous phase
βopt
TTF
ApertureG
Rsh /Q0
Target Q0
Qext
P0
Eacc
Vacc at Eacc = 6.8 MV/m, β = 0.078
Epeak /Eacc
Bpeak /Eacc
Amplifier output
Beam current

wards lowering the resonant frequency, and therefore,
the frequency variation is reduced by fine tuning thestem of each cavity and the total length of the outerconductor during assembly.25)
The inner surface of the cavity was chemically polished to 110 µm after assembly, annealed at 750◦ C,
and then chemically polished to 20 µm to maximize
the performance of the SC cavity. The cavity was thenhigh-pressure washed with ultrapure water from eachport and vacuum sealed in an ISO class-1 clean room.
After vacuum sealing, it was baked at 120◦ C, and performance tests were conducted on the single unit. As
shown in Ref. 24), all ten actual cavities fabricated exceeded the target Q0 value of 1 × 109 in the test. The
cavity must be operated in compliance with the High

Value
4.5 K
73.0 MHz100%
3.6 MeV/nucleon
6.5 MeV/nucleon
2.4 MVQWR (TEM)
10
−25◦
0.078
0.9
ϕ40 mm
22.4 Ω
579 Ω
1.0 × 109
(1.0–4.5) × 106
8W
6.8 MV/m
2.16 MV
6.2
9.6 mT/(MV/m)
7.5 kW∼100 electric µA

SRILAC cryomodule
The SRILAC comprises three CMs that contain atotal of ten SC cavities.23,24) CM1 and CM2 each contain four SC cavities, and CM3 contains two SC cavities (Fig. 4). The SC cavity of SRILAC is based on a
coaxial QWR made of pure niobium. The resonant frequency is 73.0 MHz and the cavity is operated at 4.5 K
cooled by liquid helium. The SC-QWR is fabricatedusing 3.5 mm and 4 mm pure niobium plates pressed
together to make the top plate, stem, outer conductor,
and bottom plate, and these are then assembled byelectron beam welding. This is the first actual QWR
made of pure niobium in Japan. Each QWR is designed to provide an acceleration voltage of 2.4 MV or
higher at 8 W per unit. The design parameters of thecavity are summarized in Table 1.
Cross-sectional views of the QWR and CM are
shown in Fig. 6. A pure titanium jacket is attachedoutside the cavity to store liquid helium. Permalloyis inserted into the space between the cavity and titanium jacket for magnetic shielding. The resonant frequency shifts because of external disturbances such as
fluctuations in the liquid helium pressure. The tuner
slightly pushes and deforms the cavity’s beam port,
which changes its capacitance and tunes its frequency
to compensate for the slow shift. However, the frequency adjustment range of this tuner is 14 kHz to-

Fig. 6. Cross-sectional views of SC-QWR (top) and cryomodule that contains four SC-QWRs (bottom).

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Table 2. Requirements from cryomodules for SRILAC.

Pressure Gas Safety Act in Japan, and therefore, it
was fabricated after preliminary evaluation and thencommissioned for inspection.
A fundamental power coupler (FPC) and RF pickup
are mounted on the bottom plate of the cavity. The
FPC is a coaxial capacitively coupled type, vacuum
sealed with a single ceramic window in the normal temperature section; it can handle the RF input power of
5 kW or more.26) The FPC inner conductor is fabricated from oxygen-free copper, and the outer conductor from stainless steel with a copper plating on
the inner surface. The thickness of the copper plating
was determined by balancing heat penetration with theheat transfer to the low temperature side and heat generation caused by RF power.
The vacuum vessel of the CM is made of steel anddivided into the top plate, top box, middle box, bottom box, and bottom plate. Electroless nickel plating
was applied to prevent corrosion. The cavity is builtwith four glass-epoxy pillars on the bottom plate. One
support is ﬁxed in place, while the other three slide
horizontally to allow for repositioning during cooling.
Liquid helium buﬀer pipe is installed at the top of
the cavity to control the liquid level for stable cooling. An aluminum plate is used for the 80-K thermal
shield, which is cooled by liquid nitrogen ﬂowing in series through three CMs. Cernox sensors are used asthermo sensors for the cavity, Pt-Co for the 4.5 K region, and Pt100 for the 80 K region. The heat loadof the CM is estimated to be about 18 W for heat intrusion and about 32 W for RF loss in the cavity during steady state operation in a module containing four
cavities. However, a heat load of 100 W per CM was
set as the design standard value for operation duringperformance degradation.
The ﬁrst step in assembling the CM is to move thebottom plate with the cavity and the middle box into
the clean room and to fasten the cavity and beam pipe

Item
No. of SC cavities
No. of cryomodules
Temperature of SC cavities
Temperature of thermal shield
Weight of cold mass
Heat load to 4.5 K cold mass
Dynamic
StaticHeat load to thermal shield
Cooling power
Inventory
Design pressure of the He vessel
Allowable pressure fluctuation

Value
10
2+1
4.5 K
80 K
1475 kg
120 W
30 W
120 W
≥500 W
313 L
0.125 MPa(A)
4.0 × 10−4 MPa

to seal their vacuum so that no dust can enter thecavity. Then, helium piping, liquid nitrogen piping,tuners, thermal shields, super insulators, etc. were installed, and the upper and lower boxes were covered
after moving to the installation site (Fig. 7).
A total of ten sets of digital low-level RF (LLRF)
circuits and 7.5 kW transistor ampliﬁers were introduced to excite the cavities. A digital low-level circuit
is equipped with an FPGA that stabilizes the RF voltage and phase by PID control and obtains the tuning
phase from the directional coupler signal. Internal parameters of the digital low-level circuit can be set remotely from a programmable logic controller (PLC).
Transistor ampliﬁers can operate with full output reﬂection, and they are equipped with ﬁve 1.5 kW output units with built-in isolators to continue operationin the event of unit failure. A control system using
the PLC is provided for each CM to control these RF
equipment.
Cryogenic system for SRILAC
The requirements from CMs for the SRILAC aresummarized in Table 2. SC cavities work at 4.5 K.
The thermal shield is designed to be cooled down byliquid nitrogen, and the total weight of the cold massis 1.5 ton. Heat load to 4.5 K and 80 K are 150 and
120 W, respectively. The inventory of liquid helium is313 L and the allowable ﬂuctuation of pressure in the
SC cavities is as small as 4 hPa because a change inpressure can change the resonance frequency of the SC
cavities. The design pressure of the vessel is as low
as 0.125 MPa(A) because the cavity has bellow, whichcannot sustain higher pressure.
The cryogenic system was designed to have a cooling power of 500 W at 4.5 K. This system comprises ahelium compressor, refrigerator, and buﬀer tank. The
cooling power is four times that of the heat load because we like to have a big margin to ensure contin-

Fig. 7. Photographs of cryomodule. (Left) After assembling and sealing the cavities and beam pipes in theclean room. (Right) After alignment at the installation
site.

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uous operation even if the condition of the surface on
the cavities is not so good that the cavities need considerably more cooling power. Figure 8 shows a cooling diagram of the cryogenic system. The compressed
helium gas is introduced to a cold box and liqueﬁed.
Liquid helium is then supplied to the three headersin the CMs from the top. The evaporated cold helium gas is returned to the cold box and the helium
compressor via heat exchangers. During pre-cooling,helium gas is supplied from the bottom to cool down
the cavities eﬃciently. Green lines are used for liquid
nitrogen supplied for shield cooling. A backup compressor for the superconducting ring cyclotron (SRC)
was used for this cryogenic system to reduce the total cost. The required pressure ﬂuctuation of 4 hPa
looks tight; however, from experience, it is possible
by control return pressure by the return valve witha precise pressure gauge. The Air Liquide company
supplied devices for the cryogenic system other thanthe compressor. Radiation-resistant valve positioners
were adopted because we install the refrigerator in theaccelerator room.
The stand-alone operation of the helium refrigerator
demonstrated a cooling capacity of 700 W at 4.5 K before the ﬁrst cooling of the SRILAC. Figure 9 shows thecooling down curves. The cold mass was successfully
cooled down to liquid helium temperature in four days
although pre-cooling was halted because of the trouble in the thermal insulation vacuum system for halfa day. The heat load was estimated from the heaterin the helium refrigerator to be 150 W for 2 + 1 CMs.
The pressure ﬂuctuation was hit within 4 hPa.

Fig. 9. Temperature of cold masses in the three CMs in thefirst cooling down.

Beam energy position monitoring system for
SRILAC
It is crucial to monitor a beam to accelerate it stablemanner. When the SRILAC beam is accelerated, beamloss must be reduced to under 1 W/m. Furthermore,
destructive monitors generate outgassing; if they areused, it becomes diﬃcult to maintain the Q-value andsurface resistance of the SC cavities over a long periodof time. Therefore, we developed a new BEPM system that can simultaneously measure the beam position and energy by measuring the time-of-ﬂight (TOF)
to continuously monitor the beam nondestructively. A
great advantage of this system is that it can handle
a time-chopped beam by synchronizing the measurement system with the beam-chopping signal. At thestart of commissioning, the beam was chopped to several percent duty cycle to protect the SC cavity frombeam loss. Although the beam intensity was 20 electric nA, we measured the beam position and energy
to accuracies of ±0.1 mm and several 10−4 precision,respectively.
Depending on the installation location, three typesof BEPMs (Types I, II, and III) were designed and
11 BEPMs were fabricated. The BEPMs are installedin the centers of the quadrupole magnets located between the CMs. Photographs of three types of BEPMs
and a cross section of a BEPM are shown in Fig. 10.
The ideal linear response of the quadrupole moments isrealized by using a parabolic design while maintaining
good linear position sensitivity.
A block diagram of the BEPMs and data-acquisition(DAQ) system is shown in Fig. 11. The DAQ system
can synchronize the RF reference with a beam chopper
signal. The ampliﬁed pickup signals are transmitted
through coaxial cables to the signal processing devices.
The upstream and downstream signals are switched bymultiplexers and digitized by digitizers (PXIe-5160).
Although the sampling speed is 1.25 GS/s, a consider-Fig. 8. Cooling diagram for SRILAC.

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ably higher sampling speed of 50 GS/s can be achievedby using the random interleave mode under the condition that the signal is repeating continuously. Thus,
highly accurate TOF measurements can be realized.
All modules are integrated into a PXI express chassis. The signal process procedures are controlled by
the LabVIEW 2019 graphical programming language,
and module drivers are supported by the National Instruments Corporation. The obtained data are sharedusing the CA Lab that is a user-friendly, lightweight,
and high-performance interface between the LabVIEW
program language and EPICS-based control system.
It allows easy reading and writing of EPICS process
variables (PV). Measurement results are displayed ona remote desktop. Further, once these data are saved,
the Control System Studio (CSS), which is an Eclipsebased tool to operate a large-scale control system, candisplay the results anywhere in the control room.
The ﬁrst 40 Ar13+ beam acceleration commissioning
was conducted using nine SC cavities. Figure 12 shows
the displayed results of the BEPM measurements immediately after the beam was successfully accelerated
to 6.2 MeV/nucleon (2020/01/28 21:02). The waveforms, beam positions, and beam energies at each station are displayed; the value circled in red indicatesthe ﬁnal accelerated energy.
The BEPM system worked extremely well when determining phases of SC cavities and conﬁrming beamenergies and positions, which enabled stable beam acceleration. The measured beam energy is plotted inFig. 13 as a function of the phase of the ﬁnal SC cavity. In the focusing region, the lower energy beam gains

Fig. 11. Block diagram of BEPMs and DAQ system.27)

energy, whereas in the defocusing region, the lower
energy beam loses energy. This measurement clearlyshows us the region we should select to accelerate thebeam stably. The phases of SC cavities are currently
set to −25◦ . Each phase of the SC cavity was measured
and set in sequence from upstream to downstream (See“Beam Commissioning of SRILAC” for detail).
Overview of Control System for SRILAC
Project
A distributed control system that uses Experimental Physics and Industrial Control System (EPICS)
should be adopted as in RIBF to operate the SRILAC
project eﬃciently, and a higher-level application protocol needs to be integrated to the EPICS Channel
Access (CA) protocol. Further, the SRILAC control
system requires corrections and upgrades to the shortcomings of previous RILAC control system, for example control protocol for an electromagnet power supply
and a machine protection system.
In this project, the R28G-K was installed at the frontend of RILAC to increase the beam intensity. The
new SC-ECRIS control system consists of PLCs embedded with EPICS.28) The ion source control systemdiﬀers from other control systems in that control stations with digital and analogue modules need to beinstalled on the high-voltage stage. At RIBF, a reliability of the conventional SC-ECRIS control system
is not so high because interlock signals are exchanged
via TCP/IP between the safety system and control stations on the high-voltage stage. The new SC-ECRIS
control system uses two diﬀerent types of CPUs (sequence CPU and Linux CPU) in the main PLC station, and it was connected to ﬁve PLC substations witha star-topology ﬁeld bus communication using opticalﬁbers for insulation. As a result, the interlock signal

Fig. 10. Photographs of the three types of BEPMs: (a)Type I, (b) Type II, and (c) Type III. (d) Cross section
drawing of a BEPM. (e) Schematic of Type I.27)

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exchanges the control station on the high-voltage stage
through field bus communication on the optical fiber;
system reliability was improved compared with the system that uses the TCP/IP-based interlock signal.
With this SRILAC project, the layout of the beamline has changed and new electromagnet power supplies have been introduced for the LEBT electromagnet. Old electromagnet power supplies were utilized
for MEBT electromagnets. These electromagnet power
supplies control used GPIB as the communication protocol, and their performance was relatively low compared with the modern protocol. Therefore, we upgraded the power supplies to replace the GPIB communication with the standard method of RIBF control
system such as FA-M3 PLC and NIO.29) In beam commissioning, approximately 30 modified electromagnet
power supplies were controlled via EPICS CA protocol
without problems.
With the installation of the SRILAC downstream of
the normal conducting RILAC, a machine protection
system has become necessary. For the previous RILAC control system, the machine protection system,
which comprises a simple electromagnetic relay circuit has been implemented. The machine protection
system is called the Beam Interlock System (BIS) at
RIBF; further, we newly developed and implemented
BIS for SRILAC. The BIS has a mechanism that activates the beam chopper for a signal triggered by anerror from the control equipment and stops the beam.
The speed at which the trigger signal is transmitted to
the CPU is improved compared with that of the conventional BIS by adopting the field bus connection forinter-station communication. In addition, by adopting
a ring-topology, we designed it to increase redundancy.
In the previous RILAC control system, hard-wired

Fig. 13. Measured beam energy plotted as a function of thephase of the ﬁnal SC cavity.27)

control that directly connects the accelerator room andcontrol room with a wire was already replaced and all
operations were based on remote control. However,various systems such as data collection and RF control were not integrated with the EPICS CA protocol,and these were stand-alone systems. When the control system was updated in the SRILAC project, allcontrol protocols for the higher-level application were
integrated in the EPICS CA protocol. For example,
BEPM was a LabVIEW-based system using National
Instrument PXI, and by introducing CA Lab in the
middle layer, we succeeded to operate it using the
EPICS CA client.27)
Since we succeeded to access to almost all control equipment including the above-mentioned electromagnet power supply, BIS, BEPM, and RF using
the EPICS CA protocol, it had become possible tounify the development method of the operator interface(OPI) and realize various OPIs using CSS (Fig. 14).
In addition, the Archiver Appliance has been newly
introduced as the EPICS-based data archive system;
it has become possible to store nearly 10,000 signal
points as data at a cycle of 10 Hz or higher.30) Thissystem has the ability to search for arbitrary data by
the timestamp and visualize the data on a Web-based
application. During SRILAC beam commissioning, theArchiver Appliance was very useful for clarifying the
behavior of SC cavity and the cause of troubles, and it
is currently one of the essential tools for SRILAC beamtuning. In the RILAC control room (Fig. 1), consoles
for hard-wired control system have been removed andnew consoles ideal for the remote-control system havebeen introduced (Fig. 15).
In the near future, we plan to improve the performance of BIS and implement another type of machine
protection system driven by the behavior of electri-

Fig. 12. Displayed BEPM measurement results immediately after the 40 Ar13+ beam was successfully accelerated to 6.2 MeV/nucleon (2020/01/28 21:02). Positions
at station 4 were oﬀ scale, and it was corrected after theﬁrst trial acceleration.27)- S9 -

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cal current for the electromagnet 31) because of the increase in the beam intensity from SRILAC.
Beam Commissioning of SRILAC
The design parameters of the SRILAC are listed inTable 1, and its layout is shown in Fig. 4. The TEM
cavities for the SRILAC are designed to operate in the
CW mode. The gap length of the cavity is optimized
for β = 0.078 particles with a transit time factor of
0.9. The maximum gap voltage is 2.4 MV, which corresponds to an acceleration gradient Eacc of 6.8 MV/mwith a synchronous phase of −25◦ .
The FPC is designed with a tunable coupling so thata Qext range from 1 × 106 to 4.5 × 106 can be achievedby changing the insertion distance of its antenna. The
maximum beam current is about 100 electric µA for
the SHE synthesis experiments; therefore, beam loading is negligible. A low Qext as small as 106 was selected to broaden the resonance curve with a ±60 Hz
operational-frequency-range achieved by an RF input
power of 7.5 kW. In October 2019, the ﬁrst RF testwith an operational temperature of 4.5 K was performed without signiﬁcant trouble, except SC05 encountered a vacuum leakage from the ceramic windowof the coupler. During the RF test, amplitude feedback
and phase-lock loop parameters of the newly developed
digital LLRF were optimized and a stable RF-ﬁeld was
successfully obtained.
After a successful RF test, in January 2020, thebeam acceleration test was conducted for the ﬁrst time.
An 40 Ar beam was accelerated based on the requirement for SHE synthesis experiments. However, one of
the SC-QWRs (SC05) was not available; therefore, theFig. 14. Screenshot of CSS-based OPI for Faraday cup operation.

10

Fig. 15. New consoles for remote operation in the RILAC
control room.

acceleration energy was lowered to 6.2 MeV/nucleon
from the designed energy of 6.5 MeV/nucleon.
The 40 Ar13+ beam with an intensity of approximately 23 electric nA (duty 3%, chopper frequency
1 kHz) was accelerated to 6.2 MeV/nucleon with a
gap voltage of 1.13 MV. For the SC-linac tuning, SCQWRs were energized one-by-one and the beam energy was measured with a systematic variation of the
RF-ﬁeld phase (Fig. 16). The beam energy was precisely obtained by a TOF measurement with a pair of
BEPMs with a low beam current as described above.
The phase-scan plot, where Eout is plotted as a function of the RF-ﬁeld phase for each cavity, is shownin Fig. 16. The synchronous phase ϕs = −25◦ was
obtained by shifting the RF-ﬁeld phase from the zeroacceleration/bunching phase by 65◦ towards the topof the sine curve. The beam position remained almost
at the center of beam aperture during the phase scanbecause of the geometrical correction caused by thesteering eﬀect of the QWR cavity.23) The accelerated
beam energy successfully reached 6.2 MeV/nucleon at
9 PM on January 28, 2020.
After elaborate tuning, the transmission eﬃciency
from FC6A1 to FCe11 in Fig. 4 reached 100% witha beam current of 6.11 electric µA. The vertical andhorizontal beam positions monitored by BEPM were
centralized and the beam loss which occurred at the
MEBT was minimized keeping the deterioration of thevacuum pressure below 1 × 10−7 Pa.
A 51 V13+ beam with an energy from 4.2 MeV/nucleon
to 6.3 MeV/nucleon was delivered for a user service
time. To achieve a beam current of 10 particle µA,
the transmission eﬃciency of the low-energy part of
the RILAC and optimization of the beam transport of
the SRILAC are currently being analyzed. The dataarchive system 30) for many accelerator parameters in-- S10 -

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cluding not only the RF-field of the RF cavities, butalso the excitation current of the magnets, vacuum,
temperature of the cooling water, and BEPMs, is very
helpful to understand what occurs during beam tuning. Each cavity achieved the acceleration gradient of
5.7 MV/m that accelerates ions with M/q of 5.4 to
6.5 MeV/nucleon with ten cavities. The newly developed digital LLRF will be adopted to each RF systemof the RT-DTLs, RFQ, and bunchers to improve thestability of their RF-field.
Beam transport optimization from SRILAC to
GARIS-III
This section reports on beam transport. Heavy-ion
beams accelerated to approximately 6 MeV/nucleon
by SRILAC are transported to GARIS-III through thetransport line called the high energy beam transport(HEBT) line. The configuration of the beam line is
TQ–TQ–D–SQ–SQ–DQ (TQ = Triplet Quadrupole,
D = Dipole, SQ = Singlet Quadrupole, DQ = Doublet Quadrupole) as shown in Fig. 4. Further, there
is one dipole magnet between the second SQ and DQ,
but this is not excited when the beam is transported
to GARIS-III. The duct diameter is 60 mm in mostplaces; however, it is narrowed to 15–25 mm just before the target because of DPSG.
The requirements for the beam transport of theHEBT line are (A) beam loss less than a few percent
and (B) the adjustability of beam spot shape on the
GARIS-III target depending on the experimental conditions. The first requirement is important for maintaining the outside radiation dose. Since the side wallof GARIS-III is relatively thin, it is necessary to measure and confirm the dose while optimizing beam transport. For the second requirement, a horizontal ellipse
is desired in the production run to prevent the local de-

Fig. 16. Phase scan plot for first 40 Ar 6.2 MeV/nucleon
acceleration test.

Fig. 17. Data of emittance measurement after phase-ellipse
adjustment at an object point e00. (Left) Measured
values (red dots) and fit results (black dots) of beamwidths at the point denoted as e01. (Right) Phase ellipse estimated by fitting results. Top and bottom figures correspond to horizontal and vertical directions,
respectively.

pletion of the rotating target, while a large circle shapeis desired in the calibration run. To satisfy these requirements, the beam envelope should be narrower justbefore the target, where there is a relatively smaller acceptance, and it should be wider at the target.
Detailed optical calculation is required according to
the phase ellipse of the beam at that time to realize
the ideal optics with a limited number of optical elements. The optics are adjusted in the following threesteps. First, the phase ellipse of the beam at e00, which
is defined as the object point in the optical design,
is measured using the wire scanners at e00 and e01(Fig. 4). The beam width at e01 is measured withseveral optics between e00 to e01 by changing the TQ
magnets. Comparing the obtained widths and transfer
matrices, the phase ellipse at e00 is estimated. Second,
the phase ellipse at e00 is adjusted to be upright by the
TQ upstream of e00 based on an optical calculation.
Third, the optics from the object point to GARIS-III
are tuned using optical simulation 32) based on an adjusted phase ellipse at e00 and an experimental requirement for beam spot shape. In the default optics, theposition magnifications from e00 to GARIS-III are 1.0
in both of the horizontal and vertical directions. Basedon the measured phase ellipse and experimental requirements, position magnifications are adjusted while
suppressing the beam envelope in the entire beam line.
Finally, the optical system is optimized with a few particle µA beam by fine-tuning the quadrupole magnets- S11 -

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References

Fig. 18. Beam spot picture on viewer at GARIS-III target taken by CCD camera. The beam spot shape is ahorizontal ellipse as expected.

and steerers based on the baﬄe inside the diﬀerential
pumping system and viewer on the target.
Figure 17 shows an example of the estimated e00
phase ellipse after step 2, which causes the phase ellipse to be upright. This measurement was performed
in a commissioning run in June 2020, in which Ar11+
accelerated to 5 MeV/nucleon with intensity of 30 electric nA was utilized. The graphs shown on the left represent the beam widths (rms) measured by the e01 wire
scanner in each optics, the red dots represent the measurements, and black dots represent ﬁt results. The
contour plots shown on the right are phase ellipses at
e00 estimated from the ﬁt results. Here, the phase ellipses are assumed to be two-dimensional Gaussian distributions. As shown in the ﬁgures, the phase ellipses
were adjusted to be upright as calculated. The horizontal 4 rms emittance was ϵh = 3.1 (πmm·mrad), andthe vertical 4 rms emittance was ϵv = 6.5 (πmm·mrad),respectively. These values were consistent within 20%
with the values before the phase-ellipse adjustment.
The measurement and adjustment of the phase ellipses
are almost automated except for the data acquisitionby the wire scanners; they are completed in about anhour.
After the phase-ellipse adjustment, the optics frome00 to the GARIS-III target were optimized. As shownin Fig. 18, the beam spot on the target was tuned to
be a horizontal ellipse, as expected for the rotation
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leakage radiation was within the allowable range. In
these adjustments, the calculation of optics and theapplication of calculated currents to magnets were automated; the optics optimization was completed in a
few hours including the ﬁne adjustment of the steerers.
Optics in the HEBT line was optimized as expectedbased on the phase ellipse measurement and opticalsimulation. A new method to estimate the phase ellipse with non-destructive detector BPEMs 33) is underdevelopment.

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I. HIGHLIGHTS OF THE YEAR<< Selection process of highlights >>Highlights are selected by a two-step process. In the first step, a referee who reviews a manuscript decides
whether she/he would recommend it as one of the highlights.
Members of the editorial board then make additional recommendations if they think an important contribution
has not been recommended by the referee.
The second step involves the editor-in-chief proposing a list of highlights based on the recommendation given
above to the editorial board. After discussing the scientific merits and uniqueness of the manuscripts fromviewpoints of experts/non-experts, the editorial board makes the final decision.

I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Oblate shapes and metastable states of 92, 94 Se†
P. -A. Söderström,∗1,∗2,∗3,∗4 C. Lizarazo,∗1,∗2 V. Werner,∗1 N. Pietralla,∗1 P. M. Walker,∗5 G. X. Dong,∗6
F. R. Xu,∗7 T. R. Rodríguez,∗8 F. Browne,∗9 P. Doornenbal,∗3 S. Nishimura,∗3 C. R. Nit, ă,∗10 and
A. Obertelli∗1,∗3,∗11 for the SEASTAR2015 collaboration
The main goal of the second SEASTAR campaign1)
performed at the RIBF was the exploration of the nuclear structure evolution in the region of a possible onset of deformation and shape transition between the twocorner-stone nuclei 78 Ni2) and 110 Zr.3) As this region is
known for the large abundance of nuclear isomers,4) the
EURICA decay setup5,6) was installed at the end of the
ZeroDegree spectrometer in addition to the SEASTAR
instrumentation. Thus, complementary to the in-beamspectroscopy data of the Se chain,7) it was possible toobserve internal isomeric decay using high-resolution γray spectroscopy.8)
The type of metastable conﬁgurations observed in deformed atomic nuclei, whereby two quasiparticle states
are formed by breaking pairs of nucleons close to the
Fermi level, signiﬁcantly changing the angular momentum projection on the symmetry axis is known as
K isomers. These typically originate from deformed
Nilsson orbitals coming up from lower-lying shells inwell deformed prolate nuclei. Analogously, the typical
downsloping of these orbitals on the oblate side opens
up the possibility for a new region of K isomers at low
Z and oblate deformation for exotic nuclei, involving
the same orbitals from higher-lying shells as within the
prolate deformed Z ∼ 72 region.
In Ref. 8), we report on the observation of suchstates for 92, 94 Se from EURICA during the SEASTAR
campaign, see Fig. 1, as well as the impact of theirdecay pattern on the discussion of shape evolution
at N = 60. Potential energy surface calculations
suggest oblate K π = 7− (ν11/2− [505] ⊗ ν3/2+ [402])
and K π = 9− (ν11/2− [505] ⊗ ν7/2+ [404]) conﬁgurations for the negative-parity states in 92 Se, and K π =7− (ν11/2− [505] ⊗ ν3/2+ [411]) for the isomer of 94 Se.
For 94 Se, this leads to a hindrance factor of FW =2.49 × 108 and a reduced hindrance fν ∼ 25. Characteristic values for E1 K-trap decays with ν = 6 arewithin 27 ≲ fν ≲ 42.9,10)
Also, the observed J π = 7− states have very diﬀerent
Condensed from the article in Phys. Rev. Lett. 124, 222501(2020)∗1 Institut für Kernphysik, Technische Universität Darmstadt∗2 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗3 RIKEN Nishina Center∗4 ELI-NP, IFIN-HH∗5 Department of Physics, University of Surrey∗6 School of Science, Huzhou University∗7 State Key Laboratory of Nuclear Physics and Technology,
Peking University∗8 Departamento de Física Teórica, Universidad Autónoma de
Madrid∗9 School of Computing Engineering and Mathematics, University of Brighton∗10 DFN, IFIN-HH∗11 IRFU, CEA, Université Paris-Saclay†(9- ) T1/2 =15.7(7)μs

3072
3005

(7- )

+

+

2502 (6 , 5 )

2430

(7- )

T1/2=0.68(5) μs(6+1 ) 1935++

1605 (42 , 31 )(4+1 ) 1252968(2+1 ) 539(4+1 ) 1113(2+1 ) 470
92

0+
gs

(2+
2)

Se58

0+
gs

94

Se60

Fig. 1. Level schemes constructed for 92, 94 Se. The arrow
width of each transition indicates its intensity.

decay paths for the two isotopes. The decay properties
can partially be explained considering that the collective wave functions predicted by the SCCM method for92Se7) are relatively soft, implying that K is not a goodquantum number due to the lack of well-deﬁned rigid
axial symmetry. For 94 Se, however, the SCCM method
proposes a rigid oblate ground state and a rigid prolate yrare band, increasing the wave-function overlap
between an oblate isomer and the oblate ground state
relative to the prolate yrare band.
This work presents the observation and interpretationof 92, 94 Se isomeric states. The diﬀerent isomeric decay
paths of each isotope contrast the relatively smooth systematics of the ground-state and K = 2 excited bands
observed from in-beam spectroscopy.7) Also, a similar
32 ns isomer was recently observed for 94 Kr at the ALTO
facility of the IPN Orsay with the ν-Ball array,11) allowing the systematic evaluation of the 7− and 9− statesalong N = 58.
References

1) P. Doornenbal et al., RIKEN Accel. Prog. Rep. 49, 35(2016).
2) R. Taniuchi et al., Nature 569, 53 (2019).
3) N. Paul et al., Phys. Rev. Lett. 118, 032501 (2017).
4) D. Kameda et al., Phys. Rev. C 86, 054319 (2012).
5) S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006 (2012).
6) P. -A. Söderström et al., Nucl. Instrum. Methods Phys.
Res. B 317, 649 (2013).
7) S. Chen et al., Phys. Rev. C 95, 041302(R) (2017).
8) C. Lizarazo et al., Phys. Rev. Lett. 124, 222501 (2020).
9) G. D. Dracoulis et al., Rep. Prog. Phys. 79, 076301 (2016).
10) Z. Patel et al., Phys. Rev. C 96, 034305 (2017).
11) R. -B. Gerst et al., Phys. Rev. C 102, 064323 (2020).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Properties of 187 Ta revealed through isomeric decay†
P. M. Walker,∗1 Y. Hirayama,∗2 G. J. Lane,∗3 H. Watanabe,∗4,∗5 G. D. Dracoulis,∗3 M. Ahmed,∗2,∗6 M. Brunet,∗1
T. Hashimoto,∗7 S. Ishizawa,∗5,∗8,∗2 F. G. Kondev,∗9 Yu. A. Litvinov,∗10 H. Miyatake,∗2 J. Y. Moon,∗7
M. Mukai,∗6,∗2,∗5 T. Niwase,∗2,∗5,∗11 J. H. Park,∗7 Zs. Podolyák,∗1 M. Rosenbusch,∗2 P. Schury,∗2 M. Wada,∗2,∗6
X. Y. Watanabe,∗2 W. Y. Liang,∗12 and F. R. Xu∗12
We report results from the production and separation of a low-energy beam of the neutron-rich tantalum
isotope, 187 Ta114 , together with its high-spin isomericstate. The production process exploits multi-nucleon
transfer (MNT) reactions which have been shown to beeﬀective for making neutron-rich nuclei.1) The large angular momentum transfer in MNT reactions is a key aspect for the formation of high-spin isomers.
The experiment was performed at the RIKEN Nishina
Center with the recently commissioned KEK Isotope
Separation System (KISS) facility.2) This is the ﬁrst facility of its kind, capable of stopping heavy-ion reaction
products in a high-pressure (80 kPa) argon gas cell, performing laser resonant ionization for element (Z) selectivity, and achieving mass (A) separation of the electrostatically extracted, singly charged, 20 keV ions in a
dipole magnet with a resolving power A/∆A = 900.
The 187 Ta ions were produced by MNT reactions of
a 50 particle-nA beam of 136 Xe at 7.2 MeV/nucleon,
delivered by the RIKEN Ring Cyclotron. The beam
was incident on a 5 µm thick natural tungsten target atthe entrance to the argon gas cell.
The 20 keV secondary beam of laser-ionized tantalum was mass separated (1.5 ions/s of 187 Ta) and transported to a moving-tape collection point, surrounded bya low-background, 32-element gas proportional counter
with 80% of 4π solid angle for β particles and conversion
electrons3) and four Super Clover germanium γ-ray detectors with a total absolute full-energy-peak eﬃciencyof 15% at 150 keV. The tape transport was operated
with equal beam-on/beam-oﬀ periods, with the radioactivity moved to a shielded location at the end of eachcycle. The chosen beam-on periods were 30 s, 300 s and1800 s, with ﬁve days of data taking.
An isomer in 187 Ta at 1789(13) keV had been identiﬁed in the Experimental Storage Ring at GSI,4) but
without observation of the decay radiations. Details of
the excited-state structure of 187 Ta have now been reCondensed from the article in Phys. Rev. Lett. 125, 192505(2020)∗1 Department of Physics, Surrey University∗2 Wako Nuclear Science Center (WNSC), IPNS, KEK∗3 Department of Nuclear Physics, ANU∗4 School of Physics, Beihang University∗5 RIKEN Nishina Center∗6 Graduate School of Science and Engineering, Tsukuba University∗7 Rare Isotope Science Project, Institute for Basic Science (IBS)∗8 Graduate School of Science and Engineering, Yamagata University∗9 Physics Division, ANL∗10 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗11 Department of Physics, Kyushu University∗12 School of Physics, Peking University†

Fig. 1. Level scheme for 187 Ta based on γ-ray transitions
observed following the decay of a T1/2 = 7.3(9) s isomer.

vealed by the isomeric γ-ray emissions, as illustrated inFig. 1. The isomer is found to have an excitation energyof 1778(1) keV, with a half-life of 7.3(9) s.
Despite the proximity to N = 116, which is predicted to be the critical point for a ground-state prolateoblate shape transition, the reduced hindrance for the
191.7 keV, E2 isomeric decay remains substantial, withfν = 27(1), indicating that K is approximately conserved, and therefore that axial symmetry is not strongly
violated. Nevertheless, weak violation of axial symmetry
is indicated by the observed irregularity in the 9/2[514]rotational band that is populated through the isomer decay. Comparison with the rhenium isotone, 189 Re, supports calculations showing that axial symmetry is better
conserved for the lower-Z nuclei, through the N ≈ 116
shape transition region.
The new capability to produce low-energy beamsof neutron-rich tantalum isotopes and isomers demonstrates the power of the gas-stopping technique for nuclear structure studies of exotic neutron-rich nuclei, evenwith refractory elements. This marks a milestone on theway to the exploration of nuclei predicted to have welldeformed oblate ground states.
References

1) Y. X. Watanabe et al., Phys. Rev. Lett. 115, 172503 (2015).
2) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
463, 425 (2020).
3) M. Mukai et al., Nucl. Instrum. Methods Phys. Res. B
463, 421 (2020).
4) M. W. Reed et al., Phys. Rev. Lett. 105, 172501 (2010).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

In-gas-cell laser resonance ionization spectroscopy of 196, 197, 198 Ir†
M. Mukai,∗1,∗2,∗3 Y. Hirayama,∗3 Y. X. Watanabe,∗3 S. Schiﬀmann,∗4,∗5 J. Ekman,∗6 M. Godefroid,∗5 P. Schury,∗3
Y. Kakiguchi,∗3 M. Oyaizu,∗3 M. Wada,∗3 S. C. Jeong,∗7 J. Y. Moon,∗7 J. H. Park,∗7 H. Ishiyama,∗1 S. Kimura,∗1
H. Ueno,∗1 M. Ahmed,∗2 A. Ozawa,∗2 H. Watanabe,∗8 S. Kanaya,∗9 and H. Miyatake∗3
The experimentally measured nuclear quadrupole deformation parameters of mercury, gold, platinum, andiridium approach the value for the spherical shape withincreasing neutron number.1) However, for iridium isotopes, the ﬁnite-range droplet model (FRDM)2) predicts
a shape transition from prolate (A ≦ 196) to oblate(A ≧ 197) at A = 197. We have investigated the evolution of nuclear structure of iridium isotopes, 196–198 Ir(Z = 77, N = 119–121), with in-gas-cell laser ionization spectroscopy as the ﬁrst step of a systematic studyof nuclear structures for nuclei around N = 126 at theKEK Isotope Separation System (KISS).3) In the present
work, we report the magnetic dipole moments (µ), meansquare charge radii, and nuclear quadrupole deformation
parameters (β2 ), as determined from hyperﬁne structure(HFS) measurements.
Neutron-rich iridium isotopes were produced using multi-nucleon transfer reactions of a 198 Pt target (12.5 mg/cm2 ) and 136 Xe beam (9.4 MeV/nucleon,
50 particle-nA).4) The target-like fragments were thermalized and neutralized in a gas cell ﬁlled with puriﬁed
Ar gas of ∼1 atm3) and re-ionized element-selectively
by using a laser resonance ionization technique at theexit of the gas cell. The excitation transition of 5d7 6s2
4
F9/2 → 9/2◦ (λ1 = 247.587 nm) was chosen for the
spectroscopy, and the excitation laser was produced bya dye laser pumped by an excimer laser. The mass number was chosen using a dipole magnet with a mass resolving power of A/∆A ∼ 900. The mass-analyzed ionswere transported to a decay station, which consists ofa tape transport device, a multi-segmented proportional
gas counter, and four clover-type germanium detectors.
The extraction of each nucleus was conﬁrmed throughthe measurement of β-decay half-life. The HFS spectra
were measured by counting β-rays as a function of excitation laser frequency, as shown in Fig. 1. The measured
spectra were ﬁtted using the Voigt function for each transition between HFSs of ground and excited states to determine the µ and isotope shift values.
The µ value of 197 Ir (I π = 3/2+ ) was determined to be
†

∗1
∗2
∗3

∗4

∗5

∗6

∗7
∗8

∗9

Condensed from the article in Phys. Rev. C 102, 054307 (2020)
RIKEN Nishina Center
Graduate School of Sciences and Technology, University ofTsukuba
Wako Nuclear Science Center (WNSC), Institute of Particle
and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
Department of Physics, Lund University
Spectroscopy, Quantum Chemistry and Atmospheric Remote
Sensing (SQUARES), Université libre de Bruxelles
Materials Science and Applied Mathematics, Malmö University
Rare Isotope Science Project, Institute for Basic Science
International Research Center for Nuclei and Particles in the
Cosmos, Beihang University
Department of Physics, Osaka University

Fig. 1. Spectrum of 197 Ir ion counts as a function of the excitation laser frequency with the best ﬁt (red solid line).
The black dotted line indicates the ﬁtted backgroundlevel. The spectrum was measured at an argon gas pressure of 74 kPa.

+0.27+0.10−0.03 µN . In the case of the unknown spin nuclei
196
Ir (I π = (0− )) and 198 Ir, the results of chi-square
ﬁtting strongly indicate that their nuclear spin are I > 0with ﬁtted µ values of +(0.31–0.36) µN (I = 1–3) for196
Ir and +(0.13–0.26) µN (I = 1–3) for 198 Ir.
The quadrupole deformation parameter was deduced
from the measured isotope shifts while assuming anaxial-deformed nuclear charge distribution and theoretical electronic factor of the excitation transition fromlarge-scale atomic calculations.5) The deduced |β2 | values were 0.06(2) and 0.07(2) for 197 Ir and 198 Ir, respectively.
The experimental µ values were compared with calculated µ values based on the strong coupling model.6,7)
The comparison shows good agreement in the µ value
for 197 Ir with the assumption of prolate deformation andsuggests I = 1− or 2− for 196 Ir and I = 2− for 198 Ir.
References

1) D. Verney et al., Eur. Phys. J. A 30, 489 (2006); G. Ulm
et al., Z. Phys. A 325, 247 (1986); K. Wallmeroth et al.,Nucl. Phys. A 493, 224 (1989); Th. Hilberath et al., Z.
Phys. A 342, 1 (1992).
2) P. Möller et al., At. Data Nucl. Data Tables 59, 185 (1995).
3) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
353, 4 (2015); Y. Hirayama et al., Nucl. Instrum. Methods
Phys. Res. B 412, 11 (2017).
4) Y. X. Watanabe et al., Phys. Rev. Lett. 115, 172503 (2015).
5) S. Schiﬀmann, M. Godefroid, J. Quant. Spectrosc. Radiat.
Transf. 258, 107332 (2020).
6) I. Hamamoto, Phys. Rev. C 99, 024319 (2019).
7) A. Bohr, B. R. Mottelson, Mat. Fys. Medd. K. Dan. Vidensk. Selsk. 27, 16 (1953).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Fragmentation of single-particle strength around the doubly-magic
nucleus 132 Sn and the position of the 0f5/2 proton-hole state in 131 In†
V. Vaquero,∗1 A. Jungclaus,∗1 T. Aumann,∗2,∗3 J. Tscheuschner,∗2 E. V. Litvinova,∗4 J. A. Tostevin,∗5
H. Baba,∗6 D. S. Ahn,∗6 R. Avigo,∗7,∗8 K. Boretzky,∗3 A. Bracco,∗7,∗8 C. Caesar,∗2,∗3 F. Camera,∗7,∗8
S. Chen,∗9,∗6 V. Derya,∗10 P. Doornenbal,∗6 J. Endres,∗10 N. Fukuda,∗6 U. Garg,∗11 A. Giaz,∗7
M. N. Harakeh,∗3,∗12 M. Heil,∗3 A. Horvat,∗2 K. Ieki,∗13,∗6 N. Imai,∗14 N. Inabe,∗6 N. Kalantar-Nayestanaki,∗12
N. Kobayashi,∗14,∗6 Y. Kondo,∗15,∗6 S. Koyama,∗14,∗6 T. Kubo,∗6 I. Martel,∗16 M. Matsushita,∗17 B. Million,∗8
T. Motobayashi,∗6 T. Nakamura,∗15,∗6 N. Nakatsuka,∗6,∗2 M. Nishimura,∗6 S. Nishimura,∗6 S. Ota,∗17 H. Otsu,∗6
T. Ozaki,∗15,∗6 M. Petri,∗2 R. Reifarth,∗18 J. L. Rodríguez-Sánchez,∗19,∗3 D. Rossi,∗2 A. T. Saito,∗15,∗6
H. Sakurai,∗6,∗14 D. Savran,∗3 H. Scheit,∗2 F. Schindler,∗2,∗3 P. Schrock,∗2 D. Semmler,∗2 Y. Shiga,∗13,∗6
M. Shikata,∗15,∗6 Y. Shimizu,∗6 H. Simon,∗3 D. Steppenbeck,∗6 H. Suzuki,∗6 T. Sumikama,∗6 D. Symochko,∗2
I. Syndikus,∗2 H. Takeda,∗6 S. Takeuchi,∗6 R. Taniuchi,∗14,∗6 Y. Togano,∗15,∗6 J. Tsubota,∗15,∗6 H. Wang,∗6
O. Wieland,∗8 K. Yoneda,∗6 J. Zenihiro,∗6 and A. Zilges∗10
The neutron-hole and proton-hole nuclei 131 Sn andIn were studied using one-nucleon removal reactions
from doubly-magic 132 Sn at relativistic energies. In
131
In, a 2910(50)-keV γ ray was observed for the firsttime, see Fig. 1, mainly thanks to the good energy andtime resolution of the eight LaBr3 detectors employedin this experiment. This high-energy γ ray was tentatively assigned to the decay of the 0f5/2 proton-holestate to the known 1/2− level at 365 keV. Thus, theexcitation energy of the last so far unknown protonhole state in 132 Sn was fixed to 3275(50) keV. From theabsolute intensities of the observed γ rays, the spectroscopic factors for the 1d5/2 and 0g7/2 neutron-holestates in 131 Sn and the 1p3/2 and 0f5/2 proton-holestates in 131 In were determined. They nicely agreewith those of the analog states with quantum numbersn(ℓ + 1)j+1 in 207 Pb and 207 Tl indicating that the close
resemblance between the shell structures around the
doubly-magic nuclei 132 Sn and 208 Pb established sincelong also holds for the spectroscopic factors. To investigate the origin of the strong fragmentation of singleparticle strength state-of-the-art calculations based on
131

Condensed from the article in Phys. Rev. Lett. 124, 022501(2020)∗1 Instituto de Estructura de la Materia, CSIC
∗2 Institut für Kernphysik, TU Darmstadt∗3 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗4 Department of Physics, Western Michigan University∗5 Department of Physics, University of Surrey∗6 RIKEN Nishina Center∗7 Dipartimento di Fisica dell’Università degli Studi di Milano∗8 INFN, Sezione di Milano∗9 School of Physics and State Key Laboratory of Nuclear
Physics and Technology, Peking University∗10 Institut für Kernphysik, Universität zu Köln
∗11 Department of Physics, University of Notre Dame
∗12 KVI-CART∗13 Department of Physics, Rikkyo University∗14 Department of Physics, The University of Tokyo∗15 Department of Physics, Tokyo Institute of Technology∗16 Departamento de Fsica Aplicada, Universidad de Huelva∗17 Center for Nuclear Study, The University of Tokyo∗18 Institut für Kernphysik, Goethe University Frankfurt∗19 Universidad de Santiago de Compostela†

Fig. 1. Doppler-corrected γ-ray spectra of 131 In populated
via one-proton removal from 132 Sn measured with a) 96
NaI crystals of DALI2 covering polar angles in the range
θ = 50–150◦ and b) eight LaBr3 detectors placed at θ =30◦ (adopted from Fig. 1 of the original article).

the relativistic particle-vibration coupling model were
performed. While the coupling to the first excited 3−
states in the core nuclei 132 Sn and 208 Pb was identified
as the main origin for the reduced spectroscopic factors
measured for the 1d5/2 /1f7/2 single-particle states in
131
Sn/207 Pb and the 1p3/2 /1d5/2 levels in 131 In/207 Tl,
clearly more complex coupling scenarios are responsible
for the strong fragmentation and the small measured
spectroscopic factors in the case of the 0g7/2 /0h9/2
states in 131 Sn/207 Pb and the 0f5/2 /0g7/2 levels in
131
In/207 Tl.

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Experimental studies of the two-step scheme with an intense radioactive132
Sn beam for next-generation production of very neutron-rich nuclei†

Production yields (cps)The usefulness of a two-step scheme with a 132 Sn
beam proposed1) for the eﬃcient production of midheavy very-neutron-rich RIs was investigated, as an alternate method for the in-ﬂight ﬁssion of a 238 U beam
(one-step scheme). The two-step scheme is a combination of an isotope-separation online (ISOL) system witha thick U target and a high-intensity proton beam as
the ﬁrst step, and the projectile fragmentation of reaccelerated RI beams (e.g., 132 Sn) as the second step.
We measured production cross sections beyond 125 Pd,
up to which the cross sections had already been measured at GSI together with the neighboring RIs,2) toevaluate the yields of RIs using the two-step scheme witha 132 Sn beam. The 278-MeV/nucleon 132 Sn beam was
supplied from BigRIPS, and the very neutron-rich RIs
around the neutron number N = 82 were produced in
the ZeroDegree spectrometer with a 5.97-mm Be target.
Yields obtained by the two-step and one-step schemes
were estimated based on the measured cross sections,and we examined whether and to what extent the twostep scheme at future 1-MW beam facilities can reachfurther into the neutron-rich region.
Figure 1 shows the production yields of Pd isotopes
obtained using the two-step scheme with a 132 Sn beam

10

8

Pd isotopes

106
104
10

2

two-step0
10 two-step(COFRA)
one-step-2
10
116 118 120 122 124 126 128 130 132

Mass number
Fig. 1. Yield comparison between the two-step scheme witha 132 Sn beam (orange circles) and the one-step in-flightfission of a 238 U beam (blue squares) for Pd isotopes.
†
∗1
∗2
∗3
∗4
∗5

Condensed from the article in Phys. Rev. C 102, 064615(2020)RIKEN Nishina Center
Center for Nuclear Study, University of Tokyo
National Superconducting Cyclotron Laboratory, Michigan
State University
Division of Physics, Argonne National Laboratory
Physik Department, Technische Universität MünchenZ

H. Suzuki,∗1 K. Yoshida,∗1 N. Fukuda,∗1 H. Takeda,∗1 Y. Shimizu,∗1 D. S. Ahn,∗1 T. Sumikama,∗1 N. Inabe,∗1
T. Komatsubara,∗1 H. Sato,∗1 Z. Korkulu,∗1 K. Kusaka,∗1 Y. Yanagisawa,∗1 M. Ohtake,∗1 H. Ueno,∗1 T. Kubo,∗1
S. Michimasa,∗2 N. Kitamura,∗2 K. Kawata,∗2 N. Imai,∗2 O. B. Tarasov,∗3,∗1 D. P. Bazin,∗3,∗1 J. Nolen,∗4,∗1 andW. F. Henning∗4,∗5,∗1

50
48
46
44
42
40
65

70

75

80

N

102
10
1
10−1
10−2
10−3
10−4
10−5

Fig. 2. Ratios of the Y2step with a 132 Sn beam to the Y1step .
Orange and blue regions indicate that the two- and onestep schemes are more useful than the other, respectively.
Dark-blue square dots represent the supernova r-process
path.

and the one-step scheme with 1-MW beam powers. The
two-step yields (Y2step ) decrease more slowly with neutron numbers than the one-step yields (Y1step ), andY2step becomes larger than Y1step beyond 124 Pd. The
ratio of Y2step /Y1step around the N = 82 region is shownin Fig. 2. This ratio systematically increases, as moving
away from the stability line. Thus, the two-step scheme
is more favorable than the one-step scheme to yield moreneutron-rich region beyond our results, especially for theregion of the supernova r-process path. The calculated
Y2step with a cross-section formula COFRA4) indicatedby black lines reproduces the experimental results well.
ISOL systems can provide various RIs over the nuclear chart; thus, a wide region of very neutron-rich RI
beams can be produced by the two-step scheme. By using the ISOLDE yield database3) and the cross-section
formula COFRA, the Y2step in the whole region was estimated. The Y2step was expected to be larger than theY1step around the neutron-rich N = 50, 60, 82, and 90,
including the supernova r-process path. The two-step
scheme is considered a powerful tool to open a new window into the unknown region of mid-mass to heavy, very
neutron-rich nuclei.
References

1) K. Helariutta et al., Eur. Phys. J. A 17, 181 (2003).
2) D. Pérez-Loureiro et al., Phys. Lett. B 703, 552 (2011).
3) ISOLDE Yield Database web page,
http://isoyields-classic.web.cern.ch .
4) COFRA web page, http://www.usc.es/genp/cofra .

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RIKEN Accel. Prog. Rep. 54 (2021)

On-line commissioning of the new SLOWRI/ZD-MRTOF system
M. Rosenbusch,∗1 S. Chen,∗2 Y. Hirayama,∗1 D. S. Hou,∗3 S. Iimura,∗4,∗5 H. Ishiyama,∗4 Y. Ito,∗6 S. Kimura,∗4
J. Liu,∗3 S. Michimasa,∗7 H. Miyatake,∗1 S. Naimi,∗4 S. Nishimura,∗4 T. Niwase,∗8,∗1,∗4 P. Schury,∗1
A. Takamine,∗4 M. Wada,∗1 Y. X. Watanabe,∗1 H. Wollnik,∗9 W. Xian,∗2 and S. Yan∗10
The new combined gas cell and MRTOF spectrographdeveloped for high-precision atomic mass measurements
at BigRIPS has been ﬁnalized and transported to theF11 position behind the ZeroDegree spectrometer of
RIBF. The combination of the new cryogenic gas cell1)
with the MRTOF system was initially tested in October
2020, where stable 39 K+ ions were extracted from thegas cell and detected at the system’s downstream TOF
detector. The system was ready to operate on-line justbefore the start of the 2020 HiCARI campaign, which enabled the ﬁrst on-line commissioning of the new setup.
The commissioning run took place in parasitic on-line
operation during the HiCARI experiments (see HiCARI
APR publications in this volume). After passing the HiCARI target and detectors, the reaction products weretransported through the ZeroDegree spectrometer andstopped in the new cryogenic gas cell. Energy degraders
were used to reduce the beam energy to match the He
gas cell’s stopping power. The stopped reaction products were extracted mostly as singly-charged ions andtransported to the MRTOF setup2) where their masses
were determined with high precision and accuracy. The
2020 HiCARI campaign lasted throughout the month ofNovember with ﬁve separate experiments, and anothertwo experiments took place in December. During ourcommissioning, mass measurements covering four diﬀerent regions in the nuclide chart have been carried out(see Fig. 1). Total system eﬃciencies, determined bycomparing the incoming rate from F11 at the PID system with the detected rate after MRTOF, varied according to the presence of contaminants in the helium gas.
While some of the radioactive species were dispersed
across molecular sidebands (e.g. 55 ScOH+ ), very reasonable ion transport could be reached for many otherspecies, e.g. 85 As+ with 0.16% and 137 Te+ with 1.3% total eﬃciency. In sum, the commissioning campaign was
highly successful with more than 70 atomic masses measured during the HiCARI campaign. Notable results
have been achieved in four diﬀerent regions. Aroundneutron-rich Ti and V isotopes, our results include isotopes from Ca to Fe with 55 Sc, 58 Ti, and 59 V being
the most exotic, which improve nuclear masses very recently measured using the TOF-Bρ method at NSCL3)∗1

Wako Nuclear Science Center (WNSC), IPNS, KEK
Department of Physics, the University of Hong Kong
∗3 IMP Lanzhou∗4 RIKEN Nishina Center∗5 Department of Physics, Osaka University∗6 Advanced Science Research Center, JAEA Ibaraki∗7 Center for Nuclear Study, the University of Tokyo∗8 Department of Physics, Kyushu University∗9 Dep. of Chem. and Biochem., New Mexico State University∗10 Jinan University∗2

Fig. 1. Nuclear mass measurements during the HiCARI campaign and the results by the ZD-MRTOF system. Backround color code illustrates the measured precision from
AME2016 (see Nucleus-win for reference).

and RIBF4) denoting the front line of nuclear mass studies in this region. In the neutron-rich region above Ni,
nuclides have been studied reaching from Ga to Kr with84
Ga, 86 Ge, 89 As, and 91 Se as most exotic isotopes. In
this group the isotopes 88, 89 As have been measured forthe ﬁrst time while three other isotopes provide a signiﬁcant improvement of the previously performed measurements. Another region addressed with success is fromMo to Rh isotopes including the ﬁrst mass measurementof 112 Mo. In the fourth region addressed, i.e. near 132 Sn,
we have demonstrated the isomeric mass separtion of
134g, mSb (W. Xian, APR same volume). In total, threeisotope masses have been measured for the ﬁrst timeand eleven other isotope masses improve the present uncertainty signiﬁcantly. By performing this ﬁrst on-line
commissioning of a gas stopper connected to BigRIPS
in a parasitic mode, we were able to eﬃciently identify
and resolve issues that could not be studied oﬄine. This
will allow for a very rapid improvement in performancegoing forward. In March 2021, the next commissioning
run takes place, wherein the neutron-rich Ni region will
be addressed by HiCARI group. Furthermore, two different beam times with the ZD-MRTOF system as main
experiment have been approved for 2021.
References

1) A. Takamine et al., RIKEN Accel. Prog. Rep. 53 (2018).
2) M. Rosenbusch et al., Nucl. Instrum. Methods Phys. Res.
B 463, 184 (2020).
3) Z. Meisel et al., Phys. Rev. C 101, 052801(R) (2020).
4) S. Michimasa et al., Phys. Rev. Lett. 125, 122501 (2020).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Mapping of a new deformation region around 62 Ti†
S. Michimasa,∗1 M. Kobayashi,∗1 Y. Kiyokawa,∗1 S. Ota,∗1 R. Yokoyama,∗2 D. Nishimura,∗3 D. S. Ahn,∗4
H. Baba,∗4 G. P. A. Berg,∗5 M. Dozono,∗1 N. Fukuda,∗4 T. Furuno,∗6 E. Ideguchi,∗7 N. Inabe,∗4 T. Kawabata,∗6
S. Kawase,∗8 K. Kisamori,∗1 K. Kobayashi,∗9 T. Kubo,∗10,∗11 Y. Kubota,∗4 C. S. Lee,∗1 M. Matsushita,∗1
H. Miya,∗1 A. Mizukami,∗12 H. Nagakura,∗9 H. Oikawa,∗12 H. Sakai,∗4 Y. Shimizu,∗4 A. Stolz,∗11 H. Suzuki,∗4
M. Takaki,∗1 H. Takeda,∗4 S. Takeuchi,∗13 H. Tokieda,∗1 T. Uesaka,∗6 K. Yako,∗1 Y. Yamaguchi,∗1
Y. Yanagisawa,∗4 K. Yoshida,∗2 and S. Shimoura∗1

Condensed from the article in Phys. Rev. Lett. 125, 122501(2020)∗1 Center for Nuclear Study, The University of Tokyo∗2 Dept. of Physics & Astronomy, University of Tennessee∗3 Dept. of Physics, Tokyo City University∗4 RIKEN Nishina Center∗5 Dept. of Physics, University of Notre Dame
∗6 Dept. of Physics, Kyoto University∗7 RCNP, Osaka University∗8 Dept. of Advanced Energy Engineering Sciences, Kyushu University∗9 Dept. of Physics, Rikkyo University∗10 FRIB, MSU∗11 NSCL, MSU∗12 Dept. of Physics, Tokyo University of Science∗13 Dept. of Physics, Tokyo Institute of Technology
†

14
LZU

12
S2n (MeV)

The mass of atomic nuclei is a fundamental quantity
as it reﬂects the sum of all interactions within the nucleus, which is a quantum many-body system comprisedof two kinds of fermions, protons and neutrons. Changes
in the shell structures of nuclei far from stability can bedirectly probed by mass measurements.
In the neutron-rich Cr and Ti region, the shell evolution around the ls-closed neutron number of 40 has
attracted considerable attention in recent years. The
onset of island of inversion (IoI), which was discoveredaround 32 Mg1) for the ﬁrst time, was theoretically predicted along the N = 40 isotones.2) The IoI is well characterized by the emergence of the Jahn-Teller (JT) stabilization,3,4) which is promoted by conﬁguration mixing
on the Fermi surface. The goal of the present experiment was to conﬁrm the presence or absence of thiseﬀect through the ﬁrst mass measurements of neutronrich Ti isotopes around N = 40.
The experiment was performed at the RI Beam Factory (RIBF) at RIKEN, which is operated by RIKEN
Nishina Center and Center for Nuclear Study, University of Tokyo. The masses were measured directly by using the TOF-Bρ technique. Neutron-rich isotopes were
produced by fragmentation of a 70 Zn primary beam at
345 MeV/nucleon in a 9 Be target. The fragments wereseparated by the BigRIPS separator,5) and transported
in the High-Resolution Beamline to the SHARAQ spectrometer.6)
Figure 1 shows the present results of the twoneutron separation energy (S2n ) of Sc, Ti, and V isotopes, together with theoretical S2n systematics obtained from the macroscopic-microscopic WeizsäckerSkyrme-type formula with treatments of two radial basis
functions corrections (LZU).9) This model largely reproduces the S2n trends including the present results. How-

V

10

23

8

22

6

Ti

Sc

21

4
32

34
36
38
40
Neutron Number N

Fig. 1. Two-neutron separation energies (S2n ) of Sc, Ti, andV isotopes around N = 40. Closed symbols indicate values determined from the present experimental masses,
and open symbols are literature values.7,8) . Solid lines
connect isotopes, and dashed lines show theoretical predictions by the LZU model.9)

ever, it is obvious that the model underestimates the S2nvalues in 61, 62 Ti isotopes. The results, therefore, conﬁrm that 62 Ti becomes very stable.
Since the behavior of the mass surface is similar tothat in the N = 20 IoI, it is reasonably demonstrated
that the JT stabilization arises in the vicinity of 62 Ti.
The theory4) suggests that this enhancement of the JT
stabilization around 62 Ti is caused by conﬁguration mixing among neutron f pgd orbitals enhanced by the degeneracy of the neutron orbitals.
References

1) E. K. Warburton, J. A. Becker, B. A. Brown, Phys. Rev.
C 41, 1147 (1990).
2) B. A. Brown, Prog. Part. Nucl. Phys. 47, 517 (2001).
3) H. A. Jahn, E. Teller, Proc. Poy. Soc. A161, 220 (1937).
4) P. -G. Reinhard, E. W. Otten, Nucl. Phys. A420, 173(1984).
5) T. Kubo, Nucl. Instrum. Methods Phys. Res. B 204, 97(2003).
6) T. Uesaka et al., Prog. Theor. Exp. Phys. 2012, 03C007(2012).
7) M. Wang et al., Chin. Phys. C 41, 030003 (2017).
8) Z. Meisel et al., Phys. Rev. C 101, 052801(R) (2020).
9) N. -N. Ma et al., Chin. Phys. C 43, 044105 (2019).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Surface localization of the dineutron in 11 Li†

A unique aspect of nuclei with respect to otherfermionic many-body systems is the emergence ofa spatially compact two-neutron pair, dineutron,1)
which is completely diﬀerent from the Bardeen-CooperSchrieﬀer-(BCS)-like pairings that appear in momentum space. The dineutron correlation is presumed to
be important for elucidating the stabilities and exotic
structures of neutron drip-line nuclei, as well as the inﬁnite nuclear matter. Studies on the dineutron formationand the density dependence of 11 Li are crucial because
it has a halo structure: the matter density graduallyvaries from the saturated core to the very low-density
tail where only valence neutrons exist. It allows thestudy of the density-dependent properties of the dineutron correlation.
The quasifree (p, pn) reaction was employed to probe
the entire volume of 11 Li with the least eﬀect of absorption. The measurement was performed at RIBF using
the SAMURAI spectrometer,2) combined with the 15cm-thick liquid hydrogen target MINOS3) and dedicated(p, pn) setup.
The strength of the dineutron in 11 Li was evaluatedby using the correlation angle θnf , which is the angle
between the momentum vectors of two valence neutrons.
The spatially compact dineutron should have an angle
larger than 90◦ . Figure 1 shows that the mean value ofCondensed from the article in Phys. Rev. Lett. 125, 252501(2020)∗1 RIKEN Nishina Center∗2 Center for Nuclear Study, University of Tokyo∗3 Département de Physique Nucléaire, IRFU, CEA, Université
Paris-Saclay∗4 Department of Physics, Technische Universität Darmstadt∗5 Department of Physics, Peking University∗6 IPN Orsay, Université Paris Sud∗7 LPC Caen, ENSICAEN, Université de Caen Normandie∗8 Department of Physics, Tohoku University∗9 Department of Applied Physics, University of Miyazaki∗10 Tokuyama College, National Institute of Technology∗11 Department of Physics, Osaka City University∗12 Department of Physics, University of Tokyo∗13 Department of Physics, Tokyo Institute of Technology∗14 Center for Exotic Nuclear Studies, Institute for Basic Science∗15 Institute for Nuclear Research, Hungarian Academy of Sciences∗16 Department of Physics, Kyoto University∗17 Department of Physics, Kyushu University∗18 Research Center for Nuclear Physics, Osaka University∗19 Department of Physics, Technische Universität München†

Correlation angle 〈θ nf 〉 (deg)Y. Kubota,∗1,∗2 A. Corsi,∗3 G. Authelet,∗3 H. Baba,∗1 C. Caesar,∗4 D. Calvet,∗3 A. Delbart,∗3 M. Dozono,∗2
J. Feng,∗5 F. Flavigny,∗6 J. -M. Gheller,∗3 J. Gibelin,∗7 A. Giganon,∗3 A. Gillibert,∗3 K. Hasegawa,∗8 T. Isobe,∗1
Y. Kanaya,∗9 S. Kawakami,∗9 D. Kim,∗14 Y. Kikuchi,∗10,∗1,∗11 Y. Kiyokawa,∗2 M. Kobayashi,∗2 N. Kobayashi,∗12
T. Kobayashi,∗8 Y. Kondo,∗13 Z. Korkulu,∗14,∗15 S. Koyama,∗12 V. Lapoux,∗3 Y. Maeda,∗9 F. M. Marqués,∗7
T. Motobayashi,∗1 T. Miyazaki,∗12 T. Nakamura,∗13 N. Nakatsuka,∗16 Y. Nishio,∗17 A. Obertelli,∗3
K. Ogata,∗18,∗11 A. Ohkura,∗17 N. A. Orr,∗7 S. Ota,∗2 H. Otsu,∗1 T. Ozaki,∗13 V. Panin,∗1 S. Paschalis,∗4∗3
E. C. Pollacco,∗3 S. Reichert,∗19 J. -Y. Roussé,∗3 A. T. Saito,∗13 S. Sakaguchi,∗17 M. Sako,∗1 C. Santamaria,
Thu Jan 21 22:40:29 2021
∗1
∗1
∗13
∗1
∗17
∗14,∗1∗8
M. Sasano, H. Sato, M. Shikata,Y. Shimizu, Y. Shindo,
L. Stuhl,
T. Sumikama, Y. L. Sun,∗3
∗17
∗13
∗13
∗1
∗17
M. Tabata,
Y. Togano,
J. Tsubota,
Z. H. Yang, J. Yasuda,
K. Yoneda,∗1 J. Zenihiro,∗1 T. Uesaka∗1

100
9Li

95

θnf

K'
k

n2
n1

90
85
80

This work
Quasifree model

0

0.5
1
1.5
Missing momentum k (fm -1)

Fig. 1. Mean values of the correlation angle. Black dashedline shows the expected ⟨θnf ⟩ value for the two uncorrelated neutrons. Inset shows a schematic of θnf in 11 Li.

θnf clearly depends on the missing momentum k, whichis the measure of the radial position of the two neutronsin 11 Li. The peak structure of ⟨θnf ⟩ at k ∼ 0.3 fm−1
can be interpreted as the localization of the dineutron,
which is maximized at r ∼ 3.6 fm from the center of
the 9 Li core. The quasi-free model4) well reproduces theexperimental data.
The result implies that the dineutron correlation isprominent only around the 9 Li core surface where thedensity is 10−3 ≲ ρ/ρ0 ≲ 10−2 , and it becomes weakerat the tail of the halo, where the density is extremely low.
It is consistent with the Hartree-Fock-Bogoliubov calculation5) for inﬁnite nuclear matter. If this is a universal
characteristic of the dineutron correlation, it should appear at the low-density surface of any neutron-rich nuclei. Future (p, pn) experiments should investigate thenature of the dineutron correlation in nuclei of interest,
such as 6 He, 16 C, and 24 O.
References

1) A. B. Migdal, Soviet J. Nucl. Phys. 16, 238 (1973).
2) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
3) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).
4) Y. Kikuchi et al., Prog. Theor. Exp. Phys. 2016, 103D03(2016).
5) M. Matsuo, Phys. Rev. C 73, 044309 (2006).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Probing alpha clusters in the low-density region of the nuclear surface†
J. Tanaka,∗1 Z. H. Yang,∗2 S. Typel,∗3,∗4 and T. Uesaka∗1 for the RCNP (p, pα) Collaboration

Alpha knockout reaction
protonGrand Raiden
Spectrometer
proton detection

neutron skin

Tin target
proton beam

0 1 2 3malpha particle
Large-AcceptanceSpectrometeralpha-particle detection

Fig. 1. Schematic illustration of the experimental setup.
†

∗1
∗2
∗3
∗4

1000

60

800
600

20 40

400

0

0

200

20

80

116

0

Sn(p, pα)

112

Cd

80

dσ/dMX (pb / MeV)

60
40
20

0

d

0
10
MX (MeV)

20

200

116

80

Sn(p, pα)112Cd

60
40
20
0

200

40

600

400

0.5

0.4

200

experiment0

TheoryThicker neutron skintheoryExperiment Less alpha clusters

58-30

d

62-20

66 -10 70

0 74 10 78
M (MeV)

20

X
Neutron number

124

80

Nα

120

116

20

400

112

30

Sn(p, pα)120Cd

108

0.1

Sn(p, pα)

120

Cd

400
200

X

0.6

800
600

0.4

0.2

0

-20

-10

0

10
MX (MeV)

20

30

0.0

112

116
120
Mass number A

1241) G. Gamow, Z. Phys. 51, 204 (1928).
2) S. Typel et al., Phys. Rev. C 81, 015803 (2010).
3) S. Typel, Phys. Rev. C 89, 064321 (2014).
4) M. Fujiwara et al., Nucl. Instrum. Methods Phys. Res.
A 422, 484 (1999).
5) J. Tanaka et al., Science 371, 260 (2021).

- S21 -

400

0

0.0

0

124

800

200

0
a0 scattered proton is analyzed
by0 the Grand Raideng
al-20
spectrometerat10an 20angleof40 45.3◦ .-30 A -20knocked-out
-10
0
10
-30
-20
-10
0
30
M (MeV)M (MeV)pha particle is analyzed by the LAS spectrometeratan angle of 60.0◦ .
The momenta of scattered protons and knockedout alpha particles were analyzed with the Grand
Raiden spectrometer4) and a large acceptance spectrometer, respectively. The missing-mass spectra ofSn(p, pα)Cd reactions were constructed from these momenta, and strong transitions from the ground state of
Sn to the vicinity of the ground state of Cd were observed. Figure 2 shows (a) the missing-mass spectrumof 112 Sn(p, pα)108 Cd. The peak indicated by the arrow is the transition from the ground state of 112 Sn
to the vicinity of the ground state of 108 Cd. Figure 2(b) shows the isotope dependence of cross sections.5) The black filled circles indicate experimental
data, and the red open squares indicate theoretical predictions, where the theoretical alpha-cluster formation
probabilities were converted to the (p, pα) cross sections using nuclear reaction calculations based on the
distorted wave impulse approximation. A good agreement with the theoretical conjecture is observed.
The theoretical study further suggested not only thecontrol of the formation of alpha clusters by neutron
skins, but also the suppression of neutron skins by theappearance of alpha clusters. The series of experimental studies of surface alpha clusters have the potential
to revise the parameters correlated with the neutronskin thickness in the nuclear equation of state in the
future.
200

40

600

20

References

Condensed from the article in Science 371, 260 (2021)
RIKEN Nishina Center
Research Center of Nuclear Physics, Osaka University
Technische Universität Darmstadt, Fachbereich Physik, Institut für Kernphysik
GSI Helmholtzzentrum für Schwerionenforschung GmbH

0Sn(p, pα) Cd
Fig. 2. (a) Missing-mass spectrum of60the0.3
reaction.
(b) Neutron-number
dependence of theSn(p, pα) Cd
40
40
200
(p, pα) reaction cross sections.
600
0.2
60

Cd

20

0.00

400

116

40

0.05

f

Sn(p, pα)

0.15

0.10

400

0

X

80

30

Counts / MeV-10Counts / MeV

c-20

Excitation energy of 108Cd (MeV)Counts / MeV

dσ/dMX (pb / MeV)

-30

dσ/dMX (pb / MeV)

0

800

120

60

-200

40

b

1000

Thinner neutron skinMore alpha clusters

80
(b)

1200

0

400

60

20

1400 0.20

600

-200

c

e

1600

Counts per 1 MeV

1200Counts per 1 MeV

1600

dσ/dMX (pb / MeV)

Cd

1

30

40

Counts per 1 MeV

b108

Counts per 1 MeV

40

Sn(p, pα)1121081400
112Sn(p,pα)
CdSn(p, pα)108Cd

dσ/dMX (pb / MeV)

dσ/dMX (pb / MeV)

Cross section(pb/MeV)dσ/dMX (pb/ MeV)

60

112

(a)

σ (nb)
Cross section
(nb)

80

σ/Nα (nb)a80Counts / MeVadσ/dMX (pb / MeV)

The formation of alpha clusters in the ground stateof heavy nuclei has been unclear for many years, boththeoretically and experimentally. Although the existence of preformed alpha particles in alpha-decay nuclei is an essential element in the theory of alpha decay,1) it was challenging to explain the appearance ofalpha clusters with the conventional mean-field models. In recent years, theoretical research based on thegeneralized density functional made progress and predicted that alpha clusters can exist in the low-density
region of the nuclear surface.2) It was shown that theformation amplitudes of alpha clusters on the nuclear
surface of tin isotopes decrease monotonically with increasing neutron excess, and the formation amplitudeof 124 Sn is approximately half that of 112 Sn.3) To directly prove the existence of alpha clusters in the surface of nuclei, the quasi-free alpha knockout reaction
is appropriate.
Our group performed an experiment at the ResearchCenter for Nuclear Physics of Osaka University. A proton beam at 392 MeV generated at the cyclotron facility bombarded stable tin targets (112 Sn, 116 Sn, 120 Sn,
124Sn) with an intensity of 100 nA. To achieve the highprecision measurement of knocked-out alpha particles,
we used double-arm spectrometers. The experimental setup is shown in Fig. 1. A proton beam impinges
on a tin target (red arrow from the left). Following aA
Sn(p, pα)A−4 Cd reaction (emphasized in the inset),I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Reaction cross sections on a deuteron as a probe of nuclear radii†
W. Horiuchi,∗1 Y. Suzuki,∗2,∗3 T. Uesaka,∗3,∗4 and M. Miwa∗3,∗4

where r = (s, z) with z being the beam direction.
In most measurements, the interaction cross section
σd:I is observed but not σd . Since σd includes all inelastic cross sections, σd > σd:I always holds. However, acalculation of σd:I demands all bound-state wave functions of the projectile, which is diﬃcult in general. For
the deuteron target, provided the projectile has only
one bound state, i.e., its ground state, one can evaluthe same inputs required to evaluate
ate σd − σd:I withσd as ∆0 σ = db (P0 (b) − Pd (b)) with

 P
2
P
1
1


P0 (b) = dr |ϕd (r)|2 eiχp (b+ 2 s)+iχn (b− 2 s)  . (2)If the projectile has more than one bound state, ∆0 σ
gives the lower bound of σd − σd:I .
Figure 1 displays σd , σp , and σn for 30 Ne as a
†
∗1
∗2
∗3
∗4

Condensed from the article in Phys. Rev. C 102, 054601(2020)
Department of Physics, Hokkaido University
Department of Physics, Niigata University
RIKEN Nishina Center
Department of Physics, Saitama University

1400

Cross sections (mb)

Total reaction or interaction cross section measurement has been used as a standard tool to determine
the nuclear radii of unstable nuclei. The total reaction
cross section of a proton target is known to exhibit
strong incident energy dependence that can be used todeduce both the neutron and proton radii.1,2) A neutron target may also be useful for the structual studyof the unstable nuclei as it has a diﬀerent sensitivity
compared to that of the proton target but no neutron
target exists. Since the deuteron is composed of neutrons and protons, the total reaction cross section ona deuteron target must include both information on
the nucleus-neutron and the nucleus-proton scattering
proﬁles.
To describe high-energy nucleus-deuteron reactions,
we employ the Glauber model,3) wherein the nucleusnucleon total reaction cross section σN (N = n, p) can P 2be obtained by σN = db (1 − eiχN (b)  ). Under
the optical-limit approximation, the optical phase-shiftPfunction eiχN (b) at the impact parameter vector b can
be evaluated using the projectile’s density and nucleonnucleon (NN ) scattering proﬁles. A unique advantageof the deuteron target is that one can calculate thephase-shift function accurately using its ground-state
wave function ϕd (r). The nucleus-deuteron total reaction cross section σd = db (1 − Pd (b)), and it can beobtained with

2
P
P
1
1


Pd (b) =  dr |ϕd (r)|2 eiχp (b+ 2 s)+iχn (b− 2 s)  , (1)

1200

30

Ne

1000

σd
σp
σn
σd:I
Δ0σ (x5)

800
600
400

(x5)

200
0

100

1000

Incident energy (MeV/nucleon)

Fig. 1. Various cross sections for 30 Ne adopted from theoriginal paper. See text for details.

function of incident energy. σd is always signiﬁcantly
smaller than σp + σn by about 70–90% of σp + σn due
to the “eclipse” of the constituent neutron and proton.3) The energy dependence of these cross sections
follows that of the NN total cross section. The information of the nucleus-neutron scattering proﬁle isincluded in σd . As already mentioned, the deuterontarget has the advantages that the upper bound of theinteraction cross section can be evaluated reliably using the deuteron wave function. Further, Fig. 1 displays the upper bound of the interaction cross section
σd:I and ∆0 σ for 30 Ne. ∆0 σ has at maximum 60–
70 mb at around 80 MeV/nucleon, which is about 6%of σd . In addition, ∆0 σ decreases with increasing incident energy. The ratio ∆0 σ/σd becomes at most few
percent beyond 300 MeV/nucleon. For the unstable
nuclei near the dripline that has only one bound state,a reliable interaction cross section can be obtained,
and this greatly improves the accuracy of the radius
extraction. We conclude that measuring the total reaction cross sections on both deuteron and proton targets is the most unambiguous and promising approachto determine the neutron and proton radii of unstable
nuclei.
References
1) W. Horiuchi, Y. Suzuki, T. Inakura, Phys. Rev. C 89,
011601(R) (2014).
2) W. Horiuchi, S. Hatakeyama, S. Ebata, Y. Suzuki,
Phys. Rev. C 93, 044611 (2016).
3) R. J. Glauber, Lectures in Theoretical Physics, edited by
W. E. Brittin, L. G. Dunham (Interscience, New York,
1959), Vol. 1, p. 315.

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Mean-square radius of the neutron distribution and skin thickness
derived from electron scattering†
H. Kurasawa,∗1 T. Suda,∗2,∗3 and T. Suzuki∗2
To the authors’ knowledge, this is the ﬁrst study todeduce the neutron distribution from electron scattering data in the history of nuclear physics.1)
The question how neutrons are distributed in nuclei
has been a longstanding problem. Although it is oneof the most fundamental problems in nuclear physics,
the neutron distribution has not been well determined
yet, because there is no simple and reliable method to
explore it experimentally.2) In contrast to the neutron
distribution, the proton distribution has been widely
investigated through the nuclear charge density deduced from electron scattering.3) Electron scattering
is an unambiguous and unique tool to examine thecharge distribution, because the electromagnetic interaction is well understood and allows reactions that do
not disturb the nuclear ground-state properties.4)
So far, electron scattering has been believed to be
useful for the study of the only proton distribution andhas not been discussed in the context of the neutron
distribution in nuclei.4) The SCRIT in RIKEN5) also
constructed with the primary objective of exploring
the proton distribution in unstable nuclei, although theneutron distribution plays a crucial role in the stabilityof neutron-rich nuclei. Such dogma is based on thefact that the neutron charge density is approximately
1% of the total nuclear charge density and oscillates
as a function of the nuclear coordinate, yielding zero
integrated charge.
Recently, the precise expressions for the moments of
the nuclear charge density were derived according torelativistic quantum mechanics.6) It has been shownthat the second-order moment of the nuclear charge
density(Rc2 ) is dominated by the mean-square radius(msr) of the point proton distribution (Rp2 ), while thenth (≥ 4)-order moment depends on the (n-2)th-ordermoment of the point neutron distribution also. For
example, the fourth-order moment (Q4c ) of the charge
density depends on the msr of the point neutron distribution (Rn2 ). The contribution of Rn2 to Q4c is dominated by the number of excess neutrons.
The present authors have analyzed experimental
data of Rc2 and Q4c deduced from the electron scattering oﬀ 40 Ca, 48 Ca, and 208 Pb, which are available atpresent.3) First, using relativistic and non-relativistic
mean ﬁeld models accumulated over the last 50 years
in nuclear physics, the linear relationship between the
†
∗1
∗2
∗3

various moments are explored with the use of the leastsquares method. Next, from the intersection of thepredicted least-square lines and the lines of the experimental value for Rc2 or Q4c , the values of Rn2 together
with Rp2 of those nuclei have been estimated. They are
obtained within 1% accuracy, including both experimental error and the standard deviation of the leastsquare lines.1)
This paper opens a new possibility of electron scattering as a clean and practical probe to extract neutron
density information. As the contributions from theneutron density to the charge density are expected toincrease in neutron-rich nuclei, the new electron scattering facilities in the world5) which are led by the
SCRIT7) would make the forthcoming study of unstable nuclei more eﬃcient and stimulating, both experimentally and theoretically.
References
1) H. Kurasawa, T. Suda, T. Suzuki, Prog. Theor. Exp.
Phys. 2021, 013D02 (2021).
2) M. Thiel et al., J. Phys. G 46, 093003 (2019).
3) H. De Vries, C. W. De Jager, C. De Vries, Atom. Data
Nucl. Data Tables 36, 495 (1987).
4) T. deForest, J. D. Walecka, Adv. Phys. 15, 1 (1966).
5) T. Suda, H. Simon, Prog. Part. Nucl. Phys. 96, 1 (2017).
6) H. Kurasawa, T. Suzuki, Prog. Theor. Exp. Phys. 2019,
113D01 (2019).
7) K. Tsukada et al., Phys. Rev. Lett. 118, 262501 (2017).

Condensed from the article in Prog. Theor. Exp. Phys.
2021, 013D02 (2021)
Department of Physics, Chiba University
Research Center for Electron-Photon Science, Tohoku University
RIKEN Nishina Center- S23 -

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Isotopic production of high-radiotoxic nuclide 90 Sr via proton- anddeuteron-induced reactions†
R. Matsumura,∗1,∗2 H. Otsu,∗1 H. Wang,∗1 N. Chiga,∗1 S. Kawase,∗3 K. Nakano,∗3 H. Sakurai,∗1,∗4
M. Shikata,∗5 S. Takeuchi,∗5 and Y. Togano∗5 for the ImPACT-RIBF Collaboration
210(a) Y (Z = 39)(b) Sr (Z = 38)

σp Exp.
σd Exp.
σp PHITS
σd PHITS

101
0

10

-1

Cross section σ [mb]The processing of spent fuels from nuclear power
plants is a worldwide problem. The by-products of
the reprocessing of spent fuels are high-level radioactive wastes, which contain minor actinides and ﬁssion
products. In this study, we focus on 90 Sr, which is themost radiotoxic nuclide in ﬁssion products.1) There is astrong desire to develop nuclear transmutation technology using accelerator facilities to reduce these harmful
nuclides. The simplest method is to irradiate the radioactive waste with a neutron beam. However, it is
not well known how much and into which nuclide 90 Sr
is transmuted in this reaction. Therefore, it is essential
to study the reaction cross sections to each nuclide from90
Sr in advance. From this perspective, the inverse kinematics, i.e., incident 90 Sr beam on light-particle targets,is an eﬀective method for identifying reaction productsin the forward direction.
The experiment was performed at RIBF. A secondary
beam including 90 Sr was produced by the in-ﬂight ﬁssion of 238 U at 345 MeV/nucleon on a 3-mm-thick 9 Be
production target, selected and identiﬁed event-by-event
using the TOF-Bρ-∆E method.2) Beam particles at
104 MeV/nucleon bombarded CH2 , CD2 , and C reaction targets placed at the entrance of ZDS. The residual
nuclei produced in reactions were identiﬁed in ZDS withthe same method as BigRIPS. Because the momentum
acceptance of ZDS is limited to ±3%, the experiment
was conducted using ﬁve diﬀerent momentum settings(∆ (Bρ) /Bρ = −9, −6, −3, 0, and +3%) for each target to accept a wide range of the mass-to-charge ratio
A/Q. The reaction cross sections were deduced from thenumber of incident 90 Sr nuclides, the number of residual
particles of each species, and the thickness of the target.
The backgrounds of carbon from CH2 and CD2 targets
and beam-line materials were subtracted using empty
and carbon target runs.
The data points above 1 mb were obtained with good
statistics. These were compared with the calculations
using the Particle and Heavy Ion Transport code System(phits),3) as shown in Fig. 1. The Liége Intranuclear
Cascade model (incl4.6) and the Generalized Evaporation Model (gem) were employed in the calculations. It
is observed that the calculation results were overestimated around the mass number of the projectile. Few-

10
2
10

(c) Rb (Z = 37)(d) Kr (Z = 36)(e) Br (Z = 35)(f) Se (Z = 34)

1

10

0

10

-1

10
102
101
100

10-1

75

80

85
90
75
Mass number A

80

85

90

Fig. 1. Isotopic-production cross sections of proton- (circles)
and deuteron-induced (diamonds) reactions and those obtained from the phits calculations (proton for solid anddeuteron for dotted lines).

nucleon removal reactions are not interpreted properly
in incl because momentum distributions of the nuclear
surface are treated in a semiclassical way.4) In addition,even-odd staggering eﬀects appeared excessively for nuclides produced by emitting many nucleons. This may
be controlled to some extent by considering the competition between particle and γ-ray emissions, as well as
the discrete energy levels, in the gem.
In the lower energy deuteron-induced reaction, it
has been observed that the initial reaction mechanism
changes drastically due to the breakup into proton andneutron during the reaction.5) Thus, we would also liketo obtain the reaction data for 90 Sr in the near future.
References

†

∗1
∗2
∗3
∗4
∗5

Condensed from the proceedings in JAEA-Conf 2021-001
RIKEN Nishina Center
Department of Physics, Saitama University
Department of Advanced Energy Engineering Science, Kyushu
University
Department of Physics, The University of Tokyo
Department of Physics, Tokyo Institute of Technology

1) K. Nishihara, JAEA-Data/Code 2010-012 (2010).
2) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
3) T. Sato et al., J. Nucl. Sci. Technol. 55, 684 (2018).
4) D. Mancusi et al., Phys. Rev. C 91, 034602 (2015).
5) H. Wang et al., Commun. Phys. 2, 78 (2019).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

CP -odd gluonic operators in QCD spin physics†
Y. Hatta∗1,∗2
The explanation of matter-antimatter asymmetry of
the universe requires new origins of CP -violation beyond the Standard Model (BSM). One of the interesting CP -violating operators that can be induced in
the QCD Lagrangian due to BSM physics is the Weinberg operator.1) In this report I point out a novel relation between the hadronic matrix element of the Weinberg operator and a certain twist-four correction inpolarized Deep Inelastic Scattering (DIS). Such a relation suggests an exciting possibility that polarized
DIS experiments can provide useful information to thephysics of the nucleon electric dipole moment (EDM),
or more generally, BSM-origins of hadronic CP violations.
The Weinberg operator is a dimension-six purely
gluonic operator
νa
Fbµα Fcα.
OW = gfabc F̃µν

νO4 ≈ ∂ (ψ̄g F̃µν γ ψ),

†
∗1
∗2

(8)

OW +

γ12
9Nc2
O4 .
O4 = OW −γW − γ4
3Nc2 + 4(9)Since this operator has a rather large anomalous dimension γW ∼ 10, in particular larger than γ4 by a factor of about 2, at high enough renormalization scalesµ2 one has⟨OW ⟩ ≈

9Nc2
⟨O4 ⟩ ≈ 2.61⟨O4 ⟩,3Nc2 + 4

(10)

(5)

Condensed from the article in Phys. Rev. D 102, 094004(2020)RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory⟨P |ψ̄g F̃ µν γν ψ|P ⟩ = −2f0 M 2 S µ

(11)

1
a
ν
Fbµσ Fcσ|P ⟩ = 4E ū′ iγ5 u.
⟨P ′ |gf abc F̃µν
M3

(12)

I get
E≈

(3)

where
7
2
N c + nf33

γ12 = −3Nc .

It immediately follows that the following linear combination is the eigenstate of the RG evolution(2)

to linear order in partial derivative ∂ µ . Such mixing is
usually neglected in the literature because O4 is a total
derivative and hence does
∫ not contribute to the CP violating eﬀective action d4 xO4 = 0. However, whenit comes to hadronic matrix elements, mixing becomes
crucial because only the nonforward matrix element isnonvanishing. Speciﬁcally, their RG equation takes the
form
(
(
)
)
)(
αs γW γ12
d
OW
OW
=
−
(4)
O4
0
γ4
d ln µ2 O4
4π
γW =

(7)

In terms of the nucleon matrix elements

Eq. (2) shows that one can choose OW and O4 as theindependent basis of operators and study their mixing.
Due to the equation of motion, one can writeµ⟨0|T{ψ(−k)Aρa (q)ψ̄(p)OW }|0⟩with oﬀ-shell momenta and nonzero momentum transfer ∆ = k − p − q ̸= 0. The result is(1)

This operator violates CP and can be induced in
the QCD Lagrangian by physics beyond the Standard
Model. It is considered as one of the candidate operators to generate a large EDM of the nucleons andnuclei.
The key observation is the following exact operator
identity←→←→1
OW = −∂ µ (F̃µν D α F να ) − F̃µν D 2 F µν
2
≡ O4 + OD ,is the anomalous dimension of the Weinberg operator.2) The anomalous dimension of O4 is the sameas that of the undiﬀerentiated, twist-four operator
ψ̄g F̃ µν γν ψ and is known to be3)82(6)
γ 4 = C F + nf .
3
3
To determine the oﬀ-diagonal component γ12 , I evaluate the following three-point Green’s function

9Nc2
f0 ≈ 1.3f0 .
2(3Nc2 + 4)

(13)

Therefore, one can evaluate the matrix element E of
the Weinberg operator through the measurement of the
f0 parameter relevant to the twist-four corrections inpolarized DIS.4,5) f0 can be extracted from the g1 (x)structure function measured at the future ElectronIon Collider (EIC) in the U.S. This is a new connection between the EIC and physics beyond the Standard
Model. It will demonstrate the EIC’s unique capability to address low-energy nucleon observables in a highenergy collider.
References

1) S. Weinberg, Phys. Rev. Lett. 63, 2333 (1989).
2) A. Y. Morozov, Sov. J. Nucl. Phys. 40, 505 (1984).
3) E. V. Shuryak, A. I. Vainshtein, Nucl. Phys. B 199, 451(1982).
4) E. V. Shuryak, A. I. Vainshtein, Nucl. Phys. B 201, 141(1982).
5) X. D. Ji, P. Unrau, Phys. Lett. B 333, 228 (1994).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Start the operation of AVF-BIS and its performance evaluation as a
successor system to BIS
M. Komiyama,∗1 A. Uchiyama,∗1 M. Fujimaki,∗1 M. Hamanaka,∗2 T. Nakamura,∗2 and N. Fukunishi∗1
The beam interlock system (BIS) for machine protection began operation in 2006 along with the beam commissioning of RIBF.1) The BIS is still under stable operation; however, its maintenance has become graduallydiﬃcult because some of the modules used in the system
are discontinued and cannot be replaced. In addition,
another problem is the declining performance of the system because of the increase in the number of inputs tothe system during its 14 years of operation. Measurements performed in summer 2020 show that the average
response time of BIS, the time from when the system receives the interlock signal to when the beam is stopped,
is approximately 18 ms, which is greater than the systemdesign value of 10 ms. To operate higher-power beams in
the future more safely, a response speed of 10 ms or lessis required. Therefore, we have been developing a successor system to the BIS for a few years, and we applied theprototype to the AVF cyclotron and its low-energy experimental facility as AVF-BIS in summer 2020. We willreport its operation status and performance evaluation.
The hardware constitution and process ﬂow of the prototype are shown in Fig. 1; the details are reported inRef. 2). One new advantage of the prototype is that it
has a multi-central processing unit (CPU) conﬁgurationthat can shorten the response time of the system by using
diﬀerent CPUs according to the speed required by eachprocess such as stopping the beam after receiving the interlock signal and parameter setting of the system. We
set up the prototype comprising two programmable logic
controller (PLC) stations: one with a Linux-based CPU
and a sequence CPU was installed in the vault for the polarized ion source, and the other with a sequence CPU
was installed in vault C for the power supplies for themagnets. The communication between the two stations
was performed through FL-net (an open network protocol used for interconnection between controllers) using
dedicated wiring; the signal setting and monitoring are
performed by the terminal in the control room via the
Ethernet. In AVF-BIS, 25 digital inputs and 24 analog
inputs are used as the interlock signals; 5 digital outputs
are used to stop a beam in total.
As a result of the oscilloscope-measured signal transmission speed in the AVF-BIS, the observed responsetime averaged 2 ms and 5.7 ms, respectively, within
one station and with both stations. The average response time is 1.4 ms and 3.8 ms for the operation within
one station and using two stations, respectively, in thetest prior to the introduction of the prototype as AVFBIS. The diﬀerence between the two measurements is attributed to the diﬀerence in the length of the ladder pro∗1∗2

RIKEN Nishina Center
SHI Accelerator Service Ltd.

Fig. 1. Hardware constitution and process flow in the prototype. Blue lines represent communication via Ethernet,
green lines represent communication via PLC bus, andpurple lines represent communication via FL-net.

gram executed on the sequence CPU: the ladder program
became longer as a result of the repeated program modiﬁcations when operating the prototype as the AVF-BIS.
However, it is suﬃcient as the performance of the AVFBIS. When deploying the AVF-BIS in the same scale as
the BIS that consists of 5 PLC stations with roughly
400 signals, the response time is estimated to be almost
10 ms. The basis for the estimation is as follows: increase
the number of total signals and the time required for thesignal transmission via FL-net increases depending on
the number of PLC stations.
The above result shows that it is possible to achievehalf the response time of the existing BIS by expanding
the prototype to the successor system of the BIS; however, simultaneously, it shows that it limits the performance of the system. In a system with insuﬃcient performance, it may not be possible to maintain the increasein the number of signals required to be monitored by the
BIS in the future when a higher-power beam accelerated
by RIBF, and another higher performance system may
be required again. To avoid such a scenario, we havestarted to study a system with a ﬁeld-programmablegate array (FPGA). The process that requires high speed
is executed on the FPGA while the system is designed
based on PLC. The system aims to reduce the responsetime to digital input signals to less than 1 ms.
References

1) M. Komiyama et al., RIKEN Accel. Prog. Rep. 39, 239 (2006).
2) M. Komiyama et al., Proc. ICALEPCS2019, 2019-10,
pp. 384–387.

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RIKEN Accel. Prog. Rep. 54 (2021)

HiCARI: High-resolution Cluster Array at RIBF
K. Wimmer,∗1,∗2 P. Doornenbal,∗2 N. Aoi,∗3 H. Baba,∗2 F. Browne,∗2 C. Campbell,∗4 H. Crawford,∗4
H. De Witte,∗5 C. Fransen,∗6 H. Hess,∗6 S. Iwazaki,∗3 J. Kim,∗2 A. Kohda,∗3 T. Koiwai,∗7,∗2 B. Mauss,∗2
B. Moon,∗2 T. Parry,∗8 P. Reiter,∗6 D. Suzuki,∗2 R. Taniuchi,∗9,∗2 S. Thiel,∗6 and Y. Yamamoto∗3
The RIKEN Nishina Center and the RIBF have been
conducting in-beam γ-ray spectroscopy experiments at
the forefront of nuclear structure research. Studies on
exotic nuclei have focused on experiments employing
beams with the largest possible isospin asymmetry. Low
beam intensities require thick secondary reaction targets to achieve reasonable luminosity for measurements
as well as a high eﬃciency γ-ray detector. The NaI(Tl)detector array DALI2 1) features a very high detection
eﬃciency, ∼20% for 1 MeV γ rays, but it has very limited resolution for the transition energies (approximately
10% FWHM for typical in-beam experiments). This detector is ideally suited for ﬁrst spectroscopy experiments
for nuclei at the limits of the known nuclear chart, as well
as for studies featuring low level densities or selective
population of states such as magic nuclei or Coulomb
excitation. The detailed spectroscopy of complex level
schemes and measurements of excited state lifetimes are
not possible with the DALI2 array.
To overcome these limitation for in-beam γ-ray spectroscopy experiments at the RIBF, the HiCARI project
was initiated. The HiCARI array comprises segmented
high-purity germanium detectors. This provides excellent energy resolution to in-beam experiments by improving both the intrinsic energy resolution of the detector material itself and the position resolution for theinteraction points of the γ ray with the detector material, which is required for the Doppler reconstructionof transition energies. The high resolution also allows
determining the lifetimes of excited states by analyzing the shape of the peak in the Doppler reconstructed
spectrum. For the HiCARI array, eight Miniball triple
cluster detectors,2) 8(4)-fold segmented Clover detectors
from IBS Korea (two clusters) and IMP China (four clusters), the RCNP quad-type 36-fold segmented tracking
detector, and a triple segmented tracking detector P3
from LBNL Berkeley, which is also 36-fold segmented,
are available. The ﬁnal array installed at the F8 focus
for experiments employing the ZeroDegree spectrometercomprises six Miniball triples, four Clovers, and the two
tracking detector modules; it is shown in Fig. 1.
The readout electronics is based on the digital data acquisition of the GRETINA array.3) The signals of eachcentral contact and segment electrode are digitized with
∗1
∗2
∗3
∗4
∗5

∗6
∗7
∗8
∗9

IEM-CSICRIKEN Nishina Center
RCNP, Osaka University
Nuclear Science Division, Lawrence Berkeley National Laboratory
Instituut voor Kern- en Stralingsfysica, KU Leuven
Institut für Kernphysik, Universität zu Köln
Department of Physics, University of Tokyo
Department of Physics, University of Surrey
Department of Physics, University of York

Fig. 1. HiCARI array located at the F8 focus. The beam
enters through the beam pipe from the left. The forward
ring (θlab ∼ 22–55◦ ) comprises six Miniball detector modules (MB). The tracking detectors (P3 and Quad) are located in the horizontal plane, with the Clover detectors(CL) arranged on top and bottom of the θlab ∼ 60–85◦
ring.

a 100 MHz sampling rate and recorded. The energy
is derived using a trapezoidal ﬁlter algorithm. For the
tracking detectors, the energy and three-dimensional position information of individual interaction points within
the segments is derived from the GRETINA signal decomposition analysis.
Before the experimental campaign (for details on individual experiments, see contributions in this volume),a series of characterization and commissioning measurements was performed. In-beam measurements using an
intense 82 Ge beam of approximately 260 MeV/nucleon
impinging on Be and Au targets of various thicknesses
were used to characterize the in-beam eﬃciency and resolution of the HiCARI array. The response to the highintensity, low-energy radiation from atomic processes in
the collision of beam and target was also investigated,
and the eﬀect of diﬀerent shielding materials was explored.
References

1) S. Takeuchi et al., Nucl. Instrum. Methods Phys. Res. A
763, 596 (2014).
2) N. Warr et al., Eur. Phys. J. A 49, 40 (2013).
3) S. Paschalis et al., Nucl. Instrum. Methods Phys. Res. A
709, 44 (2013).

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RIKEN Accel. Prog. Rep. 54 (2021)

Removing non-isobaric ions from an MRTOF-MS by periodic electricpulsesS. X. Yan,∗1,∗2 M. Rosenbusch,∗2 W. D. Xian,∗3,∗2 S. D. Chen,∗3,∗2 Y. Hirayama,∗2 D. S. Hou,∗4,∗2 S. Iimura,∗5,∗6
H. Ishiyama,∗5 Y. Ito,∗7 S. Kimura,∗5 J. J. Liu,∗3,∗2 H. Miyatake,∗2 S. Nishimura,∗5 T. Niwase,∗8,∗5,∗2 P. Schury,∗2
A. Takamine,∗5 M. Wada,∗2 Y. X. Watanabe,∗2 and H. Wollnik∗9

Lens

Drift tube

Ions in

Lens

Eject mirror
To detector

Inject mirror 5, 6, 7, 8

Pulse on (600 V)
Pulse off (0 V)

Fig. 1. Schematic of cleaning mode and potential distribution along the axis in MRTOF-MS.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

Institute of Mass Spectrometry and Atmospheric Environment, Jinan University
Wako Nuclear Science Center(WNSC), IPNS, KEK
Department of Physics, The University of Hong Kong
Institute of Modern Physics, Chinese Academy of Science
RIKEN Nishina Center
Department of Physics, Osaka University
Advanced Science Research Center, JAEA Ibaraki
Department of Physics, Kyushu University
Department of Chemistry and Biochemistry, New Mexico
State University

Counts

103
102
10
1

CountsIn the recent SLOWRI/ZD-MRTOF1) commissioning
run, radioactive ions were extracted with stable molecular ions spanning a wide mass range from impurities
in the helium gas cell. Owing to the periodic natureof an MRTOF mass spectrometer (MRTOF-MS), thisleads to an overlapping of ions with ions of varying
A/q performing diﬀerent numbers of laps in the TOF
spectra. Unwanted stable molecular ions with higher
abundance than the ions of interest prevented theidentiﬁcation of exotic isotopes from BigRIPS. Thus,
it was necessary to devise a new puriﬁcation method
to remove contaminant ions as much as possible in our
online measurement. An in-trap mass separation system
for the ZD-MRTOF system was not yet installed duringcommissioning runs. Such systems are scheduled forthe future based on existing knowledge, e.g., selection
methods called in-trap potential lift technique2) andin-trap deﬂector technique.3) Both techniques apply
electric pulses to eject unwanted ions, where a single
pulse on the order of a kilovolt is used at the moment ofion ejection (only applicable for isobaric ion separation)in the ﬁrst method, and periodic low-voltage pulses areapplied to a deﬂector inside the MRTOF device forthe wideband ejection of ions in the second method.
Here, we implement a new mass ﬁlter method based on
periodic 600 V pulses of 2–4 µs duration using mirror
electrodes that were on the ground potential previously.
This periodic rectangular pulse is applied to injectionside mirror electrodes 5–8 (see graphic and simulated

102
10
1
15.7080

15.7085

15.7090

15.7095

TOF [ns]

15.7100

15.7105

15.7110(×106 )

Fig. 2. Measured TOF spectrum without and with thecleaning mode; spectral peak marked in red is 82 Ge.

potentials in Fig. 1).
The√ ﬂight time depends on the mass-to-charge ratiot ∝ (A/q) of the ions. Diﬀerent ion species of equal
initial energy separate during ﬂight in the MRTOF
analyzer according to their A/q. The “on”/“oﬀ” stageof the pulses is synchronized with the wanted A/qvalue, and therefore, it is ensured that the ions ofinterest always experience the “oﬀ” stage when crossing
the pulsed electrodes. In turn, the unwanted A/qions are not synchronized, and they cross the pulsed
region randomly in time. Being aﬀected by the pulses
once or several times changes their kinetic energy andadditionally scatters the ions in a radial direction, whichleads to unstable trajectories and ejection of ions. Thisejection scheme was ﬁrst tested in a simulation, and thenapplied in the experiment. After about 100–200 laps,ions of undesirable A/q crossed this region several times,
and they could mostly be removed from the system. In
our online experiments, the cleaning mode was applied;
a comparison without and with the cleaning is shownin Fig. 2. Only the selected mass range is retained,
and other mass areas are considerably clean in the
spectrum. Although a very slight peak shift may occur
due to the ﬂuctuation of mirror potentials, this canbe measured and corrected in the mass analysis. The
new cleaning method was successful and enabled our
ﬁrst online measurements to determine low count rate
nuclides.
References

1) M. Rosenbusch et al., Nucl. Instrum. Methods Phys. Res.
B, 463, 184 (2020).
2) F. Wienholtz et al., Int. J. Mass. Spectrom., 421, 285 (2017).
3) P. Fischer et al., Rev. Sci. Instrum. 91, 023201 (2020).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Development of the gaseous Xe scintillation detector for heavy RI beams

Fig. 1. Photograph of the new version of the gaseous Xe
scintillation detector. Four 2-inch-ϕ PMTs (Hamamatsu,
R6041-406) were attached to the corners.
∗1

Department of Physics, Kyoto University
RIKEN Nishina Center∗3 CNS, University of Tokyo∗4 Department of Physics, Toho University∗5 CYRIC, Tohoku University∗6 Department of Natural Sciences, Tokyo City University∗7 RCNP, Osaka University∗8 Department of Physics, Rikkyo University∗9 School of Physics, Beihang University∗10 Department of Physics, University of Tokyo
∗2

37

Z

In this contribution, we brieﬂy report on the performance test of the gaseous Xe scintillation detector installed in the F7 vacuum chamber of BigRIPS. In thistest, we use the detector for the particle identiﬁcationof heavy RI beams up to the atomic number Z ∼ 90
for the ﬁrst time. At present, RIBF is the best facility
for the generation of high-intensity and high-energy RI
beams in the world. However, the use of high-intensity
RI beams is now limited because of radiation damage
and/or the slow responses of the standard detectors of
BigRIPS.1) As machine time is also limited because of
the hogh cost of electric power, failure to use the highintensity RI beams would be a signiﬁcant loss.
Therefore, we proposed a new detector using scintillation photons from Xe gas. Because the average energy
expended per scintillation photon is very small (<20 eV)
and its lifetime is relatively short (5 ns and 100 ns),2)
the detector is expected to have a good energy resolution
and a fast response time. The Xe detector is promising
for the ∆E measurements of high-intensity RI beams(>100 kcps), where the ion chamber (IC) cannot work
because of the slow response. To replace the IC with the
Xe detector, we must ﬁrst compare its energy resolution

Z

Y. Hijikata,∗1 J. Zenihiro,∗1 H. Baba,∗2 M. Dozono,∗3 S. Enyo,∗1 N. Fukuda,∗2 T. Harada,∗2,∗4 Y. Matsuda,∗5
S. Michimasa,∗3 D. Nishimura,∗6 S. Nishimura,∗2 S. Ota,∗3 H. Sakaguchi,∗7 H. Sato,∗2 Y. Shimizu,∗2
S. Sugawara,∗6 H. Suzuki,∗2 H. Takahashi,∗6 H. Takeda,∗2 S. Takeshige,∗8 J. Tanaka,∗2 S. Terashima,∗9 R. Tsuji,∗1
T. Uesaka,∗2 S. Yamamura,∗10 and K. Yoshida∗2

36

10

35

37

36

10

35
1

34

1

34

33

33

−1

10

−1

10
32

2.44

2.48

2.52

2.56

2.60

32

A/Q

2.44

2.48

2.52

2.56

2.60

A/Q

Fig. 2. Z obtained using the IC (left) and the Xe detector(right) vs. A/Q spectra with the Ge setting.

to that of the IC. A prototype of the detector was tested
using a cocktail secondary beam at 300 MeV/nucleon up
to Z = 55 at HIMAC, QST in Chiba. An rms resolutionof ∆Z = 0.2 around Z = 55 in sigma was achieved.3)
However, it is diﬃcult to install the prototype in thevacuum chambers at the focal planes in the BigRIPS
beamline owing to the thick detector material, which
consists of 4-atm and 12-cm-thick Xe gas and 2-mmthick Al windows. We recently built a new version of
the Xe detector with 2-atm and 9-cm-thick Xe gas and125-µm-thick Kapton windows, as shown in Fig. 1. The
material thickness is approximately 100 mg/cm2 , whichis comparable to that of the IC.
In November 2020, we installed the new detector in
the F7 vacuum chamber for the ﬁrst time and performed
a test experiment by using several heavy RI and primary beam settings such as Ge, Sb, Er, Th, and U.
We successfully acquired data of particles of diﬀerent Z
and diﬀerent beam intensities. For the readout circuits,
ﬂash ADC (CAEN V1730) have been used in addition to
the conventional QDC and TDC modules to check thehigh-rate torelance. Figure 2 shows the obtained twodimensional PI spectra with the Ge setting. To deduce
Z and A/Q values, the energy loss ∆E of the IC and theXe detector as well as time of ﬂight between the F3 andF7 plastic scintillators are used. The rms resolution of∆Z ∼ 0.22 determined from the ∆E in the Xe detector
is very close to that of the IC. Although the analysis
is ongoing, the preliminary spectra show that the Xe
detector will be helpful under high-intensity beam conditions.
References

1) T. Kubo et al., Nucl. Instrm. Methods Phys. Res. B 204,
97 (2003).
2) M. Mimura et al., Jpn. J. Appl. Phys. 48, 076501 (2009).
3) J. Zenihiro et al., RIKEN Accel. Prog. Rep. 51, 156 (2018).
- S29 -

1

RIKEN
54(2021)(2021)RIKENAccel.
Accel.Prog.
Prog. Rep.
Rep. 54

I. HIGHLIGHTS OF THE YEARµSR study of slightly pressurized organic superconductor κ-(ET)4 Hg2.89 Br8

∗1
∗2
∗3

College of Engineering, Shibaura Institute of Technology
RIKEN Nishina Center
Department of Physics, Saitama University

Normalized Asymmetry

0.0
‒ 0.2
‒ 0.4
‒ 0.6
‒ 0.8
‒ 1.0 0

(a)
1

35

2
3
4
Temperature (K)

5

6

(c)

0.8
0.6
0.4
0.2
0.0

0

2

4

6
8
Time (μs)

1

2

10

12

0.35

λ (μs ‒1)

25
20
15
10

0.30
0.25

5
0
0

1.0

0.40

30

H c1 (Oe)Organic superconductors are single-band system, similar to high-critical-temperature (high-Tc ) cuprates superconductors. A distinct diﬀerence can be observed intheir lattice, i.e., squared cuprates and triangular organics. In the case of squared cuprates, the Mott insulating state has an antiferromagnetic (AF) ground statein the 1/2-ﬁlled band case, while the anisotropic triangular (t = t′ ) organics also exhibit AF state. Here, t
and t′ are the nearest and next nearest transfer integral between sites, respectively. For a triangular lattice
Mott insulator, owing to geometrical frustration (t ∼ t′ ),the system cannot be magnetically ordered down to themili-Kelvin order, i.e., a spin liquid state. Owing to hole
doping, it should also become metallic and superconducting (SC). However, the realistic candidate material
was limited until the discovery of hole-doped organic superconductor κ-(ET)4 Hg2.89 Br8 (κ-HgBr). In metallic
state, resistivity exhibits the linear-temperature dependence, ρ ∝ T , which is not a Fermi-liquid behavior. The
susceptibility from 300 to 2 K is nearly perfectly scaled
to that of a non-doped spin liquid organic insulator κ(ET)2 Cu(CN)3 .1) By pressure, this non-Fermi-liquid behavior turns into conventional Fermi-liquid behavior at
the Pc = 0.5 GPa, where Tc is also the highest (∼7 K)
in the pressure-temperature phase diagram.2) The nonFermi-liquid behavior at low-pressure region is similar
to the metallic state of high-Tc cuprates or low-pressure
range of multi-band heavy fermion CeCoIn5 , and it isreferred to as a strange metallic region.1,2) Because κHgBr exhibits similarities with other strongly correlated
electron systems, it is interesting to determine the typeof Cooper pairing that occurs in κ-HgBr.
We aim to determine the pairing symmetry in κHgBr by µSR. We performed µSR measurement down
to 0.3 K on the ARGUS spectrometer at the RIKENRAL muon facility with HELIOX cryostat and ﬂy-path
setup. We developed a technique for applying a decent pressure on κ-HgBr crystals because at ambientpressure, the SC state of κ-HgBr is not bulky due tothe inhomogeneous state.3) Approximately 130 mg crystals were carefully aligned and stuck together using diluted polymer glue. This strategy was eﬀective for applying enough pressure on the sample as we conductedmagnetization measurement using SQUID with a similar sample setup. Figures 1(a) and (b) show the resultof SQUID measurement. The demagnetization eﬀect due
to sample shape was treated for all analyses. The temperature dependence of susceptibility determined Tc =4.6(2) K whereas the ﬁeld dependence of magnetization(MH-curve) was measured at several temperatures; theSC volume fractions were estimated at each temperature. Consequently, the estimated SC volume fraction
at 2 K was found to be approximately 90%, as shown inDiamagnetic Volume Fraction

D. P. Sari,∗1,∗2 Y. Ishii,∗1 I. Watanabe,∗2 and H. Taniguchi∗3

(b)
1

2
3
4
5
Temperature (K)

6

0.20
0.1

(d)
2

4 6

4 6

10
Field (G)

2

4 6

100

Fig. 1. (a) Temperature dependence of SC volume fraction
measured by SQUID. (b) Temperature dependence of Hc1
measured by SQUID down to 2 K compared with µSR
measurement. (c) ZF-µSR time spectra before and after
applying TF of 40 G. The solid lines are the exponential
decay fitting lines. (d) Relaxation rate of ZF-µSR time
spectra after applying several TF, from 2 to 40 G.

Fig. 1(a). Comparing this with the referred result obtained from ac-susceptibility measurement,3) a pressureof at least 0.3 GPa was applied to the sample. This expectation was conﬁrmed by the estimation of the lowercritical ﬁeld, Hc1 , by SQUID, resulting in the absolutevalue of Hc1 at 0 K, i.e., 27 Oe. The result is consistent
with the measurement performed using zero-ﬁled (ZF)
µSR at 0.3 K. Hc1 was estimated as follows. The sample was ZF-cooled to 0.3 K. Transverse-ﬁeld (TF) wasapplied for approximately 10 min to destroy the shielding ﬁeld. After cutting oﬀ the TF, the ZF-relaxation
rate was measured. At TF = 25 Oe, the relaxation
rate started to increase. Therefore, we concluded thatthe sample was in bulk condition and a slight pressure,P ≳ 0.3 GPa, was applied. Using these results, we measured the ZF-µSR relaxation rate in κ-HgBr down to
0.3 K. The temperature independence of ZF-relaxation
rate was observed, indicating that spontaneous internalﬁelds do not appear in the superconducting state. This
result is consistent with that in Ref. 4), in which the measurement was performed down to 1.5 K and at ambientpressure. Thus, the possibility of spin triplet and d + idwave symmetry in κ-HgBr due to the expected triangularlattice in κ-HgBr becomes very low. The temperaturedependence of London penetration depth measurement
using TF-µSR is necessary for determining the SC gap
symmetry, which will be discussed in the future work.
References

1) H. Oike et al., Nat. Commun. 8, 756 (2017).
2) H. Taniguchi et al., J. Phys. Soc. Jpn. 76, 113709 (2007).
3) H. Oike et al., Phys. Rev. Lett. 114, 067002 (2015).
4) K. Satoh et al., Physica B 404, 597 (2009).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Targeted alpha therapy of cancer: Evaluation of [211 At] AAMT
targeting LAT1†
K. Kaneda-Nakashima,∗1,∗2 Z. Zhang,∗2 Y. Manabe,∗1,∗2 A. Shimoyama,∗1,∗2 K. Kabayama,∗1,∗2 T. Watabe,∗1,∗2
Y. Kanai,∗1,∗3 K. Ooe,∗1,∗3 A. Toyoshima,∗1,∗2 Y. Shirakami,∗1,∗2,∗3 T. Yoshimura,∗1 M. Fukuda,∗2,∗4
J. Hatazawa,∗1,∗3 T. Nakano,∗2,∗4 K. Fukase,∗1,∗2 and A. Shinohara∗1,∗2

Methods
The 209 Bi(α, 2n)211 At reaction using the AVF Cyclotron at the Research Center for Nuclear Physics, Osaka University (Ibaraki, Japan) was used to produce
211At.4) Further 211 At was produced with the same nuclear reaction at the Nishina Center for AcceleratorBased Science, RIKEN, and it was then transported to
the Osaka University.
PANC-1 cells were cultured at 37◦ C in D-MEM containing 10% fetal bovine serum and 1% antibiotics ina humidiﬁed incubator with 5% CO2. Cultured cells
were washed in PBS (-) and harvested with trypsin.
Tumor xenograft models were established by the subcutaneous injection of 1 × 107 cells in 0.2 mL of serumfree medium and Matrigel (1:1) into female BALB/cnu/nu mice. PANC-1 xenograft mice (10 weeks old;body weight = 19.3 ± 1.4 g) were used when the tumor
size reached approximately 50 mm3 on average.
The mice were divided into two groups according to
the injected dose [0.4 MBq (n = 4, 4.0 ± 0.2 MBq/mL);
control (n = 4)]. The control group only received sol†

∗1
∗2
∗3
∗4

Condensed from the article Cancer Sci. 112(3), 1132 (2021)
Institute for Radiation Sciences, Osaka University
Graduate School of Science, Osaka University
Graduate School of Medicine, Osaka University
Research Center for Nuclear Physics, Osaka University

3000

Tumor volume (mm3)L-type amino acid transporter 1 (LAT1) is an isoform of the system L, which is Na+ -independent neutralamino acid transport agency. LAT1 is expressed in primary human cancers originating in various organs suchas the brain, lung, thymus, and skin, it is a well-known
speciﬁc cancer marker. Amino acid tracers containing
radioactive halogen have attracted attention for use asprobes in single photon emission computed tomography(SPECT) and positron emission tomography (PET). L3-[18 F]- α-methyl-tyrosine (18 F-FAMT) has higher potential for tumor speciﬁcity than 2-deoxy-2-[18 F] ﬂuoroglucose (18 F-FDG), which is widely employed as a PET
probe for cancer staging. Further FDG has the potential for false-positive accumulation within inﬂammation
related to high glucose metabolism in macrophages orneutrophils, whereas 18 F-FAMT accumulates in tumors
via LAT1, which is expressed only in cancer cells.1) In
contrast, 18 F-FAMT is not transported by other isoforms of the system L (e.g., LAT2, LAT3, and LAT4),
that are expressed in normal tissues.2,3) Therefore, ourL-3-[211 At] - α-methyl-tyrosine (211 At-AAMT) is expected to exhibit LAT1 speciﬁcity and to have the potential to be used as a targeting alpha therapy (TAT)
treatment.

Distribution
in mice■ Control○ 211At-AAMT

2000

1000

0

0

10

20

30

40

Days after injection (Days)

Fig. 1. Eﬃcacy of 211 At-AAMT using the PANC-1
xenograft model. Tumor growth inhibition by 211 AtAAMT (Left). Coronal images of 211 At-AAMT intumor-bearing model (Right).

vents.
Tumor sizes and body weights were measured threetimes per week. Mice were sacriﬁced when the tumor
size reached more than 10% of the total weight. The
mice were observed for 40 days. Uptakes were normalized by the injected dose (MBq) and body weight (g).
Results
In the PANC-1 model, the control mice were injected only with solvents (0.2 w/v% AcOH and 1 w/v%
ascorbic acid solution) and the 211 At-AAMT treatmentgroup received i.v. injections of the 0.4 MBq/mouse
211
At-AAMT solution. No inﬂammation or abnormalities were observed around the injection site. In the
211
At-AAMT treatment group, the tumor growth was
clearly inhibited and the body weight was not signiﬁcantly decreased compared to the control group (Fig. 1).
Conclusion
211
At-AAMT may be considered a novel anti-cancer
drug. While 211 At-AAMT could inhibit tumor growthwith a single treatment, the tumor was not completely
abolished, and therefore, a single injection was insuﬃcient to decrease the tumor size continuously. Multiple
doses may be necessary to exploit the high anti-tumor
eﬀect of 211 At-AAMT. In conclusion, 211 At-AAMT may
be an eﬀective anti-cancer drug when administered multiple times or in combination with existing anti-cancer
drugs.
References

1) A. Achmad et al., BMC Med. Imaging 17, 66 (2017).
2) L. Wei et al., J. Pharmacol. Sci. 130, 101 (2016).
3) L. Wei et al., Cancer Sci. 107, 347 (2016).
4) T. Watabe et al., J. Nucl. Med. 60, 1301 (2019).
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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Influence of antibody stabilization with sodium ascorbate onradioimmunotherapy with an 211 At-conjugated anti-tissue factor
antibody†
H. Takashima,∗1,∗2 Y. Koga,∗1,∗2 S. Manabe,∗3,∗4,∗5 K. Ohnuki,∗6 R. Tsumura,∗1 T. Anzai,∗1 N. Iwata,∗1
Y. Wang,∗2 T. Yokokita,∗2 Y. Komori,∗2 D. Mori,∗2 H. Haba,∗2 H. Fujii,∗6 Y. Matsumura,∗7 and M. Yasunaga∗1
Alpha radiation is characterized by higher linear transfer compared to other types of ionizing radiation and arange of 50–100 µm in tissue. Therefore, the selective
tumor accumulation of alpha emitters exerts potent antitumor eﬀects without serious toxicity against normal
cells adjacent to the tumor. Astatine-211 (211 At) is analpha emitter, its high production yield is suﬃcient to
prepare 211 At-labeled radiopharmaceuticals for administration at clinical doses.
Tissue factor (TF), a transmembrane glycoprotein initiating the extrinsic blood coagulation cascade, is overexpressed in tumors such as gastric cancer, pancreaticcancer, and malignant gliomas.1,2)
Immunoglobulin G (IgG) selectively accumulate in tumor via the enhanced permeability and retention (EPR)eﬀect.3) In addition, the antigen-antibody reaction enhances the tumor accumulation of antibodies.2) Therefore, we focused on applying anti-TF monoclonal antibodies (mAbs) established by us to armed antibodies
such as antibody-drug conjugate (ADC)4–6) and antibody labeled with therapeutic radionuclides.
We synthesized 211 At in the 209 Bi(α, 2n)211 At reaction using the RIKEN azimuthally varying ﬁeld (AVF)
cyclotron, and we labeled an anti-TF mAb with the radionuclide as previously reported.7)
To evaluate 211 At-conjugaed anti-TF mAb, we performed sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and ﬂow cytometry analyses.
In the SDS-PAGE analysis, 211 At-conjugated anti-TF
mAb was smeared, which was in contrast to band patterns in 211 At-unlabeled anti-TF mAbs. Consequently,
ﬂow cytometry analysis revealed that the binding activity of the astatinated mAb was disturbed comparedwith 211 At-unlabeled mAbs. These ﬁndings suggest thatanti-TF mAb was denatured by the 211 At-induced radiochemical reaction. Then, to protect anti-TF mAb fromdenaturation, we puriﬁed astatinated mAbs using an elution buﬀer containing sodium ascorbate (SA), which is afree radical scavenger. In the SDS-PAGE analysis, band
patterns were demonstrated in 211 At-conjugated anti-TF
mAbs eluted in phosphate-buﬀered saline (PBS) contain†

∗1
∗2
∗3

∗4
∗5

∗6

∗7

Condensed from the article in Cancer Sci. 112, 1975 (2021)
Developmental Therapeutics, EPOC, National Cancer Center
RIKEN Nishina Center
Laboratory of Functional Molecule Chemistry, Pharmaceutical Department and Institute of Medicinal Chemistry, Hoshi
University
Research Center for Pharmaceutical Development, Tohoku
University
Glycometabolic Biochemistry Laboratory, RIKENDivision of Functional Imaging, EPOC, National Cancer Center
Department of Immune Medicine, National Cancer Center Research Institute, National Cancer Center

Purification
without SA

211At-induced

Disturbed binding activity
Disturbed antitumor effect

211At-induced

Maintained binding activity
Maintained antitumor effectantibody denaturation (+)

211At labeling

Purification
with SA

antibody denaturation (‒)

Fig. 1. Summary of 211 At-induced antibody denaturationand protective eﬀect of sodium ascorbate.

ing 0.6 or 1.2% SA and 211 At-unlabeled mAbs. Consequently, the binding activities of the astatinated anti-TF
mAbs in the SA solution were comparable to those of
211
At-unlabeled mAbs.
211
At-conjugated anti-TF mAbs stabilized with SA exerted greater cytocidal eﬀects on gastric cancer cells than
the astatinated mAb eluted in PBS. Similar to ADC,
the cytotoxicities of the stabilized immunoconjugates depended on the level of TF in the cancer cell.
To evaluate in vivo toxicities, we observed the bodyweight loss in mice administered SA, 211 At-conjugatedanti-TF mAb, or free 211 At. Although body weightloss was observed in mice administered PBS containing
1.2% SA, the loss was transient and the radioprotectant
seemed tolerable. Body weight loss after the administration of the astatinated anti-TF mAb in PBS containing
1.2% SA was milder than free 211 At dissolved in 1.2%
SA solution.
211
At-conjugated anti-TF mAb eluted in PBS containing 1.2% SA showed signiﬁcantly greater antitumor effects in a high TF-expressing gastric cancer xenograftmodel than the non-stabilized immunoconjugate. Similar to ADC, the antitumor eﬀect of the astatinated antiTF mAb in 1.2% SA soution depended on the TF expression on the cell membrane of cancer cells.
In summary, SA protected the astatinated anti-TF
mAb from 211 At-induced antibody denaturation, which
resulted in the maintained binding and antitumor activities of the immunoconjugate (Fig. 1). Without intolerable side eﬀects, 211 At-conjugated anti-TF mAb eluted
in PBS containing 1.2% SA showed potent antitumor effects in gastric cancer xenograft models dependent on
the level of TF on the cancer cell membrane.
References

1) Y. W. van den Berg et al., Blood 119, 924 (2012).
2) H. Takashima et al., Sci. Rep. 7, 12341 (2017).
3) Y. Matsumura et al., Cancer Res. 46, 6387 (1986).
4) Y. Koga et al., Int. J. Cancer 137, 1457 (2015).
5) R. Tsumura et al., J. Control. Release 284, 49 (2018).
6) R. Tsumura et al., Oncol. Rep. 45, 329 (2021).
7) H. Takashima et al., RIKEN Accel. Prog. Rep. 53, 172 (2020).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Kinetics of Rad51 foci in G2 phase after heavy-ion irradiation in
mammalian cells
M. Izumi∗1 and T. Abe∗1

Ratio of Rad51/γH2AX

*

*

1.0
0.8
0.6
0.4
0.2
0

X

C

Ar

Fig. 1. Ratio of Rad51/phosphorylated histone H2AX
(γH2AX) foci 1 h after irradiation in HeLa cells. Aphidicolin (10 µM) was added 30 min before irradiation, andcells were irradiated with 2 Gy of X-rays, carbon ions
(LET = 80 keV/µm), or argon ions (LET = 300 keV/µm)
and incubated in the presence of aphidicolin for 1 h after
irradiation. The foci formation of Rad51 and γH2AX wasdetected by immunostaining. Student’t t test: ∗ P < 0.01.
Error bars represent SD.
∗1

RIKEN Nishina Center

X-ray
Number of γH2AX or Rad51
foci/cell (%)

DNA double-strand breaks (DSBs) are the most lethal
type of damage caused by ionizing irradiation and are
repaired mainly by non-homologous end joining (NHEJ)
or homologous recombination (HR) in mammalian cells;
alternative NHEJ and/or single-strand annealing work
only when both NHEJ and HR are impaired. Accelerated heavy-ion particles with high linear energy transfer(LET) induce complex and fragmented DNA damageaﬀecting the pathway choice and the eﬃciency of DSB
repair.
Several published results of survival assay using Chinese hamster mutant cell lines deﬁcient in NHEJ or
HR suggest that NHEJ is inhibited after heavy-ion irradiation.1,2) In contrast, studies using inhibitors andmouse mutant cell lines suggest that NHEJ is a major repair pathway after heavy-ion irradiation, although
HR is more important for higher-LET radiation.3,4) It
is also reported that clustered DNA damage enhances
end resection, which could promote HR, alt-NHEJ, andSSA.5,6) Therefore, the DNA repair mechanism after
heavy-ion irradiation is still controversial in higher eukaryotes.
Our previous study using human ﬁbroblast and a speciﬁc inhibitor against NHEJ or HR suggests that NHEJ
and HR work competitively and compensate for eachother after X-irradiation.7) On the other hand, NHEJ
is the major repair pathway after heavy-ion irradiation,and HR does not seem to compensate for NHEJ. How-

Carbon(LET = 80 keV/μm)

Argon(LET = 300 keV/μm)

γH2AX
Rad51

γH2AX
Rad51

100
80
60
40
γH2AX
Rad51

20
0

1

3

5

8

1

3

5

8

1

3

5

8

Time from irradiation (h)Fig. 2. Time course of phosphorylated histone H2AX
(γH2AX) and Rad51 foci after irradiation in G2 cells.
The percentage of foci per cell was plotted by normalizing the numbers at the maximum time point as 100%after irradiation.

ever, it is unknown whether HR eﬃciently repairs DSBs
caused by heavy ions or whether the DNA damage checkpoint delays the entry into the S/G2 phase, where HR
occurs.
In this study, we examined the DNA repair kinetics
as well as the repair pathway usage in the G2 phase.
Exponentially growing HeLa cells were irradiated with
X-rays, carbon ions, or argon ions and incubated in thepresence of aphidicolin to arrest S-phase progression andinhibit transition from the S to the G2 phase. The repair eﬃciency and pathway usage were estimated by the
kinetics of the phosphorylated histone H2AX foci andRad51 foci, which reﬂect the DSBs and HR, respectively.
S-phase cells were identiﬁed by the pan-nucleic stainingof the phosphorylated histone H2AX and excluded fromanalysis.
The ratio of Rad51/phosphorylated histone H2AX
foci induced by heavy-ion irradiation was higher thanthat induced by X-rays (Fig. 1). The number of Rad51
foci decreased more slowly after heavy-ion irradiation
than after X-ray irradiation, with the kinetics similar to
those of phosphorylated histone H2AX (Fig. 2). These
results suggest that HR is favored after heavy-ion irradiation, although HR repairs DSBs less eﬃciently after
heavy-ion irradiation.
References

1) H. Wang et al., DNA Repair 7, 725 (2008).
2) S. C. Genet et al., Oncol. Rep. 28, 1591 (2012).
3) H. Ma et al., Radiat. Oncol. 10, 225 (2015).
4) A. Gerelchuluun et al., Rad. Res. 183, 345 (2015).
5) H. Yajima et al., DNA Repair 12, 936 (2013).
6) A. Shibata et al., EMBO J. 30, 1079 (2011).
7) M. Izumi, T. Abe, RIKEN Accel. Prog. Rep. 53, 24 (2020).

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I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Improvement of rotifer as the new food item in larviculture†
K. Tsuneizumi,∗1 M. Yamada,∗1 K. Ichinose,∗1 H. Ichida,∗1 and T. Abe∗1
In larviculture, rotifers (Brachionus plicatilis sensestrict) are generally used as the initial food source.1) The
lorica length of rotifers is distributed in the range of 170–
320 µm in individuals carrying amictic eggs. The next
food item Artemia nauplii has a body length of 400–
1,000 µm. Although the proper management of feed
size and density associated with ﬁsh larval growth isneeded,2) there is a size gap between rotifers and Artemia
nauplii. No feed items to bridge the size gap of 320–
400 µm have been developed in the food scheme of ﬁshlarvae.
To improve the mass mortality and abnormal development of ﬁsh larvae during the period of growth corresponding to the size gap, this study applied carbon
and argon heavy-ion-beam irradiation in mutation breeding3,4) to select rotifer mutants with larger lorica sizes.
In our previous study, the Notojima strain, known
as the largest rotifer strain in Japan, was irradiatedwith carbon (C) and argon (Ar) ion beams at diﬀerent
doses. We developed a screening method with the lorica
length as an indicator and established 56 large mutants(Table 1).5) In this study, we measured the population
growth rate as the parameter of good bait. The population growth rate of each large mutant line was observedwith 5-mL cultures. For each line, every ﬁve individuals were inoculated into 6 wells containing 5 mL offresh culture medium (18 practical salinity units) with
Chlorella. The total number of rotifers in each well wascounted after 5 days. The population growth rate of eachwell was calculated with the following equation: population growth rate = ln (total population/5 individuals)/5

Fig. 1. Photograph of rotifer lines with proliferative diﬀerence and the control. (a) Control rotifer. (b1-3) Largeand proliferative mutants with higher population growth
rates than the control. Values are mean ± standard errors, and images of rotifer lines are of individuals withthe average lorica lengths. Scale bars represent 200 µm.
†∗1Condensed from the article in Biosci. Biotech. and Biochem.
(DOI: 10.1093/bbb/zbaa094) (2021)
RIKEN Nishina Center

Table 1. Frequency of large and rapid-proliferative mutants

days). The average values of each large mutant line were
calculated using data obtained with six replications andstandardized using the control group.
The following 3 mutant lines showed a signiﬁcantly
higher population growth rate than the control: TYA41(Steel’s multiple comparison tests, P < 0.05), TYC78,
and TYC176 (P < 0.01) (Fig. 1). The large mutant
lines showed an equal or higher growth rate than thecontrol are categorized as the rapid proliferation in Table 1. The frequency of appearance was calculated using
the mutant lines showing active proliferation after irradiation: mutant frequency (%) = (number of rapid proliferation)/(number of active proliferation) × 100. The
highest frequency was observed at 100 and 200 Gy with
the C-ion beam. For TYC78 produced at 200 Gy, we
decided that a C-ion beam of 200 Gy was the optimal
irradiation condition to establish a large rotifer. Similarly, the highest frequency was observed at 50 Gy with
the Ar-ion beam, and TYA41 was selected from the same
condition. This was also determined to be the optimum
irradiation dose. Thus, these three mutants are suitable
to solve the feed-size gap between rotifers and Artemia
nauplii and should improve the marine ﬁsh larviculture
system.
Food shortages due to population growth and increased consumption are a major global concern, andcountries around the world are searching for ways to increase food production. The enlarged rotifers obtainedin this study could potentially provide a stable supply oflarger rotifers at low cost, enhancing aquaculture.
References

1) S. Mills et al., Hydrobiologia 796, 39 (2017).
2) T. Kotani et al., J. World Aquac. Soc. 40, 383 (2009).
3) T. Abe et al., in Plant Mutation Breeding and Biotechnology,
edited by Q. Y. Shu et al. (CABI, Oxfordshire, 2012), p. 99.
4) A. Tanaka et al., J. Radiat. Res. 51, 223 (2010).
5) K. Tsuneizumi et al., RIKEN Accel. Prog. Rep. 53, 213 (2020).

- S34 -

1

II. RESEARCH ACTIVITIES I(Nuclear, Particle and Astro-Physics)

1. Nuclear Physics

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

RI beam production at BigRIPS in 2020
H. Takeda,∗1 N. Fukuda,∗1 H. Suzuki,∗1 Y. Shimizu,∗1 N. Inabe,∗1 K. Kusaka,∗1 M. Ohtake,∗1 Y. Yanagisawa,∗1
H. Sato,∗1 K. Yoshida,∗1 and T. Uesaka∗1
The radioactive isotope (RI) beam production at the
BigRIPS fragment separator1) in 2020 is presented here.
Table 1 summarizes the experimental programs that involved the use of the BigRIPS separator in this period
and the RI beams produced for each experiment. All theexperiments originally scheduled for the spring beamtime were postponed owing to the COVID-19 pandemic.
In the autumn beamtime, 238 U and 70 Zn primary beams
were provided.
The 238 U beam campaign started in October. During
a tuning phase of BigRIPS at startup, an auto-focusing
and auto-centering system was tested with a 82 Ge beam
for the ﬁrst time at RIBF.2) After the BigRIPS tuning phase followed by the commissioning of HiCARI,a PALIS experiment was performed with an RI beamaround 191 Bi to evaluate the extraction eﬃciency usingalpha emitters in the 191 Bi region.
Five HiCARI experiments were subsequently performed with the ZeroDegree spectrometer. A cocktail
beam of 84 Ge/83 Ga/82 Zn was produced to study neutron
intruder states and collectivity. 86 Se/84 Ge, 88 Se/86 Ge,
and 90 Se beams were produced to explore quadrupole
and octupole collectivity. A cocktail 111 Nb/112 Mo/113 Tc
beam was produced to perform high-resolution spectroscopy and lifetime measurements. A 130 Cd beam
was produced to study single-particle states in 129 Ag.
A 136 Te beam was produced to characterize a strongly
Coulomb-excited state above 4 MeV in 136 Te. During these HiCARI experiments, mass measurementswith a multi-reﬂection time-of-ﬂight mass spectrometer (MRTOF-MS) located downstream of the ZeroDegree spectrometer were performed symbiotically. Subsequently, a machine study for the Rare RI Ring was

performed with a 75 Ga beam.
At the end of the 238 U beam campaign, a machine
study for a high-purity Th-beam development including performance evaluations of beamline detectors for ahigh-Z, high-rate RI beam was performed using a 220 Th
beam.3)After switching to the 70 Zn primary beam, two HiCARI experiments were conducted with the ZeroDegree
spectrometer. 56 Ti and 58 Ti beams were produced to
study the evolution of collectivity in Ti isotopes. 36 Ca,
38
Ca, 48 Ca, and 54 Ca beams were produced to investigate systematically the reduction factor for the deduced
spectroscopic factors. A symbiotic MRTOF experiment
was performed again.
A new isotope search experiment was conductedaround the 45 Si region at the end of the 70 Zn beam campaign.4)
The RI beam production at BigRIPS from the startof operation in March 2007 is summarized in our
database.5) At ﬁrst, you will be redirected to the welcome page. Follow the links “Database of RI Beams Produced at BigRIPS” → “List of Experiments” → “Summary” to reach the summary page; you can reach thepage in subsequent attempts.
References

1) T. Kubo, Nucl. Instrum. Methods Phys. Res. B 204, 97(2003).
2) Y. Shimizu et al., in this report.
3) N. Fukuda et al., in this report.
4) H. Suzuki et al., in this report.
5) Y. Shimizu et al., Nucl. Instrum. Methods Phys. Res. B,
463, 158 (2020). Available at https://ribeam.riken.jp/ .

Table 1. List of experimental programs together with RI beams produced at the BigRIPS separator in 2020.
Primary beam (Period)

Exp. Prog. No.

Spokesperson

CourseRI beams

U
345 MeV/nucleon(Oct. 25–Nov. 24)

NP1712-RIBF166-03
NP1912-RIBF196-01
NP1912-RIBF190-01
NP1912-RIBF187-01
NP1912-RIBF189-02
NP1912-RIBF193-01
PE19-02 / PE20-01
MS-EXP20-04
MS-EXP20-02

T. Sonoda
F. Flavigny
F. Browne
W. Korten
Z. Podolyak
A. Jungclaus
M. WadaY. Yamaguchi
N. Fukuda

PALIS
ZeroDegree
ZeroDegree
ZeroDegree
ZeroDegree
ZeroDegree
ZeroDegree
Rare RI Ring
ZeroDegreeBi
Ge/83 Ga/82 Zn
86
Se/84 Ge, 88 Se/86 Ge, 90 Se
111
Nb/112 Mo/113 Tc
130
Cd
136
Te
(symbiotic)
75
Ga
220
Th

Zn
345 MeV/nucleon(Dec. 2–Dec. 13)

NP1912-RIBF142R1-01
NP1912-RIBF170R1-01
PE20-02
DA20-03

T. Koiwai
H. Crawford
M. WadaH. Suzuki

ZeroDegree
ZeroDegree
ZeroDegree
BigRIPSTi, 58 Ti
Ca, 38 Ca, 48 Ca, 54 Ca(symbiotic)
45
Si

238

70

∗1

191
84

56

36

RIKEN Nishina Center-1-1II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production cross-section measurement and new-isotope search forvery-neutron-rich RIs produced from 70 Zn beam at 345 MeV/nucleaon
by BigRIPS separator
H. Suzuki,∗1 M. Yoshimoto,∗2 N. Fukuda,∗1 H. Takeda,∗1 Y. Shimizu,∗1 Y. Yanagisawa,∗1 H. Sato,∗1 andK. Yoshida∗120

Production cross section (mb)

We performed production cross-section measurements
and a new-isotope search in the neutron-rich region
with the atomic numbers Z = 12–19, located southeast of 48 Ca in the nuclear chart. The neutron-rich radioactive isotopes (RIs) were produced by the projectile fragmentation of a 600-particle-nA 70 Zn beam at
345 MeV/nucleon impinged on a 10-mm-thick Be target
in the BigRIPS separator. Particle identiﬁcation basedon the TOF-Bρ-∆E method1) was performed in the second stage of BigRIPS. Three BigRIPS settings were usedwith 45 S, 43 Si, and 45 Si as centeral particles. The former
two settings were for the cross-section measurements,
and the last one was for the new-isotope search. The
production cross sections were deduced from the measured production rates and their transmission eﬃciencies

(a)

-4

10

Ar

Ca

Z

14

10

-10

10

-12

8
6
2.7

Ti

Production cross section (mb)

Sc

10

P

Cl

K

40

45

50

V

10-8

10

-10

10

-12

10

-14

2012 data
2014 data

45
S setting43
Si setting45

Si setting

25

30

35

Mass number

55

60

65

∗2

3.1

3.2

3.3

3.4

References

701) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
2) O. B. Tarasov, D. Bazin, lise++ site, http://lise.nsc
l.edu,MichiganStateUniversity .
3) H. Suzuki et al., Nucl. Instrum. Methods Phys. Res. B
317, 756 (2013).
4) B. Mei, Phys. Rev. C 95, 034608 (2017).
5) K. Sümmerer, B. Blank, Phys. Rev. C 61, 034607 (2000).
6) K. Sümmerer, Phys. Rev. C 86, 014601 (2012).

Fig. 1. Measured production cross sections of RIs producedin the 70 Zn + Be reaction at 345 MeV/nucleon with semiempirical cross-section formulae. (a) Results for even-Z
isotopes. (b) Results for odd-Z isotopes.
∗1

3

in BigRIPS, which were simulated with lise++ calculations.2) In the simulation, parameters that control the
momentum and angular distribution2,3) are not changed
from the default values in the current preliminary analysis.
Figure 1 shows the production cross sections of RIs
obtained in this work (ﬁlled symbols), together withmeasurements in 2012 and 2014 (open symbols). The
solid, dashed, and dotted lines show the cross sections
predicted by the semi-empirical formula FRACS1.1,4)
EPAX2.15,5) and EPAX3.1a.6) Overall, FRACS1.1 best
reproduces the measured cross sections among these formulae; however, around the very-neutron-rich region,
the discrepancy between the measured and predictedcross sections becomes larger. A new isotope, 45 Si,
was discovered in this work, as shown in Fig. 2. One
event was also observed at the location of 46 Si, althoughmore elaborate analysis, such as background removal, isneeded for conﬁrmation as a new isotope. The detailed
analysis is currently in progress.

Al

-6

10

2.9

Cr

EPAX3.1a
EPAX2.15
10-14 FRACS1.1

(b)

2.8

A/Q

Mg

-4

12
10

-6

-8

Si

16

10
10

45

Fig. 2. PID plots obtained in the 45 Si setting. Events of a
new isotope, 45 Si, were clearly observed.

S

Si

18

RIKEN Nishina Center
Department of Physics, Gifu University-2-1II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

N = 32 shell closure below calcium: Low-lying structure of 50 Ar†
M. L. Cortés,∗1,∗2 W. Rodriguez,∗3,∗1,∗4 P. Doornenbal,∗1 A. Obertelli,∗5,∗6 J. D. Holt,∗7,∗8 J. Menéndez,∗9,∗10
K. Ogata,∗11,∗12 A. Schwenk,∗6,∗13,∗14 N. Shimizu,∗9 J. Simonis,∗15 Y. Utsuno,∗16,∗9 K. Yoshida,∗16 and theSEASTAR2017 Collaboration
An interesting region to study shell evolution isaround Ca isotopes, where the development of shell closures for N = 32 and N = 34 has been suggested.
The N = 32 sub-shell closure was evidenced by its
relatively high E(2+ ) energy,1) and confirmed by twoproton knockout cross sections2) and mass measurements.3) For the N = 34 shell closure, evidence wasprovided by E(2+ ),4) systematic mass measurements,5)and neutron-knockout cross sections.6) The preservation of the N = 32 shell closure has been determinedin Ti and Cr via spectroscopy, reduced transition probabilities, and precision mass measurements, while for
N = 34, it has been suggested to disappear above Ca.
In contrast, the recent measurement of the E(2+ ) of52
Ar suggests the conservation of the N = 34 shell closure for Z = 18.7) The first spectroscopy of 50 Ar showeda relatively high E(2+ ),8) hinting at the conservation of
the N = 32 shell closure below Ca. A candidate for the
4+ state was also reported. No further spectroscopic information is available for this very exotic nucleus. This
work reports low-lying states in 50 Ar.
A beam of 70 Zn with an average intensity of 240 particle nA was fragmented on a Be target. Isotopes
were identified using BigRIPS9) and delivered to the151.3(13)-mm-long liquid hydrogen target of MINOS10)
placed in front of the SAMURAI magnet. Outgoing
fragments were identified using SAMURAI and associated detectors.11) The DALI2+ array,12,13) composed of
226 NaI(Tl) detectors, was used to detect the emitted
γ-rays. Doppler-corrected γ-ray spectra were obtainedusing the reaction vertex and the velocity of the fragment reconstructed with MINOS.
Based on the spectra and γγ analysis of the
proton- and neutron-knockout, inelastic-scattering, andmultinucleon-removal reactions, the level scheme shown

Fig. 1. Experimental level scheme of 50 Ar.

in Fig. 1 was constructed. The two previously reported
transitions and five new ones were identified. Theoretical level energies and spectroscopic factors for the
proton- and neutron-knockout reactions were obtainedwith shell-model calculations using the SDPF-MU interaction, as well as with ab initio calculations using the
VS-IMSRG approach. Tentative spin assignments weremade based on the comparison of the calculations andthe experimental results. In both calculations, stateswith J π = 2+ are preferably populated by the reactions, as shown in the figure. In addition, a (3− ) stateis suggested to be populated following the proton inelastic scattering. Both theoretical calculations provide
consistent results and a relatively good agreement withthe experimental data, emphasizing the subshell closure
at N = 32 and strengthening our understanding of shellevolution in this region.
References

Condensed from Phys. Rev. C. 102, 064320 (2020)
RIKEN Nishina Center∗2 INFN-Legnaro∗3 Departamento de Física, Universidad Nacional de Colombia∗4 Departamento de Física, Pontificia Universidad Javeriana∗5 IRFU, CEA, Université Paris-Saclay∗6 Institut für Kernphysik, Technische Universität Darmstadt∗7 TRIUMF∗8 Department of Physics, McGill University∗9 Center for Nuclear Study, The University of Tokyo∗10 Departament de Física Quàntica i Astrofísica, Universitat deBarcelona∗11 RCNP, Osaka University∗12 Department of Physics, Osaka City University∗13 ExtreMe Matter Institute (EMMI)∗14 Max-Planck-Institut für Kernphysik∗15 Institut für Kernphysik and PRISMA Cluster of Excellence,
Johannes Gutenberg-Universität∗16 Advanced Science Research Center, JAEA†

1) A. Huck et al., Phys. Rev. C 31, 2226 (1985).
2) A. Gade et al., Phys. Rev. C 74, 021302 (2006).
3) F. Wienholtz et al., Nature 498, 346 (2013).
4) D. Steppenbeck et al., Nature 502, 207 (2013).
5) S. Michimasa et al., Phys. Rev. Lett. 121, 022506 (2018).
6) S. Chen et al., Phys. Rev. Lett. 123, 142501 (2019).
7) H. N. Liu et al., Phys. Rev. Lett. 122, 072502 (2019).
8) D. Steppenbeck et al., Phys. Rev. Lett. 114, 252501 (2015).
9) T. Kubo et al., Prog. Theor. Exp. Phys. 2012, 03C003(2012).
10) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).
11) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
12) S. Takeuchi et al., Nucl. Instrum. Methods Phys. Res.
A 763, 596 (2014).
13) I. Murray et al., RIKEN Accel. Prog. Rep. 51, 158 (2017).

∗1

-3-

1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Proton removal and lifetimes in the Ca isotopes: Spectroscopy andreaction studies
H. L. Crawford,∗1 S. Paschalis,∗2 and M. Petri∗2 for the RIBF170R1 Collaboration
Nucleon knockout reactions are an essential andpowerful tool to study the single-particle structure of
nuclei far from stability. Through comparison of measured (σexp ) and theoretical (σth ) inclusive and exclusive cross-sections they provide a method to assign speciﬁc single-particle conﬁgurations and occupancies ofstates in nuclei. However, the theoretical descriptionof knockout reactions is challenging, requiring both atreatment of the reaction dynamics and the nuclear
structure of initial and ﬁnal states.
The ratio R = σexp /σth has been found, in stable
nuclei and speciﬁcally for (e, e′ p) and single-nucleon
transfer reactions1,2) to be consistently less than 1(R ∼ 0.6), a reduction attributed to short and longrange correlations not captured in the shell-model.
However, moving away from β-stability, a study by
Tostevin and Gade3) using available one-nucleon removal data on unstable isotopes performed at intermediate energies (∼100 MeV/nucleon) shows a dependence of R on the diﬀerence in the proton and neutron separation energies of the initial system. Thisdependence is in contrast to both transfer reaction
data taken at lower energies and to new data reported
recently by the R3 B collaboration4) and RIBF5) for
quasi-free one-proton knockout at higher energies.
Given the important implications of disentangling
the reaction and structure eﬀects related to the originof the ∆S dependence of R observed in knockout reactions, we have performed an experiment to directly
explore the isospin dependence of proton knockout on
both C and H targets at RIBF energies. In addition to
the reaction cross-sections, we were also able to takeadvantage of the opportunity presented by the HiCARI
high-resolution γ-ray array6) at RIBF to simultaneously explore lifetimes in the neutron-rich Ca isotopes,
which provide an important testing ground for interactions derived from chiral Eﬀective Field Theory andmany-body methods.
The experiment was performed in December 2020 at
the RIBF as part of the HiCARI campaign. A 70 Zn
primary beam was accelerated to 345 MeV/nucleon
and fragmented on a 9 Be primary target to produce
secondary beams centered on 38, 48, 54 Ca. Fragments
were separated and identiﬁed within BigRIPS using
the standard ∆E-TOF-∆E method. The secondary
beam impinged on 1 g/cm2 thick C and 1.2 g/cm2
thick CH2 targets at the F8 focal plane, which induced
knockout reactions. The reaction residues were identiﬁed in the ZeroDegree spectrometer. The preliminary∗1∗2Fig. 1. (Top) Particle identification plot for incoming beam
particles in BigRIPS for the setting of 54 Ca. (Bottom)
Reaction residue particle identification in the ZeroDegree spectrometer, gated on incoming 54 Ca particles.

particle identiﬁcation plots for the setting on 54 Ca areshown in Fig. 1. De-excitation γ-rays were detected
within the HiCARI array.
Currently, the proton removal inclusive and exclusive cross-sections from 38, 48, 54 Ca to ﬁnal states in37, 47, 53
K are under analysis. In addition, γ-ray spectrain the most neutron-rich Ca isotopes, namely 53, 54 Ca
are being carefully analyzed. Preliminary energy spectra show evidence for lifetimes within the sensitivity
range for line-shape analysis, which will be pursued in
the next stages of analysis.
References

1) B. P. Kay et al., Phys. Rev. Lett. 111, 042502 (2013).
2) G. Kramer et al., Nucl. Phys. A 679, 267 (2001).
3) J. A. Tostevin, A. Gade, Phys. Rev. C 90, 057602(2014).
4) L. Atar et al., Phys. Rev. Lett. 120, 052501 (2018).
5) S. Kawase et al., Prog. Theor. Exp. Phys. 2018, 021
D01 (2018).
6) K. Wimmer et al., in this report.

Nuclear Science Division, Lawrence Berkeley National Lab
Department of Physics, University of York-4-1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Evolution of collectivity in Ti isotopes towards the N = 40 island of
inversion
T. Koiwai∗1,∗2 and K. Wimmer∗3,∗2 for the RIBF142R1 Collaboration
Over the past decade, signiﬁcant eﬀorts on both theexperimental and theoretical fronts have focused on
the development of nuclear collectivity in exotic isotopes around N = 40. It was revealed that the newisland of inversion, where the intruder conﬁguration isstrongly favored in the ground state, at N = 40 is centered around 64 Cr.1,2) It is then interesting to question
whether this enhanced collectivity established in theregion around the Fe and Cr isotopes presents itself in
exotic systems with fewer protons, namely, Ti isotopes.
Several theoretical calculations2–6) show the diﬀerencein the reduced transition rates, B(E2; 0+ → 2+ ) values, for neutron-rich Ti isotopes beyond 56 Ti when
considering diﬀerent model spaces. Although the energies for the ﬁrst 2+ state are consistent and agree withexperimental data, the B(E2) values diﬀer, dependingon whether the gd shell is included in the calculations.
This suggests that the boundary of the island of inversion is located between 56 Ti and 58 Ti. To answer
these questions, the Coulomb excitation of 56, 58 Ti wasmeasured.
The experiment was conducted at the RIBF as apart of the HiCARI campaign. A 70 Zn primary beamwith a maximum intensity of 600 particle nA was accelerated to 345 MeV/nucleon and impinged on a 11mm-thick 9 Be primary target to produce a secondary
beam for 56, 58 Ti. The beam fragments were separated and identiﬁed by the BigRIPS using the standard∆E−TOF−Bρ method. The secondary beam impinged on a 1-mm-thick Au target to induce a Coulomb
excitation reaction. A 3-mm-thick Be target was also
used to determine the nuclear contribution to the excitation. The reaction residuals were identiﬁed by the
ZeroDegree spectrometer. De-excitation γ rays weredetected by the HiCARI array7) at the F8 focal plane.
The preliminary particle identiﬁcation plots are shownin Fig. 1. Tails will be removed by further analysis.
Currently, the data are under analysis. The preliminary Doppler-corrected energy spectra show the clear
transition peaks at known energies of the ﬁrst 2+ statein both 56, 58 Ti. Moreover, candidates of peaks arefound in coincidence with the one-neutron knockout
channel from 56, 58 Ti, which will reveal the conﬁguration of the ground-state wave function of these nuclei.

∗1
∗2
∗3

24
23
22
21
20
19

24
23
22
21
20
19

Fig. 1. Particle identification plots for both the incoming
beam and outgoing residuals. The top panel shows the56
Ti setting and the bottom the 58 Ti setting.

References

1) H. L. Crawford et al., Phys. Rev. Lett. 110, 242701(2013).
2) S. M. Lenzi, F. Nowacki, A. Poves, K. Sieja, Phys. Rev.
C 82, 054301 (2010).
3) A. Poves, J. Sánchez-Solano, E. Caurier, F. Nowacki,
Nucl. Phys. A 694, 157 (2001).
4) M. Honma, T. Otsuka, B. A. Brown, T. Mizusaki, Eur.
Phys. J. A 25, s01, 499 (2005).
5) Y. Tsunoda et al., Phys. Rev. C 89, 031301(R) (2014).
6) L. Coraggio, A. Covello, A. Gargano, N. Itaco, Phys.
Rev. C 89, 024319 (2014).
7) K. Wimmer et al., in this report.

Department of Physics, University of Tokyo
RIKEN Nishina Center
IEM-CSIC-5-1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

RIBF190: Exploring collectivity beyond 78 Ni
F. Browne∗1 and V. Werner∗2 for the RIBF 190 Collaboration∗1∗2

Atomic number

Recently, it has been indicated that the doubly
magic 78 Ni has competing low-lying spherical andprolate-deformed states.1) In its north-east quadrant,+measurements of E(2+1 ) and E(41 ) of the N = 52, 54
Zn isotopes show deformation of ground-states becomes prominent beyond N = 50.2) Shell model3,4)
and interacting boson model calculations5) that reproduce the available spectroscopic information of N > 50
Se and Ge isotopes predict them as transitioning fromtheir N = 50 sphericity to collective structures. In thecase of the Ge isotopes this takes the form of soft andrigid triaxiality, while the Se isotopes start to exhibit
prolate-oblate shape coexistence. Initial spectroscopy
seems to agree with the models that predict these interesting features.6,7) In addition to the quadrupole degrees of freedom, octupole collectivity may be expected
to be enhanced in the neutron-rich Ge/Se region due totheir proximity to the “doubly octupole magic” numbers, N = 56 and Z = 34
An experiment was performed over 4 days withthree BigRIPS settings to extract the reduced transition probabilities of low-lying states in 84, 86 Ge and86, 88, 90
Se in order to clarify the quadrupole and octupole collectivity of the region. Exotic nuclei were
produced from the in-ﬂight ﬁssion of a 238 U beam
which was accelerated to 345 MeV/nucleon. Following ﬁssion, the isotopes of interest were selected in theﬁrst stage of BigRIPS using the Bρ-∆E-Bρ techniqueand identiﬁed with the second stage using their Bρ,∆E, and time-of-ﬂight (TOF) values. The BigRIPS
particle-identiﬁcation plots for the three settings ofthe experiment are shown in Fig. 1. Secondary targets of Be (3.8-mm-thick) and Bi (1.1 mm-thick) weresituated at the F8 focal plane to induce nuclear andCoulomb excitations, respectively. Gamma rays emitted from excited states were detected with the HiCARI
array8) which surrounded F8. The trajectory of incoming and outgoing ions with respect to the target
was measured with PPACs. Following the reaction
targets, ions were transported through the ZeroDegree
spectrometer where they were identiﬁed, again using
their Bρ, ∆E, and TOF values. Finally, the ions were
stopped in a gas cell and their masses recorded usinga MR-TOF setup.
While oﬀ-line data analysis is yet to begin, the online γ-ray spectra show clearly that the main objectivesof the experiment are attainable. In addition to the
Coulomb excitation to the 2+
1 states being observed in
all objective nuclei, some nuclei show 2+
2 excitations
on the heavy target.

86

35

Se

34
84

33

Ge

32
31

Atomic number

2.5

2.55

2.6

2.65

2.7

2.75

88

35

Se

34
86

33

Ge

32
31

Atomic number

2.5

2.55

2.6

2.65

2.7

2.75

90

35

Se

34
88

33

Ge

32
31
2.5

2.55

2.6

2.65
2.7
2.75
Mass-to-charge ratio

Fig. 1. On-line particle identification plots for the three
BigRIPS settings employed during the experiment. Labels refer to the identified ions below them.

References

1) R. Taniuchi et al., Nature (London) 569, 53 (2019).
2) C. Shand et al., Phys. Lett. B 773, 492 (2017).
3) K. Sieja, T. R. Rodríguez, K. Koloz, D. Verney, Phys.
Rev. C 88, 034327 (2013).
4) K. Sieja, Private communication (2019).
5) K. Nomura, R. Rodríguez-Guzmán, L. M. Robledo,
Phys. Rev. C 95, 064310 (2017).
6) M. Lettmann et al., Phys. Rev. C 96, 011301(R) (2017).
7) S. Chen et al., Phys. Rev. C 95, 041302(R) (2017).
8) K. Wimmer et al., in this report.

RIKEN Nishina Center
IKP, TU Darmstadt-6-1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Neutron intruder states and collectivity beyond N = 50 towards 78 Ni
F. Flavigny,∗1 M. Górska,∗2 and Zs. Podolyák∗3 for the RIBF196 and HiCARI Collaborations

∗1
∗2
∗3

104

34
33

103

32

Z

The recent spectroscopy of 78 Ni,1) together with
the identiﬁcation of shape coexistence just below theN = 50 shell closure for 80 Ge2) and 79 Zn,3) indicates that deformed intruder conﬁgurations could
play a crucial role in low-energy structure properties in this region and towards the limits of the nuclear chart. Such conﬁgurations are predicted to originate from multiparticle-multihole excitations4) above
the N = 50 and Z = 28 shell gaps pushed down inenergy due to neutron-proton correlations, which enhance quadrupole collectivity. Quantifying how collectivity develops near 78 Ni is crucial because it inﬂuences binding energies and the drip-line location5)
with consequences for nucleosynthesis calculations relying on these inputs. Because these states involve
many-particle excitations, their theoretical description
is challenging, and identifying them experimentally is,thus, of prime interest to constrain models. So far,very few experimental indications of these conﬁgurations have been obtained in 80 Ge and 79 Zn, but no direct evidence of these conﬁgurations exist for N = 50
or above in more exotic species.
During the RIBF196 experiment in November 2020,
we sought to identify and characterize for the ﬁrst timesuch 2p-1h intruder states in 83 Ge and 81 Zn which are
the last two odd-even N = 51 isotones above 79 Ni. To
do so, we used neutron knockout from 84 Ge and 82 Zn,
both having two neutrons in the s1/2 d5/2 valence space
above N = 50. This direct reaction allows the removalof one of the neutrons from the quasi-full g9/2 orbital
below N = 50 to selectively populate 9/2+ intruder
states based on a ν(g9/2 )−1 (s1/2 d5/2 )+2 conﬁgurationand extract their spectroscopic factors.
In addition, the ﬁrst spectroscopy of low-lying levels in 82, 84 Zn6) recently indicated that magicity wasstrictly conﬁned to N = 50 in 80 Zn with the onset of
deformation developing towards heavier Zn isotopes.
To reproduce these ﬁndings, it was demonstrated thatstate-of-the-art shell model calculations needed to include suﬃcient valence orbitals above N = 50 (fullgds valence space) and to allow the breaking of the78
Ni core. Simultaneously to the study of the intruder
states mentioned above, these low-lying states in 82 Zn
were populated using proton removal from 83 Ga, andtheir lifetimes will be studied by line-shape analysis.
To reach these scientiﬁc goals, we performed an experiment in which a primary beam of 238 U with a mean
intensity of 60 particle nA at 345 MeV/nucleon collided with a 4-mm thick 9 Be primary target at the

102

31
30

10

29
2.55

2.6

2.65

2.7

1

2.75

A/Q
Fig. 1. Preliminary particle identification of the secondary
beam in BigRIPS. Black, red and purple ellipsoids indicate 84 Ge, 83 Ga, 82 Zn respectively, see text for details.

object point of the BigRIPS separator. The secondary
beam was puriﬁed using Al degraders at the F1 andF5 dispersive planes (8- and 2-mm thick). The secondary cocktail beam containing approximately 61%,
7.4% and 0.2% of 84 Ge,83 Ga and 82 Zn, respectively, ataveraged rates of approximately 6100, 740, and 20 s−1
impinged for 2.5 days on a 6-mm-thick 9 Be target at
253, 248, and 242 MeV/nucleon. Event-by-event identiﬁcation of projectiles and reaction residues in termsof the atomic number (Z) and mass-to-charge ratio(A/Q) was achieved using the TOF-Bρ-∆E method
in both the BigRIPS and ZeroDegree spectrometers.
A preliminary particle identiﬁcation plot in BigRIPS
without higher-order optical corrections is shown in
Fig. 1. De-excitation γ-rays of the neutron and proton
knockout residues 83 Ge,82 Zn and 81 Zn were detectedusing the HiCARI germanium array (described separately7) ) surrounding the secondary reaction target. A
0.5-mm-thick lead shield was placed around the beam
pipe surrounding the target to reduce the rate of lowenergy atomic background in the detectors. Knownand unknown transitions in 83 Ge were clearly identiﬁed online. The statistics obtained in this neutronknockout channel will allow clear identiﬁcation of thestates populated and their possible intruder character
after careful analysis of the feeding pattern.
References

1) R. Taniuchi et al., Nature 569, 53 (2019).
2) A. Gottardo et al., Phys. Rev. Lett. 116, 182501 (2016).
3) X. F. Yang et al., Phys. Rev. Lett. 116, 219901 (2016).
4) K. Heyde, J. L. Wood, Rev. Mod. Phys. 83, 1467 (2011).
5) J. Erler et al., Nature 486, 509 (2012).
6) C. Shand et al., Phys. Lett. B 773, 492 (2017).
7) K. Wimmer et al., in this report.

LPC Caen, CNRS/IN2P3
GSI Helmholtzzentrum für Schwerionenforschung GmbH
Department of Physics, University of York

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RIKEN Accel. Prog. Rep. 54 (2021)

High-resolution spectroscopy and lifetime measurements inneutron-rich Zr and Mo isotopes
W. Korten,∗1 B. Moon,∗2,∗3 and K. Wimmer∗4,∗3 for the RIBF187 Collaboration
One of the most interesting cases of shape evolution
in nuclei is encountered along the semi-magic (Z = 40)
Zr isotopes. While 90 Zr, at neutron number N = 50,
shows properties of a doubly-magic nucleus, neutrondeﬁcient Zr isotopes become well-deformed towards
80
Zr. On the neutron-rich side, a sudden onset of deformation is also indicated by the dramatic lowering of
the ﬁrst excited 2+ state from 98 Zr to 100 Zr.
When going towards even more neutron-rich isotopes the question about the further shape evolution
arises since the theoretical predictions diverge. Many
theoretical calculations have been performed for 110 Zr
since it combines the magic numbers Z = 40 and
N = 70 of the harmonic oscillator potential and could
be another quasi doubly-magic nucleus. This question
was answered in a previous SEASTAR experiment at
the RIBF,1) which measured the ﬁrst excited states of110
Zr and showed that this isotope is rather well deformed. However, several questions remain open, suchas the possibility of shape coexistence or triaxial deformation at Z = 40, N = 70 as predicted by diﬀerent
theoretical models.3–5)
We performed high-resolution spectroscopy of nuclei around 110 Zr in an experiment with the HiCARI
array2) in order to measure lifetimes of their (ﬁrst) excited states . The high-resolution γ-ray detectors from
HiCARI will allow to resolve level schemes by measuring γ rays from ∼100 keV, and to measure lifetimes of
excited states between ∼20 ps and 1 ns. The results
will also allow to conﬁrm the level scheme of 110 Zr andto measure decay branching ratios of states beyond the2+
1 for the ﬁrst time.
The nuclei of interest were populated by protonremoval reactions from projectiles around 112 Mo, produced from a primary 238 U beam, impinging on a secondary Be target. Particle identiﬁcation of the radioactive beams for selecting the proper reaction channel was performed with the BigRIPS and the ZeroDegree spectrometers. Examples of the particle identiﬁcation plots are shown in Fig. 1. Average intensities
and purities of the projectiles of interest amounted to
81 and 3000 pps and 0.8% and 34% for 111 Nb and113
Tc, respectively. Additionally, 112 Mo was transmitted at a high rate as well. 110 Zr was populated throughproton removal reactions from 111 Nb and 112 Mo. The
high intensity of 113 Tc allowed to obtain signiﬁcantly
more statistics for 112 Mo than in the previous exper∗1
∗2
∗3
∗4

Fig. 1. Preliminary particle Identification (PID) for BigRIPS (top) and ZeroDegree (ZD) spectrometer (bottom).

iment.1) Additionally, the neighbouring even-even nuclei, 108 Zr and 110 Mo, have been populated strongly toallow for a detailed lifetime analysis.
In order to optimize the experiment for the long lifetimes of the 2+ states, expected to be several hundred
ps, the Be target was positioned 10 cm upstream of
the center of HiCARI. Lifetimes will be extracted using the line-shape method6) and will give access to thecollective properties. The experiment will allow to distinguish between predictions of diﬀerent nuclear models concerning the shape of 110 Zr, the key isotope forthe evolution of collective properties along the N = 70
isotones.
References
1) N. Paul et al., Phys. Rev. Lett. 118, 032501 (2017).
2) K. Wimmer et al., in this report.
3) M. Borrajo et al., Phys. Lett. B 746, 341 (2015).
4) J. Libert, Phys. Rev. C 60, 1 (1999).
5) T. Togashi et al., Phys. Rev. Lett. 117, 172502 (2016).
6) P. Doornenbal et al., Nucl. Instrum. Methods Phys. Res.
A 613, 218 (2010).

IRFU, CEA Paris-Saclay
CENS, IBSRIKEN Nishina Center
IEM-CSIC-8-1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Single particle structure of semi-magic 129 Ag82
T. Parry,∗1 Zs. Podolyák,∗1 M. Górska,∗2 M. Armstrong,∗2 and A. Yaneva∗2 for the RIBF189 Collaboration
The shell structure is one of the fundamental ingredients in the understanding of mesoscopic systems,
which includes the atomic nucleus. One crucial question in nuclear physics is how the quantum orbitals
evolve as the number of protons and neutrons change.
The ordering of the nuclear orbitals can change drastically in neutron-rich nuclei. In extreme cases, traditional magic numbers can disappear and new ones canemerge. Such changes were already observed for lightnuclei, and are predicted for middle-mass ones. The
evolution of orbitals and shell gap has obvious consequences on the r-process nucleosynthesis, which is responsible for the production of half of the nuclei heavier than iron. The abundances of nuclei with magic
neutron numbers are enhanced due to their lower neutron capture probabilities. Thus the A ∼ 130 r-process
abundance peak is the consequence of the N = 82 neutron shell closure. The unknown evolution of the shellstructure in this region is one of the main sources ofnuclear physics uncertainty in r-process calculations.
One has to rely on theoretical models whose predictions for regions far oﬀ stability diverge signiﬁcantly.
129
Ag is a singly magic N = 82 nucleus. With three
protons holes below 132 Sn it is neutron-rich, and any
experimental information to be obtained on its structure is directly applicable for the understanding of theinﬂuence of the N = 82 nuclei on the r-process path.
Using proton knockout from 130 Cd single proton statesin 129 Ag can be populated.
The experiment was performed in November
2020.
For an approximate length of 3 days a
345 MeV/nucleon beam of 238 U with an average inten-

350

Counts/2 keV

300

100

500

104
132

Sn
103

131

49

Z

In
130

48

Cd

102

47
10

46

2.6

2.62

2.64

2.66

2.68

2.7

2.72

2.74

1

Fig. 1. Particle identification in BigRIPS with N = 82 nuclei including 130 Cd required for the main expected production channel of 129 Ag.

∗2700
Energy (keV)

800

900

1000

sity of around 60 particle nA impinged on a 4 mm 9 Be
target. Fission fragments were separated and identiﬁed
in ﬂight with the BigRIPS separator centred on 130 Cd.
Identiﬁcation was achieved by using the Bρ-∆E-Bρ
technique on an individual particle basis. A preliminary BigRIPS particle identiﬁcation plot is shown in
Fig. 1. This secondary radioactive beam impinged onanother target of 6 mm 9 Be located at F8. The newgermanium HiCARI array1) was located around thissecond beryllium target and used to detect the emitted γ rays with high resolution. The reaction products
were identiﬁed in the ZeroDegree spectrometer, centred on 129 Ag, using the same methods as in BigRIPS.
The obtained data set is under analysis. As an early
indication of the ability of the HiCARI array to achieve
in-ﬂight gamma-ray spectroscopy the isotope 128 Cd
was selected to conﬁrm the array was functioning as
intended. 128 Cd was selected due to its high yield andits known structure.2) A preliminary Doppler corrected
γ-ray spectrum of 128 Cd populated in one-proton removal from 131 In showing the 4+ and 2+ gamma rays
is presented in Fig. 2. Note that using β values determined for individual particles, as well as updated
calibrations, will result in a much better improved energy resolution.
References

1) K. Wimmer et al. (HiCARI Collaboration), in this report.
2) A. Scherillo et al., Phys. Rev. C 70, 054318 (2004).

A/Q

∗1

600

Fig. 2. Doppler corrected γ-ray spectrum of 128 Cd as
measured by the full HiCARI. Clearly visible are theknown2) 646 keV 2+ to 0+ and 785 keV 4+ to 2+ transitions.

51
50

200

150

105

52

250

Department of Physics, University of Surrey
GSI Helmholtzzentrum für Schwerionenforschung GmbH

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Characterization of a strongly Coulomb-excited state at an excitationenergy above 4 MeV in 136 Te
A. Jungclaus∗1 and P. Doornenbal∗2 for the NP1912-RIBF193 Collaboration
In April 2015, the experiment NP1306-RIBF98R1
was performed aiming for a methodical study of thesystematic uncertainties inherent to the analysis of
Coulomb excitation experiments at relativistic energies, using 136 Te as a high-statistics test case. The
analysis of the obtained data is ﬁnished and the results are published.1–3) In that experiment, besides+
the known 607-keV, 2+
1 → 01 transition, additional γ
strength in the range 3.0–4.5 MeV was observed in the
inelastic excitation of 136 Te on a gold target.4) The experimental spectra are nicely described assuming thattwo γ rays are detected, whereas the bump at highenergy is too broad to be described by one single transition. However, due to the limited in-beam energy
resolution of the DALI2 spectrometer, the individual
γ-ray energies can only be determined with rather large
uncertainties. The intensity ratio between the two lines
clearly depends on the γ-ray multiplicity of the event.
The line at higher energy has a higher yield when only
one γ ray is detected, while the one at lower energy
is more intense for events with γ-ray multiplicity two.
From this observation, it can be concluded that theγ ray with higher energy is emitted in cascades withlower multiplicity. Unfortunately, however, due to random coincidences with background γ rays, it is not possible to go beyond this qualitative statement. Based on
the available experimental information it is not possible to determine whether the two transitions populate
+
+
+
136
the 4+
Te.
1 and 21 or the 21 and 01 states of
The large cross section measured for the excitationof a state above 4 MeV in a heavy nucleus such as 136 Te
in the inelastic scattering on a gold target is diﬃcult
to explain. Whatever the spin of the newly identiﬁed
state is, the corresponding transition probability is exceptionally large. Theoretical studies suggest that the
new excited state in 136 Te may be related to the existence of loosely-bound neutrons outside the 132 Sn core.
It is therefore of utmost interest to better characterize
this unusual state.
The availability of the HiCARI array at RIKEN in
2020 oﬀered the unique opportunity to further investigate this interesting case. The superb position resolution of the tracking detectors translates into a very
good in-beam energy resolution for high-energy γ rays.
Therefore, the inelastic excitation of 136 Te on a gold
target was measured again with the goal to determine
the energies of the two high-energy γ rays emitted in
the decay of the new state with suﬃcient precision inorder to establish to which low-lying levels of 136 Te the∗1∗2Fig. 1. HiCARI γ-ray spectrum of 136 Te populated via inelastic excitation on a gold target, considering either all
γ-ray multiplicities (black) or Mγ = 1 (red).

decay proceeds. In addition, also the inelastic excitation on a Be target was studied in order to allow for adetermination of the nuclear deformation length fromthe measured cross section. The aim of this part ofthe experiment was to obtain further information withrespect to the spin of the new state above 4 MeV in
136
Te.
The experiment NP1912-RIBF193 was performed
during the HiCARI campaign in November 2020. For
both the Au and Be targets the expected counting
statistics was accumulated and the taken data in theexperiment is currently under analysis. The selectionof the reaction channel was achieved via event-by-event
ion identiﬁcation in the BigRIPS and ZeroDegree spectrometers. A preliminary γ-ray spectrum of 136 Te in+
the region around the known 2+
1 → 01 transition, takenwith the HiCARI array following the inelastic excitation on a gold target, is shown in Fig. 1.
References

1) V. Vaquero et al., Phys. Rev. Lett. 118, 202502 (2017).
2) V. Vaquero et al., Phys. Lett. B 795, 356 (2019).
3) V. Vaquero et al., Phys. Rev. C 99, 034306 (2019).
4) V. Vaquero, PhD thesis, Universidád Autónoma de
Madrid, 2018.

IEM-CSIC, Madrid
RIKEN Nishina Center- 10 -1

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Study of the 9 C proton breakup reaction
A. I. Chilug,∗1,∗2,∗3 V. Panin,∗4 L. Trache,∗1 D. State,∗1,∗2 I. C. Stefanescu,∗1,∗2 J. Tanaka,∗3 H. Otsu,∗3
T. Motobayashi,∗3 A. Spiridon,∗1 and T. Uesaka∗3 for HI-p Collaboration

45

1500
120
1000
100

PDC_θX [mrad]

The 9 C proton breakup reaction was studied during
the SAMURAI29 experiment at RIKEN. The reaction
was studied by two methods: Coulomb dissociation andnuclear breakup. The physics goal of the experiment
was to evaluate the astrophysical S18 -factor of the inverse process, the 8 B(p, γ)9 C, at energies relevant for
astrophysics.
The SAMURAI29 experiment is the first performed
among a series of 4 experiments with proton-richsecondary beams and was carried out with a 160MeV/nucleon 9 C beam produced from an 18 O primarybeam, at the F13 focal plane using the SAMURAI magnetic spectrometer. The whole experimental setup isdetailed in Ref. 1) and in Ref. 2). The detection system was prepared to ensure the inclusive and exclusive
measurements of the 9 C breakup reaction. Therefore,a silicon GLAST-type detector system and a set of two
new drift chambers (PDC1 and PDC2) were used to detect the protons produced in the breakup. Both systems
were used for the first time during the experiment.
The silicon detectors, the signals of which were processed using a combination of HINP16 electronics andthe new Dual-Gain Preamplifiers developed by the
RIKEN-ATOMKI collaboration,3) enabled the simultaneous detection of the proton and 8 B from the reaction.
Therefore, they cover a large dynamic energy range, as
shown in Fig. 1. Having these tracking detectors together with other SAMURAI standard detectors enabled

proton40

Counts35

9

C unreacted
beam

30
25

B

15
10
5
0
0

2000

4000

6000

8000

10000

12000

Eloss_SSD1 [keV]
Fig. 1. Energy deposited by the proton and 8 B recorded simultaneously in the first layer of the silicon detector.
∗1
∗2
∗3
∗4

80
0
60

−500

40

−1000
−1500
−1000

20

−500

0

500

0
1000

PDC_X [mm]Fig. 2. Protons tracked in the proton drift chambers (PDCs).

the reconstruction of the proton momentum distribution, which provides information on the shell occupiedby the removed proton in 9 C.
A serious complication in the analysis is the background from the interaction of the beam particles withthe experimental detectors, which must be excluded
from the events. One example is the protons producedin the plastic scintillator bars of the HODF, which weredetected in the PDCs. In Fig. 2, the red dots indicate theprotons produced in the target with the condition of coincident proton signals in the silicon detectors, whereas
the events marked with the black box area in the figure
are protons produced in the HODF detector.
The following steps have been achieved so far in thedata analysis.
(1) The one-proton removal channel from 9 C nucleus
is clearly separated in the data.
(2) With the tracked positions in the silicon detectors
placed after the target, it was possible to reconstruct the reaction vertex.
(3) The proton and 8 B momentum distributions were
determined.
(4) The Coulomb dissociation yield of the 9 C breakup
as a function of the relative energy between the
proton and 8 B was obtained.

8

20

500

Further analysis of the experimental data is inprogress.
References

1) A. I. Chilug et al., RIKEN Accel. Prog. Rep. 52, 27 (2019).
2) A. I. Chilug et al., AIP. Conf. Proc. 2076, 060001 (2019).
3) V. Panin et al., RIKEN Accel. Prog. Rep. 51, 148 (2018).

Department of Nuclear Physics, IFIN-HH
Doctoral School of Physics, University of Bucharest
RIKEN Nishina Center
GSI Helmholtzzentrum fur Schwerionenforschung GmbH- 11 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Gamow-Teller giant resonance in 11 Li neutron drip-line nucleus
L. Stuhl,∗1,∗2,∗3 M. Sasano,∗3 J. Gao,∗3,∗4 Y. Hirai,∗5 K. Yako,∗2 T. Wakasa,∗5 D. S. Ahn,∗3 H. Baba,∗3
A. I. Chilug,∗6,∗3 S. Franchoo,∗7 Y. Fujino,∗8 J. Gibelin,∗9 I. S. Hahn,∗1,∗10 Z. Halász,∗11 T. Harada,∗12
M. N. Harakeh,∗13,∗14 D. Inomoto,∗5 T. Isobe,∗3 H. Kasahara,∗5 D. Kim,∗1,∗15 G. G. Kiss,∗11 T. Kobayashi,∗16
Y. Kondo,∗17 Z. Korkulu,∗1,∗3 S. Koyama,∗18 Y. Kubota,∗3 A. Kurihara,∗17 H. N. Liu,∗19 M. Matsumoto,∗17
S. Michimasa,∗2 H. Miki,∗17 M. Miwa,∗20 T. Motobayashi,∗3 T. Nakamura,∗17 M. Nishimura,∗3 H. Otsu,∗3
V. Panin,∗3 S. Park,∗10 A. T. Saito,∗17 H. Sakai,∗3 H. Sato,∗3 T. Shimada,∗17 Y. Shimizu,∗3 S. Shimoura,∗2
A. Spiridon,∗6 I. C. Stefanescu,∗6 X. Sun,∗3,∗4 Y. L. Sun,∗19 H. Suzuki,∗3 E. Takada,∗21 Y. Togano,∗8
T. Tomai,∗17,∗3 L. Trache,∗6 D. Tudor,∗6,∗3 T. Uesaka,∗3 H. Yamada,∗17 M. Yasuda,∗17 K. Yoneda,∗3 K. Yoshida,∗3
J. Zenihiro,∗3 and N. Zhang∗22,∗2
Recent nuclear physics studies are increasingly focused on the region far from the valley of stability,
thereby leading to an increase in the intensity of available exotic isotopes. We started a program1) at the
RIKEN Radioactive Isotope Beam Factory with the objective of measuring the spin-isospin responses of lightnuclei along the neutron drip line. There are no available data on nuclear collectivity (giant resonances) on
any drip-line nucleus.
In the SAMURAI30 experiment, we studied the mostbasic nuclear collectivity, the Gamow-Teller (GT) giant
resonance, in 11 Li (at 181 MeV/nucleon) and 14 Be (at198 MeV/nucleon) nuclei. The charge-exchange (CE)(p, n) reactions in inverse kinematics are eﬃcient tools
for extracting the B(GT) strengths of unstable isotopes,
up to high excitation energies, without Q-value limitation.2) The uniqe setup of the Particle Analyzer Neutron
Detector Of Real-time Acquisition (PANDORA)3) lowenergy neutron counter + SAMURAI magnetic spectrometer,4) together with a thick liquid hydrogen target
allowed us to perform such measurements with high luminosity and low background. In our previous study on
132
Sn, we veriﬁed that with this setup, we can extract
the strength distribution of isovector spin-ﬂip giant resonances in unstable nuclei with quality comparable tothose on stable nuclei.5)
In the 11 Li(p, n)11 Be reaction, we identiﬁed clear kine∗1

Center for Exotic Nuclear Studies, Institute for Basic Science(IBS)∗2 Center for Nuclear Study, University of Tokyo∗3 RIKEN Nishina Center∗4 School of Physics, Peking University∗5 Department of Physics, Kyushu University∗6 Horia Hulubei Nat. Inst. of Phys. and Nucl. Eng.
∗7 Inst. de Physique Nuclaire, Univ. Paris-Saclay∗8 Department of Physics, Rikkyo University∗9 LPC CAEN
∗10 Department of Physics, Ewha Womans University∗11 ATOMKI, Institute for Nuclear Research, HAS∗12 Department of Physics, Toho University∗13 University of Groningen∗14 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗15 Department of Physics, Korea University∗16 Department of Physics, Tohoku University∗17 Dept. of Physics, Tokyo Institute of Technology∗18 Department of Physics, University of Tokyo∗19 Dépt. Physique Nucl., CEA, Univ. Paris-Saclay∗20 Dept. of Physics, Saitama University, Saitama∗21 National Institute of Radiological Sciences (NIRS)∗22 Institute of Modern Physics, Chinese Acad. of Sci.

Fig. 1. Excitation energy spectrum in the 6◦ –8◦ center-ofmass system for 8 Li + t.

matical correlations6) between the neutron energy andlaboratory scattering angle for more than ten diﬀerent
decay channels of 11 Be: 10 Be + n, 9 Be + 2n, 9 Li + p + n,
8
Li + p + 2n, 9 Li + d, 8 Li + t, 8 Li + d + n, 7 Li + t + n,
7
Li + d + 2n, 6 Li + t + 2n, α + 6 He + n and 2α + 3n.
The excitation-energy spectra up to approximately
40 MeV have been reconstructed. The background subtraction and acceptance correction are performed. As
an example, Fig. 1 presents the excitation energy spectrum in the daughter nucleus 11 Be for the 8 Li + t decay channel for θC.M. = 6◦ –8◦ . A forward scatteringpeak in the 0◦ –10◦ center-of-mass system indicates astrong GT transition in all decay channles at approximately 19 MeV, below the Isobaric analogue state,7)
which agrees well with previous beta-decay studies.8)
References

1) L. Stuhl et al., RIKEN Accel. Prog. Rep. 48, 54 (2015).
2) M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011).
3) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. A 866,
164 (2017).
4) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
5) J. Yasuda et al., Phys. Rev. Lett. 121, 132501 (2018).
6) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. B 463,
189 (2020).
7) T. Teranishi et al., Phys. Lett. B 407, 110 (1997).
8) R. Raabe et al., Phys. Rev. Lett. 101, 212501 (2008).

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RIKEN Accel. Prog. Rep. 54 (2021)

One proton removal cross section of 25 F with a carbon target
Y. Yoshitome,∗1,∗2 Y. Kondo,∗1,∗2 T. Nakamura,∗1,∗2 J. A. Tostevin,∗3 R. Tanaka,∗1,∗2 R. Minakata,∗1,∗2
S. Ogoshi,∗1,∗2 N. A. Orr,∗4 N. L. Achouri,∗4 T. Aumann,∗5,∗6 H. Baba,∗2 F. Delaunay,∗4 P. Doornenbal,∗2
N. Fukuda,∗2 J. Gibelin,∗4 J. W. Hwang,∗7 N. Inabe,∗2 T. Isobe,∗2 D. Kameda,∗2 D. Kanno,∗1,∗2 S. Kim,∗7
N. Kobayashi,∗1,∗2 T. Kobayashi,∗8,∗2 T. Kubo,∗3 S. Leblond,∗4 J. Lee,∗2 F. M. Marqués,∗4 T. Motobayashi,∗2
D. Murai,∗9 T. Murakami,∗10 K. Muto,∗8 T. Nakashima,∗1,∗2 N. Nakatsuka,∗10,∗2 A. Navin,∗11,∗14 S. Nishi,∗1,∗2
H. Otsu,∗2 H. Sato,∗2 Y. Satou,∗7 Y. Shimizu,∗2 H. Suzuki,∗2 K. Takahashi,∗8 H. Takeda,∗2 S. Takeuchi,∗2
Y. Togano,∗9 A. G. Tuﬀ,∗12 M. Vandebrouck,∗13 and K. Yoneda∗2target was measured using the SAMURAI device at
RIBF, as a by-product of the measurement of the oneproton removal of 26 F and 27 F into 25 O and 26 O,
respectively.5) For details of the experimental setup
and method, see Ref. 5). The 25 F secondary beam
was produced by the projectile-fragmentation of 48 Ca
at 345 MeV/nucleon with a thick beryllium target.
The beam intensity of 25 F reached 1.1×103 particles/s with a purity of 3.4%. The 25 F projectile thenimpinged on the carbon target with a thickness of
1.8 g/cm2 . The mean energy at the middle of thetarget was 218 MeV/nucleon, with momentum acceptance of |∆P/P | ≤ 0.6%. The particle identiﬁcation(PID) for 25 F was obtained by the standard method at
the BigRIPS.5) The PID of the 24 O residue was madeby the measurements of the time of ﬂight (TOF), andenergy loss ∆E at the hodoscope (HODF), with themagnetic rigidity (Bρ) obtained by the tracking withthe two multi-wire drift chambers, FDC1 and FDC2,
at the entrance and exit of the SAMURAI superconducting magnet, respectively.5,6) The central ﬁeld of
the magnet was 3.0 T.
The 25 F(−p) removal cross section was extracted using the ratio of the counts of the outgoing 24 O to thoseof 25 F, where the background events measured withthe empty target were subtracted. The eﬀect of reaction loss in the thick target was incorporated using
the procedure in Ref. 7). The obtained preliminary
value of the one-proton removal cross section of 25 F is
7.1(8) mb. usdb-interaction shell- and eikonal-model
calculations give the theoretical cross section 14.9 mb,
resulting in the reduction factor Rs = 0.48(5). Further
evaluation of nucleon removal cross sections in neighboring neutron-rich isotopes is in progress.

Experimental one-proton (neutron) removal crosssections σ−1p (σ−1n ) with light target nuclei (Be andC) at intermediate energies have been shown to behindered with respect to the corresponding theoreticalvalues. Their ratio Rs = σexp /σth (reduction factor)
shows a strong linear dependence on the diﬀerence between the 1p and 1n separation energies, ∆S = Sp −Sn(Sn −Sp ).1,2) This dependence has been recognized as a
key to understand correlations beyond the shell-modelbased picture of atomic nuclei. The theoretical crosssections are evaluated using shell-model spectroscopic
factors C 2 S combined with an established reaction theory at intermediate energies, such as eikonal and impulse approximation. The reduction factor depends on
the reaction used and the reduction mechanisms are
yet to be clariﬁed.3)
We report a preliminary result of the one-proton
removal cross section of 25 F with a carbon target at
218 MeV/nucleon. This data point is a useful addition
to the systematics of the one-nucleon removal cross sections. It should be noted that 25 F has one proton morethan doubly-magic 24 O. Accordingly, we expect thatthe spectroscopic factor for proton removal from 25 F isclose to unity. However, the recent 25 F(p, 2p) measurement at SHARAQ at RIBF4) obtained a much-reduced
value of 0.36(13) from 25 F to the bound 24 O. We also
note that the ∆S value of 10.17(24) MeV for 25 F lies
between those of the stable nuclei (|∆S| < 8 MeV) anddrip-line nuclei (|∆S| = 15–30 MeV). As such, the onenucleon removal cross section from 25 F on the carbon
target is a valuable addition.
The 25 F(−p) removal cross section on the carbon∗1

Department of Physics, Tokyo Institute of Technology
RIKEN Nishina Center∗3 Department of Physics, University of Surrey∗4 LPC-Caen, ENSICAEN, Université de Caen, CNRS/IN2P3∗5 Institut für Kernphysik, Technische Universität Darmstadt∗6 ExtreMe Matter Institute (EMMI) and Research Division,
GSI∗7 Department of Physics and Astronomy, Seoul National University∗8 Department of Physics, Tohoku University∗9 Department of Physics, Rikkyo University∗10 Department of Physics, Kyoto University∗11 GANIL, CEA/DSM-CNRS/IN2P3∗12 Department of Physics, University of York
∗13 Institut de Physique Nucléaire, Université Paris-Sud,
IN2P3-CNRS∗14 Present address: GANIL CEA/DRF-CNRSI/N2P3∗2

References
1) A. Gade et al., Phys. Rev. C 77, 044306 (2008).
2) J. A. Tostevin, A. Gade, Phys. Rev. C 90, 057602(2014).
3) T. Aumann et al., Prog. Part. Nucl. Phys., in press.
4) T. L. Tang et al., Phys. Rev. Lett. 124, 212502 (2020).
5) Y. Kondo et al., Phys. Rev. Lett. 116, 102503 (2016).
6) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
7) N. Kobayashi et al., Phys. Rev. C 86, 054604 (2012).

- 13 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Particle identification of SAMURAI11 experiment
J. Gao,∗1,∗3 M. Sasano,∗1 L. Stuhl,∗6,∗2 Y. Hirai,∗4 T. Wakasa,∗4 D. S. Ahn,∗1 J. K. Ahn,∗13 H. Baba,∗1
K. Chae,∗20 A. Chilug,∗5,∗1 K. Cook,∗15 Y. Fujino,∗7 N. Fukuda,∗1 B. Gao,∗19 S. Goto,∗4 I. S. Hahn,∗6,∗8
Y. Hamano,∗4 Z. Halász,∗9 T. Harada,∗10 S. Hong,∗20 S. Huang,∗1,∗3 N. Inabe,∗1 D. Inomoto,∗4 T. Isobe,∗1
H. Kasahara,∗4 D. Kim,∗6,∗8 T. Kobayashi,∗14 Y. Kondo,∗15 Z. Korkulu,∗6,∗1 A. J. Krasznahorkay,∗9 H. Miki,∗15
K. Miki,∗14 S. Mitsumoto,∗4 M. Miwa,∗18 T. Motobayashi,∗1 T. Nakamura,∗15 M. Nishimura,∗1 H. Oshiro,∗4
H. Otsu,∗1 V. Panin,∗1 S. Sakaguchi,∗4 D. Sakai,∗14 H. Sakai,∗1 S. Sakaki,∗4 H. Sato,∗1 T. Shimada,∗15
Y. Shimizu,∗1 B. Sun,∗21 X. Sun,∗1,∗3 H. Suzuki,∗1 J. Tanaka,∗1 Y. Togano,∗7 T. Tomai,∗15,∗1 T. Uesaka,∗1
Y. Utsuki,∗14 H. Wang,∗15 X. Xu,∗19 K. Yako,∗2 A. Yasuda,∗15 K. Yoneda,∗1 K. Yoshida,∗1 Y. Yoshitome,∗15
and J. Zenihiro∗1
In this report, we present the particle identiﬁcation (PID) results of the decay fragments from the48
Cr(p, n)48 Mn reaction in the SAMURAI11 experiment.1)
The charge number Z and mass to charge ratio
A/Z are used to identify particles, where Z is calculated using the energy loss ∆E and time-of-ﬂight measured in the hodoscope and A/Z is calculated using
the rigidity and ﬂight path from the simulation andthe time-of-ﬂight. With the position and angle information from the drift chambers before and after the
SAMURAI magnet, the rigidity and trajectory of theparticle could be extracted by simulation. The simulation program uses a 4th-order Runge-Kutta method
to simulate the trajectory and it iterates several times
to determine the rigidity that reproduces the position
and angle measured in the drift chambers.
Our hodoscope detector consists of seven bars. The
size of each bar is 1200 mm(H) × 100 mm(W) ×
10 mm(T). The PID in one hodoscope bar is shownin Fig. 1. Because the position on the PID plot of one
particle could be slightly shifted in diﬀerent bars, weevaluate the resolution on one bar only. The resolutionof the charge number Z is σZ,48 Cr = 0.20 and σZ,46 V= 0.19, corresponding to 5.0σ separation for Z = 23
and Z = 24. The resolution of the mass to charge ratio A/Z is σA/Z,46 V = 0.0099 and σA/Z,47 V = 0.0083,

corresponding to 4.3σ separation.
This work was funded by the China ScholarshipCouncil, KAKENHI project 16H06716, the Japan Society for the Promotion of Science, and Kurata Grant
from the Kurata Memorial Hitachi Science and Technology Foundation.

30

Cr
V
44
Ti

48

25

47

Z

46

V

count
150

20

100
50

15

10
1.9

2.0

A/Z

2.1

2.2

Fig. 1. PID in one bar of hodoscope. This bar is the one
next to the bar hitting by beam particles, on the higher
rigidity side. Some particles are labeled on the figure.

∗1

RIKEN Nishina Center∗2 Center for Nuclear Study, University of Tokyo∗3 School of Physics, Peking University∗4 Department of Physics, Kyushu University∗5 Horia Hulubei Nat. Inst. of Phys. and Nucl. Eng.
∗6 Center for Exotic Nuclear Studies, Institute for Basic Science∗7 Department of Physics, Rikkyo University∗8 Department of Physics, Ewha Womans University∗9 ATOMKI, Institute for Nuclear Research∗10 Department of Physics, Toho University∗11 KVI - CART, University of Groningen∗12 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗13 Department of Physics, Korea University∗14 Department of Physics, Tohoku University∗15 Dept. of Physics, Tokyo Institute of Technology∗16 Department of Physics, University of Tokyo∗18 Dept. of Physics, Saitama University∗19 Institute of Modern Physics, Chinese Acad. of Sci.
∗20 Department of Physics, Sungkyunkwan University∗21 School of Physics and Nuclear Engineering, Beihang University

Reference

1) M. Sasano et al., RIKEN Accel. Prog. Rep. 53, 40(2019).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Symmetry energy investigation with pion production from Sn + Sn
systems†
G. Jhang,∗1,∗2,∗3 J. Estee,∗1,∗2,∗3 J. Barney,∗1,∗2,∗3 G. Cerizza,∗1,∗2,∗3 M. Kaneko,∗1,∗4 J. W. Lee,∗1,∗5
W. G. Lynch,∗2,∗3 T. Isobe,∗1 M. Kurata-Nishimura,∗1 T. Murakami,∗1,∗4 C. Y. Tsang,∗2,∗3 M. B. Tsang,∗2,∗3
R. Wang,∗2 H. Baba,∗1 N. Fukuda,∗1 B. Hong,∗5 T. Kobayashi,∗6 P. Lasko,∗7 J. Łukasik,∗7 A. B. McIntosh,∗8
H. Otsu,∗1 P. Pawłowski,∗7 H. Sakurai,∗1 C. Santamaria,∗1,∗2 R. Shane,∗2 D. Suzuki,∗1 S. Tangwancharoen,∗2
Z. G. Xiao,∗9 S. J. Yennello,∗8,∗10 Y. Zhang∗9 for the SπRIT Collaboration
andM. Colonna,∗11 P. Danielewicz,∗2,∗3 C.-M. Ko,∗8,∗12 A. Ono,∗6 H. Wolter∗13 for the TMEP collaboration
In the last couple of decades, pions produced in
the high density regions of heavy ion collisions havebeen considered to be one of sensitive probes to investigate the symmetry energy term in the nuclear
equation of state at high densities, a key property
to understand neutron stars. In our new experiment
designed to study the symmetry energy, the multiplicities of negatively and positively charged pions
have been measured with high accuracy for central
132
Sn + 124 Sn, 112 Sn + 124 Sn, and 108 Sn + 112 Sn collisions at E/A = 270 MeV with the SπRIT Time Projection Chamber2,3) placed inside the SAMURAI spectrometer4) at RIBF. While individual pion multiplicities are measured to 4% accuracy, those of the charged
pion multiplicity ratios are measured to 2% accuracy.
We compare these data to predictions from seven major transport models which have taken part in theTransport Model Evaluation Project (TMEP).5–7) The
calculations reproduce qualitatively the dependence ofthe multiplicities and their ratios on the total neutron
and proton number in the colliding systems.
As shown in Fig. 1, however, the predictions of thetransport models from diﬀerent codes diﬀer too muchto allow extraction of reliable constraints on the symmetry energy from the data even using the double pion
ratio. This ﬁnding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au + Au system.8–12) These
new results call for still better understanding of the differences among transport codes, and new observables

that are more sensitive to the density dependence ofthe symmetry energy.

Fig. 1. (Left panel) Experimental charged pion yield ratios as a function of N/Z together with the results ofseven transport-model predictions for the soft and stiﬀ
symmetry energies (the diﬀerence of predictions are presented by the height of colored boxes). The dashed blueline is a power-law ﬁt with the function (N/Z)3.6 , while
the dotted blue line represents (N/Z)2 of the system.
(Right panel) Double pion yield ratios for 132 Sn + 124 Sn
and 108 Sn + 112 Sn. The data and their uncertainty are
given by the red horizontal bar and the results of thetransport models are shown by the colored boxes, in asimilar way as in the left panel. Taken from Ref. 1).

References

1) G. Jhang et al., Phys. Lett. B 813, 136016 (2021).
2) J. Barney et al., arXiv:2005.10806.
3) R. Shane et al., Nucl. Instrum. Methods Phys. Res. A
784, 513 (2015).
4) H. Otsu et al., Nucl. Instrum. Methods Phys. Res. B
376, 175 (2016).
5) A. Ono et al., Phys. Rev. C 100, 044617 (2019).
6) J. Xu et al., Phys. Rev. C 93, 044609 (2016).
7) Y.-X. Zhang et al., Phys. Rev. C 97, 034625 (2018).
8) J. Hong, P. Danielewicz, Phys. Rev. C 90, 024605(2014).
9) B. -A. Li, Phys. Rev. Lett. 88, 192701 (2002).
10) Z. -Q. Feng, G .-M. Jin, Phys. Lett. B 683, 140 (2010).
11) Z. Xiao et al., Phys. Rev. Lett. 102, 062502 (2009).
12) W. -J. Xie, J. Su, L. Zhu, F. -S. Zhang, Phys. Lett. B
718, 1510 (2013).

Condensed from the article in Phys. Lett. B 813, 136016(2021)1)∗1 RIKEN Nishina Center∗2 National Superconducting Cyclotron Laboratory, Michigan
State University∗3 Department of Physics, Michigan State University∗4 Department of Physics, Kyoto University∗5 Department of Physics, Korea University∗6 Department of Physics, Tohoku University∗7 Institute of Nuclear Physics PAN∗8 Cyclotron Institute, Texas A&M University∗9 Department of Physics, Tsinghua University∗10 Department of Chemistry, Texas A&M University∗11 INFN-LNS, Laboratori Nazionali del Sud∗12 Department of Physics and Astronomy, Texas A&M University∗13 Faculty of Physics, Ludwig-Maximilians-University of Munich†- 15 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Proton eﬃciency function for high-multiplicity events in the
SπRIT-TPC investigated by the embedding technique
M. Kaneko,∗1,∗2 J. Barney,∗2,∗3 G. Cerizza,∗2,∗3 J. Estee,∗2,∗3 T. Isobe,∗2 G. Jhang,∗2,∗3 M. Kurata-Nishimura,∗2
P. Lasko,∗5,∗2 J. W. Lee,∗4,∗2 J. Łukasik,∗5 W. G. Lynch,∗3 T. Murakami,∗1,∗2 P. Pawłowski,∗5,∗2
C. Santamaria,∗2,∗7 C. Y. Tsang,∗2,∗3 M. B. Tsang∗3 for the SπRIT Collaboration

∗1
∗2
∗3
∗4
∗5
∗6
∗7

Department of Physics, Kyoto University
RIKEN Nishina Center
NSCL and Dept. of Phys. & Ast., Michigan State University
Department of Physics, Korea University
Institute of Nuclear Physics, PAN, Kraków
Department of Physics, Tsinghua University
Lawrence Berkeley National Laboratory, UC Berkeley

dN/dy020

Raw data
IterNo. 1
IterNo. 2
IterNo. 3

Proton yieldin central 132Sn+124Sn

15

10
5

1.2
1
0.8
0.6

Eff.

The SπRIT-time projection chamber (TPC)1) project
aims to constrain the high-density nuclear symmetry energy by using heavy-ion collisions. We measured lightcharged particles emitted from central Sn + Sn collisions at 270 MeV/nucleon, which have been predicted
to provide sensitive probes of the symmetry energy
at supra-saturation densities.2) In this report, we describe the reconstruction eﬃciency of protons in central
132
Sn + 124 Sn collisions.
The Sn target is placed approximately 1 cm upstream
from the TPC; hence, the charged particles emitted inforward angles are mainly observed. In central Sn + Sncollisions producing high charged-particle multiplicity,
signals induced by charged particles can interfere witheach other, causing the tracks to be merged and/or broken. As it would be diﬃcult to fully simulate realistic
situations, the embedding technique3) is applied. The
digitized signal of a single proton traversing the TPC
is generated based on a Monte Carlo simulation. Subsequently, the generated signal is embedded into real
events, which are analyzed by the same track reconstruction algorithm as for the physical tracks. The proton’sreconstruction eﬃciency with a given track multiplicity
can be estimated by comparing the embedded tracks andthe reconstructed tracks.
The spectrum of transverse momentum pT vs. scaledc.m.
− 1 of protons is corrected by the
rapidity y0 = y/yNNc.m.
are the rapidity
following procedure, where y and yNNof the detected proton and the center-of-mass rapidityof the nucleon-nucleon system, respectively. It is notedthat the momentum resolution of the TPC can distort
the measured spectrum. To consider this bin-smearing
eﬀect in the eﬃciency calculation, the distribution ofembedded protons needs to be properly weighted. First,
the measured pT -y0 spectrum is used as the weighting
factor. The eﬃciency as a function of pT -y0 is obtained
as the ratio of reconstructed protons to embedded ones.
Subsequently, the corrected pT -y0 spectrum of protons is
obtained as the raw spectrum divided by the eﬃciency.
In the next iteration, the corrected spectrum is used as
the weighting factor. This process is iterated until thecorrection converges.
As shown in Fig. 1, the correction converged after two
iterations. Since we limited the azimuthal angle of tracks

−2

−1

0

1

2

y0 = y/ yc.m.
-1
NN

Fig. 1. The top panel shows pT -integrated dN/dy0 spectraof protons in central 132 Sn + 124 Sn collisions with andwithout eﬃciency corrections (colored and black markers, respectively). The bottom panel shows the eﬃciency
obtained with respect to their ratios.

to −30◦ ≤ ϕ ≤ 20◦ in the analysis, which is expected
to be the eﬃcient region of the TPC, the reconstruction
eﬃciency of protons is estimated to be approximately
90%. The eﬃciency exceeds 100% at y0 > 1.8 because
the original statistics of protons is quite low at such ahigh y0 and overcounting occurs owing to the smearing of
the proton rapidity at a lower y0 . In addtion to protons,
the pT -y0 spectra of deuterons and tritons are also corrected, which are being compared with theoretical predictions to extract physics statements for publicationsin the future.
This work is supported by the Japanese MEXT
KAKENHI under grant No. 24105004; the U.S. DOE
under Grant Nos. DE-SC0004835, DE-SC0014530,
and DE-NA0002923; the U.S. NSF under Grant
No. PHY-1565546; and the Polish NSC underGrant Nos. UMO-2013/09/B/ST2/04064 and UMO2013/10/M/ST2/00624. The computing resources were
provided by the HOKUSAI system at RIKEN.
References

1) R. Shane et al., Nucl. Instrum. Methods Phys. Res. A
784, 513 (2015).
2) M. B. Tsang et al., Phys. Rev. C 95, 044614 (2017).
3) M. Anderson et al., Nucl. Instrum. Methods Phys. Res.
A 499, 659 (2003).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Observation of anisotropic collective flow of charged particles andneutrons in heavy-ion collisions at beam energies of 400 MeV/nucleon
S. Yamamura,∗1,∗2 S. Nishimura,∗2 T. Isobe,∗2 V. H. Phong,∗2 M. Kaneko,∗2,∗3 T. Murakami,∗3 Y. Nakai,∗2
D. Nishimura,∗4 M. Nishimura,∗2 N. Chiga,∗2 and E. Takada∗5
The anisotropic collective ﬂow of protons and neutrons
in heavy-ion collisions is expected to provide experimental information on the equation of state (EOS) of highdensity and neutron-rich nuclear matters because it reﬂects the symmetry energy at the high-density region.1)
The anisotropy is expressed by the distribution functionof particle emissions observed from the reaction plane as
(
)
∑
N0
dN
=
1+2
vn cos nφ ,
(1)
dφ
2π
n

where φ, N0 and vn represent the emission angle of theparticles observed from the reaction plane, normalization
constant, and the anisotropic strength, respectively. The
diﬀerence between the v1 (directed ﬂow) of neutrons andof protons is theoretically expected to be highly sensitive
to EOS around target rapidity2) even though only a few
experimental data are available.
A pilot experiment (H355) was conducted at HIMAC
by impinging 400 MeV/nucleon 132 Xe beam on a CsItarget (500 mg/cm2 ) at a high intensity of 106 particles/spill to measure the proton and neutron ﬂows precisely. In this experiment, 32 plastic scintillators (EJ29933, 30 × 55 × 127 mm3 ) were used to identify neutrons
using pulse-shape discrimination. The detectors wereplaced parallel to the beam axis and in a cylindrical conﬁguration to detect particles at target rapidity. Charged
and neutral particles can be identiﬁed by combining
these detectors called NiGIRI (Neutron, ion, and γ-ray
identiﬁcation for radioactive isotope beam) and charged
particle veto scintillators. Figure 1 shows the prototype
NiGIRI array.3) Energies of the detected particles are
deduced from the time-of-ﬂight between the CsI target

Fig. 1. NiGIRI detectors3) (16 arrays 2 layers).
∗1
∗2
∗3
∗4
∗5

Department of Physics, University of Tokyo
RIKEN Nishina Center
Department of Physics, Kyoto University
Department of Natural Science, Tokyo City University
NIRS

Fig. 2. Measured distribution functions dN/φ of charged particles (left), neutrons (center), and γ rays (right). The
spectra were integrated over momentum and impact parameter.

and NiGIRI detectors. Another set of 32 plastic scintillators called the Kyoto-array were used to cover the midrapidity region. The emitted angles of the charged particles were measured for determining the reaction plane.
The plane was determined by the beam axis and Q vector obtained using∑ (cos θk ),(2)Q=sin θkkwhere θk denotes a hit angle of Kyoto-array; the summation is taken over the number of detected particles.
The cross-talk events observed in the Kyoto-array were
mostly rejected in the Q-vector determination to minimize the detector bias.
Emission angles of charged particles, neutrons, and γ
rays with respect to the angle of Q vector were studied
at target rapidity using the data of NiGIRI. Figure 2
shows the measured distribution functions (dN/dφ) of
the charged particles, neutrons, and γ rays. The results
indicate a clear anisotropy for charged particles and neutrons, and show ﬂatter distribution for γ rays; the results
are expected to indicate collective ﬂow, particularly v1 ,and therefore a pressure gradient is observed in the highdensity region in heavy-ion collisions.
To the best of the author’s knowledge, this experiment
prooves for the ﬁrst time that it is possible to directlycompare the collective ﬂow among light charged ions andneutrons around target rapidity. An upgraded experiment with a higher resolution of the reaction plane detector arrays will be performed at HIMAC and possibly
RIBF in the future.
References

1) B. A. Li, et al., Phys. Rep. 464, 113 (2008).
2) Z. Q. Feng, Phys. Rev. C 85, 014604 (2012).
3) H. Matsuzawa et al., RIKEN Accel. Prog. Rep. 48, 212(2015).
- 17 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of proton elastic scattering from 132 Sn at
300 MeV/nucleon in inverse kinematics
T. Harada,∗1,∗2 J. Zenihiro,∗3 Y. Matsuda,∗4 S. Terashima,∗5 H. Sakaguchi,∗6 N. Aoi,∗6 H. Baba,∗2 M. Dozono,∗7
F. Endo,∗7 S. Enyo,∗3 Y. Fujikawa,∗3 S. Hanai,∗7 S. Hayakawa,∗7 Y. Hijikata,∗3 J. W. Hwang,∗7 N. Imai,∗7
K. Inaba,∗3 S. Ishida,∗4 T. Isobe,∗2 T. Kawabata,∗8 S. Kiyotake,∗9 A. Kohda,∗6 H. Kurosawa,∗4 R. Kojima,∗7
R. Maeda,∗4 Y. Maeda,∗9 S. Y. Matsumoto,∗3 R. Matsumura,∗1,∗2 B. Mauss,∗2 S. Michimasa,∗7 T. Murakami,∗3
D. Nishimura,∗10 T. Nishimura,∗9 K. Nosaka,∗3 S. Ota,∗7 K. Sakanashi,∗3 H. Shimizu,∗7 D. Suzuki,∗2 J. Tanaka,∗2
R. Tsunoda,∗7 T. Uesaka,∗2 and K. Yamamoto∗4
The equation of state (EOS) of nuclear matter is expressed as the EOS of the symmetric nuclear matter andthe symmetry energy. Particularly, the symmetry energy is important for understanding astrophysical phenomena, such as neutron stars. The EOS of symmetric nuclear matter is understood from previous experiments on stable nuclei, however there is much less understanding of the the symmetry energy. From many
theoretical studies, it is known that the slope parameter of the symmetry energy is strongly correlated withneutron skin thickness, which is deﬁned as the diﬀerence
between the neutron and proton root-mean-square radii.
In neutron-rich nuclei, the excess neutrons form a neutron skin structure. It is expected that this symmetryenergy can be constrained by determining the neutron
skin thickness from the neutron and proton density distributions.
We employed proton elastic scattering to extract neutron and proton density distributions. For stable nuclei,
we have established a method to extract the proton andneutron density distributions using proton elastic scattering.1) To employ this method to unstable nuclei with
30000

Count

25000
20000
15000
10000
5000
0
2.56

2.58

2.60

2.62

2.64

2.66

2.68

A/Q
Fig. 1. A/Q spectrum of secondary beam including 132 Sn
deduced from position and time-of-flight information at
BigRIPS. The peak of 132 Sn is located at A/Q = 2.64
shown in red. The A/Q resolution in r.m.s is 0.058%.
∗1

Department of Physics, Toho University
RIKEN Nishina Center∗3 Department of Physics, Kyoto University∗4 CYRIC, Tohoku University∗5 School of Physics, Beihang University∗6 RCNP, Osaka University∗7 CNS, University of Tokyo∗8 Department of Physics, Osaka University∗9 Department of Applied Physics, Miyazaki University∗10 Department of Natural Sciences, Tokyo City University∗2

Fig. 2. Kinematical correlations of 132 Sn between scattering
angles θ and kinematic energies of scattered protons Tp .
The red dotted line indicates elastic scattering events between 132 Sn at 303.9 MeV/nucleon and protons.

large asymmetry, we started a new project to measure
the elastic scattering of protons with RI beams (ESPRI)
in inverse kinematics. We developed a recoil proton
spectrometer (RPS), which consists of a 1-millimeterthick solid hydrogen target (SHT2) ), two multi-wire drift
chambers (MWDCs), two plastic scintillators, and fourteen NaI rods. We measure the angle and energy of therecoil protons from the SHT using the RPS. We successfully performed ESPRI measurements for several light
unstable nuclei.3)132
Sn has a larger isospin asymmetry than 208 Pb, andis expected to have a thicker neutron skin thickness. In
Novenver 2019, we performed proton elastic scatteringfrom 132 Sn at 300 MeV/nucleon at the F12 area.4) The
total beam rate was up to 600 kcps, and the purity of132
Sn was 20%. The A/Q spectrum of the secondary
beam including 132 Sn under high intensity is shown in
Fig. 1. We identiﬁed elastic events of 132 Sn from the correlation of the kinematic energies and recoil angles of thescattered protons with NaI rods and MWDCs as shownin Fig. 2. Data analysis for deducing the excitation energy spectrum of 132 Sn and the angular distribution of
the cross section is now in progress.
References

1) H. Sakaguchi et al., Prog. Part. Nucl. Phys. 97, 1 (2017).
2) Y. Matsuda et al., Nucl. Instrum. Methods Phys. Res. A
643, 6 (2011).
3) Y. Matsuda et al., Phys. Rev. C 87, 034614 (2013).
4) J. Zenihiro et al., RIKEN Accel. Prog. Rep. 53, 44 (2019).
- 18 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Results on the β decay of 60 Ge and 62 Ge measured at RIBF

Counts / 2 ms

The investigation of the structure of nuclei close to
the limits of stability is a topic of paramount importancein modern nuclear physics. The Tz = −2, 60 Ge nucleus
is a semi-magic, N = 28 isotone whose decay is almost
unknown. An exotic feature seen in other Tz = −2 nuclei1,2) is the competition between the γ de-excitationand the (isospin-forbidden) proton emission from theT = 2 isobaric analog state populated by β decay in thedaughter nucleus. Little was known about the decay of
the Tz = −1, 62 Ge nucleus. In other Tz = −1 nuclei asuppression of isoscalar γ transitions between J π = 1+ ,T = 0 states (Warburton and Weneser quasi-rule3,4) )has been observed.5)
Heavy proton-rich nuclei can be produced with un-

60

Ge

2

10

T1/2 = 25.0(3) ms

10

1−200 −100

0

100

200

300
400 500
600
Correlation time [ms]Fig. 1. Time correlations between 60 Ge implants in
WAS3ABi and subsequent β-delayed protons (Ep >1 MeV) detected in the same pixel of WAS3ABi.
∗1

IFIC, CSIC-Univ. Valencia
Department of Physics, Surrey University∗3 Chilean Nuclear Energy Commision∗4 MTA ATOMKI∗5 RIKEN Nishina Center∗6 CEN Bordeaux Gradignan∗7 National Institute for Physics and Nuclear Engineering, IFINHH∗8 INFN Sezione di Padova∗9 Department of Physics, Istanbul University∗10 Department of Physics, Tokyo University of Science∗11 INFN Laboratori Nazionali di Legnaro∗12 GANIL∗13 Institute of Nuclear Physics, University of Cologne∗14 Department of Physics, Osaka University∗15 Dept. of Physics and Astronomy, University of Tennessee∗16 Physik Department E12, Technische Universität München∗17 Department of Natural Sciences, Tokyo City University∗18 Faculty of Physics, VNU University of Science∗19 Department of Physics, University of Tokyo∗2

Counts / 2 ms

S. E. A. Orrigo,∗1 B. Rubio,∗1 W. Gelletly,∗1,∗2 P. Aguilera,∗1,∗3 A. Algora,∗1,∗4 A. I. Morales,∗1 J. Agramunt,∗1
D. S. Ahn,∗5 P. Ascher,∗6 B. Blank,∗6 C. Borcea,∗7 A. Boso,∗8 R. B. Cakirli,∗9 J. Chiba,∗10 G. de Angelis,∗11
G. de France,∗12 F. Diel,∗13 P. Doornenbal,∗5 Y. Fujita,∗14 N. Fukuda,∗5 E. Ganioğlu,∗9 M. Gerbaux,∗6
J. Giovinazzo,∗6 S. Go,∗15 T. Goigoux,∗6 S. Grévy,∗6 V. Guadilla,∗1 N. Inabe,∗5 G. G. Kiss,∗4,∗5 T. Kubo,∗5
S. Kubono,∗5 T. Kurtukian-Nieto,∗6 D. Lubos,∗16 C. Magron,∗6 F. Molina,∗3 A. Montaner-Pizá,∗1 D. Napoli,∗11
D. Nishimura,∗17 S. Nishimura,∗5 H. Oikawa,∗10 V. H. Phong,∗5,∗18 H. Sakurai,∗5,∗19 Y. Shimizu,∗5 C. Sidong,∗5
P. -A. Söderström,∗5 T. Sumikama,∗5 H. Suzuki,∗5 H. Takeda,∗5 Y. Takei,∗10 M. Tanaka,∗14 J. Wu,∗5 S. Yagi∗1062GeT1/2 = 73.5(1) ms

104

0

200

400

600
800
Correlation time [ms]Fig. 2. Time correlations between implanted 62 Ge ions andβ decays in the same or adjacent pixel of WAS3ABi.

precedented statistics at the Radioactive Isotope Beam
Factory (RIBF) of the RIKEN Nishina Center. In the
NP1112-RIBF82 experiment, 1.5×104 60 Ge and 2.1×106
62
Ge ions were recorded. They were produced by fragmenting a 78 Kr primary beam (345 MeV/nucleon andintensity up to 250 particle nA) on a Be target. The
fragments were selected and identiﬁed by the BigRIPS
separator by means of the Bρ-∆E-ToF method. They
were then implanted in the WAS3ABi setup, consistingof three 1-mm-thick double-sided Si strip detectors of
a 6 × 4 cm2 area. The EURICA array, arranged in 12
clusters containing 7 high-purity Ge crystals each, wasused for γ detection.
For 60 Ge, the ﬁrst experimental information on boththe β-delayed proton and γ emissions has been extracted. By gating on the β-delayed proton emission,a half-life value of 25.0(3) ms has been obtained for60
Ge (Fig. 1). For 62 Ge, new information on the βdelayed γ emission has been obtained, indicating thepersistence of the quasi-rule.3,4) A half-life value of
73.5(1) ms has been extracted for 62 Ge (Fig. 2). The
precision on both 60 Ge and 62 Ge half-lives has been improved in comparison with values in the literature.
References

1) S. E. A. Orrigo et al., Phys. Rev. Lett. 112, 222501 (2014).
2) S. E. A. Orrigo et al., Phys. Rev. C 93, 044336 (2016).
3) G. Morpurgo, Phys. Rev. 110, 721 (1958).
4) D. H. Wilkinson, Isospin in Nuclear Physics, (Elsevier
Science Publishing Co Inc.,U.S., 1969).
5) F. Molina et al., Phys. Rev. C 91, 014301 (2015).

- 19 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

On the β-decay of 70 Kr
A. Vitéz-Sveiczer,∗1,∗2,∗3 A. Algora,∗1,∗2 A. I. Morales,∗1 B. Rubio,∗1 G. Kiss,∗2 J. Agramunt,∗1 V. Guadilla,∗1
A. Montaner-Pizá,∗1 S. E. A. Orrigo,∗1 A. Horváth,∗3 G. de Angelis,∗4 D. Napoli,∗4 F. Recchia,∗5
S. Lenzi,∗5 A. Boso,∗5 S. Nishimura,∗6 V. H. Phong,∗6 J. Wu,∗6 P. -A. Söderström,∗6 T. Sumikama,∗6
H. Suzuki,∗6 H. Takeda,∗6 D. S. Ahn,∗6 H. Baba,∗6 P. Doornebal,∗6 N. Fukuda,∗6 N. Inabe,∗6 T. Isobe,∗6
T. Kubo,∗6 S. Kubono,∗6 H. Sakurai,∗6 Y. Shimizu,∗6 C. Sidong,∗6 B. Blank,∗7 P. Ascher,∗7 M. Gerbaux,∗7
T. Goigoux,∗7 J. Giovinazzo,∗7 S. Grévy,∗7 T. Kurtukián Nieto,∗7 C. Magron,∗7 W. Gelletly,∗1,∗8 Zs. Dombrádi,∗7
Y. Fujita,∗9 M. Tanaka,∗9 P. Aguilera,∗10 F. Molina,∗10 J. Eberth,∗11 F. Diel,∗11 D. Lubos,∗12 C. Borcea,∗13
E. Ganioglu,∗14 D. Nishimura,∗15 H. Oikawa,∗15 Y. Takei,∗15 S. Yagi,∗15 W. Korten,∗16 G. de France,∗17
P. Davies,∗18 J. Liu,∗19 J. Lee,∗19 T. Lokotko,∗19 I. Kojouharov,∗20 N. Kurz,∗20 and H. Shaﬀner∗20
In this contribution, we present preliminary resultsof the analysis of the β-decay of 70 Kr from the experiment NP1112-RIBF93. The main goal of the experiment was to study isospin-related eﬀects and p-n
pairing signatures in the region of A ∼ 70 using theinformation obtained from the β-decays of 70, 71 Kr.
To produce the isotopes of interest the fragmentation of a 78 Kr primary beam with an energy of
345 MeV/nucleon was used. Average beam currents of
40 particle nA were provided by the RIKEN Nishina
Center accelerator complex. The 78 Kr primary beam
impinged on a 5 mm thick 9 Be target to produce
a cocktail radioactive beam. The fragments produced were then separated and selected using the BigRIPS separator. The ions were then implanted in the
WAS3ABi active stopper, surrounded by the EURICA
γ-ray spectrometer1) for the study of their β decay.
Gamma rays associated to the de-excitation of states
populated in the daughter nucleus 70 Br were identiﬁed using conventional β-γ and β-γ-γ coincidence techniques similarly to the procedure followed in Ref. 2).
For more details see Refs. 3, 4). The analysis has also
allowed us to improve the precision of the deduced βdecay half-life and construct the level scheme of states
populated in the decay, which extends up to 3.3 MeV
excitation energy in 70 Br.
In Fig. 1 we present the deduced Gamow-Teller β

Fig. 1. Preliminary comparison of the experimental (black)and calculated accumulated B(GT) values for the 70 Kr→ 70 Br β decay.5) The experimental B(GT) uncertainties are determined by the feeding error of the levels
and the error of the half-life. The orange solid line
corresponds to the values calculated for the oblate minimum, the blue dashed line corresponds to the prolate
minimum of the ground state of 70 Kr.

strength in the daughter nucleus compared to the predictions of the pn quasiparticle random-phase approximation (pnQRPA) calculations for two possible deformation minima in 70 Kr.5) The calculations presented
here are based on the SLy4 force, which is a well tested
force throughout the whole nuclear chart. Alternative theoretical calculations are also performed usinga pseudo-LS model.6) We are presently working in theﬁnal details of a publication7) based on this study.

∗1

IFIC, CSIC-Univ. Valencia
MTA ATOMKI∗3 ELTE TTK Fizikai Intézet∗4 INFN Laboratori Nazionali di Legnaro∗5 INFN Sezione di Padova∗6 RIKEN Nishina Center∗7 CEN Bordeaux-Gradignan∗8 Department of Physics, Surrey University∗9 Department of Physics, Osaka University∗10 Comisión Chilena de Energía Nuclear (CCHEN)∗11 Institut für Kernphysik, Universität zu Köln
∗12 Physik Department, Technische Universität München∗13 National Institute for Physics and Nuclear Engineering,
IFIN-HH∗14 Department of Physics, University of Istanbul∗15 Department of Physics, Tokyo University of Science∗16 IRFU, CEA, Université Paris-Saclay∗17 GANIL∗18 Department of Physics, York University∗19 Department of Physics, University of Hong Kong
∗20 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗2

References

1) S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006(2012).
2) A. I. Morales et al., Phys. Rev. C 95, 064327 (2017).
3) A. Vitéz-Sveiczer et al., RIKEN Accel. Prog. Rep. 53,
28 (2019).
4) A. Vitéz-Sveiczer et al., Acta Phys. Pol. B 51, 587(2020).
5) P. Sarriguren, private communication.
6) P. Van Isacker, private communication.
7) A. Vitéz-Sveiczer et al., in preparation.

- 20 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measuring β-decay strength distribution in the 78 Ni region using
VANDLE
M. Singh,∗1 R. Yokoyama,∗1 R. K. Grzywacz,∗1,∗2 T. King,∗2 S. Nishimura,∗3 N. T. Brewer,∗1,∗2 P. Brionnet,∗3
J. Bundgaard,∗1 I. Cox,∗1 A. Fijalkowska,∗4 L. Fraile,∗5 S. Go,∗6 A. Gottardo,∗7 M. Karny,∗4 A. Keeler,∗1
A. Korgul,∗4 M. Madurga,∗1 K. Miernik,∗4 S. Neupane,∗1 M. Niikura,∗8 M. Pfutzner,∗4 M. Piersa,∗4
M. Rajabali,∗9 B. C. Rasco,∗2 K. P. Rykaczewski,∗2 M. Silkowski,∗4 M. Stepaniuk,∗4 J. L. Tain,∗10 A. Tolosa,∗10
M. Wolinska-Cichocka,∗4 and Z. Xu∗1 for the VANDLE Collaboration
The properties of nuclei away from the line of stability, revealed in the β-decay of the neutron-rich side,
are crucial in understanding nuclear structure evolution
and providing inputs for r-process simulations. Measurements of half-lives, one- and two-neutron emission
probabilities (Pn,2n ), and neutron energy spectra provide information on the β-decay strength distribution(Sβ ). The Sβ measurement for Ga with N > 50, 83, 84 Ga
showed that the decay properties of the r-process isotopes near 78 Ni are dominated by the Gamow-Teller
decay of the 78 Ni-core states.1) Through their work on
86, 87Ga using BRIKEN,3) R. Yokoyama et al.,2) demonstrated a need to consider the competition between oneand multi-neutron emissions to predict branching ratiosof r-process nuclei. It also strengthened the argument
for the necessity of neutron energy measurements forunderstanding the details of the neutron emission process. The Versatile Array of Neutron Detector at Low
Energy (VANDLE)4) experiment at RIBF RIKEN aims
to provide measurements of Sβ for the decay of 78 Ni
and neighboring nuclei using time-of-flight (ToF) based
neutron spectroscopy. The isotopes of interest were produced from a 345 MeV/nucleon ∼46-particle-nA 238 U
beam impinged on 4-mm-thick Be target by projectile

Fig. 2. Neutron energy spectrum of 81 Cu measured by VANDLE.

fragmentation. The nuclei identified by the BigRIPS5)
facility were supplied to the F11 focal plane, where they
were implanted in a segmented-YSO based implantation detector6) for ∼4 days. A YSO detector consistsof a segmented YSO crystal (75 × 75 × 5 mm3 ) coupled
to a position-sensitive photo-multiplier tube. YSO isused to establish ion-beta correlations and provides thestart time of the ToF. VANDLE, consisting of EJ200
scintillator bars coupled at both ends to PMTs, provides the stop time of neutron ToF. A set of 48 medium(3 × 6 × 120 cm3 ) VANDLE bars were arranged in a 100cm radius circle with YSO at the center, as shown in
Fig. 1. In addition, two HPGe clovers and ( ten 3” × 3”
and two 2” × 2”) LaBr3 were set up in a close geometryaround the YSO detector to record γ-transitions fromthe decays. All the signals were read using XIA Pixie16 revF digitizers at 250 MHz and 12-bit digitization.7)
Neutron spectra were measured for 78–81 Cu isotopes toestablish the role of the N = 50 shell gap on the βdecay properties. We show the first measurement of
the neutron energy spectrum of 81 Cu52 decay in Fig. 2.
The spectrum indicates that neutrons with energies of
0.4–3 MeV were emitted from excited states in 81 Zn.
References

Fig. 1. VANDLE setup at the F11 focal plane of ZDS.
∗1

Dept. of Physics and Astronomy, University of Tennessee
Physics Division, Oak Ridge National Laboratory∗3 RIKEN Nishina Center∗4 Faculty of Physics, University of Warsaw∗5 Grupo de Física Nuclear IPARCOS, Universidad Complutensede Madrid∗6 Department of Physics, Kyushu University∗7 INFN-LNL∗8 Department of Physics, University of Tokyo∗9 Department of Physics, Tennessee Tech University∗10 IFIC, CSIC-Universitat de Valencia∗21) M. Madurga et al., Phys. Rev. Lett. 117, 092502 (2016).
2) R. Yokoyama et al., Phys. Rev. C 100, 031302 (2019).
3) A. Tarifeño-Saldivia et al., J. Instrum. 12, P04006 (2017).
4) W. A. Peters et al., Nucl. Instrum. Methods Phys. Res. A
836, 122 (2016).
5) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2003).
6) R. Yokoyama et al., Nucl. Instrum. Methods Phys. Res.
A 937, 93 (2019).
7) S. V. Paulauskas et al., Nucl. Instrum. Methods Phys.
Res. A 737, 22 (2014).

- 21 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Constraining multi-neutron emission models with spectroscopy ofneutron-rich Ga isotopes using BRIKEN array
R. Yokoyama,∗1 R. Grzywacz,∗1,∗2 B. C. Rasco,∗1,∗2 N. T. Brewer,∗1,∗2 K. P. Rykaczewski,∗2 I. Dillmann,∗3
J. L. Tain,∗4 S. Nishimura,∗5 and the BRIKEN collaboration

∗1
∗2
∗3
∗4
∗5

daughters calculated by the shell model were replacedwith experimental data. Compared with the feedingof the experimental 624-keV state in 84 Ge, the statistical model predicted the γ intensity as 33%, whichis in good agreement with the experimental value wemeasured. The statistical model also reproduced the γbranching ratio of other γ rays in the decay. The detailed β-n-γ analysis of other neutron-rich Ga isotopes
is in progress.
(a) 100

40

0n
50

5

107

365

15

1n

1n 0 - 80 ms

473

10

1n 200 - 280 ms

598

250

5

1032 1063

773

2n 0 - 80 ms

624 (84Ge 2+→0+)
Iγ_stat. = 33%

200

86Ga

Excitation energy (keV)

2n 200 - 280 ms

Iγ_exp = 37(8)%

2n

0
0

(b)

0n 200 - 280 ms

1024

20

0
15
10

0n 0 - 80 ms

400

600

800

1000

1200

1400

Gamma-ray energy (keV)

0

β-

β-n

β-2n

P0n=24(3)%P1n=61(3)%P2n=14.7(14)%

1000
500
0

(2+)
0+

1024.3
527.3
0

86Ge

85Ge

881.4
472.9
249.9
107.9
0

2+

0+

623.9 [5.5(12)]50

Ga decay773.5 [2.8(8)]472.9 [3.2(7)]365.0 [3.9(7)]249.9 [7.6(9)]107.9 [13.3(12)]

0
100

86

527

1024.3 [2.8(9)]527.3 [7.3(9)]Counts per keV

As we move further from the line of β-stability towards the neutron drip line, Qβ values become larger
than the two-neutron separation energy (S2n ), whichallows multi-neutron emissions after β-decay. In theneutron-rich nuclei along the astrophysical r-process
path, multi-neutron emissions are considered to be
dominant decay modes.1) The numbers of neutrons
emitted in the β-decays of exotic nuclei modify the
decay path back to stability and aﬀect the ﬁnal abundance calculation. However, experimental data thatenable the evaluation of multi-neutron emissions forthe r-process nuclei are almost non-existent. Until
quite recently, theoretical predictions of the neutron
emission branching ratio (Pn ) were based on a cut-oﬀ
model that assumes only the higher-multiplicity neutron emission prevails in the energy regions open to
multiple neutron-emission channels. In order to include the competition of one-neutron emission from thestates above S2n , Kawano et al. developed a HauserFeshbach statistical model calculation.2)
We studied neutron-rich Ga isotopes by means of
β-n-γ spectroscopy at RIBF using the high-eﬃciency
neutron counter array BRIKEN,3–5) with two Ge
clover detectors. The result that one-neutron emission
is dominant for all the four Ga isotopes was interpreted
as competition in one-neutron emission among twoneutron unbound states, and we demonstrated thatthe inclusion of the statistical model reproduces thebranching ratio better than the cut-oﬀ model.6)
Recently, we analyzed γ-ray spectra of the decay of
84–87
Ga. Figure 1 shows γ spectra gated by the neutron multiplicity of the BRIKEN array for the decay of86
Ga. γ rays from 84, 85, 86 Ge are clearly identiﬁed in
the 2n, 1n, and 0n gated spectra. The 2+ → 0+ γ rayfrom 84 Ge in the two-neutron branches was observed
at 624 keV. The intensity of the 624-keV γ ray per 100
two-neutron decays was 37(8)%. We performed ourHauser-Feshbach statistical model calculation by using
the strength distribution and level densities from shellmodel calculations. This model was used to validate
the measurement of the neutron spectra in the decay of
83, 84Ga.7) The shell model produced less states below
S2n than the number of the default levels generated by
the statistical model using the Gilbert-Cameron formula. When known, the low-lying states in the decay

623.9

0

84Ge

Fig. 1. (a) γ-ray spectra of the decay of 86 Ga gated byneutron multiplicities in the BRIKEN array. (b) Decay
scheme. γ branching per 100 decays is shown in thesquare brackets.

References

1) P. Möller et al., At. Data Nucl. Data Tables 125, 1 (2019).
2) T. Kawano et al., Nucl. Phys. A 913, 51 (2013).
3) A. Tarifeño-Saldivia et al., J. Instrum. 12, P04006(2017).
4) A. Tolosa-Delgado et al., Nucl. Instrum. Methods
Phys. Res. A 925, 133 (2019).
5) B. C. Rasco et al., Nucl. Instrum. Methods Phys. Res.
A 911, 79 (2018).
6) R. Yokoyama et al., Phys. Rev. C 100, 031302(R) (2019).
7) M. Madurga et al., Phys. Rev. Lett. 117, 092502 (2016).

Department of Physics and Astronomy, the University ofTennessee, Knoxville
Physics Division, Oak Ridge National Laboratory
TRIUMF
IFIC, CSIC-Universitat de Valencia
RIKEN Nishina Center- 22 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Spectroscopy of 99 Cd and 101 In from β decays of 99 In and 101 Sn†
J. Park,∗1 R. Krücken,∗2 D. Lubos,∗3 R. Gernhäuser,∗3 M. Lewitowicz,∗4 S. Nishimura,∗5 and H. Sakurai∗6 , for
the EURICA Collaboration

†
∗1
∗2
∗3
∗4
∗5
∗6

(9/2+) T1/2 = 3.11(6) s(Park 2019)
β+/EC

0

Experimental knowledge in the doubly magic 100 Sn
region, relevant for tests of nuclear shell models (SM),proton-neutron interactions in N ≈ Z ≈ 50 nuclei
and the end of the rapid proton-capture process (rpprocess) in nuclear astrophysics, has been expanded
through a β-decay spectroscopy campaign at RIBF.1)
The literature on β decays of 99 In and 101 Sn has been
either nonexistent or contentious due to low statistics,
but subsequent analyses of the β-delayed γ-ray spectroscopy data from the RIBF9 experiment revealed
new states in 99 Cd and addressed the ambiguity concerning the level scheme of 101 In.
Using WAS3ABi2) and EURICA3) detectors whichwere deployed at the end of the ZeroDegree spectrometer, decay events following 99 In and 101 Sn ion implantations were correlated. 30 new γ rays belonging to99
Cd were observed, and a subset of γ rays previously
assigned to 101 In has been conﬁrmed in this measurement. Two new high-energy γ rays were assigned to101
In in this work. The available γ-γ coincidence data
was analyzed to build on the level scheme of 99 Cd,
as shown in Fig. 1. Alternatively, the experimental
energies and intensities of the γ rays were comparedwith the SM calculations based on the SR88MHJM4)
interaction, in a model space of π(2p1/2 , 1g9/2 ) andν(1g7/2 , 2d5/2 , 2d3/2 , 3s1/2 , 1h11/2 ) orbitals above the88
Sr core. The eﬀect of varying eﬀective charges andtheoretical transition energies on the branching ratiosof γ rays was assessed. Tentative assignments of new
excited states were made for both 99 Cd and 101 In,
where a good agreement was found within theoreticaluncertainties. No signiﬁcant inconsistencies in the intensities of γ rays were found between the experimentand theory in a γ-ray energy range of 0–2500 keV.
β-delayed proton emission events from the decay of101
Sn were recorded and incorporated in the γ-ray intensity analysis. The competition between branchingratios of protons versus γ rays from high-energy statesin 101 In was evaluated using a semi-empirical theory
on proton emission.5) The two competing hypotheses
concerning the ground-state spin of 101 Sn, being either
the 5/2+ based on the 2d5/2 single-neutron conﬁguration or the 7/2+ based on the 1g7/2 conﬁguration,
were examined by comparing the experimental γ-ray

99In(9/2+)

2227
2057 (17/2+)
1975
226
1831 (13/2+)1781
1675
1607

(9/2+)

1234

2487

1077
883

(1/2+)

883
1077

441

9/2+

2664

9/2+

2376

9/2+

17/2+ 1930
1915
13/2+ 1835

9/2+
5/2+
11/2+

1543
1537

5/2++
7/2

1242

1104

3/2+

886

1/2+

557

7/2+

9/2+

(7/2+)

441

1224

783

(9/2+) 2037
(5/2+) 1769
(11/2+)(7/2+)(3/2+)

1607(9/2+)

1340
1534
1786
1987

607

2428

1224

2956

(9/2+)

2928(5/2+)

099

Cd EXP

5/2+

0
99

Cd SM

Fig. 1. Experimental level scheme of 99 Cd, compared to SM
calculations. Only the states revealed by the β decayof 99 In are shown. The blue arrows indicate new γ rays
observed in this work.

intensities and the integrated β-delayed proton emission branching ratio to theoretical values. Due to theimprecise knowledge of the proton separation energyof 101 In and low experimental γ-ray statistics, there
was insuﬃcient circumstantial evidence for an unambiguous spin assignment of the ground state of 101 Sn.
Determining the single-particle energies of the N = 51
isotones, 99 Cd and 101 Sn, would result in an enhanced
systematic review of the N = 50 shell evolution in the
proton-rich nuclei close to 100 Sn.
References

1) J. Park et al., Phys. Rev. C 99, 034313 (2019).
2) S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006(2012).
3) P. -A. Söderström et al., Nucl. Instrum. Methods Phys.
Res. B 317, 649 (2013).
4) D. T. Yordanov et al., Phys. Rev. C 98, 011303(R)(2018).
5) D. S. Delion, R. J. Liotta, R. Wyss, Phys. Rep. 424,
113 (2006).

Condensed from the article in Phys. Rev. C. 102, 014304(2020)
Center for Exotic Nuclear Studies, Institute for Basic Science
TRIUMF
Physik Department, Technische Universität München
Grand Accélérateur National d’Ions Lourds (GANIL)RIKEN Nishina Center
Department of Physics, University of Tokyo- 23 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Total absorption γ-spectroscopy study of the beta decay of 100 Sn
J. A. Victoria,∗1 A. Algora,∗1,∗2 B. Rubio,∗1 J. L. Tain,∗1 A. Tolosa,∗1 J. Agramunt,∗1 E. Nacher,∗1
S. E. A. Orrigo,∗1 V. Guadilla,∗3 G. Kiss,∗2 D. Sohler,∗2 I. Kuti,∗2 T. Davinson,∗4 O. B. Hall,∗4 D. M. Kahl,∗4
C. G. Bruno,∗4 C. J. Appleton,∗4 P. J. Woods,∗4 S. Nishimura,∗5 N. Fukuda,∗5 H. Suzuki,∗5 D. S. Ahn,∗5
H. Baba,∗5 Y. Shimizu,∗5 H. Takeda,∗5 D. Nishimura,∗5 T. Isobe,∗5 M. Kaneko,∗5 S. Kubono,∗5 H. Sakurai,∗5
H. Shimizu,∗5 T. Sumikama,∗5 P. Doornenbal,∗5 M. L. Cortes,∗6 Zs. Podolyak,∗7 W. Gelletly,∗7 E. Ganioglu,∗8
Y. Fujita,∗9 F. Molina,∗10 J. Liu,∗11 J. Lee,∗11 K. P. Rykaczewski,∗12 M. Wolinska-Cichocka,∗13 M. Labiche,∗14
C. J. Griﬃn,∗15 S. Bae,∗16 J. Ha,∗16 and Y. Litvinov∗17

Fig. 1. Parameters employed in the deﬁnition of the ﬁgureof merit for the time distribution of the β particles. The
area S stands for signal, B for background, b is the highof the background. B is estimated using the backward
correlation time interval [−ts , 0]. Tib stands for implantβ time.
∗1

IFIC, CSIC-Univ. of Valencia
MTA ATOMKI∗3 Subatech/Ecole des Mines, CNRS/IN2P3, Université deNantes∗4 School of Physics and Astronomy, University of Edinburgh∗5 RIKEN Nishina Center∗6 INFN Laboratori Nazionali di Legnaro∗7 Department of Physics, Surrey University∗8 Department of Physics, University of Istanbul∗9 Department of Physics, Osaka University∗10 Comisión Chilena de Energía Nuclear (CCHEN)∗11 Department of Physics, University of Hong Kong
∗12 Physics Division, Oak Ridge National Laboratory∗13 Heavy Ion Laboratory, Warsaw University∗14 STFC Daresbury Laboratory∗15 Physical Sciences Division, TRIUMF∗16 Dept. of Physics and Astronomy, Seoul National University∗17 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗2300

CountsIn this report we are presenting the progress on theanalysis of the NP1612-RIBF147 experiment. The goalof this experiment was to study the beta decay of 100 Sn
and neighbouring nuclei using the total absorption technique. In our measurement the total absorption spectrometer DTAS1) was used in combination with the implantation detector AIDA.2) Details of the experimentcan be found in Ref. 3).
One key aspect of the work performed was to improve
the signal to background ratio of the coincident data asmuch as possible. The sorting conditions of the data
and the number of parameters available for the analysis
makes this task daunting without proper quantiﬁcationof the code optimisations. For that reason we introduced
a ﬁgure of merit. The ﬁgure quantiﬁes the improvements

250
200
150
100
50
0
−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

Time beta - Time implants [s]Fig. 2. Time distribution of the β particles emitted after the
decay of 100 Sn in coincidence with DTAS.

made by the changes in the analysis code looking for the
reduction of the accidental correlations associated to the
decay of 100 Sn. In our study we changed several sorting parameters and compared the area of the true correlations (S) with the area of the background (B) (seeFig. 1. for an schematic view). The optimisation consisted in looking for conditions that increase the S to B
ratio. Note that the correlation time window (ts ) is related to the decay half-life of the implanted nucleus ofinterest. Some improvements on the AIDA sorting code
were also necessary.4)
In Fig. 2 we show the present status of the implant-βtime correlation (gated with the condition on the DTAS
ﬁring) after implementing all cleaning conditions for the100
Sn. Thanks to the procedures applied, an increaseof the signal to background ratio of the order of 20%
was achieved, improving the DTAS gamma correlated
data. In the near future we will reﬁne the calibrationof the detectors and calculate the response function of
the setup, which is mandatory for the total absorption
spectrum analysis. Due to technical problems during ourrun we were only able to take data for 4 days from a totalof 10 approved days. The continuation of the experimentis expected to occur in 2021.
References

1) J. L. Tain et al., Nucl. Instrum. Methods Phys. Res. A
803, 36 (2015).
2) C. J. Griﬃn et al., Proc. XIII Nuclei in the Cosmos 1., 97(2014).
3) A. Algora et al., RIKEN Accel. Prog. Rep. 53, 30 (2019).
4) O. B. Hall, private communication.

- 24 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Shape evolution of 106, 108, 110 Mo in the triaxial degree of freedom†

The properties of the 2+
2 band in even-even nuclei
are closely connected with the triaxial motion in the
direction of the γ degree of freedom, such as the γvibration, rigid triaxial rotor,1) or γ-unstable rotor.2)
The lowering of the known 2+
2 -state energy in neutronrich molybdenum isotopes (Z = 42) is interpreted as thedevelopment of these triaxial motions associated withthe ground-state shape. We studied the neutron-rich
106, 108, 110
Mo isotopes with higher statistics by measuring the β-delayed γ rays.
A neutron-rich cocktail beam was produced from thefragmentation of a 345-MeV/nucleon 238 U86+ beam.
The nuclides were separated and identiﬁed on the BigRIPS separator and delivered to F11. The ions andβ particles were detected by the WAS3ABi active stopper. A high-purity Ge array, EURICA,3) and fast-timing
LaBr3 (Ce) array were used to measure the energy andtime of γ rays.
Figure 1 shows B(E2) determined from the lifetime
measurement of the 2+
1 states using the LaBr3 (Ce) array. The quadrupole deformation parameters β2 of106, 108, 110
Mo were deduced to be 0.349(13), 0.327(10),and 0.305(7), respectively. The results were compared
Condensed from the article in Phys. Rev. C 101, 044311(2020)∗1 Department of Physics and Astronomy, Seoul National University∗2 RIKEN Nishina Center∗3 Department of Physics, Tohoku University∗4 School of Computing, Engineering, and Mathematics, University of Brighton∗5 Center for Computational Sciences, University of Tsukuba∗6 Department of Physics, University of Surrey∗7 National Physical Laboratory∗8 IRCNPC, School of Physics and Nuclear Energy Engineering,
Beihang University∗9 Department of Physics, Osaka University∗10 Department of Physics, University of York∗11 Department of Physics, Peking University∗12 Department of Physics, University of Tokyo∗13 Department of Physics, University of Hong Kong
∗14 IPHC, CNRS/IN2P3, Université de Strasbourg∗15 LPSC, Université Grenoble-Alpes∗16 ILL∗17 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗18 Department of Physics, University of Sofia∗19 CSNSM, CNRS/IN2P3, Université Paris-Sud∗20 Departamento de Física Teórica, Universidad Autónoma de
Madrid∗21 Instituto de Estructura de la Materia, CSIC
∗22 A.W. Wright Nuclear Structure Laboratory, Yale University∗23 Institut für Kernphysik, Technische Universität Darmstadt∗24 INFN Sezione di Milano†

B(E2;2+1→ 0+1) [e2b2]

J. Ha,∗1,∗2 T. Sumikama,∗2,∗3 F. Browne,∗2,∗4 N. Hinohara,∗5 A. M. Bruce,∗4 S. Choi,∗1 I. Nishizuka,∗3
S. Nishimura,∗2 P. Doornenbal,∗2 G. Lorusso,∗2,∗6,∗7 P. -A. Söderström,∗2 H. Watanabe,∗2,∗8 R. Daido,∗9
Z. Patel,∗2,∗6 S. Rice,∗2,∗6 L. Sinclair,∗2,∗10 J. Wu,∗2,∗11 Z. Y. Xu,∗12,∗13 A. Yagi,∗9 H. Baba,∗2 N. Chiga,∗2,∗3
R. Carroll,∗6 F. Didierjean,∗14 Y. Fang,∗9 N. Fukuda,∗2 G. Gey,∗15,∗16 E. Ideguchi,∗9 N. Inabe,∗2 T. Isobe,∗2
D. Kameda,∗2 I. Kojouharov,∗17 N. Kurz,∗17 T. Kubo,∗2 S. Lalkovski,∗18 Z. Li,∗11 R. Lozeva,∗14,∗19 H. Nishibata,∗9
A. Odahara,∗9 Zs. Podolyák,∗6 P. H. Regan,∗6,∗7 O. J. Roberts,∗4 H. Sakurai,∗2 H. Schaﬀner,∗17 G. S. Simpson,∗15
H. Suzuki,∗2 H. Takeda,∗2 M. Tanaka,∗9 J. Taprogge,∗2,∗20,∗21 V. Werner,∗22,∗23 and O. Wieland∗24

0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0

Mo isotopes

58

60

62
64
66
Neutron number

SLy5+T
SLy4

68+
Fig. 1. B(E2; 2+
1 → 01 ) of the neutron-rich Mo isotopes.
The theoretical results calculated with SLy4 and SLy5+T
interactions are shown.

with beyond-mean-ﬁeld calculations using SLy4 andSLy5+T interactions, for which the predicted groundstate shapes were oblate and prolate, respectively. The
prolate shape was indicated because the calculation with
the SLy5+T interaction reproduces both B(E2) and theenergies of the ground-state band.
110
The 2+
Mo was extended up to the 7+
2 band instate. The energy staggerings of the 2+
2 bands in
106, 108, 110
Mo are close to that of the axially symmetricrotor of the γ-vibrational state, rather than Davydov’s
rigid-triaxial rotor model or Wilets-Jean model for γunstable nuclei. A candidate of the two-phonon γ vibrational band with K π = 4+ , which has not been wellestablished yet, was found in 110 Mo. The K π = 4+ band
decays only to the γ-vibrational band, and the energyof the K π = 4+ state is 2.5 times larger than that of+
the 2+
2 state. Moreover, new 02 states were assigned in
108
110
Mo andMo.
The spin and parity of parent nuclei were assigned
from the log f t values to be 4− and 2− for the groundstate in 106 Nb and 108 Nb, respectively. Two β-decaying
states were identiﬁed in 110 Nb, and their spin-parities
were asigned as 2− and 6− .
References

1) A. S. Davydov, G. F. Filippov, Nucl. Phys. 8, 237 (1958).
2) L. Wilets, M. Jean, Phys. Rev. 102, 788 (1956).
3) P. -A. Söderström et al., Nucl. Instrum. Methods Phys.
Res. B 317, 649 (2013).

- 25 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Evolution of proton single-particle states in neutron-rich Sb isotopes
beyond N = 82†
A. Jungclaus,∗1 J. M. Keatings,∗2 G. S. Simpson,∗3 H. Naïdja,∗4 A. Gargano,∗5 S. Nishimura,∗6 P. Doornenbal,∗6
G. Gey,∗3,∗7,∗6 G. Lorusso,∗6 P. -A. Söderström,∗6 T. Sumikama,∗8 J. Taprogge,∗1,∗9,∗6 Z. Y. Xu,∗6 H. Baba,∗6
F. Browne,∗10,∗6 N. Fukuda,∗6 N. Inabe,∗6 T. Isobe,∗6 H. S. Jung,∗11 D. Kameda,∗6 G. D. Kim,∗12
Y. -K. Kim,∗12,∗13 I. Kojouharov,∗14 T. Kubo,∗6 N. Kurz,∗14 Y. K. Kwon,∗12 Z. Li,∗15 H. Sakurai,∗6,∗16
H. Schaﬀner,∗14 Y. Shimizu,∗6 H. Suzuki,∗6 H. Takeda,∗6 Z. Vajta,∗17 H. Watanabe,∗6 J. Wu,∗15,∗6 A. Yagi,∗18
K. Yoshinaga,∗19 S. Bönig,∗20 J. -M. Daugas,∗21 R. Gernhäuser,∗22 S. Ilieva,∗20 T. Kröll,∗20 A. Montaner-Piza,∗23
K. Moschner,∗24 D. Mücher,∗22 H. Nishibata,∗18 A. Odahara,∗18 R. Orlandi,∗25 M. Scheck,∗26 K. Steiger,∗22 andA. Wendt∗24
The chain of Sb isotopes, with a single proton outside
the closed Z = 50 proton shell, has attracted for many
years a special interest since it oﬀers the unique possibility to study the evolution of the proton single-particle
states in the Z = 50–82 major shell over a wide rangeof neutron number. Prior to this work, excited-state information was available from the very neutron-deﬁcientisotope 105 Sb, close to the presumably doubly-magic
100
Sn, up to the neutron-rich isotope 135 Sb. Above theN = 82 neutron shell gap, when the neutrons start ﬁlling the 1f7/2 orbital, a dramatic decrease of the energy
133
Sb to 281 keV inof the 5/2+
1 state from 962 keV in
135
1,2)
Sb was observed.
The present work aimed for an extension of the exFig. 1. Excitation energy diﬀerence between the 5/2+
1 and
7/2+
1 states in the odd Sb isotopes. Experimental values
are shown as open (literature) and ﬁlled (present work)
diamonds while solid blue (green) lines represent the results of SM calculations employing the Napoli (N3LOP)
interactions. The diﬀerences between the eﬀective SPEof the 1d5/2 and 0g7/2 orbitals are shown by dashed lines(adopted from Fig. 7 of the original article).

Condensed from the article in Phys. Rev. C 102, 034324(2020)∗1 IEM-CSIC∗2 School of Computing, Engineering, and Physical Sciences,
University of the West of Scotland∗3 LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3,
Institut National Polytechnique de Grenoble∗4 Laboratoire de Physique Mathematique et Subatomique,
Constantine University∗5 INFN Sezione di Napoli∗6 RIKEN Nishina Center∗7 Institut Laue-Langevin∗8 Department of Physics, Tohoku University∗9 Departamento de Física Teórica, Universidad Autónoma de
Madrid∗10 School of Computing, Engineering and Mathematics, University of Brighton∗11 Department of Physics, Chung-Ang University∗12 Rare Isotope Science Project, Institute for Basic Science(IBS)∗13 Department of Nuclear Engineering, Hanyang University∗14 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗15 School of Physics and State key Laboratory of Nuclear
Physics and Technology, Peking University∗16 Department of Physics, University of Tokyo∗17 Atomki∗18 Department of Physics, Osaka University∗19 Department of Physics, Faculty of Science and Technology,
Tokyo University of Science∗20 Institut für Kernphysik, Technische Universität Darmstadt∗21 CEA, DAM∗22 Physik Department E12, Technische Universität München∗23 IFIC, CSIC-Univ. Valencia∗24 IKP, University of Cologne∗25 Advanced Science Research Center, Japan Atomic Energy
Agency∗26 School of Engineering, University of the West of Scotland†

perimental information towards more neutron-rich Sb
isotopes. Excited states in 136, 137, 138 Sb, populated inthe β decay of the semi-magic Sn isotopes 136, 137, 138 Sn,
were studied within the EURICA campaign. The clean
ion identiﬁcation and high γ-ray detection eﬃciency allowed to observe for the ﬁrst time the decay of excitedstates in the N = 86 isotope 137 Sb, which is considered as one of the key nuclei to pin down the evolutionof the single-particle structure beyond N = 82. As
shown in Fig. 1, the experimental energy of the 5/2+
1state, Ex = 84 keV, lies in the middle between the results of shell-model calculations performed using two
diﬀerent realistic eﬀective interactions, labeled Napoli
and N3LOP. Together with a similar comparison for
136, 138
Sb, the new experimental information thus allows to trace the evolution of the single-particle energies
above the N = 82 shell closure.
References

1) M. Sanchez-Vega et al., Phys. Rev. C 60, 024303 (1999).
2) J. Shergur et al., Phys. Rev. C 71, 064321 (2005).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

BRIKEN measurements of Pn -values and half-lives for understanding
the formation of the r-process rare-earth peak: progress on the Ce to
Nd region
A. Tarifeño-Saldivia,∗1 G. G. Kiss,∗2 J. L. Tain,∗3 A. Estrade,∗4 S. Nishimura,∗5 J. Agramunt,∗3 A. Algora,∗3
N. T. Brewer,∗6 R. Caballero-Folch,∗7 F. Calvino,∗1 T. Davinson,∗8 I. Dillmann,∗7 N. Fukuda,∗5
R. K. Grzywacz,∗9 O. Hall,∗6 N. Mont-Geli,∗1 A. I. Morales,∗3 A. Navarro,∗1 N. Nepal,∗5 M. Pallàs,∗1
B. C. Rasco,∗6 K. P. Rykaczewski,∗6 N. T. Szegedi,∗2 A. Vitz-Sveiczer,∗2 A. Tolosa-Delgado,∗3 P. Vi,∗10
R. Yokoyama,∗9 M. Wolinska-Cichocka,∗11 and P. Woods∗8 for the BRIKEN Collaboration∗12
The Rare-Earth Peak (REP) is a distinctive local
maximum observed around mass A ∼ 160 in the elemental abundance distribution of the rapid-neutron capture process (r-process). Because the REP is formed after neutron exhaustion,1) it provides a unique probe forstudying the late-time environmental conditions of the rprocess site.2) According to theoretical models, β-decay
rates (T1/2 ) and delayed neutron emission probabilities(Pn -values) play important roles in the formation of the
REP.3) The region of nuclei with the most significant
impact on the formation of the REP has been determined via sensitivity studies.4) Most of the T1/2 on thisregion have already been measured by the EURICA collaboration.7) However, the experimental determinationof Pn -values is yet to be achieved.
The NP1612-RIBF148 experiment exploits the uniquecapabities of the BRIKEN setup5,6) for the measurement of β-delayed neutrons. This experiment attemps tostudy Pn -values and T1/2 for the nuclei which are important to REP formation.4) In the 2018 experimental run,a 60-particle-nA 238 U beam, with 345 MeV/nucleon, hitting a 4 mm thick Be target was used to produce the secondary radioactive beam. The neutron-rich fragments
were filtered out by the BigRIPS fragment separator
and the ZeroDegree spectrometer. The beam setting
was centered on 165 Pm.
Here, we report preliminary results from the 2018 experimental run. Figure 1 shows the measured beta-decay
half-lives in the region from Ce to Nd isotopes. The experimental results are compared with previous measurements performed by the EURICA collaboration,7) andwith FRDM + QRPA theoretical calculations.8,9) The
BRIKEN experimental data agree well with the previous measurements. In addition, our results exhibit an
improved precision for the heavier nuclei region. Basedon the current status of the data analysis for this experiment, we expect to obtain at least one new T1/2 per
atomic number on the heavier isotopes from the Ce to
Nd region. These results will be reported in the future.

∗1

References

Half-life (s)

1

58Ce

EL

0.1

PR

Half-life (s)

1

IM

0.1

0.01

59Pr

AR

BRIKEN / this work
EURICA / Wu et al 2017
FRDM+QRPA (2003)
FRDM+QRPA (2019)

Y

Half-life (s)10.1

BRIKEN / this work
EURICA / Wu et al 2017
FRDM+QRPA (2003)
FRDM+QRPA (2019)

IN

Universitat Politècnica de Catalunya (UPC)
Institute for Nuclear Research (Atomki)∗3 Instituto de Física Corpuscular (IFIC)∗4 University College of Science and Engineering, CMU∗5 RIKEN Nishina Center∗6 Physics Division, Oak Ridge National Laboratory∗7 Physical Sciences Division, TRIUMF∗8 School of Physics and Astronomy, University of Edinburgh∗9 Department of Physics and Astronomy, University of Tennessee∗10 Faculty of Physics, VNU University of Science∗11 HIL, University of Warsaw∗12 www.wiki.edu.ac.uk/display/BRIKEN/Home∗2

BRIKEN / this work
EURICA / Wu et al 2017
FRDM+QRPA (2003)
FRDM+QRPA (2019)

60Nd
94

96

98
100
Neutron number N

102

104

Fig. 1. Systematic trends in BRIKEN results of β-decay
half-lifes (blue) compared with previous measurements(red),7) and theoretical calculations.8,9)1) R. Surman et al., Phys. Rev. Lett. 79, 1809 (1997).
2) M. R. Mumpower et al., Astrophys. J. 752, 117 (2012).
3) A. Arcones et al., Phys. Rev. C 83, 045809 (2011).
4) M. R. Mumpower et al., Phys. Rev. C 85, 04580 (2012).
5) I. Dillmann et al., Nucl. Phys. News 28, 28 (2018).
6) A. Tolosa-Delgado et al., Nucl. Instrum. Methods Phys.
Res. A 925, 133 (2019).
7) J. Wu et al., Phys. Rev. Lett. 118, 072701 (2017).
8) P. Möller et al., Phys. Rev. C 67, 055802 (2003).
9) P. Möller et al., At. Data Nucl. Data Tables 125, 1 (2019).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Precision measurement of ground-state electric quardrupole momentfor neutron-rich 21 O
A. Gladkov,∗1 H. Yamazaki,∗1 Y. Ichikawa,∗1 A. Takamine,∗1 H. Nishibata,∗2 K. Asahi,∗1 K. Kawata,∗1,∗3
K. Imamura,∗1 M. Tajima,∗1 K. Tsubura,∗1 and H. Ueno∗1
The anomalous nuclear properties had been experimentally indicated for the neutron-rich 23 O isotope,such as the formation of halo structure 1) and the presence of the new neutron magic number at neutron
number 2) N = 16. This originates the interest in theshell evolution in this region of neutron-rich oxygen isotopes. Such information can be directly provided by
the knowledge about the nuclear properties of neighboring isotopes, such as 21 O.
Previously, we have conducted the measurements ofthe electromagnetic moments of 21 O 3) and the groundstate magnetic moment has been successfully determined. However, due to RF tank circuit limitations,the obtained spectrum for the quadrupole moment (Qmoment) measurement was insuﬃcient to make ﬁrm
conclusions and required further study. Since then, theexperimental setup was improved and the Q-moment
has been successfully measured.
The present experiment was carried out using the
RIPS separator at the RIBF facility. A spin-polarized
beam of neutron-rich 21 O was produced in the projectile fragmentation reaction of a 22 Ne beam at
270 MeV/nucleon on a 185-mg/cm Be target. To ensure polarization, the momentum window and emission angle of the secondary fragments were selected
to be pF = p0 × (0.97 ± 0.03) and θF > 1.5◦ , respectively. Here, p0 is the fragment momentum corresponding to the projectile velocity. The secondary
beam of 21 O was then puriﬁed by the momentum andmomentum-loss analyses and delivered to the β-ray
detected nuclear magnetic resonance (β-NMR) apparatus installed downstream the beam line. The wellestablished method of β-NMR 4) in combination withadiabatic fast passage technique5) was applied to measure quadrupole moment.
The obtained nuclear quadrupole resonance (NQR)
spectra are shown on Fig. 1. It consists of the two series of measurements. The black circles represent themeasurement with ±44 kHz modulation of quadrupole
coupling constant νQ = eqQ/h, where q, Q and h denote the electric ﬁeld gradient of the stopper material,
the Q-moment and the Planck’s constant, respectively.
The spectra are plotted with Aβ P values measured aspeak,
a function of deviation from the peak frequency νQwhere Aβ P is the β-decay asymmetry parameter, andP the 21 O nuclear spin polarization. A resonant peakformed by the β rays emitted from 21 O stopped at the
∗1
∗2
∗3

Fig. 1. β-NQR spectra of 21 O in TiO2 single crystal. The
figure shows the results of two series of measurementswith νQ modulation of ±44 kHz (black circles) and±17 kHz (red circles) are shown.

substitution site of TiO2 is clearly identiﬁed in Fig. 1.
Due to the improvement in polarization detection, thesignal-to-noise ratio was greatly increased and a lesspronounced additional NQR eﬀect was detected at alower Q-moment region.
In order to investigate this minor peak in moredetail, a measurement with narrower scan width of±17 kHz was conducted. The result of this measurement is represented on Fig. 1 by the red solid circles. The centroid position of the small peak is consistent with the previous nuclear quadrupole resonance(NQR) measurement of 21 O at RIPS in 2016.3) The
origin of the additional lower-amplitude peak is under analysis. In overall, the two NQR measurements
conﬁrmed the existence of a major peak at higher Qmoment region that could not be detected in 2016 due
to several experimental limitations. The Q-moment
value of 21 O can be then ﬁrmly assigned based on theobtained results. The uncertainty assignment basedon the peak shape analysis and the discussion of theresults in terms of 21 O nuclear structure are work-inprogress.
References

1) C. Nociforo et al., Phys. Lett. B 605, 79 (2005).
2) D. Cortina-Gil et al., Phys. Rev. Lett. 93, 062501(2004).
3) A. Gladkov et al., RIKEN Accel. Prog. Rep. 51, 74 (2018).
4) D. Nagae et al., Nucl. Instrum. Methods Phys. Res. B
266, 4612 (2008).
5) A. Abragam, The Principles of Nuclear Magnetism(Springer, Oxford, 1961).

RIKEN Nishina Center
Department of Physics, Kyushu University
Center for Nuclear Study, The University of Tokyo- 28 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Investigations of magnetic moments in Coulomb fission
G. Häfner,∗1,∗2 R. Lozeva,∗1 M. Si,∗1 Y. Ichikawa,∗3,∗4 H. Ueno,∗3 D. S. Ahn,∗3 K. Asahi,∗3 T. Asakawa,∗3,∗5
H. Baba,∗3 A. Esmaylzadeh,∗2 N. Fukuda,∗3 A. Gladkov,∗3 K. Imamura,∗3 N. Inabe,∗3 K. Kawata,∗3,∗6
L. Knaﬂa,∗2 A. Kusoglu,∗7 M. Niikura,∗8 Y. Sasaki,∗3,∗5 H. Sato,∗3 Y. Shimizu,∗3 H. Suzuki,∗3 M. Tajima,∗3
A. Takamine,∗3 H. Takeda,∗3 Y. Takeuchi,∗3,∗5 Y. Yanagisawa,∗3 H. Yamazaki,∗3 and K. Yoshida∗3

∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8

800

Counts / 2.5 ns

1000

103

PID gate: 125AgCounts / keV

Ge2

125

2

10

Ag, (E = 670 keV)
60
Co (source)

10

600
1
−20

400

0

20

40

#

200

60

80 100Time [ns]

670
684
714
728

Magnetic moments present an important tool tostudy the single-particle character of excited states.
They are directly related to the g factor and provide a
crucial test for the wave functions of particular states
predicted by theoretical models. One experimental requirement for the measurement of g factors is the spinalignment of the nuclear ensemble that is obtained in
the reaction populating a nucleus of interest. In thisexperiment, Coulomb ﬁssion is used to produce the nuclear alignment, and the magnetic moments of isomericstates are investigated.
The region around the doubly magic 132 Sn has beenof prime interest in the past decades owing to its importance from the perspectives of astrophysics andnuclear structure. The investigation of nuclei withfew valence particles is interesting because several isomeric structures emerge in them. For example, thethree-proton-hole Z = 47 isotopes 124, 125 Ag have isomers based on the unique parity orbitals π(0g9/2 ) andν(0h11/2 ).1)
The experiment is performed at the RIBF using the
BigRIPS spectrometer. A primary 238 U beam at anenergy of 345 MeV/nucleon impinged on a thin 184 W
production target with an average beam intensity of
approximately 100 particle nA. The momentum distribution is selected with slits at the F1 focal plane. The
nuclei of interest are separated and identiﬁed using the
BigRIPS separator.2) The secondary ions are stopped
in a 3-mm-thick Cu host at the F8 focal point. The detection setup consisted of four high-purity Ge (HPGe)and two LaBr3 (Ce) detectors, arranged with each detector type at 90◦ with respect to each other. To measure the magnetic moments, the TDPAD method isused; it has been applied successfully at the RIBF.3–5)
In the experiment, approximately 5·106 ions of 124 Ag
and approximately 3·106 ions of 125 Ag are identiﬁed ineach of the experimental settings. The particle identiﬁcation (PID) of these secondary ions is achieved after
the identiﬁcation and tracking detectors are fully calibrated oﬄine. The spectroscopy could be performed
after calibration and various corrections of the γ-ray
detectors in energy and time. Figure 1 shows the de-

#
#

0
0

100

200

300

400

500

600

700

800

Energy [keV]
Fig. 1. Delayed HPGe energy spectrum for the 125 Ag ions.
Background transitions are labelled with “#.” The inset
shows the time-resolution spectrum of one detector fora source and in-beam measurement.

layed γ-ray energy spectrum of all Ge detectors witha PID gate for the 125 Ag ions. All transitions below
the known (17/2− ) isomer can be identiﬁed. For the
TDPAD analysis, a good in-beam time resolution is essential. The setup is optimized using 60 Co and 152 Eu
sources, with a typical resolution of 8(1) ns (FWHM)
achieved by the detectors in the range of interest. This
corresponds to a resolution of 12(1) ns in-beam forthe same detector, e.g., for the 670 keV transition in
125
Ag. As an example, the inset of Fig. 1 shows thetime-resolution spectrum for one of the HPGe detectors, demonstrating the capabilities of this setup. The
analysis of the magnetic moment from the oscillation
pattern is currently in progress. Therefore, it is necessary to have spin alignment, which will be shown bymeasuring the magnetic moment of a known calibration case.
References

1) S. Lalkovski et al., Phys. Rev. C 87, 034308 (2013).
2) T. Kubo et al., Nucl. Instrum. Methods Phys. Res. B
204, 97 (2003).
3) Y. Ichikawa et al., Nat. Phys. 8, 918 (2012).
4) Y. Ichikawa et al., Nat. Phys. 15, 321 (2019).
5) F. Boulay et al., Phys. Rev. Lett. 124, 112501 (2020).

Université Paris-Saclay, CNRS/IN2P3, IJCLabIKP, University of Cologne
RIKEN Nishina Center
Department of Physics, Kyushu University
Department of Advanced Sciences, Hosei University
Center for Nuclear Study, University of Tokyo
Department of Physics, Istanbul University
Department of Physics, University of Tokyo- 29 -1

II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Re-measurement of the 4 He(8 He, 8 Be) reaction

In our previous study, the candidate resonance ofthe 4n system (tetra-neutron) was determined using the4
He(8 He, 8 Be)4n reaction with a 186 MeV/nucleon 8 He
beam.1) A new measurement with better statistics andbetter accuracy was performed to conﬁrm the existenceof the tetra-neutron system.2)
The intensity of the 8 He beam was 3.5 × 106 particles per second at the liquid helium target, and approximately twice compared to that of the previous experiment. Low pressure multi-wire drift chambers (LPMWDCs) were installed at the focal planes F3, F6, andF-H10(S0), to measure the trajectory and momentum of
the beam. The time reference to determine the drift timein LP-MWDCs was obtained from a plastic scintillator
at F3.
We present the analysis of the LP-MWDCs developed
to eliminate accidental coincidence events induced by thehigh intensity beam. The 8 He beam from the SRC had
a bunch structure with a periodic cycle of 73 ns. There
are two cases of accidental coincidence as illustrated inFig. 1(a) and (b). The ﬁlled circles represent the particle, which triggered the data acquisition. The other par(a)

beam
(b)

Triggered bunch

Next bunchtime

TRF = 73 ns
Fig. 1. Time structure of the beam bunch. The solid circles show particles triggering data acquisition, and theopen circles are accidental particles. (a) Beam contains
both the ‘Triggered bunch’ and ‘Next bunch.’ (b) Two
particles are in the triggered bunch.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8

Center for Nuclear Study, the University of Tokyo
RIKEN Nishina Center
Department of Physics, Toho University
Research Center for Nuclear Physics, Osaka University
Department of Physics, Tokyo Institute of Technology
Faculry of Engineering, Univ. of Miyazaki
Laboratorie de Physique Corpusculaire, IN2P3-CNRS, ENSICAEN et Université de Caen
Department of Physics, the University of TokyoCounts (a.u.)

S. Masuoka,∗1,∗2 S. Shimoura,∗1 M. Takaki,∗1 S. Ota,∗1 S. Michimasa,∗1 M. Dozono,∗1 C. Iwamoto,∗1
K. Kawata,∗1 N. Kitamura,∗1 M. Kobayashi,∗1 R. Nakajima,∗1 H. Tokieda,∗1 R. Yokoyama,∗1 D. S. Ahn,∗2
H. Baba,∗2 N. Fukuda,∗2 T. Harada,∗3 E. Ideguchi,∗4 N. Imai,∗1 N. Inabe,∗2 Y. Kondo,∗5 T. Kubo,∗2 Y. Maeda,∗6
F. M. Marqués,∗7 M. Matsushita,∗1 T. Nakamura,∗5 N. Orr,∗7 H. Sakai,∗2 H. Sato,∗2 P. Schrock,∗1 L. Stuhl,∗1,∗2
T. Sumikama,∗2 H. Suzuki,∗2 H. Takeda,∗2 K. Taniue,∗6 T. Uesaka,∗2 K. Wimmer,∗8 K. Yako,∗1 Y. Yamaguchi,∗1
Y. Yanagisawa,∗2 K. Yoshida,∗2 and J. Zenihiro∗2
3500
3000
2500
2000
1500
1000
500
3

0

2

4

6

8

10

12

×10

Sum of drift charge (a.u.)

Fig. 2. Energy distribution of LP-MWDC.

ticle in the next bunch (open circle) hits in (a), whereas
two particles together hit in the same bunch in (b). In
the analysis, we carefully treated these events, which
created multiple hits within the maximum drift time of
120 ns in the LP-MWDCs. The events of Fig. 1(a) weresuccessfully identiﬁed by selecting the drift-time regionof the LP-MWDC and the total traveling time from F3
to S2 focus corresponding to the beam energy.
In the case of Fig. 1(b), we simply eliminated such
events because the triggered beam particle and accidental particle in the same bunch cannot be distinguished.
To identify such cases, we estimated the total energy
spectrum obtained by using the Time-Over-Thresholddata of its signal. Figure 2 shows the total energy distributions measured at LP-MWDC; two peaks are visible.
The peak at higher energies results from multiple-hit
events, and 75% of the multiple hit events were rejectedby selecting energies below 6,000. This value is consistent with the probability of an occurrence of pile up
events.
After the treatment, the tracking eﬃciency of thebeam was 95%. In the present experiment, one of the
LP-MWDCs installed at F-H10 was damaged under theintense irradiation of the 8 He beam and operated witha low eﬃciency of 48%. The overall tracking eﬃciencyof the 8 He beam is therefore 80%, which still ensuresbetter statistics than the previous experiment.
Data analysis is in progress toward the ﬁnal result.
References

1) K. Kisamori et al., Phys. Rev. Lett. 116, 052501 (2016).
2) S. Masuoka et al., RIKEN Accel. Prog. Rep. 50, 198 (2017).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Alpha-decay correlated mass measurement of 206, 207 Ra using an
MRTOF-MS system equipped with an α-TOF detector
T. Niwase,∗1,∗2,∗3 M. Wada,∗3 P. Schury,∗3 P. Brionnet,∗2 S. D. Chen,∗4,∗3 T. Hashimoto,∗5 H. Haba,∗2
Y. Hirayama,∗3 D. S. Hou,∗6,∗7,∗8 S. Iimura,∗9,∗2,∗3 H. Ishiyama,∗2 S. Ishizawa,∗10,∗2 Y. Ito,∗11 D. Kaji,∗2
S. Kimura,∗2 J. Liu,∗4,∗3 H. Miyatake,∗3 J. Y. Moon,∗5 K. Morimoto,∗2 K. Morita,∗1,∗2 D. Nagae,∗1
M. Rosenbusch,∗3 A. Takamine,∗2 T. Tanaka,∗12 Y. X. Watanabe,∗3 H. Wollnik,∗13 W. Xian,∗4,∗3 and S. X. Yan∗14∗1

Department of Physics, Kyushu University
RIKEN Nishina Center∗3 Wako Nuclear Science Center (WNSC), KEK∗4 Department of Physics, The University of Hong Kong
∗5 Institute for Basic Science, Rare Isotope Science Project∗6 Institute of Modern Physics, Chinese Academy of Science∗7 University of Chinese Academy of Science∗8 School of Nuclear Science and Technology, Lanzhou University∗9 Department of Physics, Osaka University.
∗10 Graduate School of Science and Engineering, Yamagata University∗11 Japan Atomic Energy Agency∗12 Department of Nuclear Physics, The Australian National University∗13 Department of Chemistry and Biochemistry, New Mexico
State University∗14 Institute of Mass Spectrometer and Atmospheric Environment, Jinan University∗2

207Ra-singles

207Fr-singles

2

10Counts / 3 ns

Toward the precise mass measurement of heavy andsuperheavy nuclides, the SHE-Mass-II facility1) was constructed with a multi-reflection time-of-flight mass spectrograph (MRTOF-MS)2) coupled with the gas-filled recoil ion separator GARIS-II.3) We installed an α-TOF4)
detector, which simultaneously records the time-of-flight(TOF) signal and subsequent α-decay. In order todemonstrate the α-TOF detector, an experiment was
performed using the 51 V + 159 Tb reaction. A 51 V beam
was accelerated to 6.0 MeV/nucleon by the RIKEN Ring
Cyclotron (RRC). The beam energy on the target was
reduced by an aluminum degrader to 4.8 MeV/nucleon.
The beam impinged upon 460 µg/cm2 -thick 159 Tb targets with a 3 µm Ti backing, mounted in a rotatingtarget wheel.
The fusion evaporation residues (ERs) were separated
from the primary beam and transported using GARISII. After decelerating ERs using a Mylar foil, the ERs
were stopped in a cryogenic helium gas catcher, and thethermalized ions were extracted by a radio frequency(RF) carpet and transported to the MRTOF-MS via
multiple RF ion traps.
We observed ERs, 206, 207 Fr, and 206, 207 Ra as doubly
charged ions. The subsequent α-decays were additionally detected by the α-TOF detector. Using 206, 207 Fr
as the isobaric references, the masses of 206, 207 Ra weredirectly determined. The mass excess of 206 Ra was3540(54) keV, which agrees with the values reported in
AME2016.5)
The TOF spectrum for the A/q = 103.5 region isshown in Fig. 1. The singles events and 207 Ra decaycorrelated events are plotted. In the case of the groundstate of 207 Ra, the correlated events of the TOF and the
α-decay could not be observed, because the incoming

207Ra-correlated
E > 7.32 MeV
dt < 180 ms

10

1

9410.59410.69410.79410.8Time-of-ﬂight [s]9410.9Fig. 1. Time-of-flight spectrum around the 207 Ra2+ region.
The red histogram indicates the decay-correlated events.
The green and blue lines show the fitting of the groundand isomeric states of the singles (solid lines) and decaycorrelated events (dot lines).

rate was higher than the decay rate, while the decaycorrelated events were observed in the isomeric state207m
Ra owing to its short half-life. The energies of the
α-decay were selected as higher than 7.32 MeV, 2σ apartfrom the centroid of 207g Ra, to avoid contamination from
207g
Ra.
The peaks of singles 207g/m Ra2+ and decay-correlated
207m
Ra2+ were fitted. The shape of the peak was determined by 207 Fr2+ . The mass excess of 207g Ra was determined to be 3538(15) keV, and the excitation energy of207m
Ra was Eex = 552(42) keV from the α-decay correlated TOF spectrum. These values are consistent withthose evaluated by α-decay spectroscopy.5)
The alpha branching ratio of 207m Ra was determinedfrom the counting of TOF and α-decay events. The spinparity was expected to be 13/2+ based on its singleparticle level energy and the analogous reduced alphawidth to the neighboring nuclei.
References

1) M. Wada et al., RIKEN Accl. Prog. Rep. 52, 136 (2019).
2) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
335, 39 (2014).
3) D. Kaji et al., Nucl. Instrum. Methods Phys. Res. B 317,
311 (2013).
4) T. Niwase et al., Nucl. Instrum. Methods Phys. Res. A
953, 163198 (2020).
5) M. Wang et al., Chin. Phys. C 41, 030003 (2017).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

First high-precision direct determination of the atomic mass of asuperheavy nuclide
P Schury,∗1 T. Niwase,∗1,∗2,∗3 M. Wada,∗1 P. Brionnet,∗2 S. Chen,∗4 T. Hashimoto,∗5 H. Haba,∗2 Y. Hirayama,∗1
D. S. Hou,∗6,∗7,∗8 S. Iimura,∗9,∗2,∗1 H. Ishiyama,∗2 S. Ishizawa,∗10,∗2 Y. Ito,11,∗2,∗1 D. Kaji,∗2 S. Kimura,∗2
H. Koura,∗11 J. J. Liu,∗4,∗1 H. Miyatake,∗1 J. -Y. Moon,∗5 K. Morimoto,∗2 K. Morita,∗12,∗13 D. Nagae,∗13
M. Rosenbusch,∗1 A. Takamine,∗2 Y. X. Watanabe,∗1 H. Wollnik,∗14 W. Xian,∗4,∗1 and S. X. Yan∗15
decay-correlated ToF events
Po coincidental decay-correlated ToF events
Uncorrelated ToF singles

257

2
A/q - 85 702.006 [mu/e]

We present the ﬁrst direct measurement of theatomic mass of a superheavy nuclide. Atoms of 257 Db(Z = 105) were produced online at the RIKEN Nishina
Center for Accelerator-Based Science using the fusionevaporation reaction 208 Pb(51 V, 2n)257 Db. The gasﬁlled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and sometransfer products, prior to delivering the energetic
beam of 257 Db ions to a helium gas-ﬁlled ion stopping cell wherein they were thermalized. Thermalized 257 Db3+ ions were then transferred to a multireﬂection time-of-ﬂight mass spectrograph for mass
analysis. An alpha particle detector embedded in
the ion time-of-ﬂight detector allowed disambiguationof the rare 257 Db3+ time-of-ﬂight detection eventsfrom background by means of correlation with characteristic α-decays (see also T. Niwase in this issue). The extreme sensitivity of this technique allowed a precision atomic mass determination from
11 events. The mass excess was determined to be
100 063(231)stat (72)sys keV/c2 .
In recent experience, elements with a second ionization potential below 24 eV have been near uniformly
extracted from the gas cell as doubly charged ions.
Surprisingly, no counts were seen for 257 Db2+ , while257
Db3+ was observed with the rate which, based oncross-section, target thickness, and primary beam intensity, indicated it constituted the preponderance of257
Db ions. The rate of 257 Db3+ extracted from thegas cell was roughly 4 per day. These ions were analyzed by the MRTOF-MS with the α-TOF detector,1)
which allowed us to correlate ToF events with subse-

211

Db 3+

1

E8

E1

0

E11

E3
E2

E6
E5

E9

E12

E13
E14

-1
-2
0

1

2

3

4

Time of observation [Days]

5

6

Fig. 1. Apparent A/q evaluated for each ToF single near
the expected position of 257 Db3+ . The data are plottedin terms of deviation from the A/q for 257 Db3+ as determined from AME16.2) Statistical uncertainties are
only evaluated for α-decay correlated ToF events.

quent α-decays. Such correlations allowed removal ofeven low-intensity backgrounds and conﬁrm that wewere truly measuring 257 Db3+ .
Figure 1 shows the data measured over 105 hours ofbeam on target. As the MRTOF was operated with aresolving power of Rm ≈ 300 000, the A/q range presented is about 10-FWHM. The red points represent
events where the ToF signal was followed within 120 s
by an α decay event with energy Eα ≥ 7.0 MeV to encompass all possible α-decays from 257 Db and its decay
products; some α-decay-correlated ToF events within
this gate were attributed to the α-decay of 211 Po.
Based on the 11 alpha decay correlated ToF events,
the mass of 257 Db could be determined with a precision of 231 keV/c2 (82 µu/e). The value is in agreement with indirect measurements.2,3) Unfortunately,
the mass resolution of the MRTOF and the energy resolution of the α-TOF were insuﬃcient to resolve isomeric states. With recent improvements in the mass
resolving power (See S. Yan in this issue) we should be
able to resolve the isomer and ground state provided
the isomer has excitation energy above 250 keV/c2 .
A followup eﬀort to determine the state order via
MRTOF mass analysis is planned for FY2021.

∗1

Wako Nuclear Science Center (WNSC), IPNS, KEK
RIKEN Nishina Center∗3 Department of Physics, Kyushu University∗4 Department of Physics, The University of Hong Kong
∗5 Institute for Basic Science∗6 Institute of Modern Physics∗7 University of Chinese Academy of Sciences∗8 School of Nuclear Science and Technology∗9 Department of Physics, Osaka University∗10 Graduate School of Science and Engineering, Yamagata University∗11 Advanced Science Research Center, Japan Atomic Energy
Agency∗12 Department of Physics, Kyushu University∗13 Research Center for SuperHeavy Elements, Kyushu University∗14 New Mexico State University∗15 Institute of Mass Spectrometer and Atmospheric Environment, Jinan University∗2

References

1) T. Niwase et al., Nucl. Instrum. Methods Phys. Res. A,
953, 163198 (2020).
2) M. Wang et al., Chin. Phys. C, 41 030003 (2017).
3) Y. Ito et al., Phys. Rev. Lett. 120, 152501 (2020).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

β-decay spectroscopy of 187 Ta
M. Mukai,∗1 Y. Hirayama,∗2 Y. X. Watanabe,∗2 S. C. Jeong,∗2 H. Miyatake,∗2 S. Ishizawa,∗1,∗2,∗3
T. Niwase,∗1,∗2,∗4 M. Rosenbusch,∗2 P. Schury,∗2 M. Wada,∗2 H. Watanabe,∗1,∗5 M. Brunet,∗6 F. G. Kondev,∗7
G. J. Lane,∗8 Yu. A. Litvinov,∗9 Zs. Podolyák,∗6 and P. M. Walker∗6
The nuclear data of neutron-rich nuclei around N =126, such as the nuclear mass, decay half-life, and decay scheme, are key for understanding the formation of
the third peak around A = 195 through the r-process
in explosive stellar environments, and the data are required to be investigated experimentally. Furthermore,
the neutron-rich region around Z = 75 is not only a transition region of nuclear deformation, but also expected tocontain high-energy long-lived isomers. Owing to the astrophysical and nuclear physics interests in this nuclear
region, nuclear spectroscopy has been performed at theKEK Isotope Separation System (KISS) 1,2) installed in
the Radioactive Isotope Beam Factory (RIBF), RIKEN.
The isomeric states of 187 Ta (Z = 73, N = 114) wereﬁrst observed in the Experimental Storage Ring (ESR)at GSI.3) In that study, the half-lives and excited energies were determined to be 2.3(6) min for the groundstate (gs), 22(9) s for the ﬁrst isomeric state (m1) at theexcitation energy Ex = 1789(13) keV, and >5 min forthe second isomeric state (m2) at Ex = 2935(14) keV.3)
We performed the β- and γ-decay spectroscopy of 187 Ta
to investigate the nuclear structure of the ground andtwo isomeric states at KISS. They are predicted to havenuclear spins of 25/2− and 41/2+ for the m1 and m2
states, respectively. The results of successful experiments on the m1 isomer were reported in Ref. 4). The
present report describes the progress of the analysis investigating the unknown β-decays of 187gs, m1, m2 Ta.
187gs, m1, m2
Ta were produced using multi-nucleon
transfer reactions of a natural tungsten target (5 µm
thick) and 136 Xe beam (7.2 MeV/nucleon, 50 particlenA). The target-like fragments were thermalized andneutralized in a gas cell ﬁlled with puriﬁed Ar gas of∼1 atm2) and re-ionized element-selectively by using alaser resonance ionization technique5) at the exit of thegas cell. Subsequently, the mass number was chosen byusing a dipole magnet with a mass resolving power ofA/∆A ∼ 900. The mass-analyzed ions were transported
to the decay station, which consists of a tape transport
device, a multi-segmented proportional gas counter,6)
∗1
∗2

∗3
∗4
∗5
∗6

∗7
∗8

∗9

RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), Institute of Particle
and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
Graduate School of Science and Engineering, Yamagata University
Department of Physics, Kyushu University
International Research Center for Nuclei and Particles in the
Cosmos, Beihang University
Department of Physics, University of Surrey
Physics Division, Argonne National Laboratory
Department of Nuclear Physics, Australian National University
GSI Helmholtzzentrum für Schwerionenforschung GmbH

Fig. 1. Energy spectrum of γ-rays associated with the βdecay of 187 Ta and 187 W, as well as some of the internaltransitions of 187m1 Ta. The labels indicate the energy(keV) and possible origin of the observed γ-rays. The
inset shows a part of the low-energy level scheme in 187 W.
The values in parentheses are the relative intensities oftransitions.7)

and four clover-type germanium detectors.
Figure 1 shows the γ-ray energy spectrum in coincidence with events of the gas counter telescope, which
are sensitive to electron energies of >100 keV.6) The
measurement was performed with the time sequence ofbeam-on/oﬀ = 1800/1800 sec. We observed γ-rays originating from β-decays of 187 Ta as well as 187 W (T1/2 =24.0 h), which is the daughter nucleus of 187 Ta, and fromthe internal decay of 187m1 Ta (T1/2 = 7.3(9) sec)4) emitting high-energy (>100 keV) conversion electrons. The
γ-ray transitions were assigned not only through comparison with previously reported transition energies,7)
but also by checking the half-lives from the energy-gatedtime spectra for each gamma peak. Consequently, all of
the observed γ-rays emitted from 187 W were identiﬁed(upper right scheme in Fig. 1). The observed γ-rays
emitted from 187 Re agree with those measured in previous decay studies.
Further analysis to determine the decay branch fromthe three states of 187 Ta is ongoing.
References

1) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
353, 4 (2015).
2) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
412, 11 (2017).
3) M. W. Reed et al., Phys. Rev. C 86, 054321 (2012).
4) P. M. Walker et al., Phys. Rev. Lett. 125, 192505 (2020).
5) Y. Hirayama et al., Rev. Sci. Instrum. 90, 115104 (2019).
6) M. Mukai et al., Nucl. Instrum. Methods Phys. Res. A
884, 1 (2018).
7) V. Bondarenko et al., Nucl. Phys. A 811, 28 (2008).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

β-γ Spectroscopy of 192 Re
H. Watanabe,∗1,∗2,∗3 Y. X. Watanabe,∗3 Y. Hirayama,∗3 A. N. Andreyev,∗4,∗5 T. Hashimoto,∗6 F. G. Kondev,∗7
G. J. Lane,∗8 Yu. A. Litvinov,∗9 J. J. Liu,∗10 H. Miyatake,∗3 J. Y. Moon,∗6 A. I. Morales,∗11 M. Mukai,∗2,∗3,∗12
S. Nishimura,∗2 T. Niwase,∗2,∗13 M. Rosenbusch,∗3 P. Schury,∗3 M. Wada,∗3 and P. M. Walker∗14
Decay spectroscopy of 192 Re has been carried out using the KEK Isotope Separation System (KISS).1–3) A
RI beam of 192 Re was produced via multi-nucleon transfer between a 50-particle-nA projectile of 136 Xe anda natural Pt target with a thickness of 10.7 mg/cm2 .
The 10.75-MeV/nucleon primary beam from the RIKEN
Ring Cyclotron was decelerated to 8.8 MeV/nucleon after passing through Ti degraders placed in front of thePt target. The reaction products were thermalized andneutralized in a doughnut-shaped gas cell ﬁlled with 80kPa gaseous argon, and then transported by a gas ﬂow
to the cell outlet, where a two-color, two-step resonant
laser ionization technique was applied for an unambiguous selection of a single element. The singly charged
192
Re+ ions were extracted through the RF ion guides
and reaccelerated at 20 keV, followed by mass separation
using the KISS spectrometer.
During 4.2 days of data run, about 1.5×105 192 Re nuclides were collected with an average intensity of 0.3 particles/s on a 12-µm-thick aluminized mylar tape at theend of the KISS beamline. The decay measurements
were carried out with three diﬀerent beam-on/oﬀ conditions of 90/180, 24/48, and 45/15 s in order to accommodate decays both from the ground state (T1/2 =16(1) s4) ) and from a previously reported long-lived iso5)
192
Re. The implantation posimer (T1/2 = 61+40−20 s ) intion was surrounded by a multi-segmented proportional
gas counter (MSPGC) that covered 80% of the 4π solid
angle with two layers of 16 counters.6) The MSPGC was
surrounded by four large-volume Clover-type HPGe detectors in a close geometry, having a γ-ray add-backed
full-energy peak eﬃciency of 7.8% at 1 MeV.
Figure 1 shows an example of the β-delayed γ-ray coincidence spectrum and the decay scheme of 192 Re obtained in the present work. More details about the experimental results and physics discussion are describedin Ref. 7).
∗1

School of Physics, Beihang University
RIKEN Nishina Center∗3 Wako Nuclear Science Center (WNSC), IPNS, KEK∗4 Department of Physics, University of York
∗5 Advanced Science Research Center, Japan Atomic Energy
Agency (JAEA)∗6 Rare Isotope Science Project, Institute for Basic Science (IBS)∗7 Physics Division, Argonne National Laboratory∗8 Department of Nuclear Physics, Australian National University∗9 GSI Helmholtzzentrum für Schwerionenforschung∗10 Department of Physics, the University of Hong Kong
∗11 Instituto de Fisica Corpuscular (CSIC-Universitat de Valencia)∗12 Graduate School of Sciences and Technology, University ofTsukuba∗13 Department of Physics, Kyushu University∗14 Department of Physics, University of Surrey∗2

Fig. 1. Top: γ-ray energy spectrum measured in coincidencewith MSPGC following implantation of 192 Re. Transitions in 192 Os are labeled with their energy values, while
γ-ray peaks that originate from the room background andbeam contaminants are marked with crosses and asterisk,
respectively. The inset magnifies a high-energy region.
Bottom: Level scheme of 192 Os populated in the β decay of 192 Re. The observed γ rays are consistent withthose reported in Ref. 4). The superscript “1u” indicatesfirst-forbidden unique β decay.

References

1) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
353, 4 (2015).
2) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
376, 52 (2016).
3) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
412, 11 (2017).
4) C. M. Baglin, Nucl. Data Sheets 113, 1871 (2012).
5) M. W. Reed et al., Phys. Rev. C 86, 054321 (2012).
6) M. Mukai et al., Nucl. Instrum. Methods Phys. Res. A
884, 1 (2018).
7) H. Watanabe et al., Phys. Lett. B 814, 136088 (2021).

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II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Insight into the reaction dynamics of proton drip-line nuclear system
17
F + 58 Ni at near-barrier energies†
L. Yang,∗1 C. J. Lin,∗1,∗16 H. Yamaguchi,∗2,∗3 J. Lei,∗4 P. W. Wen,∗1 M. Mazzocco,∗5,∗6 N. R. Ma,∗1 L. J. Sun,∗1
D. X. Wang,∗1 G. X. Zhang,∗7 K. Abe,∗2 S. M. Cha,∗8 K. Y. Chae,∗8 A. Diaz-Torres,∗9 J. L. Ferreira,∗10
S. Hayakawa,∗2 H. M. Jia,∗1 D. Kahl,∗1 A. Kim,∗11 M. S. Kwag,∗8 M. La Commara,∗12 R. Navarro Pérez,∗13
C. Parascandolo,∗14 D. Pierroutsakou,∗14 J. Rangel,∗10 Y. Sakaguchi,∗2 C. Signorini,∗5,∗6 E. Strano,∗5,∗6
X. X. Xu,∗1 F. Yang,∗1 Y. Y. Yang,∗15 G. L. Zhang,∗7 F. P. Zhong,∗1,∗16 and J. Lubian∗10
In recent times, the availability of high-quality radioactive beams has greatly increased our ability to
study the reactions induced by exotic nuclei.1) In contrast to neutron-halo projectiles, reactions induced byweakly bound proton-rich nuclei, especially those with
proton-halo or valence-proton structures, present distinctive properties. Both the core and valence proton
have long-range Coulomb interaction with the target;
thus, the dynamic Coulomb polarization eﬀect is of particular importance.2) So far, research on reactions with
proton drip-line nuclei is still in its infancy, and the reaction mechanism is not yet clear.
17
F can be treated properly with a two-body model
as an inert 16 O core and a loosely bound proton.3) In
this report, we present the results of complete kinematics measurements to investigate the reaction mechanisms of 17 F interacting with 58 Ni at energies around the
Coulomb barrier. The experiment was performed at theCenter for Nuclear Study Radioactive Ion Beam separator (CRIB).4) The Multi-layer Ionization-chamber Telescope Array (MITA)5) was used to detect the reaction
products over a large range of Z. Angular distributionsof elastic scattering, exclusive and inclusive breakup, as
well as the total fusion (TF) cross sections were derived
simultaneously for the ﬁrst time.
The excitation functions of the total reaction (σR ),inclusive (σInc.16 O ) and exclusive (σExc.16 O ) 16 O, as wellas the TF from evaporation protons are shown in Fig. 1.
Fusion is dominant in the above-barrier region, andit reduces exponentially as the energy decreases. The
σInc.16 O and σExc.16 O , however, vary smoothly with
Condensed from the article in Phys. Lett. B 813, 136045(2021)∗1 Department of Nuclear Physics, China Institute of Atomic
Energy∗2 Center for Nuclear Study, University of Tokyo∗3 National Astronomical Observatory of Japan∗4 Institute of Nuclear and Particle Physics, and Department of
Physics and Astronomy, Ohio University∗5 Dipartimento di Fisica, Universita di Padova∗6 Istituto Nazionale di Fisica Nucleare-Sezione di Padova∗7 School of Physics, Beihang University∗8 Department of Physics, Sungkyunkwan University∗9 Department of Physics, University of Surrey∗10 Instituto de Física, Universidade Federal Fluminense∗11 Department of Science Education, Ewha Womans University∗12 Department of Pharmacy, University Federico II∗13 Department of Physics, San Diego State University∗14 Istituto Nazionale di Fisica Nucleare-Sezione di Napoli∗15 Institute of Modern Physics, Chinese Academy of Sciences∗16 Department of Physics, Guangxi Normal University†

the energy, and σInc.16 O becomes the major component in the sub-barrier region. The behavior of the TF
cross section can only be reproduced by the continuumdiscretized coupled-channels (CDCC) calculation considering the couplings from the continuum states, indicating that the enhancement of TF at the sub-barrierenergy is mainly due to the breakup coupling.

Fig. 1. Excitation functions of the total reaction (stars), exclusive (squares) and inclusive (triangles) breakups, andthe TF (circles). The curves denote the corresponding theoretical results: the solid line denotes the coupled channel (CC) result; the dot-dot-dashed and dottedcurves are the CDCC results for TF and elastic breakup,
respectively; the dashed line shows the CDCC calculations performed by switching oﬀ the couplings from thecontinuum states (NCC); and the dot-dashed line is theresult of the three-body model proposed by Ichimura,
Austern, and Vincent6) plus CDCC. The arrow indicatesthe nominal position of the Coulomb barrier.

References

1) L. F. Canto et al., Phys. Rep. 596, 1 (2015).
2) M. Ito, K. Yabana, T. Nakatsukasa, M. Ueda, Nucl. Phys.
A 787, 267c (2007).
3) C. A. Bertulani, P. Danielewicz, Nucl. Phys. A 717, 199(2003).
4) Y. Yanagisawa et al., Nucl. Instrum. Methods Phys. Res.
A 539, 74 (2005).
5) N. R. Ma et al., Eur. Phys. J. A 55, 87 (2019).
6) M. Ichimura et al., Phys. Rev. C 32, 431 (1985).

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12. Nuclear Physics (Theory)

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Dineutron and eﬀective pairing forces in momentum space
M. Yamagami ∗1

cm

q

rel

The spatial two-neutron correlation, called dineutron
correlation, is one of the unique features around the neutron drip line. The dineutron correlation has been discussed extensively in light-mass nuclei such as 11 Li,1,2)
but it is considered to be a universal phenomenon over
all mass-number regions.3)
We propose a new eﬀective pairing force by focusing on the spatial structure of a neutron pair.
First, we discuss the necessity by performing a threebody model calculation with the density-dependentzero-range force (DD δ(r)-force),1,2) Vδ (r 1 , r 2 ) =V (0) {1 − η[ρ(r 1 )/ρ0 ]} δ(r 1 − r 2 ). The DD δ(r)-force iswidely used in nuclear structure calculations.1–3) It mustbe supplemented with a cutoﬀ in the two-particle spectrum, ε1 + ε2 ≤ Ecut . The parameters V (0) and η are
adjusted for each Ecut so as to reproduce the propertiesof low-energy neutron-neutron (nn) scattering and thetwo-neutron energy E2n of ﬁnite nuclei. The parameterρ0 = 0.16 fm−3 is the saturation density.
In Fig. 1, the root-mean-square (rms) values krel andqcm of the relative and center of mass (cm) momenta ofpaired neutrons in 11 Li and 12 Be are shown. krel converges, while qcm diverges as a function of Ecut owing toundesirable coupling to high-momentum components ofsingle-particle states in the continuum.
In order to overcome the diﬃculties, we consider
a new eﬀective pairing force in momentum space (kspace) that has a non-local separable form (k-SEP(0)
force), VSEP = − 2π1 2 Vk g(k)g(k′ )h(q)h(q ′ ). Here, theYamaguchi-type form factor g(k) = 1/(k2 + Λ2 ) and√2
2
the Gaussian distribution h(q) = ( πq0 )−3 e−q /q0 for
the relative momentum k and the cm momentum q of(0)
paired neutrons are adopted. The parameters Vk andFig. 2. Two-neutron energies E2n obtained with the k-SEP
force (q0 = 0.209 and 0.171fm−1 ) and the DD δ(r)-force
with fixed Ecut = 40 MeV and η = 0.849, in comparison
with the experimental data.

Λ are ﬁxed so as to reproduce the properties of lowenergy nn scattering.4) The parameter q0 is ﬁxed by the
two-neutron energy E2n of ﬁnite nuclei.
The krel and qcm obtained with the k-SEP force areshown in Fig. 1. They converge well above Ecut =100 MeV. Here, the parameter q0 = 0.209 fm−1
(0.171 fm−1 ) is used for 11 Li (12 Be). The small cm momentum qcm indicates that the pairing correlation occurs
only around the nuclear surface region in real space. The
relative momentum krel in 12 Be becomes larger than thatin Borromean 11 Li owing to the high-momentum component in the bound 1p1/2 state.
The two-neutron energies E2n of three-body systems
can be classiﬁed into two categories as shown in Fig. 2.
The Borromean nuclei (6 He, 22 C, 11 Li) are well described with q0 = 0.209 fm−1 , while q0 = 0.171 fm−1
for non Borromean nuclei. Because the parameter q0
introduces a cutoﬀ for correlations in the opening angle
θk between k1 and k2 as cos θk ≲ q02 /(2k1 k2 ) in h(q),the pairing correlations have a more collective nature in
calculation with a larger q0 .
In conclusion, we proposed a new eﬀective pairing
force that describes well the structure of the neutronpair. It is also easily utilizable in various frameworks
such as the density functional theory in k space.5)
References

Fig. 1. Relative momentum krel and cm momentum qcm of
the neutron pair in 11 Li and 12 Be. The results using the
k-SEP force and the DD δ(r)-force are shown.
∗1

Department of Computer Science and Engineering, Universityof Aizu

1) G. F. Bertsch, H. Esbensen, Ann. Phys. (NY) 209, 327(1991).
2) H. Esbensen, G. F. Bertsch, K. Hencken, Phys. Rev. C
56, 3054 (1997).
3) M. Matsuo, K. Mizuyama, Y. Serizawa, Phys. Rev. C 71,
064326 (2005).
4) H. Tajima, T. Hatsuda, P. van Wyk, Y. Ohashi, Sci. Rep.
9, 18477 (2019).
5) M. Yamagami, Phys. Rev. C 100, 054302 (2019).

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1

II-2. Nuclear Physics (Theory)

RIKENAccel.
Accel.Prog.
Prog. Rep.
Rep. 54
RIKEN
54(2021)(2021)

Structure of 12 C studied by the no-core Monte-Carlo shell model
T. Abe,∗1 P. Maris,∗2 T. Otsuka,∗1,∗3 N. Shimizu,∗4 Y. Utsuno,∗5,∗4 and J. P. Vary∗2
Carbon-12 is of particular importance in our life. This
nucleus is produced by the triple-α reactions through thesecond 0+ state known as the Hoyle state. The properties of this state are still being investigated actively bothin the experimental and theoretical ways. On the theoretical side, ab initio approaches for low-energy nuclear
structure calculations have been developed rapidly in recent years, owing to recent computational and methodological developments. Here, we report the low-lying
states of 12 C examined by the ab initio calculations in
the no-core Monte Carlo shell model (MCSM).1)
We have performed the large-scale calculations in the
no-core shell-model (NCSM) method,2) applying the
MCSM technique for conventional shell-model calculations.3–5) The no-core MCSM calculations have been
done with 100 basis states in the basis space of Nshell = 7
with the harmonic-oscillator energy of h̄ω = 20 MeV. We
have adopted the Daejeon16 N N interaction,6) which isbased on an N N interaction from chiral eﬀective ﬁeld
theory (χEFT).
Figure 1 shows preliminary results of the no-core
MCSM calculations in comparison with the experimental data.7) In Fig. 1, the absolute energies and transition strengths for three low-lying states are shown.
The no-core MCSM results with the Daejeon16 interaction provide a reasonable agreement with the experimental data for the ground 0+ and the ﬁrst-excited
2+ states. The experimental ground-state energy is−92.16 MeV, while our result is −91.9 MeV and well
reproduces the no-core full-conﬁguration (NCFC, one ofthe other NCSM approaches) result with the same interaction of −92.9(1) MeV.6) The point-proton radius
for the ground state is ∼2.29 fm both in the no-core
MCSM and the NCFC methods, corresponding to theexperimental value of 2.33 fm. The excitation energyof the ﬁrst-excited 2+ state is 5.01 MeV in the no-core
MCSM and 4.57(15) MeV in the NCFC. These energies are also comparable with the experimental value of
4.44 MeV. The electric quadrupole and monopole transition strengths are also in reasonable agreement withthe experimental values.
The excitation energy of the second 0+ state, however,is higher than the experimental value by ∼3 MeV and thepoint-proton radius is 2.60 fm, which is smaller than thevalues by the phenomenological calculations, typicallylarger than 3 fm (see, for example, Ref. 8) and references
therein). It is because the Hoyle state is believed tohave the loosely-bound three-α-cluster structure and is
∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
Department of Physics and Astronomy, Iowa State University
Department of Physics, the University of Tokyo
Center for Nuclear Study, the University of Tokyo
Advanced Science Research Center, Japan Atomic Energy
AgencyDaejeon16 NN, Nshell = 7, hw = 20 MeV
w/o energy-variance extrapolationǆ;ϬͿсϭϬ͘ϳϵDĞsǆ;ϬͿсϳ͘ϲϱϰDĞs

;,ŽǇůĞͿD;ϬͿсϱ͘ϰ;ϮͿĞĨŵǆ;ϮͿсϰ͘ϰϯϵϴDĞsD;ϬͿсϱ͘ϳϲĞĨŵǆ;ϮͿсϱ͘ϬϭDĞs;ϮͿсϳ͘ϰϬĞĨŵ;ϮͿсϳ͘ϲ;ϰͿĞĨŵ;Ő͘Ɛ͘Ϳ

Fig. 1. Excitation spectra of 12 C. The right (left) side in theﬁgure shows no-core MCSM results (experimental data)with the red (black) color. The energy levels of three
low-lying states are shown by horizontal bars. The electric quadrupole and monopole transition strengths are denoted by arrows. The experimental data are taken from
Ref. 7).

challenging to be described in the harmonic-oscillator
basis at least with the basis space employed here. It isawaited to extrapolate our results obtained in the ﬁnite
basis-space size into the inﬁnite basis-space-size limit soas to compare with the experimental values and also
the other theoretical calculations in more detail. Basedon our preliminary calculations, the investigation of the
intrinsic structure of 12 C is currently underway, aiming
to elucidate the α-cluster structure in light-mass nuclear
systems from ﬁrst principles.
References

1) T. Abe, P. Maris, T. Otsuka, N. Shimizu, Y. Utsuno,
J. P. Vary, Phys. Rev. C 86, 054301 (2012).
2) B. R. Barrett, P. Navrátil, J. P. Vary, Prog. Part. Nucl.
Phys. 69, 131 (2013).
3) T. Otsuka, M. Honma, T. Mizusaki, N. Shimizu, Y. Utsuno, Prog. Part. Nucl. Phys. 47, 319 (2001).
4) N. Shimizu, T. Abe, Y. Tsunoda, Y. Utsuno,
T. Yoshida, T. Mizusaki, M. Honma, T. Otsuka,
Prog. Theor. Exp. Phys. 2012, 01A205 (2012).
5) N. Shimizu, T. Abe, M. Honma, T. Otsuka, T. Togashi,
Y. Tsunoda, Y. Utsuno, T. Yoshida, Phys. Scr. 92, 063001(2017).
6) A. M. Shirokov, I. J. Shin, Y. Kim, M. Sosonkina,
P. Maris, J. P. Vary, Phys. Lett. B761, 87 (2016).
7) F. Ajzenberg-Selove, Nucl. Phys. A 506, 1 (1990).
8) M. Chernykh, H. Feldmeier, T. Neﬀ, P. von NeumannCosel, A. Richter, Phys. Rev. Lett. 98, 032501 (2007).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Double charge-exchange phonon states†
X. Roca-Maza,∗1,∗2 H. Sagawa,∗3,∗4 and G. Colò∗1,∗2
The possibility of inducing double charge-exchange(DCX) excitations by means of heavy-ion beams at
intermediate energies has recently fostered interest in
new collective excitations such as double isobaric analog states (DIAS) and double Gamow-Teller giant resonances (DGTR). A research program based on a newreaction, (12 C, 12 Be(0+2 )), is planned at the RIKEN
RIBF facility with high-intensity heavy-ion beams at
the optimal energy of Elab = 250 MeV/nucleon to excite the spin-isospin response.1) A big advantage ofthis reaction is based on the fact that it is a (2p, 2n)type DCX reaction, and one can use a neutron-richtarget to excite DGTR strength. In this report, we
present some formulas to evaluate diﬀerent combinations of the average excitation energies of DIAS and
DGTR by ∑using commutator relations for the douA
ble isospin i,j=1 t− (i)t− (j) and spin-isospin operator∑Ai,j=1 σ(i)t− (i)σ(j)t− (j). Here, t = τ /2, and σ andτ denote the Pauli matrices in spin and isospin space,respectively. Speciﬁcally, we present formulas to estimate EDIAS − 2EIAS from the most relevant isospin
symmetry breaking (ISB) terms in the nuclear Hamiltonian and EDGTR − EDIAS − 2(EGTR − EIAS ) from a
simple albeit realistic Hamiltonian including separable
residual interactions.
The expectation value for the energy of the DIAS isdeﬁned as
EDIAS ≡ ⟨DIAS|H|DIAS⟩ − ⟨0|H|0⟩ ,in other words, there is no isospin mixing, andT+ |0⟩ = 0. Remembering that the EIAS is writtenas, within the same approximation (i.e., no isospin
mixing in the ground state), EIAS = ⟨IAS|H|IAS⟩ −⟨0|H|0⟩ = ⟨0|[T+ , [H, T− ]]|0⟩/⟨0|T+ T− |0⟩, one caneventually write
EDIAS = 2EIAS +The energy of the double GT state can be deﬁned in
an analogous way to Eq. (3) as
EDGTR =

T− |IAS⟩⟨IAS|T+ T− |IAS⟩1/2⟨0|[T+2 , [H, T−2 ]]|0⟩,⟨0|T+2 T−2 |0⟩⟨0|[O+ , [O+ , [[H, O− ], O− ]]]|0⟩.
2(N − Z)(N − Z − 1)
(6)
Double GT and IAS average excitation energies havebeen determined for the ﬁrst time using double andquartic commutator relations.
In order to provide semi-quantitative theoretical estimates, we haveadopted two approximations. First, an independent
particle picture has been assumed. We have also provided expressions in which, by simplifying further, theneutron and proton distributions have been taken as
hard spheres. This simpliﬁcation has turned out to bevery useful to capture the main terms dominating the
calculated quantities.
In conclusion, within our approach, double IAS andGT resonance energies in neutron-rich nuclei are dominated by the same physics as their single counterparts because the main contribution is from 2EIAS
and 2EGTR , respectively. Hence, the eﬀect of twobody Coulomb interaction has a decisive eﬀect on the
average energy EDIAS , while the spin-orbit and residual isospin and spin-isospin interactions play a substantial role in the average energy EDGTR − EDIAS .
More speciﬁcally, we have found that the corrections
due to quartic commutators follow the approximate
laws EDIAS − 2EIAS ≈ 23 A−1/3 MeV (even the isospin
mixing eﬀects are accounted in EIAS ) and EDGTR −EDIAS − 2(EGTR − EIAS ) ≈ 16A−1 MeV.

(1)

(2)

(3)

assuming that the ground state has good isospin;
†
∗1
∗2
∗3
∗4

(5)

EDGTR = 2EGT +is the deﬁnition of the DIAS state in terms of
the IAS that, in turn, can be written as |IAS⟩ ≡∑A
T |0⟩/⟨0|T+ T− |0⟩1/2 , where T+ = i t+ (i) and T− =∑−A
i t− (i) are the isospin raising and lowering operators, respectively.
Starting from Eq. (1) and the deﬁnitions of DIAS
and IAS previously given, one may write the excitationenergy of DIAS as
EDIAS =

2
2⟨0|[O+, [H, O−
]]|0⟩
,
2
2
⟨0|O+ O− |0⟩

where the GT transition operators are O± =∑A
i σz (i)t± (i). After some algebraic manpulations, we
can rewrite the energy of DGTR (5) as

where |0⟩ represents the ground state, and|DIAS⟩ ≡⟨0|[T+ , [T+ , [[H, T− ], T− ]]]|0⟩. (4)2(N − Z)(N − Z − 1)

Reference

Condensed from the article in Phys. Rev. C. 101, 014320(2020)
Dipartimento di Fisica, Università degli Studi di Milano
INFN, Sezione di Milano
RIKEN Nishina Center
Center for Mathematics and Physics, the University of Aizu

1) M. Takaki et al., Proposal for Nuclear Physics Experiment at RI Beam Factory, “Search for double GamowTeller giant resonances in ββ-decay nuclei via the heavyion double charge exchange 48 Ca(12 C, 12 Be(0+2 )) reaction.”- 39 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Exotic nuclear shape due to cluster formation at high angularmomentum†Balaram Dey,∗1 Shan-Shan Wang,∗2 Deepak Pandit,∗3 Srijit Bhattacharya,∗4 Xi-Guang Cao,∗5 Wan-Bing He,∗6
Yu-Gang Ma,∗7 N. Quang Hung,∗8 and N. Dinh Dang,∗9
It is now well established that clustering plays a very
important role in self-conjugate light nuclei and is also
associated with strongly deformed shapes of nuclei.1,2)
One of the probes to study this deformation experimentally at high temperature (T ) and angular momentum (J) is the γ-decay from the giant dipole resonance(GDR) built on excited states.1,2) The GDR lineshapegets fragmented in deformed nucleus providing crucial
information about the nuclear deformation. As a matterof fact, it has been successfully employed experimentallyto study the Jacobi shape transition, an abrupt changeof shape from non-collective oblate to collective triaxial
or prolate shape above a critical spin, in several light nuclei such as 31 P, 45 Sc, 46 Ti and 47 V.1,2) However, when
this shape transition is examined in self-conjugate nuclei 32 S1) and 28 Si2) through the reactions 20 Ne + 12 C
and 16 O + 12 C, respectively, the GDR lineshape fragments into two prominent peaks at high J(∼20h̄) providing a direct evidence of the large deformation but,intriguingly, the shapes found are completely diﬀerent
from those seen from Jacobi shape transition (signatureof which is a sharp peak at 10 MeV arises due to the
Coriolis splitting of the GDR frequencies). Therefore,
these observations clearly highlight that the clustering
is not only important in mass A < 20 region but could
also play major role in A ∼ 30, which has not beenstudied enough.
Microscopic eﬀects such as shell structure, pairingand isospin eﬀects play important role in deciding thenuclear structures at low excitation energy. However,even after incorporating these eﬀects, the experimental GDR lineshapes (T ∼ 2.0 MeV and J ∼ 20h̄)
could not be explained for 28 Si and 32 S nuclei.3) In thepresent work, an extended quantum molecular dynamics (EQMD) model4) has been carried out to understandthe GDR lineshapes of 28 Si and 32 S nuclei, and to inves†
∗1
∗2
∗3
∗4
∗5
∗6
∗7

∗8
∗9

Condensed from the article in Phys. Rev. C 102, 031301(R)(2020)
Bankura University
Shanghai Institute of Applied Physics, Chinese Academy of
Sciences
Variable Energy Cyclotron Centre
Dept. of Phys., Barasat Govt. College
Shanghai Advanced Research Institute and Zhangjiang Laboratory
Key Laboratory of Modern Physics and Ion-Beam application(MOE), Institute of Modern Physics, Fudan University
Shanghai Institute of Applied Physics, Chinese Academy of
Sciences, and Key Laboratory of Modern Physics and IonBeam application (MOE), Institute of Modern Physics, Fudan
University
Institute of Fundamental and Applied Sciences, Duy Tan University
RIKEN Nishina Center

Fig. 1. EQMD calculations for both 32 S and 28 Si nuclei.

tigate how the exotic shapes due to cluster formation
at high T and J are manifested through GDR strength
function.
The results of EQMD calculation have been comparedwith the existing experimental data of 32 S and 28 Si as
shown in Fig. 1. It should be mentioned that the alphacorrelation is included in the EQMD model based on
the fact that the many body nucleon-nucleon correlation
is intrinsically embedded in all microscpic QMD typemodel and the details of EQMD results are discussed inRefs. 3, 4). It is found that the EQMD predicts the general trend of the experimental GDR strength functionsfor 32 S and 28 Si by considering the ring or toroidal conﬁguration. Nevertheless, the peak around 25 MeV canonly arrive due to cluster formation highlighting the existence of the α-clustering structure at such high T and J
since this peak could not be predicted within the meanﬁeld calculations. Interestingly, the rotation of these
exotic shapes will not lead to the Coriolis splitting of
the GDR strength function (due to larger moment of inertia leading to smaller angular frequency), which could
be the reason for the absence of the Jacobi shape transition in 32 S and 28 Si. The present result highlights therole of α cluster states above the decay threshold, whichis still an open ﬁeld of investigation.
References

1) D. Pandit et al., Phys. Rev. C 95, 034301 (2017).
2) B. Dey et al., Phys. Rev. C 97, 014317 (2018).
3) B. Dey et al., Phys. Rev. C 102, 031301R (2020).
4) W. B. He et al., Phys. Rev. Lett. 113, 032506 (2014).

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1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Probing dilute nuclear density by antiproton-nucleus scattering†
K. Makiguchi,∗1 W. Horiuchi,∗1 and A. Kohama∗2

16

10Theory
Expt.

14

10

12

dσ/dΩ (mb/sr)

10

40
8
p-- Ca (x10 )

1010
10

8

106

16
4
p-- O (x10 )

104
10

2

10

0

10

-2

10

-4

180 MeV
0

10

12
p-- C

20

30

40

50

60

Fig. 1. Elastic scattering diﬀerential cross sections for
antiproton-nucleus scattering at 180 MeV/nucleon
adopted from the original paper.

∗1
∗2

1.8
1.7
1.6
1.5

31

F (halo)(nonhalo)
29
F

1.4
100

1000

Incident energy (MeV)
Fig. 2. Ratio of total reaction cross sections of 29, 31 F for
antiproton and proton scattering as a function of the incident energy adopted from the original paper.

cantly consistent with the experimental data without
any adjustable parameter using harmonic-oscillator typedensity distributions that reproduce the observed charge
radii.
We found that strong absorption occurs even beyond
the nuclear radius owing to the large p̄N elementarycross sections, resulting in strong sensitivity in the nuclear tail. This sensitivity is quantiﬁed by taking an
example of a possible halo nucleus 31 F, which is locatedat the ﬂuorine dripline; however, the antiproton scattering on unstable nuclei is still not feasible. According to
the investigations in Ref. 4) the shell gap between 0f7/2
and 1p3/2 orbits is essential and the dominance of the(1p3/2 )2 conﬁguration forms the halo structure in 31 F.
We considered these density distributions of 31 F with
(1p3/2 )2 (halo) and (0f7/2 )2 (nonhalo) dominance from
Ref. 4) and calculated the ratio of the total reaction crosssections of antiproton and proton scattering. Figure 2
displays the ratios of 31 F as a function of incident energy.
The ratios of 29 F with harmonic-oscillator type density
distributions are also plotted for comparison. 31 F withthe halo tail yielded the largest ratios, while the nonhalo density produced almost the same behavior as 29 F,
which demonstrates the advantage of antiproton scattering in the analysis of dilute density distribution.
Referencesθ (deg)†1.9

Cross section ratio

Nuclear density distributions are the basic propertiesof atomic nuclei. Traditionally, the charge density distributions have been measured using electron-nucleus scattering. Hadronic probes have been used to study matter
density distributions, especially via proton-nucleus scattering. Recently, we proposed a practical approach to
extract the nuclear surface diﬀuseness of unstable nuclei using proton-nucleus elastic scattering diﬀerential
cross sections.1,2) As a natural extension of the previous study, we investigated antiproton-nucleus scattering because it could provide a diﬀerent sensitivity to
the nuclear structure than the proton probe because theantiproton-nucleon (p̄N ) total cross sections are typically 3–4 times larger than those of N N at incident energies varying from a few hundreds to thousands MeV.
High-energy antiproton-nucleus reactions can be efﬁciently described by the Glauber model.3) The total
reaction and elastic scattering cross sections can be obtained by evaluating the optical phase-shift functioneiχ(b) as a function of the impact parameter vectorb. ∫ In optical limit approximation, we have iχ(b) =− ρN (r)ΓN̄ N (b − s) dr, where r = (s, z) with z denoting the beam direction, nucleon (N ) one-body density ρN (r), and antinucleon-nucleon N̄ N proﬁle function
ΓN̄ N (b). The parameters of the proﬁle function were determined to reproduce the p̄N and p̄-12 C cross-section
data. The validity of the present model is demonstrated
in Fig. 1. The theoretical cross sections were signiﬁ-

Condensed from the article in Phys. Rev. C 102, 034614(2020)
Department of Physics, Hokkaido University
RIKEN Nishina Center

1) S. Hatakeyama, W. Horiuchi, A. Kohama, Phys. Rev. C
97, 054607 (2018).
2) S. Hatakeyama, W. Horiuchi, A. Kohama, RIKEN Accel.
Prog. Rep. 52, 7 (2019).
3) R. J. Glauber, in Lectures in Theoretical Physics, edited
by W. E. Brittin, L. G. Dunham (Interscience, New York,
1959).
4) H. Masui, W. Horiuchi, and M. Kimura, Phys. Rev. C
101, 041303(R) (2020).

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II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Nuclear charge radii with a trained feed-forward neural network†
D. Wu,∗1 C. L. Bai,∗1 H. Sagawa,∗2,∗3 and H. Q. Zhang∗4
During the last few decades, theoretical and experimental studies of the isotopic changes of ground- andlow-lying states have been performed intensively to elucidate the evolution of the shell structure, shape coexistence phenomena, and shape transitions. In particular, charge radii and electromagnetic moments are very
sensitive quantities from which precise information of
the nuclear structure can be extracted.
Machine learning (ML) is one of the most popular algorithms for dealing with complex systems owing to its powerful and convenient inference abilities.
The neural network, which is an algorithm of machinelearning, has been widely used in diﬀerent ﬁelds: artiﬁcial intelligence (AI), medical treatment, and physics
of complex systems. In this work, we attempt to train
a ML model for a description of the nuclear charge
radii based directly on some experimental or quasiexperimental data, such as proton and neutron numbers, shell eﬀect, and deformation. We search for any
other physical quantities that are correlated to thecharge radii.
To this end, we employ a standard fully connected
feed-forward neural network (FNN), which can build acomplex mapping between the input space and output
space through multiple compounding of simple nonlinear functions. The FNN is a multilayer neural network with an input layer, hidden layers, and an output
layer. The structure of the neural network is labelled
as [N1 , N2 , . . ., Nn ], where Ni denotes neuron numbers of the ith layer and i = 1 and n represent the
input and output layer, respectively. In this study, we
adopt the input layer N1 = 3 and the output layer
Nn = 1. The model is trained with the input data setof proton number Z, neutron number N , the excitation energy of the ﬁrst 2+ state E2+ , and the symmetry
1energy. The deformation and shell eﬀects on charge radius are included by the E2+ values. We adopt as the1data set all the nuclei for which the experimental values of both E2+ , and charge radii are available. The
1data set includes 347 nuclei in total. As the data set
is not large enough, we must choose a small network
structure, which includes 44 neurons and involves 201
parameters.
In the present ML study, all the charge radii of Ca,
Sm, and Pb isotopes are included in the testing set
to check the prediction power of models. The model
reproduces well not only the slope of isotopic depen†
∗1
∗2
∗3
∗4

Fig. 1. Charge radii of Ca isotopes calculated by the modeltrained with and without taking the symmetry energy
input into account. The ML results obtained with andwithout the symmetry energy input are labelled by the
red stars and green diamonds, respectively. The experimental data taken from Refs. 1), 2) are labelled by thefilled black circles.

dence, but also the kink of charge radii at the magic
numbers N = 82 of Sm isotopes and N = 126 of Pb
isotopes. The obtained charge radii of Ca isotopes
with and without symmetry energy input are shownin Fig. 1. Experimental results taken from Refs. 1),2) show a sharp kink structure at N = 28 and a peak
between two closed shells at N = 20 and 28, followed
by a rapid increase after N = 28. This ﬁgure indicatesthat the symmetry energy input is critical for the qualitative and quantitative description of the Ca isotopes.
We also perform Hartree-Fock-Bogolyubov (HFB)
calculations for the radii of Ca isotopes. The HFB
calculations show a clear correlation between the symmetry energy and charge radii in Ca isotopes as far as
the absolute magnitude is concerned. Whereas the MLshows that the symmetry energy input has a remarkable eﬀect on the precise descriptions of charge radii of
Ca isotopes including the kink structure, the HFB calculation shows that the symmetry energy changes theabsolute magnitude of charge radii, but the kink structure at N = 28 is not well reproduced. The physicalimplication of the present successful ML study remains
an open question and needs to be studied in the future.
References

Condensed from the article in Phys. Rev. C. 102, 054323(2020)
College of Physics, Sichuan University
RIKEN Nishina Center
Center for Mathematics and Physics, University of Aizu
China Institute of Atomic Energy

1) R. F. Garcia Ruiz et al., Nat. Phys. 12, 594 (2016).
2) I. Angeli, K. P. Marinova, At. Data Nucl. Data Tables 99, 69 (2013).

- 42 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Eﬀects of ﬁnite nucleon size, vacuum polarization, andelectromagnetic spin-orbit interaction on nuclear binding energies
and radii in spherical nuclei†
T. Naito,∗1,∗2 X. Roca-Maza,∗3,∗4 G. Colò,∗3,∗4 and H. Z. Liang∗1,∗2
In the density functional theory (DFT) for nuclear
physics, the ground-state energy is usually given by
Egs = T0 + Enucl [ρp , ρn ] + ECd [ρch ] + ECx [ρch ], where
T0 is the Kohn-Sham kinetic energy and Enucl , ECd ,and ECx are the energy density functionals (EDFs) of
the nuclear, Coulomb direct, and Coulomb exchange
parts, respectively. Here, ρp and ρn are the groundstate density distributions of protons and neutrons,
respectively, and ρch is the charge density distribution.
The Coulomb EDF EC = ECd + ECx is, in principle,
written in terms of the charge density ρch 1) because the
Coulomb interaction involves the charge itself, insteadof the point protons. Nevertheless, the protons andneutrons are assumed to be point particles, i.e., ρch ≡ρp , in most self-consistent nuclear DFT calculations.
In this paper, the ﬁnite-size eﬀects of nucleons are implemented to the self-consistent steps of the Skyrme
Hartree-Fock calculation, where only the electric form
factors of nucleons are considered. The Coulomb direct term ECd holds the conventional form, while themodiﬁed Perdew-Burke-Ernzerhof GGA Coulomb exchange functional 2,3) is used instead of the exact Fockterm.
The charge density distribution ρch is written interms of ρp , ρn , and the electric form factors ofprotons( ) and neutrons,( G̃) Ep and G̃En , as ρ̃ch (q) =G̃Ep q 2 ρ̃p (q) + G̃En q 2 ρ̃n (q), where the quantities
with the tilde denote those in the momentum space.
Once the ﬁnite-size eﬀects are considered, i.e., ρch ̸≡ρp , the chain rule of the functional derivative should
be applied to derive the eﬀective potential of the nuδE[ρ ,ρ ]cleon τ , Veﬀτ (r) = δρτp(r)n . Finally, the Coulomb
potential for nucleons with the ﬁnite-size eﬀects reads
VCτ (r) = {VC [ρch ] ∗ GEτ } (r), where VC [ρch ] is theconventional form of the Coulomb potential and ∗ denotes the convolution. The Coulomb potential forthe neutrons does not vanish within the self-consistentﬁnite-size eﬀects, because GEn ̸≡ 0.
Other possible electromagnetic (EM) contributions,
i.e., the vacuum polarization and EM spin-orbit interaction, are also considered. We used eﬀective one-bodypotential of the vacuum polarization for a charged
particle under the Coulomb potential caused by ρch ,known as the Uehling potential.4) The EM spin-orbit
†
∗1
∗2
∗3
∗4

interaction, which originates from the interaction between the nucleon spin and VCτ , is also considered byusing the ﬁrst-order perturbation theory.
The isospin-symmetry breaking (ISB) terms of thenuclear force are also implemented to compare the contributions of the EM interaction with those of the ISB
terms of nuclear force. The SAMi functional5) is used
for the nuclear EDF for most calculations, and the
SAMi-ISB functional6) is used instead when the ISB
originating from Enucl is considered explicitly.
The proton ﬁnite-size eﬀect makes the nuclei morebound; for example, the nucleon ﬁnite-size eﬀect decreases the binding energy by 8.2 MeV in 208 Pb. In
contrast, the neutron ﬁnite-size eﬀect makes the nuclei
less bound, and its contribution is almost one order ofmagnitude smaller than the proton contribution, forexample, by 1.2 MeV in 208 Pb, which is non-negligible
in heavy nuclei. The contribution of the vacuum polarization to the total energy is also non-negligible, and it
makes the nuclei less bound, for example, by 3.7 MeV
in 208 Pb. The contribution of the electromagnetic spinorbit interaction to the total energy is approximately
50 keV. Systematically, the contribution of the ISB
terms of the nuclear force to the total energy is comparable to that of the proton ﬁnite-size eﬀect in heavy
nuclei, while the former is more signiﬁcant than thelatter in light nuclei. The neutron ﬁnite-size eﬀect andvacuum polarization are also non-negligible. On theother hand, the contribution of the electromagnetic
spin-orbit interaction to the total energy depends on
the shell structure.
The mass diﬀerence between the mirror nuclei 48 Ca
and 48 Ni was also calculated. All the corrections to the
Coulomb functional with the SAMi-ISB functional cooperate to reproduce the mirror-nuclei mass diﬀerence
within 300 keV accuracy, while the error is 1.5 MeV if
the conventional Coulomb functional is used.
References
1) A. Bulgac, V. R. Shaginyan, Nucl. Phys. A 601, 103(1996).
2) J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett.
77, 3865 (1996).
3) T. Naito, X. Roca-Maza, G. Colò, H. Liang, Phys. Rev.
C 99, 024309 (2019).
4) E. A. Uehling, Phys. Rev. 48, 55 (1935).
5) X. Roca-Maza, G. Colò, H. Sagawa, Phys. Rev. C 86,
031306 (2012).
6) X. Roca-Maza, G. Colò, H. Sagawa, Phys. Rev. Lett.
120, 202501 (2018).

Condensed from the article in Phys. Rev. C 101, 064311(2020)
Department of Physics, The University of Tokyo
RIKEN Nishina Center
Dipartimento di Fisica, Università degli Studi di Milano
INFN, Sezione di Milano- 43 -

1

II-2. Nuclear Physics (Theory)

RIKENAccel.
Accel.Prog.
Prog. Rep.
Rep. 54
RIKEN
54(2021)(2021)

Trajectory in 2D plot of IS and IV densities of 48 Ca and 208 Pb†
S. Yoshida,∗1 H. Sagawa,∗2,∗3 J. Zenihiro,∗2,∗4 and T. Uesaka∗2

†
∗1
∗2
∗3
∗4

Condensed from the article in Phys. Rev. C 102, 064307(2020)
Science Research Center, Hosei University
RIKEN Nishina Center
Center for Mathematical Sciences, the University of Aizu
Department of Physics, Kyoto University

0.025

48

Ca

0.020

IV ( fm-3 )Recently, the neutron skin thicknesses of doubly
48
closed shell nuclei 208
82 Pb126 and 20 Ca28 have been investigated intensively. Theoretical studies with modern energy density functionals (EDFs) indicate that the
thickness of the neutron skin, ∆rnp ≡ rn − rp , embodies
the stability of pure neutron matter and provides important information on the symmetry energy of neutron
matter equation of states (EoS), which is a sum of thewell-known EoS of the symmetric nuclear matter andthe symmetry energy. The two EoSs govern the formation of not only nuclei but also astrophysical phenomena
such as neutron stars and supernova explosions.
In this paper, we propose a model to examine the details of the symmetry energy by using the isoscalar (IS)and isovector (IV) density distributions. The neutron
skin is an integrated quantity extracted from neutron
and proton density distributions. However, the radial
density distributions will provide more information to
elucidate quantitatively the EoS of both nuclear matterand neutron matter. To this end, it is essential to study
the radial dependence of IS and IV densities, which canbe extracted from neutron and proton densities.
The IS and IV densities are deﬁned as ρIS (r) =ρn (r) + ρp (r) and ρIV (r) = ρn (r) − ρp (r), respectively.
Experimental IS and IV densities of 48 Ca1) are plottedin Fig. 1. The solid black curve sandwiched by the dotted lines is the experimental trajectory of IS versus IV
densities at diﬀerent radii r. The equi-energy contour
lines of HF EDF, ε(ρn , ρp ) = ε(ρIS , ρIV ) = constant, arecalculated using SAMi-J27 and plotted for the values
from 3 MeV at ρIS = ρIV ≈ 0 to −15 or −16 MeV at thesaturation density ρIS ≈ 0.16 fm−3 with an energy stepof 1 MeV.
The dashed lines correspond to the constant IV density line ρIV = ρIS (N − Z)/A of the asymmetric nuclear matter. The experimental trajectory is above theconstant density limit in the surface region. This feature suggests a strong IV pressure to push the IV density towards the surface region rather than the interiorof nucleus. The Fermi liquid of a ﬁnite nucleus may
ﬁll the valley determined by EDF from the bottom atapproximately ρIS = 0.16 fm−3 to the top of valley atρIS = ρIV = 0.0 fm−3 . The trajectory plots are started
from the right-hand side at r = 0 fm and ends at theleft corner at r = 6 fm. The dots on the solid line indicate diﬀerent radius points with r = 0, 1, 2, 3, . . . fm
from the right to the left. The positive IV density at
r = 0 fm reﬂects a larger neutron density than that of

r=4

0.015
r=3

r=0

0.010 r = 5
r=2

0.005

0.000
0.00

SAMi-J27
SAMi-J29
SAMi-J31

r=6
0.05

0.10

r=1

SAMi-J33
SAMi-J35
Exp.

0.15

0.20

IS ( fm-3 )Fig. 1. Trajectories of isoscalar (IS) and isovector (IV) densities of 48 Ca. The experimental curve (black solid line)
is compared with theoretical ones with Skyrme interactions. The equi-energy contour lines are calculated using
the SAMi-J family. The equi-energy contour lines areplotted for SAMi-J27. See the text for details.

protons at the central region corresponding to r = 0 fm.
Keeping the ρIS almost constant, the experimental curve
rises to the surface region at r = 3 fm, where the dots
are separated largely because of a rapid change in the
IV density. This can be understood qualitatively froma ﬂat contour map around the IS density ρ = 0.16 fm−3
so that the IV density can have large freedom within thelimit of the equi-energy contour line.
We can see a clear J-dependence for the enhancementof IV density at r = 4 fm; a larger J value yields agreater neutron density at the surface. Compared withthe experimental data, SAMi-J27 shows the best agreement in the entire region of this plot.
In summary, we propose a new 2D plotting methodof IS-IV densities to extract not only the empirical symmetry energy coeﬃcients J, L, and Ksym , but also theasymmetric isospin term Kτ in the nuclear incompressibility. We found strong correlations between the curvature of the 2D density at the density ρIS = 0.1 fm−3 andthe symmetry energy coeﬃcients J, L, and Kτ . The
optimal values are found to be J = 27.2 MeV, L =31.6 MeV, Ksym = −154.7 MeV, and Kτ = −300.6 MeV
for the SAMi-J EDF from the IS-IV density plots of 48 Ca
and 208 Pb.
Reference

1) J. Zenihiro et al., arXiv:1810.11796 (2018).

- 44 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Energy-weighted sum rule for Gamow-Teller giant resonances inhigh-spin isomeric states of N = Z nuclei†
M. Sasano,∗1 H. Sagawa,∗1,∗2 T. Suzuki,∗3,∗4 and M. Honma∗2
Among collective modes,1) the Gamow-Teller (GT)
giant resonance is an interesting excitation mode. It isa 0 h̄ω excitation that is characterized by the quantumnumber changes in the orbital angular momentum(∆L = 0), spin (∆S = 1), and isospin (∆T = 1).
It is induced by the transition operator στ .
Recently, an experimental project was proposed tomeasure the GT transitions from the 52 Fe(12+ ) highspin isomeric state provided as an RI beam.2) Inspiredby this, herein, we derived an energy-weighted sum
rule (EWSR) to estimate the energies of GT giant resonances in high-spin isomeric (HSI) states in N = Z
nuclei and evaluated the spin and isospin residual interactions by comparing the EWSR with the shell model
calculations.
The sum rules provide a reliable tool for evaluating
the natures of giant resonances. In the calculations ofsum rules, the contributions from all the ﬁnal states
are summed up. Therefore, the sum-rule values solely
depend on the properties of the initial ground state
and the Hamiltonian of the system, but they are notsensitive to the details of the ﬁnal states. Roughly
speaking, the non-energy-weighted sum rule (NEWSR)
provides a criterion for the collectivity of the observed
resonances, while the EWSR provides a measure of theinteraction strength driving the oscillation.
By dividing EWSR with NEWSR, the average energy of the resonance can be derived. We found that,with the simple Bohr-Mottelson Hamiltonian,3) the average energy relation is written as
ν=−1
ν=−1
EGT
− EM1
=4

κστ − κσ⟨i |S0 | i⟩ .
A

instead of κστ −κσ , κστ −κτ appears. The GT energies
in high-spin isomers with N = Z have diﬀerent sensitivies from those in N > Z 0+ nuclei. This is because
these states have diﬀerent symmetries in the spin andisospin space.
We used the newly derived energy relation to analyze the results of the shell model calculations for the
GT transition from 52 Fe(12+ ) and 94 Ag(21+ ) N = Z
high spin isomers. In the shell-model calculations, theeﬀective interactions, GXPF1J5) and PIGD5G36) wereused for Fe and Ag, respectively. From the analysis,κστ − κσ was derived as 20.4–20.5 MeV. By assuminga κστ value of 23 MeV, the strength of the spin residual interaction, κσ was deduced as 2.5 MeV. Thus, wedemonstrated that the GT energies in high spin isomers are useful for evaluating the short-range part ofthe spin residual interaction, which is important to describe the onset of the pion condensation in nuclear
matter.
We thank Haozhao Liang for the valuable discussions.
This work was supported in part by
JSPS KAKENHI (Grant Numbers JP19K03858 and
JP19K03855).
References

1) M. N. Harakeh, A. M. van der Woude, Giant Resonances, (Oxford University Press, Oxford, 2001).
2) K. Yako et al., private communications.
3) A. Bohr, B. R. Mottelson, Nuclear Structure SingleParticle Motion, Vol.I, (Benjamin, New York 1969).
4) T. Suzuki, Phys. Lett. B 104, 92–94 (1981); T. Suzuki,
Nucl. Phys. A 379, 110–124 (1982).
5) M. Honma et al., J. Phys. Conf. Series 20, 002 (2005).
6) M. Honma et al., RIKEN Accel. Prog. Rep. 48, 77(2015).

(1)

Here, κστ and κσ are the spin-isospin and spin coupling
constants used in the hamiltonian. A is the mass numν=−1
ν=−1
ber of the nucleus. ⟨i |S0 | i⟩, and EGT
and EM1
correspond to the expectation value of the spin excess
along the elongation axis of the nucleus, the averageenergies of the GT and M1 transitions, respectively.
This relation is analogous to the average energy relation derived in Ref. 4) for N > Z 0+ nuclei. In thelatter case, the left-hand side of the relation is the energy diﬀerence between the GT giant resonance andthe isobaric analog state. ⟨i |S0 | i⟩ in the right-handside is replaced with the neutron excess N − Z. Thus,
†
∗1
∗2
∗3
∗4

Condensed from the article in Phys. Rev. C 103, 014308(2021)RIKEN Nishina Center
Center for Mathematics and Physics, University of Aizu
Department of Physics, College of Humanities and Science,
Nihon University
National Astronomical Observatory of Japan- 45 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A fully microscopic model of total level density in spherical nuclei†
N. Quang Hung,∗1,∗2 N. Dinh Dang,∗3 L. Tan Phuc,∗1,∗2 N. Ngoc Anh,∗4 T. Dong Xuan,∗1,∗2 and T. V. Nhan Hao5

†
∗1
∗2
∗3
∗4
∗5

10 6

108 Exp. data
106k Vib =1

10 4
10(a) 60Ni

2100
0Exp. data

Ref. 4)
Ref. 5)
Ref. 6)

λ = 0,+ 1λ = 0,+ 1,- 2+
λ = 0,+ 1,- 2,+ 3+ + -ρ (MeV -1)

ρ (MeV -1)

The nuclear level density (NLD) is one of important inputs for the calculations of low-energy nuclear
reactions and astrophysics. It also contains various information on the internal structure of atomic nuclei
such as single-particle levels, pairing correlations, spin
distributions, collective (vibrational and/or rotational)
excitations, nuclear thermodynamics, etc. Althoughmany theoretical studies have been carried out during
the last seven decades to ﬁnd a reliable and fully microscopic model of NLD, there has still been lacking a fully
microscopic NLD model. Recently, we have proposeda microscopic NLD model based on the exact pairing
plus independent-particle model at ﬁnite temperature(EP+IPM).1) The latter, which has a very short computing time and contains no ﬁtting parameters to theexperimental NLD data, can describe quite well the
NLDs and thermodynamic properties of several hot
nuclei. Nevertheless, the EP+IPM still contains two
shortcomings, which limit its fully microscopic foundation. These shortcomings come from the use of empirical formulas for the spin cut-oﬀ σ and collective
enhancement factors. The latter is a multiplication of
the vibrational kvib and rotational krot enhancement
factors.1)
In this paper, we develop a fully microscopic version of the EP+IPM, limited to spherical nuclei (rotational enhancement factor krot = 1), in which threesigniﬁcant improvements are included. First, thesingle-particle spectra are taken from the HartreeFock mean ﬁeld plus exact pairing (HF+EP) with aneﬀective MSk3 interaction,2) instead of the WoodsSaxon potential in the original version of EP+IPM.
Second, the spin cut-oﬀ parameter is directly calculated by∑using the statistically() thermodynamic method
σ 2 = 12 k m2k sech2 12 Ek /T , where mk is the singleparticle spin projection (in the deformed basis) and
Ek is the quasiparticle energy. Last, the vibrational enhancement of NLD is directly calculated
based on the vibrational partition function Zvib (T ) =∑−Eiλ /T, where Eiλ are all the eigenvalues
λ,i (2λ + 1)eobtained by solving the self-consistent HF+EP+RPA(SC-HFEPRPA) equation3) for the corresponding multipolarity λ, which runs from 0 to 5. The total partition function of the system is then calculated by combining this vibrational partition function with that

λ = 0, 1, 2, 3, 4+
λ = 0,+ 1,- 2,+ 3,- 4,+ 5-

5

10 15 20 25
E* (MeV)

10

4Ref. 7)
Ref. 8)10 2(b) 90Zr100

λ = 0,+ 1λ = 0,+ 1,- 2+
λ = 0,+ 1,- 2,+ 3- +λ = 0,+ 1,- 2,+ 3,- 4
λ = 0,+ 1,- 2,+ 3,- 4,+ 5-0k Vib =1

4

8

E* (MeV)

12

Fig. 1. Total NLDs obtained within the fully microscopic
EP+IPM by gradually adding higher collective vibrational modes λ to the vibrational partition function versus the experimental data for 60 Ni (a) and 90 Zr (b).
Experimental data are taken from Refs. 4–8).

of the EP+IPM (without vibrational enhancement),′′′= ln ZEP+IPM+ ln Zvib, where Z ′ (T )namely ln Ztotal
is the excitation partition function.1)
The numerical tests for two spherical 60 Ni and 90 Zr
nuclei (see Fig. 1) show that the monopole and dipole
excitations (λ = 0+ and 1− ) have little enhancement to
the total NLD. By adding the quadrupole λ = 2+ and
octupole 3− excitations, the EP+IPM NLDs are in excellent with the experimental data. However, adding
higher hexadecapole λ = 4+ and quintupole λ = 5−
excitations enhances the NLD further but the results
obtained slightly overestimate the experimental data
because these states are always located at a very highexcitation energy, which goes beyond the vibrational
excitation region. The results shown in Fig. 1 are ofparticular valuable as they are the ﬁrst microscopic
calculation, which conﬁrms the important role of thequadrupole and octupole excitations in the descriptionof NLD. We also found that the vibrational enhancement factor obtained within our fully microscopic approach is smaller than that calculated using the empirical and phenomenological formulas. In addition,
the spin cut-oﬀ factor obtained within our microscopic
approach are larger than that obtained by using theempirical formula.
References

1) N. Q. Hung, N. D. Dang, L. T. Q. Huong, Phys. Rev.
Lett. 118, 022502 (2017).
2) L. T. Phuc, N. Q. Hung, N. D. Dang, Phys. Rev. C 97,
024331 (2018).
3) L. T. Phuc, N. Q. Hung, N. D. Dang, Phys. Rev. C 99,
064322 (2019).
4) A. V. Voinov et al., Phys. Rev. C 76, 044602 (2007).
5) J. R. Huizenga et al., Phys. Rev. 182, 1149 (1969).
6) A. V. Voinov et al., EPJ Web Conf. 21, 05001 (2012).
7) https://www-nds.iaea.org/RIPL-3/ .
8) Y. Byun et al., Phys. Rev. C 90, 044303 (2014).

Condensed from the article in Phys. Lett. B 811, 135858(2020)
Institute of Fundamental and Applied Sciences, Duy Tan
University
Faculty of Natural Sciences, Duy Tan University
RIKEN Nishina Center
Dalat Nuclear Research Institute, Vietnam Atomic Energy
Institute
Faculty of Physics, Hue University of Education- 46 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Isobaric analog state energy in deformed nuclei: A toy model†
X. Roca-Maza,∗1,∗2 H. Sagawa,∗3,∗4 and G. Colò∗1,∗2
The eﬀects of deformation on the energy of the isobaric analog state (IAS) are studied through microscopic
deformed Hartree-Fock-Bogolyubov calculations. A simple yet physical toy model is also presented to provide
guidance when predicting unknown IAS energies of deformed nuclei. The deformed HFB calculations are performed for several neutron-deﬁcient medium-mass andheavy nuclei to predict the IAS energies.
Isospin is one of the most important (approximate)symmetries in nuclei. The validity of isospin symmetry
has been established by the experimental observationof IASs by charge-exchange reactions. Recently, thesestates have been investigated extensively in connection
with the symmetry energy, particularly to determine theso-called slope parameter L. Thus far, theoretical studies
of IAS have mainly focused on spherical nuclei such as
48
Ca, 90 Zr, and 208 Pb. However, a large number of deformed nuclei exist, but transparent information on theeﬀects of deformation on IAS is still lacking. In this paper, we derive a general formula for the eﬀects of deformation on the Coulomb direct contribution to the energyof the IAS and provide a simple albeit physical model.
Then, we study several neutron-deﬁcient medium-massand heavy nuclei, which are now planned to be studied
experimentally in RCNP, Osaka within the LUNESTAR
project.
The IAS energy EIAS can be deﬁned as the energy
diﬀerence between the analog state |A⟩ and the parent
state |0⟩ as follows:
EIAS = ⟨A|H|A⟩ − ⟨0|H|0⟩ =⟨0|T+ [H, T− ]|0⟩, (1)⟨0|T+ T− |0⟩∑A
where T± = i t± (i) are the isospin raising/lowering
operators. The direct Coulomb term of IAS energy foran axially symmetric nucleus can be evaluated as[β2n β2p
Cd,sphCd
EIAS = EIAS
1−4π]
(β2n − β2p )(β2n + β2p ) (β2n − β2p )2
+
,(2)
+
4π
4π
where β2n(2p) is the quadrupole deformations for neutrons (protons). For β2n = β2p , this reduces to[]
β2
Cd,sphCd
1− 2 .
(3)= EIAS
EIAS
4π
From Eq. (3), one should expect that a larger quadrupole
deformation corresponds to a smaller IAS energy. Fora qualitative understanding of the eﬀect of deformation
†

∗1
∗2
∗3
∗4

Condensed from the article in Phys. Rev. C102, 064303 (2020)
Dipartimento di Fisica, Università degli Studi di Milano
INFN, Sezione di Milano
RIKEN Nishina Center
Center for Mathematics and Physics, the University of Aizu

Table 1. Results of deformed HFB calculations with SAMi
HFB
EDF.1) All energies are in MeV. EIAS
is the sum of thedirect Coulomb, exchange Coulomb, and isospin mixing
contributions. The deformation eﬀect on IAS energy has
HFB≡
been estimated from the HFB calculations, ∆EIAS
HFB
HFB
EIAS
(β2n , β2p ) − EIAS
(β2n = 0, β2p = 0).
Nucl.

β2n

β2p

HFB
EIAS

102
46 Pd
106
48 Cd
112
50 Sn
120
52 Te
124
54 Xe
130
56 Ba
136
58 Ce
138
58 Ce
142
60 Nd
144
62 Sm
156
66 Dy
158
66 Dy
162
68 Er
164
68 Er
168
70 Yb
174
72 Hf
176
72 Hf
180
74 W
184
76 Os
190
78 Pt
196
80 Hg

0.186
0.255
0.192
0.039
0.000
0.000
0.126
0.040
0.000
0.000
0.201
0.197
0.348
0.346
0.385
0.304
0.267
0.278
0.335
−0.147−0.180

0.174
0.256
0.199
0.042
0.000
0.000
0.158
0.047
0.000
0.000
0.225
0.217
0.378
0.377
0.413
0.319
0.276
0.299
0.355
−0.141−0.18713.34613.81014.08514.35314.74915.11415.35215.33115.50915.95016.75516.72316.97516.88117.17117.62917.53817.91118.22318.64918.906exp 2)
EIAS

14.01916.07516.861
16.77817.388

HFB∆EIAS−0.162−0.089−0.001−0.0010.000
0.000−0.081−0.0100.000
0.000−0.003−0.028−0.112−0.110−0.212−0.091−0.086−0.101−0.171−0.037−0.070on the IAS energy, Eq. (3) predicts, for very deformed
nuclei with β2 ≈ 0.8, a relative reduction in EIAS ofapproximately 5% with respect to the spherical nucleus.
Table 1 lists the results of deformed HFB calculations
for several neutron-deﬁcient nuclei as predicted by SAMi
HFB
is the sum of the direct Coulomb, exchange
EDF. EIAS
Coulomb, and isospin mixing contributions. The deforHFB
mation eﬀect is also shown as ∆EIAS, and it varies from168
Yb at the maximum to zero for no de−212 keV information cases.
The deformed HFB results reproduce well the experimentally known IAS energies within an error of approximately100 keV and previde a good guide for the experimental search for new IAS states of these neutrondeﬁcient nuclei. In general, the deformation eﬀect issmall, but it might be important for the precise prediction of IAS energy within an accuracy of several tenthsof keV.
References

1) X. Roca-Maza, G. Colò, H. Sagawa, Phys. Rev. C 86,
031306 (2012).
2) M. Antony, A. Pape, J. Britz, At. Data Nucl. Data Tables 66, 1 (1997).

- 47 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Parity-conserved self-consistent CHFB solution
K. Sugawara-Tanabe∗1,∗2 and K. Tanabe∗3
We developed a new program for solving the constrained Hartree-Fock-Bogoliubov (CHFB) equation
without parity mixing. In this scheme (CHFB5), we
require ﬁve constraints, one each on the total angularmomentum I, proton number Z+ in the + parity shell(p+ ), proton number Z− in the − parity shell (p− ),neutron number N+ in the + parity shell (n+ ), andneutron number N− in the − parity shell (n− ). As
an example, we choose 134 Nd with the same parameter set as that adopted in Ref. 1). Here, we solved
the full CHFB equation2) including all exchange terms(Fock terms), while Ref. 1). adopts only the Hartree
terms. The values of (Z+ , Z− , N+ , N− ) are selected inreference to the usual CHFB solutions with three constraints (CHFB3). The usual CHFB3 solutions show
(Z+ , Z− , N+ , N− ) = (14.59, 17.41, 13.87, 10.13) at I =0, while (14.04, 17.96, 14.0, 10.0) at I = 26. Here,(Z, N ) = (32, 24) are numbers outside the closed core
(28, 50). Thus, we select (14, 18, 14, 10) for the CHFB5
equation. The intrinsic diﬀerence between CHFB3 andCHFB5 solutions is in the quasi-particle (QP) energies. In Fig. 1, we compare the behavior of the lowest
QP energies of Λ with its time-reversed energy Λ̃ vs.
I. The equations for Λ and Λ̃ have been provided inRef. 2). The degeneracy is lifted by the Coriolis antipairing eﬀect with increasing I. Figure 1(A) shows theneutron shell, and (B) the proton shell. In both panels, ± speciﬁes the ± shell; the ﬁlled symbols expressΛ̃ and the open symbols Λ. Those in the abbreviation “with" denote CHFB5 solutions, while the others
denote CHFB3 solutions. At low I, QP energies by
CHFB3 and CHFB5 solutions coincide in the neutron
shells (A); however, there is a considerable diﬀerence
among the p+ shell (B). The negative value of Λ in then+ shell is observed at I = 10 in both CHFB3 andCHFB5 solutions; this indicates the ﬁrst backbendingis caused by the i13/2 level in the n+ shell. There occur
negative values of Λ in the n+ and n− shells aroundI = 20 to 26, and they correspond to decreasing ∆n ,i.e., 0.00021 (CHFB3) and 0.00035 (CHFB5).

lowest QP energies  &  MeV3∗3

A Neutron shells in the Yrast band




















1































































5










10























0


n

with 10n  n  with 14
n









15













20

n with 14






 n


 n
 n with 10

25

30

35

I 

3.0

lowest QP energies  &  MeV

134

2.5





2.0
1.5








Nd

B Proton shells in the Yrast band
























































1.0
































p with 14

































0.5
0.0
0





p
p  with 18
p with 18







p

p





p





p with 14



5

10

15

20

25

30

35

I 

Fig. 1. (A) Lowest QP energies Λ and Λ̃ in the neutron shell
as functions of angular momentum I. The red opencircles represent Λ, and the red filled-circles representΛ̃ in the n+ shell by the CHFB3 solutions; the orange
open-triangles denote Λ, and the orange filled-triangles
represent Λ̃ in the n+ shell by the CHFB5 solutions.
The open squares represent Λ, and the filled squares
represent Λ̃ in the n− shell by the CHFB3 solutions,while the blue open-triangles-down represent Λ, and theblue filled-triangles-down represent Λ̃ in the n− shell by
the CHFB5 solutions. (B) The lowest QP energies ofΛ and Λ̃ in the proton shell as functions of I. The
red open-circles represent Λ, and the red filled-circles
represent Λ̃ in the p+ shell by the CHFB3 solutions,while the orange open-triangles represent Λ, and theorange filled-triangles represent Λ̃ in the p+ shell by
the CHFB5 solutions. The open squares represent Λ,and the filled squares represent Λ̃ in the p− shell by the
CHFB3 solutions, while the blue open-triangles-down
represent Λ and the blue filled-triangles-down representΛ̃ in the p− shell by the CHFB5 solutions.

References

∗2

2

Nd




1
0

1) K. Tanabe, K. Sugawara-Tanabe, Phys. Lett. 259B, 12(1991).
2) K. Sugawara-Tanabe, K. Tanabe, RIKEN Accel. Prog.
Rep. 52, 1148 (2019).

∗1






134

RIKEN Nishina Center
Department of Information Design, Otsuma Women’s University
Department of Physics, Saitama University- 48 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Role of exact treatment of thermal pairing in radiative strength
functions of 161, 163 Dy nuclei†
L. Tan Phuc,∗1,∗2 N. Quang Hung,∗1,∗2 N. Dinh Dang,∗3 L. T. Quynh Huong,∗4 N. Ngoc Anh,∗5 N. Ngoc Duy,∗6
L. Ngoc Uyen,∗7 and N. Nhu Le,∗8

where σE1 is the GDR cross section which is obtained microscopically within the PDM, ΓE1 is the temperaturedependent GDR width, and SE1 is the GDR strength
function.
Figure 1 depicts the total RSFs obtained within
the PDM with and without EP the experimental
data5) as well as those obtained within the microscopic
D1M+QRPA (E1 and E1 + M 1) and phenomenological GLO-SLO models. The results obtained show that,
due to the eﬀect of EP, the EP+PDM can describe reasonably well the RSF data in both low and high-energy
regions without adding any extra strength function. As aresult, at least eight free parameters have been reduced
within the EP+PDM calculations as compared to thedescription by the phenomenological GLO-SLO model.
†
∗1
∗2
∗2
∗3
∗4
∗5

∗6

∗7

Condensed from the article in Phys. Rev. C 102, 061302(R)(2020)
Institute of Fundamental and Applied Sciences, Duy Tan University
Faculty of Natural Sciences, Duy Tan University
RIKEN Nishina Center
Department of Natural Science and Technology, University of
Khanh Hoa
Dalat Nuclear Research Institute, Vietnam Atomic Energy InstituteDepartment of Physics, Sungkyunkwan University
Department of Engineering Science, University of ElectroCommunications
University of Education, Hue University

fRSF (Eγ ) (MeV -3 )

10-5
10-6

a) 161Dy

EP+PDM T=0.59 MeV
PDM T=0.59 MeV

10-7
161

10-8

fRSF (Eγ ) (MeV -3 ) fRSF (Eγ ) (MeV -3 )The photon or radiative strength function (RSF), deﬁned as the average electromagnetic transition probability per unit of γ-ray energy Eγ ,1) has an importantrole in the study of nuclear reaction properties such as
γ-ray emission rate, reaction cross section, and/or nuclear astrophysical processes.2) Very recently, we haveproposed a microscopic model to simultaneously describe
the nuclear level density and RSF.3) For the RSF, weemployed the phonon damping model (PDM),4) which
consistently includes the exact thermal pairing (EP), in
order to take into account both temperature-dependent
giant dipole resonance (GDR) width (within the PDM)
and thermal pairing (within the EP). The goal of thecurrent work is to shed a light on the microscopic nature of the low-energy enhancement in the RSF datacaused by the PDR (Pygmy Dipole Resonance). Three
dysprosium isotopes 161, 162, 163 Dy are selected to do
the calculations within the EP+PDM. The results will
be compared with the phenomenological models (standard Lorentzian-SLO and generalized Lorentzian-GLO)
and the other microscopic model (Quasiparticle randomphase approximation-QRPA). The RSF at each energy
Eγ and temperature T is deﬁned as follow
fE1 (Eγ , T ) =)((1)
π σE1 ΓE1 (Eγ , T )SE1 (Eγ , T )
1
,
2
2
2
3π ℏ c2Eγ

10-6Dy( 3He,3 He)
Dy( 3He,α )162
Dy(γ, n)163
Dy(γ, n)162

E1QRPA(E1+M1)QRPA

EP+PDM T=0.56 MeV
PDM T=0.56 MeVb) 162Dy

10-7
10-8

10-6

162

E1QRPA(E1+M1)QRPAc) 163Dy

Dy( 3He,3 He)
Dy( 3He,α )162
Dy(γ, n)163

EP+PDM T=0.59 MeV
PDM T=0.59 MeV

10-7
10-8
0

E1QRPA(E1+M1)QRPA

2

164

Dy( 3He,α )Dy(γ, n)163

4 6 8 10 12
Eγ (MeV)Fig. 1. Total RSFs obtained within the PDM (thin solidlines), EP+PDM (thick solid lines) versus the QRPA
RSFs for the E1 and E1 + M 1 excitations and the experimental data5) for 161–163 Dy. The dashed, dash-dotted,
and dotted lines stand for the RSFs obtained within
the phenomenological GLO-SLO models with 2 PDRs,
1 PDR, and without PDR, respectively.

Temperature is found to have a signiﬁcant eﬀect on the
RSF at the low energy Eγ ≤ Sn , whereas it does notchange much the RSF in the high-energy one Eγ > Sn ,questioning the validity of the Brink-Axel hypothesis.
In addition, due to the eﬀects of EP and couplings of
all ph, pp, and hh conﬁgurations within the PDM, the
EP+PDM can also partially reproduce the scissors resonance in 161–163 Dy nucleus at low Eγ without adding a
SR strength function in the RSF. These ﬁndings indicate
the importance of EP and couplings to non-collective pp
and hh conﬁgurations at ﬁnite temperature in the microscopic description of total RSF in excited nuclei.
References

1) J. M. Blatt, V. F. Weisskopf, Theoretical Nuclear Physics(Wiley, New York, 1952).
2) J. Kopecky, M. Uhl, Phys. Rev. C 41, 1941 (1990).
3) N. Q. Hung, N. D. Dang, L. T. Q. Huong, Phys. Rev. Lett
118, 022502 (2017).
4) N. D. Dang, A. Arima, Phys. Rev. Lett. 80, 4145 (1998).
5) https://www.mn.uio.no/fysikk/english/research/about/infrastructure/ocl/nuclear-physics-researc
h/compilation/ .

- 49 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Non-relativistic expansion of Dirac equation by the reconstituted
Foldy-Wouthuysen transformation†
Y. X. Guo∗1,∗2 and H. Z. Liang∗2,∗1
In the past few decades, the density functional theory(DFT) has been successfully applied in both the nonrelativistic and relativistic frameworks to describe theground-state and excited-state properties of thousandsof nuclei in a microscopic and self-consistent manner.
However, the connection between these two frameworks
remains unclear. The non-relativistic expansion of the
Dirac equation is considered to be a potential bridgeconnecting these two frameworks.1,2)
Recently, the reconstituted similarity renormalization group (SRG) method was proposed.3) Compared toconventional methods, the reconstituted SRG method
not only showed a much faster convergence, but also
yielded single-particle densities ρv (r) = ψ † (r)ψ(r) thatare closer to the exact values. Moreover, for the singleparticle scalar densities ρs (r) = ψ † (r)γ0 ψ(r), the γ0matrix should be transformed in the same manner as
the Dirac Hamiltonian. However, the original Dirac
Hamiltonian is operated with inﬁnite steps of unitarytransformations in both the conventional and reconstituted SRG methods. Therefore, the calculations of
single-particle scalar densities are not trivial in SRG
methods.
Meanwhile, with the consideration of the strong
scalar potential, we further applied another well-known
technique, the Foldy-Wouthuysen (FW) transformation, to the general cases in the covariant DFT andperformed the corresponding expansion up to the 1/M 4order.4) With the present FW transformation, all theunitary transformations involved hold explicit forms.
On this basis and with inspiration from the reconstituted SRG method, we developed the reconstituted FW
transformation. By replacing the bare mass M with the
Dirac mass M ∗ and deﬁning the corresponding new operators, the contributions related to the higher powersof the quotient of the scalar potential and the bare mass
are absorbed into the lower orders.
As a step forward, the so-called picture-change error,5,6) i.e., the diﬀerence between the densities calculated in the Schrödinger picture and those obtained in
the Dirac picture, has also been investigated throughcalculations starting from basic ﬁeld operators. Afterconsidering such picture-change errors, i.e., the relativistic corrections, both the single-particle vector andscalar densities become much closer to the exact results.
In addition, the diﬀerence between ρv and ρs originatesfrom the 1/M ∗ 2 order, as does the relativistic correc†
∗1
∗2

0.20
2d5/2

Exact
Without corr.
2
1/M* corr.
3
1/M* corr.

-3-3

ρv - ρs (10 fm )

0.15

0.10

0.05

0.00
2

4

6

8

10

r (fm)
Fig. 1. Diﬀerence between the single-particle density andthe single-particle scalar density for the neutron 2d5/2state of nucleus 208 Pb.

tion ∆ρ. Therefore, the relativistic corrections also playa crucial role in the diﬀerence between the vector andscalar densities.
By taking the 2d5/2 state of 208 Pb as an example, thediﬀerence between the single-particle density and thesingle-particle scalar density is shown with the blacksolid line in Fig. 1. The result without any relativistic correction is shown with the olive dashed line, while
the results calculated with the consideration of relativistic corrections up to the 1/M ∗ 2 and 1/M ∗ 3 orders areshown with the blue dotted and red dash-dotted lines,
respectively. It can be seen from Fig. 1 that the diﬀerences between the results without the relativistic corrections and the exact values are systematic. There are
diﬀerences in the positions of peaks and nodes as wellas the amplitudes. In contrast, the results with the relativistic corrections remarkably reproduce the behaviorof the exact values, particularly in terms of the positionsof peaks and nodes.
Based on the above discussions, the reconstituted
FW transformation is a promising method to connect
the relativistic and non-relativistic DFTs for futurestudies.
References

1) P. G. Reinhard, Rep. Prog. Phys. 52, 439 (1989).
2) M. Bender, P. H. Heenen, P. G. Reinhard, Rev. Mod.
Phys. 75, 121 (2003).
3) Y. X. Guo, H. Z. Liang, Phys. Rev. C 99, 054324 (2019).
4) Y. X. Guo, H. Z. Liang, Chin. Phys. C 43, 114105 (2019).
5) M. Douglas, N. M. Kroll, Ann. Phys. (N. Y.) 82, 89(1974).
6) B. A. Hess, Phys. Rev. A 33, 3742 (1986).

Condensed from the article in Phys. Rev. C 101, 024304(2020)
Department of Physics, The University of Tokyo
RIKEN Nishina Center- 50 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

On the role of three-particle interactions in nuclear matter†
W. Bentz∗1 and I. C. Cloët∗2
In a previous publication1) we discussed an interesting relation( between the) skewness J of nuclear matter(J = 27ρ3 d3 EA /dρ3 , where ρ is the baryon density
and EA the energy per nucleon in isospin symmetricnuclear matter) and the isoscalar three-particle interaction parameters. In this paper, we wish to discuss
an equally interesting relation between the slope pas
rameter L of the symmetry energy (L = 3ρ dadρ , whereas ≃ 32 MeV is the symmetry energy) and the isovector three-particle interaction parameters.
We extend Landau’s basic formula2) for the variation of the energy density of nuclear matter to include the third order term, which involves the spinaveraged three-particle forward scattering amplitudeh(τ1 τ2 τ3 ) (⃗k1 , ⃗k2 , ⃗k3 ). Here τi = (p, n), and h is symmetric under simultaneous interchanges of the momentum
variables ⃗ki and the isospin variables τi . Taking ﬁnally
the isospin symmetric limit, we can derive the following
relations for J and L in terms of the incompressibility
K and the symmetry energy as :ttHere F0 , F0′ , G0 , G′0 are the dimensionless ℓ = 0 twoparticle Landau-Migdal parameters, as deﬁned for ex(2pc)
is positive
ample in Ref. 2). While the isoscalar H0deﬁnite and of the order of unity or even larger, depending mainly on the magnitude of G′0 , the isovector
′
(2pc)
H0
is negative and small compared to unity formost of the published sets of Landau-Migdal parameters. Because the p-wave term H1 is suppressed bylarge factors,1) this simple estimate makes it plausiblethat the three-body interactions give a large positive
contribution to J, and a small negative contribution
to L. To obtain more quantitative results, it would beinteresting to apply the Faddeev method in the framework of eﬀective ﬁeld theories for nuclear matter.

∆M ∗ = M ∗(p) − M ∗(n) on the isovector density ρ(3) =ρ(p) − ρ(n) . The dimensionless isoscalar and isovector
three-particle interaction parameters()()
2pF M ∗
2pF M ∗
′
ρ
h
,
H
=
ρ
h′ℓ
Hℓ =
ℓ
ℓ
π2
π2

are the ℓ = 0, 1 moments of the isoscalar (hℓ =
(ppp)
(ppn)
(ppp)
1
+ 3hℓ
)) and isovector (h′ℓ = 14 (hℓ
−
4 (hℓ
(ppn)
hℓ
)) combinations of the 3-particle forward scattering amplitude at the Fermi surface.
By using empirical information, it was shown in
Ref. 1) that the above expression for J requires a largeM
positive 3-particle term M∗ (H0 − H1 ) > 1.24. On theother hand, if we use the canonical value as = 32 MeV∗2t

together with µ ≃ 0.27, which is the central value ofthe empirical range µ = 0.27±0.25 reported in Ref. 3),
the sum of the ﬁrst two terms in [. . . ] in the expression for L is ∼ 0.6, almost independent of M ∗ within
the empirical range 0.7 < M ∗ /M < 1. The empirical range of the slope parameter3) L = 59
( ±′ 16 1MeV)
M
then implies that the 3-particle term M
H 0 − 3 H1∗
is negative, with a magnitude smaller than unity.
Theoretically the three-particle amplitudes should
be calculated from the Faddeev equation, which is illustrated by Fig. 1. The driving term, which we callthe “2-particle correlation (2pc) term,” can be easily
estimated by using eﬀective contact interactions of the
Landau-Migdal type. Restricting the calculation to swaves (ℓ = 0) for simplicity gives the analytic results)′′
ln 2 ( 2(2pc)
F0 + 3F02 + 3G20 + 9G02 ,
=
H0
4(
)
′
′
1 ′2
ln 2 1 2 4
(2pc)
2
′
2
′
F + F0 F0 − F0 + G0 + 4G0 G0 − G0 .
H0=
4 3 0 3
3

Here pF is the Fermi momentum, M the free nucleon∗
mass, M ∗ the Landau eﬀective mass, ∂M∂pF refers to the∗momentum dependence() of M at the Fermi surface,∂∆M ∗and µ = ρ ∂ρ(3)expresses the dependence of
M

∗1

...
t

Fig. 1. First two terms in the Faddeev series. Circles represent two-body t-matrices.

9p2
J = −9K + F
M )
[(
]
8 M
4 M pF ∂M ∗ M
× −3++(H0 −H1 ) ,−3 M∗
3 M ∗2 ∂pF M ∗p2
L = 3as − F
2M
[(
)
(
)2
(
)]
2 M
M
1
M
′
× 1−
− ∗ H 0 − H1
+µ
.
3 M∗
M∗
M
3

†

t

References

1) W. Bentz, I. C. Cloët, Phys. Rev. C 100, 014303 (2019).
2) J. Negele, H. Orland, Quantum Many-particle systems(Springer, 1980).
3) B. -A. Li, B. -J. Cai, L. -W. Chen, J. Xu, Prog. Part.
Nucl. Phys. 99, 29 (2018).

Condensed from an article by W. Bentz and I. C. Cloët, tobe published in Phys. Rev. C (2021)
Department of Physics, Tokai University
Physics Division, Argonne National Laboratory- 51 -

1

II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A3-Foresight theory collaboration for nuclear data library: A3LIB
K. Yoshida∗1 for the A3LIB Collaboration
A quantitative understanding of the r-process nucleosynthesis requires nuclear data across the nuclear
chart, including the vicinities of the neutron drip line,
which are experimentally inaccessible. Thus the nuclear theory plays a decisive role to bridge between
nuclear experiments at RI beam facilities and microscopic inputs of the r-process simulation.
The condition of the r-process is given by an astrophysical environment of explosive phenomena withsome possible scenarios. Although nuclear physics thatenters the reaction network may depend on the scenario, the most important nuclear data are the nuclear masses, β-decay properties, and neutron capture
rates;1,2) Given the neutron-number density, temperature, and entropy, the seed nuclei are formed throughthe nuclear statistical equilibrium. Here, the nuclear
masses are a key nuclear physics quantity. When thetemperature decreases in the order of 100 keV, various
nuclear reactions take place, and the neutron-capture
process generates neutron-rich nuclei. If the neutronnumber density is high, it proceeds to the productionof the heaviest nuclei, and ﬁssion occurs. In every process, competition with the β-decay should be considered. The β-decay and the β-delayed neutron emission
play a role in shaping the ﬁnal abundance distributions
observed in nature.
The nuclear energy-density functional (EDF) approach is a possible theoretical model to describe theabove-mentioned nuclear properties in a vast mass region of the nuclear chart in a single framework. Researchers in the A3 (Chine, Japan, and Korea) countries have developed the nuclear EDF method andcomputational techniques. It is natural to start collaboration on the construction of the nuclear data tablenecessary for the r-process modeling and the development of the associated nuclear many-body theory.
I brieﬂy explain a rough plan of the theory collaboration. As shown in Fig. 1, the development of thetheory and model for each nuclear property is strongly
related. The key to success is the construction of the
EDF. Given the EDF, the binding energy of a nucleus and the single-particle level density are obtainedin a Kohn–Sham scheme. Parallel to an attempt at
the microscopic construction of EDF from an interparticle interaction, a phenomenological constructionis planned in collaboration with the researchers in Korea. The KIDS functional was introduced to better
describe the neutron-star equation of state. We apply
the KIDS functional to open-shell nuclei, where the nucleonic superﬂuidity and shape deformation show up.
Subsequently, the KIDS functional is improved for ﬁ∗1

FY

2020

2021

2022

KIDS for mass table

Level density

microscopic evaluationtransitions between excited states

β-decay
Fission2024

describing odd-A and odd-odd nuclei

Massn-capture2023

E1 strengths in odd-A nuclei

QRPA and beyond QRPA

extension to odd-A nuclei

fission rates for symmetric fission

spontaneous fission rates for asym. fission

neutron-induced fission

Fig. 1. Plan for the development of A3LIB.

nite nuclei. We developed a novel method for describing odd mass nuclei for a systematic calculation of thenuclear mass. The implementation is performed in the
KIDS code.
To describe the neutron capture and β decay rates,
we employ the EDF-based quasiparticle RPA (QRPA).
In neutron-rich nuclei where the neutron separationenergy is approximately a few MeV, the direct capture
process dominates over the compound process. In sucha case, the low-lying excited states and transitions areevaluated microscopically. The description of the transitions among excited states is in progress. For β decay,
we take two approaches: a beyond QRPA method formagic nuclei to describe the spreading eﬀect and the
QRPA for deformed nuclei.
The microscopic calculation of the ﬁssion rate is a
big challenge in nuclear theory. The mass parametersand potential energy in the collective (eﬀective) Hamiltonian for ﬁssion are microscopically calculated in an
EDF approach. The ﬁssion rate is then evaluated, e.g.,
by WKB approximation. Hybrid modeling for the ﬁssion yield is planned, where the parameters of the phenomenological model, such as the Langevin approach,are evaluated by a microscopic EDF method.
Finally, the uncertainty quantiﬁcation is essential indeveloping a new generation of the nuclear data table.
The A3LIB is based on the EDF method; thus, all the
calculated quantities are correlated through the coupling constants of EDF. We plan to perform the correlation analysis at each step of the calculation. The
results will be provided in the existing data library online.
References

1) M. R. Mumpower et al., Prog. Part. Nucl. Phys. 86, 86(2016).
2) T. Kajino et al., Prog. Part. Nucl. Phys. 107, 109(2019).

Department of Physics, Kyoto University- 52 -

1

3. Nuclear DataII-3. Nuclear Data

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

EXFOR compilation of RIBF data in 2020
T. Tada,∗1 M. Kimura,∗1,∗3 M. Aikawa,∗2,∗4 and N. Otuka∗4,∗5
Table 1. Entry numbers with references compiled fromRIBF data in 2020.

Nuclear reaction data support the most essential
part of nuclear technologies (power production, nuclear fuel cycles, environmental monitoring, dosimetry, radiation safety, radioisotope production, radiotherapy, and medical diagnostics, etc.) and sciences(nuclear physics, nuclear chemistry, geophysics, andastrophysics). Nuclear databases are compilations ofmeasured reaction data, and they play a vital rolein providing the best estimate for nuclear reactions
to various science ﬁelds and related areas. One of
the largest and globally used public nuclear reaction
databases is the EXFOR library (EXchange FORmat
for experimental nuclear reaction data).1) The EXFOR
library is a universal common repository for nuclear reactions established in 1967. The International Networkof Nuclear Reaction Data Centres (NRDC) maintains
the EXFOR library under the auspices of the International Atomic Energy Agency (IAEA).2) The EXFOR
library covers a wide range of nuclear reactions suchas neutron-, charged-particle- and photon-induced reactions.
Our group, the Hokkaido University Nuclear Reaction Data Centre (JCPRG),3) was founded in 1973 andjoined the NRDC as the ﬁrst member of the Asian
countries in 1975. We are responsible for the compilation of the charged-particle- and photon-induced nuclear reactions measured in Japanese facilities.4) Our
contributions to the EXFOR database reaches approximately 10% of the total amount. The database
compilation process involves the scanning of peerreviewed journals for published papers within the EXFOR scope. A unique entry number is assigned to eachselected paper to be compiled for the EXFOR library.
We extract the information of the bibliography, experimental setup, measured physical quantities, measured
numerical data and uncertainties. The information is
input in a single entry of EXFOR. During this process,we contact the corresponding authors for questions on
the contents of the papers and requests for numericaldata.
JCPRG has been cooperating with the RIKEN
Nishina Center for the compilation of data obtained
by RIBF since 2010, which aims to enrich the availability of RIBF data. In 2020, we compiled 45 newarticles produced at Japanese facilities and modiﬁed
18 old entries. This includes 17 articles from RIKEN,
15 new articles, and 2 old entries. The compiled data
∗1
∗2
∗3
∗4
∗5

Entries
New

5)

E2625
E26348)E264511)
E265014)
E265417)

E26266)
E26419)E264612)E265215)
E265518)

Revised
Total

E255720)

E261621)
17

E26337)
E264410)
E264813)
E265316)
E265719)

are accessible by entry numbers listed in Table 1. We
thank the authors of these papers for their kind cooperation.
We acknowledge that collaboration with RIKEN is agreat help for us to establish an eﬀective procedure forthe compilations. Most RIKEN data are very quickly
compiled after publication and end-users can accessit smoothly. We also thank all authors of RIKEN
articles who kindly provided numerical data. This
greatly helps increase the accuracy and quality of thedatabase.
References

1) N. Otuka et al., Nucl. Data Sheets 120, 272 (2014).
2) https://www-nds.iaea.org/ .
3) Hokkaido University Nuclear Reaction Data Centre,
http://www.jcprg.org/ .
4) M. Kimura, AAPPS Bulletin 28, 24 (2018).
5) J. Yasuda et al., Phys. Rev. Lett. 121, 132501 (2018).
6) N. Paul et al., Phys. Rev. Lett. 122, 162503 (2019).
7) A. Corsi et al., Phys. Lett. B 797, 134843 (2019).
8) M. L. Cortes et al., Phys. Lett. B 800, 135071 (2020).
9) K. Nakano et al., Phys. Rev. C 100, 44605 (2019).
10) S. Chen et al., Phys. Rev. Lett. 123, 142501 (2019).
11) D. S. Ahn et al., Phys. Rev. Lett. 123, 212501 (2019).
12) V. Vaquero et al., Phys. Rev. Lett. 124, 22501 (2020).
13) Z. Tsoodol et al., Appl. Radiat. Isot. 159, 109095(2020).
14) A. R. Usman et al., Nucl. Instrum. Methods Phys. Res.
B 469, 42 (2020).
15) M. U. Khandaker et al., Nucl. Instrum. Methods Phys.
Res. B 470, 1 (2020).
16) M. Sakaguchi et al., Nucl. Instrum. Methods Phys.
Res. B 472, 59 (2020).
17) M. Saito et al., Nucl. Instrum. Methods Phys. Res. B
471, 13 (2020).
18) T. Lokotko et al., Phys. Rev. C 101, 34314 (2020).
19) K. Sugihara et al., Nucl. Instrum. Methods Phys. Res.
B 470, 15 (2020).
20) V. Vaquero et al., Phys. Rev. Lett. 118, 202502 (2017).
21) X. H. Sun et al., Phys. Rev. C 101, 64623 (2020).

Graduate School of Science, Hokkaido University
Faculty of Science, Hokkaido University
Research Center for Nuclear Physics (RCNP), Osaka University
RIKEN Nishina Center
NDS, IAEA- 53 -

1

4. Hadron Physics

II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Transverse momentum dependence of forward neutron single spin√
asymmetries in polarized p↑ + p collisions at s = 200 GeV†
B. Mulilo∗1,∗2 for the PHENIX Collaboration
The PHENIX Collaboration has, for the ﬁrst time,
explicitly measured the transverse momentum (pT )dependent single spin asymmetries (AN ) for inclusive neutrons produced in the forward region of the
PHENIX detector with η > 6.8 using 2015 data. During this time, a proton with transverse
polarization col√lided with another proton at s = 200 GeV. Owing to
the limited acceptance and resolution of the detector,
the measured quantities were considerably smeared.
We, therefore, corrected for the smearing in the measured pT and azimuth (ϕ) using unfolding.1)
As the physics of forward neutron production is
not clearly understood, we performed detailed simulations using diﬀerent event generators as input to afull geant3 simulation.2) The generators dpmjet3.1,
pythia6.1, and pythia8.2 were used because diﬀractive processes are very diﬀerently handled. Anothergenerator was an empirical distribution of forward neutrons in pT , mimicking a one-pion exchange (OPE)model in which a pion balancing the momentum between the incoming proton and outgoing neutron collided with the other proton beam using pythia 8.
Ultra-peripheral collisions (UPCs) also play a role inforward neutron production.3) The distribution of photons was, therefore, simulated using the starlight4)
generator, and the photons collided with the proton
beam using pythia 8. As all Monte Carlo (MC) generators were intrinsically spin independent, we simulated
spin eﬀects by re-weighting events as a function of thegenerated pT (pT,g ) and azimuth (ϕg ) with the spinstates (↑) and (↓) randomly assigned. Furthermore, as
the shape of pT -dependent AN is not precisely known,
we used three weight forms to provide as much ﬂexibility as possible. The weight (w) based on a polynomial of third order (Pol3), power law, and exponential
forms is given by Eqs. (1), (2), and (3), respectively,
with Pol3 being the most general one:)(w = a · pT,g +b · p2T,g +c · p3T,g sin(ϕg +λ · π), (1)Fig. 1. Overall pT -dependent AN values shown as blacksolid square points averaged over all parameterizations,MC, and unfolding. Shaded boxes display total uncertainties from the unfolding, choice of MC, and functional form. Light-green, brown, and yellow shaded regions show χ2 below 10 units for Pol3, power-law, andexponential forms, respectively, while the corresponding broken lines show the best matching parameterizations.

The performance of parameters, functional form, andMC generator in reproducing AN values was evaluatedby the minimum χ2 between the measured MC anddata asymmetries. The 2D spin-dependent neutron
yields in pT and ϕ were then unfolded using the TSVDUnfold class based on a singular value decomposition(SVD)1) of the smearing response matrix. Overall AN
values were ﬁnally calculated from the unfolded yields
using the left-right AN formula5) after ﬁtting a sinemodulation having magnitude and phase as free parameters. In Fig. 1, overall AN values rapidly increaseat low pT (≲ 0.1 GeV/c) and slowly level oﬀ at high pT .
With this result, the ﬁrst reliable tests of mechanisms
producing these asymmetries can be performed.

where λ (±1) is the spin state and a, b, and c are freeparameters. Accordingly, the power-law weight is,)((2)
w = a · pbT,g sin(ϕg + λ · π),References

and the last parameterization is an exponential form,
which eventually decays asymptotically as)((3)
w = a 1 − eb·pT ,g sin(ϕg + λ · π).

†

∗1
∗2

1) A. Hocker et al., Nucl. Instrum. Methods Phys. Res. A
372, (1996).
2) A. Adare et al., Phys. Rev. D 90, 012006 (2014).
3) C. Aidala et al., Phys. Rev. Lett. 120, 022001 (2018).
4) S. R. Klein et al., Comput. Phys. Com. 212, (2017).
5) A. Adare et al., Phys. Rev. D 88, 032006 (2013).

Condensed from article in Phys. Rev. D 103, 032007 (2021)
RIKEN Nishina Center
Department of Physics, Korea University- 55 -

1

II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Transverse single-spin asymmetry for very forward neutral pion√
production in polarized p + p collisions at s = 510 GeV†

In high-energy polarized p + p collision, the left-rightcross section asymmetry, which is called as transverse
single-spin asymmetry (AN ) of very forward (η > 6)
particle production, plays an important role in understanding the spin-involved production mechanism fromthe view points of perturbative and nonperturbativeinteractions. The RHICf experiment1) measured the
AN of very√forward neutral pion in polarized p + p collisions at s = 510 GeV in June, 2017 at the Relativistic Heavy Ion Collider (RHIC).
The nonzero asymmetries of the neutral pion havebeen measured by many experiments2,3) in the forward(2 < η < 4) kinematic range, and they have been
explained only by quarks and gluons’ degrees of freedom. However, a possible contribution from the nonperturbative interaction has been recently highlighted
because larger asymmetries were observed in more isolated neutral pion events4,5) that could be connected
to nonperturbative event topology. A straightforward
approach to studying the role of nonperturbative interaction is measuring the AN of the neutral pion in
the very forward kinematic area where the nonperturbative interaction is expected to dominate.
We installed an electromagnetic calorimeter (RHICf
detector) at the zero-degree area 18 m away from thebeam collision point at the STAR experiment. The
RHICf detector consists of two sampling calorimeterswith lateral dimensions of 20 mm × 20 mm and 40 mm
× 40 mm, respectively. Both calorimeters are composed of 17 tungsten absorbers, 16 GSO plates for energy measurement, and 4 layers of GSO bars for position measurement. Since the radiation length of thedetector is 44 X0 , the electromagnetic shower stops
its development in the middle of the detector. The
RHICf detector has an energy resolution of 2.5–3.5%
for 100–250 GeV π 0 s and the pT resolution of 3.0–4.5%
in 0.0 < pT < 0.8 GeV/c.
To the best of our knowledge, we observed large
asymmetry in a very forward neutral pion production
for the ﬁrst time, which means a possible contribution from the nonperturbative interaction. Comparison between RHICf and previous forward neutral pionmeasurements are depicted in Fig. 1. At very low
pT < 0.07 GeV/c, the asymmetries are consistent withzero. However, as pT increases, the asymmetries increase as a function of xF , approximately showing thesame magnitudes and tendency of the forward ones.
†
∗1
∗2

AN

M. H. Kim∗1,∗2 for the RHICf Collaboration
0.2

p↑+p → π0+X
RHICf π0 6<η s=510 GeV 0.00<p <0.07 GeV/c
RHICf 0.07<p <0.19 GeV/c

0.15

T

T

RHICf 0.19<p <0.30 GeV/c
T

RHICf 0.50<p <0.69 GeV/cT

PHENIX π0 3.1<η<3.8 s=62.4 GeV

0.1

0E704 πs=19.4 GeVSTAR π0 <η>=3.3 s=200 GeV

0.05
0
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8
xF

Fig. 1. Forward (black) and very forward (color) neutralpion asymmetries as a function of xF in diﬀerent pT
regions.

It may be necessary to consider nonperturbative interaction to understand both forward and very forward
neutral pion asymmetries.
However, RHICf data can be aﬀected by perturbative interaction in the low pT region. The perturbativeand nonperturbative interactions may make their own
nonzero asymmetries respectively. Since the result of
this report is the one analyzed inclusively, more detailed analysis is necessary to reduce the diverse possibilities.
We have started combined analysis with STAR. Signals in the STAR detectors will identify whether theneutral pions of the nonzero asymmetries come fromperturbative or nonperturbative interaction. Further,
we are preparing a series of follow-up experiments fordeveloping a larger detector. In the near future, further analysis and experiments will provide a powerful
input to understand the origin of both forward andvery forward neutral pion asymmetries.
References

1) RHICf Collaboration, LOI, arXiv: 1409. 4860v1.
2) A. Adare et al. (PHENIX Collaboration), Phys. Rev. D
90, 012006 (2014).
3) B. I. Abelev et al. (STAR Collaboration), Phys. Rev.
Lett. 101, 222001 (2008).
4) S. Heppelmann (STAR Collaboration), Proc. Sci. 191(DIS2013), 240 (2013).
5) M. M. Mondal (STAR Collaboration), Proc. Sci. 203(DIS2014), 216 (2014).

Condensed from the article in Phys. Rev. Lett. 124, 252501(2020)RIKEN Nishina Center
Department of Physics, Korea University- 56 -

1

II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Transverse single spin asymmetry in charged pion production at
midrapidity in polarized p + p collisions at 200 GeV
J. H. Yoo∗1 for the PHENIX Collaboration
One of the main goals of the RHIC spin program isthe determination of the transverse-spin structure of the
proton, which can in turn provide some insight into the
angular-momentum component of partons. For reaching the goal, we measure Transverse Single-Spin Asymmetries (TSSAs) which are left-right asymmetries of ﬁnal stage particles produced in the transversely polarized p + p collision.1) The TSSAs (AN ) of pion at midrapidity in p + p collision is expected to be helpful tounderstand the transversity distributions of quark andgluons, the transverse intrinsic parton momentum, initial and ﬁnal state eﬀects. In PHENIX the charged pionsat mid-rapidity can be measured by the central arm detectors that consist of the Electro-Magnetic Calorimeter(EMCal), Ring-Imaging Cherenkov Detec tor (RICH),
Drift Chamber (DC), Pad Chamber (PC). Trigger ﬁred
if pions deposited energy over than 1.4 GeV on EMCal and we can detect charged pion’s track and energy. In mid-rapidity charged pion measurement, thebackground is categorized into two sources which are
hadron background(kaon and proton) and electron background(electron and positron). Pions with momentum
above 5 GeV/c create Cherenkov light in the RICH but
kaons and protons can’t create Cherenkov light under
E/p

5

10

0.2 0.4 0.6 0.8 1 1.2 1.4

5

104

5

10 10

105

104 104

104

3

3

3

10 10

103

2

2

2

10

CountsE/p

0.2 0.4 0.6 0.8 1 1.2 1.4

10

10 10

102

10

10 10

10

1

105

0.2

0.4

0.6

T

0.8

1

1.2

1.4

0.2

0.4

0.6

T

0.8

1

1.2

104

103

103 103103

102

102 102

102

10

10 10

10

1

7 GeV/c < p < 8 GeV/c 1 1 8 GeV/c < p < 11 GeV/c

Countse±T
0.2 0.4 0.6 0.8
1 1.2 1.4
0.2

0.4

0.6

0.8

1

1.2

1.4 5
10
1050.2

104

104 1043

10

103 1032

10

102 102

10

10 10
T

T

0.4

0.6

0.8

1

1.2

1

1.4

DATA: π±MC: π±+e±
MC: π±±
MC: e
Fit to Data: π±+e±
Fit to Data: π±
Fit to Data: e±±
Fit to Sim : e

0.2 0.4 0.6 0.8 1 1.2 1.4

rπ,e0.0436
0.06880.13750.11920.21540.00652
0.06569
0.16460.85600.9178Aπ,Sig(1 + rπ ) − Ae,Sigrπ (1 + re )NN
1 − r π ree
NMC
N π,BgAeDATA
lumi_scaledrπ ≡ π,Sig = e×π+eN
AMClumi_scaled
NDATA

AπN =

(1)
(2)

Aπ,Sig, Ae,Sig
are asymmetry in the pion and electronNNenhanced sample, respectively. AeDATA , AeMClumi_scaled
are amplitude of the Gaussian centered at around one
in the data and the luminosity scaled MC simulation,π,eπ,eand NMCare number ofrespectively. NDATA
lumi_scaled
entries in the E/p distributions for the data and the luminosity scaled MC simulation in pion enhanced sample,
respectively. Figure 1 shows E/p distribution of pion
data and distributions of pion and electron in MC, respectively. Background fraction tended to increase withincreasing pT (Table 1). These values are used to calculate corrected AN for charged pion.
References

Fig. 1. E/p distribution in pion enhancement sample for five
PT bins.
Department of Physics, Korea University

pT bin (GeV/c)
5–6
6–7
7–8
8–11
11–15
5–6
6–7
7–8
8–11
11–15

16 GeV/c and 30 GeV/c, respectively. Only electron
background remained an object to subtract. In EMCal, electrons lost most of their energy by electromagnetic interactions. Therefore, primary electron’s energy/momentum (E/p) distributed around 1. A secondary electron track from photon conversion would beincorrectly reconstructed with large momentum. Therefore secondary electron’s energy/momentum would bein the low area. because we can know only backgroundfraction but we can’t distinguish electron event frompion event, Eq. (1) is used for background correctionof the asymmetries.2) By using Monte Carlo simulation,
we calculated electron background fraction in both pion
enhancement sample (0.2 < E/p < 0.8) and electron
enhancement sample (E/p < 0.2 and 0.8 < E/p).

1.4

104 104

Countsπ±

5105 100.2
0.2 0.4 0.6 0.8 1 1.2 1.4
0.4 0.6 0.8 1 1.2 1.4 105

1 11 GeV/c < p < 15 GeV/c 1 1∗1

particle

1
5 GeV/c < p < 6 GeV/c 1 1 6< p0.8 < 71 GeV/c
0.2 GeV/c
0.4
0.6
1.2
1.4

104

105

Table 1. Background fraction of two samples.

1) C. Aidala et al. (PHENIX Collaboration), Phys. Rev. D
95, 112001 (2017).
2) T. B. Moon, Analysis Note No. 1268 in PHENIX Collaboration.

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Improvement of the DCA resolution for PHENIX
G. Nukazuka,∗1 Y. Akiba,∗1 T. Hachiya,∗1,∗2 and T. Todoroki∗3

DCA vs residual of clusters in s direction
350

300

300

DCA (µm)

200

250

100

200

0

−100

150

−200

100

−300

50

−400
−0.1 −0.08 −0.06 −0.04 −0.02 0 0.02 0.04 0.06 0.08
Residual in s direction (cm)0.1

Entries400

0Fig. 1. Correlation between DCA and the cluster residual in
the s direction in the innermost layer of the west arm withthe selection 1.5 < pT < 2.0 GeV/c.
∗1
∗2
∗3

RIKEN Nishina Center
Department of Mathematical and Physical Science, Nara
Women’s University
Tomonaga Center for the History of the Universe, Universityof Tsukuba

DCA distributions
6000

DCA
Entries
104869Mean
2.233
Std Dev
83.08
χ2 / ndf
29.88 / 24
Constant
4256 ± 20.2
Mean
3.666 ± 0.366
Sigma
76.26 ± 0.49
Corrected DCA
Entries
104869Mean
0.1347
Std Dev
59.66
χ2 / ndf
23.21 / 17
Constant
5853 ± 27.5
Mean
1.18 ± 0.26
Sigma
55.62 ± 0.35

DCA

5000

Fitting to DCA with gaussianCorrected DCA

Entries

4000

Fitting to corrected DCA
with gaussian

3000
2000
1000
0

−400

−300

−200

−100

0
100
DCA (μm)

200

300

400

Fig. 2. DCA (dark black) and corrected DCA (light blue)
distributions taken by the west arm with the selection
1.5 < pT < 2.0 GeV/c.
100

DCA resolution as a function of pT
Nominal in 2011
West in 2016 without correction

90
DCA resolution (µm)

The PHENIX experiment accumulated data from theRelativistic Heavy Ion Collider at Brookhaven National
Laboratory from 2001 to 2016 to study quark-gluon
plasma and the spin structure of the nucleon.
The measurement of the distance of closest approach(DCA), which is the minimum distance from a beamcollision point to the trajectory of a reconstructed particle, significantly suppress the background to heavy-flavor
production measurements in a single electron channel.
The vertex tracker (VTX)1,2) consists of two layers withsilicon pixel sensors and two layers with silicon strip sensors. The VTX in each of the west and east arms measures the trajectory, and the beam-beam counter determines the Z-coordinate of the beam collision point. DCA
is calculated event by event using this information.
In 2016, PHENIX measured Au-Au collisions at the√collision energy sN N = 200 GeV. One of the tasksneeded to start the data summary tape production of
the data is the alignment of the VTX detector. In thealignment process, we found strong linear correlations
between DCA in the transverse direction with respect tothe beam-axis and the residual in track fitting in the direction s = r∆ϕ (Fig. 1), where r is the distance from thebeam axis and ∆ϕ is the relative azimuth angle between
hits and track projections on the VTX plane. The abscissa and ordinate axes represent the residual in the s direction and the transverse DCA, respectively. Only clusters with a transverse momentum pT between 1.5 GeV/cand 2.0 GeV/c are shown in Fig. 1. Green points show
average values over the DCA of a residual bin. A linear
fitting shown with the red line estimates the correlation.
The correlation strength depends on pT , the arm, andthe VTX layer. The correlations can be used to correct
the DCA value and to improve the DCA resolution. The
corrected DCA distribution is narrower than the raw dis-West in 2016 with correction
East in 2016 without correction

80

East in 2016 with correction

70
60
50
40
30
0

1

2

3

4
5
6
p (GeV/c2)

7

8

9

10

T

Fig. 3. DCA resolutions as a function of pT . Points except
black ones are slightly shifted for visibility.

tribution (Fig. 2). The dark and light blue histograms
represent the raw and corrected DCA distributions, respectively. Fittings with a Gaussian function to the raw
DCA (red) and the corrected DCA (orange) yield DCA
resolutions.
Figure 3 shows DCA resolution as a function of pT .
The dark and light blue graphs are the raw and corrected
DCA resolutions in the west arm, respectively, while thegraphs in dark and light red are those in the east arm.
The black points indicate the nominal DCA resolution
for a run in 2011.2) By applying all corrections, the resolution is improved by 15% to 35%.
In 2016, VTX was operated without one strip layer inthe west arm owing to a beam accident in 2015. Under those severe conditions, a DCA resolution less than
50 µm was achieved in pT > 2.0 GeV/c, while it wasapproximately 60 µm in 2011.2)
This method may reduce background in the heavy flavor measurements because it is valid for data from other
PHENIX runs, in principle.
References

1) K .Adcox et al., Nucl. Instrum. Methods Phys. Res. A
499, 469 (2003).
2) A. Adare et al., Phys. Rev. C 93, 034904 (2016).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Recent progress of polarized Drell–Yan experiment at Fermilab,
SpinQuest (E1039)
K. Nagai,∗1 Y. Goto,∗2 Y. Miyachi,∗3 K. Nakano,∗2,∗4 G. Nukazuka,∗2,∗3 S. Sawada,∗2,∗5 and T. -A. Shibata∗2,∗6
The SpinQuest (E1039) experiment aims to investigate the structure of the proton through the polarized ﬁxed-target Drell–Yan process at Fermilab. In the
Drell–Yan process, an antiquark (q̄) in a hadron anda quark (q) in another hadron annihilate and decay
into a lepton pair (ℓ + ℓ̄) via a virtual photon (γ ∗ ):q + q̄ → γ ∗ → ℓ + ℓ̄. The Drell–Yan process is a suitable probe to study antiquarks in the proton because
the antiquark is always involved in this process.
One of the most important unresolved puzzles of the
proton is the “proton spin puzzle.” The proton spinhas been considered to be carried by the quark spins.
However, the EMC experiment at CERN showed thatthe contributions of spins of quarks and antiquarks tothe proton spin are much less than 100%.1,2) Further
experiments later conﬁrmed that these contributions
constitute only approximately 30% of the proton spin.
Many possible contributions have been considered tosolve this puzzle. One of them is the contribution of
the orbital angular momenta (OAM) of quarks andantiquarks.
The Sivers function, which is a function of the
Bjorken x and the transverse momentum of the quarks,
can give some hints about the OAM contributions.
The Sivers function is a kind of so-called transversemomentum-dependent parton distribution function(TMD). It represents the correlation beween the transverse momentum of a quark and the spin of the parent
hadron. If the Sivers functions of antiquarks are nonzero, then the contributions of the OAM of antiquarks
to the proton spin are not zero. The Sivers function(fSivers ) is proportional to the single-spin asymmtry(AN ): fSivers ∝ AN ∝ (NL − NR )/(NL + NR ), where
N is the number of Drell–Yan dimuons and the subscripts L and R denote the direction of the virtual photon (left and right, respectively). Therefore, the Sivers
functions can be experimentally accessed by measuring
the single-spin asymmetry.
The semi-inclusive deep inelastic scattering (SIDIS)
experiments have found the non-zero value of singlespin asymmetries of quarks. The contributions ofquarks and antiquarks are not separated by SIDIS.
The SpinQuest experiment will measure the single-spin
asymmetry of d¯ and ū in the Drell–Yan process using
a 120 GeV proton beam and polarized hydrogen anddeuterium targets.
∗1
∗2
∗3
∗4
∗5
∗6

Fig. 1. The E906 spectrometer.3) The target system has
been renewed, and dark-photon hodoscopes are installed for SpinQuest.

The SpinQuest spectrometer is basically the same as
the SeaQuest (E906) spectrometer3) (Fig. 1). We are
now updating it for the SpinQuest experiment. The
major update is the installation of the polarized targets, as the E906 experiment used only unpolarizedtargets. The details have already been reported in theprevious progress report.4) We installed another setof hodoscope planes to detect potential dark photon
events. Its optimization is underway.
The detectors are being repaired and updated. All
the drift chambers for SpinQuest were used in the E906
experiment, but one of the drift chambers was damaged after the E906 experiment was completed. We
have determined the cause of damage and have repaired the drift chamber. Some of the less eﬃcient
proportional tubes and hodoscopes have also been repaired. The optimization of their operation is now inprogress.
The beam time is expected to begin in the middleof 2021. After two years of data aquisition, we expect
to ﬁnd an important piece in the proton spin puzzle.
References

1) J. Ashman et al. (EMC Collaboration), Phys. Lett. B
206, 364 (1988).
2) J. Ashman et al. (EMC Collaboration), Nucl. Phys. B
328, 1 (1989).
3) C. A. Aidala et al. (SeaQuest Collaboration), Nucl. Instrum. Methods Phys. Res. A 930, 49 (2019).
4) Y. Miyachi et al., RIKEN Accel. Prog. Rep. 53, 81(2020).

High Energy Nuclear Physics, LANLRIKEN Nishina Center
Faculty of Science, Yamagata University
School of Science, Tokyo Institute of Technology
Institute of Particle and Nuclear Studies, KEK
College of Science and Technology, Nihon University- 59 -

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II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of J/ψ productions in p + d and p + p at SeaQuest
K. Nakano,∗1,∗2 Y. Goto,∗2 Y. Miyachi,∗3 K. Nagai,∗4 S. Sawada,∗2,∗5 and T. -A. Shibata∗2,∗6
for the E906/SeaQuest Collaboration
The partonic structure of the proton is one of the mostvital topics in hadron physics. The SeaQuest (E906) experiment at the Fermi National Accelerator Lab (FNAL)
in USA is aimed at measuring the ﬂavor asymmetry¯
of light antiquarks in the proton, d(x)/ū(x),at large
Bjorken x (≳ 0.3). It utilizes the 120-GeV proton beamfrom the FNAL Main Injector and targets of liquid hydrogen and liquid deuterium. The preliminary result¯of d(x)/ū(x)using the Drell–Yan process has been reported.1)
The data recorded by SeaQuest include J/ψ productions. The p + d/p + p ratio of J/ψ cross sections issensitive to distributions of both antiquarks and gluons
through the q q̄ annihilation (q q̄ → J/ψ) and gluon fusion (gg → J/ψ), as shown in Fig. 1. The q q̄ annihilation dominates at large Feynman x (xF ≳ 0.4) where
SeaQuest can measure. Therefore, this measurement is
expected to provide additional constraints on parton distribution functions (PDFs), particularly of antiquarks at
the middle Bjorken x. The systematic uncertainties ofthe measurement are largely reduced by taking the ratioof the cross sections.
Muon pairs from J/ψ decays were detected by the
SeaQuest spectrometer.2)
SeaQuest acquired physics data from 2013 to 2017 torecord 1.4 × 1018 beam protons on targets. The ﬁrst halfof the recorded data were analyzed. Figure 2 shows the
distributions of the invariant mass of muon pairs. The
yield of J/ψ was evaluated based on the fraction of theJ/ψ component in this ﬁt. The detection eﬃciency ofJ/ψ was corrected by simulation. The beam intensity
was measured with a secondary-electron emission monitor (SEM) for normalizing the p + d and p + p crosssections.

Fig. 1. Leading diagrams of J/ψ productions.
∗1
∗2
∗3
∗4
∗5
∗6

School of Science, Tokyo Institute of Technology
RIKEN Nishina Center
Faculty of Science, Yamagata University
High Energy Nuclear Physics, Los Alamos National Lab
Institute of Particle and Nuclear Studies, KEK
College of Science and Technology, Nihon University

Figure 3 shows the p + d/p + p ratio of the J/ψ crosssections as a function of xF . The systematic uncertainty of the SeaQuest result arises from the modelingof the combinatorial background and the relative luminosity normalization between targets. The experimental
result is consistent with the two predictions as shown inthe ﬁgure. The analysis including the latter half of therecorded data is underway.

Fig. 2. Distributions of invariant mass of muon pairs. The
points are experimental data obtained by SeaQuest. They
were ﬁtted by the components of the four processes,
namely the Drell-Yan process, J/ψ production, ψ ′ production, and combinatorial background. The sum of thefour components is represented by the thick line. :Fig. 3. Cross-section ratio vs. xF . The points are experimental data obtained by SeaQuest. The two lines are predictions3) by the color evapolation model with diﬀerent PDF
sets.

References

1) K. Nagai et al., RIKEN Accel. Prog. Rep. 52, 86 (2019).
2) C. A. Aidala et al., SeaQuest, Nucl. Instrum. Methods
Phys. Res. A 930, 49 (2019).
3) M. L. Mangano et al., Nucl. Phys. B 405, 507 (1993).
- 60 -

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II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Expression of interest for EIC-Japan
Y. Goto,∗1 Y. Akiba,∗1 I. Nakagawa,∗1 and R. Seidl∗1 for the EIC-Japan GroupThe Electron-Ion Collider (EIC) is a great research
opportunity for Japan, and we are working to form aJapanese group (EIC-Japan). We will form a highenergy accelerator-based experimental group in theﬁeld of both nuclear and particle physics. In responseto the “Call for Expressions of Interest (EOIs) for Potential Cooperation on the EIC Experimental Program” by BNL and JLab, we submitted an EOI by
the EIC-Japan group in November, 2020. The EOI is
non-binding, and its purpose is to guide expectations
and better understand the potential EIC experimental
equipment scope.
In Japan, the Science Council of Japan (SCJ) developed a master plan for large-scale research programs inacademia (Master Plan 2020) in 2019–2020. The EIC
was recognized as an important international collaborative research project with a long-term research planby the Future Planning Committee of the Committee
on Nuclear Physics, and it was proposed to the Master
Plan. Consequently, the EIC was selected as an academic major research project although it was not yet
selected as a priority project in the Master Plan 2020.
The EIC-Japan group plans to design and construct forward detectors of the EIC detector, especially calorimeters, to lead the study on forward andvery forward physics. Forward detectors are one of themost important detectors for precisely reconstructing
certain events of the deep inelastic scattering (DIS)
process, which is the basis of all research at the EIC.
We can precisely determine the spin and internal orbital motion of partons in the nucleon, which is still
poorly understood, by measuring the forward and mostforward jets, hadrons, photons, and electrons and by
studying their correlations. In particular, the contribution of gluons, sea quarks, and orbital angular momentum to the proton spin remains a mystery. In addition, our understanding of the most forward events
is expected to greatly enhance the development of
QCD-based event generators. Further, this will greatly
contribute to eliminating uncertainties in other highenergy particle experiments and cosmic ray observations.
We participated in the development of the forward
hadron calorimeter,1) which is essential for forward
jet reconstruction and hadron energy measurements,
as well as triggering. Designing and developing thecalorimeter is a joint project with the EIC genericdetector R&D group eRD1 and the STAR upgrade
project. A prototype calorimeter developed as theSTAR forward calorimeter comprises 38 layers of ironabsorbers and plastic scintillator plates. A wavelength∗1

shifting (WLS) plate provides uniform and eﬃcient
light collection from all scintillation tiles along thedepth of the tower. The light from the WLS plateis measured with SiPMs.
√ Since the energy resolutionof this detector is 70%/ E(GeV)) with an additional
constant term, the one for the EIC requires higher energy resolution.
We proposed the development of a zero-degree apparatus in the EIC experiment,2) and it has been approved as eRD27 this year. Zero degree detectors serve
critical roles for a number of important physics topics at the EIC. We study the requirements and technologies of zero-degree detectors, and we develop a
position-sensitive zero-degree calorimeter (ZDC). In
this program, we will conduct 1) a photon detector
study at a low energy <300 MeV, cooperating with
eRD1 for crystal and glass scintillators; 2) a prototype study of ZDC with position sensitivity, with the
ALICE-FoCal technology and the LHC-ZDC technology with fused silica; and 3) a radiation hardness studyof scintillators.
Subsequently, in addition to the proposals in themaster plan, we have expanded our activities as aJapanese group to include a group interested in building a silicon tracking detector. The team is open to
new collaborators. Heavy ﬂavor quarks are highlighted
at the EIC as the ideal probe to study open questions
in QCD, such as mass and ﬂavor dependence of energy
loss, fragmentation and hadronization modiﬁcation ina nuclear medium, nuclear parton distributions, andso on. Silicon sensor detectors are the key technology
employed for heavy ﬂavor detection by observing theirdecay vertex precisely. The performance of silicon sensors thus plays a crucial role in pursuing the research inheavy ﬂavor physics at a satisfactory level. We propose
to apply a silicon sensor based on silicon-on-insulator
monolithic pixel (SOIPIX) detector technology3) thathas been developed by the KEK group. SOIPIX has
demonstrated the world’s best tracking resolution of
0.680 ± 0.006 µm in a silicon detector using 120 GeV
FNAL’s test beam. Further SOIPIX is employed as
the inner vertex detector of 4π silicon hybrid detector
proposed by ANL and BNL collaborators.
References

1) Y. Goto et al., RIKEN Accel. Prog. Rep. 52, 87 (2019).
2) Y. Goto et al., RIKEN Accel. Prog. Rep. 53, 82 (2020).
3) Y. Arai et al., Nucl. Instrum. Methods Phys. Res. A
636, S31–S36 (2011).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Semi-inclusive deep inelastic scattering at the Electron Ion Collider
R. Seidl∗1
The electron-ion collider, EIC, will be a newly build
accelerator at Brookhaven National Laboratory to collide polarized electrons with polarized protons andlight ions, as well as unpolarized heavier nuclei. It willbe the perfect place to study the√ strong interaction
with collision energies between s = 29 to 141 GeV
and luminosities that are expected to be three ordersof magnitude higher than achieved at the HERA ringin Germany. In early 2020 the US DOE oﬃce of science acknowledged the EIC oﬃcially as a project thatwill be built in the next 10 years. A large community of more than 1000 members has already formed
with interest in the EIC, organized as the EIC usergroup.1) Within this group a call for a comprehensive
Yellow report was formed that updates earlier publications on the physics goals2,3) and closely looks at
the technological options for EIC detectors to have inorder to fulﬁll these physics goals. The main process
at the EIC is deeply inelastic lepton-nucleon (or nucleus) scattering, DIS, in which only the scattered lepton is detected. The kinematic variables x, which is
the momentum fraction of the nucleon a parton has,and the momentum transfer of the process Q2 can beextracted. Typically scales of Q2 > 1 GeV2 are considered as in that case the extracted cross sections andspin asymmetries can be factorized into hard scattering processes between partons that can be describedby perturbative QCD and nonperturbative parton distribution functions, PDFs. PDFs describe the distribution of quarks and gluons within the nucleon as a function of the momentum fraction x at a given scale Q2 .
In semi-inclusive DIS at least one ﬁnal state hadron is
also detected and the type, charge, momentum fraction z and transverse momentum relative to the boson
mediating the lepton-parton scattering informs on the
ﬂavor, spin and intrinsic transverse momentum of thestruck parton with the help of fragmentation functions.
These semi-inclusive DIS processes cover most of themain physics goals of the EIC. For example, the spin
contribution by individual sea quark ﬂavors to the total
nucleon spin can be probed this way. Also the threedimensional momentum picture of the nucleon can beobtained via SIDIS measurements and the closely related Sivers function and the tensor charges for quarks,
sea-quarks and gluons (gluons only for the Sivers function).
As an example of the work by the SIDIS group of theyellow report, the four-dimensional coverage of SIDIS
hadrons was studied at all envisioned collision energies
taking into account a potential detector conﬁguration
ranging from −3.5 < η < 3.5 with varying particle∗1

Fig. 1. Particle identification acceptance ratios for pionsfrom semi-inclusive events at the EIC as a function of
momentum fraction z and transverse momentum PT , inbins of x and Q2 .

identiﬁcation (PID) ranges depending on suitable technologies. Figure 1 displays the coverage for pions. One
can see that at intermediate x and Q2 the maximum
PID momentum of only 6 GeV limits the expected coverage while elsewhere the coverage is suﬃcient. Thisis caused by the fact that at central rapidities no compact PID detector can cover a larger momentum range.
Using these detector coverages and realistic smearing,
pseudo-data was created resembling actual measurements extrapolated to about 10 fb−1 , which corresponds to about a year of EIC running. This pseudodata was then used in global ﬁts by theorists to extract
the impact on various physics goals of the EIC such as
the tensor charges that potentially relates to physics
beyond the standard model,4) the Sivers function,5)
as well as the expected scale dependence of the functions that relate to the three-dimensional momentum
picture of the nucleon. The Yellow Report is now publicly available6) and provides the basis for the ongoing
review process of the DOE.
References

1) http://www.eicug.org/ .
2) A. Accardi et al., Eur. Phys. J. A 52, 268 (2016)(arXiv:1212.1701 [nucl-ex]).
3) D. Boer et al., arXiv:1108.1713 [nucl-th].
4) L. Gamberg, Z. B. Kang, D. Pitonyak, A. Prokudin,
N. Sato, R. Seidl, Phys. Lett. B 816, 136255 (2021).
5) A. Vladimirov, R. Seidl, in preparation.
6) R. Abdul Khalek et al., arXiv:2103.05419 [physics.insdet].

RIKEN Nishina Center- 62 -

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Bus-extender development for sPHENIX INTT detectorsPHENIX is a major upgrade of the PHENIX experiment at RHIC, and it aims to study the properties of quark-gluon plasma by measuring jet and upsilon productions and their modiﬁcations. An intermediate tracker (INTT) is a silicon strip barrel detector for sPHENIX.1) A bus-extender is a special cableused for signal transfer between the INTT detector andread-out electronics placed at least 120 cm away fromthe INTT. The bus-extender has the following requirements: (1) ﬂexibility, (2) length, (3) high-density signal
line (128 lines/5 cm), and (4) high-speed signal transfer(by LVDS).
We developed a bus-extender in the past three
years.2) We found that the prototype of our 120 cmlong bus-extender exhibits good electrical performancein terms of signal loss and reﬂection. Some issues were
found in the prototype. The ﬁrst issue is the formation of the through hole. The bus-extender comprises afour-layer ﬂexible printed cuicuit, and the through holeis used to connect the signal lines between layers. We
found that the through hole had a nodule structure,
which can cause instability during long-term use. Figure 1 shows the layer structure of the bus-extender (left)
and the cross section view of the through hole (middle);
the nodule structure is formed in the through hole. We
attempted the production procedure by changing thedrilling methods and Cu-plating methods to remove
the nodules; however, they still existed. We changed

Resistance (Ω)

T. Hachiya,∗1,∗4 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 S. Hasegawa,∗5 D. Imagawa,∗9 H. Imai,∗9 T. Kondo,∗6
C. Kuo,∗3 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1 Y. Namimoto,∗4
S. Nishimori,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗7

∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

sample2

sample3

3.0
2.5
2.0
1.5
1.0
2020/10/5

2020/10/15

2020/10/25

2020/11/4

2020/11/14

2020/11/24

Fig. 2. Result of the thermal cycling test (1000 cycles in 50days).

the glue used to laminate the multiple layers; this newglue works eﬀectively. Figure 1 (right) shows the crosssection of the hole with the new glue.
We performed a thermal cycling test to test its longterm stability. The test employs the application of high(75◦ C) and low (−15◦ C) temperatures for 30 min each;the temperature are changed at short time intervals(5 min). We repeated this test for 1000 cycles. We prepared three samples and measured the resistance of thethrough holes to evaluate the stability. These samples
had 400, 600, and 1000 through holes that are daizy
chained. During the test, the polymer of the sample
expands and shrinks because of changes in temperature. This results in cracks in the through hole. If
the through holes have cracks, the resistance becomesa large value. Figure 2 shows the result of the thermal
cycling test. The resistances changes repeatedly within
a valid range because of the changes in temperature forthe entire periods. This indicates that the through hole
has suﬃcent stability.
The second issue is that the peel strength of the prototype is about 4 N. This value is very small comparedwith the standard FPC (20 N). We found that the newglue improved the peel strength to 30–40 N. The results
are summized in Ref. 3).
The radiation hardness and yield rate of the busextender are also studied. The current status of thestudies are summarized in the Refs. 4, 5).
We successfully developed the bus-extender, and weplan to start mass production in 2021.

Fig. 1. (left) Layer structure of the bus-extender. (middle)
Cross section of the through hole made by the originalglue; nodules are formed. (right) Cross section of thehole with the new glue.
∗1

sample1

3.5

RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University

References

1) I. Nakagawa et al., in this report.
2) T. Hachiya et al., in this report.
3) M. Morita et al., in this report.
4) H. Imai et al., in this report.
5) D. Imagawa et al., in this report.

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5. Hadron Physics (Theory)

II-5. Hadron Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Non-global logarithms in hadron collisions at Nc = 3†
Y. Hatta∗1,∗2 and T. Ueda∗3
Recently, there have been a lot of activities in developing Monte Carlo algorithms for simulating parton showers beyond the large-Nc (leading-Nc ) approximation where Nc = 3 is the number of colors. Traditionally, in most event generators, the large-Nc approximation has been the only practical way to keep
track of the color indices of many partons involved.
Among other observables, the ﬁnite-Nc corrections are
particularly important but diﬃcult to quantify for theso-called non-global observables1) which are sensitive
to the wide-angle emission of soft gluons in restricted
regions of phase space. In Ref. 2), we have developed a framework to resum non-global logarithms at
Nc = 3 by improving and completing the earlier attempt.3) Numerical results are so far available only
for two observables in e+ e− annihilation: interjet energy ﬂow2) and the hemisphere jet mass distribution.4)
In this work we demonstrate that our approach canbe practically applied to hadron collisions where it isprobably most useful. We do so by explicitly computing the rapidity gap survival (or ‘veto’) probabilities in
Higgs plus dijet production pp → HjjX. The relevant
logarithms are of the form (αs ln Q/Eout )n where Q is
the hard scale (Higgs mass or jet transverse momentum) and Eout ≪ Q is the veto scale.
Consider quark-quark scattering qi (p1 )qj (p2 ) →qk (p3 )ql (p4 )H where i, j, k, l = 1, 2, 3 are color indices.
The outgoing quarks with momenta p3 , p4 are backto-back and detected as two jets in the forward andbackward directions. We are interested in the probability that the energy emitted in the central rapdiity
region π − θin > θ > θin is less than Eout .
The leading-order amplitude can be written as
Mijkl = M1 δki δlj + M8 taki talj .

Fig. 1. Gap survival probability in qq → qqH, color-octet
channel.

⟩1 ⟨tr(U3 U1† )tr(U4 U2† ) ,
(3)
2
Nc
⟩
⟨
tr(U3 U1† )tr(U4 U2† )tr(U3 U2† )tr(U4 U1† )−
2
Nc
8
, (4)
=
Pqq
Nc2 − 1
1
Pqq=

where Uα is the fundamental Wilson line in the direction of α. We compute these probabilities as a functionofτ=

Nc2 − 1 2 8
M8 Pqq .
4Nc2

(1)

(2)

References

P 1,8 are the gap survival probabilities in the singlet
and octet channels.
†
∗1
∗2
∗3

(5)

8
for θin = π/3 is shown in Fig. 1 toThe result for Pqq
gether with its various approximations. Surprisingly,
we ﬁnd a very good agreement with the large-Nc approximation in which P is simply computed from thesolution of the Banﬁ-Marchesini-Smye equation.5) A
similar conclusion is reached for other channels including gluons in the initial state. While we do not fully
understand the reason of this agreement at the moment, if it turns out to be a robust feature, it is goodnews because one can approximately get full-Nc resultsin hadron collisions using the known large-Nc frameworks.1,5)

where M1,8 are amplitudes in the singlet and octet
channel. We dress up (1) by attaching soft gluons toexternal legs in the eikonal approximation. We thensquare it and average over color indices to get the crosssection1
M12 Pqq
+

PT
αs
ln
.
π
Eout

1) M. Dasgupta, G. Salam, Phys. Lett. B 512, 323 (2001).
2) Y. Hatta, T. Ueda, Nucl. Phys. B 874, 808 (2013).
3) H. Weigert, Nucl. Phys. B 685, 321 (2004).
4) Y. Hagiwara, Y. Hatta, T. Ueda, Phys. Lett. B 756,
254 (2016).
5) A. Banfi, G. Marchesini, G. Smye, J. High Energy Phys.
08, 006 (2002).

Condensed from the article in Nucl. Phys. B 962, 115273(2021)RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Faculty of Science and Technology, Seikei University- 65 -

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Veriﬁcation of the QED tenth-order electron g −2:
Diagrams without a fermion loop
A. Hirayama∗1,∗2 and M. Nio∗1,∗2
A comparison between the measured value of theelectron anomalous magnetic moment and its theoretical prediction is the most stringent test of the quantum electrodynamics (QED) and, hence, the standard
model (SM) of elementary particles. The measurement
was performed by trapping a single electron in a cylindrical Penning trap. The deviation of the g value ofthe electron from Dirac’s prediction, ae = (g − 2)/2,
was determined as1)

So far, two independent numerical evaluations of
Set V have been executed by two groups.5,6) There is,however, 4.8 σ tension between the results. The difference is still negligible for the current precision of ae
but will certainly become crucial in the near future.
In Ref. 5), numerical integration was performed on
389 self-energy-like diagrams each, which are concatenations of nine vertex diagrams via the WardTakahashi identity. In contrast, 3,213 integrals derived
from vertex diagrams were evaluated in Ref. 6). Because the renormalization schemes used to construct
integrands are diﬀerent, the numerical result of one integral of the former does not coincide with the sumof the corresponding nine integrals of the latter. The
direct comparison of numerical results of integrals is
nontrivial.
The gap can be ﬁlled by calculating the diﬀerencein vertex renormalization constants, δL, of two renormalization schemes for every vertex diagram. The difference in numerical results of Set V integrals can be
expressed in terms of these δL’s and lower-order contributions of the anomalous magnetic moment.
We numerically computed all the necessary δL’s thatare derived from 1 second-, 4 fourth-, 28 sixth-, and269 eighth-order vertex diagrams. The computation
took approximately 120,000 hours in total. This is asmall and quick calculation compared with the numerical evaluation of Set V integrals.
Diagram-by-diagram comparison was performed forthe fourth-, sixth-, and eighth-order cases, and our veriﬁcation method worked very well. For the tenth order,
we examined numerical results representing the 2,232
Set V vertex diagrams that have no self-energy subdiagram and correspond to 135 integrals of self-energylike diagrams. No inconsistency was found in any of
the 135 integrals between Refs. 5) and 6). The investigation of the remaining 4,122 diagrams that have atleast one self-energy subdiagram is in progress and will
be completed soon.
We thank Prof. T. Aoyama and Prof. M. Hayakawa
for useful discussions. This work is supported inpart by JSPS KAKENHI 16K95338, 19K21872, and
20H05646. Numerical calculations were conducted on
HOKUSAI-BigWaterfall of RIKEN.

ae [expt.] = 0.001 159 652 180 73 (28) [0.24 ppb]. (1)A new experiment aiming at a 20-fold improvement in
the uncertainty is in progress.
To match the precision of measurement, theory musttake into account small but non-negligible contributions from hadronic and electroweak interactions. The
QED contribution is dominant and required up to thetenth order of perturbation theory because (α/π)5 ∼6.8×10−14 , where α is the ﬁne-structure constant. By
now, all terms up to the eighth order have been ﬁrmly
established. The tenth-order term was obtained only
by one group and has not yet been cross-checked.2) To
theoretically predict ae , a value of α is needed. Recently, two very precise values of α became available,both of which were determined using atom interferometry. The Cs3) and Rb4) atom experiments yielded
α−1 (Cs) = 137.035 999 046 (27)[0.20 ppb],

(2)

−1

[81 ppt],(3)α(Rb) = 137.035 999 206 (11)respectively. The diﬀerence is about 5.5 σ. A new Cs
experiment has already started to reveal one more digitof α. We then have two SM predictions of ae :ae [theory : α(Cs)] = 0.001 159 652 181 62 (23), (4)ae [theory : α(Rb)] = 0.001 159 652 180 265 (94), (5)where the uncertainty is solely governed by that fromα in both cases. Note that the discrepancy between
measurement and theory is positive in sign for α(Cs),while it is negative for α(Rb).
Considering the accuracy required for future experiments, the tenth-order QED term must be carefully
reexamined. A total of 12,672 Feynman vertex diagrams contributes to the tenth-order term. Amongthem, 6,354 diagrams without a fermion loop form agauge-invariant set called Set V. This is the most difﬁcult set to evaluate, and the uncertainty of the QEDcontribution to ae entirely originates from Set V.
∗1∗2

References
1) D. Hanneke et al., Phys. Rev. Lett. 100, 120801 (2008).
2) T. Aoyama et al., Phys. Rev. Lett. 109, 111807 (2012).
3) R. H. Parker et al., Science 360, 191–195 (2018).
4) L. Morel et al., Nature 588, 61–65 (2020).
5) T. Aoyama et al., Phys. Rev. D 97, 036001 (2018).
6) S. Volkov, Phys. Rev. D 100, 096004 (2019).

RIKEN Nishina Center
Department of Physics, Saitama University- 66 -

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6. Particle Physics

II-6. Particle Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Time development of conformal field theories associated with L1 andL−1 operators†
T. Tada∗1,∗2
An unconventional time development of the twodimensional conformal ﬁeld theory (CFT) induced by
the L1 and L−1 operators was studied by employing
the formalism previously developed in a study of sinesquare deformation (SSD).1) Consequently, we foundthat the retention of the Virasoro algebra naturally
leads to the presence of a cut-oﬀ near the ﬁxed points(shown as gray blobs in Fig. 1). The introduction of ascale by the cut-oﬀ may appear at odds with the conformal symmetry; however, it is essential to derive theformula for entanglement entropy.2,3)
The SSD of two-dimensional CFT4) has been explained with a formalism developed in Refs. 5, 6), in
which unconventional time developments, other than
the radial time development, were utilized to study
CFTs. One such time development suited with thestudy of SSD was named “dipolar quantization.” Further generalization was investigated by Wen, Ryu
and Ludwig,7) where the entanglement Hamiltonianand other interesting deformations of two-dimensional
CFT were studied.
In this study, we visit the following particular timedevelopment, which was not studied in Ref. 6):

are not accessible from each other by the sl(2, R) action. Typical operators for each group are: L0 represents c(2) > 0, L0 − 12 (L1 + L−1 ) represents c(2) = 0,
and L1 + L−1 represents c(2) < 0. Thus, we could
investigate the L1 + L−1 operator by applying the formalism developed in Refs. 5, 6) and demonstrate thatthe aforementioned three cases, including L1 + L−1 ,can be studied in a uniﬁed manner.
z
L

L

Lc

(1)

L1 + L−1 + L̄1 + L̄−1 ,Fig. 1. Flow of time t can be considered to begin at a section of space with length L (solid line). The remaining
space, including infinity, is depicted as a dashed line
and denoted by Lc . The setup corresponds to the entanglement entropy for the segment with length L.

instead of ordinary L0 + L̄0 . We found that this timedevelopment corresponds to the entanglement Hamiltonian as discussed in Ref. 7).
The signiﬁcance of the operator (1) can be understood in the following way. The L0 , L1 , and L−1 operators constitute sl(2, R) algebra. A linear combinationof these operators,
(0)

(1)

(−1)

L−1 ,

(2)

x′(0) L0 + x′(1) L1 + x′(−1) L−1 ,(3)x

L0 + x

L1 + xc

References

1) A. Gendiar, R. Krcmar, T. Nishino, Prog. Theor. Phys.
122, 953 (2009), Erratum: [Prog. Theor. Phys. 123,393 (2010)].
2) C. Holzhey, F. Larsen, F. Wilczek, Nucl. Phys. B 424,443 (1994).
3) H. Casini, M. Huerta, R. C. Myers, J. High Energy
Phys. 1105, 036 (2011).
4) H. Katsura, J. Phys. A 45, 115003 (2012).
5) N. Ishibashi, T. Tada, J. Phys. A 48, 315402 (2015).
6) N. Ishibashi, T. Tada, Int. J. Mod. Phys. A 31, 1650170(2016).
7) X. Wen, S. Ryu, A. W. W. Ludwig, Phys. Rev. B 93,235119 (2016).

can be mapped toby the adjoint action of sl(2, R); however, the following
quadratic form of the coeﬃcients, which is known as
the quadratic Casimir element, remains the same:()2c(2) ≡ x(0) − 4x(1) x(−1) .

(4)

Using this c(2) , the general linear combinations (2)can be categorized into three distinctive groups that†
∗1
∗2

Condensed from the article in J. Phys. A Math Theor. 53,
255401 (2020)
RIKEN Nishina Center
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II-6. Particle Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Study of Lorentzian sine-square deformed CFT†
X. Liu∗1,∗2 and T. Tada∗2,∗3
The concept of sine-square deformation (SSD) was
ﬁrst introduced into two-dimensional conformal ﬁeld
theory (2D CFT) in Ref. 1). In previous studies, wefound that the introduction of SSD in 2D CFT deﬁnes a new time translation generated by the SSD
Hamiltonian.1) The SSD CFT processes the Virasoro
algebra with a continuum index.2) Further, inspiredby the discovery in SSD CFT, we generalized thisstudy to CFT using more general modular Hamiltonians, and found three diﬀerent types of Virasoro algebra in the Euclidean CFT.3) In this study, we extend
our analysis to Lorentzian CFT. To consider CFT in
the Minkowski spacetime, the universal covering spaceof the Minkowski spacetime must be introduced. Generally, a spacetime is mapped to a Penrose diamondon the cylinder, which is the universal covering of thePenrose diamond. The time translation is deﬁned on
the universal covering using the Luscher-Mack Hamiltonian P̂0 +2K̂0 .4) Consider the worldline for a particle ina Penrose diamond; if we perform a special conformaltransformation, the worldline may cross the boundary of the Penrose diamond and move on to the next
patch. This problem can be solved if the time translation for the CFT is deﬁned to be conﬁned in a single Penrose diamond, implying that the CFT becomes
eﬀectively non-compact under such time translations.
This can be achieved by applying SSD in Lorentzian
CFT; the non-compactness of CFT can be observed
from the continuum index of the Virasoro Algebra.5)
We performed similar analysis as that in the Euclidean
signature.2,3) Next, we investigate the three diﬀerent
cases with Hamiltonians having plus, minus, and zero
values in the quadratic Casimir element. We selectthree examples from the three cases:

i0L

∗3

− π2

i−

Fig. 1. The universal covering space of the Penrose diamond (shaded region) is charted by u+ and u− . Whilethe conformal symmetry is represented using the entire
covering space, the time flow by P0 (arrowed line) is
confined within a single Penrose diamond.

must bear discrete indices to remove the ambiguities and preserve the local conformal symmetry.
There is UV divergence in the central extensionalterm in the Virasoro Algebra.
• The Naive type: The Virasoro generators can havecontinuum indices. This corresponds to the SSD
case, where the theory is eﬀectively non-compact.
Thus, the time translation is conﬁned inside a single Penrose diagram. See Fig. 1.
The conformal invariance requires the introductionof the universal covering space; moreover, occasionally,
the Lorentzian CFT is considered to be unphysical owing to the existence of a closed time-like curve. In thisstudy, our analysis ensured that there is no closed timelike curve if the Naive Hamiltonian is selected insteadof the Luscher-Mack Hamiltonian.5)
References

1) H. Katsura, J. Phys. A 45, 115003 (2012).
2) N. Ishibashi, T. Tada, J. Phys. A 48, 315402 (2015).
3) T. Tada, J. Phys. A 53, 255401 (2020).
4) M. Luscher, G. Mack, Commun. Math. Phys. 41, 203(1975).
5) X. Liu, T. Tada, Prog. Theor. Exp. Phys. 2020, 061B01(2020).

• Luscher Mack type: The Virasoro generators inthis type must bear discrete indices; otherwise,
ambiguities are observed in the generators.
• Rindler type: The Virasoro generators in this type

∗2

i0R
− π2

We deﬁne diﬀerent mode decompositions of theenergy-stress tensor with 0th modes corresponding toeach Hamiltonian in the three cases. By applying thecommutation relation of the energy-stress tensor, we
can obtain three types of Virasoro Algebra:

∗1

u+
π
2

π
2

• The Luscher Mack Hamiltonian P̂0 +2K̂0 ,• The Rindler Hamiltonian M̂01 ,• The Naive Hamiltonian P̂0 .

†

i+

u−

Condensed from the article in Prog. Theor. Exp. Phys.
2020, 061B01 (2020)
Department of Physics, University of Tokyo
RIKEN Nishina Center
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II-6. Particle Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 00 (0)Empirical formulas for the standard-model parameters
Y. Akiba∗1
We report empirical formulas for the parameters of
the standard-model. Table 1 lists the formulas for themass of the charged leptons (e, µ, τ ), three neutrinos(ν1 , ν2 , ν3 ), six quarks (u, c, t, d, s, b), and gauge bosons(W , Z), and Higgs boson (H). The formulas yield themasses in terms of the Planck mass

the mass values from the formulas and neutrino oscillation data. Table 3 lists the formulas for the CabibboKobayashi-Maskawa quark mixing parameters. Table 4 lists the formulas for the neutrino-mixing angles.
Table 5 lists the formulas for the ﬁne structure constant α and the strong coupling constant αs . These
formulas yield 24 of 25 free parameters of the standardmodel. The remaining one, the neutrino CP violation
angle δCP , has not been measured. The values calculated from the formulas are in good agreement withthe data. The one common constant in the mass formulas, ϵ0 = 2 × (6π)−48 , which agrees with the Hubble
constant H0 times the Planck time tpl (ϵ0 ≃ H0 × tpl )within the accuracy of H0 , suggests that the particle
masses are related to the expansion of the universe.
A model to explain these formulae is reported in thenext article,1) and implications to gravity and cosmology are reported in the article appearing after that.2)

Mpl = 1.220910 ± 0.000029 × 1019 GeV.
The last column of the table presents the relative difc
ference |mcp /mm
p −1| of the calculated value mp and themmeasured value mp for particle p. Table 2 compares
Table 1. Formulas for the masses of the SM particles.
pformula (µp = mp /Mpl )

e

1 1/3
ϵ
12π 2 0

µ
τ

(

ν3

s
d

1+

)

1 −1
2 1/2
1+
ϵ
3 0 (
6π )
1 −1
1/2
2ϵ0
1−
6π
)
(
1 −1
1/2
4πϵ0
1+
6π

ν2

b

)−1

1 1
4 (6π)2
)−1
(
3 1/3
3
27 1
1−
ϵ0
+
2
6π
4 (6π)2
(
)−1
3 1
5 1
1/3
9πϵ0
1−
+
4 6π
4 (6π)2

ν1

t
c
u

(

W

2−1/4 1/4
ϵ
(8π 2 0H

21/2 1/4
ϵ
8π 2 0

(

1−

3 1
9 1
−
2 6π
4 (6π)2

3 1
9 1
1+
−
2 6π
2 (6π)2

Table 3. Formulas of the CKM matrix elements.

1.6 × 10−5

(

)−1/2

)−1/2

)−1/2

5.5 × 10−3
3.8 × 10−2
3.9 × 10−3
5.6 × 10−3

2.2 × 10−2

1.6 × 10

(

1
6π

s12

−2

( (

(

formula

1
1
1−
3
6π

calculated

(

)(

1+

)(

1
6π

)−1 )1/2)−1 )1/2

1
1
3
1+
1−
2π
6π
6π
(
) (
)(
)
1
1 −1
1 1/2
1−
1+
s13
12π
6π
6π
s23

1.5 × 10−5
1.0 × 10−4

measured

calculated

measured

0.547

0.545 ± 0.016

0.729

0.714 ± 0.053

0.146

0.147 ± 0.003

Table 5. Formulas of the coupling constants α and αs (MZ )3.4 × 10−4

−1

Table 2. Comparison of the calculated masses of neutrinos
with the neutrino oscillation data.

αs (MZ )Quantity
m22 − m21
m23 − m21

References∗1) )1/2

Table 4. Formulas of the neutrino-mixing matrix.

α

Calculated
7.39 × 10−5 eV22.58 × 10−3 eV2formula

1 −1
Vus
1+
0.22445 0.22452 ± 0.0044
6π( )1/2
2
1
Vcb
0.04332 0.04214 ± 0.00076
36π
4 10.003753 0.00365 ± 0.00012
Vub
3 (6π)2()
3 1 27 1
1
1++0.34970.355+0.012
η̄−0.0112 6π 4 (6π)2 π

See Table 2

1 1
1 1
1+
+
12 6π
12 (6π)2(

5.2 × 10−5

See Table 2

1/3(

5.9 × 10−6

See Table 28(6π)2 ϵ0
1/3
12ϵ0
1/3
8(6π)−2 ϵ0
)−1
(
3 1
27 1
1/3
3(6π)ϵ01++
2 6π
4 (6π)2
1/3
ϵ0
(
)
1 −1
−1 1/3(6π) ϵ0
1+
6π

1 1/4
Z
ϵ
(8π 2 ) 0

|mcp /mm
p − 1|

Measured−5
7.37+0.20
eV2−0.15 × 10
−3
2.56 ± 0.04 × 10 eV2formula)1 1 −1/2
44π 1 +
√ ( 3 6π )
1
2
1+
4π
6π

(

calculated

rel. error

137.0238

8.9 × 10−50.11851

3.5 × 10−3

1) Y. Akiba, in this report.
2) Y. Akiba, in this report.

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II-6. Particle Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Quarternion-spin-isospin model for the standard-model parameters
Y. Akiba ∗1
Table 1. Values of elementary action densities.

The standard model (SM) successully describes thenature, but it has at least 25 free parameters. In
the preceding article1) we reported empirical formulas with no free parameter for 24 SM parameters: 15
particle masses, four Cabbibo-Kobayashi-Masukawa(CKM) quark mixing parameters, three neutrino mixing angles, the ﬁne structure constant, and the strong
coupling constant.
The pattern of the formulas suggests that there isan algebraic model underpinning them and that the
numbers 6π and ϵ0 = 2 × (6π)−48 play key roles inthis model. The fact that ϵ0 agrees with the Hubble
constant H0 times the Planck time tpl , ϵ0 ≃ H0 tpl ,suggests that there is a relation between the mass of
the SM particles and the metric of spacetime.
In this article, we introduce the quarternion-spinisospin (QST) model, which explains these formulas
and the relation H0 tpl = ϵ0 . The QST model is so
named because it is based on operators that are products of unit quarternions and operators of spin andweak isospin.
The QST model is based on the following 64 operators that are introduced here as normalized primordial
action (NPA):(6π)2 ϵ0 iτ 3 (6π)2 ϵ0 i (6π)ϵ0 iτ 3 (6πϵ0 i) (6π)ϵ0 ϵ0 iτ 3 ϵ0 i ϵ0
3∗a
L̂g3D
2a
L̂g2D
24∗a
L̂GG
8a
L̂uG
24∗b
L̂cG
8b
L̂tG
18b
L̂m
B
e
4a
1
3∗b
µ
4a
−12a
27a
3∗c
τ
4a
−3
3∗a 1 + 4
ν1
12a
12
2b
ν2
−4a
4
2b
ν3
12a
12
2
12a
12
−2
ν3′
U15
−12a
2a
U17 3 × (−4)
−12b
2b
D
−12a
1
u
4b
−8a
c
4b + 4c
−24∗
t
4c
−8b
d
−12a
−12a
−3∗
s
−12b
3∗d
b
4d
6
3∗b
27b 18a
Z
12∗b
1
1
H
−4
−6
18c
W
12∗b
−18∗
−27

}
{ I µ σ ν τ a ετ a εi εI c τ c εiτ 3 −εI c −εi
,
,
,
,
,
,
, −ε, ε, i, 1 .
6π
6π 6π 6π6π
4π 2πThe QST model has ﬁve primary ansatzes.
(A1) The Planck time tpl = 5.3912 × 10−44 s is theminimum duration of time in nature. The time t is
an integer n in the unit of tpl , and the physics state
at t = n is represented as |n⟩. tpl is a fundamental
constant of nature, as are the speed of light in vacuumc and the Planck constant h̄.
(A2) The change of |n⟩ for tpl is represented by a setof 49 operators L̂EAD
we name as elementary actionpdensity (EAD). An EAD corresponds to a term of the
SM Lagrangian.
(A3) An EAD is a sum of the equivalent vee productP48 (S48 , σ) of 48 NPAs,
∑
∑
NP A
L̂EAD
=
P48 (S48, σ) =∂ˆσ(p1 ) ∨ · · · ∨ ∂ˆσ(p48 ) ,p(τ 1 , τ 2 , τ 3 ) → (τ 1 , τ 2 , τ 3 ), (τ 2 , τ 3 , τ 1 ), (τ 3 , τ 1 , τ 2 ).
(1)
(A5) The SM emerges as a continuous approximationof the QST model as each EAD becomes a term of the
SM Lagrangian in the limit of tpl → 0.
We found 49 EADs that correspond to the elementary particles of the SM, which are summarized in Table 1. All of the 24 formulas of the parameters of thestandard model can be derived from the 49 EADs in
the table. The model also predicts that the CP violation in the neutrino sector is 100%. Thus, all of
the 25 free parameters of the standard model are derived from the QST model. In additon, the model predicts that the Hubble constant times the Planck timeis H0 tpl = 2 × (6π)−48 . We discuss the implications forgeneral relativity and cosmology in the next article.2)

NP A= {∂ˆp1 , · · · , ∂ˆp48 } is a set of 48 NPAs andwhere S48
σ is a permutation (k → σ(k), 1 ≤ k ≤ 48).
(A4) All 49 EADs are invariant for the following permutations:

References
1) Y. Akiba, in this report.
2) Y. Akiba, in this report.

(I 1 , I 2 , I 3 ) → (I 1 , I 2 , I 3 ), (I 2 , I 3 , I 1 ), (I 3 , I 1 , I 2 ),(σ 1 , σ 2 , σ 3 ) → (σ 1 , σ 2 , σ 3 ), (σ 2 , σ 3 , σ 1 ), (σ 3 , σ 1 , σ 2 ).
There are 12 EADs that are invariant for permutations:∗1

RIKEN Nishina Center- 70 -

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II-6. Particle
Physics
RIKEN
Accel.
Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

R = 12H02 and its implications to gravity and cosmology
Y. Akiba ∗1
In the preceding article,1) I report a model (QST
model) that can yield the formulas of the standard
model (SM) parameters. The model implies that the
product of the Hubble constant H0 and the Plancktime tpl is H0 tpl = 2 × (6π)−48 = ϵ0 . This relation isderived as follows.
The spacetime metric of the Hubble expansion ismetric (Sp-metric):2

ds = −dt +e

√

√

(

)
dr2
2
2
2
2
+r (dθ +sin θdϕ ) .
1− 2rrs

Rtt = 3H02 , Rrr = 3H02 −2rs −2H0 te,r3

rs −2H0 te,r3
R = Rtt + Rrr + Rθθ + Rϕϕ = 12H02 .

Rθθ = Rϕϕ = 3H02 +−g of this metric

R = 12H02 ,This metric describes the spacetime metric outside avery large spherical mass, e.g., a star or a planet. It is ametric with spherical symmetry, like the Schwartzchild
metric, but with R = 12H02 . Note that Rµν = 0 and
R = 0 for the Schwartzchild metic.
One can solve Keplerian moton in this metric. The
solution implies that the radius r of a circular orbit ofan object around the large mass at the origin increases
with time as√ṙ/r = 2H0 = 1.0104 × 10−10 /yr.
√
The factor 2 arises from the fact that the Keplerianmotion is a two dimensional motion. One can showthat the scale expansion√ rate of two-dimensional radius
ρ with R = 12H02 is 2H0 .
This prediction agrees with the observed rate of expansion of the the Moon’s orbit radius rMoon aroundthe Earth2) within the uncertainty of the data.

−g = e3H0 t .

√For t = tpl , we have −g = e3H0 t ≃ 1 + 3H0 tpl . In the
QST model, the correspondence relation is√−g ↔ 1 + L̂g3D = 1 + 3ϵ0 .
Thus, we have H0 tpl = ϵ0 . Because H0 = ϵ0 /tpl isa constant, R is a constant. The QST model implies
that R = 12H02 (constant). We discuss the implicationof this equation in general relativity and cosmology
below.
We can generalize the metric to allow local changesof the scale with a constraint R = 12H02 :ds2 = −e2u(x,y,z) dt2 + e2H0 t (dx2 + dy 2 + dz 2 ).
The R of this metric is
R = −(2∆u + 3(∇u)2 )e−2H0 t + 12H02 e−2uṙMoon = 3.82 ± 0.07cm/yr,ṙMoon /rMoon = (0.994 ± 0.0182) × 10−10 /yr.

= 12H02 .

We can show that Coulomb gravity can be derived fromthis metric. When we take the approximation H0 ≃ 0,
we have
R = −2∆u − 3(∇u)2 = 0.

This good agreement indicates that the expansion of
the lunar-orbit radius is due to Hubble expansion.
We found a few emprical formulas of cosmologicalparameters that are similar to those of the SM parameters. For CMB temperature, we found
(
)1/2
1
1
1
1/2
T =
−
ϵ0
.
1+
(6π)2
4π (6π)2

If u is small, we can ignore the (∇u)2 term, and wehave ∆u = 0. In general relativity, g00 ≃ −1 − 2ϕG ,where ϕG is the gravitational potential. As e2u = −g00
and e2u ≃ 1 + 2u, u ≃ ϕG . Therefore,∆ϕG ≃ ∆u = 0.

calc
This formula yields TCMB
= 2.7249 K, which agrees
with the obsrved value TCMB = 2.7255 ± 0.0006 K
within the uncertainty of the data. The QST model
can explain the emprical formula.

Thus, the relation R = 0 implies Coulombic gravitational potential under the weak gravity approximation.
If we take into account the fact that H0 ̸= 0, the potential equation for gravity becomes non-linear.
Next, we discuss the eﬀect of R = 12H02 for the motion of an astronomical object. Consider the following
∗1

2H0 t

One can show that the Ricci tensor Rµν and the Ricci
scalar curvature R of this metric are

ds2 = −dt2 + e2H0 t (dx2 + dy 2 + dz 2 ).
The Ricci scalar curvature R andare

2

References
1) Y. Akiba, in this report.
2) B. G. Bills, R. D. Ray, Geophys. Res. Lett. 26, 3045
(1999).

RIKEN Nishina Center- 71 -

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7. Astrophysics and Astro-GlaciologyII-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A novel high-resolution laser-melting sampler for discrete analyses ofion concentrations and stable water isotopic compositions in firn and ice
cores
Y. Motizuki,∗1 Y. Nakai,∗1 K. Takahashi,∗1 J. Hirose,∗1 Y. V. Sahoo,∗1 Y. Yano,∗1 M. Yumoto,∗2 M. Maruyama,∗2
M. Sakashita,∗2 K. Kase,∗2 and S. Wada∗2
Ice cores preserve past climatic changes and, in somecases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser
melting (see Fig. 1). In our system, a hole in an ice coreapproximately 3 mm in diameter is melted and heatedwell below the boiling point by laser irradiation, and the
meltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser
ﬁber. The advantage of sampling by laser melting isthat molecular ion concentrations and stable water isotope compositions in ice cores can be measured at highdepth resolution, which is advantageous for ice cores withlow accumulation rates, such as ice cores drilled around
Dome Fuji station in Antarctica.
This device takes highly discrete samples from ice
cores, attaining depth resolution as small as ∼3 mm withnegligible cross contamination; the resolution can also be
set at longer lengths suitable for validating longer-term
proﬁles of various ionic and water isotopic constituentsin ice cores.
The laser beam used to melt the ice is supplied throughthe wall of the freezer container by a continuous-wave
operated Er-doped ﬁber laser (CEFL-TERA, Keopsys
Inc.) through optical ﬁbers (core/clad diameter =200/220 µm). The laser wavelength is 1.55 µm (nearinfrared) and the maximum output power is 10 W. The
1.55-µm wavelength takes advantage of the strong absorption bands of ice and water from 1.4–1.6 µm. In addition, because 1.55-µm lasers are commonly used in optical communication technologies, suitable optical ﬁbers
are commercially available.
To check the stability of the sampler in the −20◦ C

Fig. 1. Photo showing a newly-developed laser-melting ice
core sampler.
∗1∗2

RIKEN Nishina Center
RIKEN Center for Advanced Photonics

Fig. 2. Photo showing an ice block after the continuous extraction of 100 meltwater samples in a stability test.

environment, we performed a continuous sampling testin which 100 vials were ﬁlled with a minimal volume(0.65 mL) of meltwater. In this test, the laser power was
set at 1.9 W, the nozzle intrusion speed was 0.52 mm/s,
the pumping speed was 5.5 mL/min, and the horizontal
and vertical pitch of the nozzle was 2.5 mm. It took 8hours 47 minutes to complete this test with no issues
the ∼ −20◦ C environment. Figure 2 shows a dummy ice
block made up from ultrapure water (Milli-Q water) after
this stability test. We conclude that the sampling rate
will not be a bottleneck during high-throughput isotopic
and ionic ice-core analyses.
We also conducted experiments to check whether there
was any leaching of ions from inner components and tocheck the degree by which samples mixed with each otherduring continuous sample collection. We found a 2.4%
“memory eﬀect,” which is usually signiﬁcantly less than
the analytical accuracy (a few µg/L) of ion analyses by
ion chromatography. We conclude that internal contamination and cross contamination are negligible with thissampler.
With this new sampler design, the analysis of the
2,000-year record embodied in the Dome Fuji ﬁrn core,
which took us several years, could now be ﬁnished inabout 30 working days by using two isotopic analyzers. For the ﬁrst time, we can now realistically contemplate strategic plans for cores recovered from lowaccumulation sites that include large numbers of repeated operations, such as compiling continuous 2,000year proﬁles with annual resolution of ionic and water isotopic constituents. Finally, our sampler has thecapability to proﬁle ionic and isotopic constituents atmonthly resolution to pursue intriguing transient signals,
potentially by annual layer counting.
Reference

1) Motizuki et al., submitted to Cold Reg. Sci. Technol.

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RIKEN Accel. Prog. Rep. 54 (2021)

Annually resolved d-excess record from a shallow ice core (DFS10) near
Dome Fuji station, East Antarctica
Y. V. Sahoo,∗1 , Y. Motizuki,∗1 , Y. Nakai,∗1 , and K. Takahashi,∗1
Ice cores are well preserved and utilized as proxies forpast climates and temperature reconstruction. A secondorder equation given by the deuterium excess 1) (referred
to as d-excess), d = δD − 8 × δ 18 O, is defined from
the Meteoric Water Line. Here, δD and δ 18 O are theisotopic water compositions given by δD or δ 18 O () =(Rmeasured − RVSMOW )/RVSMOW , where R is the ratio
2
H/1 H or 18 O/16 O, RVSMOW is the reference standard,
Vienna Standard Mean Ocean Water, and Rmeasured isthe measured ratio of a sample.
The d-excess is primarily related to physical parameters such as relative humidity, air temperature, sea surface temperature of the oceanic source or precipitation
at the site, and the trajectory of moisture source.2) On
a global scale, an annual average value of d is relatively
constant around 10.
Vimeux et al.3) demonstrated the d-excess changes
during transition from the glacial and interglacial periods of Vostok deep ice core data; the changes were wellcharacterized in the plot of d-excess versus δD, implicating changes in oceanic moisture sources as a resultof changes in Earth’s orbital obliquity. The d-excess
records for the Dome Fuji site have been studied withdaily snow precipitation 4,5) and a deep ice core spanningthe past 360,000 years.6) So far, moisture sources andclimate changes have been studied for deep ice cores in
Antarctica which span a long period; however, is it possible to determine the same tendency on short scales withannually-resolved d-excess data from shallow ice cores?
Here, we briefly report the correlation of d-excess withδ 18 O in a shallow ice core.
The shallow ice core (DFS10) was drilled in 2010 fromthe site at 10 km south of Dome Fuji station, East
Antarctica. The DFS10 site is located (77◦ 40’S, 39◦ 62’E)
at 3,800 m above sea level. The ice core drilling project
was conducted by Japanese Antarctic Research Expedition. The analyzed samples represent a temporal resolution of about one year ranging from 2 m to 60 m in depth(∼1300 years). All samples were analyzed using Liquid
Water Isotope Analyzer (Los Gatos Research, Inc.) at
RIKEN.
A linear relation between δD and δ 18 O, with a slope of
7.77, R2 = 0.987 for DFS10 was determined. This is close
to the local meteoric water line. The d-excess shows nocorrelation with δ 18 O (δD) on an annual or short scale;
however, simulation studies established a correlation on
longer scales with other ice cores drilled in Antarctica.
Fig. 1a shows a smoothed 50 data points running average of d-excess plotted against smoothed δ 18 O, andclusters into groups are evident. This case shows hierarchal structures: For groups of ∼500 years, a gen∗1

Fig. 1. (a) Deuterium excess versus δ 18 O; the data aresmoothed using 50 data points running average. The color
highlights the bunched ∼500 years period to show thechanges in d-excess. (b) The same, but for data points
from 1496 to 1973 CE (blue highlight from a) are subdivided into ∼50 years period.

eral decrease in d-excess with time is observed, suggesting that the moisture source could have systematicallychanged through the years. Each group subdivided into
shorter time scales (∼50 years) reveals smaller clusters ofd-excess pattern changing with time (Fig. 1b). As seen
here, the d-excess/δ 18 O small clusters follow a patternwith time. This pattern is not observed in a similar plot
with the raw data (R2 = 0.04, Pearson’s R = −0.19).
The d-excess variation depends on a number of factors and intensive simulation or modeling studies arenecessary to provide an insight into climate change ona shorter scale, which needs to be assessed using shallow
ice cores.
References

RIKEN Nishina Center- 74 -

1) W. Dansgaard, Tellus 16, 436 (1964).
2) L. Merlivat, J. Jouzel, J. Geophys. Res. 84, 5029 (1979).
3) F. Vimeux et al., Nature 398, 410 (1999); J. Geophy.
Res. 106(31), 863 (2001).
4) H. Motoyama et al., J. Geophy. Res. 110, D11106 (2005).
5) K. Fujita, O. Abe, Geophys. Res. Lett. 33, L18503 (2006).
6) R. Uemura et al., Clim. Past. 8, 1109 (2012).

1

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RIKEN Accel. Prog. Rep. 54 (2021)

High-intensity vanadium-beam production to search for a newsuper-heavy element with Z = 119†
T. Nagatomo,∗1 Y. Higurashi,∗1 J. Ohnishi,∗1 T. Nakagawa,∗1 and O. Kamigaito∗1
In March 2020, we successfully accelerated theﬁrst beam (40 Ar13+ ) using several superconducting
quarter-wavelength resonators (SC-QWRs)2) installedin RIKEN heavy-ion linear accelerator (RILAC)1) toachieve enough energy to synthesize new super-heavy
elements (SHEs) with an atomic number greater than118. To overcome the extremely small production
cross section of SHE with Z = 119, it was necessary to provide a highly charged vanadium (V)-ion
beam such as 51 V13+ with very high intensity. Thus,
we constructed a superconducting electron cyclotron
resonance ion source (SC-ECRIS) for RILAC, which
was named RIKEN 28-GHz SC-ECEIS “KURENAI”(R28G-K).3) R28G-K has essentially the same structure4) as another SC-ECRIS that is the only source ofheavy ions including uranium for RIBF, which is renamed RIKEN 28-GHz SC-ECEIS “SUI” (R28G-S).5,6)
When operating the SC-QWR, the particulate mattersputtered from the beam pipe irradiated by the beamis thought to signiﬁcantly reduce the gap voltage byincreasing the surface resistance of the cavity, thus wemust suppress the beam loss as much as possible. For
this purpose, we installed “slit triplet” in the low energy beam transport to limit the transverse emittance.3)
This indicates that only a portion of the beam extracted
from R28G-K is available despite the demand for an
unprecedented beam intensity. Therefore, we systematically studied the eﬀects of the amount of the V vapor and power of the microwaves, which heat up theplasma in the ion source, on the beam intensity, andthe optimal parameters that would allow long-term experiments with the highest possible beam intensity.
The upper ﬁgure in Fig. 1 shows the two high temperature ovens (HTOs)7) installed in the ion source. The
HTO was developed as an evaporator for high melting
point materials such as vanadium. The V-vapor amount
was equivalent to the sum of the consumption rates ofthe metallic V sample in each HTO crucible. The capacity of each crucible was approximately 2.2 gram of
the granular metallic V. The 51 V13+ -beam intensity extracted from R28G-S was obtained as a contour plot
in the lower ﬁgure in Fig. 1 as a function of the consumption rate of the V metal and the total power ofthe 18- and 28-GHz microwaves. As a consequence ofthe contour plot, it was deduced that a 400-electric µA
V13+ -beam can be produced at ∼6-mg/h consumption
and 2.5-kW microwaves. Because the total capacity ofthe two HTO crucibles is 4.4 gram, we can provide the†∗1high intense V beam for one month without interruption. Furthermore, at 24-mg/h consumption and 2.9kW microwaves, we also obtained the V-ion beam withan intensity of 600 electric µA that is suitable for essential development, for example, target development.

28-GHzwave guide

Crucible
HTO2

18-GHzwave guide

Biased disk

Crucible
HTO1

51V13+ beam intensity (electric µA)

0

200

400

600

Supporting gas : 14N2
Acceleration voltage:12.6 kVConsumption rate (mg/h)
Fig. 1. Two HTO mounted on the injection flange of theplasma chamber of R28G-K (upper), and obtained contour plot of the 51 V13+ beam intensity as a function of
the consumption rate and the microwave power (lower).

References

1) E. Ikezawa et al., in Proc. HIAT2015, (Yokohama, Japan,2015), p. 222.
2) N. Sakamoto et al., Proc. SRF2019, (Dresden, Germany,2019), p. WETEB1.
3) T. Nagatomo et al., Rev. Sci. Instrum. 91, 023318 (2020).
4) G. D. Alton et al., Rev. Sci. Instrum. 65, 775 (1994).
5) T. Nakagawa et al., Rev. Sci. Instrum. 81, 02A320 (2010).
6) Y. Higurashi et al., Rev. Sci. Instrum. 85, 02A953 (2014).
7) J. Ohnishi et al., Proc. ECRIS2018, (Catania, Italy,2018), p. 180.

Condensed from the article in the Proc. of 24th Int. Workshop on ECR Ion Sources (ECRIS’20), East Lansing, USA,
September 2020, in press
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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

R&D in AVF cyclotron
J. Ohnishi,∗1 A. Goto,∗2 and Y. Kotaka∗3
We aim to increase the beam intensity and energy
in the AVF cyclotron. In 2020, 7.25 MeV/nucleon He
beams with intensity greater than 40 µA were stably supplied for RI-production experiments, and the
maximum beam energy was successfully increased from
14 MeV to 30 MeV for protons. This paper describes the
supply of a 30 MeV proton beam and the temperaturemonitoring system in the deﬂector septum for extracting
beams with an intensity greater than 1 kW.
Previously, the maximum energy of the AVF cyclotron
for protons was 14 MeV; however, in the summer of
2017, the new central region was installed to acceleratebeams with higher energies, for example, a 30 MeV proton (Harmonic H = 1 acceleration) and 14 MeV/nucleon
deuteron.1) The shape of the old and new central regions,orbits of 30 MeV protons, and the central orbit of normal H = 2 operation are shown in Fig. 1. In February
2020, an acceleration test was conducted because the RIproduction experiment using the 30 MeV proton beam
was scheduled. The results of this test showed that apart of the beam in the second turn hit the phase slit,
which was modiﬁed in 2019, and the shape of the slit wascorrected in a hurry. As a result, a 30 MeV proton beamwith a current of 10 µA was successfully accelerated andsupplied for the user’s experiment in June. The passing
eﬃciency in the AVF cyclotron was approximately 7%.
To prevent the deﬂector septum from melting due tobeam loss, a system was installed to monitor the temperature of the septum with thermocouples (TCs) andto stop the beam when an abnormal temperature riseis detected. Figure 2 shows a part of the deﬂector towhich the TCs are attached. The septum is made ofFig. 1. New and old central region of the AVF Cyclotron.
Hatched area indicates the old region. Beam orbits for
30 MeV protons and the central orbit of the normal H = 2
acceleration are also shown.
∗1
∗2
∗3

RIKEN Nishina Center
Institute of Materials Structure Science, KEK
Center for Nuclear Study, University of Tokyo

Fig. 2. Tip of the deflector septum to which thermocouples
are attached.

Fig. 3. Time response of temperatures on the septum calculated by ansys.

copper, and it has a thickness of 0.3 mm and a heightof 12 mm. As shown in the ﬁgure, the septum has anotch with a length of 20 mm in the beam direction for
dispersing beam loss. The two TCs were attached 6 mmabove and below the tip of the septum notch. Figure 3
shows the time response of the temperatures at the tipof the septum notch (beam loss point) and the TC position calculated with ansys2) for a beam loss of 300 W(assuming a beam diameter of 2 mm). These calculation
results show that the maximum temperature of the septum exceeds the melting point of copper (1085◦ C) within
1 s with a beam loss of approximately 370 W. Further,
it is found that the temperature rise at the TC position
was as small as one tenth of the maximum temperatureand its response speed was slow. Therefore, we will stop
the beam before the septum melts when the temperaturerise for each 0.1 s measurement interval exceeds a predetermined value owing to any abnormal beam loss. The
system will be used in 2021 when the permission limiton the radiation protection for the 7.25 MeV/nucleon He
beams will be increased to 70 µA.
References

1) J. Ohnishi et al., RIKEN Accel. Prog. Rep. 51, 137 (2018).
2) https://www.ansys.com/ .

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RIKEN Accel. Prog. Rep. 54 (2021)

Charge stripper ring for RIKEN RI beam factory†
H. Imao∗1
The use of charge strippers is almost inevitable forthe eﬃcient acceleration of particularly heavy ions suchas uranium in heavy-ion accelerator complexes. At
the RIKEN RI Beam Factory (RIBF), the total charge
stripping eﬃciency of two strippers, He gas1,2) and rotating graphite sheet disk strippers,3) used for uranium
acceleration is less than 5%, which creates a serious
bottleneck for potential intensity upgrades in the near
future. We have proposed the use of charge stripper
rings (CSRs)4,5) as a cost-eﬀective method to achieve a
10-fold increase in the intensity of the 238 U beams at
RIBF.
Figure 1 shows a design view of the CSR for theﬁrst stripper (CSR1), which is a compact isometricring with the same design circumferences of 37.1953 m(15 times the distance interval of the beam bunchesfrom the RIKEN Ring Cyclotron (RRC) at a frequency of 18.25 MHz) for all circulating uranium beams
with eight diﬀerent charge states from 59+ to 66+.
CSR1 consists of gas strippers (He and nitrogen strippers), eight main bending magnets (BM1-8), two acceleration cavities, a re-buncher, four charge-dependent
quadrupole stations, injection magnets (IBM and injector quadrupole triplets), extractor bending magnets(EBM1 and EBM2), steerers for closed-orbit distortion
corrections, and diagnostic boxes involving beam diagnostics and vacuum pumps. In the CSR1, beams otherthan the selected U64+ beams reenter the stripper witha ring after recovering the energy lost in the stripper.
The U35+ beams are injected simultaneously into thecharge stripper ring using the charge exchange injection method. The recycling cycles are repeated, andonly the U64+ beams are continuously extracted, using a magnetic deﬂection channel. The isometric ringis used to hold the bunch structure of beams to matchthe acceptance of the latter-stage cyclotrons.
The CSR1 lattice is a mirror-symmetric reversed lattice with the symmetry plane at the center of the
stripper section. The high-density quadrupole stations
equipped with a quadrupole doublet or triplet for all
charge states will be used to control the optics for all
charge states. The design of a compact quadrupole
magnet is a key issue. We have already ﬁnished the calculations and are preparing to manufacture “hourglasslike” quadrupole magnets6) as shown in Fig. 1.
We conducted some calculations for the key design issues of CSR1. A realistic lattice for 8 charge states circulating in CSR1 was derived. Possible sources of emittance growth with a new multi-stage stripper scheme
were also investigated. We also performed calculations
for the beam transport of U35+ from RRC to CSR1 andthen those of U64+ from CSR1 to fRC. The eﬀective
charge stripping eﬃciency of CSR1 in the present calculation was approximately 60%, and further detailed
calculations and optimizations were conducted.
References

1) H. Okuno et al., Phys. Rev. ST Accel. Beams 14, 033503(2011).
2) H. Imao et al., Phys. Rev. ST Accel. Beams 15, 123501(2012).
3) H. Hasebe et al., EPJ Web Conf. 229, 01004 (2020).
4) H. Imao et al., Proc. CYC2016, Zurich, Switzerland,
2016, pp. 155–159.
5) H. Imao et al., Proc. IPAC2018, Vancouver, Canada,
2018, pp. 41–46.
6) Patent application filed by RIKEN and HITACHI Engineering Co., Ltd. with the application number JP2020056540 in Japan.

Fig. 1. Design view of the CSR1 (left) and “hourglass-like” quadrupole magnet (right).
†∗1

Condensed from the article in J. Instrm. 15, P12036 (2020)
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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

2020 operational report for the Nishina RIBF water-cooling system
T. Maie,∗1 K. Kusaka,∗1 E. Ikezawa,∗1 Y. Watanabe,∗1 K. Kobayashi,∗2 J. Shibata,∗2 M. Oshima,∗3
H. Shiraki,∗3 and H. Hirai∗3
Operation Condition

ment for enhancing the RRC cooling capacity, which
was completed in 2019, is scheduled for March. If themeasurement result is satisfactory, the cooling systems
are planned to be used in the operation of RIBF from
April 2021. The cooling systems are expected to contribute greatly to the mitigation of the ﬂuctuationsin the magnetic ﬁeld due to temperature variations in
the RRC cooling water, which has been the problem
for many years.

As the COVID-19 pandemic aﬀected the operation of the cooling systems of Nishina and RIBF in
FY2020, the RIBF operation planned for the H1 term
was completely cancelled. In FY2020, RIBF’s cooling systems were operated for approximately two andhalf months, and Nishina’s cooling systems for AVFstandalone, AVF + RRC, AVF + RRC +IRC and RILAC2 + RRC + GARIS-II were operated for approximately ﬁve months. No signiﬁcant troubles that could
cause the long-term interruption of accelerator operation occurred, and the cooling systems operated stably,with the exception of some minor problems.

References
1) T. Maie et al., RIKEN Accel. Prog. Rep. 52, (2018).
2) T. Maie et al., RIKEN Accel. Prog. Rep. 59, (2019).

Trouble Report
In troubleshooting, the symptoms were fortunately
minor. Therefore, instead of interrupting the machinetime for repairs, while providing emergency measures,
repairs such as the switching of beams or summer
maintenance were performed during the long-term accelerator outage period. The typical examples of troubles that occurred in FY2020 are a water leak fromthe cooling plumbing joint and deterioration of cooling water purity due to water leakage, failure in thecooling water pump motor bearing, failure in the control instrumentation air compressor, and device outages caused by an instantaneous voltage drop due to alightning strike (1–2 times a year).
Periodic MaintenanceAlthough the operation time was shorter overall because the COVID-19 pandemic, regular maintenancewas conducted as planned. As we report it every year,
we omit details about the periodic maintenance
UpgradesThe construction of cooling systems dedicated to thediagnostic device (named “New FC-G01”) for highintensity beams began this year, as planned. Afterthe completion of the construction in March 2021, theconstruction of the power systems and control systems
is planned to start in April 2021 with the goal of starting a comprehensive test run within FY2021. Furthermore, an actual load test using the beam of the equip∗1∗2∗3

RIKEN Nishina Center
SHI Accelerator Service Co., Ltd.
Nippon Air Conditioning Service Co., Ltd.

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Status of vacuum pumping systems in accelerator facilities
Y. Watanabe,∗1 E. Ikezawa,∗1 M. Fujimaki,∗1 S. Watanabe,∗1 K. Yamada,∗1 M. Nishida,∗2 K. Oyamada,∗2
J. Shibata,∗2 K. Yadomi,∗2 and A. Yusa∗2
Vacuum pumping systems in accelerator facilities havethe following two problems: vacuum leakage and update
issue. The vacuum leakage is a malfunction of old accelerator facilities caused by age-related deterioration. The
update issue is that almost all old vacuum pumps andaccessories cannot be replaced with new units owing to abudget limitation. In this paper, we discuss the current
status of vacuum pumping systems.1,2)
A vacuum pumping system in an accelerator facility1) comprises cryopump systems, turbomolecular pump(TMP) systems, rough pumping systems, additional
chamber (AC) pumping systems, and subpumping systems (subvacuum of a resonator). Table 1 lists the number of vacuum pumping systems in accelerator facilities.
Each ring cyclotron contains more than 80 sets of cryopump systems,2) more than 120 sets of TMP systems, and
2–8 sets of rough pumping, AC pumping, or sub-pumping
systems. In addition, more than 160 module-type vacuum gauges (total pressure gauge controller) combinedwith Pirani and cold cathode gauges are used to monitor
vacuum pressure and interlocking vacuum process control in accelerator facilities. Table 2 lists the number ofmalfunctions in the pumps and gauges from 2018 to 2020.
In a year, three to nine malfunctions occur in each unit.
The number of malfunctions may have been lower before
2017 because of the shutdown of the RILAC due to the
SRILAC installation in 2017–2019 and the closure of the
RIBF due to the COVID-19 pandemic in 2020.
Vacuum pumping systems have been in operation for
14–42 years.2) In particular, RRC cryopumps, large RILAC TMPs (5000 L/s), and large RRC TMPs (5000 L/s)
were manufactured in 1985, 1978–1987, and 1985, respectively. In addition, the doses in the SRC, IRC, and AVF
room are extremely high during beam irradiation. Therefore, the number of malfunctions caused by age-related
deterioration and environmental radiation will increase
further in the future. New spare units of vacuum pumping systems were purchased gradually, but these spareunits are still not suﬃcient. The following requirements
remain.
(1) All the existing RRC cryopump compressors havebeen discontinued by the manufacturer; therefore,

Table 2. Number of malfunctions from 2018 to 2020.
Cryopumpa
Turbomolecular pumpb
Rotary pump
Vacuum gaugec

2018
4
3
5
4

2019
6
8
3
6

2020
7
4
7
9

a Includes a compressor. b Includes an attached power supply.
c Includes a controller, Pirani gauge, and cold cathode gauge.

at least six cryopump compressors must be replaced with new ones within a few years. Basedon such measures, one cryopump system set of the
IRC-NE valley cavity was relocated to the RRC-VS
valley cavity in 2019, and two cryopump systems
operate in the IRC-NE valley cavity. Six SRC cryopump compressors should be also replaced withnew ones in the future.
(2) In the case of large TMPs, although one 5000 L/s
TMP of the RRC was replaced with a new one
in 2017 and one of the RILAC is scheduled to be
updated, the other 5000 L/s TMPs are not yetscheduled for replacement. In addition, a few malfunctions of large rotary pumps (RPs) have been
occurring in the rough pumping system of ring cyclotrons and have not been repaired. Therefore,
these large RPs must be replaced with new units
in the future, although their operating times arelower.
However, small TMPs and RPs as well as vacuum
gauges have been repaired or updated, and these havebeen relatively stable. Oil leaks in small RPs were mainly
repaired by replacing new O-rings and seals, and vacuum
gauges were repaired by replacing some boards and parts.
Consequently, if more cryopumps or TMPs malfunction in a year, it will be diﬃcult to operate accelerator
facilities depending on the number of spare units. Therefore, the priority would be to purchase a suﬃcient number of spare units.
References

1) S. Yokouchi et al., RIKEN Accel. Prog. Rep. 41, 101 (2008).
2) Y. Watanabe et al., RIKEN Accel. Prog. Rep. 50, 154 (2016).

Table 1. Number of vacuum pumping systems in accelerator facilities.
Cryopump system
TMP system (TMP + RP)
Rough pumping system (MDPe + RP)
AC pumping system (TMP + RP)
Sub-pumping system (TMP + RP)
Module-type vacuum gauge

RILACa
11
14
−
−
−
16

RILAC2a AVFa
8
2
11
1
−
−
−
−
−
−
9
1

RRC
14
4
2d
4
−
14

fRC
6
2
2
−
−
3

IRC
14b
4d
2
4
4
14

SRC
22
4d
2
−
8
10

BTa
3c
78
−
−
−
78

a Excludes ion sources, SRILAC, or charge strippers. b One set was relocated to RRC. c Includes a re-buncher and D6-BEA.
d One is out of order or oﬄine. e Mechanical booster pump.

∗1∗2

RIKEN Nishina Center
SHI Accelerator Service Ltd.

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II-9. Instrumentation
RIKEN
Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Development of 216 Th and 220 Th beams at the BigRIPS separator
N. Fukuda,∗1 H. Suzuki,∗1 Y. Shimizu,∗1 H. Takeda,∗1 J. Tanaka,∗1 and K. Yoshida∗1
We report the status of the development of 216 Th and
Th beams that are to be used in the recently proposed
nuclear-reaction experiment at SAMURAI. The goal ofthis development is to determine the BigRIPS separator
settings that completely meet the requirements for thebeams used in the experiment.
The Th (216 Th or 220 Th) beam is produced by meansof the projectile fragmentation of a 345 MeV/nucleon
238
U beam and separated using the BigRIPS separator. The essential requirements for the beam are as
follows:
220(1) Th-beam rate ≥104 Hz(2) Total beam rate at BigRIPS-F7 ≤ 5 × 104 Hz(3) Beam energy ≥250 MeV/nucleon

In order to meet the requirments of (1) and (2) simultaneously, the purity of the Th beam must be 20%
or heigher. Meanwhile, to achieve a higher beam energy (requirement (3)), the thicknesses of the production target and degrader must be small, which could result in insuﬃcient isotope separation and thereby makeit diﬃcult to obtain high purity. Another concern isthe particle identiﬁcation (PID) of heavy fragments.
In BigRIPS, in-ﬂight PID based on the TOF-Bρ-∆E
method1) has successfully been performed for heavy
fragments with Z = 82–90 and beam energies of approximately 200 MeV/nucleon.2) However, for fragments withhigher beam energy (≥250 MeV/nucleon in the presentcase), PID might be more diﬃcult because of the deterioration in Z resolution caused by possible energy-loss
straggling due to charge-state ﬂuctuations.3)
A test of the Th-beam production was conducted asa machine study (MS-EXP20-02) in November 2020. In
consideration of the limited beam time of 12 h, we focused on the evaluation of PID performance and theinvestigation of contaminants. The RI beams around220
Th were produced by the projectile fragmentation ofa 238 U beam impinging on a 1-mm-thick beryllium target. The setting of the BigRIPS separator was nearly
optimized for the production of a 220 Th beam, in which
the magnetic rigidity Bρ values at D1, D2, and the second stage (D3–D6) of BigRIPS were tuned for He-like,
H-like, and He-like 220 Th ions, respectively, to remove
huge contaminants from large ﬁssion-fragment yields.
A 1-mm-thick aluminum degrader was installed at F5,
while there was no suitable (suﬃciently thin) degrader
installed at F1. Instead, the parallel-plate avalanche(PPAC) detector at F1 served as a charge-exchange foil
to reduce the amount of contaminants.
Figure 1 shows the Z vs. A/Q PID plot for fragments
produced (a) without and (b) with the F5 degrader. The
A/Q values of the fragments were deduced under theassumption that the charge states of the ions did not∗1

RIKEN Nishina Center

Fig. 1. Particle identification plot of Z vs. A/Q for fragments
produced in the 238 U+Be reaction a) without energy degraders and b) with an energy degrader (1-mm-thick Al)
was used at F5. The red solid circle indicates the expected location of 220 Th88+ (A/Q = 2.5, Z = 90).

change at F5. The relative A/Q resolution is evaluatedto be 0.08% in 1σ. No signiﬁcant amounts of contaminants were observed in either setting. In the presence of
the F5 degrader, fragments in the region of Z = 85–95
were extracted as intended, showing that a thickness of
1 mm is suﬃcient for the aluminum degrader. The expected location of 220 Th88+ is indicated by the red solid
circle, in which no blobs of isotopes are found in each setting. This is probably because most of the ions transmitted to F7 changed their charge state at F5, and consequently, their A/Q values could not be deduced correctly
under the present assumption. Therefore, charge-state
identiﬁcation based on accurate Bρ analysis is required
to achieve correct PID. It should also be noted that therelative Z resolution is as poor as 0.69% (1σ). Elaborate
data analysis is currently in progress.
References

1) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
2) T. Sumikama et al., Nucl. Instrum. Methods Phys. Res.
B 463, 237 (2020).
3) H. Weick et al., Nucl. Instrum. Methods Phys. Res. B
168, 164 (2000).

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RIKEN Accel. Prog. Rep. 54 (2021)

BYACO ecosystem for innovative online operation of BigRIPS
experiments with seamless connection to comprehensive analysis
T. Sumikama,∗1 Y. Shimizu,∗1 and H. Baba∗1
Device and detector settings can be optimized online by using information based on histograms createdin an online analysis. The particle identiﬁcation (PID)
of a radioactive isotope (RI) beam is often necessary
to check the detector response. PID analysis is one of
the most important issues, especially for RI-beam tuning, to produce the required RI beams at the BigRIPS
fragment separator.1) RI-beam separation and PID are
diﬃcult for heavy or low-energy RI beams, since thecharge state of the RI beam could be diﬀerent fromthat of the fully-stripped ion and/or the accuracy ofthe energy-loss prediction may be insuﬃcient. For the
PID analysis of RI beams having diﬀerent charge statesfrom that of the main RI beam or occasionally having
any charge states, comprehensive analyses including
ﬁne calibrations and consistency checks among diﬀerent RI-beam settings were performed after the experiments.2–4) In order to operate the BigRIPS separator
for these types of RI beams, it is desirable to performthe comprehensive analysis online.
The BeYond Analysis, Control, or Operation alone(BYACO) ecosystem is being developed for the innovative online operation of BigRIPS experiments byconnecting the comprehensive analyses seamlessly withother components such as device and detector controls
and data acquisition systems. BYACO connects eachcomponent using REST and WebSocket application
programming interfaces (APIs) by applying rapidly
evolving web technologies, as shown in Fig. 1. The
BYACO main server is built using Node.js5) and distributes a single-page application in the web browser,
which is written using the React JavaScript library.6)
The main server handles requests as the proxy server.
Other servers return a response for the forwarded request and can generate an event-driven request to others. To share information in real time, push notiﬁcations are sent using WebSocket technology. A client or
each server sends a list of interest to the main server.
When each server detects updates, they are sent torequesting clients through the main server.
The data analysis is divided into real-time and comprehensive analyses, as shown in Fig. 1. The rawdata calibration and PID reconstruction are processedin the real-time analysis. The obtained variables including the raw data are stored as a TTree object
in root.7) When waveform data are taken in the future, high-throughput processing will be necessary before the real-time PID reconstruction. For the comprehensive analysis, a root-based graphical user interface (GUI) analyzer for the BigRIPS experiment∗1

Browserinterface
Sequencer
programming

REST API
WebSocket

Device(EPICS)
Detector

Database

BYACO
Main server

Comprehensive
analysisAnalyzed Data
TTree object (ROOT)DAQ
Raw data

Real-time
analysis

Highthroughput
processing

Fig. 1. Conceptual diagram of the BYACO ecosystem. The
REST and WebSocket APIs are used for the communication. The sequencer programming is for sequential
operations such as automatic RI-beam tuning.

(BigROOT) was developed. Macro programs used in
the oﬄine analysis are implemented as selectable tools
working on PROOF-Lite in root,7) which provides
functions for the event loop as well as histogram drawing and ﬁnal analyses. The GUIs to perform simple
curve ﬁtting and to make projection and proﬁle histograms have been implemented.
The sequential operation consisting of the data acquisition, analysis, device control, etc. needs to await a
response or status change. At present, the sequence of
these asynchronous tasks, which are performed by referring to many types of information, are managed using the Redux and Redux-Saga libraries8,9) on Node.js.
As the ﬁrst application of the sequential operation, theautomatic focusing and centering of RI beams were
tested online in 2020 with great success.10)
References

1) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res.
B 317, 323 (2013).
2) N. Fukuda et al., J. Phys. Soc. Jpn. 87, 014202 (2018).
3) T. Sumikama et al., Nucl. Instrum. Methods Phys.
Res. B 463, 237 (2020).
4) T. Sumikama et al., Nucl. Instrum. Methods Phys.
Res. A 986, 164687 (2021).
5) Node.js, https://nodejs.org/ .
6) React, https://reactjs.org/ .
7) R. Brun, F. Rademakers, Nucl. Instrum. Methods
Phys. Res. A 389, 81 (1997), https://root.cern.
ch/ .
8) Redux, https://redux.js.org/ .
9) Redux-Saga, https://redux-saga.js.org/ .
10) Y. Shimizu et al., in this report.

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RIKEN Accel. Prog. Rep. 54 (2021)

Development of auto-focusing and auto-centering system for the
BigRIPS separator
Y. Shimizu,∗1 N. Fukuda,∗1 H. Takeda,∗1 H. Suzuki,∗1 T. Sumikama,∗1 T. Baba,∗1 and K. Yoshida∗1

p1 = +1.80

F340

p1 = -225.81

F3

20

40
0
−20

20

−40
0

−40

−20

0

20

−40

40

−20

0

20

40

p1 = +0.84

F5

30

40

x (mm)

θ (mrad)Countsx (mm)
40

p1 = -6.35

F5

20
0

20

−20

10

−40
0

−40

−20

0

20

−40

40

−20

0

20

Countsp1 = +1.71

F7

40

40

x (mm)

θ (mrad)x (mm)

1. Start DAQ,
2. Start analysis,
3. Provide analyzed results,
4. Stop DAQ,
5. Evaluate new magnet currents,
6. Apply new magnet currents, and7. Output the stability of the magnets.

40

p1 = -60.34

F7

20

30
0
20
−20
10
−40

The realtime analysis program is always running to convert raw data into analyzed data stored as a TTree object in root.7) Presently, when the step shifts from 5
to 6, one of the choices “APPLY TO TUNE,” “NEXT
FOCAL PLANE,” and “FINISH” must be selected on
the browser interface.
The system test of the auto-focusing and autocentering system was conducted online for the 82 Gebeam production required for HiCARI commissioning.
The auto-centering was performed for each focal planein the order of F2, F5, and F7. Subsequently, the autofocusing was performed for each focal plane in the orderof F1, F2, F3, F5, and F7. Figure 1 shows the positions
and phase spaces at each focal plane after the autofocusing and auto-centering. These auto-tunings weresuccessfully demonstrated. Furthermore, the operation
time became shorter than that of conventional manual
tuning.
In future work, the simultaneous tuning of the STQs
∗160

θ (mrad)and dipole magnets will be continuously automated in
the order of F1 to F7.
CountsVarious radioactive isotope (RI) beams have been
produced by the superconducting in-ﬂight separator BigRIPS since 2007.1) We are developing the technologiesof the RI-beam separation2,3) and particle-identiﬁcation
analysis.4) We developed eﬃcient RI beam production,
including a control system for the magnetic ﬁeld witha feedback algorithm.5) In the case of a 132 Sn beam,
the production time was reduced by a factor of approximately 1/4 in the past decade. To further improvethe eﬃciency of RI beam production, we are developing a fully automatic RI beam production system basedon our technological developments and experiences. As
the ﬁrst step, auto-focusing and auto-centering systems
were developed to automatically tune the STQs anddipole magnets on the BigRIPS separator.
In the auto-focusing and auto-centering systems, weused the BYACO (BeYond Analysis, Control, or Operation alone) ecosystem developed for online operation of
the BigRIPS separator by connecting the comprehensive analyses seamlessly with others, such as devices
and data acquisition (DAQ) systems.6) The sequencer
programming of the auto-focusing and auto-centering
includes an automated loop, which consists of 7 steps

0

−40

−20

0

20

40

x (mm)

−40

−20

0

20

40

x (mm)

Fig. 1. Positions (left column) and phase spaces (right column) at each focal plane (F3, F5, and F7) after the
auto-focusing and auto-centering. The pink curves andlines show the fitted functions of the Gaussian and 1storder polynomial, respectively. The p1 values show thefitted results.

References

1) T. Kubo, Nucl. Instrum. Methods Phys. Res. B 204, 97(2003).
2) N. Fukuda et al., J. Phys. Soc. Jpn. 87, 014202 (2018).
3) T. Sumikama et al., Nucl. Instrum. Methods Phys. Res.
B 463, 237 (2020).
4) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
5) Y. Shimizu et al., RIKEN Accel. Prog. Rep. 50, 206 (2017).
6) T. Sumikama et al., in this report.
7) R. Brun, F. Rademakers, Nucl. Instrum. Methods Phys.
Res. A 389, 81 (1997).

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RIKEN Accel. Prog. Rep. 54 (2021)

Thermo-mechanical simulation of high-power rotating target for
BigRIPS separator
K. Yoshida∗1 and Y. Yanagisawa∗1
Thermo-mechanical simulations have been performed
for the high-power rotating target system 1,2) of the BigRIPS separator in order to evaluate the stability of therotating target against high-power beam irradiation. A
2-mm-thick Be target rotating at 300 rpm is expected toheat up to 1230◦ C 3) with a 238 U beam at an energy of
345 MeV/nucleon and intensity of 1 particle µA, whichmeets the target beam intensity of RIBF. The Be target does not melt in the heat of the beam, because themelting point of Be is 1287◦ C. However, it is not clear
whether the target is stable under thermal deformationor the destruction of the target at such a high temperature. Thus, the thermo-mechanical simulation of therotating target was performed to check its stability.
Coupled transient thermal-structural ﬁnite-element
analysis using the simulation code ansys 4) was utilized
for the thermo-mechanical simulation. In the ﬁrst step,
the temperature distribution of the rotating target was
obtained through a transient thermal calculation withthe moving heat-source model described Ref. 3). The
simulation model consisted of the Be target with a diameter of 300 mm and thicknesses of 2, 3, 4 mm anda cooling disk with a diameter of 240 mm and a thickness of 25 mm in which a cooling water channel wasformed. The temperature dependence of thermal conductivity and heat capacity were taken into account in
the calculation. Heat transfer coeﬃcients of 10.5 and3 kW/m2 K were used for thermal contacts between thecooling water and cooling disk and between the cooling disk and Be target, respectively. The obtained timedependent temperature distribution was then transferredto the transient structural calculation with ansys under elastic and plastic deformation. The deformationand stress caused by the thermal expansion of the target at the given temperature distribution were calculated
in a time-dependent manner. The temperature dependence of the Young’s modulus, strain-stress curve (bilinear hardening is assumed), and thermal expansion coefﬁcient of the Be target were taken into account in thecalculation.
Figure 1 shows the calculated results for a 238 U beamat 345 MeV/nucleon and 1 particle µA with a size of
1 mm2 impinging on a 2-mm-thick Be target rotating at
300 rpm. In the ﬁgure, only half of the model is displayed in order to show the cross section of the target.
In Fig. 1(a), the temperature distribution is mapped incolor on the original model shape. The highest temperature is observed at the beam spot, and the hightemperature region is spread along the beam trajectory.
The Von Mises stress due to the thermal expansion ismapped on the deformed model shape in Fig. 1(b). The∗1

RIKEN Nishina Center

Fig. 1. Results of thermo-mechanical calculation of the rotating target. Only half of the simulation model is displayedin the figure to show the cross section of the target. (a)Temperature distribution of the target displayed in color
on the original model shape (not deformed). (b) von
Mises stress distribution displayed in color on the deformed shape. Deformation was magnified by a factor
50 so that the deformation can be viewed easily.

deformation is magniﬁed by a factor 50 and shown in
Fig. 1(b). The Be target is enlarged by 0.6 mm in theradial direction and bent toward the cooling disk by
0.3 mm at the circumference. Thus, the deformationis very small compared with the 300-mm diameter of therotating target. A small but ﬁnite plastic deformation isobserved along the beam trajectory. This is why the vonMises stress at the beam trajectory decreases after the
beam passes. A plastic expansion occurs at the beamspot, and the expanded shape is retained even when thetemperature drops after the beam passes through.
The maximum von Mises stress of 260 MPa appearedat the contact region between the target and cooling disk.
The value is well below the ultimate tensile strength of
440 MPa. The calculation results show that the rotatingtarget is stable under thermal deformation and destruction.
References

1) A. Yoshida et al., Nucl. Instrum. Methods Phys. Res. A
521, 65 (2004).
2) A. Yoshida et al., Nucl. Instrum. Methods Phys. Res. A
590, 204 (2008).
3) K. Yoshida et al., RIKEN Accel. Prog. Rep. 53, 103 (2020).
4) ansys. Inc Product Release 20.

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RIKEN Accel. Prog. Rep. 54 (2021)

Incidents involving the DMT3 magnet in the beam transport line from
SRC to BigRIPS
K. Kusaka,∗1 K. Yoshida,∗1 M. Ohtake,∗1 and Y. Yanagisawa∗1
The DMT3 magnet in the “T-course” beamline is designed as a resistive-type magnet with saddle-shaped
correction coils in addition to main coils. The correction coils are installed in the gap of the magnet andwere originally excited with the main coils in series.
The main coil has 72 turns and consists of 6 double
pancakes, in which a 13.5 × 13.5 mm hollow conductor
is wound 6 times in each layer. The correction coil, on
the other hand, is a 12-turn double pancake. However,the layer isolation of the lower correction coil was damaged in an October 2017 incident.1) Furthermore, theupper correction coil was found to be short-circuitedin November 2019.2) We then investigated the possible
use of the DMT3 magnet without correction coils by
increasing the energizing current.
As the maximum current of the original DMT3
power supply was 650 A, an additional auxiliary DC
power supply was introduced in the DMT3 excitation
circuit in a parallel connection. Water-cooled protection diodes were also used for safety.2) At the end of
the beam time in December 2019, we excited only themain coils in the DMT3 magnet using two power supplies with currents of 150 A and 563 A. We conﬁrmedthat the uranium beam focused on the BigRIPS target
well and the main coils were well cooled with suﬃcientwater ﬂow. However, ramping the DMT3 power supply from 0 to 563 A with the simultaneous use of theauxiliary power supply with a current of 150 A caused
instability; therefore, we were forced to ramp up in a
stepwise manner to avoid instability.
In March 2020, we again tested power supplies forthe operation of the DMT3 magnet without correction
coils. Using the same excitation circuit, we energized
the main coils while monitoring the voltage of eachcoil pancake. We found that the lower main coil wasdamaged.
Figure 1 shows the excitation voltage at each pancake of the DMT3 coils. Firstly, we energized the magnet by using the auxiliary power supply only with acurrent of 150 A. The voltages of all the pancakes coincided. We then further energized the magnet using
the DMT3 power supply with a maximum current of
650 A. The total current was 800 A, which was larger
than the current of 710 A used to transport uranium
beams from SRC. The excitation voltages of the second and the fourth pancakes of the lower main coils
decreased with time, while the voltage of other four
pancakes increased because of the temperature rise of
conductors. These unstable behaviors in excitation
voltage indicate damage to the isolation between coil∗1

Fig. 1. Excitation voltage at each pancake of the DMT3
lower main coil.

layers. We then decreased the current and re-energizedwith currents of 100 A and 610 A. The excitation voltage of all pancakes coincided in this case. We consider
that the two pancakes are not critically damaged.
Although the lower main coil of DMT3 was damaged, 238 U and 70 Zn beams were successfully transported from SRC to BigRIPS targets in 2020 beamtime. We excited the DMT3 magnet with the main
coils and undamaged lower correction coil, which was
installed in 2018.
New main coils for the DMT3 magnet are now being
designed and fabricated. The new main coil is designed
so as to ﬁt in the DMT3 iron pole and yoke. Furthermore, we increased the number of turns from 72 to 84
such that the original DMT3 power supply energizes
the magnet without an auxiliary power supply. New
main coils will be installed in early summer 2021.
References

1) K. Kusaka et al., RIKEN Accel. Prog. Rep. 51, 173(2018).
2) K. Kusaka et al., RIKEN Accel. Prog. Rep. 53, 104(2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

Trace-back method for dispersion matching conditions of primarybeams at RIBF
A. Sakaue,∗1 D. S. Ahn,∗1 H. Baba,∗1 N. Fukuda,∗1 N. Fukunishi,∗1 N. Inabe,∗1 K. Itahashi,∗1 K. Kusaka,∗1
T. Nishi,∗1 Y. Shimizu,∗1 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 T. Uesaka,∗1 Y. Yanagisawa,∗1
K. Yoshida,∗1 S. Y. Matsumoto,∗2,∗3 R. Sekiya,∗2,∗3 Y. K. Tanaka,∗3 K. Yako,∗4 and H. Geissel∗5

∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
Department of Physics, Kyoto University
RIKEN Cluster for Pioneering Research
CNS, University of Tokyo
GSI Helmholtzzentrum für Schwerionenforschung GmbH

800

10

700

xF0 [mm]

600
5

500
400

0

300
200

−5
−0.2

100
−0.1
0
δ [%]

0.1

10

0

300
250

xF0 [mm]

We are preparing for an experiment to search for
double Gamow-Teller giant resonance (RIBF-141R1,
DGTGR) at RIBF. We use a part of BigRIPS, F0-F5,
as a spectrometer;1) this is a common setup for spectroscopic experiments at the pionic Atom Factory (RIBF135R1, piAF).
In these experiments, the energy spread of the primary beam has the largest contribution to the energy
resolution. To remedy this situation, we are developing
dispersion-matching optics, where the energy spread iscanceled out under the condition that the dispersion at
the target position F0 (x|δ)F0 is 34.1 mm/% for DGTGR
and 44.6 mm/% for piAF.
In order to satisfy these conditions with suﬃcient precision, we need to develop diagnostic methods of thephase distributions at F0 based on tracking informationand the tuning method by using the optical elementsin the upper stream. Owing to severe radiation conditions, detectors in the upstream sections require radiation hardening, and the information obtained in the section is limited. Here, we employ the trace-back method
to obtain the phase distributions from distributions measured by tracking detectors at the F3, F5, and F7 planes.
In this method, a set of the horizontal position x, angle
a, and relative momentum deviation from the reference
particle δ (= δp/p) at F3 is converted to one at a certain plane by multiplying with a transfer matrix. The
x and a at F3 are instantly obtained by measuring the
trajectory of the beam using the tracking detectors. The
δ is deduced from the horizontal positions x at F5 andF7, which are dispersive and achromatic focal planes,
respectively.
We attempted to apply the method by analyzing
data taken in June 2018 for study of the superconducting ring cyclotron-BigRIPS (SRC-BigRIPS) opticalsystem. A primary beam of 18 O8+ with an energy of
230 MeV/nucleon was transported to F7. The beam trajectory was measured by parallel-plate avalanche counters (PPACs) at F3, F5, and F7 for diﬀerent settings of
optics between SRC and F0.
We obtained reconstructed phase distributions at F0
by using the trace-back method. Figure 1 shows the
distributions at F0 for two diﬀerent settings of optics,
which are (x|δ)F0 = 34.1 mm/% for the upper panel
and 44.6 mm/% for the lower panel. Each slope corresponds to the dispersion at F0, and the deduced values

5

200
150

0

100
50

−5
−0.2

−0.1
0
δ [%]

0.1

0

Fig. 1. Correlation between the deduced x and δ at F0 for
two diﬀerent settings: (x|δ)F0 = 34.1 mm/% (upper
panel) and (x|δ)F0 = 44.6 mm/% (lower panel). Fitting
results obtained using linear functions are shown with redlines. Each slope corresponds to the deduced dispersion.

are 30.8 mm/% and 37.3 mm/%, respectively. The ﬁtregion corresponds to the momentum spread for the welltuned beam (σ ∼ 0.03%).2) The precision of determination of the dispersion at F0 is approximately 3 mm/%,which is suﬃcient as the experimental resolution. The
absolute values of dispersion in this measurement wereslightly diﬀerent from the ideal values. By referring to
the reconstructed distribution, we can tune the optics
so as to cancel the diﬀerence. We are now reﬁning thetuning method to provide an online feedback based on
the diagnosis.
In summary, we have developed the trace-backmethod for tuning the dispersion at F0 so as to fulﬁll
the matching condition. We are now working on an optimization of the tuning method for the beam time.
References

1) T. Nishi et al., Nucl. Instrum. Methods Phys. Res. B 317,
290 (2013).
2) T. Nihsi, Doctoral Thesis, University of Tokyo (2015).
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RIKEN Accel. Prog. Rep. 54 (2021)

Conceptual design of a heavy ion storage ring RUNBA
M. Wakasugi,∗1,∗2 T. Ohnishi,∗1 R. Ogawara,∗1,∗2 S. Takagi,∗2 K. Kuze,∗2 and Y. Yamaguchi∗1
We plan to construct a heavy ion storage ring,
RUNBA (Recycled-Unstable-Nuclear Beam Accumulator) adjacent to the SCRIT facility in the E21 experimental room. RUNBA will be a research and development machine for developing and establishing a beam
recycling technique in a storage ring for application to
nuclear reaction studies for rare RI beam. This project isongoing under the joint research program between ICR
Kyoto University and RIKEN Nishina Center (RNC). In
the last year, we transfered the storage ring (sLSR),1)
which was avandoned for more than ten years, from ICR
to RNC. RUNBA is a rebuilt machine of sLSR and weare designing the lattice structure and machine layout inE21. Figure 1 shows a current ﬂoor plan of the RUNBA
facility. RUNBA will be connected to ERIS, which is an
ISOL system for SCRIT experiments.
Continuous singly-charged ion beams from ERIS are
converted into a pulsed ion beam by FRAC and a highlycharged ion beam by RECB (Resonant Extraction
Charge Breeder),2) which is under development at ICR.
A fully-stripped pulsed ion beam with 10 keV/nucleon
is injected into RUNBA with a multi-turn injection
method. Consequently, it can be accelerated up to
10 MeV/nucleon by repeating ﬁve times the acceleration
process in which the ion velocity doubled by sweeping
an RF frequency at the non-resonant ferrite cavity andsynchronously ramping up the magnetic ﬁeld.
The concept of beam recycling is that the energy loss,
energy straggling, and transverse angular straggling produced when the beam passes through the internal target are corrected turn by turn and particle by particle, and beam circulation is stably maintained until nuclear reaction occurs at the target. Therefore, devices
required to be equipped in RUNBA in addition to theFig. 1. A plane view of RUNBA facility.
∗1∗2

RIKEN Nishina Center
ICR, Kyoto University

Fig. 2. Beta and dispersion functions of RUNBA.
Table 1. Lattice structure and properties of RUNBA.
Circumference (m)Maximum Bρ (Tm)Transition γ
Harmonics (10 keV/nucleon, 10 MeV/nucleon)
RF frequency (MHz)
Tunes (νx , νy )Max. dispersion functions (ηx , ηy ) (m)at focal point
Beta functions (βx , βy ) (m)Dispersion functions (ηx , ηy ) (m)26.5571.05
1.855(32, 1)1.674–3.348(2.368, 1.695)(3.497, 0.0)
(0.697, 0.527)(0.0, 0.0)

fundamental optical elements include an internal target
system, acceleration cavity, energy-dispersion corrector,
and transverse emittance corrector. The fundamental
properties in the current design of RUNBA are summarized in Table 1. The beta and dispersion functions over
the whole ring are shown in Fig. 2. RUNBA optics isformed with 6 bending magnets, 3-family 12 quadrupole
magnets, 2-family 4 sextupole magnets, and a triplebend achromatic arc structure that is adopted to provide achromatic focus points for internal target insertionin the straight section. In another straight section, an
energy-dispersion corrector will be installed and emittance correctors in the horizontal and vertical directions
are placed at positions where the betatron phase advances are 0.75 from the target. The diﬀusion of energy
spread would be suppressed by giving appropriate positive or negative energy gain determined from the diﬀerence in ﬂight time from the target to energy-dispersion
corrector. The emittance correctors transversely kickions according to the transverse position measured at
the target. These new feedback systems are now being
developed at ICR.
References

1) A. Noda et al., Proc. EPAC2006, 237 (2006).
2) R. Ogawara et al., in this report.

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RIKEN Accel. Prog. Rep. 54 (2021)

Development of Resonant-Extraction Charge Breeder (RECB)
R. Ogawara,∗1,∗2 S. Takagi,∗2 K. Tsukada,∗2 H. Tongu,∗2 Y. Kuriyama,∗2 and M. Wakasugi∗1,∗2
Potential oscillation ON (Non)Potential oscillation OFF(Noff)

Event rate [cps]

40
30
20
10
0

50

100

150

200

250

300

Frequency of potential oscillation ω [kHz]Fig. 2. Spetrum of extracted 12 C4+ ions.
12 4+

C

2.5

Enhancement factor

In the RUNBA project,1) RI ions from ERIS2) are
accelerated in the storage ring (RUNBA) for nuclear reaction experiments. For eﬃcient acceleration, RI ionsshould be a highly charged ion beam. Although an EBIT
type charge breeder (CB) is widely used to increase
the charge state, an eﬃciency of only 20% hase beenachieved do far because of ﬁnite spread in charge state
distribution.3) We developed a prototype of a resonantextraction charge breeder (RECB) to improve the eﬃciency, the RECB can selectable extract only the desired
charge state ions.
In a RECB, a longitudinal electrostatic potential for
ion trapping is designed as a quadratic shape on an electron beam axis (Fig. 1). The longitudinal motion ofions in the potential is a simple harmonic oscillation forwhich the frequency depends on the mass-to-charge ratio. Thus, the ion motion is excited by adding an oscillation to the electrostatic potential at the resonant
frequency. Then, ions of a selected charge state are extracted from the trapping regions, and the others areleft in the RECB. When we apply a time-dependent potential Vtrap (z, t) = (a + b sin(ωt))z 2 (z, ω, and a andb represent the position, frequency of the potential oscillation, and constants, respectively), the ion motion is
described by Mathieu’s diﬀerential equation.
As shown in Fig. 1, RECB consists of an electron gun,a solenoid coil, an electron beam collector, and 20 electrodes that form the trapping potential Vtrap (z, t) usinga DC power supply and a function generator. In thetrapping region, the energy, current, and beam radius,of the electron beam were −32 keV, 10 mA, and 0.06 mm,
respectively. Collection eﬃciency at the electron beamcollector was more than 99.5% when the solenoid magnetic ﬁeld was 0.13 T. Extracted ions with an energyof 10 keV/q from the RECB were separated by the analyzing magnet, and then, they were detected with achanneltron.

(Non-Noff) / Noff

2
1.5
1
0.5

+

H

H2+

12 2+ 16 2+

C

12 +

C

O

14 +
N
2+ 16 +

O

H2O+

+

OH+ 19F+

CO

0

CH3
0

5

10

Mass-to-charge ratio (A/q)

15

20

Fig. 3. Enhancement factors of extracted of 12 C4+ ions.

We evaluate the performance of the potential oscillation by measuring the extracted residual gas ions (vacuum pressure = 5 × 10−6 Pa). Figure 2 shows an example of a 12 C4+ ion extraction where the depth of thequadratic shape potential is 150 V and the function generator supplies a 1.0 Vpp sine wave for a short durationof 0.5 ms with a repetition rate of 500 Hz. The red andblue plots indicate the spectrum of the extracted 12 C4+ions from the RECB with and without the potential
oscillation (Non and Noﬀ ), respectively. We conﬁrmedthat 12 C4+ ions were extracted at their fundamental frequency (90 kHz) and second order harmonic frequency(180 kHz). The spread of the spectrum was attributed
to a distortion of the electrostatic potential produced by
the space charge of trapped ions. Figure 3 shows the enhancement factor estimated by the event rate for (Non −Noﬀ ) divided by that for Noﬀ at a frequency of 90 kHz.
The enhancements for the 12 C4+ ions were 30, 42, and
9.0 times greater than those for the 12 C+ , 12 C2+ , and
12 6+C ) ions, respectively. In futureH+
2 (same A/q ofwork, we will optimize the electrostatic potential form
to improve charge state selectivity for extraction.
References

Fig. 1. The schematic diagram of the prototype RECB.
∗1∗2

RIKEN Nishina Center
Institute for Chemical Research, Kyoto University

1) M. Wakasugi et al., in this report.
2) T. Ohnishi et al., Nucl. Instrum. Methods Phys. Res. B,
317, 357 (2013).
3) F. Wenander, J. Instrum. 5, C10004 (2010).
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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Development of a forward detector for the measurement of the meansquare radius of the neutron distribution of unstable nuclei by electron
scattering
H. Wauke,∗1,∗2 A. Enokizono,∗1 T. Suda,∗1,∗2 K. Tsukada,∗1,∗3 T. Ohnishi,∗1 M. Wakasugi,∗1,∗3 M. Watanabe∗1
In nuclear physics, the nucleon density distribution isan essential physical quantity because it directly reﬂects
the wave function of nucleons. Electron scattering provides detailed information of the nucleus’s charge density distribution, dominated by the proton distribution.
However, it is diﬃcult to determine the neutron distribution by electron scattering because its contribution to
the charge density distribution is less than a few percent.
It was recently suggested that the mean square radius (msr) of the neutron distribution could be accessedby measuring the fourth–order moment of the charge
density distribution.1,2) The charge form factor deduced
from elastic electron scattering at the low momentum
2transfer can be Taylor-expanded as F (q) ∼ 1− <r6>c q 2 +<r 4 >c 4<r 6 >c 6
120 q − 5040 q · · · , where F is the form factor, q is
the momentum transfer, and < rn >c is the nth-ordermoments of the charge density distribution. Figure 1
shows the q 2 dependence of the 132 Xe form factor andthe contribution of each term of the above equation. The
msr of the neutron distribution measurement of unstable
nuclei by electron scattering will be obtained in a region
that covers the forward scattering angle (12–25◦ for theelectron beam energy Ee = 150 MeV). In the low momentum transfer region (less than 0.09 fm−2 in the case of Xe
isotopes), the form factor is sensitive almost to only thesecond- and fourth-order moments of the charge density
distribution.
The study of the msr of the neutron distribution of Xe

Fig. 1. q 2 dependence of the 132 Xe form factor obtained by
the past experiment.4) The black line shows the form factor for which all moments are calculated. The red andblue lines show the form factor up to the second- andfourth-order moment of the charge density distribution,
respectively.
∗1
∗2
∗3

RIKEN Nishina Center
ELPH, Tohoku University
Institute for Chemical Research, Kyoto University

SCRIT device(500 mm)

Vertex in the beam direction [mm]Fig. 2. Reconstructed vertex distribution of electron scattering events from the target region (blue line). The red line
shows the events where the scattered electrons have kinetic energies higher than 100 MeV. The events at −450
to −200 mm are from the material upstream of the target
region. The blue line shows events containing low energy.

isotopes (stable : 124–136 Xe, unstable : 138, 140 Xe) by electron scattering is under consideration at the SCRIT facility.3) A forward detector for measuring the fourth-ordermoment of the charge density distribution is under discussion. A series of background studies were performed
using an alternative detector to investigate the number ofbackground events at the new setup for the measurementin the low momentum transfer region. This is because it
may not be possible for the forward detector to distinguish between the elastic scattered electrons signals fromthe target nuclei and the background signal if there are
more or similar amounts of background events than thetrue one in the target region (length is 500 mm). The
background study was performed with a calorimeter array of seven CsI crystals and two drift chambers, which
covered a scattering angle of 18 ± 1◦ from the center of
the SCRIT device and measured the scattered electronsenergy Ee′ by summing energy deposits of CsIs.
Figure 2 shows the reconstructed vertex distributionof electron scattering events from the target region. The
red line in Fig. 2 denotes those of Ee′ > 100 MeV and is
identiﬁed as the elastic events. These events at −450 to−200 mm are considered as the elastic scattering eventsof the electron beam halo from the material upstream of
the target region. The forward detector cannot separate
these events from the vertex distribution of the target
nuclei. It needs to consider approaches to reduce background events, for example, by reducing the material
around the SCRIT device.
References

1) H. Kurasawa, T. Suzuki, Prog. Theor. Exp. Phys. 2019,
113D01 (2019).
2) H. Kurasawa, T. Suda, T. Suzuki, in this report.
3) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res. B
317, 668 (2013).
4) K. Tsukada et al., Phys. Rev. Lett. 118, 262501 (2017).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Ion-beam-profile monitor using MCP at the SCRIT electron scattering
facility
T. Ohnishi,∗1 S. Ichikawa,∗1 and M. Wakasugi∗1,∗2
At the SCRIT electron scattering facility,1) ion-beamproﬁle monitors2) are installed in the ion-beam transport line for injecting low-energy (∼10 keV) ions into the
SCRIT device.1) They are composed of a meshed Faraday cup, a CsI(Tl) scintillator, an optical prism, and a
network-based CCD camera. Using these monitors, ionbeam tuning is performed in real time. However, it isdiﬃcult to apply them to a low-rate ion beam, such as acontinuous beam with 107 ions/s or a pulsed beam with
106 ions/pulse, because the number of produced photons
is considerably less than the expected value calculatedusing the conversion factor, 2 × 104 photons/MeV. Oneof the reasons for this suppression is that the low-energy
ions stop near the surface of a CsI(Tl) scintillator and thenumber of involved CsI molecules is insuﬃcient. Thus,
a new ion-beam-proﬁle monitor is required for real-time
beam tuning with low-energy RI beams. This year, wetested a new monitor using a micro channel plate (MCP)
and report out ﬁrst results in this paper.
Figure 1 presents a schematic view and photograph ofan ion-beam-proﬁle monitor using an MCP. This monitor
consists of two MCPs equipped with a phosphor screen(HAMAMATSU F2806 with P46), an optical prism,
and a network-based CCD camera (Basler scA640-70gc).
The horizontal and vertical dimensions of the eﬀective
area of the MCP are 45 mm and 35 mm, respectively. A
collimator, which has a 28-mm diameter hole, is installedin front of the optical prism to deﬁne the eﬀective detection area because the eﬀective area of the MCP is larger
than the entrance size of the optical prism, 30 mm2 . In
the present setting, ion beams are directly observed with
MCPs. The applied voltages of MCP-in, MCP-out, andPhos-in, which are electrodes shown in Fig. 1, are 0, 2,
CCD
Viewport
Phos-in
MCP-out
MCP-inPhotons
Ion beam

Optical prism
Collimator

MCP×2

Phosphor screen

Fig. 1. Schematic view and photograph of the ion-beamprofile monitor. MCP-IN, MCP-OUT, and Phos-in represent electrodes of the monitor.
∗1∗2

RIKEN Nishina Center
ICR, Kyoto University

Fig. 2. Beam profile of 1 pulse with a 104 ions/pulse beam.
Left figure is the image of the beam profile and right figure
is its digital number distribution.

and 6 kV, respectively. The extracted electron cloud resulting from the beam encountering the MCP surface isconverted to photons in the phosphor screen, which aretransported to the CCD camera through the collimatorand the optical prism. The exposure time of the CCD
camera is set to 500 µs. Data from the CCD camera
are monitored through a network in real time. With apulsed beam, the trigger of the CCD camera is synchronized with the injection timing.
The commissioning of the new ion-beam-proﬁle monitor was performed using a 138 Ba-ion beam of 6 keV. Figure 2 shows the measured beam proﬁle of only 1 pulse
using a 1-Hz pulsed beam with 104 ions/pulse. The number of ions with a low-intensity pulsed beam was estimated with the current of a continuous beam, 13 pA,
measured at the Faraday cup installed in front of theion-beam-proﬁle monitor. Calibration was performed using a 0.3-nA continuous beam and a pulsed beam with
5×105 ions/pulse. Figure 2 shows an image of the beam
proﬁle (left) and its digital number distribution (right).
More detailed analysis is being performed to estimate
the number of injected ions using only the digital number distribution.
We tested the new ion-beam-proﬁle monitor using an
MCP with a low-intensity pulsed ion beam. The beam
proﬁle of a low-intensity pulsed ion beam was successfully measured in real time. In the case of RI beams using the present monitor, electrons corresponding to the
decay of the RIs can cause background events. To avoid
this problem, a thin foil is installed in front of the MCPs
to stop RI beams, and electrons produced during the decay of RIs are used as an MCP signal. Next year, we
will test a new setup using RI beams and evaluate its
applicability considering the eﬃciency and position resolution.
References

1) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res. B
317, 668 (2013).
2) M. Togasakai et al., RIKEN Accel. Prog. Rep. 44, 173 (2011).

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II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Extraction test of stopped Bi isotopes in PALIS gas cellT. Sonoda,∗1 I. Katayama,∗1 M. Wada,∗2 H. Ishiyama,∗1 V. Sonnenschein,∗3 H. Tomita,∗3 R. Terabayashi,∗3
K. Hattori,∗3 H. Iimura,∗4 S. Iimura,∗1 T. M. Kojima,∗1 M. Rosenbusch,∗2 A. Takamine,∗1 N. Fukuda,∗1
T. Kubo,∗1 S. Nishimura,∗1 Y. Shimizu,∗1 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 M. Tanigaki,∗5 andK. Yoshida∗1
We are developing a scheme of parasitic low-energy
RI-beam production (PALIS)1) in the second focal
chamber (F2) of BigRIPS to eﬀectively use rare isotopes and to perform comprehensive measurements ofthe physical properties of exotic nuclei.
In our previous experiment,2) we conﬁrmed the feasibility of a new gas-cell geometry that separates high- andlow-radiation areas with a long gas tube. The current
setup for the PALIS on-line examination evaluates RI extraction by detecting alpha rays via alpha-emitter decay,
which results in enhanced sensitivity because of the extremely low background environment. While the alphaemitter element should be available on resonant laser
ionization in an oﬀ-line or on-line experiment. Therefore, we chose a bismuth (191 Bi) beam that can be produced by projectile fragmentation via a uranium beamand beryllium target. In a 12 hours online PALIS experiment, we focused on two objectives: 1) identify the
stopped Bi isotope and 2) extract the stopped Bi isotope
from the gas cell.
To achieve the ﬁrst objective, we observed alpha rays
created via decays from the alpha emitters that were
stopped in the ∆E solid-state detector (SSD) placedin front of the gas cell by adjusting the energy degrader, as shown in Fig. 1. As the energy resolution was considerably low because of the high electriCounts
20

Counts
T1/2=11.87

0.73

10

15

1

10

0

20

40

60

80

100

time(s)

5

0
3000

4000

5000

6000

7000

8000

alpha energy (keV)

Fig. 1. Alpha spectrum observed using a ∆E Solid-state detector (SSD) placed in front of the gas cell. The inset
shows the alpha counts versus time in the beam-oﬀ period in the energy range of 6.1–6.6 MeV in the alpha
spectrum.
∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
Faculty of Engineering, Nagoya University
Advanced Science Research Center, JAEA
Institute for Integrated Radiation and Nuclear Science, Kyoto
University

Counts
14

12

10

8

6

4

2

0
0

100

200

300

400

500

600

700

800

ADC channel

Fig. 2. Alpha spectrum observed using a silicon PIN diodeplaced after the gas-cell exit.

cal background at F2, isotope identiﬁcation by alphaenergy (Eα ) was impossible from this energy spectrum.
However, we obtained other information from the timing chart by using a pulsed BigRIPS beam. The halflives extrapolated by decay ﬁtting to individual timing
charts for speciﬁc energy ranges were 42.12 ± 4.66 s (5.4–
6.1 MeV), 11.87 ± 0.73 s (6.1–6.6 MeV) and 7.7 ± 0.3 s(6.6–7.5 MeV). The tentative isotope candidates forthese half-lives are 192 Bi (T1/2 = 39.6 s, Eα = 6060 keV),
191
Bi (T1/2 = 12.4 s, Eα = 6309 keV), and 190 Bi (T1/2 =6.4 s, Eα = 6456 keV).
To achieve the second objective, we performed an
extraction test of RIs that were stopped in argon gas(50 kPa) and transported to the gas-cell exit via a longgas tube by simple gas ﬂow to ﬁnally impinge on a silicon
PIN diode detector located after the gas-cell exit hole.
We conﬁrmed the extracted RIs from alpha spectra observed using the silicon PIN diode, as shown in Fig. 2.
These extracted RIs included species of all charge statessuch as neutral and positive/negative ions. By comparison with the total number of alpha counts detected
at the ∆E SSD, normalizing primary beam intensity,and considering the solid angle of the detector, we preliminarily evaluated the extraction eﬃciency as approximately 1%.
The extraction of stopped RIs out of the gas cell was
conﬁrmed. In the next beam time, we will apply laser
ionization for producing low-energy RI beam.
References

1) T. Sonoda et al., Prog. Theor. Exp. Phys. 2019, 113D02(2019).
2) T. Sonoda et al., RIKEN Accel. Prog. Rep. 53, 105 (2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Improvement of evacuation time of RI from argon gas cellT. Sonoda,∗1 M. Wada,∗2 K. Hattori,∗3 H. Iimura,∗4 S. Iimura,∗1 H. Ishiyama,∗1 I. Katayama,∗1 T. M. Kojima,∗1
M. Rosenbusch,∗2 V. Sonnenschein,∗3 R. Terabayashi,∗3 A. Takamine,∗1 and H. Tomita∗42e-12

An argon gas cell coupled to a resonant laser ionization is a powerful tool for the production of high-purity
low-energy RI-beam. This method utilizes neutral RI
transportation using simply a gas ﬂow, until it reaches
the location for laser ionization which is typically close
to the exit of the gas cell. A feasible RI is restricted byits half-life, which should be longer than the evacuation
time of the gas cell. The evacuation time can be determined from the conductance of a small exit aperture andgas cell volume. Under adiabatic expansion, the conductance depends only on the diameter of the exit aperture1)
as follows:
C = 0.14 × ϕ2 .

V
.
C

(2)

For example, when the gas cell volume is 100 cm3 andthe exit diameter is 1 mm, the evacuation time is 714 ms.
This value makes it diﬃcult to aim for very rare RI regions, where the half-lives are typically less than 100 ms.
In order to address a fast evacuation, two solutions
can be considered: (1) using a small volume for the gas
cell and (2) using a large exit aperture. However, these
improvements are limited by the stopping eﬃciency for

Gas cell
Ar 50kPa

Laser

compressor

exit hole(>2mm )

~500Pa1Pa

10-3Pagas jetrf-carpet(exit:0.4mm

spig/
-qpig

skimmer

Dry
pump1
Dry
pump2
T.M.P

Fig. 1. Proposed gas cell and diﬀerential pumping layout incombination with rf-carpet.
∗1
∗2
∗3
∗4

Ion current (A)1.6e-12RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
Faculty of Engineering, Nagoya University
Advanced Science Research Center, JAEA

I.P.=
58762.31cm-1

6p27S4P1/2

32588.17cm-1

1.4e-121.2e-12

F.C @rf-carpet

83Bi
306.86 nm

6p34S3/2

0cm-1

1e-12
8e-13

F.C @spig

6e-13
4e-13
2e-13
0
-2e-13306.84(1)

where the units are L/s for C and mm for ϕ. The gas
is argon. The evacuation time of a gas cell of volume V
can be written as:t=

355 nm (YAG355)

1.8e-12306.845306.85306.855

306.86306.865306.87306.875

306.88

Wavelength(nm)Fig. 2. Ionization spectrum by scanning ﬁrst step excitation
when rf-carpet/spig is used as Faraday cup.

high-energy RIs, which require a large volume acceptance. They are also limited by the capability of differential pumping. Here we propose installation of an
rf-carpet with a very small exit aperture in the initialdiﬀerential pumping room while using a large aperture
for the gas cell exit. Figure 1 shows a schematic layout. The rf-carpet is placed after the gas cell exit. The
pressure in this room can be increased up to 1 kPa atwhich the ion extraction by the rf-carpet is still practical without a discharge problem. The ions move witha gas jet toward the rf-carpet after exiting the gas cell;subsequently they are guided by the rf- and dc-electricﬁelds to the exit of the rf-carpet. Owing to the small
exit aperture of the rf-carpet, the loads from the following diﬀerential pumping are suppressed. When the exit
aperture of the gas cell is large, the total gas throughput becomes very high, leading to an extremely high gas
consumption cost. However, by using a gas circulation
system,2) the gas consumption rate can be drasticallysaved.
A preliminary oﬀ-line experiment was conducted with
a 0.4 mm rf-carpet aperture for photo-ionized Bi ions.
The pressure at the rf-carpet was approximately 500 Pa.
Bi atoms were produced inside the gas cell, and subsequently they were ionized by the laser and extracted
from the gas cell exit (2 mmϕ). Figure 2 shows the resultof the comparison when the ions are collected on the rfcarpet and on the spig rods placed next to the rf-carpet.
We conﬁrmed a reasonable extraction eﬃciency for the
rf-carpet. The feasibility study is in progress.
References

1) A. Roth, Vacuum Technology (North-Holland, Amsterdam 1982).
2) T. Sonoda, et al., Rev. Sci. Instrum. 87, 065104 (2016).
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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Fourth report on oﬄine tests for RF carpet transportation in RF ion
guide gas cell at the SLOWRI facility
A. Takamine,∗1 S. Iimura,∗1,∗2,∗3 D. Hou,∗3,∗4,∗5 M. Wada,∗3 M. Rosenbusch,∗3 S. Chen,∗3,∗6 W. Xian,∗3,∗6
S. Yan,∗3,∗7 P. Schury,∗3 Y. Ito,∗1,∗8 T. M. Kojima,∗1 T. Sonoda,∗1 Y. X. Watanabe,∗3 H. Ueno,∗1 and
H. Ishiyama∗1

1st
RFC

2nd
RFC

1st
RFC

Ion trajectory
Fig. 1. Sketch of 1st RFC and 2nd RFCs around the exit
hole with an ion trajectory in blue.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8

RIKEN Nishina Center
Department of Physics, Osaka University
Wako Nuclear Science Center (WNSC), IPNS, KEK
Institute of Modern Physics, Chinese Academy of Sciences
School of Nuclear Science and Technology, Lanzhou University
Department of Physics, The University of Hong Kong
Institute of Mass Spectrometry and Atmospheric Environment, Jinan University
Advanced Science Research Center, JAEA

1
150 kHz125 kHz100 kHz75 kHz
50 kHz
30 kHz
10 kHz0.8
Transport efficiency

A new gutter structure RF ion guide gas cell1) was developed at the SLOWRI facility. The gas cell comprises
two RF carpet (RFC) stages. We previously reported
on the transportation eﬃciencies of the 1st stage RFC
for various gas pressures and various RF frequencies.2,3)
In this report, the transport eﬃciency including the 2ndstage RFC is presented.
The 2nd RFC comprises concentric ring electrodes
with a pitch of 0.26 mm (electrode width of 0.1 mm andinter-electrode spacing of 0.16 mm); there is a ϕ0.65 mm
exit hole at the center of the 2nd RFC. Ions are collected
onto the 1st carpet and transported to the inner edgesof the pair of the 1st RFCs. After they are pulled overthe edge to the 2nd RFC by a DC ﬁeld, they are delivered to the exit hole by the “ion surﬁng” transporttechnique that uses the combination of two-phases RF
and four-phases audio-frequency (AF) ﬁelds4) (Fig. 1).
A segmented quadrupole ion beam guide (smQPIG) is
placed behind the exit hole. The ions are transported toa high vacuum region by the smQPIG through diﬀerential pumping stages.
We recently investigated the transport eﬃciency including the 2nd RFC in oﬄine tests. Cesium ions were
produced from a surface ionization ion source at the in-

0.6
0.4
0.2
0

0

5

10

15

20

25

AF voltages applied to 2nd RFC [Vpp]Fig. 2. Oﬄine test results on the transport eﬃciency for Cs+
as a function of AF voltages at various AF frequencies.

ner wall of the gas cell. The entire setup has been described in Ref. 1). We measured the ion currents on
the RFCs and subsequently on the smQPIG. The RFC
transport eﬃciency was deﬁned as the ratio of the twocurrents.
Figure 2 shows the test results in 133 mbar of room
temeperature He gas as a function of the AF voltages
for various AF frequencies. The RF voltages applied
to the 1st and 2nd RFCs were 103 Vpp at 8.15 MHz
and 111 Vpp at 10.06 MHz, respectively. The push DC
ﬁeld between the 1st and 2nd RFCs was ∼40 V/cm.
We achieved ∼90% transport eﬃciency with an AF frequency of 125 kHz in this measurement. The plotsshow a sudden drop at 12–15 Vpp for AF frequencies≥125 kHz, because the AF signals became highly distorted by the AF/RF coupling circuitry. An attempt toimprove the circuit characteristics is afoot.
This gas cell was coupled to an MRTOF mass spectrograph for a parasitic experiment during the HiCARI
campaign in 2020. The online experiment results about
this gas cell are reported in other articles by S. Iimura
and D. Hou in this issue.
References

1) A. Takamine et al., RIKEN Accel. Prog. Rep. 52, 139 (2019).
2) S. Iimura et al., RIKEN Accel. Prog. Rep. 53, 107 (2020).
3) A. Takamine et al., RIKEN Accel. Prog. Rep. 53, 108 (2020).
4) G. Bollen, Int. J. Mass Spectrom. 299, 131 (2011).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

High mass resolving power and isomeric state separation at
SLOWRI/ZD-MRTOF system
W. Xian,∗1,∗2 M. Rosenbusch,∗2 S. Chen,∗1,∗2 Y. Hirayama,∗2 D. Hou,∗3,∗2 S. Iimura,∗5,∗4 H. Ishiyama,∗4
Y. Ito,∗6 S. Kimura,∗4 J. Liu,∗3 H. Miyatake,∗2 S. Nishimura,∗4 T. Niwase,∗7,∗4,∗2 P. Schury,∗2 A. Takamine,∗4
M. Wada,∗2 Y. X. Watanabe,∗2 H. Wollnik,∗8 and S. Yan∗9
With high precision and accuracy, as well as shortmeasuring times, the multi-reﬂection time-of-ﬂight mass
spectrograph (MRTOF-MS) has become competitive
with Penning traps for measuring masses of short-lived
nuclei.1) In 2013, the ﬁrst MRTOF built at RIKEN wastested online by measuring 8 Li ions. The mass excess of
8
Li was accurately reported to be 20947.6(15)(34) keV(∆m/m ∼ 6.6 × 10−7 ). The mass resolving power
achieved at that time was Rm > 150k.2) In 2020, a
next-generation device of similar design has been put
into operation at the ZeroDegree spectrometer of RIBF
with the goal of measuring very exotic nuclides andtheir isomers with a higher resolving power.
In the MRTOF reﬂection chamber, ions are conﬁned
and reﬂected back and forth between a pair of ion
reﬂection mirrors, allowing the ions to have a ﬂight
path of up to or beyond one kilometer. In any ﬁeld-free
drift region, more energetic ions have a shorter time-ofﬂight, but in the reﬂection region inside the ion mirrors,
this can change because of the shape of the potential
distribution. It is possible to make more energetic
ions penetrate deeper into the mirrors to achieve a
longer ﬂight path that compensates for their higher
energy and equilibrates the time-of-ﬂight with thatof less energetic ions. The better this compensation
works, the narrower the ﬁnal TOF distribution canbe as ions with diﬀerent energies can simultaneously
reach the detector.3) However, this requires a nontrivial search for complex mirror potentials and thoseof ion-optical focusing elements located in the central
drift tube section. In our case, this would require asearch in 11-dimensional parameter space.
In a ﬁrst-order approach, every possible potential
distribution is the generator of a function mapping
the TOF of an ion to a kinetic energy TOF(E). In
recent oﬄine experiments using the new ZD-MRTOF
system, by use of a pulsed drift tube between theion trap and MRTOF, we measured these response
functions in a much wider energy range than done
before. This measurement was repeated after changing
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

Department of Physics, The University of Hong Kong
Wako Nuclear Science Center (WNSC), IPNS, KEK
Institute of Modern Physics, Chinese Academy of Science
RIKEN Nishina Center
Department of Physics, Osaka University
Advanced Science Research Center, JAEA
Department of Physics, Kyushu University
Dep. of Chem. and Biochem., New Mexico State University
Institute of Mass Spectrometry and Atmospheric Environment, Jinan University

279 keV(AME2016)

Fig. 1. TOF spectrum of 134g Sb+ and 134m Sb+ in the online
experiment of the ZD-MRTOF system.

some voltage of each ion mirror. In this manner,the eﬀect of changing each mirror potential on thisfunction could be studied. This allowed for an improved
local search around the present conditions to fulﬁll thecondition ∂TOF(E)/∂E ≈ 0 for a particular numberof reﬂections. The diﬀerent shapes of the TOF(E)functions have been added in an appropriate manner,which resulted in a new voltage conﬁguration withexcellent energy compensation.
In the corresponding oﬄine tests, by using 39 K+ ionsfrom a thermal ion source to perform the procedure
mentioned above,a mass resolving powerRm ∼ 700k was achieved for the ﬁrst time at RIBF,
with a ﬂight time of ∼9 ms after 490 laps.
The ﬁrst online commissioning experiment of the
MRTOF at ZeroDegree terminal was conducted at theend of 2020. Even under online conditons, we weregenerally able to maintain a mass resolving powerin excess of 500k during the commissioning. Thishigh mass resolving power allowed us to demonstrate
an isomeric separation of 134m, g Sb+ , which has anisomeric state with an excitation energy of 279(1) keV[T1/2 = 10.07(5) s] above the ground state [T1/2 =0.78(6) s]. As shown in Fig. 1, we could successfully
identify the ground state (134g Sb+ ) and the isomericstate (134m Sb+ ) in the TOF spectrum owing to the very
high mass resolving power that the ZD-MRTOF systemachieved.
References

1) Y. Ito et al., Phys. Rev. C 88, 011306(R) (2013).
2) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
335, 39 (2014).
3) R. N. Wolf et al., Int. J. Mass Spectrom. 313, 8(2012).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Oﬄine ion source for laser spectroscopy of RI at SLOWRI†
M. Tajima,∗1 A. Takamine,∗1 M. Wada,∗2 and H. Ueno∗1# of ions / pulse# of ions / pulse

The collinear laser spectroscopy of radioactive iso- (a)tope (RI) beams is a powerful technique used to diTarget
RFQ
rectly measure the nuclear properties of ground or isomeric states. Isotope shift measurement is planned usRFCPCylindricaling RI ion beams supplied from the universal slow RIelectrodes
QPIG
beam facility (SLOWRI) at RIBF. The main targets are
medium-mass nuclei of refractory elements, for which
experimental studies are insuﬃcient. To achieve highprecision, it is essential to determine a reference frequency with well-studied isotopes for the planned spectroscopy apparatus to minimize systematic uncertain- (b)x103ties. In this work, an ion source combining the laser
500
ablation of solid targets in helium gas and a radio fre400
quency (RF) ion guide system with an RF carpet1) was
300
constructed for the reference measurement of isotope
200
shifts.
100
Figure 1(a) shows a sketch of the ion source. It0consists of cylindrical DC electrodes, an RF carpet,
89
90
91
92
93
94
95
96
97
m/q
a quadrupole ion beam guide, and an RF quadrupole(c)(RFQ). A solid target for laser ablation was ﬁxed on
the surface of the cylindrical DC electrodes. Helium
80000
gas was continuously introduced into the ﬁrst cham60000
ber via a piezo valve while the second and the third
40000
chambers were evacuated. The pressure of the ﬁrst
20000
chamber was measured using a capacitance manome0
ter and stabilized by controlling the piezo valve with181 182 183 184 185 186 187 188
m/q
proportional-integral-derivative (PID) feedback. A Qswitched Nd:YAG laser (532 nm, ∼5 ns width) was inFig. 1. (a) Sketch of the ion-source system. (b) Mass specstalled outside the chamber. The laser light was fotrum of Zr+ . (c) Mass spectrum of W+ .
cused using a lens, and the light passed through a view
port normal to the ablation target surface. The laser
power was 25 mJ per pulse at maximum, and it could
system was studied separately using a Cs+ emitter,be varied using a manual attenuator. The spot size wasand the transport eﬃciency was approximately 60–80%.
≤1 mm, which corresponds to a maximum ﬂuence of
The laser-intensity threshold of ion formation was 1–
3.2 J/cm2 . The lens was moved using XY linear stages
1.3 J/cm2 , and weak dependence on the repetition rate
remotely controlled via a labview program on a stepof laser ablation was observed. Consequently, 105 –107
by-step basis such that the laser spot moved randomly
singly charged ions per laser pulse, consistent with theon the surface of the target. This ion source systemnatural abundance, were successfully observed for metal
was connected to a test beamline through an insulatargets of Ni, Ag, Zr, Ta, W, and a barium compoundtion ﬂange. The ion source could be biased to 10 kV to(BaF2 ). The energy spread of the extracted ions was
extract ion beams to the downstream beamline, which
evaluated to be <1 eV via a comparison of the width ofwas grounded. A dipole magnet with movable slits was
the obtained mass spectra with trajectory simulations
placed in front of and behind the magnet to observeassuming various initial temperatures, although direct
mass spectra.
measurements are needed for conclusive evidence.
Figures 1(b) and (c) show the observed mass specTherefore, singly charged ion beams of one selectra when solid targets of the refractory elements Zr andtive isotope including refractory elements are available
W were used for laser ablation, respectively. The rafor the reference measurement of collinear laser spectio of intensity among the isotopes was consistent withtroscopy. Background reduction will be possible using anatural abundance. The performance of the ion guide
time gate in coincidence with the pulsed ablation laser.
†∗1∗2

Condensed from the article in Nucl. Instrum. Methods Phys.
Res. B 486, 48 (2021)
RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK

References

1) M. Wada et al., Nucl. Instrum. Methods Phys. Res. B
204, 570 (2003).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Temperature and pressure dependence of ion extraction
from RF gas cell
D. Hou,∗1,∗2,∗3 A. Takamine,∗4 S. Iimura,∗4,∗5 S. Chen,∗2,∗6 Y. Hirayama,∗2 H. Ishiyama,∗4 Y. Ito,∗7 S. Kimura,∗4
J. Liu,∗1 H. Miyatake,∗2 S. Nishimura,∗4 M. Rosenbusch,∗2 P. Schury,∗2 M. Wada,∗2 Y. X. Watanabe,∗2
H. Wollnik,∗8 W. Xian,∗2,∗6 and S. Yan∗2,∗9The SLOWRI facility relies on gas catcher cells to
employ the radio-frequency (RF) ion guide method forthermalizing and transporting radioactive ions.1) During an online experiment, we studied the pressure andtemperature dependence of ion extraction from the gascell. Molecular impurities in the gas cell can react andexchange charge2) with the ions of interest during theirtransport, and even after extraction, the ions can be neutralized and combined with molecular impurities. Because of the relatively low mobility of molecular impurities, they decrease the overall extraction eﬃciency of thegas cell. To reduce the amounts of molecular contaminants, we used high-purity helium and a gas puriﬁcation
system and operated the gas cell at very low temperatures. At temperatures below 50 K, most of these molecular impurities are absorbed at the wall of the gas cell.
In this online test setup, secondary beams passed
through the ZeroDegree spectrometer and stopped in thegas cell. Subsequently they were extracted from the gas
cell and transported to a multi-reﬂection time-of-ﬂight(MRTOF) mass spectrograph for mass measurements.
The setup, as implemented in the commissioning runs,
allowed for cooling the gas cell to ≈180 K. To avoid convoluting the stopping and extraction eﬃciencies, a pressure regulation system maintains a constant gas densityof ≈33 µg/cm3 for all temperatures. As shown in Fig. 1,

Fig. 1. Rates of 135 Sb+ at diﬀerent temperatures of the gascell chamber.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

Institute of Modern Physics, Chinese Academy of Sciences
Wako Nuclear Science Center (WNSC), IPNS, KEK
School of Nuclear Science and Technology, Lanzhou University
RIKEN Nishina Center
Department of Physics, Osaka University
Department of Physics, The University of Hongkong
Advanced Science Research Center, JAEA Ibaraki
Dep. of Chem. and Biochem., New Mexico State University
Institute of Mass Spectrometer and Atmospheric Environment, Jinan University

Fig. 2. Rates of 135 Sb+ and 136 Te+ observed at MRTOF as
functions of RTE gas-cell pressure.

the extraction of 135 Sb+ increases dramatically as thetemperature falls below 210 K, at which some molecular
impurities, such as H2 O, SO2 , and Cl2 , start to decrease.
As the cryogenic cooling system reaches its lower limit
before the extraction eﬃciency saturates, we intend to
implement improvements to allow better cooling prior
to the next online campaign.
By varying the gas density, we can probe the stopping
eﬃciency. Figure 2 shows the results of such a measurement, performed with the gas cell at ≈180 K, with theobserved rate of 136 Te+ and 135 Sb+ plotted as functionsof room temperature-equivalent (RTE) helium pressure.
As one might expect, the stopping fraction increased as
the gas density increased. As such, we must consider
how to safely operate at the highest possible gas density.
We used lise++ to evaluate the stopping eﬃciency inthe gas cell. With a pressure of 220 mbar RTE, 6.4%of 136 Te and 6.5% of 135 Sb should be stopped in helium gas, while decreasing the pressure to 133 mbar RTE
would result in the reduction of stopping eﬃciencies to
2.3% and 2.4%, respectively. As shown in Fig. 2, therates improved by a factor of 3.4 for 136 Te and 4.3 for
135
Sb, while lise++ indicated that the stopping eﬃciencies should only increase by a factor of 2.7 from 133 mbar
to 220 mbar. The diﬀerence likely results from the pressure dependence of the RF ion guide eﬃciency and ion
mobility. Detailed analysis is underway to ﬁnd an optimum operation condition ahead of the next online experiment.
References

1) M. Wada et al., Nucl. Instrum. Menthods Phys. Res. B
204, 570 (2003).
2) D. J. Morrissey et al., Nucl. Instrum. Menthods Phys. Res.
B 266, 4822 (2008).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Degrader optimization for ZeroDegree gas cellFig. 1. Sketch of the ZeroDegree gas cell and degrader system.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

Department of Physics, The University of Hong Kong
Wako Nuclear Science Center (WNSC), IPNS, KEK
Institute of Modern Physics, Chinese Academy of Science
RIKEN Nishina Center
Department of Physics, Osaka University
Advanced Science Research Center, JAEA
Department of Physics, Kyushu University
Department of Chemistry and Biochemistry, New Mexico
State University
Institute of Mass Spectrometry and Atmospheric Environment, Jinan University

100

LISE
unstopped in He gas
stopped in He gas

50

x5

0

30

x5

40

50

85

Ge

Z

As

85

40

As
85

33

Ge

32

0.2

30

31
2.55

2.6

2.65

A/Q

0.1

20

EXP

10

rate @ MRTOF (cps)

34

85

0.3

pass-through fraction

Using a high-quality beam provided by BigRIPS andthe ZeroDegree spectrometer, a system combining a gas
cell and a multi-reﬂection time-of-ﬂight (MRTOF) mass
spectrograph was set up at F11 to study the massesof exotic nuclei.1) The ﬁrst online commissioning was
conducted in the winter of 2020 as parasitic experiments during the HiCARI campaign. To achieve themass measurement in the MRTOF device, the radioactive beams received from ZeroDegree must be stopped
in the gas cell, which is 500-mm long and ﬁlled with
He gas. The typical beam energy behind ZeroDegree is100–200 MeV/nucleon. To stop such high-energy beams
in the He gas, a degrader is essential, and its thickness
must be precisely adjusted. Therefore, a movable degrader system was introduced.
Figure 1 shows a sketch of the gas cell with the degrader system. The degrader system contains a rotational ﬂat degrader placed in front of the gas cell and adownstream silicon detector array inside the outer chamber. The ﬂat degrader was coupled to a step motor,
which can rotate the degrader plate from 0◦ to 55◦ insteps of 0.0072◦ ; therefore, it can ﬁnely adjust the effective thickness of the degrader. The downstream silicon detectors contain 15 Si PIN photodiods s3204-09,
arranged in a 5 × 3 array to cover the full range of thebeam spot. After losing most of its energy in the ﬂat
degrader, part of the beam is stopped in the He gas,
while the rest deposits energy in the Si detectors. The
signal from the Si detectors was acquired in coincidencewith the beam-line detectors of ZeroDegree for particle

rate (arb. units)

S. Chen,∗1,∗2 Y. Hirayama,∗2 D. Hou,∗3,∗2 S. Iimura,∗4,∗5 H. Ishiyama,∗4 Y. Ito,∗6 S. Kimura,∗4 J. Liu,∗3
H. Miyatake,∗2 S. Nishimura,∗4 T. Niwase,∗7,∗4,∗2 M. Rosenbusch,∗2 P. Schury,∗2 A. Takamine,∗4 M. Wada,∗2
Y. X. Watanabe,∗2 H. Wollnik,∗8 W. Xian,∗1,∗2 and S. Yan∗9,∗2

x100

0

30

40

50

Degrader Angle (degree)

Fig. 2. Degrader optimization for 85 Ge (solid) and 85 As(dash). The black curve shows the ratio of the rate detected by an Si detector to the rate at F11. Only one Si
detector was used in the analysis. The red curve is therate of isotope identiﬁcation in the mass spectrum. The
inset shows the ZeroDegree particle identiﬁcation. The
upper panel displays the corresponding lise calculations
using the beam energy measured in ZeroDegree.

identiﬁcation; therefore, optimization can be performed
for speciﬁc isotopes. The stopping in He gas can be optimized according to the beam energy loss measured by
the Si detectors2) or simply using the beam rate fromthe Si detectors.
Figure 2 demonstrates the degrader optimization witha 2.5-mm-thick Al ﬂat degrader for 85 Ge and 85 As during the commissioning run. The fractions (black), calculated as the beam rate detected in the Si detectors
compared with the rate at F11, decrease with increasing degrader angle. The rates of isotopes observed in
the MRTOF mass spectrum (red) show peak structures,from which we can determine the optimized degrader
angle for each isotope. The lise calculations well reproduce the measured pattern; however, discrepancies
in the absolute angles are observed, which emphasize
the importance of such direct measurement in experiments. For low-intensity isotopes (rate in MRTOF as
low as 1 count/h), the direct measurement of the rate
curve in MRTOF is not feasible. In this case, the fraction curve from Si can still be measured. Combined withthe lise calculation, the optimized degrader angle can be
determined in future experiments.
References

1) M. Wada, RIKEN Proposal NP1912-RIBF176.
2) J. Liu, RIKEN Accel. Prog. Rep. 53, 133 (2020).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Online extraction eﬃciency from RF ion guide gas cell at SLOWRI
S. Iimura,∗1,∗2,∗3 A. Takamine,∗1 D. Hou,∗4,∗3,∗5 M. Rosenbusch,∗3 M. Wada,∗3 S. Chen,∗3,∗6 J. Liu,∗4
W. Xian,∗3,∗6 S. Yan,∗7,∗3 P. Schury,∗3 S. Kimura,∗1 T. Niwase,∗8,∗1,∗3 Y. Ito,∗9 T. Sonoda,∗1 T. M. Kojima,∗1
Y. X. Watanabe,∗3 S. Naimi,∗1 S. Michimasa,∗10 S. Nishimura,∗1 A. Odahara,∗2 and H. Ishiyama∗1
We have been developing a radio-frequency carpet(RFC)–type ion guide1) gas catcher cell (RFGC) at the
SLOWRI. In oﬄine tests, the maximam transport eﬃciency for the RFGC was more than 80%,2) where theeﬃciency was deﬁned as the ratio of ion current extracted from the cell to that corrected at the ﬁrst-stage
RFC. Here, the eﬃciency does not include factors suchas ion survival probability and ion losses due to molecular formation. In order to obtain the “real” eﬃciency,
an online test was performed using radioactive isotopes(RIs) provided by BigRIPS with an energy of several
100 MeV/nucleon as a symbiotic experiment behind the
ZeroDegree spectrometer (ZD), in conjunction with the
HiCARI campaign.
A multi-reﬂection time-of-ﬂight (MRTOF) mass spectrometer3) installed at the downstream of the RFGC wasused for particle identiﬁcation (PID) and mass measurements, as shown in Fig. 1. The RIs partly stop in the
RFGC, after passing through a rotational energy degrader. Subsequently, the stopped ions are extracted
from the RFGC and transported to the MRTOF systemthrough quadrupole ion guides and ﬂat-type ion trap.
Table 1 presents the preliminary result for the eﬃciencies for several RI species. After identiﬁcation at
ZD, the total eﬃciency (εtotal ) for each RI was deter!$  
! !! !""  "  !!

 
"!!!"!" !

$

#!!
!$$

!  "!"" "!

Fig. 1. Schematic view of the experimental setup. The RFGC
is 50 cm long. It was operated at a nominal temperatureof 180 K and pressurized with helium to 200 mbar roomtemperature equivalent.
∗1

RIKEN Nishina Center
Department of Physics, Osaka University∗3 Wako Nuclear Science Center (WNSC), IPNS, KEK∗4 Institute of Modern Physics, Chinese Academy of Sciences∗5 School of Nuclear Science and Technology, Lanzhou University∗6 Department of Physics, The University of Hong Kong
∗7 Institute of Mass Spectrometry and Atmospheric Environment, Jinan University∗8 Department of Physics, Kyushu University∗9 Advanced Science Research Center, JAEA Ibaraki∗10 Center for Nuclear Study, the University of Tokyo∗2

Table 1. Total eﬃciencies (εtotal ) measured with the detectors on ZD and the MRTOF. Stopping eﬃciencies (εstop )were calculated from lise++ The transport eﬃciencies(εtrans ) correspond to ion transmission after stopping in
the gas cell.
Nuclide (ions)
134

+

Sb
Te+
88
Se+
90
Se+
85
As+
55
ScOH+
48
CaOH+
137

εtotalεstop

εtrans

1.1%
1.3%
0.33%
0.36%
0.16%
0.0007%0.014%

9.1%
9.2%
3.4%
2.0%
3.6%
2.9%
3.2%

12%
14%
10%
18%
4%
0.02%
0.44%

mined as the ratio between the observed count rate after
the MRTOF and the count rate before the RFGC. The
stopping eﬃciency (εstop ) is the fraction of RIs stopped
in the RFCG, which was evaluated using lise++ basedon the measured energy distribution of each RI. By future application of mono-energetic beam optics,4) εstop
is expected to improve by a factor of more than 5.
The transport eﬃciency (εtrans ) was obtained to subtract εtotal from εstop . It should be noted that εtransincludes transmission not only for RFGC but also for
the ion guide, ion trap, and MRTOF. As indicated inTable 1, for many RIs, a reasonable εtrans higher than
10% could be obtained. In this situation, εtrans can depend on several factors such as the incoming beam intensity contributing to space-charge eﬀects,5) mass-tocharge ratio sensitive to RF trap stability,2) and half-life
providing decay loss. Another important dependency
originates from the chemical properties of the incoming species when impurities are present in the He gas;e.g., 55 ScOH+ was identiﬁed. Those molecular formations can be suppressed by further improvement of thecooling performance of the RFGC, based on our experience of the cryogenic gas cell at GARIS II.6) Further
improvement of the gas cell is ongoing.
We have successfully measured the masses of morethan 70 nuclides in this experiment and are in the processof further analysis and simulation.
References

1) M. Wada et al., Nucl. Instrum. Methods Phys. Res. B
204, 570 (2003).
2) A. Takamine et al., RIKEN Accel. Prog. Rep. 53, 108 (2020).
3) M. Rosenbusch et al., Nucl. Instrum. Methods Phys. Res.
B 463, 184 (2020).
4) S. Chen et al., RIKEN Accel. Prog. Rep. 53, 100 (2020).
5) A. Takamine et al., Rev. Sci. Instrum. 76, 103503 (2005).
6) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B
407, 160 (2017).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Development of MCP timing detector for low-energy heavy ionsT. T. Yeung,∗1,∗2 S. Nishimura,∗2 W. Xian,∗1,∗3 and H. Ishiyama∗2

Count

tizer. The pulse height of the MCP fast ampliﬁer signal was calculated by subtracting the baseline from the
maximum of the pulse. The response was sensitive andincreased with the beam energy linearly, as shown in
Fig. 4. We conﬁrmed that the MCP timing detector
could be a complementary option for a timing detector
instead of MagneTOF and α-TOF.2)
9 MeV
5+

300

250

150

0

0

2000

4000

6000

8000

10000

 !

0

∗2
∗3

4000

6000

8000

12000

Energy (keV)

3500

3 MeV He
3 MeV He (degrader)
3 MeV He (stopper)
0.6 MeV He
9 MeV Au
9 MeV Au (degrader)
3 MeV Au
3 MeV Au (degrader)
2 MeV Au
2 MeV Au (degrader)
2 MeV Au (stopper)

2000

 

1500

 

Department of Physics, The University of Hong Kong
RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK

10000

3000

1000

Fig. 1. Schematic of experimental setup, including degraderand MCP timing detector, with voltage settings. Positionof aluminum plate is adjustable. Ion beam, secondary
electrons, and decay particle are shown. Decay is not in
scope of this experiment.
∗1

2000

Fig. 3. MCP eﬃciencies for He and Au against ion energy.

 

beam

3 MeV He
3 MeV He (degrader)
3 MeV He (stopper)
0.6 MeV He
9 MeV Au
9 MeV Au (degrader)
3 MeV Au
3 MeV Au (degrader)
2 MeV Au
2 MeV Au (degrader)
2 MeV Au (stopper)

2500



14000

Energy (keV)
5+

0.95

0.85

MCP PH



12000

1

0.9

"#

 

2893

Fig. 2. Calibrated energy spectrum for 9 MeV Au
with labelled energy and charge state.





6744

Std Dev

12 MeV7+50
 

20505

Mean

100

0.8

  Entries

3 MeV
1+
4.5 MeV
6 MeV
2+
3+

200

MCP eﬃciency

A prototype microchannel plate (MCP) timing detector was developed for correlated measurement of timeof ﬂight and decay properties by coupling with a multireﬂection time-of-ﬂight mass spectrograph. The detector consists of a silicon PIN photodiode S3590-19 andan MCP F2223-21SH, as shown in Fig. 1. We investigated the performance of the detector using ﬁve typesof beams: 2, 3 and 9 MeV 197 Au and 0.6 and 3 MeV 4 He
at the Pelletron accelerator. Three degrader settings
were available to reduce the beam intensity and provide
various beam energies. The beam was collimated by a
0.2-millimeter-wide hole, degraded by a 2-micrometerthick mylar foil, or stopped by a 0.5-millimeter-thickaluminum sheet, as shown in Fig. 1.
Energy calibration of a silicon detector for 197 Au wasconducted by evaluating its dead layer thickness andpulse height defect using the Stopping and Range of Ionsin Matter (srim) code1) and assuming the charge state
assignment for the multi-peak 9 MeV Au5+ spectrum in
Fig. 2. From the srim results, the entrance window effect and the nuclear collision eﬀect account for 7% and48%, respectively, of 9 MeV Au. By considering botheﬀects, the calculated dead layer thickness of the silicondetector was 0.266 μm and the energy-response function
was obtained.
Based on coincidence of the MCP and silicon detector
signals, the detection eﬃciency of the MCP was evaluated. The MCP eﬃciency for detecting Au is over 90%
down to 2 MeV, as shown in Fig. 3. Pulse height analysis was performed to determine the energy responseof the MCP using the oﬄine data produced by a digi-

0

2000

4000

6000

8000

10000

12000

Energy (keV)

Fig. 4. MCP pulse height for He and Au against ion energy.

References

1) J. F. Ziegler et al., Nucl. Instrum. Methods Phys. Res. B
268, 1818 (2010).
2) T. Niwase et al., Nucl. Instrum. Methods Phys. Res. A
953, 163198 (2020).
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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Improvement of kicker system for rare-RI ring
Y. Yamaguchi,∗1 D. Nagae,∗1,∗2 S. Naimi,∗1 A. Ozawa,∗1,∗3 and M. Wakasugi∗1,∗4
The kicker system at the rare-RI ring (R3) facility has
contributed to successful event-by-event measurements.
Thus far, three kicker units have been utilized for injecting and ejecting particles using the same ﬁeld waveform.
However, this is not ideal because the top of waveform is
not ﬂat (see Fig. 1(a)). It causes an approximately 10%
ﬂuctuation in the kick angle within an eﬀective injection duration of 100 ns. In addition, because the ejection duration is the same as the injection duration, it
is impossible to eject all nuclides having diﬀerent revolution times.1) In the following, we report a successful
improvement in these issues by the addition of a kicker
magnet.
Recent R3 experiments are conducted with an injection energy of around 165 MeV/nucleon. Revolution
time at R3, which has a circumference of 60.35 m, isapproximately 380 ns. It is necessary to make the magnetic ﬁeld strength negligibly small when particles pass
the kicker in the next revolution after injection. Hence,
a ﬂat-top with a duration of 100 ns is appropriate considering the fall time of the magnetic ﬁeld. Furthermore,
it is possible to eject all circulated particles in a single
ejection duration by lengthening the ﬂat-top to 380 ns
or more.
The magnetic ﬁeld shown in Fig. 1(a) is achieved by

Fig. 1. Black line shows measured magnetic field, whereas
blue line shows field experienced by particle (see text).
Black and Blue dots indicate kicked events of 78 Kr and75
Ga, respectively.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Research Center for SuperHeavy Elements, Kyushu University
Institute of Physics, University of Tsukuba
ICR, Kyoto University

Fig. 2. Time-of-flights of ejected nuclides in single ejection
as function of their momentum.

trial and error by adding a capacitor to suppress thereﬂections.2) In this study, two diﬀerent types of magnetic ﬁeld waveforms with and without this additional
capacitor are produced. When passing through thesetwo diﬀerent ﬁelds, which are generated by two kicker
units, a particle experiences a total magnetic ﬁeld thathas a ﬂat-top (see Fig. 1(b)). Each kicker unit can generate a magnetic ﬁeld twice within 0.7 ms. For injection,
two kicker units are used, whereas for ejection, two additional kicker units are needed. To ensure a long ﬂattop ejection waveform, the delay between the ﬁring of
the ﬁrst two kicker units and the additional two units is
ﬁxed to approximately 350 ns.
Blue dots in Fig. 1(b) indicate the kicked 75 Ga particles counted by a plastic scintillator with a width of
5 mm installed in the center orbit of the R3. This measurement was performed while changing the kicker trigger timing in 10 ns steps. It can be clearly seen that thecount rate is constant compared with the 78 Kr case in
the range of 100 ns, for which a ﬂat-top has been realized. Kick angle ﬂuctuation on the ﬂat-top is expected
to be 1%.
Figure 2 shows the measured ﬂight times of the ejectednuclides as a function of momentum obtained from theposition information of the PPAC at BigRIPS-F5. We
succeeded in ejecting all injected nuclides in a single ejection. The events of 76 Ge that were not ejected in the ﬁrst
kick were ejected in the next kick. Thus, a long ﬂat-top
of approximately 400 ns was realized. Consequently, experimental eﬃciency became at least twice better thanthat achieved using the previous method, where diﬀerent
ejection timings were needed to eject all particles.
References

1) S. Naimi et al., J. Phys. Conf. Ser. 1643, 012058 (2020).
2) H. Miura et al., RIKEN Accel. Prog. Rep. 49, 154 (2016).

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RIKEN Accel. Prog. Rep. 54 (2021)

Improved position resolution of the beam diagnostics detector for the
Rare-RI Ring
G. Hudson-Chang,∗1 S. Naimi,∗1 T. Moriguchi,∗2 S. Suzuki,∗2,∗3 M. Hayashi,∗2 N. Kaname,∗2 K. Tomita,∗2
A. Yano,∗2 A. Ozawa,∗2 Y. Abe,∗4 D. Nagae,∗5 and the Rare-RI Ring collaboration
To measure masses of rare isotopes at RIBF using theRare-RI Ring, it is essential to increase the eﬃciency by
better monitoring the beam condition at the injection
into the ring. Therefore, we are developing a large area
position-sensitive detector with a thin foil. The principleof the detector operation is based on secondary electrons(SEs) emitted from a thin foil when the beam passes
through. The SEs are ﬁrst accelerated by the acceleration grid and then reﬂected by the mirror grids potential(see Fig. 1). The beam position is inferred from SEs position measurement with the delay line MCP placed 90◦
from the foil. To achieve high position resolution the SEs
velocity spread should be minimized inside the detector
by simply increasing the acceleration voltage. However,increasing the voltage led to undesirable eﬀects such as
bending of the grid’s wires and electrical discharges. We
report here on the improvements introduced to minimize
these eﬀects. We tested diﬀerent versions of the detector during four experiments conducted at HIMAC witha 200 MeV/nucleon 84 Kr beam. The details of the experimental setup can be found eslewhere.1) The position
resolution as well as the accuracy of the detector for eachexperiment are shown in Fig. 1. In Table 1 are summarized the improvements introduced for each version of
the detector as well as the acceleration potential that
could be applied. The new wiring method for the grids
is based on the method developed in this Ref. 2). With
this method, the grids’ wires were tighter and higher
voltage could be applied resulting in improved resolution. By reducing the thickness of the spacer between
the mirrors and acceleration grids, higher voltage up to
7 kV could be applied. This could be understood in thecontext of the Paschen Curve that related the productof the gas pressure and distance between the grids tothe discharge voltage. By a systematic study of diﬀerent spacer sizes we deduced that reducing the spacer size
was necessary for the same vacuum condition. The reso-

lution achieved in this condition was the best resolution
ever achieved for large area detector of this type. We
also tested the detector with a larger pitch size (2 mm)
for a better transparency of the detector. However, it
showed the worst performance. To improve further the
position resolution we are planning to test a compact
version of the same detector.
Acceleration spacer

Mirror grids

Thin foil

Y
X

SEs

Z

Beam
Mirror spacer

Acceleration
grid
MCP plates(Not to scale)

Delay Line

Table 1. Condition for each experiment (see text)

New wiring method
Pitch of girds [mm]Mirr Spacer [mm]Acc Spacer [mm]Acc. Potential [kV]
∗1
∗2
∗3
∗4
∗5

Jul.
19
X
1
8
10
3

Nov.
19
O
2
8
10
4

Oct.
20(1)
O
1
8
10
4

Oct.
20(2)
O
1
6
8
7

RIKEN Nishina Center
Department of Physics, University of Tsukuba
IMP, CAS
National Institute of Radiological Sciences (NIRS), QST
Faculty of Sciences, Kyushu University

Fig. 1. (top) Schematic side-view of the position-sensitive
detector. (bottom) Detector resolution (A&B) and accuracy (C&D) in the horizontal X and vertical Y position from four HIMAC experiments. The accuracy is deﬁned as deviation from expected position. For Oct20(2),the accuracy is not plotted for the Y because a diﬀerent
method was used to optimize the voltage and accuracy
could not be estimated.

References

1) R. Crane et al., RIKEN Accel. Prog. Rep. 53, 117 (2019).
2) O. K. Yoon et al., J. Am. Soc. Mass Spectrom. 18, 1901
(2007).
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RIKEN Accel. Prog. Rep. 54 (2021)

Computer server and network for HiCARI experiments
H. Baba,∗1 F. Browne,∗1 P. Doornenbal,∗1 B. Mauss,∗1 B. Moon,∗1 D. Suzuki,∗1 N. Aoi,∗2 S. Iwazaki,∗2
A. Kohda,∗2 Y. Yamamoto,∗2 T. Koiwai,∗3,∗1 R. Taniuchi,∗4,∗1 and K. Wimmer∗5,∗1 for the HiCARI
Collaboration
The HiCARI project1) has been launched at the
RIKEN RIBF. To process signals from Ge detectors,
the GRETINA data acquisition system (DAQ)2) is
adopted. 100 MHz digitizers acquire information on
the energy, timing, and pulse shapes of detectors andsend data to data processing nodes. For trackingtype Ge detectors, data processing nodes perform pulse
shape analysis (PSA) to obtain position information.
Finally, processed data are merged by the event builder
node and stored into a RAID storage system. For thisDAQ system, computer servers and network equipment
were newly installed. In addition, HOKUSAI SS3) isused as a near-online analysis environment. In this report, we describe the computer server and network for
the HiCARI experiment.
Table 1 lists the computer nodes. Five nodes of HP
ProLiant DL360 G10 (16 CPU cores) were newly installed. One node is for the event builder; three nodes(48 CPU cores in total) are for the PSA of a triple segmented tracking detector from LBNL Berkeley (LBNL
P3), which has 111 signals in total; and the last one
is for the data process (DP) of Miniball and clover
detectors (152 signals in total). Since PSA is not applied for Miniball and clover detectors, the demand for
CPU resources is small. However, owing to the limitation of the GRETINA DAQ software, the numberof processes per OS is limited. To optimize the allocation of CPU resources, four virtual machines (VM)
are launched using KVM.4) Three CPU cores are allocated to each VM, and four CPU cores are reserved
for the KVM host process. In addition, ten HP ProLiant DL380 G6 (8 CPU cores) were transported from
RCNP Osaka. Eight nodes (64 CPU cores in total) areused for the PSA of the RCNP quad-type segmented
tracking detector (RCNP Quad). One of them is used
for the DAQ controller, and the last one is reserved as
Table 1. List of computer nodes.
Function
DAQ Controller
Event Builder
PSA for LBNL P3
DP for Miniball/Clover
PSA for RCNP Quad
Spare
∗1
∗2
∗3
∗4
∗5

Model
DL380 G6
DL360 G10
DL360 G10
DL360 G10
DL380 G6
DL380 G6

Unit
1
1
3
1
8
1

RIKEN Nishina Center
RCNP, Osaka University
Department of Physics, University of Tokyo
Department of Physics, University of YorkIEM-CSIC

Core
8
16
48
16
64
8

L2 Switch
B2F
B3F
to

RIBFDAQ
Network

L2 Switch

IOC
IOC
IOC
IOC
IOC
IOC
IOC
IOC ×16
DAQ Controller
PSA
PSA forfor LBNLLBNL P3
P3 ×3
DP for Miniball/Clover

to HOKUSAI SS
10 Gbps Ethernet
1 Gbps Ethernet
8 Gbps FC

Event Builder

PSA
for
PSA
for RCNP
RCNP Quad
Quad
PSA
PSA forfor RCNP
RCNP Quad
Quad ×8

FC-SAN Switch
RAID

Fig. 1. Network diagram for HiCARI experiments.

a spare node.
A data analysis environment has been prepared in
HOKUSAI SS for RIBF experiments. HOKUSAI SS
is a private cloud system based on OpenStack.5) As
of January 2021, a total of 80 cores and a disk spaceof 100 TB has been secured, and it can be expanded
upon request. These resources are allocated not only
to the HiCARI project, but also to other experimental
projects. In 2020, 64 cores out of 80 cores were tentatively allocated to the VM of HiCARI experiments.
From 2021, the resource allocation will be optimized
according to the usage.
The network diagram for the HiCARI experiment isshown in Fig. 1. Sixty digitizers are installed on the
B2F, and sixteen CPU boards (called IOC) send data
to the PSA nodes. Processed data are merged by theevent builder and stored in the RAID system via an
8-Gbps fibre channel-storage area network (FC-SAN).
For now, a total of 160 TB of space has been prepared
for the HiCARI project, and 36 TB of data were acquired in 2020. These data were also transferred to the
HOKUSAI SS through a 10-Gbps Ethernet connection
for near-online analysis.
In summary, the computer server and network equipment were set up for the HiCARI project. They worked
stably and successfully acquired data of seven experimental proposals. The equipment reported in this paper will be used for upcoming HiCARI experiments in
2021.
References

1) K. Wimmer et al., in this report.
2) J. T. Anderson et al., IEEE NSS Conference Record 56,
1751 (2007).
3) HOKUSAI SS, https://i.riken.jp/data-sci/ .
4) Kernel Virtual Machine (KVM), https://www.linux-kvm.
org/ .
5) OpenStack, https://www.openstack.org/ .

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Development of a high-bandwidth waveform processing system using
RFSoC
S. Takeshige,∗1 H. Baba,∗2 K. Kurita,∗1 Y. Togano,∗1 J. Zenihiro,∗3 and Y. Hijikata∗38x Analog Signal

So ware Trigger

Enable

FADC

External Trigger
to DDR
MemoryFig. 2. Block diagram of the implemented external trigger
function.The bold line shows the implemented part.
Plastic scintillator waveform
Amplitude[LSB]

We are developing a real-time digital signal processing unit using a GHz-band ﬂash-type analog-to-digitalconverter (FADC) to establish the next-generation dataacquisition system at RIBF. In experiments using radioactive ion (RI) beams, it is necessary to identify eachparticle. For this purpose, detectors are installed along
the beam line, and signals are acquired on an eventby-event basis. However, as the amount of beams increases, conventional CAMAC/VME ADC/TDC modules become a measurement bottleneck owing to its slow
processing rate. For germanium detectors, real-time digital signal processing is applied using 100-MHz FADCs
instead of conventional ADC/time-to-digital converter(TDC) modules.1) However, 100 MHz is insuﬃcient for
signals with high-frequency components such as thosefrom plastic scintillators used as beam-line detectors.
The Xilinx radio frwaquency system-on-chip (RFSoC)
has been commercially available since 2018. It is a device designed for 5 G communication and integrates an
FADC (up to 5 GHz) and ﬁeld-programmable gate array (FPGA) on one chip. This RFSoC has the potential
to perform real-time digital signal processing for highintensity RI-beam experiments.
In this study, we used the Xilinx ZCU111 evaluationkit2) (Fig. 1). This kit has 8 channels of ADC inputs,
8 channels of DAC outputs, and 20 channels of general-

0

− 500

− 1000− 1500− 2000

0

50

100

150

200

250

300

350

400

450
500
Time[ns]Fig. 3. An example of an acquired plastic scintillator waveform.

purpose I/O ports. The speciﬁcations of the ADC input
are as follows: 100 Ω diﬀerential impedance, AC coupling, and 1 Vppd voltage range. The maximum sampling frequency of the ADC is 4.096 GHz, and the resolution is 12 bits.
As it is not possible to impliment external triggers
with sample FPGA ﬁrmware provided by Xilinx, we
added external trigger function. The block diagram isshown in Fig. 2. When data acquisition is started, asoftware trigger is enabled. At this time, when an external trigger is issued, digitized data are stored in memory.
Finally, data are retrieved by a PC via the network. An
example of an acquired plastic scintillator waveform isshown in Fig. 3.
We added an external trigger function to the RFSoC
device and conﬁrmed that it works successfully. Basicstudies such as the measurement of the timing resolution
are in progress.
Fig. 1. Xilinx ZCU111 evaluation kit used for development.
∗1
∗2
∗3

Department of Physics, Rikkyo University
RIKEN Nishina Center
Department of Physics, Kyoto University

References

1) J. -P. Martin et al., IEEE Trans. Nucl. Sci. 55, 84 (2008).
2) Xilinx, Zynq UltraScale+ RFSoC ZCU111 Evaluation
Kit, https://japan.xilinx.com/products/boards-and-kits/
zcu111.html .

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RIKEN Accel. Prog. Rep. 54 (2021)

GPU acceleration of SAMURAI particle tracking simulation
J. Gao∗1,∗2
The possibility of graphical processing unit(GPU)acceleration of the trajectory simulation of particles
passing through SAMURAI was evaluated. To obtain
A/Z in particle identiﬁcation plot, information such as
the ﬂight path and rigidity obtained from this type ofsimulation is necessary. Usually, this tracking simulation is the most time-consuming step in the analysis of
SAMURAI data.
As with most other steps in nuclear physics data
analysis, this particle tracking simulation is performed
event by event. Therefore the simulation could be accelerated by distributing the events to large amount of
threads of a GPU to process in parallel. In principle,
all the event-by-event analysis could be accelerated byparallel computing and could take advantage of a GPU.
Another advantage of a GPU is its special cachestructure. In contrast to the linear structured cachein a CPU, the cache in a GPU could have a higherdimensional layout.1) Therefore, when interpolating in
the magnet ﬁeld map, the GPU could fetch the neighboring mesh point with fewer cache misses.
In this work, a simpliﬁed task is designed to evaluate the performance of trajectory simulation on a CPU
and GPU. The standard program used in data analysis takes the position and angle before and after themagnet and provides the rigidity as the output. It iterates several times to obtain a certain rigidity that
reproduces the position and angle measured in the experiment. This simpliﬁed version takes the position,
angle, and rigidity before the magnet and outputs the
position and angle after the megnet without any iterations. The CPU version is modiﬁed from the code used
for the particle identiﬁcation of SAMURAI11 data.2)
The program uses a fourth-order Runge-Kutta
method to simulate the trajectory of a particle in the
SAMURAI magnet. Both the CPU and GPU versions of the program were developed. The test was
performed on a server with 4 Intel Xeon Gold 6136
CPUs (each has 12 cores/24 threads), 128 GB memory, and one Nvidia Titan V GPU. The CPU version
code is written in Go programming language and optimized using the AVX2 assembly.3,4) The GPU version
is written in C++ and CUDA. 1024000 events were fed
into the programs, and each version ran 3 times.
The results are summarized in Table 1. The timer
starts immediately after the ﬁeld map is loaded into themain or GPU memory and the input data are loaded
into the main memory, and it stops as soon as the calculation ﬁnishes, which means the hard disk I/O timeis excluded so that the time of calculation is isolated.
∗1∗2

Table 1. Test results of CPU and GPU versions of the simplified simulation. The GPU could accelerate the simulation by a factor of 5 to 13 times approximately.
code
CPU 1
CPU 2
GPU
configuration 32 coroutines 126 coroutines 320 × 32
test #1
13.292 s
5.277 s0.999 stest #2
13.309 s
5.319 s1.004 stest #3
13.317 s
5.378 s1.011 saverage13.306 s
5.324 s1.004 sIn Table 1, the CPU 1 code enabled 34 threads andallocated 32 coroutines for simulation. The CPU 2
code enabled all the 128 threads and allocated 126
coroutines for simulation. The GPU version divides
the input data into 100 groups, each of which is passed
to a device function using a conﬁguration of 320 thread
blocks and 32 threads per block. Diﬀerent groups
are processed asynchronously to hide the time of datatransfer between the main memory and device memory.
For SAMURAI11 data, it takes 3.15 iterations on
average to obtain the rigidity and a maxmium of 5 iterations. For the CPU1 and CPU 2 conﬁgurations, thetime for simulation should be 13.306 × 3.15 = 41.91 s
and 5.324 × 3.15 = 16.77 s, respectively. If we consider
the worst case for the GPU, where each thread blockcontains an event that need 5 iterations, then the simulation time is 1.004 × 5 = 5.02 s, which is 8 or 3 times
faster than the CPU version, depending on the numberof threads used in the CPU code.
In conclusion, with a reasonable GPU cost and coding eﬀort, the simulation could be made signiﬁcantly
faster.
References

1) CUDA C++ Programming Guide,
docs.nvidia.com/cuda/cuda-c-programming-guide/index.html
2) J. Gao et al., in this report.
3) Intel 64 and IA-32 Architectures Software Developer’s
Manual,software.intel.com/content/www/us/en/develop/
articles/intel-sdm.html
4) A Quick Guide to Go’s Assembler,
golang.org/doc/asm

School of Physics, Peking University
RIKEN Nishina Center- 104 -

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RIKEN Accel. Prog. Rep. 54 (2021)

Observation of Rb D1 fluorescence in superfluid helium using
picosecond time-resolved detection
Y. Takeuchi,∗1,∗2 H. Kuramochi,∗3 K. Ishii,∗4 K. Imamura,∗2 A. Takamine,∗2 M. Doi,∗1,∗2 T. Yamamoto,∗1,∗2
Y. Matsuo,∗1,∗2 Y. Zempo,∗5 T. Tahara,∗4 and H. Ueno∗2
Our research group is developing a laser spectroscopy
technique (OROCHI) for atoms in superﬂuid helium (HeII). When atoms are introduced into He II, the surrounding helium atoms are pushed out by the exchange (Pauli)
repulsion force.1) The resulting vacuum region is called
an atomic bubble. Because the shape of the electron
orbit of an impurity atom is deformed according to its
energy state, the atomic bubble is also deformed following the shape change of the atomic orbit. According
to the Franck-Condon principle, the time required forthe atomic transition is 10−15 s, which is much shorter
than the time required for the bubble deformation therefore, it is considered that the bubble is deformed after
the transition. The wavelengths of atomic transitions
for both absorption and emission in He II are shiftedfrom those in vacuum owing to this deformation cycle.2)
The emission wavelength is considered to change in correspondence with the degree of bubble deformation.
It is estimated that the time required for the bubble
deformation is of the order of a few picoseconds, but
so far, the relaxation time has not been measured in
the time domain in bulk He II. In this study, we aim
to determine the relaxation time through time-resolved
emission measurements at diﬀerent wavelengths.
The OROCHI group is conducting a research projectin collaboration with the Molecular spectroscopy laboratory to observe the relaxation time of Rb atomic bubbles in He II.3) Recently, we evaluated the performanceof the time-correlated single photon counting (TCSPC)
detection system that will be used for photo-detectionin the relaxation time measurement. Observations were
performed using an avalanche photodiode (APD) andtime amplitude converter (TAC) as detectors. So far,our research group has used PMT for laser-induced ﬂuorescence (LIF) photon counting of Rb atoms. This measurement will be the ﬁrst LIF observation by the TCSPC
system.

Fig. 1. Experimental setup of LIF detection.
∗1
∗2
∗3
∗4
∗5

Department of Advanced Sciences, Hosei University
RIKEN Nishina Center
Institute for Molecular Science
Molecular Spectroscopy Laboratory, RIKEN
Department of Computer and Information Science, Hosei University

Fig. 2. Observed photon intensity as a function of delay time.

We ﬁrst conﬁrmed the ﬂuorescence detection of theD1 line of the Rb atom (absorption center wavelength
in He II: 778.0 nm). We used a picosecond modelocked Ti:sapphire laser (laser power: 130 mW, repetition rate: 80 MHz, pulse width: 1.6 ps, center wavelength: 778.2 nm) as an excitation laser, and we observed
LIF using the APD and acquired data using a TCSPC
module (SPCM, Becker & Hickl GmbH) (Fig. 1). The
Rb atoms were supplied by performing laser ablation on
the RbCl sample installed above the observation areaand laser dissociation to RbCl clusters in He II. The
monochromator wavelength was set at 793 nm, which isthe center of the emission line.
Figure 2 shows the result of the observation. The
data plotted here are the observed photon intensities as afunction of delay time. In this ﬁgure, the blue triangle isthe total detected light when all lasers are turned on, andthe orange dot is the scattered light when only the excitation laser is turned on. The fact that the peaks appear
at the same position of the horizontal axis indicates thatthe excitation laser is scattered inside the cryostat andis slightly detected, although the monochromator wavelength is 15 nm longer than that of the excitation laser.
The background also contains ambient light from sources
other than the laser in the environment. The blue curve
has a longer tail. This tail indicates the decay due tothe lifetime of the Rb D1 emission. While the excitation
pulse interval was 12.5 ns, the ﬂuorescence lifetime was
27 ns therefore, atoms are excited by the next laser pulse
before the emission vanishes and LIF photons are piled
up. Therefore, the result agreed with the expectationthat the spectrum would have the appearance of a sawtooth wave with repeated cycles of decay and rise due toexcitation on top of the piled-up signal.
With the current data, the background scattered lightis not small, and the setup should be adjusted so that
more ﬂuorescence light can be obtained. We are planningto make such improvements and move to the observationof weaker emission on the short-wavelength side.
References

1) B. Tabbert et al., J. Low Temp. Phys. 109, 653 (1997).
2) Y. Takahashi et al., Phys. Rev. Lett. 71, 1035 (1993).
3) Y. Takeuchi et al., RIKEN Accel. Prog. Rep. 53, 130 (2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

Development of ion trap system for the neutralizer toward production of
spin-polarized RI beam using atomic beam magnetic resonance method
K. Imamura,∗1 A. Takamine,∗1 and H. Ueno∗1
Spin-polarized radioactive isotope (RI) beams havebeen used for the measurements of nuclear electromagnetic moments and spins to investigate nuclear
structure. In many experiments, the polarization of nuclear spin is generated via a projectile fragmentation reaction. Although the reaction mechanisms have been
well studied so far, the achievable spin polarization istypically as low as several percentage points.1) Laser
optical pumping can realize spin polarization of greaterthan a few tens of percentage points, but the method iselement-limited. A highly eﬃcient and universal method
for producing spin-polarized RI beams is desired. For
this purpose, we are developing a spin-polarized beam
production apparatus using the atomic beam magnetic
resonance (ABMR) method. In the method, the spinpolarization of neutral atomic beams is generated by
two-step spin selection using multi-pole magnets andmagnetic resonance. The eﬃcient production of a thermal energy neutral RI atomic beam is signiﬁcantly difﬁcult from a technical perspective, although the ABMR
method itself is one of the conventional methods for investigating spin-related nuclear properties of nuclei near
the stability region.2) To overcome this diﬃculty, we propose a new ion neutralizer which, combines ion trappingwith the laser cooling technique. The main feature of
the neutralizer is that it traps and cools RIs producedby nuclear reactions to decrease the beam energy.
In the system, we ﬁrst prepare laser-cooled ions in a
linear Paul trap. RI ions of several eV are introduced tothe trap region of the laser-cooled ions and trapped using He buﬀer gas cooling. The trapped RI ions are sympathetically cooled down through Coulomb interaction
between laser-cooled ions and the RI ions. After cooling,a neutralization gas (e.g., N2 , NH3 , and so on) is blown
against the RI ions. Subsequently, neutral atoms areproduced by charge-exchange interaction. For the eﬃcient extraction of the neutral atoms, we apply a swing
ﬁeld in the beam-propagation direction to move trapped

Fig. 2. Mass spectrum obtained downstream of the linear
Paul trap.

RI ions back and forth prior to the neutralization.
In order to develop the proposed neutralizer, we initiated an oﬄine R&D experiment using Rb by constructing a linear Paul trap system and quadrupole mass ﬁlter(QMF) for selecting ions that are introduced to the trap
region. The experimental setup for the R&D experimentis shown in Fig. 1. Rb ions emitted from a surfaceionization ion source were guided to a linear Paul trap
after mass selection by a QMF. The electrodes of thetrap were assembled at the head of the cryostat, which
is used for realizing a suﬃcient high vacuum to conduct the ion trapping and laser cooling experiment. We
achieved a vacuum of ∼10−8 Pa in the current setup.
Two gas lines were prepared near the center part of the
trap. One is used for introducing He as the buﬀer gas toperform buﬀer gas cooling. The other is used for introducing a neutralization gas. A channel electron multiplier (CEM) detector was placed downstream of the trap
to detect transported ions.
Toward the Rb ion trap experiment, we conducted an
ion transportation test. Figure 2 shows a mass spectrumof the ions transported. The vertical and horizontal axes
correspond to ion counts and RF voltages applied to the
QMF electrodes, respectively. Three peaks correspondto singly charged K, Rb, and Cs. According to thisresult, we conﬁrmed that suﬃcient Rb ions to test ion
trapping are guided from the ion source to the trap. We
will proceed to the next step of Rb ion trapping. We
will then start a neutralization test in the near future.
References

Fig. 1. Schematic diagram of the setup.
∗1

RIKEN Nishina Center

1) K. Asahi et al., Phys. Lett. B 251, 488 (1990).
2) N. F. Ramsey, Molecular Beams (Oxford University
Press, New York, 1956).

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RIKEN Accel. Prog. Rep. 54 (2021)

Status of the J-PARC E16 experiment in 2020
S. Yokkaichi∗1 for the J-PARC E16 Collaboration
We proposed the experiment E161) to measure thevector meson decays in nuclei in order to investigate
the chiral symmetry restoration in dense nuclear matter.
The experiment started at the J-PARC Hadron Experimental Facility.
This experiment aims to systematically study thespectral modification of vector mesons in nuclei, particularly the ϕ meson, using the e+ e− decay channel withstatistics that are two orders larger in magnitude thanthose of the precedent E3252) experiment performed at
KEK-PS. In other words, it aims to accumulate 1 × 105
to 2 × 105 events for each nuclear target (H, C, Cu, andPb) and deduce the dependence of the spectral modification on the size of matter and meson momentum.
A scientific (“stage-1”) approval was granted to theexperiment E16 by PAC in March 2007. For the full(“stage-2”) approval, a technical design report was submitted to PAC in May 2014 and reviewed for experimental and budgetary feasibility. In the PAC meeting
held in July 2017, the stage-2 approval for 320 hoursof a commissioning run was granted. In this run, background measurement at the new beamline is required.
The construction of High-momentum beamline, where
the experiment will be conducted, has been completed
by KEK in June 2020.
Our proposed spectrometer has 26 modules. As shownin Fig. 1, a module consists of Lead-glass calorimeter(LG) and Hadron-blind detector (HBD) for electron
identification, as well as three-layers of GEM Trackers(GTR) and a single layer of silicon strip detecor (SSD) as
the tracking devices. Owing to budget limitations, thecommissioning run was started with a limited number ofmodules.
The first half of the commissioning run, called Run0a, was successfully performed in June 4–20, 2020, witha configuration of 6(SSD)-6(GTR)-4(HBD)-6(LG) modules.3) The beam was delayed from February in the original plan, owing to a bureaucratic issue and possibly because of the COVID-19 pandemic, in the Nuclear Regulatory Agency, to issue the permission for the new beamline. As a user beamtime, 159 hours were executed, including 10-hours of downtime in total; each downtime
was less than 30 min. (downtimes over 30 min were compensated). Here, “downtime” is due to problems causedby the accelerator or the beamline operation and not byusers.
As the design, a primary proton beam with an intensity of 1×1010 protons per 2 sec duration (5.2 sec cycle)
was delivered to our spectrometer. The interaction rate
at the targets (C and Cu) is 10 MHz because the totalinteraction length of the targets is 0.2%. One of ourconcerns, GEM breakdown under a high particle rate,∗1

RIKEN Nishina Center

Fig. 1. Plan view of the proposed E16 spectrometer in theeight-module configuration for Run-1. The red lines show
the parts that have been constructed as of December
2021, for the commissioning run planned for February
2021 (Run-0b). The SSD located in the innermost layer
is not shown.

was not observed in HBD. In GTR, the breakdown of 13
strips was observed in 300-GTR, which caused approximately 11% of dead region in total, but operation was
continued. The electron ID performance of HBD and
LG were roughly confirmed.
A background study was performed, and the LG single
rate was found to be two times as high as the expectation, which is a scaled value of the E325 experiment.
However, a factor of two is within the designed margin.
The origin of the background will be studied to improve
the situation.
As of January 2021, the second half of the commissioning run, Run-0b, is scheduled for February 2021.
GTR and HBD were uninstalled from the spectrometer after the Run-0a, and refurbished in J-PARC and
RIKEN, respectively. Additionally, two GTR and two
HBD modules were newly constructed, and installed in
November–December 2020 along with the refurbishedones. Consequently, a 6(SSD)-8(GTR)-6(HBD)-6(LG)were installed, as shown by the red lines in Fig. 1.
After Run-0b, Run-1 (physics run) is planned for autumn 2022. Its approval should be obtained at the JPARC PAC. We have to update the technical design
report for Run-1 based on the result of Run-0 and submit by December 2021, following which discussion will
be conducted at the PAC held in January 2022.
References

1) S. Yokkaichi et al., J-PARC proposal No. 16 (http://
j-parc.jp/researcher/Hadron/en/pac_0606/pdf/p16Yokkaichi_2.pdf); Y. Komatsu et al., JPS Conf. Proc.
12, 020005 (2017); S. Ashikaga et al., JPS Conf. Proc.
26, 024005 (2019).
2) R. Muto et al., Phys. Rev. Lett. 98, 042501 (2007).
3) S. Yokkaichi, RIKEN Accel. Prog. Rep. 53, 79 (2020).

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RIKEN Accel. Prog. Rep. 54 (2021)

Construction of GEM Tracker for J-PARC E16 experiment Run0-a
T. N. Murakami∗1 for the J-PARC E16 Collaboration
The J-PARC E16 experiment1) has started to reveal
the relationship between spontaneous chiral symmetry breaking and masses of hadrons. We measure themass spectrum of the ϕ meson in nuclei using e+ e−
decays. The momenta of e+ and e− are reconstructedfrom the curvature in a magnetic ﬁeld; therefore, tracking of the lepton pairs is quite essential. To deal withthe expected high-particle rate of 5 kHz/mm2 and tocover a wide area of 1.1 m2 , we adopted a gas electron multiplier (GEM) as the tracking device. GEM
chambers are reported to operate normally even undera 25 kHz/mm2 particle rate.2)
We have developed GEM Tracker (GTR), whose
GEM foils are manufactured by a Japanese company. Each GEM chamber consists of three diﬀerent sizes of the chambers; 100 mm × 100 mm (GTR1),
200 mm × 200 mm (GTR2), and 300 mm × 300 mm(GTR3). A GEM chamber consists of three GEM foils
and is ﬁlled with Ar+CO2 (70:30) gas. Each chamber enable measuring the positions of charged particles with a resolution of 100 µm.3) We prepared six
modules of GTR for the ﬁrst commissioning run for
E16 (Run0-a) in June 2020. They were placed to cover
the same solid acceptance surrounding the target. The
process of construction was as follows: In the ﬁrst step,
we selected good GEM foils for stable operation. We
measured the leakage current by applying 500-V between the bottom and top electrodes of the GEM foils
with a 400 mL/min N2 gas ﬂow. We required the leakage current to be less than 10 nA/100 cm2 and thenumber of discharges to be less than 10/h. The results
are summarized in Table 1. After selecting good foils,
we assembled them as a GEM chamber. Prior to installation, two steps were performed. First, we tested
the chambers for presenting suﬃcient operation stability and suﬃciently high ampliﬁcation gain of 6000, as
required for a position resolution of 100 µm. If there
were problems, such as an insuﬃcient gain or impossibility of applying a nominal voltage of 380 V to the
GEM electrodes, we disassembled the chamber and exchanged the GEM foils. Second, we transported themto the experimental area, set them on the CFRP frame,
as shown in Fig. 1, and tested them again. Here, we
checked the operation stability as well as the cable disconnections. Subsequently, we successfully installed
the GTR in the spectrometer magnet.

∗1

Table 1. Results of leak current test. Approximately 100
GEM foils were checked over 3 months.
size of GEM ( mm2 )

good

bad

sum

100 × 100
200 × 200
300 × 300
sum

21
18
19
58

15
12
11
38

36
30
30
96

Fig. 1. GEM chambers attached in CFRP frame. This issingle module of GTR, and six modules are placed surrounding targets in Run0-a.

References

1) S. Yokkaichi et al., in this report.
2) B. Ketzer et al., Nucl. Instrum. Methods Phys. Res. A
535, 314 (2004).
3) Y. Komatsu et al., Nucl. Instrum. Methods Phys. Res.
A 732, 241 (2004).

Department of Physics, Graduate School of Science, The
University of Tokyo- 108 -

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Performance evaluation of the electron identification system for the
J-PARC E16 experiment
S. Nakasuga∗1,∗2,∗3 for the J-PARC E16 Collaboration
The J-PARC E16 experiment1) is proposed for measuring the spectral modiﬁcation of vector mesons in
nucleus. Here, we detect electron-positron pairs generated in ϕ meson decays, produced in pA reactions.
It is crucial for a successful measurement to separate
electrons from huge hadronic backgrounds, especiallypions, which are a primary component of those.
For the electron identiﬁcation, we adopt two-stage
detectors comprising hadron blind detectors (HBDs)
and lead-glass electro-magnetic calorimeters (LGs).
The HBD is a gas-type Cherenkov detector with a
CF4 radiator.2) Emitted Cherenkov photons are converted into electrons at a CsI photocathode, and theseelectrons are ampliﬁed by a gas-electron multiplier(GEM).3) The LG is a calorimeter sensitive to EM
showers generated by an incident particle in lead-glass.
The high-energy electrons generate large showers compared with pions; therefore, the LG is able to distinguish electrons from pions based on the quantity of
Cherenkov photons emitted by the showers.
Both detectors were developed independently, andtheir performances were evaluated separately.4,5) If
particle detection by one detector aﬀects another detector, the combined performance of the system possibly becomes worse than expected from the individual performances. For example, an incident pion may
produce knock-on electrons in the CF4 radiator of the
HBD, one of which may have suﬃcient energy to produce EM showers in the LG, which is installed behindthe HBD. These eﬀects are expected to be small; however, experimental validation is necessary.
We performed a beam test for a total performance
evaluation of the HBD and LG in the commissioning
run of the E16 spectrometer at the high-momentum
beamline at J-PARC. As shown in Fig. 1, we constructed a novel setup, which covered the forward acceptance of the E16 spectrometer. The responses of the
HBD and the LG were examined for pions, identiﬁedby the triple coincidence of scintillation counters andtwo gas Cherenkov detectors (GCs) positioned in frontof the HBD. The primary beam intensity was typically1 × 109 protons/spill suitable for the readout systemof this measurement. We adopted one carbon and two
copper targets, whose total thickness was 0.2% interaction length. This was the same conﬁguration as theE16 experiment.
∗1
∗2
∗3

Department of Physics, Graduate School of Science, Kyoto
University
Advanced Science Research Center, Japan Atomic Energy
AgencyRIKEN Nishina Center

Fig. 1. Experimental setup for evaluating the overall performance of the electron identification system.

The HBD and LG distinguished electrons from pions by applying a threshold to the number of detected
photons. We measured the threshold dependence of
three quantities: single rejection power of the HBD(SRHBD ), that of the LG (SRLG ), and total rejection
power of the HBD and the LG (TR). Here, the rejection power was deﬁned as the number of total events
divided by that of misidentiﬁed events. If the correlation between the detectors is negligible, the productof SRHBD and SRLG is expected to be consistent with
TR. At the threshold, which will be used in the future experiment, the values of SRHBD and SRLG were
determined to be 49 ± 44 and 3.6 ± 0.1, respectively;
therefore, the product of these values was 178 ± 16.
Compared with the product, the measured value of TR
was 174 ± 29. These two values were consistent within
their statistical uncertainties; therefore, we concluded
that the HBD and LG independently work for pions.
In the coming beamtime in February and June
2021, we plan to study and evaluate the performance
minutely with the E16 spectrometer, in terms of ratecapability and the response depending on an incident
angle and momentum of incoming particles.
References
1) S. Yokkaichi, in this report.
2) W. Anderson et al., Nucl. Instrum. Methods Phys. Res.
A 646, 20–24 (2011).
3) F. Sauli, Nucl. Instrum. Methods Phys. Res. A 386,
531–534 (1997).
4) K. Kanno et al., Nucl. Instrum. Methods Phys. Res. A
819, 35–58 (2016).
5) S. Ashikaga, Master’s thesis, Kyoto University (2018).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Intermediate silicon tracker for sPHENIX experiment at RHIC
I. Nakagawa,∗1 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 T. Hachiya,∗1,∗4 S. Hasegawa,∗5 D. Imagawa,∗9 H. Imai,∗9
T. Kondo,∗6 C. Kuo,∗3 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 Y. Namimoto,∗4
S. Nishimori,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗7
The INTermediate Tracker (INTT) is the one ofthree major tracking detectors to be implemented in
sPHENIX experiment1) which is to be launched in 2023
at RHIC. It is consisted of two layers of silicon strip
sensors assembled into the barrel structure covering thecentral region of sPHENIX collision point. Silicon sensors and FPHX readout chips2) are implemented on highdensity interconnect (HDI) cables which are glued on
top of a 50 cm long cooling stave. The stave as shownin Fig. 1 is made of the carbon ﬁber reinforced plastics
and fabricated in Asuka co.
The mass production of silicon sensors, FPHX chips,
and HDI cables have been completed. The stave production is to be completed by the end of February, 2021. A
bus extender cable (BEC) and a conversion cable (CC)form series of INTT readout chain together with the
HDI cable. The development of the BEC and CC are
almost completed3) and the mass production of thesecables are scheduled in JFY2021. Several preproduction INTT ladders (Fig. 2) have been assembled in National Taiwan University and BNL. Once the ﬁnal tune
for the optimization of assembly procedure is over, themass production of the ladder assembly will be started
and expected to be ﬁnished in Spring, 2021.
The preparation for testing production ladders has
been ongoing at Nara Women’s University in both hardware and software. There 3 major items listed below areunder development.
(1) Source test fixture: The motor driven radiation source scanner of the ladder (Fig. 3)(2) FPHX readbacker: The software application
to read back the resisters of FPHX chips.
(3) Interception board: The compact circuit board
to be inserted between the readout cables whichbranches out signal traﬃc without disturbing thedata taking. To be used for debugging of any
mis-communications between ladder and readout
control board.2)

Fig. 2. Fully assembled INTT preproduction ladders.

Fig. 1. The CFRP staves for INTT ladder.
Fig. 3. The fixture for radiation source test of a ladder.
∗1
∗2
∗3
∗4
∗5

∗6
∗7
∗8
∗9

RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University- 110 -

References

1) Conceptual Design Report of sPHENIX (2018).
2) C. Aidala et al., Nucl. Instrum. Methods Phys. Res. A
755, 44 (2014).
3) T. Hachiya et al., in this report.

1II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Detection eﬃciency of the INTT test bench for sPHENIX
G. Nukazuka,∗1 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 T. Hachiya,∗1,∗4 S. Hasegawa,∗5 D. Imagawa,∗6 H. Imai,∗6
T. Kondo,∗7 C. Kuo,∗3 H. -S. Li,∗8 R. -S. Lu,∗9 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1
Y. Namimoto,∗4 S. Nishimori,∗4 R. Nouicer,∗2 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗8

CAMAC crate

NIM crate

Cosmic ray
Scintillator

・Crate cntroller
・ADC
Data transfer
・TDC
and・Intterupt reg. control
・Output reg.

NIM modules for
signal processes

PMT
Trigger input
Readout
Chip/Card

INTT Sillicon
module・FEM
・FEM-IB

Data transfer
Slow control

PC

VME crate
Scintillator

PMT

Fig. 1. Overview of the new DAQ system. See Ref. 3) forsome of the abbreviations.
∗1
∗2
∗3
∗4
∗5

∗6
∗7
∗8
∗9

RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Department of Physics, Rikkyo University
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University

1

Detection Efficiency as a function BCO phase

0.8
Efficiency

sPHENIX1) will start data acquisition in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory from 2023 to study quark-gluon plasma. The Silicon Intermidiate Trackter (INTT),2) which is one of the
crucial pieces in the detector complex, enables us to perform jet ﬂavor tagging with high precision and low background. INTT inherits the readout electronics from the
Forward Silicon Vertex Detector of PHENIX3) so thatR&D can proceed with low cost in a short period.
In a test-beam experiment at Fermilab,4) we conﬁrmedthat the prototype of INTT satisﬁed the essential speciﬁcations for position resolution and timing resolution.
Detection eﬃciency was approximately 96%, althoughalmost 100% was expected. In these measurements,
the prototype worked using the internal clock (BCO)of 9.4 MHz while the beam arrived independently from
BCO. The lower-than-expected detection eﬃciency canbe due to timing mismatch between the beam and BCO,
because of which signals of the silicon module were occasionally not detected.
To test the hypothesis, we implemented an external
trigger system using the Nuclear Instrumentation Module (NIM) and Computer Aided Measurement And Control (CAMAC) modules and integrated it into the existing data acquisition system (DAQ) (Fig. 1). The silicon
module was set between two trigger scintillators. The
transverse dimensions of the scintillators were the sameas the active area of the silicon module. One scintillator on the top was set along the silicon module, while
the other was rotated by 90◦ longitudinally to restrict
acceptance. Coincidence of signals from the two scintillators is treated as a trigger signal. The DAQ stores thefollowing parameters:• hit information on the silicon module

0.6
0.4
0.2
0
0
0

50
100

100

150

BCO phase (degree)200

TDC channel

300

200

250
400

300
500

Fig. 2. Detection eﬃciency as a function of BCO phase with
the quality cuts.

• total charge and timing information of the scintillator signals• the timing diﬀerence between the coincidence signal
and a BCO pulse, i.e., a phase of BCO.
In the analysis, quality cuts for analog-to-digital converter (ADC) and time-to-digital converter (TDC) distributions of the scintillator signals reject noise-like events.
The detection eﬃciency deﬁned as a ratio of the number of trigger events with INTT hit to the number of thetrigger events is calculated after applying the quality cuts
as a function of the BCO phase (Fig. 2). Measurement
could not be performed for a sixth of the BCO period owing to technical diﬃculties. A clear drop in eﬃciency inthe ﬁrst 100 TDC channels was found as expected. The
average eﬃciency excluding and including the dropping
region was approximately 94% and 85%, respectively.
This low-eﬃciency condition can be the reason for the
96% eﬃciency obtained in the test-beam experiments.
The eﬃciency obtained in this study is lower than thatin the test-beam experiment because the acceptance restriction was not perfect; consequently cosmic rays could
activate the trigger without impingement on the silicon
module.
We could also observe a positive correlation between
the eﬃciency and ADC for the bottom scintillator. Requiring higher ADC value to the signal may eliminate
cosmic rays, which do not penetrate the silicon sensor.
This observation suggests that optimization of the setup
can yield a higher detection eﬃciency.
In summary, we found dependency of the detection
eﬃciency on the BCO phase. It explains the lower efﬁciency observed in the test-beam experiment. Since
RHIC will provide a beam-synced trigger, this timing
mismatch cannot be an issue for sPHENIX
References

1) A. Adare et al., sPHENIX proposal (2015).
2) I. Nakagawa et al., in this report.
3) C. Aidala et al., Nucl. Instrum. Methods. Phys. Res. A
755, 44 (2014).
4) A. Suzuki, Master’s thesis, Nara Women’s Univ. (2020).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Radiation resistance of bus extender cable for sPHENIX-INTT

ratio

We are developing INTermidate Tracker (INTT),
which is a new tracking detector for the sPHENIX
experiment at RHIC in BNL, which is a successor of
PHENIX. The INTT needs to be designed to transmit approximately 14k signal lines through a very narrow space; therefore any commercial detector available in the market will not ﬁt to interconnect the
INTT and the downstream readout controller board(ROC).1) Thus, we have been developing a long andhigh-density cable, which is called “bus extender” forthe last four years.
The bus extender cable is a multilayered ﬂexible
print cable. Liquid crystal polymer (LCP) and copper
foil layers are laminated using an epoxy glue, forming
a multilayered structure. The LCP and the glue are
made of macromolecule materials; therefore, there isconcern for their use under the radiation enviroment
because macromolecules are known to be weak against
a radiation dose, in geneanl. Thus, the cable needs todemonstrate radiation hardness. We list the following
two physical characteristics as indicators of the radiation hardness: 1) loss of ﬂexibility, 2) decrease in thepeel strength of the glue. The former can be quantitatively evaluated by measuring Young’s modulus. The

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0

10

102

103

Dose [kGy]Fig. 1. Ratio of Young’s modulus as function of radiation
dose.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University- 112 -

peeling strength [N/cm]

H. Imai,∗1,∗9 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 T. Hachiya,∗1,∗4 S. Hasegawa,∗5 D. Imagawa,∗9 T. Kondo,∗6
C. Kuo,∗3 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1 Y. Namimoto,∗4
S. Nishimori,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗7
20
18
16
14
12
10
8
6
1

10

102

103

Dose [kGy]Fig. 2. Peeling strength as function of radiation dose.

latter was evaluated by a peel force measurement.
Dedicated test samples for the radiation test were
fabricated, which have the same layer structure as thebus extender but a smaller size: 40 cm length and 2 cm
width each. These test samples are exposed to gamma
ray radiation from a 60 Co source at a facility in the
National Institute of Quantum and Radiological andTechnology.
The natural frequency method was employed tomeasure Young’s modulus. The natural frequency canbe related with Young’s modulus as deﬁned in Eq. (1)where, f is the natural frequency, E is Young’s modulus, I is the moment of second-order, A is a crosssection area, ρ is the density, l is the length, and λ isa constant. λ is approximately 1.8 for basic frequency.
√
λ2
EI
(1)
f=
2
2πl
ρA
Figure 1 shows the results of the measurement. The
vertical axis shows the ratio of the observed Young’s
modulus of the samples with and without exposure.
The result is constant within the size of the error bars,
and thus, there is no indication of loss of ﬂexibility.
Figure 2 shows the radiation dose dependence of theobserved peel strength. The peel strength is measured
using SHIMAZU MST-I. A clear degradation of thepeel strength is observed. However, the degradationis still moderate within the expected radiation dose
∼5 kGy in three of sPHENIX operation. We conclude
that the bus extender demonstrates suﬃcient radiation
hardness to be used in the sPHENIX experiment.
Reference

1) T. Hachiya et al., in this report.

1II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Electrical and mechanical properties of the bus-extender
M. Morita,∗1 Y. Akiba,∗2 D. Cacace,∗3 K. Cheng,∗4 T. Hachiya,∗2,∗1 S. Hasegawa,∗5 D. Imagawa,∗9 H. Imai,∗9
T. Kondo,∗6 C. Kuo,∗4 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗3 C. Miraval,∗3 I. Nakagawa,∗2 Y. Namimoto,∗1
S. Nishimori,∗1 R. Nouicer,∗3 G. Nukazuka,∗2 R. Pisani,∗3 M. Shibata,∗1 C. Shih,∗4 M. Stojanovic,∗7
W. -C. Tang,∗4 and X. Wei∗7
The sPHENIX experiment at the Relativistic Heavy
Ion Collider (RHIC) is scheduled to start in 2023 in
Brookhaven National Laboratory (BNL). The INTermediate Tracker (INTT)1) is a silicon sensor strip detector to be implemented in the central rapidity region.
The massive raw data generated in INTT need to betransmitted to downstream readout electronics througha quite narrow and curving cabling path for 1.2 m. As
there is no commercial cable available, a high-signaldensity cable was developed using ﬂexible printed cabletechnology. The cable is called “bus-extender” and has
62 pairs of 130-µm-width signal lines. The bus extender
mainly transmits digital signals. The development of thebus extender is in the ﬁnal stage.2)
Owing to the long path length of high-density ﬂexible
printed cables, the poor performance of signal transmission of high-frequency data is a major concern. A simulation predicts 30% attenuation for a 200 MHz signal.
An eye diagram is a useful tool to visually inspect theattenuation and distortion of the signal pulse. We measured the eye diagram by overlaying the waveforms ofvarious bit patterns. The transmission eﬃciency can beevaluated qualitatively by the size of the opening of theeye. Figure 1(a) and (b) show the eye diagram of the lowvoltage diﬀerential signaling (LVDS) signals before andafter passing the bus-extender. From the comparison,
the attenuation of the signal is determined as 33%. The
result is consistent with the simulation. It is found thatthe eye opening after the bus-extender is too small to receive the signals at the readout electronics. To solve theproblem, we increase the drawing current of the LVDS

Fig. 1. Eye diagrams (a) before and (b) after the busextender in the readout chain.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

Department of Mathematical and Physical Science, Nara
Women’s University
RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University

Fig. 2. (a) Stress concerning the U-shaped curvature of test
pieces. (b) Peeling strength as a function of the peeled
length, evaluated in the region covered by a red circle.

signals from 2 mA to 8 mA to eﬀectively obtain a suﬃciently wider eye opening.
The mechanical properties are also important to assess
the long-term stability and radiation hardness. The bus
extender needs to survive at least three years of operation in a high-radiation environment. The bus-extenderis made using a liquid crystal polymer (LCP) as substrate, instead of a polyimide, which is generally used
for ﬂexible cables. LCP is a new material used for highenergy physics experiments. Therefore, we studied its
mechanical properties by comparing it with polyimide.
In addition, this study provides a baseline to assess theradiation hardness.
We measured two quantities: (1) ﬂexibility and (2)peeling strength between layers of the multilayered cable. Here, the results of the 2-cm-wide specimen used
are shown instead of results per unit. The former ismeasured by bending the cable in the middle by 180◦ as
it forms a “U-shape” inside view. The stress from thecable is recorded for several test samples as a function ofcurvature and is plotted in Fig. 2(a). The ﬂexibility isevaluated by the slope of a 4 N increase in the curvature
region from 0.02 to 0.11/mm. This result is further compared to that from cables exposed to radiation, and no
drastic change was found.3) Therefore, we could obtain
the reference value for ﬂexibility. The latter is measured
by recording the stress of peeling oﬀ the cable as a function of the stroke. The result plotted in Fig. 2(b) showsa peeling strength of 34 to 44 N. This value is twice thatof the polyimide.
We plan to start the mass production of bus-extenders
in 2021. The continuity of all signal lines will be tested
using newly developed test equipment.4)
References

1) I. Nakagawa et al., in this report.
2) T. Hachiya et al., in this report.
3) H. Imai et al., in this report.
4) D. Imagawa et al., in this report.

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RIKEN Accel. Prog. Rep. 54 (2021)

Upgrade of the Si-CsI array TiNA for transfer reactions at OEDO
B. Mauss,∗1 J. W. Hwang,∗2,∗3 D. Suzuki,∗1 N. Ma,∗2 N. Imai,∗2 M. Dozono,∗2 S. Michimasa,∗2 T. Sumikama,∗1
S. Ota,∗2 C. Iwamoto,∗1 N. Iwasa,∗3 and F. Endo∗3
TiNA is an array of silicon strip detectors (SSDs)
and CsI(Tl) crystals for measuring recoiling particles
from transfer reactions.1) Initially, TiNA had six telescopes in a lamp-shade conﬁguration. Each telescope
had a YY1-type single-sided SSD of Micron and two
CsI crystals behind the SSD, the total active area of
which is 6 × 5 cm2 . The telescopes were placed 8 to
10 cm away from the reaction point and surrounded
the beam axis. They covered a laboratory angle rangeof 100◦ to 150◦ . TiNA has been used in several transfer
experiments at RIBF.2,3)
Upcoming experiments using transfer reactions,however, require a larger solid angle and better resolutions in angle and energy. For instance, for the50
Ca(d, p) experiment at the OEDO beamline, an excitation energy resolution better than 200 keV in σshould be achieved. The upgrade project of TiNA has
been launched to fulﬁll these requirements. In this report, we present the details of the improvements ofTiNA and the results of the oﬄine test.
Figure 1 shows the upgraded structure of TiNA.
Four more telescopes are introduced to cover a larger
solid angle, and they are located between the target
and the YY1 telescopes. Each has a 0.3 mm-thick
TTT2-type double-sided SSD (DSSD) of Micron andfour 25 mm-thick CsI(Tl) crystals. The DSSD covers 97 × 97 mm2 . The CsI crystals placed behind canmeasure relatively high-energy charged particles (e.g.,
protons with E < 80 MeV). The angular resolution is
improved to be less than 0.5◦ . Three new trapezoidal
CsI crystals are brought in to fully cover the active
area of the original YY1 SSD.
A new electronic system for the TTT2 has been established. Since the additional detectors have morethan a thousand channels, we employ the General
Electronics for TPCs (GET), an integrated system forsignal processing including analog to digital converters (ADCs), trigger logic, and ampliﬁers for detectors
with many channels.4) For the connection between the
DSSDs and GET, ﬂexible-printed-circuit (FPC) connectors and circuits for the separation of signals froma DC bias are used. A new scattering chamber housing
was prepared as well.
The performance of the GET system to readout thesignal from the TTT2 was tested at RIKEN. The test
bench consisted of one TTT2 and a standard 241 Am
α-source installed inside the new TiNA chamber. The
∗1
∗2
∗3
∗4

CsI(Tl)YY1 x 6 (SSSD)

Beam
TTT2 x 4 (DSSD)
TargetHolder

RIKEN Nishina Center
Center for Nuclear Study, the University of Tokyo
Center for Exotic Nuclear Studies, Institute for Basic Science
Department of Physics, Tohoku University- 114 -

Fig. 1. Schematic drawing of TiNA after upgrade. The
YY1-type SSDs and CsI(Tl) crystals of original TiNA
are colored with blue and red, respectively. The new
TTT2-type DSSDs and CsI(Tl) crystals are coloredwith green and purple, respectively.

detector was fully depleted at −55 V. The GET system
consisted of an application-speciﬁc integrated circuit(ASIC) and ADC (AsAd) board connected to a totalof 256 strips and a reduced version of the Concentration Board (rCoBo). The system was triggered by aninternal multiplicity signal of rCoBo. A pulse-shapeanalysis is performed on the GET digitized signal toextract the energy of particle hits. The resolution obtained on the 241 Am α-spectrum is 28 keV (FWHM)
for the 5.485 MeV peak. More tests have been performed with the full system using 4 AsAd boards connected to a normal CoBo. It yielded similar results.
In conclusion, the TiNA array was upgraded by integrating new DSSDs, CsI detectors, and the GET system. The performance was tested using a standard
α-source. The results demonstrate the high resolution capabilities allowed by the new design and electronic circuit. This resolution was used to simulate
the 50 Ca(d, p) reaction. The overall excitation energy
resolution is less than 150 keV in σ, which is within
the experiment speciﬁcation. The full system of TiNA
will be tested in-beam at the Tandem accelerator of
the University of Kyushu in January 2021.
References

1) P. Schrock et al., CNS Annu. Rep. 2016, CNS-REP-96,
7 (2017).
2) K. Wimmer et al., CNS Annu. Rep. 2017, CNS-REP97, 7 (2019).
3) N. Imai et al., CNS Annu. Rep. 2018, CNS-REP-98, 1(2020).
4) E. C. Pollacco et al., Nucl. Instrum. Methods Phys. Res.
A 887, 81 (2018).

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RIKEN Accel. Prog. Rep. 54 (2021)

Heat durability test of molybdenum foil for the new CRIB cryogenic
gas target

A cryogenic gas target was developed and used forover 10 years1) for high-intensity low-energy secondary
beam productions at CRIB (Center for Nuclear Study
RI Beam separator.2) ) The basic design comprises a
stainless-steel gas cell with a 80-mm-long vs. ϕ20-mm
cylindrical aperture, where the target gas is conﬁned
by 2.5-µm-thick Havar foil windows at the beam entrance and exit sides. The gas supply duct and gas cell
are cryogenically cooled by liquid nitrogen. A forcedgas ﬂow system is employed through the entire gas line
to avoid density reduction under high heat deposition
caused by beam irradiation. The maximum intensityof the primary beam irradiation is limited by the heat
durability of the Havar foil, which is known to be 2 W.
Therefore, the gas target is always operated at a suﬃciently low heat deposition of the primary beam onto
the Havar foil windows to avoid damage.
Currently, we are developing a 26 Si RI beam withan intensity of 5×104 pps or higher for future measurements of the α-resonant scattering and 26 Si(α, p)reaction at CRIB (Exp. No. NP1812-AVF55). The
highest beam intensity of 26 Si achieved at CRIB
is 1.2 × 104 pps3) with a 24 Mg primary beam at
7.5 MeV/nucleon and 0.2 particle µA (pµA), which
is limited by the 2-W heat deposition on the Havar
windows. The above goal is possible once we achieve
the maximum heat deposition of 8 W or higher. To
this end, we consider the following design changes: (1)Using a foil material with a higher heat conductivity
and/or higher melting point than those of Havar foil;(2) Redesigning the gas cell with a higher cooling performance.
In the previous test experiment (Exp. No. NP1812AVF55-01), we conﬁrmed the advantages of molybdenum (Mo) and titanium (Ti) over Havar foil. The former has better high-temperature property due to its
higher melting point and heat conductivity, and thelatter has lower heat deposition because the minimum
required vacuum-tight thickness oﬀers smaller energy
loss of the beam passing through it. Next, we tested theheat durability of 2- and 3-µm-thick Mo foil mounted
on the currently used gas target cell in the Detector
Develop Beam Time (Exp. No. DD20-01). The target
cell was ﬁlled with 4 He gas up to 400 Torr, cooled byliquid nitrogen with forced circulation. An 16 O beam
at 6.8 MeV/nucleon was injected into the gas target
with the maximum beam intensity of 1.4 pµA. The
time course of the maximum temperature monitoredby the thermography is shown in Fig. 1 for diﬀerent∗1∗2Center for Nuclear Study, University of Tokyo
National Astronomical Observatory of Japan

Maximum thermography temperature (°C)

S. Hayakawa,∗1 N. Ma,∗1 H. Shimizu,∗1 and H. Yamaguchi∗1,∗2
80tFoil pinholed
Hole expanding
Target gas released completely

3 µm Mo, 1.4 pµAt
3 µm Mo, 1.1 pµAt
2 µm Mo, 1.3 pµAt
2 µm Mo, 1.0 pµA
Foil not broken, beam off

70
60
50

Foil suddenly
exploded

40

Foil not broken, beam off

30
20

Room temperature
Beam onset
00:00

00:02

00:04

00:06

00:08

00:10

Time from beam onset (min)Fig. 1. Time course of maximum temperatures.

foil thicknesses and beam intensities. Note that theread temperature tends to be considerably lower thanthe expected value because of the limited spatial resolution of the thermography for the beam spot size. For
an overall trend, the thicker foil is more easily heated
up because of the larger energy loss of the beam particle than the thinner one. We believe that the processof each foil above 1.3 pµA was diﬀerent; the temperature of the thinner one (blue line) increased gradually and the foil suddenly exploded at some point. In
contrast, the thicker one (red line) showed a pinhole
created right after the beam injection started, and theread temperature was decreasing as the hole expanded
to loose the gas completely at the end. Despite such
diﬀerent trends, the breaking intensity was found to be
similar (1.3–1.4 pµA), which can be attributed to themechanical strength of the thinner foil becoming too
weak to hold the gas even at a lower temperature where
the thicker foil is still stable (even with a pinhole). We
conclude that both the 2- and 3-µm-thick Mo foils canresist a beam intensity of 1.0–1.1 pµA or a heat deposition of 6–7 W at least; thicker foils are preferred forstable operation.
The remaining issue is the more eﬃcient heat releasefrom the Mo foil to the cryogenic gas cell body; thiscan be achieved by a design change (2). This is important to achieve further heat duration (>8 W) andfor a more stable long-duration operation. This will betested by another Detector Development Beam Time(Exp. No. DD20-02).
References

1) H. Yamaguchi et al., Nucl. Instrum. Methods Phys. Res.
A 589, 150 (2008).
2) Y. Yanagisawa et al., Nucl. Instrum. Methods Phys. Res.
A 539, 74 (2005).
3) H. S. Jung et al., Phys. Rev. C 85, 045802 (2012).

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RIKEN Accel. Prog. Rep. 54 (2021)

Radiation resistivity test of an optical fiber for laser cooling of francium
atoms
T. Hayamizu,∗1 K. Nakamura,∗2 T. Aoki,∗3 Y. Kotaka,∗2 H. Nagahama,∗2 S. Nagase,∗2 M. Ohtsuka,∗2,∗4
N. Ozawa,∗2 M. Sato,∗3 A. Takamine,∗1 K. S. Tanaka,∗5 H. Haba,∗1 and Y. Sakemi∗2
Francium is an alkali element in the 7th period, andall its isotopes are radioactive with half-lives of up to
20 min. The application of francium atoms to highprecision spectroscopy for testing fundamental symmetries has been implemented on a vertical beam line of
the E7 room at the RI Beam Factory. Francium is produced in the 197 Au(18 O, xn)215–x Fr reaction and ﬁnallysupplied as laser-cooled atoms into the spectroscopic region. For Fr production, a 7 MeV/nucleon 18 O6+ beam(target current 18 eµA) propagating through two beryllium foils and helium gas ﬂow is injected into a gold
target positioned at the end of the beam line. However,
the optical experimental region for spectroscopy is exposed to high radiation from the target, which is placeda few meters away. Therefore, the optical experimental
devices should be evaluated for radiation resistivity.
Laser sources were placed in the laser spectroscopy
room in the basement of the RIBF building. A titaniumsapphire laser and external cavity diode lasers supplied
718 nm light beams for the laser cooling of Fr atoms.
These light beams will be transported to the E7 room
via 400 m of optical ﬁber. The optical ﬁber consists ofa polarization-maintaining optical ﬁber (Fujikura SM63PS-U25D) covered by a stainless ﬂexible tube and ﬂameretardant polyvinyl chloride (Nippon Steel Welding &Enginering PICOFLEC). One of the concerns is radiation damage caused by boron, which has a large capture
cross section of neutrons, contained in stress-appliedparts of this optical ﬁber.1) We expected the radiation damage to cause two behaviors: transmission power
drifting and degradation of light polarizability.
To evaluate the radiation resistivity, we performed alight transmission monitoring test using 40 m of thesame model optical ﬁber wired inside the E7 room, during the Fr production beam time (maximum 7.9 eµA).
A part of the optical ﬁber (4.5 m) was stuck with plastic
masking tape on the vertical ﬂat surface of a steel rackapproximately 1.2 m away from the vertical beam line.
The ends of the optical ﬁber were connected to an optical monitoring system set downstairs of the E7 room,
where the radiation level is low. A 685 nm, 1 mW lightbeam from a diode laser was used for the monitoring
system. The output light power of the diode laser, andeach s- and p-polarized light power from the optical ﬁber
were monitored using power meters. We determined thetransmittance T by the power of the s-polarized output light from the optical ﬁber normalized by the value
∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
Center for Nuclear Study, University of Tokyo
Graduate School of Arts and Science, University of Tokyo
Waseda University Honjo Senior High School
Cyclotron and Radioisotope Center, Tohoku University

Fig. 1. The upper figure shows the integrated neutron doseat the E7 room monitoring post from the beginning of
measurement, and the lower figure shows the optical-fibertransmittance.

of the input power monitor. In addition, the radiationdose to the optical ﬁber was estimated using data fromthe E7 room monitoring posts. The peak value of theneutron dose rate was 3.7 mSv/hr, and the integrated
neutron dose at the monitoring posts over the beam timewas 21.6 mSv. Considering only the distance from thetarget, the expected dose of the optical ﬁber was several
times larger than the dose estimated at the monitoringpost.
The data obtained during the beam time are shown in
Fig. 1. Although it is clear that the cumulative neutron
dose and the ﬂuctuation of T in Fig. 1 did not correlate,T gradually reduced by less than 1% during 27 h. Inorder to identify whether this was caused by the irradiation, we carried out followup tests with a low radiation
background condition. By checking the optics used in
the monitoring system, we found that the coupling eﬃciency on the ﬁber couplers may have caused a similar
drift. In conclusion, a signiﬁcant change beyond themeasurement accuracy of the transmitted light power
and light polarization due to the irradiation was not observed with the current experimental setup. Additional
checks using a higher radiation dose are necessary to ensure that this optical ﬁber can be used for a longer beamtime.
Reference

1) S. Karasawa et al., IEEE Trans. Nucl. Sci. 34, 1105 (1987).
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RIKEN Accel. Prog. Rep. 54 (2021)

Development of novel detection system for francium ions extracted fromonline surface ionizer
N. Ozawa,∗1 H. Nagahama,∗2 T. Hayamizu,∗3 K. Nakamura,∗2 M. Sato,∗3,∗4 S. Nagase,∗1 Y. Kotaka,∗2
K. Kamakura,∗2 K. S. Tanaka,∗5 M. Otsuka,∗3 T. Aoki,∗3,∗4 Y. Ichikawa,∗3,∗6 A. Takamine,∗3 H. Haba,∗3
H. Ueno,∗3 and Y. Sakemi∗2
One of the origins of the matter-antimatter asymmetry in the Universe is considered to be the violation of
the charge conjugation and parity symmetries.1) The existence of a non-zero permanent electric dipole moment(EDM) of an elementary particle is an indicator of symmetry violation.
In particular, electron EDM (eEDM) is enhanced inparamagnetic atoms,2) up to 103 in the case of francium(Fr), which is the heaviest alkali.3,4) We are currently
developing an eEDM measurement system using lasercooled Fr atoms.
Fr atoms are produced in a surface ionizer via the nuclear
fusion-evaporation reaction, 197 Au(18 O, xn)215−x Fr.5)
An 18 O primary beam is irradiated onto a solid Au target. A fraction of the produced Fr atoms reach the surface via thermal diﬀusion, where they are released as ionsowing to the surface ionization eﬀect on the Au surface.
Using electrodes placed next to the target, the ions are
extracted at a 45-degree angle at 1 keV energy. The
Fr ion production rate depends on the Au target temperature, which is controlled using an infrared heater
installed on the opposite side of the beam irradiation
surface of the target.
The Fr yield is monitored by detecting the α particles
emitted during their decay using a Si solid state detector (SSD). In previous experiments, because the infrared
light from the heater acted as a noise source for the SSD,
the heater needed to be stopped for each measurement.
However, turning oﬀ the heater frequently caused theFig. 1. Developed Fr ion beam detector. Light from infrared
heater is shielded by shielding rings.
∗1
∗2
∗3
∗4
∗5
∗6

Department of Physics, University of Tokyo
Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Graduate School of Arts and Sciences, University of Tokyo
Cyclotron and Radioisotope Center, Tohoku University
Department of Physics, Kyushu University

Fig. 2. Typical energy spectrum of α particles emitted during
decay of ions captured on FC surface, obtained using theSSD. Labelled peaks within the range of 6.5–6.8 MeV are
identified as Fr.

Fr production to become ineﬃcient, owing to the rapid
drop in the Au target temperature.
To overcome this problem, we have developed a novel
Fr ion detection system that is insensitive to the infrared
light of the heater. The detection system, as shown in
Fig. 1, consists of an SSD, a Faraday cup (FC), and amoving rod attached to four shielding rings. The extracted Fr ions are ﬁrst irradiated onto the FC surface,where the beam intensity is observed as electronic current. Subsequently, the FC is moved to the front of theSSD, where the α particles are detected. Throughout
the operation, the shielding rings ﬁt to the cylindricalwall of the chamber with a negligible clearance; therefore the light hardly enters the SSD.
In September 2020, an experiment on Fr production was conducted. Figure 2 shows the energy spectrum of the α particles detected by the SSD. The spectrum analysis shows that a 210 Fr ion beam of 5 × 106 /s
was extracted. The Au target was heated to 960◦ C,
and an 18 O6+ beam of 1 particle µA accelerated to
7 MeV/nucleon using an RIKEN AVF cyclotron wasused as the primary beam.
Throughout the experiment, the infrared heater hada negligible eﬀect on the SSD. Therefore, the newly developed Fr ion detection system enables beam detection
without stopping the infrared heater, which is advantageous for stable production of Fr ions.
References

1) A. D. Sakharov, Sov. Phys. Usp. 34, 392 (1991).
2) M. Popeslov et al., Ann. Phys. 318, 119 (2005).
3) D. Mukherjee et al., J. Phys. Chem. A 113, 12549 (2009).
4) T. M. R. Byrnes et al., Phys. Rev. A 59, 3082 (1999).
5) G. Stancari et al., Nucl. Instrum. Methods Phys. Res. A
557, 390 (2006).
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RIKEN Accel. Prog. Rep. 54 (2021)

Experiment on hydrogen removal apparatus for helium supply andrecovery system
M. Nakamura,∗1 T. Dantsuka,∗1 and H. Okuno∗1
In the past, the liquid-helium supply and recovery
system of the Wako campus have suﬀered severe damages from hydrogen impurities in the system.1) To remove this hydrogen from the recovered helium gas, wedeveloped hydrogen removal methods utilized for oursystem. We found that the silver-zeolite “Ag400” madeby “Molecular Products Inc.” can be used as the adsorbent, and the applicability of Ag400 for hydrogen
removal was conﬁrmed.2) At that time, we did not install the hydrogen removal apparatus earnestly in oursystem. However, a new liquid-helium supply system
was constructed and operated from 2017 because of
the deterioration of the old system.3) In this system,
the newly established hydrogen removal apparatus was
installed beforehand. In this study, we examined theamount of hydrogen that can be adsorbed by Ag400,
which had not been minutely evaluated until now.
The experimental setup consists of a hydrogen tank,a pressure gauge, a buﬀer tank, three switch valves, areaction tank, a data logger, and a vacuum pump. The
volume of the buﬀer tank is approximately 550 cc, andthat of the reaction cylinder is approximately 18 cc.
These parts are connected as shown in Fig. 1.
The experiment is performed by the following threesteps. i) Approximately 20 g of Ag400 is ﬁlled in thereaction cylinder. Valve 1 is closed and the whole setup
are evacuated. ii) Valve 2 is closed, the valve 1 is released and hydrogen gas is ﬁlled to the buﬀer tank;its pressure reaches 0.4 MPaG. iii) Valves 1 and 3 areclosed and valve 2 is released. Hydrogen gas is supplied to the reaction cylinder and adsorption begins.
The change of the pressure of the buﬀer tank is monitored by the pressure gauge and recorded by the datalogger.

Fig. 2. Change of hydrogen pressure in the buﬀer tank.

The result of this experiment is shown in Fig. 2.
From this ﬁgure, it can be observed that the hydrogen pressure in the buﬀer tank reduced rapidly from
0.4 MPaG to 0.34 MPaG in approximately 30 min after the start of the adsorption reaction. After 12 h, thepressure slowly reduced to 0.32 MPaG. Finally, the hydrogen pressure reduced to approximately 0.31 MPaG
and settled at the equilibrium state. This result showsthat 20 g of Ag400 can adsorb approximately 500 scc
of hydrogen gas throughout the experimental process.
We use approximately 4 kg of Ag400 in the hydrogen
removal apparatus in the liquid helium supply and recovery system. Hence, approximately 0.10 Nm3 of hydrogen impurity gas can be removed by this apparatus.
Usually, the concentration of hydrogen contained in recovered helium gas ranges from 0.05 ppm to 1.5 ppm
in our system. Therefore, supposing that the recovered
helium gas contains 0.1 ppm of hydrogen, our apparatus can purify approximately 1000,000 Nm3 of recovered helium gas. However, the total volumes of liquid
helium supplied in one year in Wako campus were from
180,000 L to 200,000 L.3) When all this liquid helium isvaporized, approximately 135,000 Nm3 to 150,000 Nm3of helium gas is generated. In this case, we will evaluate that 4 kg of Ag400 can be used approximately 6–7
years for hydrogen removal.
In the next steps, we will evaluate other characteristics of hydrogen removal apparatus containing Ag400.
References

1) K. Ikegami et al., RIKEN Accel. Prog. Rep. 38, 286 (2005).
2) M. Nakamura et al., RIKEN Accel. Prog. Rep. 41, 111(2008).
3) T. Dantsuka et al., RIKEN Accel. Prog. Rep. 53, 221(2019).

Fig. 1. Experimental setup.
∗1

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Safety interlock system for LINAC building
A. Akasiho,∗1 H. Sakamoto,∗1 and K. Tanaka∗1
An interlock system of the LINAC building toward
human safety (LHIS) works for human radiation safety
and compliance with radiation lows. Because the previous interlock system was operated for 30 years, it was
too complicated to operate and maintain through longterm repeated system improvements and generationalchanges of developers. Further, a machine protection
system (MPS), that is applied to accelerator machinesafety, was part of the previous interlock system. This
was an operational risk wherein both machine protection
and human safety systems were in the same system as
it was possible to cause operational conﬂict. Therefore,
the new LHIS was completely separated from MPS.
Figure 1 shows the chart for a new LHIS. In this system, a programmable logic controller (PLC) controls
each safety device in the LINAC building directory. The
indicator light shows “beam on” or “beam oﬀ” at the entrance doors of the irradiation room and the accelerator room, as shown in Fig. 2. The status of the doors
are monitored, and then the LHIS determines whether
beam irradiation is possible. When the radiation workers enter the irradiation rooms, all take safety keys torecognize the LHIS where the workers are in the roomand to inhibit beam irradiation. A radiation monitor
generates a signal to the LHIS if it detects an abnormal
dose level. Radiation dose level are recorded to radiation
monitoring system. An access control PC independent
from LHIS and operated by an access management system generate a signal to the LHIS if a worker handles
its entry operation during beam irradiation.
Figure 2 shows an operational screen for the LHIS
operational PC (LHIS PC) that sends operational commands to PLC as shown in Fig. 1. The schematic di-

Fig. 2. Part of screen of LHIS PC. Positions of BSs are indicated.

agram of the LINAC building is displayed. The LHIS
covers three areas which are accelerator room, irradiation room of the Linac building, and the Connecting
building. Each area has its own beam shutter (BS) to
stop the beam discretely if an interlock incident occur.
Each BS on the accelerator is set on its upstream partto stop a beam before entering the room, as shown in
Fig. 2. In the previous systems, a faraday cup, which
is applied for accelerator operation, is also commonly
applied as BS. The BSs are independent of the faraday
cups at LHIS.
Instructions are issued from the LHIS PC to PLC remotely. The LHIS PCs are set at a radiation control
room in the Nishina building and an accelerator operation room in the LINAC building. The position of each
operated device such as doors for the accelerator roomand the irradiation room is shown in Fig. 2. Green color
for the devices shows an acceptable status of a beamirradiation, corresponds to “close” for the door case. A
yellow color door shows abnormal status of door “open.”
All operations for the devices are recorded in the LHIS
PCs.
LHIS is handled by the accelerator operators for RILAC. The operators choose a button on the screen forthe beam irradiation area. Then LHIS analyzes conditions of the safety devices for accelerator operation andbeam irradiation. A BS opens if all statuses are good.
If any status is not suﬃcient, an “abnormal” indication
is displayed and the BS does not open. While the BS
open, if a door for accelerator or irradiation rooms open,
the LHIS status changes to “abnormal” and BS closes.
The LHIS operation was successfully started at October 2019. At 2020, a rotating red light was installed at
the entrance of the irradiation room to show the X-ray
risk by the RILAC RF cavity.

Fig. 1. Conceptual diagram for new LHIS.
∗1

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Computing and network environment at the RIKEN Nishina Center
T. Ichihara,∗1 Y. Watanabe,∗1 and H. Baba∗1
We operate the Linux cluster systems1) at the RIKEN
Nishina Center (RNC).
Figure 1 shows the current configuration of the Linuxservers at the RNC.
We adopted the Scientific Linux (SL), which is a cloneof Red Hat Enterprise Linux (RHEL), as the operating
system. Since the support of SL 6 was scheduled to beterminated in November 2020,2) the SL 6 OSes installed
in some servers were replaced with SL 7 or CentOS 8.
The host RIBF.RIKEN.JP is used as the mail server,
NFS server of the user home directory, and NIS master server. This is the core server for the RIBF Linuxcluster. Mailing list services are also supported.
The hosts RIBFSMTP1/2 are the mail gateways used
for tagging spam mails and isolating virus-infected mails.
Since the OSes of RIBFSMTP1/2 were SL 6, we replaced them by SL 7 in September. The latest versionof Sophos Email Protection-Advanced (PMX 6.4.9) was
reinstalled. Figure 2 shows the mail trends in December
2020. Approximately 50% of the incoming mails were
blocked by the PMX ip-blocker.
A research record server RIBFDBOX was installed,
and it started operation in April 2015. Since five years
have passed, we replaced the research record server
RIBFDBOX by an HP-DL20G9 server in February
2020. At the same time, the OS and application software
were upgraded to CentOS 8.2 and Proself 5, respectively.
The streaming server RIBFSS started operation in2015 with the Wowza Streaming Engine V4.3 software, which can stream Real Time Messaging Protocol (RTMP) protocol. To play streaming videos of the
RTMP protocol, the Adobe flash player should be installed in the PC. Since the support of the Adobe flash
player for Windows OS and macOS was discontinued at
the end of 2020, the operation of the streaming server
RIBFSS was terminated at the same time.
The data analysis servers RIBFDATA02/03 aremostly used to store and analyze the experimental data
at RIBF. We have replaced the two RAID units (104 TBeach) for /rarf/w file system by new ones. Further, theOSes of the RIBFDATA02/03 were upgraded from SL 6
by SL 7 in September.
We have been operating approximately 70 units ofwireless LAN access points in RNC. Almost the entire
radiation-controlled area of the East Area of RIKEN
Wako campus is covered by wireless LAN for the convenience of experiments and daily work. Six units of
new wireless LAN access points (WAPM1266R) were installed in 2020.3)∗1

RIKEN Nishina Center







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Fig. 1. Configuration of the RIBF Linux cluster.

Fig. 2. Mail trends: message categories in December 2020.

References

1) T. Ichihara et al., RIKEN Accel. Prog. Rep. 53, 136 (2020).
2) https://scientificlinux.org/downloads/
sl-versions/sl6/ .
3) https://ribf.riken.jp/comp/net/wireless.html .

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1

II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

CCJ operations in 2020
S. Yokkaichi,∗1 H. En’yo,∗1 T. Ichihara,∗1 W. Nakai,∗1 and Y. Watanabe∗1Overview
The RIKEN Computing Center in Japan (CCJ)1)
commenced operations in June 2000 as the largest oﬀsite computing center for the PHENIX2) experimentbeing conducted at RHIC. Since then, CCJ has been
providing numerous services as a regional computing
center in Asia. We have transferred several hundred
terabytes of raw data ﬁles and nDSTa) ﬁles from the
RHIC Computing Facility (RCF)3) to CCJ.
Many analysis and simulation projects are being conducted at CCJ, which are listed on the web page
http://ccjsun.riken.go.jp/ccj/proposals/. As of December 2020, CCJ has contributed to 44 published papers and 45 doctoral theses.

Table 1. Number of malfunctioning HDDs in HP servers
during 2011–2020.

user

total

Computing hardware and software
The network conﬁguration and the computing hardware (nodes) and software (OS, batch queuing systems,
database engine, etc.) are almost the same as describedin the previous APR.4) We have two login servers, one
main server (users’ home directory, NIS, DNS, andNTP), and two disk servers, the disk sizes of whichare 13 and 26 TB. The main server has an external
SAS RAID (21 TB) for the home and work regions ofusers as well as system usage. Moreover, the server has
a RAID with built-in disks (13 TB) that can be used
temporarily by users and the system.
We operate 25 computing nodes, of which 16 nodes
were purchased in March 2009 and 9 nodes were purchased in March 2011. Thus, in total, 344 (= 8 × 16
nodes + 24×9 nodes ) jobs can be processed simultaneously by these computing nodes using a batch queuingsystem, LSF 9.1.3.5) Upgrade to LSF 10 is planned in
JFY 2021. Table 1 lists the number of malfunctioning
SATA or SAS disks in the HP servers, namely, computing nodes and NFS/AFS servers.
One database (postgreSQL6) ) server and one AFS7)
server are operated in order to share the PHENIX computing environment. It should be noted that only theSL58) environment is shared by the computing nodes,
which have approximately 0.9 TB of library ﬁles. We
operated two data-transfer servers, which have a 12 TB
SATA RAID with built-in disks. This year, anotherdata-transfer server, which has a capacity of 39 TB,
was deployed. Data transfer from J-PARC was performed in June during an experiment over 16 days, and
33 TB of raw data were transferred to CCJ. The data
were archived in a tape device in Hokusai.9) In addition, we operate two dedicated servers for the RHICf
group10) and two servers for the J-PARC E16 group11)

size (TB)

921

∗1
a)

RIKEN Nishina Center
Term for a type of summary data files in PHENIX

Type (Size) total 20 19 18 17 16 15 14 13 12 11
SATA (1 TB) 192
SATA (2 TB) 120
SATA (4 TB) 10
SAS (146 GB) 38
SAS (300 GB) 26

9 8 16 18
5 10 2 10
0 0 0 −
3 6 3 11 2 0 18 14 11 16 20 9
2 10 0 2 5 4− − − − − −5 3 2 0 1 1
0 1 1 0 0 1

Table 2. Tape usage in Hokusai as of December 2020.
PHENIX KEK/
RHICfoﬃcialJ-PARC
749

60

3

user-levelarchive109

in order to keep their dedicated compilation and libraryenvironments along with some data.
A server for the test of Docker12) was deployed tosupport the sPHENIX/EIC users as well as to develop
an OS-independent job submission scheme.
Joint operation with ACCC/HOKUSAI
CCJ and the RIKEN Integrated Cluster of Clusters(RICC) have been jointly operated since July 2009. In
April 2015, a new system named “HOKUSAI Greatwave” 13) was launched by RIKEN ACCC,9) and thejoint operation with CCJ continued, with the inclusionof a new hierarchical archive system in which approximately 900 TB of CCJ data are stored. A breakdownof the data is presented in Table 2.
In autumn 2020, ACCC started a system of charging
users for their usage of CPU time and storage capacity.
Tape usage is not yet charged as of 2020, and a charging
policy for the future has not yet been ﬁxed. We are indiscussiions with ACCC to set a reasonable fee.
References

1) http://ccjsun.riken.jp/ccj/ .
2) http://www.phenix.bnl.gov/ .
3) https://www.racf.bnl.gov/ .
4) S. Yokkaichi et al., RIKEN Accel. Prog. Rep. 53, 137(2020).
5) https://www.ibm.com/docs/en/spectrum-lsf/ .
6) http://www.postgresql.org/ .
7) http://www.openafs.org/ .
8) http://www.scientificlinux.org/ .
9) http://accc.riken.jp .
10) Y. Itow et al., arXiv:1409.4860 (Proposal).
11) S. Yokkaichi, in this report.
12) https://www.docker.com/ .
13) https://i.riken.jp/supercom/ .

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III. RESEARCH ACTIVITIES II(Material Science and Biology)

1. Atomic and Solid State Physics (Ion)III-1. Atomic & Solid State Physics (Ion)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Control of electrical conductivity in diamond by boron-implantation
using an ECR ion source—application of high-temperature andhigh-pressure annealing
H. Yamazaki,∗1 T. Minamidate,∗2 M. Kidera,∗1 A. Yamamoto,∗3 R. Kato,∗4 and H. Ueno∗1
Diamond is an excellent electrical insulator with alarge band-gap of 5.5 eV. It becomes a semiconductor
when doped with a small amount of boron (for p-type)or phosphorus (for n-type). Ekimov et al. reported that
B-doped diamond, when doped beyond the metal-toinsulator transition at nB ∼ 3 × 1020 B/cm3 , exhibits
superconductivity in samples grown by the high-pressureand high-temperature synthesis.1) Theoretically, the superconducting critical temperature Tc can be signiﬁcantly increased by reducing the eﬀects of the disorderin the B-doping processes.2) For a higher Tc , more subtle control of doping using CVD and/or MBE methods
is required. However, a diﬀerent method based on ion
implantation is also worth investigating, since it enables
selective ion-doping in a controlled manner. This has
great potential for future device applications.
We attempted to control the electrical conductivity indiamond by using the ion-implantation technique, utilizing RILAC at the RIBF facility. For n- and p-type semiconductors (and possibly superconductors), nitrogen andboron ions were implanted into diamonds, respectively.
By varying the beam intensity and irradiation time, theconcentration of nitrogen or boron was controlled. Notethat it is challenging to obtain the n-type semiconductor,
as well as the n-type superconductor, by nitrogen-dopingof diamond, since nitrogen behaves as a deep donor indiamond and does not contribute to conductivity.3)

Fig. 1. The process of high-temperature and high-pressure
annealing.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Faculty of Science, Tokyo University of Science
Graduate School of Engineering and Science, Shibaura Institute of Technology
Condensed Molecular Materials Laboratory, RIKEN

Fig. 2. Temperature dependence of electrical resistivity before and after annealing for B concentrations of (a)1.8 × 1021 , (b) 1.3 × 1022 , and (c) 6.8 × 1022 B/cm3 . The
possibility of the hopping conductivity in carrier-doped
semiconductor cannot be denied for these samples.

Fig. 3. Typical appearance of Ib- and IIa-type diamonds.

In this ﬁscal year, we continued studying boronimplanted diamonds. Boron ions were implanted into
diamond crystals (each size is 1 × 1 × 0.3 mm3 ) at 5 keV(implantation depth: ∼10 nm) by using an ECR ion
source.4) ) Ten samples of diﬀerent concentrations fromnB ∼ 4.9 × 1020 to 6.8 × 1022 B/cm3 were studied.
The magnetization and electrical resistivity measurements showed that the as-implanted diamonds do notexhibit superconducting transitions, even though nB ’s
are nominally beyond the metal-to-insulator transition
at 3 × 1020 B/cm3 . To reduce the lattice damage produced during the implantation, we performed annealing
treatments after implantation. The phase diagram ofcarbon shows that diamond is not stable at low pressures; we annealed the samples at 800◦ C and 4 GPa for
1 hour. The process of the annealing is shown in Fig. 1.
Contrary to our expectations, the annealed samples exhibited no sign of superconductivity (see Fig. 2).
The laser Raman spectra with 632.8 nm excitation
indicated that the annealing promoted the NV− center formation in diamond. To reduce this eﬀect, weare preparing for the boron implantation of IIa-type diamonds (Fig. 3) with nitrogen concentration less than
8 ppm.
References

1) E. A. Ekimov et al., Nature 428, 542 (2004).
2) T. Shirakawa et al., J. Phys. Soc. Jpn. 76, 014711 (2007).
3) S. J. Sque et al., Phys. Rev. Lett. 92, 017402 (2004).
4) M. Kidera et al., Eur. J. Mass Spectrom. 13, 239 (2007).

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1

III-1. Atomic & Solid State Physics (Ion)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Single-event eﬀects in SiC planar and trench power MOSFETs
M. Iwata,∗1 E. Mizuta,∗1 M. Takahashi,∗1 and H. Shindou∗1
Wide-bandgap semiconductors such as silicon carbide(SiC) have been attracting attention as materials forhigh-eﬃciency semiconductor devices. The adoption of
SiC power modules has recently progressed in the ﬁeldof railways and automobiles. In the aerospace industry,
the use of SiC devices requires the eﬀects of radiation
to be clariﬁed and these issues to be overcome. In thispaper, we report the results of radiation tests for SiC
power metal-oxide-semiconductor ﬁeld-eﬀect transistors(MOSFETs).
Two types of commercial n-channel SiC power MOSFETs were used in this experiment, as shown in Fig. 1.
The maximum rating for the drain-source breakdown
voltage of these devices is 1200 V. Test samples were
irradiated with 136 Xe ions of 638 MeV perpendicularly
at the device surface at room temperature in air using
RIKEN RILAC2 in combination with the RIKEN Ring
Cyclotron (RRC). During irradiation, the gate voltage,
VGS , was set to 0 V. The drain bias voltage, VDS , wasinitialized at 100 V and increased in 20 V steps. The
total ﬂuence at each VDS was 3.0 × 105 ions/cm2 .
Figure 2 shows the current transition of IDS during
irradiation up to VDS = 160 V. The leakage current of
the planar-type sample started to increase gradually at
VDS = 140 V, as shown in Fig. 2(a). This behavior isquite diﬀerent from that usually observed during heavyion irradiation on Si power MOSFETs, where the leakage current abruptly increases by single-event burn-out.
The tendency of gradual increase on the planar sample
is analogous to the failure modes of SiC Schottky barrier diodes.1) On the other hand, the leakage current of
the trench-type sample increased rapidly at the beginning of irradiation, as shown in Fig. 2(b). In Si trench
MOSFETs, a degradation mechanism related to a microdose eﬀect due to heavy-ion irradiation was reported,2)and we assume that the same eﬀect is caused in the SiC

Fig. 1. Cross-sectional structure of the test devices.
∗1

Fig. 2. Result of current monitoring during irradiation.

Fig. 3. Result of current monitoring before and after irradiation.

trench-type sample. The trench structure enables the irradiated ions to pass through the gate oxide along theentire length of the channel and generate electron-holepairs. Trapped holes might exist in the gate oxide because the hole diﬀusion velocity is less than that of electrons, and they might introduce a large leakage current
path immediately after the start of irradiation.
Figure 3 shows the I-V curves of the drain leakage
current before and after irradiation. The degradation byirradiation seemed worse in the trench-type sample thanin the planar sample.
Because the planar-type SiC MOSFETs did not show
the microdose eﬀect and its leakage current after irradiation was less than that of the trench-type sample, theplanar gate structure can be considered suitable for use
in space.
References

Research and Development Directorate, Japan Aerospace Exploration Agency

1) S. Kuboyama et al., IEEE Trans. Nucl. Sci. 53, 6 (2006).
2) J. A. Felix et al., IEEE Trans. Nucl. Sci. 54, 6 (2007).

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1

III-1. Atomic & Solid State Physics (Ion)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Profile measurements of dual-microbeams generated by glass capillaries
M. Mori,∗2,∗1 T. Ikeda,∗1,∗2 and W. -G. Jin∗2
Tapered glass capillary optics is known to be asimple and reliable microbeam generator for ion/laser
beams.1,2) The DNA of living cells is seriously damaged by not only ion-beam irradiation but also UV light.
However, to avoid mis-hitting of a target cell nucleus, alaser sight of a visible micrometer-sized spot is needed
prior to the UV microbeam shooting, where the visible
light never damages the DNA. We have proposed a dualmicrobeam system of visible light + ion beam (produced
at Pelletron in RIKEN Nishina Center) and visible + UV
light because any quantum beams can be transmitted
through the capillary optics. The transmission characteristics and the microbeam proﬁles of visible laser were
investigated until 2017,3) followed by the similar study
for UV microbeams.4) To realize the system of visible+ UV laser, the two microbeam spots should be on thesame position. In this report, the displacement between
the two spots as a function of possible mis-alignment of
the input beam is described, although a laser beam iswell-guided by the capillary optics.
Figure 1 shows the setup in Toho University. A UV
laser with a wavelength λ = 375 nm from a source(THORLABS L375P70MLD) entered a glass capillarywith an outlet diameter of 60 µm, where the capillary
was aligned with an accuracy better than the smallest
scale of 0.34 mrad in the mirror tuning. The microbeam
proﬁle approximately 3-mm downstream of the capillary
was obtained as shown in Fig. 2 by a knife-edge method
employing a motorized stage (SURUGASEIKI XY620G-N) and a photodiode (OPHIR PD300) connected toa power meter display. The central sharp peak like anairy disk, which is known in Fraunhofer diﬀraction fora circular aperture, was used to extract the full widthat half maximum (FWHM) as the spot size after Gaussian ﬁtting. A visible light laser (λ = 488 nm) from asource (Photochemical Research Associates Inc. LA15R)
also entered the capillary with a half mirror, which wastilted horizontally to emulate the mis-alignment with a

Fig. 2. Horizontal profile of a UV microbeam. The spot size
is defined as the FWHM of the central sharp peak.

Fig. 3. Displacement of the visible spot from the UV spot as
a function of θ, along with the spot sizes.

step of 0.68 mrad. The peak position and the spot size ofeach laser were measured according to the tilting angle
θ, where θ = 0 when the UV and visible laser enteredcoaxially.
The displacements of the visible laser spot from the
UV spot as a function of θ are plotted in Fig. 3. The
green and purple symbols show the peak positions ofvisible and UV lasers, respectively, where the UV peak
positions were set to zero. The vertical bars correspondto the spot sizes, which depend on the initial beam divergences. As expected, the UV spot sizes were almost
constant. We conﬁrmed that the visible laser peak positions were measured to be constant in the larger θ region(≥1.36). The guiding eﬀect of the laser beam throughthe capillary optics is clearly proven.5) However, for UV
spot sizes of ∼30 µm, the mis-alignment θ should be suppressed to less than 1.36 mrad to obtain the same spot
positions so that the mis-hitting in the UV microbeam
irradiation is avoided.
References

Fig. 1. Experimental setup with a knife-edge method to obtain the beam profiles. The distance L ∼ 3 mm.
∗1∗2

RIKEN Nishina Center
Department of Physics, Toho University

1) T. Ikeda et al., Appl. Phys. Lett. 89, 163502 (2006).
2) W. -G. Jin et al., J. Phys. Soc. Jpn. 84, 114301 (2015).
3) M. Koushima et al., J. Phys. Conf. Ser. 875, 112004 (2017).
4) S. Kawamura et al., J. Phys. Soc. Jpn. 89, 055002 (2020).
5) M. Mori et al., RIKEN Accel. Prog. Rep. 53, 143 (2020).

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12. Atomic and Solid State Physics (Muon)

III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Partial order of conduction electrons in Mn3 CoSi
S. Shamoto,∗1,∗2,∗3,∗4 D. P. Sari,∗5,∗3 I. Watanabe,∗3 H. Yamauchi,∗4 and L. -J. Chang∗1
Unconventional phase transitions have been discovered in various materials.1) One of them is a phase separation at the tri-critical point of quantum phase transition.2) Partial magnetic order has been observed in a
non-centrosymmetric compound of MnSi near the quantum phase transition under pressure.3,4) On the searchof new unconventional magnetic transition, we discovered the highest-temperature magnetic short-rangeorder (SRO) in a new noncentrosymmetric magnet
Mn3 RhSi by the complementary use of muon spin relaxation (HiFi and ARGUS at ISIS), neutron, X-ray scattering, electron diﬀraction, and magnetization measurements.5) It has a hyperkagome network of magnetic Mn
ions. We think that the unconventional magnetic SRO
emerges due to the spatially inhomogeneous order parameter, where the Lifshitz condition is violated by the
Dzyalonshinskii-Moriya interaction in a noncentrosymmetric magnet. The intriguing point of the SRO is not
limited in the highest-temperature record of magnetic
SRO, but also in the observed Q-position diﬀerent fromlong-range antiferromagnetic (AF) order Q-position. At
present, however, the mechanism is still unknown. To
reveal the mechanism, we believe that it is necessary tocomplete the phase diagram (Fig. 2) by measuring therelated family compounds such as Mn3 CoSi (a = 6.28 Å)with a diﬀerent lattice constant resulting in a diﬀerent

Fig. 2. Phase diagram of β-Mn type structure alloys.

bandwidth from that of Mn3 RhSi (a = 6.47 Å). The Néel
temperature of Mn3 CoSi is about 100 K, whereas that of
Mn3 RhSi is 190 K. However, it was unknown which the
SRO transition temperature of Mn3 CoSi becomes lower
than that of Mn3 RhSi.
TF µSR measurement of Mn3 CoSi (RB2070006) successfully showed SRO anomaly above Néel temperaturein the asymmetry as shown in Fig. 1. The magnetic
SRO of Mn3 CoSi is found to start at about 250 K. From
this result, we may conclude that the SRO temperature
increases with increasing the lattice constants as shownin Fig. 2. This result suggests that the present world
record of SRO temperature may further increase withincreasing the lattice constant.
References

Fig. 1. Temperature dependence of TF µSR asymmetry of
Mn3 CoSi.
∗1
∗2
∗3
∗4
∗5

Department of Physics, National Cheng Kung University
Comprehensive Research Organization for Science and Society
RIKEN Nishina Center
Advanced Science Research Center, Japan Atomic Energy
AgencyCollege of Engineering, Shibaura Institute of Technology

1) S. Shamoto, J. Phys. Soc. Jpn. 88, 081008 (2019),
arXiv:1905.03905.
2) D. Belitz, T. R. Kirkpatrick, T. Vojta, Rev. Mod. Phys.
77, 579 (2005).
3) C. Pfleiderer et al., Nature 427, 227 (2004).
4) Y. J. Uemura et al., Nat. Phys. 3, 29 (2007).
5) H. Yamauchi, D. P. Sari, I. Watanabe, Y. Yasui,
L. -J. Chang, K. Kondo, T. U. Ito, M. Ishikado, M. Hagihara, M. D. Frontzek, S. Chi, J. A. Fernandez-Baca,
J. S. Lord, A. Berlie, A. Kotani, S. Mori, S. Shamoto,
Commun. Mat. 1, 43 (2020).

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1

III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Magnetism and superconductivity in underdoped region of T*-typeLa1−x/2 Eu1−x/2 Srx CuO4−y Fy
M. Takahama,∗1,∗2 T. Taniguchi,∗1 D. P. Sari,∗3,∗4 I. Watanabe,∗3 and M. Fujita∗1
In the study of high-transition-temperature cuprates,
the doping evolution of magnetism and its relationshipwith superconductivity are important issues. It had
been considered that the superconductivity is inducedby carrier doping into Mott insulators.1) However, theappearance of superconductivity in RE2 CuO4 (RE =rare earth) without eﬀective carrier doping (undoped
superconductivity) was clariﬁed by improving material synthesis and annealing techniques.2,3) After the
discovery of undoped superconductivity, the broad superconducting (SC) phase was reported.4)
Recently, we succeeded in synthesizing T*-type
structured La1−x/2 Eu1−x/2 Srx CuO4 (LESCO) in
which the oxygen coordination around a copper ion
is ﬁve and reported the magnetic and SC properties as functions of Sr concentration.5,6) Our muon
spin rotation/relaxation (µSR) measurement of LESCO revealed the presence of a spin-glass state andthe absence of static magnetism in the as-sintered
non-SC and high-pressure oxidated SC samples, respectively. Therefore, the short-range magnetic order disappears with the emergence of superconductivity, suggesting competition between the two states.
However, as it is challenging to synthesize a singlephase sample of LESCO with a smaller x, the electronic state of the underdoped (UD) region of T*type cuprates has not been investigated. Thus, wenewly synthesized La1−x/2 Eu1−x/2 Srx CuO4−y Fy (LESCOF), in which the hole concentration can be reduced by increasing y while keeping the single-phase
T*-type structure. The evidence of low carrier density in both as-sintered and oxidation-annealed LESCO was reported by x-ray absorption spectroscopy
measurement,6) and LESCO with x ≲ 0.23 corresponds
to UD La2−x Srx CuO4 . Therefore, LESCOF with x =0.18 is expected to be located in a more UD region.
The magnetism in UD LESCOF was studied by µSR
measurements at RIKEN-RAL.
Figure 1(a) shows the temperature dependence ofthe zero-ﬁeld µSR time spectra of as-sintered LESCOF
with x = 0.18 and y = 0.14. Exponential-type spectra are observed below ∼80 K, and muon spin precession was observed at the lowest temperature of 5.1 K.
The appearance of precession suggests the emergenceof long-range magnetic order. Furthermore, the temperature at which the spectra change from Gaussiantype to exponential is higher than that in the pristine
∗1
∗2
∗3
∗4

Institute for Materials Research, Tohoku University
Department of Physics, Tohoku University
RIKEN Nishina CenterCollege of Engineering, Shibaura Institute of Technology

Fig. 1. Zero-field µSR time spectra of (a) as-sintered and(b) oxidation-annealed La1−x/2 Eu1−x/2 Srx CuO4−y Fywith x = 0.18 and y = 0.14.

LESCOF with x = 0.18,4) indicating the developmentof static magnetism upon underdoping. On the other
hand, the oxidation-annealed SC sample shows no evidence of magnetic order down to 2 K (Fig. 1(b)).
Two characteristic features of magnetism were clariﬁed in the present study. Firstly, a long-range magnetic ordered state exists in the lightly doped sampleof as-sintered T*-type LESCOF. Combined with previously reported results,4) the short-range spin-glass
state is replaced by the long-range state upon underdoping, as is the case with other cuprates. Secondly,such an ordered state disappears with annealing inconnection with the emergence of superconductivity.
Therefore, our results suggest that strong Cu-spin correlations cause the superconductivity in T*-type LESCO, and that the spin ﬂuctuations play an essential role in the mechanism of superconductivity in thelightly hole-doped region.
References

1) N. P. Armitage et al., Rev. Mod. Phys. 82, 2421 (2010).
2) A. Tsukada et al., Solid State Commun. 133, 427(2005).
3) T. Takamatsu et al., Appl. Phys. Express 5, 073101(2012).
4) O. Matsumoto et al., Physica C 469, 924 (2009).
5) S. Asano et al., J. Phys. Soc. Jpn. 88, 084709 (2019).
6) S. Asano et al., J. Phys. Soc. Jpn. 89, 075002 (2020).

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1

III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Spin dynamics in Pyrochlore Nd2 Mo2 O7
L. J. Chang,∗1 D. P . Sari,∗2 M. C. Hatnean,∗3 G. Blalkrishnan,∗3 Y. Yasui,∗4 and I. Watanabe∗5
Nd2 Mo2 O7 is metallic and exhibits a ferromagnetictransition at a Curie temperature Tc = 93 K. In contrast
with other Nd-pyrochlore systems, such as Nd2 Sn2 O7
and Nd2 Zr2 O7 , where the magnetic moments are localized, Nd2 Mo2 O7 possesses delocalized electrons, which
may host novel phenomena associated with the interaction between the localized moments Nd3+ and the itinerant moment Mo4+ . Particularly, Nd2 Mo2 O7 exhibits
unusual spin chirality,1,2) and possesses a two-in-two-out(AIAO) spin ice spin conﬁguration on Nd3+ . Unlike the
AIAO magnetic order of Ir4+ in Nd2 Ir2 O7 , the XY typeorder of Ru4+ in Nd2 Ru2 O7 , and Mo4+ in Nd2 Mo2 O7 orders along the 001 direction. In Nd2 Mo2 O7 , the anomalies appearing at 93 K in both the magnetic and heat capacity is attributed to the Mo4+ ordering temperature,
whereas the ordering of Nd3+ becomes signiﬁcant below
30 K.3) Therefore, it is interesting to study the spin dynamics in the delocalized electron system of Nd2 Mo2 O7
and compare them to those of other Nd-pyrochlores byµSR technique. Moreover, applied ﬁelds in Nd2 Mo2 O7
may change the ground state of Nd3+ .3) µSR experiments were carried out at ARGUS spectroscopy, RIKENRAL, between the temperature ranges of 5–300 K to obtain the information below and above the magnetic transition temperatures of 30 and 93 K. Figure 1(a) shows
the zero-ﬁeld mSR relaxation spectra at 7.5, 35, 95,
and 160 K and the ﬁtted curves using the function of
A1 exp(−λ1 t) + A2 exp(−λ2 t) + A3 . The plots of the ﬁtted parameters are shown in Fig. 1(b). The initial dropof the muon relaxation below 95 K indicates the magnetic order of the compound, which can also be conﬁrmedby the increasing of the relaxation rate λ1 in Fig. 1(b).

Fig. 1. (a) zero-ﬁeld µSR relaxation spectra at 7.5, 35,
95, and 160 K and ﬁtted curves using the function of
A1 exp(−λ1 t) + A2 exp(−λ2 t) + A3 ; (b) plots of the ﬁtted
parameters.
∗1
∗2
∗3
∗4
∗5

Department of Physics, National Cheng Kung University
College of Engineering, Shibaura Institute of Technology
Department of Physics, University of Warwick
Department of Physics, Meiji University
RIKEN Nishina Center

Fig. 2. Temperature-dependence of the asymmetry spectraof muon relaxation signal between 5 and 300 K in theapplied ﬁeld of 4000 G. The spectra can be separated into
three diﬀerent temperature intervals of 30 K and 93 K,
the transition temperatures of Nd3+ and Mo4+ ordering
temperatures, respectively.

The initial drop made it impossible to determine themagnetic volume fraction of the AIAO spin structure.
However, the transition at 30 K cannot be picked up
clearly by muon relaxation. The asymmetry of the slow
relaxation parameter exhibits a magnetic anomaly. Longitudinal ﬁelds were applied up to 4000 G to evaluate
the decoupling of muons on the sites. An applied constant of 4000 G in the temperature-dependent scans was
also utilized in the experiments. The transitions at 30
and 93 K can be clariﬁed in the measurements as shownin Fig. 2, in which the relaxations of the spectra areseparated to three groups in three diﬀerent temperature
ranges. Proper models have to be proposed to ﬁt thesecurves and higher ﬁelds are necessary to decouple themuon relaxations for further study on this compound.
At 5 K, the signiﬁcant diﬀerences of the asymmetry
and muon relaxation have been observed before and after an applied ﬁeld (not shown in the ﬁgure). Similar
behaviour does not appear at a higher temperature of
85 K. This hysteresis at 5 K indicates ferromagnetic
components at low temperature. In our experiments,
this hysteresis even happens in a small applied ﬁeld of
100 G. The magnetic structure of Nd2 Mo2 O7 , had beenreported as a spin chirality “umbrella” structure,4) whichis consistent with the observation made in the µSR spectra at low temperatures. This phase occurs below the
Nd3+ ordering temperature only, and does not exist below the Mo4+ ordering temperature between 93 K and
30 K. However, muon precession was not observed in theexperiments. We are working on a proper model to ﬁt
the spectra below 30 K.
References

1) K. A. Ross et al., Phys. Rev. B 84, 174442 (2011).
2) A. Maisuradze et al., Phys. Rev. B 92, 094424 (2015).
3) Y. Yasui et al., J. Phys. Soc. Jpn. 72, 865 (2003).
4) Y. Taguchi et al., Science 291, 2573 (2001).
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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel.
(2021)
RIKEN
Accel. Prog.
Prog.Rep.
Rep.5454(2021)

Possible multipolar ordering in spin-orbital-entangled d2 system on aface-centered-cubic lattice
T. Takayama,∗1,∗2 D. P. Sari,∗3,∗4 I. Watanabe,∗4 and H. Takagi∗1,∗2,∗5
The interplay of strong spin-orbit coupling (SOC)and electron correlation in heavy transition-metal compounds containing 4d and 5d elements has been revealed to give rise to unprecedented electronic statesof matter. In such systems, strong SOC produces spinorbit-entangled Jeﬀ states of d-electrons. The interactions between spin-orbital-entangled objects are distinct from those in spin-only systems, and a plethora ofnovel electronic phases has been predicted to emerge.
In d2 conﬁgurations, SOC yields Jeﬀ = 2 quintet states.
When the Jeﬀ = 2 states are placed on a face-centeredcubic (FCC) lattice, multipolar ordering phenomena
such as charge quadrupolar and magnetic octupole orderings are expected to emerge.1,2)
To explore such multipolar orderings of d-electrons,
we focused on cubic tungsten halides A2 WCl6 (A =K, Rb, Cs) with a 5d2 conﬁguration of W4+ ions. The
regular WCl6 octahedra form an FCC lattice. In thesecompounds, the magnetic susceptibility χ(T ) shows aCurie-Weiss behavior at high temperatures, and theeﬀective moments are close to the value expected forJeﬀ = 2 (µeﬀ ∼ 1.22 µB ). K2 WCl6 displays an anomaly
in speciﬁc heat C(T ) at approximately 180 K, whichcorresponds to a structural transition from cubic totetragonal, but no further anomaly was observed atlower temperatures. Rb2 WCl6 and Cs2 WCl6 show no
pronounced anomaly in C(T ) and χ(T ) down to 2 K,
although a deviation from the Curie-Weiss behavior
is observed at approximately 100 K. The magnetic
ground state of these materials is thus not clear yet.
One of the possible ground states is the formationof magnetic octupolar ordering, which has been suggested for d2 double-perovskite oxides.3) In those oxides, although any signature of magnetic dipolar ordering was found in χ(T ) and neutron diﬀraction, aclear oscillatory signal was observed in muon spin rotation (µSR) measurements, indicating time-reversalsymmetry breaking. The other possibility, especiallyfor K2 WCl6 , is that the structural transition lifts thedegeneracy of the Jeﬀ = 2 quintet and selects the nonz
= 0 singlet ground state (i.e., chargemagnetic Jeﬀ
quadrupole order), which can be regarded as a spinorbital nematic state in analogy with the S z = 0
spin-nematic state. In this case, the time-reversalsymmetry is retained, and no oscillatory signal is ex∗1
∗2
∗3
∗4
∗5

Max Planck Institute for Solid State ResearchInstitute for Functional Matter and Quantum Technologies,
University of Stuttgart
Graduate School of Engineering and Science, Shibaura Inst.
of Tech.
RIKEN Nishina Center
Department of Physics, University of Tokyo

Fig. 1. Zero-field time spectra of muon asymmetry for
Cs2 WCl6 at several temperatures.

pected in µSR.
In order to investigate the ground states, we performed a µSR measurement on powder samples of
A2 WCl6 (A = K, Rb, Cs) using ARGUS, ISIS. For all
the samples, the time dependence of muon asymmetry
at low temperatures only shows a monotonic decrease,indicating a nonmagnetic ground state. Figure 1 shows
the result for Cs2 WCl6 . The time dependence of muon
asymmetry at zero magnetic ﬁeld did not show any
pronounced change down to 2 K. For K2 WCl6 , the relaxation rate λ, obtained by ﬁtting with a Lorentzian
curve, shows a kink at approximately 180 K, wherea structural transition occurs. No such anomaly was
found in Cs2 WCl6 or Rb2 WCl6 .
This result excludes the presence of magnetic dipolar or octupolar ordering in A2 WCl6 . The questionof whether the Jeﬀ = 2 moments remain ﬂuctuating orform a quadrupolar ordering with a spin-singlet groundstate remains open. We expect that the ground statesof these compounds can be clariﬁed in combination
with other measurements, especially the analysis of
low-temperature crystal structures.
References

1) G. Chen, L. Balents, Phys. Rev. B 84, 094420 (2011).
2) S. Voleti et al., Phys. Rev. B 101, 155118 (2020).
3) D. Maharaj et al., Phys. Rev. Lett. 124, 087206 (2020).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Successive Transitions in Spin-dimer Compound Cs3 V2 Cl9
H. Kikuchi,∗1,∗3 Y. Fujii,∗2 and I. Watanabe∗3

ZF
19.7K
10.1K
5.7K
3.2K
3.7K
1.6K

Asymmetry

0.1

0
0

2

4
time (µsec)

68Fig. 1. Temperature dependence of the ZF-µSR spectra ofCs3 V2 Cl9 .
∗1
∗2
∗3

Department of Applied Physics, University of Fukui
FIR Center, University of Fukui
RIKEN Nishina Center

0.15
Zero Field
0.10

-1

λs (µs )A3 M2 X9 (A = Cs, Rb : M = transition metal elements: X = Cl, Br) compounds with trigonal spacegroup P63 /mmc are composed of isolated di-nuclear
complexes [M2 X9 ]3− and their magnetic properties are
explained within an isolated or weakly coupled spin
dimer model. Because these spin dimers are arranged
in a triangular form, the spin frustration eﬀect is expected to appear when magnetic phase transition occurs via ﬁnite interdimer interactions. Cs3 V2 Cl9 , one
member of the A3 M2 X9 family with magnetic ion V3+(S = 1), was previously studied via magnetic susceptibility and inelastic neutron scattering measurement
using powder sample1) and no magnetic ordering wasobserved above 1.5 K. We recently synthesized a single
crystal of Cs3 V2 Cl9 and measured susceptibility χ(T )and speciﬁc heat, and we found successive phase transition at TN ≈ 4 K and Tn ≈ 15 K.2)
These successive phase transitions are not explained
within the framework of the isolated dimer model, andthey show the presence of non-negligible interdimer interaction. χ(T ) shows no anomaly at Tn although TN
is accompanied by the cusp-like anomaly of χ(T ). The
lower temperature transition is suggested to be an antiferromagnetic transition although the spin structure
is not clear. The higher temperature transition is nota mere crystal structure transition because the transition temperature depends on the applied magneticﬁeld.
We measured the µSR of Cs3 V2 Cl9 to clarify the nature of the successive phase transitions. Figure 1 shows
the zero-ﬁeld muon spin relaxation (ZF-µSR) spectra

0.05

0.00
0

10
20
Temperature (K)30

Fig. 2. Temperature dependence of the relaxation rate λs .

measured down to 1.6 K. At relatively high temperatures, the spectra follow Gaussian curves. As thetemperature decreases, the spectra changes from Gaussian to an exponential curve following as exp(−λs t) +af exp(−λf t), where λs and λf denote slow and fast
relaxation rates, and as and af represent amplitudesof the asymmetry of slow and fast components, respectively. Solid lines in Fig. 1 are ﬁtted results. Figure 2
shows the temperature dependence of λs . A distinct
peak is observed at around TN , which conﬁrms that amagnetic long range order occurs at this temperature.
No anomaly of lambda is observed at Tn , which indicates that an internal ﬁeld does not appear. The phasetransition at Tn is not accompanied by the internalﬁeld, whereas the value of Tn depends on the appliedmagnetic ﬁeld. One candidate for the transition at Tn
is a spin nematic order wherein quadrupole moments,
not magnetic moments, play the role of an order parameter. Because the nematic state does not break thetime-reversal symmetry, usual magnetic probes including muon do not detect this transition.3) Several theoretical studies indicate the occurrence of the nematicorder in an S = 1 triangular lattice antiferromagnet
or spin dimer magnets. The ﬁndings obtained by thisµSR experiments make it more likely that Tn is thenematic transition.
References

1) B. Leuenberger et al., Inorg. Chem. 25, 2930 (1986).
2) H. Kikuchi, T. Tanaka, Y. Fujii, A. Matsuo, K. Kindo,
Abstract of the 19 International Conference on Magnetism. July 8–13, 2012 Busan, Korea, p. 167.
3) A. Smerald et al., Phys. Rev. B 88, 184430 (2013).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Magnetism of novel heavy fermion compound YbCu4 Ni investigated byµSR
T. Taniguchi,∗1 K. Osato,∗1,∗2 M. Fujita,∗3 D. P. Sari,∗3,∗4 and I. Watanabe∗3,∗5
The f -electron systems show many examples of quantum critical phenomena.1) In previous works, highquality crystals and advanced experimental methods
provided many instances of quantum critical phenomena
originating from antiferromagnetism. Recently, quantum critical phenomena that cannot be explained by
the self-consistent renormalization (SCR) theory haveattracted much attention. However, to study such quantum critical phenomena, actual candidate materials andadequate experimental methods are required.
We focused on YbCu4 T (T = transition metal) because this family exhibits exotic physical phenomena
such as the valence transition at zero ﬁeld and ambient pressure in YbCu4 In.2,3) In YbCu4 Au, valence andmagnetic transitions are induced by applying a magnetic
ﬁeld.4) Since the Yb site in this family has three-foldsymmetry, this system may show an ordered phase originating from geometrical frustration.
The temperature dependence of the speciﬁc heat
(C/T ) of YbCu4 Ni shows a power-law behavior. Thisbehavior is consistent with the quantum critical phenomena, but the SCR theory cannot explain the temperature dependence of C/T .5) The purpose of our research is to understand the origin of the power-law behavior of C/T in YbCu4 Ni. Magnetism usually plays
the vital role of quantum criticality. Thus, we performed
muon spin relaxation (µSR) measurements at RIKENRAL because µSR is a powerful tool to obtain information on static and dynamic spin correlations.
Figure 1 shows the temperature dependence of theµSR time spectra. To derive the magnetic ﬂuctuation of
the f -electron, we applied a longitudinal magnetic ﬁeldof 100 G. Rapid relaxation was observed at low temperatures below 2 K, indicating the appearance of magnetic
ﬂuctuation. However muon spin precession was not observed down to the lowest temperature of 0.4 K. We
determined the asymmetry of the spectrum at 0.4 K forthe time after ∼4 µs as the baseline (∼16%). These
results suggest the inhomogeneous magnetic ﬁeld at themuon stopping site even at the lowest measurement temperature.
Here, we discuss the origin of the power-law behaviorof C/T from the viewpoint of magnetic ﬂuctuation. As
in the case of antiferromagnetism, it is highly possiblethat the magnetic ﬂuctuation is the cause of the temperature dependence of C/T . There are two possible originsof the magnetic ﬂuctuations: (1) the novel quantum crit∗1
∗2
∗3
∗4
∗5

Institute for Materials Research, Tohoku University
Department of Physics, Tohoku University
RIKEN Nishina CenterCollege of Engineering, Shibaura Institute of Technology
ISIS Pulsed Neutron and Muon Facility, STFC Rutherford
Appleton Laboratory

Fig. 1. Temperature dependence of the µSR time spectra of
YbCu4 Ni in a longitudinal field of 100 G.

icality and (2) magnetic inhomogeneity. For the former
case, it was theoretically aspect pointed out that a dramatic increase in eﬀective mass should be observed near
the quantum critical point, other than that from the anitferromagnetic phase.6) For example, the temperaturedependence of C/T shows logarithmic behavior in βYbAlB4 even when the valence ﬂuctuation contributed
to the physical properties.7) For the latter case, owing
to the distribution of the Kondo temperature originatingfrom the magnetic inhomogeneity, C/T at low temperatures may show a behavior similar to quantum criticality.8) Since inhomogeneous states such as the spin-glass
state may appear because of the geometrical frustration,
the latter case is also a candidate scenario. µSR measurements below 0.4 K may provide evidence to clarify
the above two possibilities.
In conclusion, we performed the µSR measurementsof YbCu4 Ni. At low temperature, the magnetic ﬂuctuation increased. It is highly possible that the power-law
behavior of C/T is caused by this ﬂuctuation.
References

1) G. R. Stewart, Rev. Mod. Phys. 56, 755 (1984).
2) H. Nakamura et al., J. Phys. Soc. Jpn. 59, 28 (1990).
3) M. Hedo et al., Acta. Phys. Pol. B. 34, 1193 (2003).
4) S. Wada et al., J. Phys. Condens. Matt. 20, 175201 (2008).
5) J. G. Sereni et al., Phys. Rev. B. 98, 094420 (2018).
6) S. Watanabe, K. Miyake, Phys. Rev. Lett. 105, 186403(2010).
7) S. Nakatsuji et al., Nat. Phys. 4, 603 (2008).
8) E. Miranda et al., J. Phys. Condens. Matt. 8, 9871 (1996).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

ZF-µSR measurement to investigate thermal hysteresis of MgTi2 O4 at
low temperature
U. Widyaiswari,∗1,∗2 N. Hanasaki,∗3 B. Kurniawan,∗2 and I. Watanabe∗1,∗2
We investigated spinel titanate (MgTi2 O4 ) which
has a 3d1 electron (S = 1/2) within the Ti3+ ion andforms a pyrochlore lattice,1) to explore the magnetic
ground state of this strongly correlated system. The
lattice of MgTi2 O4 has a cubic structure at room temperature and shows a transition to a tetragonal structure at Tst ≃ 260 K.2) This structural phase transition is accompanied by a metal-insulator transition andchanges in magnetic properties.2) Isobe et al. proposeda spin-singlet insulator as the ground state, which did
not form any magnetic ordering.2)
Previously, we found that there was no long-rangeordered state in MgTi2 O4 down to 6 K through zeroﬁeld muon spin resonance (ZF-µSR) measurements.
Our preliminary study on MgTi2 O4 showed that thermal hysteresis occurs in the temperature dependenceof heat capacity below 3.5 K down to 2.5 K. To investigate the origin of the thermal hysteresis and magnetic
properties at a much lower temperature, we extend
the ZF-µSR measurement down to 2 K using VARIOX at the RIKEN-RAL Muon Facility in the United
Kingdom. ZF-µSR measurements were performed below 30 K with descending temperature (cooling procedure) and ascending temperature (warming procedure)
to observe the thermal hysteresis. The time spectra,
shown in Fig. 1(a), can be ﬁtted using Eq. (1).
A(t) = AGKT (1/3+2/3(1−∆2 t2 ) exp(−∆2 t2 /2))
(1)
+ AL exp(−λt),where AGKT and AL are the initial asymmetry fromGaussian and Lorentzian components at t = 0, respectively.
The absolute value of the temperature dependenceof muon spin relaxation, λ(T), was in good agreementwith the previous result3) and is shown in Fig. 1(b).
This result demonstrated that the muon spin relaxation rate does not change signiﬁcantly indicating theabsence of the ordered state down to 2 K. Furthermore, there is no diﬀerence in the muon spin relaxation
rate measured in the cooling and warming procedures.
This indicates that the thermal hysteresis observed in
the heat-capacity measurement is beyond the muonspin time window; therefore, we could not detect such
behavior down to 2 K.

∗1
∗2
∗3

Fig. 1. (a) ZF-µSR time spectra of MgTi2 O4 ; the solidline is the fitting resulted obtained using Eq. (1). (b)Temperature dependence of the muon spin relaxation
rate.

References

1) S. Torigoe et al., Phys. Rev. B 98, 134443 (2018).
2) M. Isobe, Y. Ueda, J. Phys. Soc. Jpn. 71, 1848 (2002).
3) U. Widyaiswari et al., RIKEN Accel. Prog. Rep. 53, 149(2019).

RIKEN Nishina Center
Department of Physics, Universitas Indonesia
Department of Physics, Osaka University- 133 -

1

III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Observation of Cu spin fluctuations in over-doped regime La2-x Srx CuO4
nanoparticles
S. Winarsih,∗1 T. Adachi,∗2 T. Goto,∗2 B. Kurniawan,∗3 B. Soegijono,∗3 and I. Watanabe∗4
The ﬁrst observation of exchange anisotropy or exchange bias was reported for cobalt particles capped bycobalt oxide.1) The shifted hysteresis loop in ﬁeld-cooledsuggested the occurrence of exchange coupling between
the ferromagnetic spin of cobalt with the antiferromagnetic spin of cobalt oxide. For gold nanoparticles encapsulated by butanethiol, clear evidence of magnetism wasobserved when the size of the gold cluster was 2.2 nm, as
studied by muon-spin relaxation (µSR).2) The relaxationof muon spins decreased with increasing temperaturein the longitudinal ﬁeld, (LF-µSR), indicating the existence of a magnetic moment. Even though magnetism
was clearly observed, this study could not distinguishwhether the magnetic moment was located at the encapsulated molecules or inside the gold nanoparticles.
The existence of ferromagnetic spins at the surface wasalso suggested to lead to the observation of a hysteresis
loop at 10 K in CuO nanoparticles.3) An anomalously
enhanced Curie term at low temperatures in high-Tc superconductor cuprate (HTSC), La2-x Srx CuO4 , with x =0.10–0.30, when the particle size was reduced to 113 nm
was also linked to the role of the spins at the surface.4)
This suggests that the surface eﬀect plays an importantrole in both free-standing nanoparticles, like CuO andLa2-x Srx CuO4 , and nanoparticles capped by molecules,
like oxide-coated particles of cobalt and nanogold cappedby butanethiol. However, the mechanism of the role ofthe surface causing the emergence of ferromagnetism in
nanoparticles is still an open question.
We aimed to investigate nano-sizing eﬀects in
La2-x Srx CuO4 because the observation of possible ferromagnetism is a new interesting phenomenon in HTSCs.
In the bulk case, a ferromagnetic phase was predictedin the heavily overdoped regime where the superconductance was suppressed.5,6) This appearance of ferromagnetism in La2-x Srx CuO4 from the underdoped to theoverdoped regime is a new question in HTSCs because
superconductivity and magnetic ordering are believed to
be interconnected.
To synthesize free-standing nanoparticles, the chemical reaction method is believed as one of the best methods because it is a bottom-up method.7) A bottomup method implies spontaneous self-assembly from theatomic level to the nanoparticle level. The detailed synthesis route is reported in our former paper.8)µSR measurements on La2-x Srx CuO4 with x = 0.20
and particle size of 46 nm were performed at the RIKENRAL Muon Facility, Rutherford-Appleton Laboratory,
∗1
∗2
∗3
∗4

Department of Physics, Universitas Padjadjaran
Department of Engineering and Applied Sciences, Sophia University
Department of Physics, Universitas Indonesia
RIKEN Nishina Center

Fig. 1. Temperature dependence of relaxation rate of muon
spins, λ, of La2-x Srx CuO4 with x = 0.20 and particle sizeof 46 nm.

UK, using a pulsed positive surface muon beam. Figure 1 displays the temperature dependence of the relaxation rate of the muon spins. The relaxation rate starts
rapidly increasing below 10 K. This indicates the slowing
down of the Cu spin ﬂuctuations below 10 K, which, inturn, suggests that magnetic correlations are developed
at low temperatures. Compared to the bulk case, nomagnetic correlation was observed even at 0.3 K.9)
Our present result reveals that nano-sizing induces
weak magnetism owing to the development of Cu spin
ﬂuctuation. Moreover, our magnetization results showthat the superconductivity is strongly suppressed in
La2-x Srx CuO4 nanoparticles. These results suggest an
anticorrelation between the magnetic order and the superconductivity and show that the superconductivity inan HTSC is strongly inﬂuenced by the magnetic order,
which can be explained by the stripe theory. We provided a new insight of studying Cu spin dynamics byinvestigating the nano-sizing eﬀects in an HTSC, which
is typically examined based on the impurity eﬀects on
the Cu site.9–11)
References

1) W. H. Meiklejohn, C. P. Bean, Phys. Rev. 102, 1413 (1956).
2) M. H. Dehn et al., Appl. Phys. Lett. 112, 053105 (2018).
3) M. S. Seehra, A. Punnoose, Solid State Commun. 128,299 (2003).
4) Y. Yin et al., J. Phys. Chem. C 117, 3028 (2013).
5) A. Kopp et al., Proc. Natl. Acad. Sci. USA 104, 6123 (2007).
6) J. E. Sonier et al., Proc. Natl. Acad. Sci. USA 107, 17131(2010).
7) A. G. Kolhatkar et al., Int. J. Mol. Sci. 14, 15977 (2013).
8) S. Winarsih et al., Key. Eng. Mater. 966, 357 (2019).
9) T. Adachi et al., Phys. Rev. B 78, 134515 (2008).
10) T. Adachi, et al., Phys. Rev B 70, 060504(R) (2004).
11) Risdiana, et al., Phys. Rev. B 77, 054516 (2008).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

The electron transfer channel in the sugar recognition systemassembled on gold nano particles
T. Goto,∗1 T. Hashimoto,∗1 D. P. Sari,∗2 and I. Watanabe∗3

∗1
∗2
∗3

Faculty of Technology and Science, Sophia University
SIT Research Laboratories, Shibaura Institute of Technology
RIKEN Nishina Center

0.060

GNP-B12 (d =12nm)

0.055

λLF (µsec−1)

The recently reported electrochemical sugar recognition system consisting of a gold nano particle (GNP)
with a diameter of 12 nm, a ruthenium complex and aphenylboronic acids, attracts much interest because of
its high sensitivity for various sugars such as D-glucose
or D-fructose. When sugar molecules are “recognized” by
the phenylboronic site, the response of electrochemical
voltammetry of the ruthenium complex site drasticallychanges, enabling the system to work as a highly sensitive sugar-sensor.1,2) In this recognition process, thechange in the electronic state at the phenylboronic acidssite caused by sugar must be transferred to the ruthenium complex site. The purpose of this study is to ﬁnd
out by LF-µSR technique a channel of the electron transfer from the phenylboronic acid site to the ruthenium
complex via gold nano particle. By its ﬁnding, we will
be given a better understanding of the sugar-recognition
mechanism, and also, a possibility to develop a sensor
with still higher sensitivity and more functions.
As the present system includes alkyl-chains in theruthenium complex and the phenylboronic acid site, theinjected muons pick up one electron to form a neutral
atomic state, which is soon thermalized and bonded to a
relatively-reactive site on the chain. The brought-in electrons may show one-dimensional motion along the chain,
if the electron transfer channel between the ruthenium
complex and the phenylboronic site exists.
This behavior can be detected sensitively by measuring the muon-spin relaxation process, which is causedby the magnetic interaction between the muon spin andthe moving electron produced by muon itself. In otherwords, in place of the attachment of sugar molecules tophenylboronic acid site, one utilizes muon as a trigger
to induce a moving electron and also as an observer of
it. This method is known as the muon-labelling measurement.
The characteristic dimensionality of the electron motion can be readily studied by measuring LF dependenceof µSR relaxation rate λ;3) for one-dimensional motion,
λ is expected to be proportional to (HLF )−1/2 , where
HLF is the externally applied ﬁeld along the muon spinpolarization. This method was ﬁrst applied to the polaron motion in oganic polymer chains,4) and also successfully to the typical one dimensional system, DNA.5)
Zero (ZF) and longitudinal (LF) ﬁeld-µSR measurements at room temperature were performed on a powder sample at RIKEN-RAL Muon Facility using a spinpolarized pulsed surface-muon (µ+ ) beam with a momentum of 27 MeV/c. The muon spin depolarization

0.38T

19

0.050
18

0.20T

300K
17

0.045

0

2
4
6
Time ( µsec)0.2

H −0.5

8

0.3

0.4

Magnetic Field HLF (T)

0.5

Fig. 1. Temperature dependence of dynamical component ofrelaxation rate λ under various longitudinal fields HLF .
The inset shows the typical depolarization curves of theasymmetry (%) with fitted functions. Each curve is vertically shifted for clarity.

data above 0.1 T were analyzed with the function eλτ ,where λ is the depolarization rate due to the dynamical
spin ﬂuctuation. Note that in this ﬁeld region, the effect of quasi static nuclear spins or GKT , Kubo-Toyabe
function is neglected.
The ﬁeld dependence of λ is shown in Fig. 1. Withdecreasing HLF from the highest ﬁeld 0.38 T, λ showeda slight but ﬁnite increase until HLF ∼= 0.2 T, below
which λ saturates. An appreciably high depolarization in the totally non-magnetic compound indicatesthat some muon-triggered moving electron process exists. The observed increase is weaker than expected forthe one dimensional diﬀusion case. This indicates thatthe contribution from the diﬀusion process has the lower
boundary in the ﬂuctuation spectrum, as is evident fromthe functional form of λHLF dependence, and in fact isreported for previous report.4)
In order to conﬁrm that the observed behavior of λcomes from the one-dimensional movement along alkylchain, investigation on wider ﬁeld region or equivalently
on wider ﬂuctuation spectrum, including NMR is inevitable, and is now on the progress.
References

1) A. Endo et al., Anal. Methods 6, 8874 (2014).
2) T. Goto et al., IEEE Trans. Mag. 55, 2300404 (2019).
3) Risch and Kehr, Phys. Rev. B 46, 5246 (1992).
4) F. Pratt et al., Phys. Rev. Lett. 79, 2855 (1997).
5) E. Torikai et al., Hyperfine. Int. 138, 509 (2001).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Antiferromagnetic ordering of λ-(BEST)2 FeCl4 observed by µSR
measurement
T. Kobayashi,∗1 D. P. Sari,∗2,∗3 K. Koyanagawa,∗1 K. Satoh,∗1 H. Taniguchi,∗1 A. Kawamoto,∗4 and I. Watanabe∗3
In the organic conductor λ-(BETS)2 FeCl4 (see Fig. 1
for BETS), there is a signiﬁcant strong exchange interaction between the 3d electrons of Fe ions, and π electronsof BETS molecules, i.e., π-d interaction. This results inexotic properties such as a ﬁeld-induced superconductivity1) and a metal-insulator transition with antiferromagnetic (AF) ordering, where 3d electrons are paramagnetic
even below the AF transition temperature indicated by
the heat capacity measurement.2) To understand these
phenomena, a deep understanding of the π-d interaction mechanism is required. As a clue to this, the magnetism of λ-(STF)2 FeCl4 has been recently evaluated.
As shown in Fig. 1, the STF molecule is a molecule inwhich part of the selenium in the BETS molecule is replaced by sulphur. Magnetisation, NMR, and Mössbauer
measurements showed that λ-(STF)2 FeCl4 exhibits AF
ordering at 16 K, where both 3d and π electrons are ordered, whereas further development of the internal magnetic ﬁeld owing to the polarized magnetisation of the 3d
spins was observed below 8 K.3–5) In addition, µSR measurements demonstrated that the slow precession signals
due to the AF order of π-electrons and the fast precession signals due to the polarization of 3d spins appear
from diﬀerent temperatures. The magnetic properties
that appeared when the BETS molecule was replaced by
the STF molecule are thought to be caused by changes
in the π-d and d-d interactions. Therefore, to evaluate
the relationship between the molecular substitution andthe change in the π-d interaction, we focused on the substitution from BETS to BEST molecules (see Fig. 1 forBEST). Because the electron density of the outer chalcogen atoms is small, the expansion of the orbitals by thesubstitution from S to Se is expected to cause steric hindrance and reduce the π-d interaction.
According to the reported magnetisation measurementof λ-(BEST)2 FeCl4 , it exhibits paramagnetic behaviour
down to 4 K.6) However, because the observed spin susceptibility is dominated by 3d spins, the magnetism of π
spins is almost concealed. To reveal the magnetic orderof the 3d and π electrons, a microscopic measurementthat can sensitively detect the internal ﬁeld is necessary.

∗2
∗3
∗4

For this purpose, we performed µSR measurements onλ-(BEST)2 FeCl4 .
Figure 2 shows the µSR time spectra at several temperatures. We observed that the initial asymmetry
changes abruptly between 28.4 K and 25.6 K. The time
spectra A(t) are ﬁtted by the stretched exponential function, A(t) = A exp[−(λt)β ] + Abg , where A and Abg
are the asymmetries due to the muons stopped inside
the sample and at the sample holder, λ is the relaxation rate, and β is the stretched exponent, respectively.
From this analysis, we deduced that the initial asymmetry A indeed decreases below ∼30 K, as shown in
the inset of Fig. 2, although its transition temperature
is not clear. Because the AF order of π spin was also
observed in λ-(BEST)2 GaCl4 consisting of nonmagnetic
Ga ions, the change in the initial asymmetry observedin λ-(BEST)2 FeCl4 can be understood by the AF order.
In fact, the disappearance of the paramagnetic EPR signal was observed at 25 K in recent ESR measurements,suggesting an AF transition.
Compared to λ-(STF)2 FeCl4 , it is interesting to knowwhether the fast precession signal due to the polarization of 3d spins is observed or not. Within our experimental error, no signiﬁcant spectral change was observed from 25.6 K to 2.11 K, suggesting that only theπ spins are magnetically ordered. In λ-(BETS)2 FeCl4 ,unlike λ-(BEST)2 GaCl4 , the anisotropy of the magnetic susceptibility was observed with AF transition.
Therefore, we conﬁrmed that the magnetic state of λ(BEST)2 GaCl4 is diﬀerent from that of λ-(BETS)2 FeCl4
and λ-(STF)2 FeCl4 . These results provide important
clues for the mechanism of π-d interaction.
References

Fig. 1. Structures of donor molecules.
∗1

Fig. 2. Zero-field µSR time spectra of λ-(BEST)2 FeCl4 . Inset: temperature dependence of initial asymmetry.

Graduate School of Science and Engineering, Saitama University
College of Engineering, Shibaura Institute of Technology
RIKEN Nishina Center
Graduate School of Science, Hokkaido University

1) S. Uji et al., Nature 410, 908 (2001).
2) H. Akiba et al., J. Phys. Soc. Jpn. 78, 033601 (2009).
3) S. Fukuoka et al., J. Phys. Soc. Jpn. 87, 093705 (2018).
4) T. Minamidate et al., Phys. Rev. B 97, 104404 (2018).
5) S. Fukuoka et al., Phys. Rev. B 101, 184402 (2020).
6) H. B. Cui et al., Chem. Lett. 34, 254 (2005).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Zero-field µSR on the out-of-plane superconductivity ofλ-(BETS)2 GaCl4
D. P. Sari,∗1,∗2 K. Hiraki,∗3 I. Watanabe,∗1 and Y. Ishii∗1λ-(BETS)2 GaCl4 is a quasi-two-dimensional organic
metal and it is reported as a high-anisotropic type-II superconductor. It exhibits rich physical properties once
we substitute Ga with Fe, Cl with Br, or once we reduce the Se content in the BETS molecule (BETS =(CH2 )2 S2 Se2 C6 S2 S2 (CH2 )2 ).1) In the P-T phase diagram, the neighboring phase adjacent to the superconducting (SC) state is the Mott insulating state, which isantiferromagnetically ordered, and separated by a suspicious paramagnetic insulating state with no magnetic
ordering down to 0.3 K.2) A theoretical study based on
anisotropic spin fluctuations-mediated superconductivity suggested an anisotropic gap structure with two nodal
lines,3) whereas 13 C-NMR study evidenced two types ofmagnetic fluctuations of the π-electron down to 2 K.4)
There is an urgent requirement for the detailed experimental determination of the SC gap structure. We performed a series of transverse-field (TF) µSR measurement to determine the SC gap structure. First, we foundthat the SC gap structure of λ-(BETS)2 GaCl4 was unusual as it exhibited both d-wave and s-wave symmetry
characteristics.4,5) Furthermore, considering the study
by Powell and McKenzie for entire families of organic
superconductors, we plan to confirm whether time reversal symmetry breaking is related to this unusual SC
gap structure. Zero-field (ZF) µSR is a powerful tool todetect such breaking symmetry in the SC state.
We recently performed a series of zero-field µSR using aligned single crystals. We prepared ∼130 mg single crystals and oriented them in the same direction.
Measurements were performed using the ARGUS spectrometer at the RIKEN-RAL pulse muon facility with a
HELIOX cryostat and fly-path setup. The single pulse
mode was used to collect 80M events. In a previous
report6) we showed the result when the polarized muon
beam direction was nearly perpendicular to the conducting plane. We prepared another sample setup (∼100 mg)
to measure with the polarized muon beam direction parallel to the conducting plane. In this report, we compare
both measurements to gain information regarding outof-plane superconductivity.
Figure 1 shows normalized time spectra at several
temperatures below and above the critical temperature(Tc ∼ 5.5 K). Open circle curves indicate normalized
time spectra with the muon beam direction perpendicular to the conducting plane.6) Blue solid lines indicate fitting lines using a stretched exponential function
A(t) = A0 exp(−(λt)β ). At 1.5 K, λ and β values were0.2281(35) µs−1 and 1.123(16), respectively. No temperature dependence was observed between the normal
and SC states. Closed circle curves indicate normal∗1∗2∗3

College of Engineering, Shibaura Institute of Technology
RIKEN Nishina Center
Department of Physics, Fukushima Medical University

Fig. 1. Normalized ZF-µSR time spectra with the setup ofµ+ injected parallel and perpendicular to the conducting plane. The solid lines represent fitting lines obtainedusing the stretched exponential function.

ized time spectra with the muon beam direction parallel
to conducting plane, which reflects the intrinsic behavior of the out-of-plane properties. Although there wasno temperature dependence between the normal and SC
states, we found that the shape of the spectra was distinct with the open circle spectra showing in-plane properties in λ-(BETS)2 GaCl4 . All spectra were best fit by astretched exponential function. At 1 K, λ and β values
were 1.881(21) µs−1 and 1.34(2). In-plane properties
have a stronger relaxation while the shape is toward asingle exponential function. λ-(BETS)2 GaCl4 has highanisotropy SC properties such as the large ratio of inplane/out-of-plane upper critical field and transfer integral, Hc2|| /Hc2⊥ > 4 7) and t|| /t⊥ ∼ 13,3) respectively.
Then, the stronger in-plane λ can be related to the antiferromagnetic fluctuations of the π-electron within the
conducting plane, which mediates the superconductivity.
These results confirm that the exotic SC state behavior proposed in this material based on TF-µSR could bebeyond triplet superconductivity or time-reversal symmetry breaking properties. The next step is to relate
this ZF-µSR result with the TF-µSR results using single
crystals.
References

1) H. Kobayashi et al., Chem. Rev. 104, 5265 (2004).
2) T. Minamidate, RIKEN Accel. Prog. Rep. 51, 205 (2018).
3) H. Aizawa et al., J. Phys. Soc. Jpn. 87, 093701 (2018).
4) T. Kobayashi, A. Kawamoto, PRB 96, 125115 (2017).
5) D. P. Sari, PhD Thesis, Osaka University (2018).
6) D. P. Sari, et al., submitted (2020).
7) D. P. Sari, RIKEN Accel. Prog. Rep. 53, 155 (2018).
8) M. Tanatar et al., J. Superconductivity 12, 511 (1999).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Li-ion diﬀusion in LiFeSix P1−x O4 /C with x = 0 and 0.03
F. Astuti,∗1 D. P. Sari,∗2,∗3 M. Zainuri,∗1 Darminto,∗1 and I. Watanabe∗2
The primary issue in the use of LiFePO4 in battery
applications is its low intrinsic electronic conductivity
and lithium-ion diﬀusion coeﬃcient. Furthermore, there
is an urgent need to improve the cycle life and longterm cyclability of LiFePO4 .1) Several strategies havebeen considered to enhance the electronic/ionic conductivity and cycle life of LiFePO4 , such as carbon coating,
reduction of particle size, and element doping.2)
Powder samples of LiFeSix P1−x O4 /C with x = 0 and
0.03 were prepared by a solid-state method. Singlephase samples of LiFePO4 have not been obtained sofar. Our study strongly supports that Si doping signiﬁcantly improves the electrochemical performance of
LiFePO4 as reported in Ref. 3). A sample with x = 0.03
yielded the highest speciﬁc capacity. Further study on
Li-ion diﬀusion is signiﬁcant for increasing the battery
performance. Muon spin relaxation (µSR) is a powerfultool to study Li-ion diﬀusion.
In order to study the Li-ion diﬀusion in
LiFeSix P1−x O4 /C further, we measured zero-ﬁeld andlongitudinal-ﬁeld µSR (ZF- and LF-µSR, respectively)
using the ARGUS spectrometer at the RIKEN-RAL
Muon Facility. The ZF-µSR was measured in the temperature range of 5–30 K, and the LF-µSR was measured

Fig. 2. Temperature dependences of ∆ with (a) x = 0 and(b) x = 0.03 and of λ with (c) x = 0 and (d) x = 0.03 for
LiFeSix P1−x O4 /C.

at 300 K under low magnetic ﬁelds of 5 G and 10 G.
Figure 1 shows the LF-µSR spectra of LiFeSix P1−x O4 /C with (a) x = 0 and (b) 0.03. The dynamic behavior at
300 K was clearly observed for LiFeSix P1−x O4 /C withx = 0 and 0.03 because there is only a small “decoupling”
eﬀect due to applied LF. The spectra were ﬁtted by an
exponentially relaxing dynamic Kubo-Toyabe function.
Based on Fig. 2, the ﬁeld distribution width (∆)
and ﬁeld ﬂuctuation (λ) were found to be independentof temperature down to 50 K, whereas ∆ and λ increased with temperature decreasing below 50 K for
samples with x = 0 and x = 0.03. There is no abruptchange in ∆ or λ in either sample. Following the results in Ref. 4), we obtained the diﬀusion coeﬃcient as
DLi = (1.598 ± 0.0033) × 10−10 cm2 /s, for x = 0 and
DLi = (1.751 ± 0.0037) × 10−10 cm2 /s for x = 0.03. The
present result demonstrates the slight increase of Li-ion
diﬀusion by silicon substitution, which can improve theperformance of LiFePO4 cathode materials. Additionally, from the ZF-µSR results, the magnetic transition
temperature was detected, starting from the temperature 50 K and close to the estimation of the Neel temperature, TN , LiFePO4 reported in Ref. 5).
Fig. 1. LF-µSR spectra on of LiFeSix P1−x O4 /C with (a) x =0 and (b) x = 0.03.
∗1
∗2
∗3

Department of Physics, Institut Teknologi Sepuluh Nopember
RIKEN Nishina Center
Graduate School of Engineering and Science, Shibaura Institute of Technology

References

1) M. Nishijima et al., Nat. Commun. 5, 4553 (2014).
2) Z. Xu et al., J. Electrochem. Soc. 163, A2600 (2016).
3) M. Zainuri et al., Key Eng. Mater. 860, 75 (2020).
4) M. Månsson et al., J. Phys. Conf. Ser. 551, 012037 (2014).
5) J. Sugiyama et al., Phys. Rev. B 84, 054430 (2011).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of muon spin rotation in muonic hydrogen atom
S. Kanda∗1 and K. Ishida∗2
A muonic atom is a bound-state consisting of a negative muon and a nucleus. The charge radius of thenucleus can be obtained by measuring the Lamb shift
in a muonic atom. In 2010, the Lamb shift of muonichydrogen (µp) measured at the Paul Scherrer Instituteindicated a significantly smaller proton charge radiusthan previously known from hydrogen spectroscopy
and electron-proton scattering.1)
In addition to the charge radius, the proton’s size isexpressed by the Zemach radius, which is defined byconvolving the charge and magnetic moment distribution. The Zemach radius is derived from the hyperfine
splitting (HFS), in contrast to the charge radius derived from the Lamb shift. For the Zemach radius, theconsistency between muonic and electronic measurements has not been fully discussed due to muonic measurements’ limited precision. To tackle this problem,
we are preparing for laser spectroscopy of the groundstate HFS in µp atoms.2)
In the experiment, a circularly polarized laser beam
excites µp atoms in the spin-singlet state to the spintriplet one. However, excited µp atoms are quenchedby spin-exchange collisions with protons.3) There is noexperimental result of this hyperfine quenching rate forµp atoms; therefore, we performed a muon spin rotation (µSR) measurement using a low-density gaseoushydrogen target. Only µp atoms in the spin-triplet
state show muon spin precession.
Figure 1 illustrates an experimental setup at Port 4of the RIKEN-RAL muon facility. A pulsed negative
muon beam irradiates hydrogen gas filled in an alu-

Fig. 1. Experimental setup: (a) cross-sectional view; (b)view from upstream. The numbers in the parentheses
denote (1) hydrogen gas contained in an aluminum vessel, (2-5) electron detectors, (6) Helmholtz coils. Notethat the electron detectors are not shown in (b).
∗1∗2Institute of Materials Structure Science, KEK
RIKEN Nishina Center

Fig. 2. Decay electron time spectrum with protium gas target at 0.1 atm. A transverse magnetic field of 66.7 mT
was applied. Each line corresponds to the respective
fitting result. The vertical axis is normalized by the
number of beam pulses.

minum vessel. The momentum of the beam was set
to 20 MeV/c. The gas pressure was 0.1 atm at room
temperature. A transverse magnetic field of 66.7 mT
was applied using a Helmholtz coil. Under these conditions, the quenching time of the triplet state andthe spin precession period are expected to be 500 ns
and 320 ns, respectively. The electrons from the muon
decay were counted by a detector consisting of scintillating fibers and silicon photomultipliers (SiPMs).
Kalliope front-end electronics4) processed the signal
from the SiPM, and a multi-hit time-to-digital converter (TDC) recorded the time.
Figure 2 shows a decay electron time spectrum. The
spectrum has components corresponding to hydrogen,aluminum, silver, and constant background events.
The beam has a double-pulse structure with a 320 ns
interval. The first two peaks of the spectrum correspond to prompt electrons. Detailed analysis to extract the µSR asymmetry is in progress.
This experiment was conducted under the user program RB1970003 at the RIKEN-RAL muon facility.
This work was supported by Japanese JSPS KAKENHI Grant Numbers 18K13572 and 19H04618.
References

1) R. Pohl et al., Nature 466, 213 (2010).
2) S. Kanda et al., J. Phys. Conf. Ser. 1138, 012009 (2018).
3) J. S. Cohen, Phys. Rev. A 43, 466 (1991).
4) K. M. Kojima et al., J. Phys. Conf. Ser. 551, 012063(2014).

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III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A LYSO calorimeter prototype for muonic X-ray detection
S. Kanda∗1 and K. Ishida∗2
The Weinberg angle is an energy-dependent parameter that describes the mixing of electromagnetic andweak interactions. Measurements of the Weinberg angle
at various energy scales are important as a precision testof the standard model and a search for new physics. The
Weinberg angle can be determined via neutral current
interactions. The most precise result was obtained at a
low-energy scale by observing the atomic parity violation (APV) in cesium atoms.1)
When a nuclear Coulomb potential captures a negative muon, the muon forms an exotic bound state
called a muonic atom. An APV experiment using
muonic atoms provides a unique opportunity to searchfor physics beyond the standard model. In the 1990s,
several experiments were conducted at the Paul Scherrer Institute.2) However, no parity-odd transition wasobserved because of diﬃculties in the experiment.
A new experiment using a high-intensity pulsed muon
beam and a segmented calorimeter has been proposed
to revisit this topic. The process of interest is the transition from the 2S state to the 1S state, which involves
a one-photon emission. In the experiment, a segmented
calorimeter consisting of Ce: LYSO crystals and silicon
photomultipliers (SiPMs) detects X-rays from muonicatoms. The target energy resolution is 10% (FWHM)
at 75 keV. As the ﬁrst stage of the project, a calorimeter prototype was developed and tested at Port4 of the
RIKEN-RAL muon facility.
Figure 1 illustrates the experimental setup. Muonic
X-rays and decay electrons from a graphite target weredetected using the prototype detector. The detector has
two layers, each consisting of a 2-cm-square, 3-mm-thickcrystal attached to four SiPMs (Hamamatsu S133603050CS) with an active area of 3-mm-square. The signals were ampliﬁed and shaped using EASIROC-based
electronics and recorded with a waveform digitizer using

Fig. 1. Experimental setup. The inset shows the structureof the prototype.
∗1∗2

Institute of Materials Structure Science, KEK
RIKEN Nishina Center

Fig. 2. Electron and X-rays time spectra. The prompt electrons were detected by the beam monitor.

Fig. 3. X-ray energy spectrum obtained by the calorimeter
prototype.

DRS4.
Figure 2 shows the time spectra of electrons and Xrays. Since electrons penetrate the two detector layers, the coincidence analysis allowed us to distinguishbetween electron and X-ray events. Figure 3 shows anenergy spectrum of muonic X-rays. The energy was calibrated with the 81 keV line of 133 Ba. The peak structure
was consistent with K X-rays of muonic carbon atoms.
While the prototype demonstrated a suﬃcient time resolution, there is room for improvement in the energy
resolution. A new version with improved light collection
eﬃciency is under fabrication.
The authors thank Dr. Adrian Hillier and Ms. Bethany
Hampshire for their kind assistance in preparation for
the experimental setup at RAL. This experiment was
conducted under the user program RB1970126 at the
RIKEN-RAL muon facility. This work was supported
by Japanese JSPS KAKENHI Grant Number 19H04618.
References

1) J. Guena et al., Phys. Rev. A 71, 042108 (2005).
2) K. Kirch et al., Phys. Rev. Lett. 78, 4363 (1997).
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3. Radiochemistry and Nuclear ChemistryIII-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production of 266 Bh in the 248 Cm(23 Na, 5n)266 Bh reaction and its decay
properties†
H. Haba,∗1 F. Fan,∗2 D. Kaji,∗1 Y. Kasamatsu,∗3 H. Kikunaga,∗4 Y. Komori,∗1 N. Kondo,∗3 H. Kudo,∗5
K. Morimoto,∗1 K. Morita,∗1,∗6 M. Murakami,∗7 K. Nishio,∗8 J. P. Omtvedt,∗9 K. Ooe,∗10 Z. Qin,∗2 D. Sato,∗5
N. Sato,∗1 T. K. Sato,∗8 Y. Shigekawa,∗1 A. Shinohara,∗3 M. Takeyama,∗11 T. Tanaka,∗12 A. Toyoshima,∗13
K. Tsukada,∗8 Y. Wakabayashi,∗14 Y. Wang,∗1 S. Wulﬀ,∗9 S. Yamaki,∗1 S. Yano,∗1 Y. Yasuda,∗3 and T. Yokokita∗1

Condensed from the article in Phys. Rev. C 102, 024625 (2020)
RIKEN Nishina Center∗2 Institute of Modern Physics, Chinese Academy of Sciences∗3 Graduate School of Science, Osaka University∗4 Research Center for Electron Photon Science, Tohoku University∗5 Department of Chemistry, Niigata University∗6 Department of Physics, Kyushu University∗7 Decommissioning and Radioactive Waste Management HeadOﬃce, Japan Atomic Energy Agency∗8 Advanced Science Research Center, Japan Atomic Energy
Agency∗9 Department of Chemistry, University of Oslo
∗10 Graduate School of Medicine, Osaka University∗11 Faculty of Science, Yamagata University∗12 Department of Nuclear Physics, Research School of Physics,
The Australian National University∗13 Institute for Radiation Sciences, Osaka University∗14 Center for Advanced Photonics, RIKEN†∗1

248Cm(23Na,5n)266Bh

Cross section (pb)The decay properties of the neutron-rich and longlived isotopes 267 Bh and 266 Bh, which are located aroundthe deformed shell at Z = 108 and N = 162, were studied
in the 249 Bk(22 Ne, 5;4n)266, 267 Bh,1) 209 Bi(70 Zn, n)278 Nh→ 274 Rg → 270 Mt → 266 Bh,2) 243 Am(26 Mg, 3n)266 Bh,3)
and 248 Cm(23 Na, 5;4n)266, 267 Bh4) reactions. However,
the reported decay properties such as α energies andhalf-lives of the isotopes are not in good agreement.
In this work, we investigated the excitation functions
and decay properties of 266 Bh and 267 Bh via the248
Cm(23 Na, 5;4n)266, 267 Bh reactions using the GARIS
gas-jet and MANON setups.5)
248
Cm2 O3 targets of 256–290 µg/cm2 thicknesses on
2-µm Ti backing foils were bombarded with a 23 Na7+
beam extracted from the RIKEN Heavy-Ion LINAC. The
beam energies at the middle of the target were 121.2,
125.9, 130.6, and 135.3 MeV. The typical beam intensity
was 3 pµA. The evaporation residues (EVRs) of interest were separated in-ﬂight from the beam particles andthe majority of the nuclear transfer products by GARIS.
At the focal plane of GARIS, the EVRs passed througha Mylar vacuum window foil of 0.7-µm thickness andentered the gas-jet chamber, where the EVRs were thermalized in He gas, attached to KCl aerosol particles, andtransported through a Teﬂon capillary (2.0-mm i.d. ×
10-m length) to the rotating wheel apparatus MANON
for α/SF-spectrometry. In MANON, the aerosol particles were deposited on a Au-coated (5 nm) Mylar foil
of 0.5-µm thickness, forty of which were set on the periphery of a rotating wheel. The wheel was stepped toposition the foils between 15 pairs of Si PIN photodiodes(Hamamatsu S3204-09). The step intervals of MANON
were set to 5.0, 8.5, and 15.0 s.
We searched for time-correlated α-α and α-SF event

102

101

248Cm(23Na,4n)267Bh

5n

6n

4n
3n

100
110

115

120

125

130

135

140

145

ELab (MeV)
Fig. 1. Cross sections for the 248 Cm(23 Na, 5;4n)266, 267 Bhreactions as a function of the laboratory-frame energy
ELab . The curves are the HIVAP calculations6) for the248
Cm(23 Na, xn)271−x Bh reactions (x = 3–6).

pairs in a time window of 340 s. Consequently, a totalof 23 chains were assigned to 266 Bh, its daughter nuclide 262 Db, and granddaughter 258 Lr, while no chain
was assigned to 267 Bh. The α-particle energies of 266 Bh
disperse widely in the range of Eα = 8.62–9.40 MeV. The
reported α groups of Eα = 9.29 MeV,1) Eα = 9.08 and9.39 MeV,2) Eα = 9.03 MeV,3) and Eα = 8.82, 8.84–
8.99, and 9.05–9.23 MeV4) for 266 Bh are all within our
α-energy range, except for Eα = 9.77 MeV.2) The halflife of 266 Bh was measured to be T1/2 = 10.0+2.6−1.7 s,which is an order of magnitude longer than the previously reported values of T1/2 ≃ 1 s1) and T1/2 =3)
2)
0.66+0.59
and 5 times longer than T1/2 = 2.1+2.9−0.26 s,−0.8 s.
As shown in Fig. 1, the excitation function for the248
Cm(23 Na, 5n)266 Bh reaction was measured for theﬁrst time, and it indicates a maximum of σ = 57 ± 14 pb
at 130.6 MeV. The excitation function was reproducedby the statistical model code hivap.6) The upper-limit
cross section of σ ≤ 14 pb was also derived for the248
Cm(23 Na, 4n)267 Bh reaction at 121.2 MeV.
References

1) P. A. Wilk et al., Phys. Rev. Lett. 85, 2697 (2000).
2) K. Morita et al., J. Phys. Soc. Jpn. 81, 103201 (2012).
3) Z. Qin et al., Nucl. Phys. Rev. 23, 400 (2006).
4) K. Morita et al., J. Phys. Soc. Jpn. 78, 064201 (2009).
5) H. Haba et al., Chem. Lett. 38, 426 (2009).
6) W. Reisdorf, M. Schädel, Z. Phys. A 343, 47 (1992).

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III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of the isotopic ratio of Np-236 to Np-237 in
Th-232 + Li-7 reaction products by accelerator mass spectrometry
A. Nakajima„ ∗1,∗2 K. Teranishi,∗1,∗3 A. Yokoyama,∗1,∗4 A. Sakaguch,∗1,∗5 K. Hain,∗6 R. Morita,∗1,∗3
A. Seto,∗1,∗4 A. Nagai,∗1,∗4 D. Mori,∗1 Y. Komori,∗1 T. Yokokita,∗1 Y. Wang,∗1 and H. Haba∗1
Neptunium-236 can be a useful tracer in the determination of Np-237, an isotope of the minor actinide
Np, which exists in tiny quantities in the environment
owing to its release from nuclear facilities and nuclear
tests. Such determination is of practical use in various earth science ﬁelds such as surface material circulation and environmental pollution assessment.1) The
measurement of Np-237 is expected to be quantiﬁedby accelerator mass spectrometry (AMS), although aninternal standard method for Np needs an appropriate spike. Chemical yield tracers for several elements
are available now, but the spike for neptunium has
not been developed yet. We aim to devise an eﬃcientmethod for the production of Np-236 in the groundstate of half-life 1.54 × 105 y as a candidate for the
spike nuclide, with minimal contamination by Np-237.
In this study, Np-236 tracer production was implemented in the reaction of Th-232 + Li-7 to measureNp-237. The resulting yields of Np-236m and Np-236g
were presented in the previous report.2) The yield in
the ground state (6− ) was found to be larger than thatin the excited state (1+ ) in the studied energy range.
This demonstrates that the reaction system adopted is
promising. In addition, we have to measure the isotopic ratios of Np-236g to Np-237 in the same nuclear
system.
We irradiated Th foil targets with 42 MeV Li-7 ionsfrom the RIKEN AVF cyclotron while integrating thebeam current with a Faraday cup in the irradiation
course. Chemical procedures were performed to isolate
Np atoms from the target. Details of the procedures
were described previously.2)
For the Np-236g and Np-237 measurement, samples
for AMS and inductively coupled plasma mass spectrometry (ICP-MS) were prepared through puriﬁcation with UTEVA resin after waiting for Np-236m todecay out, and they were brought to the VERA facility
in the University of Vienna, with which this project isin collaboration.
Figure 1 shows the preliminary isotopic ratios of Np236g to Np-237 isotopes measured using AMS. The
yield of Np-236 was found to be approximately 10
∗1
∗2
∗3
∗4
∗5
∗6

RIKEN Nishina Center
Master’s Program in Chemistry, University of Tsukuba
Graduate School of Natural Science and Technology,
Kanazawa University
Institute and College of Science and Engineering, Kanazawa
University
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba
Faculty of Physics, Isotope Physics, University of Vienna

Fig. 1. Preliminary isotopic ratios of Np-236g to Np-237 in
the Th-232 + Li-7 reaction system compared with thetheoretical prediction. Closed circles represent the observation, while open circles indicate data from calculation.

times larger than that of Np-237 in the studied energy range. The ﬁgure also shows the ratios calculated under a simple assumption with the nuclear reaction model code empire23) comprising various nuclear models. A large discrepancy is observed between
the observation and prediction. It may be due to difﬁculty in the yield reproduction of used models at theenergy region beyond the maximum yield energy forthe products. The observation indicates that the reaction system adopted is promising thus far, although
the data may need to be modiﬁed because of contamination by uranium nuclides and other nuclides with amass number of 236.
The analysis of the result is in progress, and additional experiments including mass spectrometry are inplanning. We aim to conﬁrm the precision and reproducibility of the data in consideration of the contamination by isobars, which aﬀects the mass measurement
and is a major concern.
References

1) W. Rund, G. S. Goﬀ, Radionuclide in the Environment,edited by D. A. Atwood (Wiley, 2013).
2) Y. Hayakawa et al., RIKEN Accel. Prog. Rep. 53, 179(2020).
3) M. Herman et al., Nucl. Data Sheets 108, 2655 (2007).

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RIKEN Accel. Prog. Rep. 54 (2021)

Production and photon measurement of 229 Pa toward the observationof radiative decay of 229m Th
Y. Shigekawa,∗1 T. Yokokita,∗1 Y. Komori,∗1 and H. Haba∗1
The first excited state of 229 Th (229m Th) has an extremely low excitation energy of ∼8.3 eV (150 nm),1)
which may enable a nuclear clock with unprecedentedly low uncertainty. So far, the radiative half-life of
229m
Th, which is an important parameter to develop
the nuclear clock, has not yet been determined. To
directly observe the radiative decay (γ-ray emission)of 229m Th, the internal conversion (IC) process witha half-life of ∼7 µs2) must be prohibited by placing
229m
Th in the chemical environments where the electron binding energy is higher than the excitation energy of 229m Th. 229m Th doped into fluoride crystals isa candidate for such chemical environments. We areaiming to dope a CaF2 crystal with 229m Th by doping with 229 Pa, which decays to 229m Th by electron
capture with a negligibly small recoil energy. Suitable doping can be realized by implanting high-energy229
Pa ions into a crystal and then annealing it. In
this study, we developed a method for producing 229 Pa(T1/2 = 1.5 d) in the 232 Th(p, 4n)229 Pa reaction andseparating it from the target. We also measured lowenergy photons from Pa isotopes on a CaF2 crystal toevaluate the background toward the future γ-ray measurement of 229m Th.
Two 232 Th metallic foils (thickness: 69.07 mg/cm2 ,purity: 99.5%) were irradiated with a 30-MeV proton beam having an intensity of 1 µA for 10 h at the
RIKEN AVF cyclotron. After the irradiation, we measured γ-ray spectra for the 232 Th foils and fractions
resulting from the subsequent chemical separation process using a Ge detector.
The chemical separation process for one of the foils
was performed as follows. First, we dissolved the foilin 2 mL of 11.3 M HCl plus 300 µL of 1 M HF andheated the solution to dryness. The sample was dissolved in 2 mL of 11.3 M HCl, following which 1.1 gof Al(NO3 )3 · 9H2 O was added as a masking agent for

Fig. 1. Setup of the photon measurement of 229 Pa.
∗1

RIKEN Nishina Center

Fig. 2. Count rates of photons as a function of the elapsed
time for the 151-nm (red circle) and 171-nm (bluesquare) filters. Red and blue lines show the decay curvesof 230 Pa fitted to the data.

the remaining F− ions. After the solution was driedup and dissolved in 2 mL of 11.3 M HCl, the solution was fed into an anion-exchange column (Muromac
1X8, 100–200 mesh, ∼1.0 mL). We poured 10 mL of
11.3 M HCl into the column to elute Th isotopes, Ac
isotopes, and some fission products. Next, we added
10 mL of 6 M HCl to elute Zr, following which 5 mLof 8 M HNO3 was added to elute Zr, Mo, Ru, Sb, andTe isotopes. After we added 1 mL of 11.3 M HCl, Pa
isotopes were eluted with 8 mL of 9 M HCl/0.1 M HF.
The chemical yield of Pa isotopes in the whole process
was 94(2)% (residual Pa isotopes were observed in the
8 M HNO3 eluate). The radioactivity of chemicallyseparated 229 Pa at the end of bombardment was evaluated to be 30(1) MBq, while those of 232 Pa, 230 Pa(T1/2 = 17.4 d), 95 Zr (T1/2 = 64.03 d), and 97 Zr(T1/2 = 16.75 h), included as impurities, were 2.18(3),0.89(4), 0.0054(7), and 0.40(2) MBq, respectively.
The 229 Pa sample dissolved with 27 M HF was
dropped on a CaF2 crystal, which was then annealed
at 900◦ C for 1 h in a He gas flow (3 L/min). Photons from the crystal were measured with a photomultiplier (PMT, Hamamatsu R10454) in vacuum (Fig. 1).
Band-pass filters for the photons of 151 ± 20 and
171 ± 20 nm (eSource Optics) placed between the crystal and the PMT were switched every 5 min. The radioactivities of 229 Pa, 230 Pa, and 232 Pa were 10.7(8),35(2), and 0.381(8) kBq at the start of the measurement (11 days after the proton irradiation).
As shown in Fig. 2, the count rates of photons forboth filters are ∼10 counts per second (cps), which- 143 -

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are much higher than the dark count rate of the PMT(0.96 cps). The detected photons would originate fromthe Cherenkov radiation caused by the passage of beta
particles though the CaF2 crystal. The long decay
time of photons (half-life >7 d) in Fig. 2 indicates that
the Cherenkov photons dominantly originate from thebeta decay of 230 Pa (0.004 photons per beta particle).
If we implant 100 kBq of 229 Pa into a CaF2 crystal,anneal it, and start the measurement one day after the
proton irradiation, the background photons from 232 Pa
and 230 Pa are estimated to be ∼30 cps, which is muchhigher than the estimated count rate of γ rays from229m
Th (2 cps). Thus, we plan to perform the mass
separation of 229 Pa to reduce the amount of 232 Pa and230
Pa by a factor of >10 when we implant 229 Pa into a
CaF2 crystal. Implanting 229 Pa into a crystal with aneﬃciency of 0.1–1% allows us to observe a growth anddecay curve of photons of several cps only for the 151nm ﬁlter, resulting in the unambiguous identiﬁcationof the γ rays from 229m Th.
References

1) B. Seiferle et al., Nature 573, 243 (2019); A. Yamaguchi
et al., Phys. Rev. Lett. 123, 222501 (2020); T. Sikorsky
et al., Phys. Rev. Lett. 125, 142503 (2020).
2) B. Seiferle et al., Phys. Rev. Lett. 118, 042501 (2017).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of extraction time and eﬃciency of 220 Rn ions using acryogenic RF-carpet gas cell for the chemistry of superheavy elements
Y. Shigekawa,∗1 A. Yamaguchi,∗2 N. Sato,∗1 A. Takamine,∗1 M. Wada,∗3 and H. Haba∗1
We have been developing a cryogenic RF-carpet gas
cell for the gas-phase chemistry of superheavy elements(SHEs) with short half-lives (<5 s) such as 283 Cn (Z =112), 284 Nh (Z = 113), and 289 Fl (Z = 114).1) We
designed and constructed the gas cell, and measured
the transportation eﬃciency of ions from the surfaceof the RF carpet to its central hole (>80%) using Cs+
ions emitted from a Cs ion source.1) In this work, wemeasured the extraction time and eﬃciency of ions to
the outlet of the quadrupole ion guide (QPIG) using
220
Rn (T1/2 = 55.6 s) ions emitted from a 224 Ra sourcewith recoil energy from alpha decay.
The 224 Ra source (45 kBq) was prepared by collecting 224 Ra ions recoiling out of a 228 Th source to thesurface of a Cu foil (diameter 10 mm).2) As shown in
Fig. 1, 220 Rn ions recoiling out of the 224 Ra source
placed 50 mm from the RF carpet were decelerated
by the He buﬀer gas, extracted from the RF carpet,
and transported to an Al foil (thickness 0.8 µm) via
QPIG. The number of 220 Rn ions on the Al foil wasmeasured by alpha-particle spectrometry using a Si detector. The extraction eﬃciency against a variety ofvoltages applied to the RF carpet and QPIG was obtained by dividing the number of 220 Rn ions extracted
on the Al foil by that emitted from the 224 Ra source.
The extraction time measurement was performed bysynchronously applying a pulsed voltage to the 224 Ra
source (55 V, width 2–10 ms) and a pulsed RF voltage
to the QPIG (1.6 MHz, 74 Vpp , width 2–100 ms). The
pulsed voltage to the source creates a pulse of 220 Rn
ions, which reach the QPIG with some delay. The
extraction time can be obtained by searching the pulse

Fig. 1. Setup of the measurement of extraction time andeﬃciency of 220 Rn ions.
∗1
∗2
∗3

RIKEN Nishina Center
Quantum Metrology Laboratory, RIKEN
Wako Nuclear Science Center (WNSC), IPNS, KEK

Fig. 2. Extraction eﬃciency of 220 Rn ions as a function of
the RF voltage applied to the RF carpet.

Fig. 3. Counts of 220 Rn ions as a function of the pulse
RF voltage applied to the QPIG for a He pressure of
100 mbar (black circle). The diﬀerentiated data (redsquare) is ﬁtted with a Gaussian function (blue line).

width of the QPIG RF voltage at which the 220 Rn
counts increase.
Figure 2 shows the extraction eﬃciency as a functionof the RF voltage applied to the RF carpet, where weﬁnd that the maximum eﬃciency is obtained with an
RF voltage of 88 Vpp for every He gas pressure (50,100, 150, and 200 mbar, room temperature equivalent).
Similarly, we determined the best values for the audiofrequency voltage of the RF carpet, and the RF and
DC voltages of the QPIG. We obtained an extraction
eﬃciency of ∼66% even for a He pressure of 200 mbar
(Fig. 2), which is higher than the value for the RFfunnel type gas cell (5% at 70 mbar).3)
Figure 3 shows an example of the results of the ex-- 145 -

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traction time measurement, where the counts of 220 Rn
ions increase and saturate with an increase in the pulse
width of the QPIG RF voltage. The diﬀerentiateddata was ﬁtted with a Gaussian function, yielding amean extraction time of 22.0(6) ms for 100 mbar. The
mean extraction times for 50, 150, and 200 mbar were
determined in the same way as 6.7(4), 30.1(11), and33.8(9) ms, respectively.
The high extraction eﬃciency (∼66%) and fast extraction time (<40 ms) indicate that the developed gas
cell is applicable to the chemistry of SHEs with halflives of less than 100 ms at low production rates. We
plan to develop a gas chromatographic apparatus connected to the gas cell, and perform online experiments.
References

1) Y. Shigekawa et al., RIKEN Accel. Prog. Rep. 53, 168(2020).
2) Y. Shigekawa et al., Rev. Sci. Instrum. 87, 053508(2016).
3) C. Droese et al., Nucl. Instrum. Methods Phys. Res. B
338, 126 (2014).

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RIKEN Accel. Prog. Rep. 54 (2021)

Anion-exchange behavior of Db in HF/HNO3 solution
M. Kato,∗1 S. Adachi,∗2 A. Toyoshima,∗3 K. Tsukada,∗4 M. Asai,∗4 T. Yokokita,∗5 Y. Komori,∗5 Y. Wang,∗5
Y. Shigekawa,∗5 D. Mori,∗5 H. Haba,∗5 A. Kashihara,∗2 A. Nakajima,∗2 K. Tokoi,∗6 Y. Suzuki,∗2 K. Nishizuka,∗2
and K. Sueki∗7
The superheavy elements with atomic number ≥104
are located in the 7th period of the periodic table. Because of the relativistic eﬀects caused by the large positive charge of their atomic nuclei, they are expected tohave diﬀerent chemical properties from those of lighter
homologues. However, since these elements have very
short half-lives and low production rates, it is diﬃcult toreveal their chemical properties.
The aqueous chemistry of Db was studied in comparison with its lighter homologues Nb and Ta and thepseudohomologue Pa. Previous studies on the aqueous
chemistry of the ﬂuoride complex of Db suggested that
Db would form [DbOF4 ]− like Nb or [PaOF5 ]2− and/or[PaF7 ]2− like Pa, but not [DbF6 ]− like Ta.1,2) However,there was no signiﬁcant diﬀerence in the Kd values between Nb and Pa in the solutions in which Db anionexchange experiments were performed. Therefore, it was
not possible to determine whether Db was similar to Nb
or Pa, and it is also diﬃcult to determine the chemical
species of the ﬂuoride complex of Db.
In our previous work, we revealed that there is a large
diﬀerence in the Kd values between Nb and Pa in the
mixture solution of HF and 1.0 M HNO3 .3) The diﬀerent
Kd values for Nb and Pa imply that they have diﬀerent
chemical species. Thus, it is considered that the chemical species of Db can be determined by obtaining the Kdvalue of Db in this mixed solution and comparing it withthose of Nb and Pa. In this study, we performed online
anion-exchange experiments of Db in HF/1.0 M HNO3
mixture solution using automated rapid chemistry apparatus (ARCA) to identify the chemical species of theﬂuoride complex of Db.
The online anion-exchange chromatography of 262 Db,
88g
Nb, and 170 Ta was performed. The nuclides were
produced in the 248 Cm(19 F, xn), nat Ge(19 F, nx), andnat
Gd(19 F, nx) reactions, respectively, at the RIKEN
K70 AVF cyclotron. In the 262 Db and 170 Ta experiments, the products were transported by the He/KCl
gas-jet system and were deposited on the collection siteof ARCA for 120 s. Subsequently, the products weredissolved in a solution of 14.5 M HF/1.0 M HNO3 . The
solution was fed onto the micro chromatographic column(1.6 mm i.d. × 7 mm) ﬁlled with anion-exchange resin(MCI GEL CA08Y) at a ﬂow rate of 1.0 mL/min. The
eﬄuent was collected on two Ta disks as fractions 1 and2. The remaining products in the column were strippedwith a solution of 0.015 M HF/6.0 M HNO3 and collected
on another two Ta disks as fractions 3 and 4.
∗1
∗2
∗3
∗4
∗5
∗6
∗7

Master’s Program in Education, University of Tsukuba
Graduate School of Science and Tchnology, University ofTsukuba
Institute for Radiation Sciences, Osaka University
Japan Atomic Energy Agency
RIKEN Nishina Center
Graduate School of Science, Osaka University
Faculty of Pure and Applied Sciences, University of Tsukuba

Fig. 1. Distribution coeﬃcients, Kd , of Nb, Ta, Pa, and Db.

These disks were rapidly evaporated to dryness andsubjected to α-particle measurements with an automated rapid α/SF detection system.4) After the measurement, γ-rays of 170 Ta were monitored with Ge detectors.
In the 88g Nb and 170 Ta experiments, the transported
reaction products were deposited on the collection siteof ARCA and were dissolved in a solution of 4.4–14.5 M
HF/1.0 M HNO3 . Subsequently, the solution was fed
onto the microcolumn under the same experimental conditions as those for Db. The eﬄuent fractions were collected in 7 polypropylene(PP) tubes, and the remaining products were collected in another PP tube. These
fractions were assayed by γ-ray spectrometry with a Ge
detector.
We conducted 350 anion-exchange experiments andobserved 5α events from 262 Db. Its adsorption probability on the resin was determined by the α counts found in
fractions 1–4. The Kd value of Db was determined using
the relation between Kd and the adsorption probability(%ads) of Nb and Ta studied in our previous work.3) Figure 1 shows the Kd values of Nb, Ta, Pa, and Db. The
Kd value of Db is close to that of Nb, while it is signiﬁcantly larger than that of Pa. In our previous study, we
found a large diﬀerence in the Kd value trends between
Nb and Pa. The increase in the Kd value of Nb indicates a change in the chemical species from [NbOF−
4 ] to[NbF−
6 ]. In contrast, the Kd value of Pa decreased monotonically, implying that the Pa species retains its form inthis [F− ] region. The present result suggests that Db issimilar to the behavior of Nb, and the chemical speciesof Db chage from ﬂuoro-oxo complex to ﬂuoride like Nb.
In the near future, we will perform further anionexchange experiments to observe the variation in Kd values of Db and identify the ﬂuoride complex of Db.
References

1) K. Tsukada et al., Radiochim. Acta, 97, 83 (2009).
2) Y. Kasamatsu et al., Chem Letts, 38, 1084 (2009).
3) S. Adachi et al., RIKEN Accel. Prog. Rep. 53, 162 (2020).
4) H. Haba et al., RIKEN Accel. Prog. Rep. 45, 204 (2012).

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RIKEN Accel. Prog. Rep. 54 (2021)

Anion exchange of Rf in H2 SO4 using the batch-type solid-liquid
extraction apparatus AMBER
T. Yokokita,∗1 Y. Kasamatsu,∗2 E. Watanabe,∗2 Y. Komori,∗1 Y. Shigekawa,∗1 Y. Wang,∗1 D. Mori,∗1
H. Ninomiya,∗2 S. Hayami,∗2 K. Tonai,∗2 K. Ghosh,∗1 A. Shinohara,∗2 and H. Haba∗1
The relativistic eﬀect on orbital electrons is relatively more pronounced for heavy elements. In particular, the chemical properties of superheavy elements(SHEs) with atomic number Z ≥ 104 are expected
to deviate from the periodicity of their lighter homologues in the periodic table. Thus, it is importantand interesting to investigate the chemical propertiesof SHEs. So far, ion-exchange experiments on SHEs
have been conducted to determine the distribution coeﬃcients (Kd ), which are deﬁned as the ratio of the elemental concentrations of the two phases.1) However,those values at equilibrium have not been obtained inmost studies. To obtain the Kd values at equilibrium,
the batch-type solid-liquid extraction apparatus called
AMBER was developed,2) and the equilibrium Kd values on the chloride complexation of Rf were successfully obtained in an Aliquat 336/HCl system.3)
To study the sulfate complexation of Rf, we plan toperform anion-exchange experiments of Rf and its homologous elements. In our previous study, by using
AMBER, we obtained the Kd value of Rf in 0.11 M
H2 SO4 .4) The obtained Kd value of Rf is ∼10 mL g−1 ,probably indicating that Rf does not form anionic2−
species or that counter ions of HSO−
4 and SO4 inhibit
the adsorption of Rf on the anion-exchange resin. In
this study, to reduce the eﬀect of counter ions, we performed an anion-exchange experiment of Rf in 0.060 M
H2 SO4 , which is lower than 0.11 M.
In the anion exchange of Rf and Hf, we simultaneously produced 261 Rf (T1/2 = 68 s) and 169 Hf (T1/2= 3.24 min) by the bombardment of a mixture of248
Cm and natGd with an 18 O beam delivered fromthe K70 AVF cyclotron at RIKEN. The products weretransported to a chemistry room by a He/KCl gasjet system. The transported products were depositedon the collection site of AMBER’s dissolution equipment for 3 min and dissolved with 0.24 mL of 0.060,
0.30, and 0.46 M H2 SO4 . The solution sample wasinjected into a chemical reaction container containing
the anion-exchange resin (MCI GEL CA08Y). Aftershaking the container with a shaker for 10, 30, and90 s, only the solution phase was discharged from thecontainer through a PTFE ﬁlter with compressed air.
The discharged solution was collected in a Ta disk on
the round table of an automated rapid α/SF detection system5) and evaporated quickly to dryness using
hot He gas and a halogen heat lamp. Subsequently,
the Ta disk was transferred to the position under a∗1∗2

Si PIN photodiode detector, and α-particle measurement was performed. After the α-particle measurement, the γ-ray was measured with a Ge detector tomonitor 169 Hf. We also performed control experimentswith 10-s shaking without the resin to determine thestandard radioactivity of the solution sample. The Kdvalues were determined from the radioactivity in theresin and solution phases, the volume of the solution
phase, and the mass of the dry resin.
We conducted 390 anion-exchange and 92 control
cycles, and observed a total of 73 α events from thedecay of 261 Rf and its daughter nuclide 257 No (T1/2 =24.5 s), including 10 time-correlated α–α correlations.
The radioactivity ratios of 261 Rf between the resin andsolution phases were estimated from the α events. In
0.060 M H2 SO4 , the Kd values of Hf were constantin all the studied time ranges, indicating that equilibrium in the anion exchange of Hf was accomplishedwithin 10 s. Those of Rf were also constant in all thetime ranges studied, yielding values of approximately
20 mL g−1 . This indicates that Rf is not adsorbed on
the resin.
We also obtained the Kd values of Rf, Zr, Hf, andTh in 0.060–0.46 M H2 SO4 . The obtained Kd values of
Rf are low (≤25 mL g−1 ) in the entire studied H2 SO4concentration range. In contrast, the Kd values of Zr,
Hf, and Th are ≥70 mL g−1 at 0.060 M H2 SO4 . These
results suggest that Rf does not form anionic species
and that Zr, Hf, and Th form anionic species in thisstudied condition. The Kd values at 0.060 M H2 SO4follow the order of Zr > Hf ≫ Th > Rf, and this sequence is consistent with the trend predicted by theoretical calculation.6) On the other hand, the sequenceof Kd values is Th > Rf > Hf ≥ Zr in the cation exchange in the H2 SO4 /HNO3 system.7) In the future,
we plan to discuss the chemical species of Rf in thisstudied condition from the obtained anion-exchange
behavior of Rf, Zr, Hf, and Th and chemical species ofZr, Hf, and Th.
References
1) Y. Nagame et al., Nucl. Phys. A 944, 614 (2015).
2) Y. Kasamatsu et al., Radiochim. Acta 103, 513 (2015).
3) T. Yokokita et al., Dalton Trans. 45, 18827 (2016).
4) T. Yokokita et al., RIKEN Accel. Prog. Rep. 53, 165(2020).
5) H. Haba et al., RIKEN Accel. Prog. Rep. 45, 204 (2012).
6) V. Pershina et al., Radiochim. Acta 94, 407 (2006).
7) Z. J. Li et al., Radiochim. Acta 100, 157 (2012).

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RIKEN Accel. Prog. Rep. 54 (2021)

Online anion-exchange experiment of Zr in H2 SO4 for the chemical
study of Rf in H2 SO4
T. Yokokita,∗1 Y. Shigekawa,∗1 Y. Wang,∗1 Y. Komori,∗1 Y. Kasamatsu,∗2 E. Watanabe,∗2 and H. Haba∗1
The chemical properties of superheavy elements(SHEs) with atomic number Z ≥ 104 are expected todeviate from the periodicity of their lighter homologues
in the periodic table. Thus, chemical studies on SHEs
are interesting. These elements are produced at accelerators by using heavy-ion-induced nuclear reactions.
The production rates of these elements are low, andtheir half-lives are short (T1/2 ≤ 1 min). Thus, thechemical studies of SHEs are conducted on a singleatom basis. Therefore, performing, the chemical experiment of SHEs is diﬃcult. Thus far, the chemical
properties of SHEs have been discussed by comparing
them with those of their homologous elements.1)
In the solution chemistry of SHEs, ion exchange andsolvent extraction are often performed.1) To study thesulfate complexation of Rf, we plan to perform anionexchange experiments of Rf along with its homologous
elements. By using the batch-type solid-liquid extraction apparatus called AMBER2) , we measured the Kdvalues of Rf in 0.060–0.46 M H2 SO4 .3,4) In our previous study, to obtain the comparison data for Rf, we
performed an online anion-exchange experiment of Zr
and Hf by using AMBER.5) However, the Kd values of
Zr had large errors, because the radioactivity of 85 Zr
was very low. In this work, we re-examined the online
anion-exchange behavior of 89m Zr with higher radioactivities.
89m
Zr was produced in the 89 Y(d, 2n)89m Zr reaction
by using the K70 AVF cyclotron at RIKEN. The nuclear reaction products were transported to a chemistry room by a He/KCl gas-jet system. The transported products were deposited on the collection siteof the AMBER’s dissolution equipment for 1 min andwere then dissolved with 0.23 mL of 0.060, 0.11, 0.26,
0.30, 0.46, and 0.72 M H2 SO4 . The solution sample
was injected into a chemical reaction container containing 1.4–3.8 mg of an anion-exchange resin (Mitsubishi
Chemical Co., MCI GEL CA08Y). After shaking thecontainer with a shaker for 10, 30, and 90 s, only thesolution phase was discharged from the container byusing a PTFE ﬁlter with compressed air. The discharged solution was collected in a PP tube, and was
assayed by γ-ray spectroscopy. We also performed control experiments with 10, 30, and 90 s shaking without
the resin to determine the standard radioactivity of thesolution sample. The Kd values were determined fromthe following equation:
Kd = Ar Vs /As wr = (Ac − As )Vs /As wr∗1∗2

RIKEN Nishina Center
Graduate School of Science, Osaka University(1)

Fig. 1. The Kd values of Zr in anion exchange as a functionof H2 SO4 concentration.

where Ar , As , and Ac are radioactivities of the resin,
the solution, and the control solution, respectively; Vs
is the volume (mL) of the solution; and wr is the massof the dry resin (g).
Figure 1 shows the H2 SO4 -concentration dependence of the Kd values of Zr in the online and oﬄine
experiments. The Kd values of Zr in the online experiment are in agreement with those in the oﬄine experiment within the error range in 0.11–0.72 M H2 SO4 .
This indicates that the Kd values of Zr in equilibrium
are obtained in the online experiment at these H2 SO4concentrations. However, at 0.060 M H2 SO4 the Kdvalue of Zr in the online experiment was lower thanthat in the oﬄine experiment. A probable reason forthis disagreement is that the Kd value at this low concentration is too high to be determined with the AMBER system. Another possibility is that the chemical
reaction time is not suﬃcient for the anion-exchange
equilibrium. Therefore, it is important to directly investigate the reaction time dependence of the anionexchange behavior of Rf to conﬁrm the anion-exchange
reaction equilibrium of Rf.
From this work, we obtained the comparison data
for Rf. We will discuss the sulfate complexation of Rf
based on the anion-exchange behavior of Rf, Zr, Hf,
and Th in a separate study.4)
References

1) A. Türler, V. Pershina., Chem. Rev. 113, 1273 (2013).
2) Y. Kasamatsu et al., Radiochim. Acta 103, 513 (2015).
3) T. Yokokita et al., RIKEN Accel. Prog. Rep. 53, 165 (2020).
4) T. Yokokita et al., in this report.
5) T. Yokokita et al., RIKEN Accel. Prog. Rep. 52, 187 (2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

Solvent extraction of Zr and Hf from HCl by Aliquat 336 using aflow-type extraction apparatus toward online chemical studiesof element 104, rutherfordium†
Y. Kasamatsu,∗1 N. Kondo,∗1 K. Nakamura,∗1 Y. Kuboki,∗2,∗3 H. Ninomiya,∗1 Y. Shigekawa,∗1 E. Watanabe,∗1
Y. Yasuda,∗1 K. Toyomura,∗1 M. Nagase,∗1 T. Yokokita,∗1,∗3 Y. Komori,∗1,∗3 H. Haba,∗3 T. Yoshimura,∗4
H. Itabashi,∗5 and A. Shinohara∗1
Chemical studies of the transactinide (superheavy) elements with atomic numbers Z ≥ 104 are imperative forsystematic understanding of all the elements in the periodic table. In particular, the inﬂuence of relativistic
eﬀects on orbital electrons of superheavy elements could
cause their unique chemical properties. For chemical
experiments on superheavy elements which can be produced only by nuclear reactions, repetitive or ﬂow-type
rapid chemistry apparatus connected with a gas-jet system which rapidly transports the nuclear reaction products from the accelerator room to the chemistry laboratory (“online” experiment) is required. The chemical
properties of heavy elements are discussed on the basis of comparison of their behaviors with those of thecorresponding homologues.
We plan to apply a ﬂow-type solvent extraction apparatus, having a chemical reaction unit which shortens
the time required for equilibrium, to transactinide chemistry in order to obtain equilibrium D values for shortlived transactinide elements. Thus, we developed such asolvent extraction apparatus for the online transactinide
chemistry and determined the conditions to rapidly obtain equilibrium D values for Zr and Hf toward the extraction of 261 Rf. In addition, we carried out the online
extraction experiment as a model experiment for Rf using the developed apparatus.
First of all, we carried out the solvent extraction ofZr and Hf by the conventional shaking (batch) method
to obtain the equilibrium D values using 88 Zr and 175 Hf
tracers. The D values were determined from the concentration ratio of the tracers between organic and aqueous
solutions.
Then, we developed an online ﬂow-type solvent extraction apparatus: ﬂow Injection Solvent Extraction
apparatus for heavy elements (ISE) for rapid solvent
extraction and phase separation toward the extractionof 68-s 261 Rf. The developed extraction apparatus isequipped with a reactor tube ﬁlled with PTFE chips
to mix aqueous and organic solutions thoroughly (extraction unit; EU).1) By this unit, the diﬀusion lengthof metal complexes between the aqueous and organic
solutions decreases, which is expected to aid the rapid
achievement of equilibrium in the extraction reactions.
†
∗1
∗2
∗3
∗4
∗5

Condensed from the article in Solvent Extr. Ion Exch. 38, 318(2020)
Graduate School of Science, Osaka University
National Institute of Technology, Ibaraki College
RIKEN Nishina Center
Radioisotope Research Center, Osaka University
Faculty of Engineering, Gunma University

Accelerator room

Chemistry room

Pump（Aq.）
Beam
Dissolution
apparatus

TargetHe gasKCl cluster
generator

ISE

Pump（Org.）
γ-raymeasurement

Fig. 1. Schematic diagram of online solvent extraction experiment for heavy elements.

For rapid phase separation between aqueous and organic
solutions, a ﬂow-type phase separation unit (PSU) using
a PTFE membrane ﬁlter (pore size: 0.8 µm) is set downstream of the EU.2) The online extraction experimentemploying the ISE was carried out using the 89g, m Zr
and 173 Hf nuclides produced at the AVF cyclotron in
RCNP as shown schematically in Fig. 1.
The D values obtained with ISE in 7.8 M HCl are
clearly lower than the equilibrium D values, suggesting that the equilibrium D values cannot be obtainedin 7 M HCl. When the extraction was carried out in
9.3 and 11.2 M HCl using a 30-cm-long EU packed with
250–500 µm PTFE chips, the D values obtained with
ISE are all equivalent with the equilibrium values, indicating that the extraction reactions rapidly reach equilibrium state under these conditions. It was also foundthat the elution of almost all the isotopes from PSU wasaccomplished within 55 s. Based on this time information, the time taken for extraction and evaporation forα measurements in Rf experiment can be estimated to
be <2 min, which is suﬃciently fast in comparison withthe previous experiment of 261 Rf (∼100 s).
A linear relationship was observed between the logarithm of D value and the logarithm of Aliquat 336
concentration for both Zr and Hf, suggesting that theextracted chloride complex determined from the slopes(net charge) could be [MCl6 ]2− . Similar discussion canbe made for Rf, which will help to understand the chloride complexation of Rf.
References

1) H. Itabashi, Y. Mesuda, J. Flow Inject. Anal. 20, 193 (2003).
2) S. Motomizu, M. Oshima, Analyst 112, 295 (1987).

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RIKEN Accel. Prog. Rep. 54 (2021)

Cation- and anion-exchange behavior and UV-vis spectroscopy of Zr in
HBr for chemical characterization of bromide complexes of Rf
T. Yokokita∗1 and H. Haba∗1
The chemical properties of superheavy elements(SHEs) with atomic number Z ≥ 104 deviate from theperiodicity of their lighter homologues in the periodic
table because of the strong relativistic eﬀects on valence
electron shells in these heavy atoms. Therefore, chemical
research studies on these elements are intriguing and ofgreat importance. However, the chemical study of theseelements is very diﬃcult because the half-lives of theseelements are short and the production rates of these elements are low.1)
Anion-exchange studies in HF and HCl have been reported for element 104, Rf.2,3) The observed adsorption
strength on the anion-exchange resin is Zr ≈ Hf > Rf in
1.9–13.9 M HF2) and Rf > Zr > Hf in 7.0–9.0 M HCl.3)
We are interested in the anion-exchange result of Rf in
HBr because the adsorption sequence is diﬀerent between
HF and HCl media. There is one report on the bromide
complex of Rf.4) In this report, the solvent extraction of
Rf and its homologous elements were performed. Rf was
not extracted from 7.75–9.0 M HBr, while Zr and Hf wereextracted. Further study on the bromide complexationof Rf is required to understand the halide complexationof Rf in detail, In this work, cation and anion exchangesof Zr were performed to obtain the comparison data for
Rf. The UV-vis spectra of Zr in HBr solution was measured to discuss the ion-exchange behavior of Zr.
The 88 Z was produced in the 89 Y(d, 3n) reaction using the RIKEN AVF cyclotron; further, 88 Zr was puriﬁedby an anion-exchange method. The cation- and anionexchange of Zr were performed by employing the batch
method in 1.1–8.8 M HBr, which is the same procedure
an in Ref. 5). Further, control experiments without theresin were performed to determine the standard radioactivity of the solution sample. The distribution coeﬃcient(Kd ) was obtained according to Kd = (Ac − As )V /As w;
here, Ac and As denote the radioactivities in the control and exchanged solutions, respectively. V denotes
the volume of the solution, and w denotes the weight of
the ion-exchange resin.

Fig. 2. UV-vis spectra of Zr in 1.1–7.9 M HBr.

The UV-vis spectra of 0.016–0.33 M Zr in the 1.1–
7.9 M HBr solution were measured with UV-vis spectrospectrophotometer (JASCO Co., V-730) to obtain the
structural information on the Zr species in HBr.
In the anion exchange, the Kd values of Zr are low (<10 mL g−1 ) for all [HBr] studied in this work, indicating
which implies Zr does not form anionic species at 1.1–
8.8 M. This anion-exchange behavior is consistent withthat using macro amounts of Zr.6) The variation of theKd values of Zr on the cation exchange resin are shownin Fig. 1. The Kd values decrease with an increase in[HBr] in the range 1.1–7.0 M, and they increase above
7.0 M.
The UV-vis spectra of Zr in HBr solution are shownin Fig. 2. At 1.1–5.2 M, one adsorption band is seenat λmax = 410–421 nm, and its molar adsorption coefﬁcient (∆ε) increases with an increase of [HBr]. Above
6.0 M, the UV-vis spectra shows two adsorption bands at
λmax = 390–391 and 463–467 nm, and both increase withan increase in [HBr], which indicates that the dominant
Zr species is changed. This spectral change at 6.0 M isreasonably reﬂected on the variation of the Kd values inFig. 1: bromide complexes are increasingly formed withan increase in [HBr], and above 7.0 M, a diﬀerent bromide complex is adsorbed on the cation-exchange resin.
It is possibility that the oxybromide complex of Zr is
protonated and the cationic species of Zr increases.
In the future, we plan to measure the Raman spectraof ZrBr4 in the HBr solution and the mass spectra of thesolvent extracted Zr species to determine the Zr species
in the HBr solution.
References

Fig. 1. Variation of the Kd values of Zr on the cation exchange resin as a function of [HBr].
∗1

RIKEN Nishina Center

1) A. Türler, V. Pershina., Chem. Rev. 113, 1273 (2013).
2) H. Haba et al., J. Am. Chem. Soc. 126, 5219 (2004).
3) H. Haba et al., J. Nucl. Radiochem. Sci. 3, 143 (2002).
4) D. C. Kacher et al., Radiochim. Acta 75, 127 (1996).
5) T. Yokokita et al., RIKEN Accel. Prog. Rep. 53, 164 (2020).
6) Gmelin Handbuch der Anorganishchen Chemie Uranium
Suppl. Vol. D3, edited by R. Warncke (Springer-Verlag,
Berlin, Heidelberg, New York, 1982).

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RIKEN Accel. Prog. Rep. 54 (2021)

Solvent extraction of Fr and Cs with calix[4]arene-bis(benzocrown-6)
Y. Komori∗1 and H. Haba∗1
Francium (Fr) is the heaviest alkali metal, with theatomic number 87. It is one of the least-studied elements among the naturally occurring elements because
all its isotopes are short-lived. The half-life of its longestlived isotope, 223 Fr, is only T1/2 = 21.8 min. Owing toexperimental diﬃculties, the chemical properties of Fr
have not been studied in detail so far. We aim to clarify
the chemical bonding nature of Fr, which is inﬂuenced
by relativistic eﬀects, through complex formation studies of Fr. For that purpose, we performed solvent extraction experiments on 212 Fr (T1/2 = 20 min) with several
crown ethers and compared the results with those on
137
Cs (T1/2 = 30.1 y).1) We found that the distribution
ratios (D) of Fr and Cs are almost the same, although the
D values of Cs are slightly higher than those of Fr in theextraction with dibenzo-21 crown-7 (DB21C7). Haverlock et al. examined the complex formation of Fr+ withcalix[4]arene-bis(benzocrown-6) (BC6B) in 2003.2) The
D values of Fr are almost one order of magnitude higher
than those of Cs. Such a large diﬀerence is surprisingbecause the ionic radius of Fr (173 pm3) ) is close to thatof Cs (167 pm4) ). However, the mechanism for the large
diﬀerence has not been clariﬁed yet. The higher aﬃnityof BC6B for Fr than for Cs is interesting and important to understand the chemical properties and chemicalbonding of Fr. In this work, we reinvestigated the solvent
extraction behavior of Fr and Cs with BC6B to conﬁrm
the large diﬀerence between Fr and Cs.2)
We used 221 Fr (T1/2 = 4.8 min) produced as the αdecay daughter of 225 Ac (T1/2 = 9.9 d). First, we prepared an 225 Ac/221 Fr generator. 4 MBq of 225 Ac wasdissolved in 1 mL of 0.01 M HNO3 . It was loaded onto
an LN resin column (100–150 µm; φ5 mm × H10 mm).
225
Ac was adsorbed on the LN resin, and its daughter nuclide 221 Fr was generated inside the column. 221 Fr wasrepetitively eluted with 0.5 mL of 0.01 M HNO3 after its
growth. The yield of 221 Fr was ≥98% with one-time elution. 500 Bq of 137 Cs dissolved in 5 µL of H2 O was added
into the 221 Fr solution. The solution was dried up, following which 221 Fr and 137 Cs were dissolved in 1.4 mL of
10−4 –3 M NaNO3 aqueous solutions to achieve 221 Fr and137
Cs concentrations of ∼10−13 –10−12 M and ∼10−10 M,
respectively. 700 µL of this aqueous solution was shaken
for 5 min together with an equal volume of an organic
phase, 1.5 × 10−3 M BC6B in 1,2-dichloroethane. Aftercentrifugation, 500 µL of each phase was subjected to γray spectrometry with Ge detectors to determine the Dvalues as D = [M+ ]organic /[M+ ]aqueous , where M denotes
221
Fr or 137 Cs. We also investigated the D values of Cs
under almost the same experimental condition as Haverlock et al.2) by dissolving 221 Fr and 137 Cs with 10−4 –3 M
NaNO3 /10−4 M CsNO3 aqueous solutions.
The time required for Fr and Cs to reach extraction equilibrium was conﬁrmed to be less than 1 min,which agrees with the results of Haverlock et al.2) Fig∗1

RIKEN Nishina Center

Fig. 1. Variation of D values of Fr and Cs as a function of NaNO3 concentration [NaNO3 ] in their extraction
from 10−4 –3 M NaNO3 and 10−4 –3 M NaNO3 /10−4 M
CsNO3 aqueous solutions into 1.5 × 10−3 M BC6B in 1,2dichloroethane.

ure 1 shows the D values of Fr and Cs as a functionof NaNO3 concentration. Closed symbols indicate the Dvalues from the 10−4 –3 M NaNO3 aqueous solutions, andopen ones indicate those from 10−4 –3 M NaNO3 /10−4 M
CsNO3 aqueous solutions. The D values of Fr and Cs arecomparable in both the solutions, although the D valuesof Cs are slightly higher than those of Fr. These results
are reasonable when considering the similar ionic radii ofFr and Cs and our previous results obtained using crownethers.1) In the 10−4 –3 M NaNO3 /104 CsNO3 aqueous
solutions, however, the D values of both Fr and Cs are
smaller by factors of 2 to 14 than those in the 10−4 –3 M NaNO3 aqueous solutions. This might be because
macro amounts of Cs (10−4 M) inhibit the extractionof Fr and Cs, although an excess amount of BC6B exists in the extraction system (the concentration ratio of[Cs]:[BC6B] = 1:15 Note that our D values of Fr from10−4 –3 M NaNO3 aqueous solutions and those of Cs from10−4 –3 M NaNO3 /10−4 M CsNO3 aqueous solutions are
consistent with those reported by Haverlock et al.2) Because Haverlock et al.2) independently obtained the Dvalues of Fr and Cs using the 221 Fr tracer and 10−4 M
CsNO3 , respectively, the large diﬀerence between the Dvalues of Fr and Cs was observed.
The slightly higher D values of Cs than those of Fr
using BC6B are similar to those using DB21C7.1) The
reason of the order of the D values of Cs > Fr in theextraction with BC6B and DB21C7 is unclear at thismoment. Quantum chemistry calculations for Fr as wellas Cs are needed to interpret the experimental results
and to discuss the electronic state and chemical bonding
nature of Fr.
References

1) Y. Komori et al., RIKEN Accel. Prog. Rep. 52, 185 (2019).
2) T. J. Haverlock et al., J. Am. Chem. Soc. 125, 1126 (2003).
3) L. H. Delmau et al., J. Phys. Chem. B 117, 9258 (2013).
4) L. H. Ahrens, Geochim. Cosmochim. Acta 2, 155 (1952).

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RIKEN Accel. Prog. Rep. 54 (2021)

Solvent extraction and speciation of astatine species via thin layer
chromatography
S. Maruyama,∗1 K. Aoi,∗1 Y. Nagai,∗2 K. Washiyama,∗3 A. Yokoyama,∗2,∗4 I. Nishinaka,∗5 Y. Wang,∗4 and
H. Haba∗4
The short path length and high linear energy transfer of α particles are expected to enable targeted alphatherapy for the treatment of cancer. A promising nuclide among various α emitters is 211 At with a half-lifeof 7.21 h, which has gained prominence owing to its appropriate half-life for labelling and drug pharmacokinetics and potential to synthesize labelled compounds as a
halogen element. This has motivated several preclinical studies on At chemistry.1) However, the successive
chemical processes for the general use of At chemistry
have not been understood well. One of the diﬃculties in
At chemistry is the coexistence of several At species ina sample. For instance, the species of At− , AtO−
3 , andAtO−
4 are identiﬁed in some solutions via thin layer chromatography (TLC).2) This makes the processes complex,
and the species need to be adjusted by varying the redox
potential, hydrogen ion concentration, and other factors
for appropriate preparation of At solutions.
We aimed to study At species in diisopropyl ether(DIPE) solvent, which was shown to extract cationicspecies of At in a previous study.3) Speciation of At
was performed via TLC similar to the method in Ref. 2)
but in an argon atmosphere, to allow preservation of thespecies during the drying and development time for the
TLC.
In this study, 211 At was produced via the 209 Bi(α, 2n)reaction at the RIKEN AVF cyclotron and delivered toKanazawa University. The irradiated Bi target was dissolved in 3 mL of 6 M HNO3 and mixed with an appropriate amount of H2 O to prepare 1 M HNO3 solution,

Fig. 1. TLC chromatogram of At species extracted from 9 M
HCl.
∗1
∗2
∗3
∗4
∗5

Graduate School of Natural Science and Technology,
Kanazawa University
Institute and College of Science and Engineering, Kanazawa
University
Fukushima Global Medical Science Center, Fukushima Medical University
RIKEN Nishina Center
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology

Fig. 2. Distributions of At species extracted to DIPE by TLC
and their extraction ratios.

7 mL of which was used to extract the 211 At nuclide into
7 mL of dodecane solvent.
Aliquots of the dodecane solution were subjected toback extractions into several solutions of various HClconcentrations ranging from 1 M to 9 M. Approximately
0.5 mL of each HCl solution was subject to solvent extraction with 0.5 mL of DIPE. TLC was performed on
10 µL of each DIPE solution to determine the 211 At
species.
Figure 1 displays the TLC chromatogram showing a
new species at approximately Rf = 0.2, which was notfound in an open air experiment, in addition to the At− ,−AtO−
3 , and AtO4 . Figure 2 demonstrates the compositions of the At species, except for the continuum composition deduced from the TLC chromatograms, in Ref. 2),
and the At extraction rates dependent on the HCl concentration. The new species increases with the increasein the HCl concentration and the extraction rate. Therefore, the species is considered to be a cation of At basedon a previous study.3)
We are in planning on applying the TLC technique toother extraction systems to identify extracted At species
and clarify the mechanism of At extraction. Such information will be useful to construct chemical processes forthe general use of At chemistry.
References

1) F. Guérard, J. -F. Gestin, M. W. Brechbiel, Cancer Biother. Radiopharm. 28, 1 (2013).
2) I. Nishinaka et al., J. Radioanal. Nucl. Chem. 318, 897(2018).
3) T. Taniguchi, Master thesis of Graduate School of Natural
Science and Technology, Kanazawa University (2015).

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99

Ru and 57 Fe Mössbauer spectroscopic studies of Na2 Ru1−x FexO3of sodium-ion battery electrode (2)K. Hamano,∗1,∗2 Y. Kobayashi,∗1,∗2 H. Haba,∗2 and H. Ueno∗2

Sodium-ion batteries have the potential to be thenext-generation batteries to replace lithium-ion batteries owing to the abundance of its raw materials.
Na2 RuO3 is a kind of Na-excess layered oxide andis promising as a cathode material for Na-ion batteries.1) In this study, we demonstrate the oxidation
states and the coordination environments of Ru ionsin Na2 RuO3 after charging and discharging processes
via Mössbauer spectroscopy, X-ray diﬀraction (XRD),
and electrochemical analysis.2)
A sample of Na2 Ru0.99 Fe0.01 O3 was prepared via
a solid-state reaction. Stoichiometric mixtures of
RuO2 , NaHCO3 , and Fe2 O3 were pressed and sintered at 850◦ C for 48 h in an Ar atmosphere. The
sample was conﬁrmed to possess a single phase by
XRD.2) In the electrochemical treatment, a mixtureof Na2 Ru0.99 Fe0.01 O3 , acetylene black, and polyvinylidene diﬂuoride as a binder was applied on an Al foil.
The Al foil with Na2 Ru0.99 Fe0.01 O3 and a carbon sheet
were used as the cathode and the anode, respectively.
As the electrolyte, 1 M NaBF4 solution was used.1)
These materials were packed in a battery cell and subsequently charged by applying with a DC current of
4 V for 0.5 h. In the XRD pattern after charging, thecharacteristic peaks of triclinic ilmenite-type NaRuO3
were assigned, in addition to those of honeycomb-type
Na2 RuO3 .
For performing 99 Ru Mössbauer spectroscopy, thesource nuclide 99 Rh (T1/2 = 16.1 d) was produced by
the nuclear reaction of 99 Ru(p, n)99 Rh at the AVF Cyclotron. 99 Ru Mössbauer spectra were measured at
5 K in a conventional liquid He cryostat.3) The 99 Ru
Mössbauer spectra of Na2 Ru0.99 Fe0.01 O3 obtained at
5 K before and after charging are shown in Figs. 1(a)and (b), respectively. The spectrum before charging
was ﬁtted by a broadened single line, indicating Ru4+
with the isomer shift δ = −0.27(1) mm/s.2,3) The
spread of the linewidth was considered to be caused by
the doping of Fe atoms. Concurrently, the spectrum
measured after charging had a poor quality owing to
the small amount of sample packed into the battery
cell. However, this spectrum was analyzed to consistof two components having hyperﬁne magnetic ﬁelds(Hhf ) with quadrupole splitting (∆EQ ). The red component (δ = −0.27(4) mm/s, ∆EQ = 0.51(9) mm/s,
Hhf = 4.7(2) T) was consistent with the oxidation
state of Ru4+ before charging. The blue component (δ = −0.01(4) mm/s, ∆EQ = 0.07(7) mm/s,
Hhf = 17.9(9) T) presented a larger isomer shift and a∗1∗2

Fig. 1. 99 Ru Mössbauer spectra of Na2 Ru0.99 Fe0.01 O3(a) before charging and (b) after charging.

larger internal magnetic ﬁeld. The value of δ indicatedthat the oxidation state of Ru after charging changed
from 4+ to 5+. It is probable that the oxidation number of Ru ions increased as Na+ ions were removed
by charging, and that Hhf was generated as the structure changed to a three-dimensional ilmenite structurefrom a two-dimensional layer structure with a Na+ deﬁciency. This speculation is supported by the observation of magnetic splitting in the 57 Fe Mössbauer spectrum at low temperatures. The ratio of the area intensity of the blue component was approximately 66%,
which is almost consistent with the Coulomb numberof the one-electron oxidation reaction under the electrochemical conditions of 4 V for 0.5 h.
References

1) B. M. de Boisse et al., Nat. Commun. 7, 11397 (2016).
2) K. Hamano et al., RIKEN Accel. Prog. Rep. 53, 167(2019).
3) Y. Kobayashi et al., Inorg. Chem. 31, 4570 (1992).

Dep. of Eng. Sci., University of Electro-Commun
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RIKEN Accel. Prog. Rep. 54 (2021)

Targeted alpha therapy for thyroid cancer: Radiation-induced toxicityof [211 At]NaAt in mice†
Y. Liu,∗2 T. Watabe,∗2,∗3 K. Kaneda-Nakashima,∗3,∗4 K. Ooe,∗1,∗2 Y. Shirakami,∗3 A. Toyoshima,∗1,∗3
E. Shimosegawa,∗2 T. Nakano,∗3,∗5 A. Shinohara,∗3,∗4 and J. Hatazawa∗3,∗5
Radioactive iodine (RAI) therapy is used for the treatment of patients with diﬀerentiated thyroid cancer.1,2)
However, a percentage of patients shows insuﬃcient131
I accumulation3) or low therapeutic eﬀect even withenough 131 I accumulation, and some patients suﬀer fromrecurrence or metastases and become RAI-refractoryduring follow-up.4,5) For these patients, a more eﬀective
treatment is required.
Astatine (211 At) is a halogen with chemical properties similar to those of iodine, but it emits alpha particles, and we have found that the radiochemical purityof astatide dramatically improves upon treatment with
1% ascorbic acid. Consequently, the uptake of 211 At increases in the thyroid gland and thyroid cancer cells.7)
In this study, we evaluated the radiation-induced toxicity of diﬀerent doses of 211 At-NaAt solution at diﬀerent
time points to estimate its time-dependent toxicity.
Methods
The biodistribution of 211 At-NaAt was measured innormal ICR mice (n = 12) and the absorbed doses inmajor organs were calculated.
Groups of ICR mice (n = 60) were injected with
0.1 MBq or 1 MBq of 211 At-NaAt using saline as the control group (n = 30). Their body weight and food intake
were followed up for 60 days. The blood cell count andserum level of biochemical parameters were measured 3,
7, 15, 29, and 60 days after injection. Histological analyses of major organs with hematoxylin and eosin staining
were performed.

Fig. 2. Evaluation of hematological toxicity in the control,
0.1 MBq, and 1 MBq groups.

Fig. 3. Histological changes in the thyroid gland (left) andtestis (right) evaluated by HE staining in the 1 MBq groupon day 29.

Results
Figure 1 revealed a high-absorbed dose in the thyroid
gland, stomach, bladder, heart, lungs, spleen, kidneys,
and testes. The 0.1 MBq group showed no abnormalities.
The 1 MBq group showed decreased body weight andfood intake. Figure 2 showed that hematological toxicity
was mild and transient. The total cholesterol, albumin,
and total protein increased with no signs of recovery,
which can be attributed to hypothyroidism. Figure 3
showed atrophy and ﬁbrosis in the thyroid gland and atransient hypospermatogenesis was found in the testis of
one mouse on day 29.
Conclusion
High-dose administration of 211 At-NaAt showed transient toxicity in the white blood cells and testis without
severe hematological or renal toxicity, suggesting its tolerable safety as targeted alpha-therapy for diﬀerentiatedthyroid cancer in the 1 MBq group.

Fig. 1. %ID/g of main organs in normal ICR mice administered with 211 At-NaAt solution.
†
∗1
∗2
∗3
∗4
∗5

Condensed from the article in Transl Oncol. 13, 4 100757(2020)RIKEN Nishina Center
Graduate School of Medicine, Osaka University
Institute for Radiation Sciences, Osaka University
Graduate School of Science, Osaka University
Research Center for Nuclear Physics, Osaka University

References

1) H. R. Maxon et al., J. Nucl. Med. 33, 1132 (1992).
2) Y. K. Maheshwari et al., Cancer. 47, 664 (1981).
3) L. M. Cobb et al., Radiother. Oncol. 13, 203 (1988).
4) Y. Jin et al., Crit. Rev. Oncol. Hematol. 125, 111 (2018).
5) M. Schlumberger et al., Lancet Diabetes Endocrinol. 2,356 (2014).
6) M. R. Zalutsky et al., Curr. Pharm. Des. 6, 1433 (2000).
7) T. Watabe et al., J. Nucl. Med. 60, 1301 (2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

Quality conﬁrmation of RIKEN 186 Re using bifunctional chelating
agents and derivatives
S. Oshikiri,∗1,∗2 M. K. -Satake,∗1,∗2 H. Kato,∗1,∗2 Y. Komori,∗1 K. Suzuki,∗1,∗2 T. Kobayashi,∗2 A. Hino,∗2 and
H. Haba∗1
Rhenium-186 (half-life T1/2 = 3.7186 days) and 188 Re(T1/2 = 17.003 hours) emit beta rays appropriate fortargeted radiotherapy use. These radioactive Re isotopes are used according to the tumor size and form
radiotheranostic pairs with 99m Tc for radiodiagnosis.1)
However, 186 Re has not been investigated as well as
188
Re has.2) One of the possible reasons is that it isdiﬃcult to obtain no-carrier-added 186 Re through theclassical production method of the 185 Re(n, γ)186 Re reaction, while no-carrier-added 188 Re can be obtained using a 188 W/188 Re generator.1,3) At RIKEN, we started
to produce no-carrier-added 186 Re (RIKEN 186 Re) in
the 186 W(d, 2n)186 Re reaction at the RIKEN AVF cyclotron. In this study, we selected DADT, ECD, MAG3,and DMSA (Fig. 1) as model compounds, which had
already been reported in many articles,4–7) and evaluated radiolabeling eﬃciencies for these compounds to
conﬁrm the quality of RIKEN 186 Re, especially in termsof its usefulness as a radioisotope (RI) material for bifunctional chelating agents and derivatives.8,9)
In this report, the method for DADT radiolabeling is
described below as the representative among the modelcompounds.
Step 1: RIKEN 186 Re (3.8 MBq) was dissolved in
0.05 M hydrochloric acid to prepare a 186 Re
stock solution (138 MBq/mL). The radioactivity of 186 Re was determined using a germanium
semiconductor detector and a dose calibrator.
Step 2: 2.2 µL of the 186 Re stock solution in Step 1 wasadded to 63.8 µL of saline to prepare a 186 Re
solution.
Step 3: 3.0 µL of the 186 Re solution in Step 2 was mixed
with 2.5 µL of DADT (1.0 µg), 1.4 µL of tin (II)dichloride dihydrate (10 µg), and 2.0 µL of Ltartaric acid (200 µg) aqueous solution.
Step 4: The mixture in Step 3 was heated to 99◦ C andheld for 15 min.
Step 5: The radiolabeling yield of 186 Re-DADT wasdetermined using the TLC method with a
C18 reversed-phase TLC plate (NAGEL RP18W/UV254) and eluted with acetone and
0.5 M ammonium acetate in a volume ratio of
13:7.
As a result, the radiolabeling yield of 186 Re-DADT at
the speciﬁc radioactivity of 4.3 GBq/mmol was 86%. In
Ref. 4), 88% of the radiolabeling yield of 188 Re-DADT
at the speciﬁc radioactivity of 23 GBq/mmol was reported. To compare these results, each activity of 186 Re
and 188 Re was converted to the amount of substance.
∗1∗2

RIKEN Nishina Center
RI Research Department, FUJIFILM Toyama Chemical Co.,
Ltd.

NH HN

EtOOC

NH HN

SH HS

SH HS

DADT

ECD

COOEt

O
O

NH HN
SH HN

O

HS

COOH

HS

COOH

COOH

MAG3

DMSA

Fig. 1. Chemical structures of DADT, ECD, MAG3 , and
DMSA.

Both 4.3 GBq of 186 Re and 23 GBq of 188 Re correspondto 3.3 nmol. This indicates that the ratio of the amountof DADT to that of 186/188 Re was constant. Therefore,
it was regarded that our result of labeling yield corresponded to that of 188 Re in Ref. 4). In a previous invivo and in vitro evaluation, the radiolabeling of 222MAMA(N -6-Ahx-OEt) with 186 Re was performed on
6.1 GBq/mmol.10) It was suggested that RIKEN 186 Re
is useful as an RI material for in vivo and in vitro studies.
Regarding the radiolabeling eﬃciencies for ECD,
MAG3 , and DMSA, the radiolabeling yields were 51%,
46%, and 95%, respectively. It was revealed that thesecompounds are also able to form 186 Re complexes, although these are preliminary results.
In conclusion, our study revealed the availability of
RIKEN 186 Re for radiolabeling and its feasibility as
an RI material with bifunctional chelating agents andderivatives. By optimizing the labeling conditions in the
future, RIKEN 186 Re is expected to be applied to targeted radiotherapy using bifunctional chelating agents,
such as a peptide moiety in their structures.11)
References
1) N. Lepareur et al., Front. Med. 6, 132 (2019).
2) L. Uccelli et al., Molecules 24, 640 (2019).
3) G. Makris et al., Mol. Imaging Biol. 23, 52 (2021).
4) J. M. Jeong et al., Nucl. Med. Biol. 28, 197 (2001).
5) T. -Y. LuO et al., Nucl. Med. Biol. 31, 671 (2004).
6) G. W. Visser et al., J. Nucl. Med. 34, 1953 (1993).
7) K. Kothari et al., Appl. Rad. Iso. 51, 43 (1999).
8) G. Liu et al., Anticancer Agents Med. Chem. 7, 367(2007).
9) U. Choudhry et al., Dalton Trans. 3, 311 (2003).
10) D. W. Demoin et al., Nucl. Med. Biol. 43, 802 (2016).
11) V. A. Sanders et al., Nucl. Med. Biol. 68–69, 1 (2019).

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RIKEN Accel. Prog. Rep. 54 (2021)

Complex formation of Rhenium-186 with lipophilic ligands—Comparison with technetium-99m—
I. O. Umeda,∗1 H. Haba,∗2 Y. Komori,∗2 H. Fujii,∗3 and T. Takahashi∗1
Technetium-99m is the most used nuclide in diagnostic nuclear medical imaging because the energy ofits gamma-ray emission (140 keV) is ideal for imaging using gamma cameras, and it can be produced on
demand at medical facilities by using 99 Mo/99m Tc generators. Various lesions can be visualized when 99m Tclabeled radiopharmaceuticals accumulate at the lesion
site because of their unique mechanisms. In recent
years, radiotheranostics have received considerable attention because radionuclide-targeted treatments are
performed based on the imaging of the same target
area.1) Although 99m Tc-radiopharmaceuticals are specialized for diagnostic imaging, their speciﬁc lesion accumulation properties are attractive for radiotheranostics. Rhenium, a group 7 congeneric element of technetium, is assumed to have chemical properties similar
to those of Tc. 186 Re is an ideal radiotheranostic nuclide because it is a beta-emitting nuclide, and it emits
gamma-ray associated with beta decay, whose energy
is suitable for radionuclide therapy and imaging. Thusfar, 186 Re has been produced by neutron irradiation in
nuclear reactors, and it is diﬃcult to obtain in Japan.
At the RIKEN RI beam factory (RIBF), we succeededin producing no-carrier-added, high-purity 186 Re using an accelerator-based ion beam irradiation. 99m Tcradiopharmaceuticals are complexes of 99m Tc and avariety of ligands. Further rhenium is expected toform complexes as an analog of Tc. Therefore, it isimportant to evaluate the complex forming ability of
Re. In this study, the complex formation of Re withlipophilic ligands was investigated using 186 Re produced at RIBF.
Rhenium-186 was produced in the 186 W(d, 2n)186 Re
reaction. A 24-MeV deuteron beam delivered from the
AVF cyclotron was irradiated onto a 186 WO3 pellet
target (isotope enrichment of 186 W: 99.79%; thickness:
580 mg/cm2 ). After irradiation, 186 Re was puriﬁed
by chemical separation procedure.2) The aqueous solution of 186 Re-perrhenate in 0.01 M HCl (radioactivity concentration: 83.0 MBq/mL) was supplied.
MRP20 (N-(2(1H pyrolylmethyl)) N′ -(4-pentene-3one-2)) ethane-l, 2-diamine), ECD (ethyl cysteinate
dimer), and BMEDA (n, n-bis(2-mercaptoethyl)n′ ,n′ -diethylethylene-diamine) were used as lipophilicchelating ligands. Stannous chloride was used as a
reductant and GH (sodium glucoheptonate) was used
as a stabilizer for 186 Re(V). The formation of 186 Religand complexes was evaluated using octanol/water
∗1
∗2
∗3

Kavli IPMU, the University of Tokyo
RIKEN Nishina Center
EPOC, National Cancer Center

Fig. 1. Profiles of the paper chromatography of the reaction products of 186 Re with various lipophilic ligands.
Development solution: methanol or physiological saline
solution. Detection: Autoradiography using imaging
plates.

extraction and paper chromatography, and it was developed in methanol or physiological saline.
We have been developing new radiopharmaceuticals by encapsulating various radionuclides in liposomes, which are capable DDS carriers.3) We used remote loading methods, to achieve a high concentration of radionuclides in liposomes, that is, a ligand exchange reaction across the liposomal membrane using
lipophilic and hydrophilic ligands. We successfully prepared 99m Tc- liposomes using MRP20 as a lipophilic
ligand. We ﬁrst examined the reaction between 186 Re
and MRP20; sit was found that 186 Re and MRP20
did not form chelate complexes under the same conditions as 99m Tc. Therefore, the optimal conditions forthe reaction of 186 Re with lipophilic ligands MRP20,
ECD, and BMEDA were investigated. 99m Tc could
form stable complexes with each of these three ligands under mild conditions. The complex formation
between 186 Re and these lipophilic ligands required 10
times more reducing agent, higher reaction temperatures, and longer reaction times than those of 99m Tc.
Representative paper chromatography proﬁles of thesereaction products are shown in Fig. 1. 186 Re and ECD
formed a lipophilic ligand complex that moved close to
the solvent front in methanol. In the reaction of 186 Re
with BMEDA, the products were diﬀerent dependingon the reaction process. The products of process A
seemed to contain [186 ReO−
4 ] and the lipophilic complex. 186 Re and MRP20 could not form a complex evenwith these severe conditions, and their chromatogram
proﬁles were almost the same as those of [186 ReO−
4 ].
Based on these results, we speculate that 186 Re wasmore diﬃcult to reduce compared to 99m Tc analogues;
further, the reaction rate with ligands was slower than

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that of 99m Tc. 186 Re seemed to be re-oxidizing withoxygen from the air back to [186 ReO−
4 ], which may
compete with the complex formation and inhibit thereaction.
It is believed that rhenium has similar chemical
properties to technetium, and it can be handled in thesame manner. However, the results of this study indicate that their chemical properties are very diﬀerent atleast in terms of the ligand-complex formation. Highly
concentrated and stable 186 Re-labeling compounds arenecessary to promote radiotheranostics. The present
ﬁndings will help establish optimized labeling methods for 186 Re.
References

1) K. Herrmann et al., Lancet Oncol. 21, e146 (2020).
2) N. Shigeta et al., J. Radioanal. Nucl. Chem. 205, 85 (1996).
3) I. Ogihara-Umeda et al., J. Nucl. Med. 37, 326 (1996).

2- 158 -

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Simultaneous imaging of Na+ /K+ by semiconductor Compton camera
GREI
S. Motomura,∗1 I. Kii,∗1,∗2 H. Haba,∗3 H. Yakushiji,∗1 Y. Watanabe,∗1 and S. Enomoto∗4
We have been studying the simultaneous imaging of
sodium (Na) and potassium (K) ions that are dynamically controlled in a living body. Na+ and K+ arevery common cations in body ﬂuids; however, interestingly, they are controlled very diﬀerently by somebiomolecules. Owing to the diﬀerent behavior anddistribution of Na+ and K+ , membrane potential canbe formed in neurons, and Na+ can be reabsorbed in
the kidneys. Therefore, the imaging of Na+ /K+ dynamics may be beneﬁcial in inspecting the function of
biomolecules.
As summarized in a previous report, we were able tosimultaneously take the images of 24 NaCl and 43 KClsolutions using our imaging apparatus GREI.1,2) However, we determined some challenges to be addressedin the imaging of 24 Na, in addition to the low detection
eﬃciency for the 1369-keV gamma ray. In the gammaray energy spectrum of 24 Na + 43 K (Fig. 1), there isa gamma-ray peak at 1732 keV that corresponds tothe double escape peak for the 2754-keV gamma rayof 24 Na. This originates from the escape of two 511keV gamma rays created by the annihilation of thepositron that was created by the pair-creation interaction of gamma rays in the gamma-ray detectors. In
addition, the E1+E2 = 1732 keV events were observedin the E1-E2 histogram (Fig. 2), where E1 and E2
represent the detected energies by the front and reardetectors, respectively. Furthermore, the E1 + E2 =2754 keV events were also observed, although the measurable energy range for each detector was less than2000 keV in the current GREI system. We inferredthat these 1732- and 2754-keV gamma events doubled
the dead time of the GREI system. Hence, to realizeeﬃcient imaging experiment, we need to further develop a proper method to process the gamma events.
To circumvent the current problem of 24 Na, we decided to use 22 Na for now. Although 22 Na is notsuitable for clinical use, owing to its long half-life of
2.6 years, we can use it for preliminary or preclinical experiments. 22 Na is a positron emitter and emits
two 511-keV gamma-rays and one 1275-keV intrinsic
gamma ray.
We performed GREI imaging experiment of 22 Na
and 43 K simultaneously injected in a live mouse. We
can use a 511-keV gamma-ray peak to identify 22 Na,
which is in the optimal imaging eﬃciency region for
∗1
∗2
∗3
∗4

GREI (Fig. 3). The E1-E2 histogram for 22 Na + 43 K
is shown in Fig. 4. Clear lines can be observed for eachgamma ray that were all covered by the energy rangeof GREI. This study is still ongoing, and the results
are being prepared to be considered for publication.

Fig. 1. Gamma-ray energy
spectrum of 24 Na and 43 K
measured by GREI.

Fig. 2. E1-E2 histogram of24
Na and 43 K.

Fig. 3. Gamma-ray energy
spectrum of 22 Na and 43 K
measured by GREI.

Fig. 4. E1-E2 histogram of
22
Na and 43 K.

References

1) S. Motomura et al., J. Anal. At. Spectrom. 28, 934(2013).
2) T. Ida et al., Jpn. J. Appl. Phys. 58, 016002 (2019).

RIKEN Center for Biosystems Dynamics ResearchCompass to Healthy Life Research Complex Program,
RIKEN
RIKEN Nishina Center for Accelerator-Based Science
RIKEN Center for Life Science Technologies- 159 -

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RIKEN Accel. Prog. Rep. 54 (2021)

Development of image reconstruction method for a multiple-isotope
PET using 44m Sc†
T. Fukuchi,∗1 M. Shigeta,∗1 H. Haba,∗2 D. Mori,∗2 T. Yokokita,∗2 Y. Komori,∗2 S. Yamamoto,∗3 andY. Watanabe∗1
Positron emission tomography (PET) is a powerfultool for radio-tracer imaging in a living biological object. However, conventional PET is useful only for singletracer imaging because of the energy constancy of annihilation photons, which are utilized for PET imaging. In
order to improve PET imaging, we have developed a newsmall-animal PET system that can be used for multipletracer simultaneous imaging. Our PET system, named
multiple-isotope PET (MI-PET), detects not only annihilation photons but also prompt γ-rays, which are emitted successively after positrons, using additional γ-ray
detectors. Previously, we succeeded in proving the basic
principle of MI-PET using a prototype system.1,2)
Because of the imperfectness of the prompt γ-ray detection in MI-PET imaging with a pure positron emitterand positron-γ emitter, an image for the pure positron
emitter taken by MI-PET is superposed by the positronγ emitter. Therefore, to create an isolated image ofthe pure positron emitter, we developed an image reconstruction method based on subtraction between datawith the absence (data-D) and presence (data-T) of
the prompt γ-ray detection. For this subtraction, thespatial normalization of the prompt γ-ray sensitivity isneeded. Therefore, long-period normalization scans of apositron-γ emitter, 44m Sc, was performed using a cylindrical phantom 180 mm in length and 78 mm in diameter. These normalization data were also used for the
analysis of the counting-rate dependence of the sensitivity based on its proper decay half-life of 58.6 h. The
initial activity of the 44m Sc phantom was 2.45 MBq, andthe measurement time was 235 h, which corresponds toapproximately 4 half-lives.
To evaluate the practical performance of the developed image reconstruction method, dual-isotope mouse
imaging was performed using 18 F-FDG and a simple substance, 44m Sc. In this experiment, 1.13-MBq of 18 FFDG and 1.23-MBq of 44m Sc were administered to an
8-week-old normal male mouse by a tail vein injection.
After 38 min from administration, a 30-min scan withbed motion was performed under anaesthesia. This animal experiment was performed in accordance with the
Principles of Laboratory Animal Care (NIH Publication
No. 85-23, revised 1985) and approved by the Institutional Animal Care and Use Committee (IACUC) of
RIKEN, Kobe Branch.
Scandium-44m was produced at RIBF via the45
Sc(d, p2n)44m Sc (for normalization scan) and
†

∗1
∗2
∗3

Condensed from the article in Jour. of Inst., (in press) (2021)
RIKEN Center for Biosystems Dynamics Research
RIKEN Nishina Center
Department of Radiological and Medical Laboratory Science,
Nagoya University

Fig. 1. Photograph (left) and reconstructed images of amouse administrated with 18 F-FDG and 44m Sc. (i) imageD (44m Sc and 18 F-FDG), (ii) image-T (44m Sc), and (iii)
image-A (18 F-FDG).
Table 1. VOI analysis of the mouse. Values are shown in kBq.
Heart
Liver
Bladder

Image-D
31.7
421.3
69.0

Image-T
10.2
427.6
9.2

D-T
21.5
−6.3
59.8

Image-A
23.9
0.9
77.3

Ca(d, 2n)44m Sc (for mouse imaging) reactions with a
24-MeV deuterium beam from the AVF cyclotron, purified by chemical processes at the hot lab, and transported to the RIKEN Center for Biosystems Dynamics
Research in Kobe.
Reconstructed mouse images from data-D (image-D:
44m
Sc and 18 F-FDG) and data-T (image-T: 44m Sc) as
well as an isolated image of the pure-positron emitter(image-A: 18 F-FDG) are shown in Fig. 1. From imageT, we can clearly observe 44m Sc accumulation in theliver, whereas from image-A, 18 F-FDG accumulated in
the heart and urinary bladder. These distributions arereasonable from a physiological viewpoint.
To make a quantitative analysis, 3D volumes of interest (VOIs) were set on the heart, liver, and bladder for image-D, image-T, and image-A. The values ofthese VOIs and direct subtraction between image-D andimage-T (D-T) are listed in Table 1. The D-T activity inthe liver was negative. However, activity in the liver ofimage-A, which has no biological specific accumulationof 18 F-FDG, was nearly zero and was comparable withother non-accumulated sections. From this result, weconcluded that our newly developed image-A isolation
method is useful for practical multiple-isotope imaging
using MI-PET.
44

References

1) T. Fukuchi et al., Med. Phys. 40(6), 2257 (2017).
2) T. Fukuchi et al., RIKEN Accel. Prog. Rep. 53, 21 (2020).

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RIKEN Accel. Prog. Rep. 54 (2021)

Double photon emission nuclides for double photon coincidence imaging
H. Takahashi,∗1 M. Uenomachi,∗1 K. Shimazoe,∗1 and H. Haba∗2
Positron emission tomography (PET) is known as avery high sensitivity imaging method. One reason forthis is that it utilizes a coincidence technique, where
two detectors are used to identify the event; therefore,a high signal-to-noise ratio is realized. However, PET
uses only 511 keV gamma rays. Thus, it cannot be used
to distinguish all positron emitters.
Some nuclides successively emit two gamma-ray photons in a very short time. The use of such gamma
photons can lead a new type of coincidence imaging method.1,2) Recently, we proposed a new conceptof time/position correlation type tomography method
based on a directionality sensitive gamma camera. For
this, we need a nuclide that emits two photons in a relatively short period. Thus far, we have proposed the useof 111 In, which emits a 171 keV photon and after thelife time of 85 ns, it emits a 245 keV photon. When themeasurement system identiﬁes a 171 keV photon, thesystem waits for a 245 keV photon for approximately
300 ns. If the system recognizes the 245 keV photon,
it records two gamma photons and their incident angles, and then, it proceeds to the next measurement.
To record angles, an electron tracking type Compton
imager can be used for 300–600 keV gamma-ray photons; however, multi-pinhole cameras can be used for
low-energy gamma rays. This enables double photon
emission computed tomography (DPECT). Although111
In is feasible for measurements, the advantage ofthe double-photon coincidence method lies in its multinuclide capability. Therefore, we are exploring othercandidates for double-photon emission nuclides. The
gamma ray energies should not be too large since thedetection eﬃciency for high energy gamma rays is lim-

Fig. 2. Single photon Compton image of a 43 K source. The
color bar shows relative intensity.

ited.
For nuclear medicine applications, the half-life of thenuclide should not be too short or too long. The doublephoton yield should be large. The gamma-ray energies
should not be too large since the detection eﬃciency
for high-energy gamma rays is limited. Further, twophotons should be emitted within a short period. Although there are various possibilities for double-photon
emission nuclides. they cannot all be used owing to theabove requirements. Then we successfully found thefollowing nuclides thus far.
43
K is a beta minus nuclide followed by gamma photon emissions. The half-life of the nuclide 43 K is 22.3 h,which is a reasonable value. The decay scheme of thisnuclide is shown in Fig. 1. It emits three pairs of gamma
rays. The ﬁrst pair is a 617 keV photon (79%) and a
372 keV photon (87%). The second pair is a 397 keVphoton (11.9%) and a 593 keV photon (11.3%). Finally,
the third pair is a 221 keV photon (4.8%) and a 372 keVphoton. The longest life time is 81 ps. Therefore, two
gamma-ray photons are observed almost simultaneously
in the measurement system. The time resolution is very
close to that of positron annihilation. The TOF method
can be used to localize the event for this nuclide. Asa ﬁrst step, the single-photon Compton image was obtained as shown in Fig. 2. In this research, 43 K was
produced at RIKEN for radioisotope imaging.
References

Fig. 1. Decay scheme of
∗1
∗2

43

K.

School of Engineering, University of Tokyo
RIKEN Nishina Center

3)1) M. Uenomachi et al., Nucl. Instrum. Methods Phys. Res.
A, 954, 161682 (2020).
2) K. Shimazoe et al., J. Instrum. 12, C12055 (2017).
3) A. Dhal et al., EPJ Web Conf. 146, 10013 (2017).

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RIKEN Accel. Prog. Rep. 54 (2021)

Production cross sections of 225 Ac in the 232 Th(14 N, xnyp) reactions at
116 and 132 MeV/nucleon
X. Yin,∗1 A. Nambu,∗1 Y. Komori,∗1 D. Mori,∗1 S. Oshikiri,∗1,∗2 H. Kato,∗1,∗2 A. Hino,∗2 and H. Haba∗1
Ac (T1/2 = 10.0 d) is one of the most promisingalpha-particle-emitting radionuclides for targeted radionuclide therapy.1) However, the current global availability of 225 Ac is too small to support large clinical trials, and a stable supply system for 225 Ac has
not yet been established in Japan even at the basic research scale of 100 MBq. A spallation reactionof 232 Th with high-energy protons is expected to bea potential production route for 225 Ac.2) At RIKEN,
radionuclides of a large number of elements, called
multitracer, have been produced by the spallation of
metallic targets such as natTi, natAg, and 197 Au irradiated with a 135 MeV/nucleon 14 N beam from the
RIKEN Ring Cyclotron (RRC).3) In this work, we investigated the feasibility of 225 Ac production via the232
Th(14 N, xnyp)225 Ac reaction for the future domestic supply of 225 Ac. We also investigated the production of 225 Ra (T1/2 = 14.9 d) because it is useful as an
225
Ac/225 Ra generator to produce high-radionuclidicpurity 225 Ac.2)
A 14 N7+ beam was extracted from the RRC. Three
metallic 232 Th foils (69 mg/cm2 ), two 27 Al plates(415 mg/cm2 ), and another three 232 Th foils wereplaced in this order from the upstream side of the beamin the multitracer production chamber.3) The targets
were irradiated for 1 h with a 20-pnA-intensity beam.
225

Fig. 1. Radioactive decay curve of the 440.5-keV γ-line of
213
Bi on the decay chain of 225 Ra → 225 Ac → 221 Fr→ 227 At → 213 Bi → · · · . The solid curve indicatesthe fitting result using the two-body successive decay
equation (225 Ra → 225 Ac → · · · ).
∗1
∗2

RIKEN Nishina Center
RI Research Department, FUJIFILM Toyama ChemicalCo., Ltd.

Fig. 2. Cross sections of the 232 Th(14 N, xnyp)225 Ac, 225 Ra
reactions in comparison with the phits calculations.

After the irradiation, the second foil of each set of three232
Th foils was subjected to γ-ray spectrometry with
Ge detectors to determine the production cross sections of 225 Ac and 225 Ra. The 27 Al plates were used
as beam-energy degraders. The beam energies on themeasured 232 Th targets were calculated to be 132 and116 MeV/nucleon using the stopping power model4) inthe lise++ program.5)
The radioactivities of 225 Ac and 225 Ra at the end of
the irradiation were determined by following the activity of 213 Bi (T1/2 = 45.59 min), which was in radioactive equilibrium as the great granddaughter of225
Ac. Figure 1 shows a typical decay curve of the440.5-keV γ-line of 213 Bi. The two-body successive decay equation (225 Ra → 225 Ac → · · · ) was applied to fit
the decay curve after subtracting the small contribution of the 440.4-keV γ-ray of 228 Ac, which originallyexisted in the 232 Th target as the granddaughter of232
Th. Some short-lived parents of 225 Ac and 225 Ra
were produced in the reactions; therefore the measured cross sections of 225 Ac and 225 Ra are cumulativefor electron-capture decay and β − decay, respectively.
The cross sections of the 232 Th(14 N, xnyp)225 Ac,225 Ra
reaction are shown in Fig. 2. The cross sections of225
Ac are larger than those of 225 Ra by a factor of
5. The experimental results were compared with those
calculated by the Particle and Heavy Ion Transport
code System (phits).6) The phits code reproduces the
cross sections of 225 Ac, while it overestimates thoseof 225 Ra by a factor of 4. The production yield of225
Ac was tentatively evaluated to be 3.3 MBq/pµA·h- 162 -

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at 132–80 MeV/nucleon by normalizing the phits calculations to the experimental cross sections. Basedon our typical experimental conditions (incident beamenergy: 132 MeV; beam intensity: 1 pµA; target thickness: 4.5 g/cm2 ; irradiation time: 2 d), approximately
150 MBq of 225 Ac can be produced at the end of theirradiation. In the near future, we will measure thecross sections of 225 Ac and 225 Ra at lower energies of
80 and 100 MeV/nucleon to evaluate their yields morereliably.
References

1) G. Maryline et al., Radiochim. Acta 107, 1065 (2019).
2) A. K. H. Robertson et al., Inorg. Chem. 59, 12156(2020).
3) H. Haba et al., Radiochim. Acta 93, 539 (2005).
4) J. F. Ziegler, J. P. Biersack, U. Littmark, The Stopping
and Range of Ions in Solid (Pergamon Press, New York,
1985).
5) O. B. Tarasov et al., Nucl. Instrum. Methods Phys. Res.
B 266, 4657 (2008).
6) Y. Iwamoto et al., J. Nucl. Sci. Technol. 54, 617 (2017).

2- 163 -

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Cross sections of alpha-particle-induced reactions on nat Ni: Productionof 67 Cu†
S. Takács,∗1 M. Aikawa,∗2,∗3,∗4 H. Haba,∗3 Y. Komori,∗3 F. Ditrói,∗1 Z. Szücs,∗1 M. Saito,∗2,∗3 T. Murata,∗2,∗3
M. Sakaguchi,∗2,∗3 and N. Ukon∗5,∗3
Cu is considered one of the most promising radioisotopes in targeted radio-immunotherapy. It is aβ − -emitter with a mean β − energy (Eβ− = 141 keV)that allows treating tumors of size up to approximately
4 mm. Its decay is followed by the emission of lowenergy gamma rays suitable for SPECT imaging. Its
half-life (T1/2 = 61.83 h) is optimal for human applications. Among the charged-particle-induced production
routes, the 64 Ni(α, p)67 Cu reaction requires much lessenriched (expensive) target material for providing a comparable amount of 67 Cu activity as compared to proton
or deuteron production routes. The available literature
data are very diﬀerent from each other in terms of bothshape and amplitude, and only one experiment provided
cross-section data above 25 MeV; therefore, we decided
to investigate this production route up to 51 MeV.
Experiments were performed at the RIKEN AVF cyclotron. The stacked-foil activation technique and highresolution γ-ray spectrometry were applied. Pure metallic foils of nat Ni and nat Ti from Nilaco Corp., Japan
with an average thickness of 5 µm were used. The foils
were paired (Ni-Ni, or Ti-Ti) in the stack to handle
the recoil eﬀect. Four irradiations were performed using
51.04, 49.42, 40.94, and 26.57 MeV alpha-particle beams.
The incident beam energy was measured by the time-ofﬂight method.1) The energy loss of the alpha particles
was calculated using the semi-empirical formula of Andersen and Ziegler.2) The average beam intensity measured using a Faraday cup was cross checked with thenatTi(α, x)51 Cr monitor reaction.3) After a small correction of the measured beam intensities, the re-measured
cross-sections for the nat Ti(α, x)51 Cr monitor reaction
agreed perfectly with their recommended value.3) Several
series of γ-ray spectra were recorded for each irradiatedfoil by using a high-resolution HPGe detector-based γspectrometer without chemical separation for increasing
cooling times to follow the decay of the reaction products. Q-values and decay data were taken from the Qvalue calculator4) and NuDat 2.7 database5) of National
Nuclear Data Center, respectively. On the nat Ni target,
67
Cu can be produced only in the 64 Ni(α, p)67 Cu reaction with an alpha-particle beam. The threshold energyof this reaction is Ethr = 4.93 MeV.
The deduced isotopic cross sections for the64
Ni(α, p)67 Cu reaction were normalized to 100% 64 Ni



67

†
∗1
∗2
∗3
∗4
∗5

Condensed from the article in Nucl. Instrum. Methods Phys.
Res. B 479, 125 (2020)
Institute for Nuclear Research, ATOMKI
Graduate School of Biomedical Science and Engineering,
Hokkaido University
RIKEN Nishina Center
Faculty of Science, Hokkaido University
Advanced Clinical Research Center, Fukushima Med. Univ.

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

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Fig. 1. Excitation function of the 64 Ni(α, p)67 Cu reaction incomparison with previously reported experimental data
and the result of the model calculation taken from the
TENDL-2019 database.5)

isotopic abundance. Additionally, direct and/or cumulative “elemental” activation cross-sections were deduced
for the formation of 64, 61, 60 Cu, 63, 62 Zn, and 57, 56 Ni
radionuclides as possible radio-contaminants. The obtained experimental data were compared with the experimental data available in the literature and the resultsof the TALYS theoretical model calculation taken fromthe TENDL-20196) data library.
Thick target yields were calculated to estimate theexpected amount of 67 Cu and the possible radiocontamination level of the other co-produced copper radionuclides by using the spline-ﬁtted experimental datain the calculation. It was concluded that the production of 67 Cu is possible on a highly enriched 64 Ni target
for local use only. To reduce the amount of co-produced
64
Cu, the bombarding alpha-particle energy should be
kept below 30 MeV. During a 24 h-long (30 MeV and30 µA) irradiation, the estimated end-of-bombardment(EOB) activity of 67 Cu is approximately 1 GBq, and the
expected activity of the co-produced 64 Cu is approximately 0.15%.
This work was conducted in the framework of a common research program between the JSPS and HAS (Contract No: FY2019-2020 and NKM-43/2019).
References

1) T. Watanabe et al., Proc. 5th Int. Part. Accel. Conf.
(IPAC2014), (2014), p. 3566.
2) H. H. Andersen, J. F. Ziegler, Helium Stopping Powers
and Ranges in all Elements (Pergamon, Oxford, 1997).
3) A. Hermanne et al., Nucl. Data Sheets 148, 338 (2018).
4) NNDC, Q-calc, https://www.nndc.bnl.gov/qcalc/ .
5) NNDC, NuDat 2.7 database, http://www.nndc.bnl.gov/
nudat2/ .
6) A. J. Koning et al., Nucl. Data Sheets 155, 1 (2019).

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1

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production cross sections of 68 Ga and radioactive by-products indeuteron-induced reactions on natural zinc†
Ts. Zolbadral,∗1,∗2 M. Aikawa,∗1,∗3,∗2 D. Ichinkhorloo,∗3,∗2 Kh. Tegshjargal,∗4 N. Javkhlantugs,∗4 Y. Komori,∗2
and H. Haba∗2
Ga (T1/2 = 68 min), a positron emitter, is a valuable medical isotope used for positron emission tomography (PET).1) Charged-particle-induced reactions using cyclotrons are preferable routes for 68 Ga production.
One of the routes is the deuteron-induced reaction on
zinc. Our literature survey revealed three experimental
studies on the cross sections of the nat Zn(d, x)68 Ga reaction were found,2–4) and there is a large discrepancy
among their experimental data. Therefore, we measured
the cross sections of 68 Ga via the deuteron-induced reaction on natural zinc. In addition, we measured the crosssections of co-produced radioisotopes to investigate possible radioactive impurities.
The experiment was performed at the AVF cyclotronof RIKEN RI Beam Factory. The stacked-foil activation
technique and γ-ray spectrometry were used to measure
the activation cross sections. The target was composedof metallic foils of nat Zn (17.64 mg/cm2 , 99.9% purity,
Nilaco Corp., Japan) and nat Ti (9.13 mg/cm2 , 99.6%
purity, Nilaco Corp., Japan) and irradiated for 22 min by
a 24-MeV deuteron beam. The incident beam energy wasmeasured using the time-of-ﬂight method. The energy
degradation in the stacked target was calculated using
the srim code.5) A beam intensity of 96 nA was measured
using a Faraday cup.
The γ-ray spectra of the activated foils without chemical separation were measured using a high-resolution
high-purity germanium (HPGe) detector. The detector
was calibrated using a multiple γ-ray point source. The
dead time was kept less than 7% in the measurement.
Each foil was measured several times after cooling times
ranging from 40 min to 18 d for diﬀerent half-lives of
products.
The cross sections of the nat Ti(d, x)48 V monitor reaction were derived to assess the beam parameters. A
comparison of the measured cross sections with the recommended values6) showed that the beam intensity wasincreased by 6.6% relative to the measured value andcorrected to 102.4 nA.
The cross sections of the nat Zn(d, x)68 Ga reaction were
derived from the measurement of the 1077.34-keV γ-line(Iγ = 3.22%) from the 68 Ga decay. The measured excitation function is shown in Fig. 1 in comparison with previous data2–4) and the theoretical estimation of TENDL2017.7)
Our result agrees with the data reported by Šimečková

250

68

†
∗1
∗2
∗3
∗4

Condensed from the article in Appl. Radiat. Isot. 159, 109095(2020)
Graduate School of Biomedical Science and Engineering,
Hokkaido University
RIKEN Nishina Center
Faculty of Science, Hokkaido University
School of Engineering and Applied Sciences, National University of Mongolia

natZn(d,x)68Ga

This work
Simeckova+(2017)
Nassiff and Munzel (1972)
Gilly+(1963,68Zn(d,2n))
TENDL2017 (67Zn(d,n))
TENDL2017 (68Zn(d,2n))
TENDL2017 (natZn(d,x))

Cross section (mb)

200

150

100

50

0

0

5

10

15

20

25

Energy (MeV)

Fig. 1. Excitation function of the nat Zn(d, x)68 Ga reaction incomparison with previous data2–4) and the TENDL-2017
data.7)et al.3) and the normalized data for the (d, 2n) reaction
on 68 Zn reported by Gilly et al.4) However, the data reported by Nassiﬀ and Münzel2) are much lower than thepresent data in the entire energy range. The TENDL2017 data overestimate the experimental data aroundthe peak in the energy range of 8–18 MeV. The contribution of the 67 Zn(d, n)68 Ga reaction is small, and the
68
Zn(d, 2n)68 Ga reaction is dominant above the threshold energy of 6.1 MeV based on the TENDL-2017 prediction. The production cross sections of co-produced
radionuclides 65, 66, 67 Ga, 63, 65, 69m Zn, 61 Cu, and 58 Co
were also determined. Enriched 68 Zn is preferable forthe production of 68 Ga because radioactive isotopic impurities are not produced below 14.6 MeV, which is thethreshold energy of the 68 Zn(d, 3n)67 Ga reaction.
The physical yield of the nat Zn(d, x)68 Ga reaction
was deduced from the spline-ﬁtted curve of the measured excitation function. The derived yield reaches
2.37 GBq/µAh at 23.2 MeV.
This work is supported by JSPS KAKENHI Grant
Number 17K07004. Ts.Z. was granted a scholarship by
the M-JEED project (Mongolian-Japan Engineering Education Development Program, J11B16).
References

1) S. R. Banerjee, M. G. Pomper, Appl. Radiat. Isot. 76, 2(2013).
2) S. J. Nassiﬀ, H. Münzel, Radiochem. Radioanal. Lett. 12,353 (1972).
3) E. Šimečková et al., EPJ Web Conf. 146, 11034 (2017).
4) L. J. Gilly et al., Phys. Rev. 131, 1727 (1963).
5) J. F. Ziegler et al., Nucl. Instrum. Methods Phys. Res. B
268, 1818 (2010).
6) A. Hermanne et al., Nucl. Data Sheets 148, 338 (2018).
7) A. J. Koning et al., Nucl. Data Sheets 155, 1 (2019).

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III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Activation cross section measurement of the deuteron-induced reaction
on yttrium-89 for zirconium-89 production†
M. Sakaguchi,∗1,∗2 M. Aikawa,∗3,∗1,∗2 M. Saito,∗1 N. Ukon,∗4,∗2 Y. Komori,∗2 and H. Haba∗2

†
∗1
∗2
∗3
∗4

Condensed from the article in Nucl. Instrum. Methods Phys.
Res. B 472, 59 (2020)
Graduate School of Biomedical Science and Engineering,
Hokkaido University
RIKEN Nishina Center
Faculty of Science, Hokkaido University
Advanced Clinical Research Center, Fukushima Medical
University

2000

Baron 1963
La Gamma 1973
Bissem 1980
Degering 1988
West 1993
Uddin 2007
Lebeda 2015
Manenti 2019TENDL-2017
This work

1500
Cross section (mb)Zirconium-89 (T1/2 = 78.41 h) is a positron emitterthat is used for positron emission tomography (PET).
Its long half-life enables its delivery over long distances and it is suitable for immuno-PET.1) Highspeciﬁc activity of the radionuclide can be produced using charged-particle-induced reactions. There are two
promising reactions, namely, the 89 Y(p, n)89 Zr and the89
Y(d, 2n)89 Zr reactions. The former has been well investigated and a large amount of experimental data ispresent. However, there is a lack of research on the latter reactions and the peak amplitudes of the excitation
functions are dispersed.2) Therefore, we performed anexperiment of the deuteron-induced reactions on 89 Y
to measure the production cross sections of 89 Zr. Additionally, the cross sections for co-produced radionuclides, 88 Zr, 90m Y, 88 Y, and 87m Sr, were determined.
The experiment was performed at the RIKEN AVF
cyclotron. We adopted well-known and establishedmethods, such as stacked-foil activation technique andhigh-resolution γ-ray spectrometry. Thin metallic foilsof 89 Y (purity 99.0%, thickness 25 µm, Goodfellow
Co., Ltd., UK) and nat Ti (purity 99.6%, thickness
20 µm, Nilaco Corp., Japan) were used as the target
foils. Their weight and area were measured and thederived thicknessess of 89 Y and nat Ti were 12.7 and9.1 mg/cm2 , respectively. The foils were then cut intoa size of 8 × 8 mm2 . Nine sets of four 89 Y and twonat
Ti pieces were stacked as the target. The nat Ti foils
were used for the nat Ti(d, x)48 V monitor reaction toassess the thicknesses of the foils and beam parameters. The stacked target in a target holder served asa Faraday cup and it was irradiated by a deuteronbeam for 1 h. The average beam intensity of 102.3 nA
was measured by the Faraday cup. The incident beamenergy of 23.6 ± 0.2 MeV was measured by the TOF
method. The energy degradation in the stacked target
was calculated using the srim code.3) γ-ray spectrafrom each irradiated foil without chemical separation
were measured using a high-resolution HPGe detector. The foils other than the ﬁrst one in the samegroups were measured to compensate the recoil lossesof the products. The eﬃciency of the detector was calibrated using 152 Eu and mixed γ-ray standard sources.
Nuclear-decay data were taken from NuDat 2.7.4)

1000

89

89g

Y(d,2n)

Zr

500

0
0

5

10
15
Energy (MeV)

20

25

Fig. 1. Cumulative cross sections of the 89 Y(d, 2n)89g Zr reaction in comparison to the previous data2) and the
TENDL-2017 data.6)

The cross sections of the nat Ti(d, x)48 V monitor reaction were derived from the measurements of the γline at 983.5 keV (Iγ = 99.98%). Based on a comparison with the IAEA recommended values,5) the thicknesses of the 89 Y foils were corrected by +2% within
their uncertainty and the measured beam parameters
were adopted without any corrections.
The cross sections of the 89 Y(d, 2n)89g Zr reaction
were derived using measurements of the 909.2-keV γline (Iγ = 99.04%) emitted with the decay of 89g Zr.
The metastable state 89m Zr (T1/2 = 4.161 min) decayed completely during cooling times. The cumulative cross sections were determined, as shown in Fig. 1,
with the previous studies and the TENDL-2017 values.6) Our experimental data were found to be consistent with the latest four works. The TENDL-2017
values were larger than all experimental data in theenergy region between 6 and 20 MeV.
This work is supported by the Japan - Hungary Research Cooperative Program, JSPS and HAS, and by
JSPS KAKENHI Grant Number 17K07004.
References

1) M. A. Deri et al., Nucl. Med. Biol. 40, 3 (2013).
2) S. Manenti et al., Nucl. Instrum. Methods Phys. Res. B
458, 57 (2019) and references therein.
3) J. F. Ziegler et al., srim: the Stopping and Range ofIons in Matter (2008).
4) National Nuclear Data Center, The NuDat 2.7
database, http://www.nndc.bnl.gov/nudat2/ .
5) A. Hermanne et al., Nucl. Data Sheets 148, 338 (2017).
6) A. J. Koning et al., Nucl. Data Sheets 113, 2841 (2012).

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III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Excitation functions of deuteron-induced reactions on 141 Pr for
medical radioisotope production
M. Aikawa,∗1,∗2 T. Maehashi,∗3 D. Ichinkhorloo,∗1,∗2 Y. Komori,∗2 and H. Haba∗2

∗1
∗2
∗3

Faculty of Science, Hokkaido University
RIKEN Nishina Center
School of Science, Hokkaido University

350
141

300
Cross section (mb)

Investigation of the production of medical radioisotopes is indispensable for the development of imaging
and therapy. Radioisotopes 140 Nd (T1/2 = 3.37 d) and142
Pr (T1/2 = 19.12 h) are expected for 140 Nd/140 Pr
generator in positron emission tomography (PET)1)
and the treatment for arteriovenous malformations,2)
respectively. Some charged-particle-induced reactions
can produce these two radioisotopes. Among them,
we focused on deuteron-induced reactions on monoisotopic element 141 Pr. In a literature survey, only two
experimental studies for these reactions were found3,4)
below 30 MeV and their experimental cross-section
data are scattered. Therefore, we performed an experiment to measure the production cross sections of140
Nd and 142 Pr to contribute to the development of
nuclear medicine.
The experiment was performed at the RIKEN AVF
cyclotron. The stacked-foil activation technique andhigh-resolution γ-ray spectrometry were adopted in theexperiment.
The stacked target consisted of pure metallic foils of141
Pr and nat Ti. The nat Ti foils were interleaved forthe nat Ti(d, x)48 V monitor reaction to assess the beam
parameters and target thicknesses. The 141 Pr (purity:
99%, thickness: 100 µm, size: 25 × 25 mm2 ) and nat Ti(purity: 99.6%, thickness: 5 µm, size: 50 × 100 mm2 )foils were purchased from Nilaco Corp., Japan. The
surface area and weight of each foil were measured
and their thicknesses were determined to be 67.6 and2.3 mg/cm2 . The foils were cut into a small size of
8 × 8 mm2 to ﬁt a target folder. Nine sets of Pr-Ti-Ti
foils were stacked into the target folder that served asa Faraday cup.
The stacked target was irradiated with a deuteronbeam for 30 min. The beam intensity of 107 nA wasmeasured by the Faraday cup. The incident energyof 24.1 MeV was measured using the time-of-ﬂight
method. Energy degradation in the stacked target wascalculated using the srim code.5)
γ rays emitted from the irradiated foils were measured using an HPGe detector. The eﬃciency of thedetector was calibrated using a standard γ-ray point
source. Each 141 Pr foil with the next nat Ti catcher
foil for recoiled products was measured ﬁve times after cooling times from 2.2 h to 40.2 d. The dead time
was kept below 5.2%. The required nuclear data wereretrieved from the NuDat 2.8 online database.6)
The nat Ti(d, x)48 V monitor reaction was used to as-

Pr(d,p)142Pr
Lange 1968
Hermanne 2009TENDL-2019
This work

250
200
150
100
50
0
0

5

10

15
20
Energy (MeV)25

30

Fig. 1. Cross sections of the 141 Pr(d, p)142 Pr reaction incomparison with the previous data3,4) and the TENDL2019 values.8)

sess the beam parameters and target thicknesses. The
cross sections of the monitor reaction were derived
from the measurement of the 983.5-keV γ line. The
result was compared with the IAEA recommended values.7) According to the comparison, the beam intensity
was corrected by −7%. The corrected intensity andmeasured thicknesses were used to deduce the production cross sections.
The cross sections of the 141 Pr(d, p)142 Pr reaction
were derived from the measurement of the 1575.6-keV
γ line (Iγ = 3.7%) with decay of 142 Pr. The resultis shown in Fig. 1 with the previous studies3,4) andthe TENDL-2019 values.8) The previous experimental
data and their trends are almost consistent with our
result within the uncertainties, which are large due tothat of the γ-ray intensity (∆Iγ /Iγ = 10.8%). The
TENDL-2019 values were found to be smaller than all
experimental data.
References

1) K. P. Zhernosekov et al., Radiochim. Acta 95, 319 (2007).
2) S. W. Lee, W. D. Reece, Phys. Med. Biol. 50, 151(2005).
3) J. Lange et al., Radiochim. Acta 9, 66 (1968).
4) A. Hermanne et al., Nucl. Instrum. Methods Phys. Res.
B 267, 727 (2009).
5) J. F. Ziegler et al., srim: the Stopping and Range ofIons in Matter (2008).
6) National Nuclear Data Center, The NuDat 2.8
database, http://www.nndc.bnl.gov/nudat2/ .
7) A. Hermanne et al., Nucl. Data Sheets 148, 338 (2017).
8) A. J. Koning et al., Nucl. Data Sheets 155, 1 (2019).

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1

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production cross sections of medical radioisotope 153 Sm inalpha-particle-induced reaction on natural neodymium
M. Sakaguchi,∗1,∗2 M. Aikawa,∗3,∗2 N. Ukon,∗4,∗2 Y. Komori,∗2 H. Haba,∗2 N. Otuka,∗5,∗2 and S. Takács∗6
Samarium-153 (T1/2 = 46.3 h) is a beta andgamma emitter that can be applied in radiology. This radionuclide is used for the palliation ofmetastatic bone cancer as the ethylenediamino-tetrakismethylenediphosphonic acid (EDTMP) chelate.1)
153
Sm is typically obtained via the neutron capture
reaction on enriched 152 Sm in nuclear reactors, but
its speciﬁc activity is rather low.2) For the practicaluse of 153 Sm in radiotherapy, other production routesof 153 Sm with relatively high speciﬁc activities are required.
This radionuclide can be generated in an alphaparticle-induced reaction on natural neodymium. Only
one excitation-function measurement has been reported
in the literature for the nat Nd(α, x)153 Sm reaction up
to 26.2 MeV.2) To conﬁrm the available data and to obtain new data of this reaction, we decided to perform anexperiment on the nat Nd(α, x) reactions up to 51 MeV.
The experiment was performed at the RIKEN AVF
cyclotron. The standard stacked-foil activation technique was adopted for this experiment. The target
was composed of twenty-one nat Nd foils (purity: 99.0%;
thickness: 16.68 mg/cm2 ; Goodfellow Co., Ltd., UK)and fourteen nat Ti foils (purity: 99.6%; thickness:
2.35 mg/cm2 ; Nilaco Corp., Japan). The thicknessesof these foils were derived by measuring their weights
and surface areas. The nat Ti foils were used for thenatTi(α, x)51 Cr monitor reaction to assess the initial
beam parameters and the energy loss of the beam in
the target. The stacked target was irradiated in a target
holder, which served as a Faraday-cup, with an alphaparticle beam for 1 h. The primary incident energy
and average beam intensity were 51.1 MeV and 172 nA,
respectively. Energy degradation through the stacked
target was calculated using the srim code.3)
After a cooling time of approximately 30 min, thetarget was disassembled, and the gamma-ray spectrometry of the foils was started. The gamma-ray spectra
were measured using a high-purity germanium (HPGe)
detector (ORTEC GMX30P4-70) without chemical separation and analyzed using the Gamma Studio (SEIKO
EG&G) software for each foil.
The cross sections of the nat Ti(α, x)51 Cr monitor reaction were derived from the 320.1-keV gamma-line
∗1
∗2
∗3
∗4
∗5
∗6

Graduate School of Biomedical Science and Engineering,
Hokkaido University
RIKEN Nishina Center
School of Science, Hokkaido University
Advanced Clinical Research Center, Fukushima Medical University
Nuclear Data Section, International Atomic Energy Agency
Institute for Nuclear Research, ATOMKI

Fig. 1. Excitation function for the nat Nd(α, x)153 Sm reaction compared with previous experimental data2) andthe TENDL data.6)(Iγ = 9.910%), and the experimental excitation function was compared with the IAEA recommended values.4) The thickness of the nat Nd foils was adjusted by−1.5% to ﬁt the recommended values and found to be
16.43 mg/cm2 according to the comparison. The thickness of nat Ti foils and the beam parameters were unchanged.
The excitation function of the nat Nd(α, x)153 Sm reaction was determined using gamma rays with the relatively low energy of 103.18 keV (Iγ = 29.25%). Therefore, the attenuation eﬀect in the metallic Nd foil was
considered and calculated from X-ray mass attenuationcoeﬃcients.5) As a result of the calculation, the net
counts of the gamma rays were corrected by +2.1%.
Figure 1 shows the corrected cross sections in comparison with the results of a previous study2) and the
TENDL-2019 data.6) The previous data are not consistent with our experimental data and the TENDL data,
underestimate both experimental data. The maximum
cross section in this work is 1.1 mb, which indicates that
this reaction may be unsuitable for the mass productionof 153 Sm.
This work was supported by JSPS KAKENHI Grant
Number 17K07004.
References

1) I. G. Finlay et al., Lancet Oncol. 6, 392 (2005).
2) S. Qaim et al., Radiochim. Acta 95, 313 (2007).
3) J. F. Ziegler et al., Nucl. Instrum. Methods Phys. Res.
B 268, 1818 (2010).
4) A. Hermanne et al., Nucl. Data Sheets 148, 338 (2018).
5) J. H. Hubbell, S. M. Seltzer, X-Ray Mass Attenuation
Coeﬃcients, https://dx.doi.org/10.18434/T4D01F .
6) A. J. Koning et al., Nucl. Data Sheets 113, 2841 (2012).

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1

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production cross sections of 155 Tb in deuteron-induced reactions
on natural gadolinium
D. Ichinkhorloo,∗1,∗2 M. Aikawa,∗1,∗3,∗4 Ts. Zolbadral,∗2,∗3,∗4 Y. Komori,∗3 and H. Haba∗3
Terbium-155 (T1/2 = 5.32 d) can be used for singlephoton emission computed tomography (SPECT)1) andproduced through charged-particle-induced reactions.
Among the reactions, we focused on the deuteroninduced reaction on natural gadolinium. In a literature survey, three experimental studies on the reaction
were found.2–4) However, some discrepancies could befound among the experimental data. Therefore, we measured the cross sections of the deuteron-induced reaction
on natural gadolinium. The result was compared withthe previously published experimental data2–4) and the
TENDL-2019 data.5)
The experiment was performed at the RIKEN AVF
cyclotron. We used the stacked-foil activation techniqueand the high-resolution γ-ray spectrometry to determine
the activation cross sections.
The stacked target consisted of 8×8 mm2 foils cut froma large nat Gd foil (25 µm, 50×100 mm2 , 99.9% purity, Nilaco Corp., Japan) and a nat Ti foil (5 µm, 50 × 100 mm2 ,
99.6% purity, Nilaco Corp., Japan). The isotopic composition of nat Gd is 152 Gd (0.2%), 154 Gd (2.2%), 155 Gd(14.8%), 156 Gd (20.5%), 157 Gd (15.7%), 158 Gd (24.8%)
and 160 Gd (21.8%).
The sizes and weights of the large foils were measured
to derive the thicknesses. The thicknesses of the nat Gd
and nat Ti foils were found to be 25.3 and 2.34 mg/cm2 ,respectively. The nat Ti foils were interleaved for thenatTi(d, x)48 V monitor reaction to assess beam parameters and target thicknesses. The cut foils were stacked
into a target holder, which served as a Faraday cup.
The stacked target was irradiated with the beam for
60 min. An average intensity of 98.1 nA was measured
by the Faraday cup. The beam energy was measured by
the time-of-ﬂight method.6) Energy degradation in thestacked target was calculated using the Stopping andRange of Ions in Matter (srim) code.7)
The γ-rays emitted from each irradiated foil were
measured using a high-resolution high-purity germanium (HPGe) detector and analyzed using the software
Gamma Studio software (SEIKO EG&G).
The total uncertainties (∼10%) were estimated fromthe square root of the quadratic summation of each component; statistical uncertainty (0.4–1.5%), target thickness (2%), target purity (1%), beam intensity (5%), detector eﬃciency (6%) and γ-ray intensity (1.3%).
The cross sections of the nat Ti(d, x)48 V monitor reaction were derived using the line at 983.525 keV (Iγ =99.98%). The derived cross sections were compared with
∗1
∗2
∗3
∗4

Faculty of Science, Hokkaido University
Nuclear Research Center, National University of Mongolia
Nishina Center for Accelerator-Based Science, RIKEN
Graduate School of Biomedical Science and Engineering,
Hokkaido University

Fig. 1. Excitation function of the nat Gd(d, x)155 Tb reaction along with the previously published data2–4) andTENDL-2019 data.5)

the values recommended by the International Atomic
Energy Agency (IAEA).8) We could obtain good agreements between the results and the recommended values.
The γ line at 105.3 keV (Iγ = 25.1%) emitted with the155
Tb decay was measured to derive the cross sections of
the nat Gd(d, x)155 Tb reaction. The measurements were
performed after a cooling time of 3 days. The result ispresented in Fig. 1 along with the previously publishedexperimental data2–4) and TENDL-2019 data.5) Our result shows good agreement with the previous experimental data within the uncertainty, except for one data pointat 22 MeV of Tárkányi et al.4) The TENDL-2019 data
substantially overestimate all the experimental data in
the lower energy region.
In the summary, we performed an experiment to measure the excitation functions of the nat Gd(d, x)155 Tb reaction up to 24.1 MeV at the RIKEN AVF cyclotron.
The production cross sections of 155 Tb were determined.
The result was compared with the experimental data
studied published previously and the TENDL data. We
good agreement between our result and the previous experimental results.
References

1) C. Müller et al., J. Nucl. Med. 53, 1951 (2012).
2) C. Duchemin et al., Appl. Radiat. Isot. 118, 281 (2016).
3) F. Szelecsényi et al., J. Radioanal. Nucl. Chem. 307, 1877(2016).
4) F. Tárkányi et al., Appl. Radiat. Isot. 83, 25 (2014).
5) A. J. Koning et al., Nucl. Data Sheets 155, 1 (2019).
6) T. Watanabe et al., Proc. 5th Int. Part. Accel. Conf.
(IPAC 2014), 3566 (2014).
7) J. F. Ziegler et al., srim: the Stopping and Range of Ionsin Matter, http://www.srim.org .
8) A. Hermanne et al., Nucl. Data Sheets. 148, 338 (2018).

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1

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production cross sections of nat Er(d, x)171 Er reactions on natural
erbium†M. U. Khandaker∗1,∗2 and H. Haba∗2
The nuclear reaction cross-sections play a key role inoptimization of production parameters for radionuclide
of interest via the use of particle accelerators. In thisstudy, the production cross-sections of nat Er(d, x)171 Er
reaction has been measured by using stacked foil
activation technique combined with HPGe gammaray spectrometry. 171 Er (T1/2 = 7.516 h; Eγ =308.291 keV, Iγ = 64%) finds remarkable applications
for the development and evaluation of pharmaceutical drug delivery systems via the well-known gamma
scintigraphic technique.1) The measured cross-sectionsfor 171 Er also find great significance as a short-lived
parent for producing medically important long-lived
daughter 171 Tm (T1/2 = 1.92 y) via the 170 Er(d, p)
171
Er → 171 Tm process. Note that considering thecommon drawbacks of (n, γ) production route, several
authors2) studied the production possibility of erbium
radionuclides via light-charged particles-induced reactions on several targets. However, since a search ofliterature shows that the status of deuteron-induced
reaction cross-sections on erbium is not satisfactory,
further study on such processes may find great significance in various respect.
Under this circumstance, the production crosssections of nat Er(d, x)171 Er nuclear reaction has beenmeasured from threshold up to 23.06 MeV by using the
AVF cyclotron of the RIKEN RI Beam Factory, Wako,
Japan. Details on the irradiation technique, radioac-

Fig. 2. Thick target integral yields (physical) for 163, 170 Tm
and 171 Er radionuclides.

tivity determination, and data evaluation procedures
are available in Ref. 3). Owing to the space limitation of this report, we present only the nat Er(d, x)171 Er
cross sections and the deduced yield in Figs. 1 and 2,
respectively. Measured cross sections with an overall
uncertainty are listed in Ref. 3). The cross-sections
were normalized by using the nat Ti(d, x)48 V monitor
cross sections recommended by IAEA. Measured data
were critically compared with the available literature
data, and an overall good agreement was found. However, only partial agreements were obtained with thedata extracted from the tendl-2017 library and empire-3.2.2 code.
Realizing the applications of measured radionuclides
including nat Er(d, x)171 Er → 171 Tm in medical andother fields, it is hope that the measured data could
play an important role in enrichment of the crosssection database that are useful for applications in
the medical, industrial and accelerator technologies.
The large discrepancy for the 170 Er(d, p)171 Er (Ethr =0.0 MeV) reaction between the model code and themeasurement is an important clue to modify the model
code.
References

Fig. 1. Excitation function of the nat Er(d, x)171 Er reaction.
†∗1∗2

Condensed from Nucl. Instrum. Methods Phys. Res. B 470,
1 (2020)
Centre for Biomedical Physics, Sunway University
RIKEN Nishina Center

1) A. F. Parr, R. M. Beihn et al., Pharm. Res. 4, 486(1987).
2) H. Uusijarvi, P. Bernhardt et al., J. Nucl. Med. 47, 807(2006).
3) M. U. Khandaker, H. Haba et al., Nucl. Instrum. Methods Phys. Res. B 470, 1 (2020).

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III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of production cross sections of 175 Hf in the nat Lu(p, x) andnat
Lu(d, x) reactions
Y. Komori,∗1 H. Haba,∗1 M. Aikawa,∗2 M. Saito,∗2 S. Takács,∗3 and F. Ditrói∗3

200

Cross section [mb]natLu(p,x)175Hf

150

175Lu(p,n)175Hf

100
50
0
0

This work (ATOMKI)
This work (RIKEN)
Bennett (2012)TENDL-2019

176Lu(p,2n)175Hf

5
10
15
Proton energy [MeV]20

Fig. 1. Excitation function for the nat Lu(p, x)175 Hf reaction.
∗1
∗2
∗3

RIKEN Nishina Center
Graduate School of Biomedical Science and Engineering,
Hokkaido University
Institute for Nuclear Research, ATOMKI

800

Cross section [mb]The chemical characterization of superheavy elements(SHEs) with atomic number ≤104 is one of the most important and challenging subjects in the ﬁeld of nuclear
chemistry. Prior to chemistry experiments on SHEs, it
is important to ﬁnd suitable chemical systems and experimental conditions using the no-carrier-added radiotracers of their lighter homologues. The long-lived Hf
isotope, 175 Hf (T1/2 = 70 d), is useful for basic studies
on element 104, Rf. The 175 Hf isotope can be produced
in proton- and deuteron-induced reactions on nat Lu. Foreﬃcient and quantitative production of this isotope, excitation functions are necessary to know. However, data
are available only for the nat Lu(p, x)175 Hf reaction1) andnot for the nat Lu(d, x)175 Hf. In this work, we measured
the excitation functions for these reactions at RIKEN
and the Institute for Nuclear Research (ATOMKI).
The excitation functions were measured using thestacked foil technique. At RIKEN, a target stackthat consisted of 9 sets of a nat Lu foil (99% purity, 27.1 mg/cm2 thickness), a nat Ta foil (99.95%,
17.0 mg/cm2 ), and 2 nat Ti foils (≤99.6%, 4.4 mg/cm2 )was irradiated with a 14-MeV proton beam supplied fromthe RIKEN AVF cyclotron. Another target stack thatconsisted of 17 sets of a nat Lu foil (99%, 27.6 mg/cm2 ),a nat Ta foil (99.95%, 17.1 mg/cm2 ), and a nat Ti foil(≤99.6%, 4.4 mg/cm2 ) was irradiated with a 24-MeV
deuteron beam. At ATOMKI, a target stack that consisted of 17 sets of a nat Lu foil (99%, 20.7 mg/cm2 ),a nat Ta foil (99.95%, 17.0 mg/cm2 ), and 2 nat Ti foils(≤99.6%, 5.4 mg/cm2 ) was irradiated with an 18-MeV
proton beam from the MGC-20E cyclotron. Anothertarget stack that consisted of 8 sets of a nat Lu foil (99%,20.7 mg/cm2 ) and a nat Ti foil (≤99.6%, 4.4 mg/cm2 )was irradiated with a 10-MeV deuteron beam. The nat Ta
foils were used to determine the excitation functions for

natLu(d,x)175Hf

600

175Lu(d,2n)175Hf

400
200
0
0

This work (RIKEN)This work (ATOMKI)TENDL-2019

176Lu(d,3n)175Hf

5

10
15
20
25
Deuteron energy [MeV]30

Fig. 2. Excitation function for the nat Lu(d, x)175 Hf reaction.

the nat Ta(p, x) and nat Ta(d, x) reactions. The nat Ti foils
were used to conﬁrm the beam energy and intensity
based on the monitor reactions of nat Ti(p, x)48 V andnat
Ti(d, x)48 V. All these target stacks were irradiatedwith 170–220 nA beam currents for 2 h. After the irradiation, each foil was subjected to γ-ray spectrometry
with Ge detectors.
The excitation functions were measured for thenatnatLu(p, x)173, 175 HfandLu(d, x)173, 175 Hf,173, 174m, 174g, 176m, 177m, 177g
Lu reactions. Figures 1 and2 show the excitation functions for the nat Lu(p, x)175 Hf
and nat Lu(d, x)175 Hf reactions, respectively. For both reactions, our data measured at RIKEN and ATOMKI are
consistent with each other. Data of the nat Lu(p, x)175 Hf
reaction are also consistent with the data previously published by Bennet et al.1) Theoretically predicted crosssections for the nat Lu(p, x)175 Hf reaction in the TENDL2019 library2) are lower than the experimental ones at
9–14 MeV. The peak energy of the excitation function in
the TENDL-2019 is approximately 1.5 MeV lower thanthe experimental one. For the nat Lu(d, x)175 Hf reaction, TENDL-2019 slightly overestimates the cross sections at 10–14 MeV and above 15 MeV. The peak energy in TENDL-2019 is approximately 1 MeV lower thanthe experimental one. Physical thick-target yields of175
Hf were deduced from the measured excitation functions. The yield of 175 Hf in the nat Lu(p, x)175 Hf reaction is 0.47 MBq/µA · h in the energy range of 4.2–
17.2 MeV, while that in the nat Lu(d, x)175 Hf reaction is
2.0 MBq/µA · h in the range of 5.7–24.0 MeV. The yieldof the nat Lu(d, x)175 Hf reaction is 4 times larger thanthat of the nat Lu(p, x)175 Hf reaction in the energy ranges
investigated in this work.
References

1) M. E. Bennet et al., Nucl. Instrum. Methods Phys. Res.
B 276, 62 (2012).
2) A. J. Koning, D. Rochman, Nucl. Data Sheets 113, 2841
(2012).

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4. Radiation Chemistry and Biology

III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Selection of high-yield rice mutant induced by heavy-ion beamirradiation
Y. Hayashi,∗1 Y. Shirakawa,∗1 K. Ichinose,∗1 R. Morita,∗1 T. Sato,∗1,∗2 and T. Abe∗1
Improvement in productivity is the main objective ofrice breeding. Rice grain yield is determined based on
three components: the number of panicles per plant,
number of grains per panicle, and grain weight. Amongthem, the grain weight is a stable varietal character andeﬀective target trait for the mutation breeding of highyield rice.
We performed mutant selection for achieving highyield rice from M2 populations obtained by heavy-ion
beams irradiation. M2 seeds used in this study were
derived from irradiated dry rice seeds of ‘Nipponbare’(Oriza Sativa L.) with C-ion, Ar-ion, and Fe-ion. Linerenergy transfer (LET) and irradiation doses are summarized in Table 1. These conditions were the most eﬃcientwith the highest mutation rate at each LET in our previous study.1,2)
There were 790 M1 lines in total and ten plants fromeach M1 line were planted in the paddy ﬁeld. In our previous study on rice, we isolated various mutants of theﬂowering period, plant height, leaf color, tillering, andweakness by visual evaluation in the paddy ﬁeld. However, the identiﬁcation of grain size in the ﬁeld for mutant
selection is not easy and is ineﬃcient. Panicle weightreﬂects the grain size and fertile grain number, which
are two major components of the yield. We adopted themethod of measuring the weight of the main panicle fromeach M1 plant to select the candidates of the mutant.
First, some lines were excluded from panicle weight selection when segregated mutations were observed in theﬁeld. We selected 18 candidates based on panicle weightfrom 462 M1 lines (Table 2).
Next year, we conducted a yield survey on a small
scale to conﬁrm their traits and narrow down the candidates. Thirty M3 seedlings of each candidate line wereplanted in a plot (0.9 m wide and 3 m long). ‘Nipponbare’ was used as control. To avoid the border eﬀect, 8plants from the inner plot (2.4 m2 ) were collected. The
panicle weight, spikelet number, seed fertility, and grain
weight were investigated on the main culms. The grainsfrom the line with the higher weight were dehulled; theTable 1. Irradiation conditions of heavy-ion beams.
Energy(MeV/nucleon)
C135
Ar (184)
160
Ar (290)
95
Fe
90
Ion

LET
(keV/µm)
30
184
290
650

Dose
(Gy)
175
20
10
20

Table 2. Number of lines selected in each generation.
Ion
C
Ar (184)
Ar (290)
Fe
Total

PlantedM1 line
200
200
200
190
790

Surveyed
M1 line
113
121
122
106
462

Candidates
M2
M3
5
2
4
0
4
1
5
2
18
5

grain width, grain length, and grain thickness were measured using a rice analyzer (RGQ1 10B, SATAKE). However, some lines which had low fertility or low number ofgrains were not included in the grain size measurement
even though their grain weight were high, because thetrade-oﬀ relationship between the single grain size andgrain number should be considered. In addition, lines
with large individual diﬀerences were excluded. Finally,
ﬁve lines were selected based on their large grain size.
There was a trend for long grains in all 5 candidates(Table 3). Among them, Ar-39 achieved the best resultsin most components. Our previous study succeeded indiscovering novel gene: LIN1 using the long grain mutant
induced by Ar-ion irradiation.3) The genetic analysis ofthese candidates to reveal relevant genes is in progress
while continuing repeated yield surveys on a large scale.
References

1) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 50, 27 (2017).
2) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 51, 238 (2018).
3) R. Morita et al., Molecular Breeding 39, 135 (2019).

Table 3. Mean ± standard error of yield-related characters and grain size for selected M3 lines.
Panicle weight Grain number Seed fertility Grain weight(g/one panicle)(/panicle)(%)(g/1,000 grain)‘Nipponbare’ 2.95 ± 0.07
130.4 ± 5.58
87.3 ± 1.86
24.2 ± 0.26
C-98
3.32 ± 0.14
135.6 ± 5.19
85.1 ± 1.44
25.0 ± 0.21
C-190
2.80 ± 0.06
118.0 ± 2.78
83.2 ± 1.70
25.8 ± 0.13
Ar-39
3.63 ± 0.14
148.8 ± 5.70
85.4 ± 0.89
25.7 ± 0.23
Fe-1343.10 ± 0.11
129.0 ± 3.91
83.5 ± 1.69
25.5 ± 0.17
Fe-1533.03 ± 0.10
126.6 ± 4.50
83.5 ± 1.48
25.2 ± 0.27
Line

∗1
∗2

Length5.02 ± 0.03
5.08 ± 0.02
5.18 ± 0.02
5.17 ± 0.02
5.12 ± 0.02
5.08 ± 0.02

Grain size (mm)WidthThickness
2.81 ± 0.02
1.88 ± 0.01
2.77 ± 0.02
1.86 ± 0.01
2.85 ± 0.02
1.89 ± 0.01
2.89 ± 0.02
1.89 ± 0.01
2.85 ± 0.02
1.88 ± 0.01
2.85 ± 0.02
1.89 ± 0.01

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Graduate School of Agricultural Science, Tohoku University- 173 -

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RIKEN Accel. Prog. Rep. 54 (2021)

Whole genome sequencing analysis for detecting mutations induced bycarbon- and argon-ion irradiations of rice (Oryza sativa L.)
R. Morita,∗1 H. Ichida,∗1 Y. Shirakawa,∗1 K. Ichinose,∗1 T. Sato,∗1,∗2 and T. Abe∗1
A mutation analysis with high-throughput sequencing is a powerful tool for characterizing the molecular nature of mutations induced by mutagen at thewhole-genome level. We have investigated the mutation eﬀect following heavy ion-beam irradiation of rice
(Oryza sativa L. cv. Nipponbare), a monocotyledonous
model plant, using high-throughput sequencing. In thisstudy, we irradiated C-ion (LET: 30 keV/µm) or Ar-ion(LET: 290 keV/µm) to rice, and investigated numbers
and types of mutations induced by both ions at wholegenome level to examine whether the diﬀerence in the
LET value of the ions inﬂuences the numbers and sizesof mutations in rice genome.
We irradiated C-ion (175 Gy, LET: 30 keV/µm) or
Ar-ion (10 Gy, LET: 290 keV/µm) to rice (Oryza sativa
L. cv. Nipponbare) dry seeds. The plants from irradiated seeds (M1 plants) were grown in a paddy ﬁeld
and self-pollinated to obtain M2 seeds. Next year, wegrew M2 plants in a paddy ﬁeld to collect mutant plants
with visible phenotypes and harvest M3 seeds from theeach plant. For this study, we selected 11 and 4 mutant plants from C-ion and Ar-ion irradiations, respectively. Genomic DNA extraction for Whole-genome sequence was performed from the leaves of individual M3
plants. Candidate mutation extraction were performed
using “bioinformatics pipeline.” 1) We extracted candidate mutations using a combination of the gatk, pindel,
delly, and manta programs. gatk adopted the following parameters of (-stand_call_conf 50 -A Coverage -A
RMSMappingQuality -baq CALCULATE_AS_NECESSARY). pindel
was used following parameters of (-window_size 1–report_long_insertions –report_breakpoints–minimum_support_for_event 3 –min_inversion_size 10).

delly and manta were run with default parameters. All
mutations detected were visually conﬁrmed using Integrated Genomics Viewer (IGV).2)
We detected 1718 mutations from 11 C-ion-irradiatedmutants, and 426 mutations from 4 Ar-ion-irradiatedmutants. The average numbers of total mutations in
a mutant genome were 156.2 and 106.5 for C-ion andAr-ion irradiations, respectively. The most abundant
mutations induced by both C-ion and Ar-ion irradiation were single-nucleotide variants (SNVs). The average numbers of SNVs in a mutant genome were 123.2
and 86.8 for C-ion and Ar-ion, respectively (Fig. 1).
The second most abundant mutations induced by both
C-ion and Ar-ion irradiation were small (<100 bp) insertions and deletions (indels). The average numbers ofindels in a mutant genome were 31.5 and 16.3 for Cion and Ar-ion, respectively. There were large deletions∗1∗2

RIKEN Nishina Center
Graduate School of Agricultural Science, Tohoku University

Fig. 1. Average number of SNV, small Indel, Large deletion,and SV induced by C-ion (blue) and Ar-ion (red) irradiations. Error bars indicate standard error.

(≥100 bp) and structural variations (SVs), such as inversion and translocation in a mutant genome derived
from both C-ion and Ar-ion irradiations. The average
numbers of large deletions and SVs in a mutant genome
were 0.2 and 1.3 for C-ion, and 1.0 and 2.5 for Ar-ion,respectively. Comparing the mutations induced by Cion and Ar-ion, the number of small mutation, such as
SNVs and small indels, tended to be higher in the Cion irradiation than in Ar-ion irradiation. Conversely,
the number of both large deletion and SVs tended to behigher in Ar-ion than in C-ion. These tendencies corresponded to the results observed in the irradiation of
Arabidopsis seeds.3) They compared the number of mutations induced by C-ion (LET: 30 keV/µm) or Ar-ion(LET: 290 keV/µm) irradiation using Arabidopsis, a dicotyledonous model plant, at the whole-genome level,and demonstrated that Ar-ions induced rearrangements(including large-deletion and SVs) more frequently thanC-ions.3) They also indicated that Ar-ions induced SNVsless frequently than C-ions. The ﬁndings obtained in thisstudy and that of Kazama et al. (2017) suggested that
C-ion irradiation tends to induce small mutations predominantly, whereas Ar-ion irradiation tends to induce
higher number of large deletions and SVs than C-ion
irradiations of both rice and Arabidopsis genomes. Because the sample size was not suﬃcient to compare thenumbers of each mutation induced by C-ion and Ar-ion
statistically in this study, we plan to increase the sample
size to perform a more detailed analysis.
References

1) H. Ichida et al., Plant J. 98, 301 (2019).
2) J. T. Robinson et al., Nat. Biotechnol. 29, 24 (2011).
3) Y. Kazama et al., Plant J. 92, 1020 (2017).

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RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Detection of structural variations in three responsible genes induced byrelatively high-LET ion beams in rice
Y. Shirakawa,∗1 R. Morita,∗1 Y. Hayashi,∗1 K. Ichinose,∗1 T. Sato,∗1,∗2 and T. Abe∗1
The molecular characteristics of mutations induced bya heavy-ion beam with a relatively high LET in rice,a model plant of monocotyledonous, has not yet been
revealed. In this study, we irradiated dry seeds of rice
(Oryza sativa L. ‘Nipponbare’) with Fe- or Ar-ion beams,
isolated 3 mutants for which the responsible gene has
been clarified, and characterized the structure of the mutated gene using polymerase chain reaction (PCR) analysis.
A pla1 mutant (Ar7-165, Fig. 1) was isolated from239 M1 lines irradiated with Ar ions (7.5 Gy, LET:
289 keV/µm). In this mutant, no PCR amplification
occurred when primers designed for amplification of thecentral area of the PLA1 gene (primer pairs F4 and R20,
F6 and R21, and uF5 and R21, as shown in Fig. 2) wereused, suggesting that structural variations (SVs) such as
inversion or translocation occurred in the gene (Fig. 2).
A dwarf mutant (Fe15-235, Fig. 1) that showed a defect in gibberellin biosynthesis was isolated from 236 M1lines irradiated with Fe ions (15 Gy, LET: 650 keV/µm).
We conducted PCR analysis with the primers for gibberellin biosynthesis-related genes and detected a deletion in the region including the 1st to 6th exon of theOsKS1 gene (Fig. 2). Additional PCR and sequencing
analyses revealed that Fe15-235 harbors a 9,843 bp deletion (Chr04: 31018475 - 31028317) in the OsKS1 gene.
We isolated the brd1 mutant (WAr30-204), whichshowed a dwarf phenotype with a defect in brassinosteroid biosynthesis from 242 M1 lines irradiated with

Fig. 2. Schematic representation of mutated genes. Purple
boxes indicate protein coding regions (exons), and yellow
marks indicate the position of the DNA double-strand
breaks induced by heavy-ion beams. In the case of theAr7-165 mutant, the position of the primers used in PCR
are shown. Red arrows indicate primers for which DNA
amplification occurs in PCR, whereas blue arrows indicate
primers for which DNA amplification did not occur in
PCR.

Ar ions generated by the WACAME line1) (30 Gy,
LET:184 keV/µm). PCR analysis revealed that this mutant harbors a 27 kb deletion involving the entire OsBRD1 gene (Fig. 2). Another deletion of approximately
5 kb was also detected 18 kb downstream from the 27kb deletion. It suggested that a complex mutation withlarge deletions occurred in the OsBRD1 gene region.
Our findings suggest that a heavy-ion beam with a relatively high LET may predominantly induce large deletions or SVs in the responsible gene region in rice. Thistendency was also observed in the PCR and sequence
analysis for Arabidopsis mutants induced by Ar-ion irradiation on dry seeds2) and rice mutants induced by
Ar-ion irradiation on imbibed seeds.3)
Fig. 1. Morphological comparison of (a) Nipponbare, (b)Ar7-165, and (c) Fe15-235 plants 24 days after sowing.
Scale bar = 5 cm.
∗1∗2

RIKEN Nishina Center
Graduate School of Agricultural Science, Tohoku University

References

1) N. Fukunishi et al., Proc. 13th Heavy Ion Accelerator
Technology Conference (HIAT2015), 42 (2016).
2) T. Hirano et al., Mutation Res. 735, 19 (2012).
3) S. Kogure et al., RIKEN Accel. Prog. Rep. 47, 289 (2014).

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III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Dose-dependent mutagenic eﬀects of 160-MeV/nucleon-argon beamin Arabidopsis thaliana
K. Ishii,∗1 S. Ohbu,∗1 Y. Shirakawa,∗1 and T. Abe∗1
Heavy-ion beams are used as an eﬀective mutagens that induce localized mutations owing to theirhigh linear energy transfer (LET). We previously reported a dose-dependent mutagenic eﬀect of a 135MeV/nucleon-carbon beam (30 keV/µm) in Arabidopsis thaliana in which the number of mutations per
genome was dose-dependently increased in the rangeof 150–350.1) In this study, we investigated the dosedependent mutagenic eﬀect of a 160-MeV/nucleonargon beam and its diﬀerence to that of a 135MeV/nucleon beam.
Dry seeds of Arabidopsis thaliana (the Col-0 wildtype strain or CS16118 strain, which possesses a heterozygous null mutation in the APG3 gene for measuring the mutation rate in M1 generation2) ) were irradiated with 160-MeV/nucleon-argon ions in doses of
0–120 Gy. The LET of the argon-ion beams was controlled to 188 keV/µm. Survival and mutation rates
in M1 generation were measured as previously described.2) Randomly selected ten M2 plants were harvested from one self-pollinated M1 plant. Genomic
DNA was extracted from a mixture of the leaves of
the ten M2 plants. Five DNA pools were sequenced
for each dose using HiSeq X-Ten sequencing systems(Illumina Inc.). The read sequences obtained were input into the mutational analysis pipeline, AMAP, as
described previously,3) with some modiﬁcations. The
mutation candidates were detected with gatk (HaplotypeCaller), pindel, and breakdancer software.
The number of mutations was counted as follows: For

Fig. 1. Mutation rate in M1 generation after irradiation of
160-MeV/nucleon-argon beam (n ≥ 500).
∗1

RIKEN Nishina Center

Fig. 2. Number of mutations in M2 generation induced after irradiation of 188 keV/µm argon-ion beam (black
circles) and 30 keV/µm carbon-ion beam (whiterhombi).

small mutations that included single nucleotide substitutions and <100 bp indels (insertions and deletions),
each mutation was counted as one. For large mutations, that included ≥100 bp indels and chromosome
rearrangements), the number of junctions in each mutant line were counted. Total number of these mutations per DNA pool was envisaged as the number ofmutations per genome.
In the M1 generation, the average survival rate (ﬂowering rate one month after cultivation2) ) was 94% at
80 Gy-irradiation and decreased to 74% at 100 Gyirradiation (data not shown). The mutation rate (appearance ratio of white sector mutation2) ) indicatedan increasing tendency with the increasing dose in therange of 10–80 Gy (Fig. 1). The highest mutation rate
was 7.7% at 60 Gy-irradiation, which is as high as that
previously reported (7.0% at 400 Gy with 30 keV/µm
of LET; p = 0.54 by chi-square test).2) The decreased
mutation rate at 100 Gy-irradiation may reﬂect theradiation overdose, as seen in the survival rate.
The number of mutations per genome in the M2 generation after 188 keV/µm argon ion beam irradiationcompared to that after 30 keV/µm carbon ion beamirradiation previously reported1,4) is shown in Fig. 2.
After 400-Gy irradiation of the 30 keV/µm carbonion beam, the mutation rate in the M1 generation wasapproximately 7%2) and the average number of mutations in the M2 generation was 59 (Fig. 2). In contrast,
after the 60-Gy irradiation of the 188 keV/µm argonion beam, the mutation rate in the M1 generation was- 176 -

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RIKEN Accel. Prog. Rep. 54 (2021)

7.7% (Fig. 1) but the average number of mutations in
the M2 generation was 29 (Fig. 2). The diﬀerence inthe average number of mutations in the M2 generation
under between the two irradiation conditions can be
attributed to the content of the mutations. Among thenumber of mutations in the M2 generation induced by
the 30 keV/µm carbon-ion beam, only 4% were derived
from large mutations, whereas 32% were obtained by
188 keV/µm argon-ion beam. Further analysis, for example, to compare the number of genes aﬀected by themutations including inversions that possibly cause thechromosomal position eﬀect of the 30 keV/µm carbonion and the 188 keV/µm argon-ion beam may provide insight into the mutagenic characteristics of eachbeam.
References

1) Ishii et al., RIKEN Accel. Prog. Rep. 52, 216 (2019).
2) Y. Kazama et al., Plant Biotechnol. 29, 441 (2012).
3) K. Ishii et al., Genes Genet. Syst. 91, 229 (2016).
4) Y. Kazama et al., Plant J. 92, 1020 (2017).

2- 177 -

III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Argon-ion-induced mutant of Arabidopsis thaliana exhibiting
accelerated leaf chlorosis†
A. Sanjaya,∗1 Y. Kazama,∗2,∗3 K. Ishii,∗2 S. Ohbu,∗2 T. Abe,∗2 and M. Fujiwara∗1,∗2
Chloroplast development in leaf tissues is crucial forplant growth and productivity. Plant leaves are composed of the epidermis, which forms the outermost layer,
and the mesophyll and vasculature inside. In the model
plant Arabidopsis thaliana, chloroplasts are distributedin leaf epidermal pavement and guard cells, as well as
in mesophyll cells. Despite vast research on the structure and function of leaf chloroplasts, there is limited
knowledge about their regulations in the plant life cycle.
To explore possible novel gene functions for leaf chloroplast development, we attempted a forward genetic approach. We created mutants of A. thaliana by exposing dry seeds of ecotype Col-0 to accelerated argon ions(290 keV/µm, 50 Gy) at RIBF.1) Following two rounds ofcultivation and selfing, as well as a macroscopic screening of the M3 generation of plants, we isolated a new
mutant, designated as Ar50-33-pg1.
During seedling development, Ar50-33-pg1 produced
slightly pale cotyledons and leaves under standard plant
growth conditions (Fig. 1A, B). As the mutant leaves expanded and matured, their chlorosis became prominent(Fig. 1C). This observation of accelerated leaf chlorosis was supported by the chlorophyll measurement of
detached leaves through spectrophotometry (data notshown). Furthermore, Ar50-33-pg1 exhibited abnormalities at the reproductive stage, including phenotypes oflate flowering, flower longevity, and low seed production(data not shown).
Microscopic examination of expanding leaves of wild-

(A)

(C)

(B)

Fig. 1. Growth and morphology of seedlings of Arabidopsis. (A) 2-week-old wild-type seedling. (B) 2-week-old
Ar50-33-pg1 seedling. In (A) and (B), images of chlorophyll autoﬂuorescence were taken at the same excitation condition by stereoﬂuorescence microscopy. Scalebar = 5 mm. (C) 4-week-old wild-type and Ar50-33-pg1
seedlings. Scale bar = 5 cm.
†

∗1
∗2
∗3

Condensed from the article in Plants 10, 848 (2021)
Department of Biology, Sophia University
RIKEN Nishina Center
Department of Biosciences and Biotechnology, Fukui Prefectural University

DIC

Guard cell
Chlorophyll

Pavement cell
DIC
Chlorophyll

A

B

Fig. 2. Fluorescence microscopy of leaf epidermal guard cells
and pavement cells of Arabidopsis. (A) Wild type. (B)Ar50-33-pg1. Diﬀerential interference contrast (DIC) and
chlorophyll autoﬂuorescence (colored in red) images ofcells from epidermal peels of growing rosette leaves. Scalebar = 10 µm.

type and Ar50-33-pg1 plants under normal observation
conditions revealed that a certain population of mutant epidermal chloroplasts lacked chlorophyll autofluorescence signal (Fig. 2). Meanwhile, mutant mesophyll
chloroplasts retained chlorophyll autofluorescence until
later stages of leaf senescence. Therefore, the chlorosis leaf phenotype of Ar50-33-pg1 might involve tissuedependent chloroplast abnormalities between the epidermis and mesophyll.
Backcrossing and segregation analyses indicated thatthe chlorotic phenotype of Ar50-33-pg1 is associatedwith impaired epidermal chloroplasts and is caused bya single nuclear recessive allele. Through whole-genome
resequencing, Ar50-33-pg1 was revealed to contain a∼0.9 Mb deletion from position 12621534 to 13561533
in chromosome V, which spans approximately 40 putative or well-characterized protein-coding genes. One ofthem encoded a known chloroplast membrane-localized,
ATP-independent metalloprotease, Ethylene-dependent
Gravitropism-deficient and Yellow-green 1 (EGY1).2)
Ar50-33-pg1 was then crossed with an egy1 mutant3)
in both directions. All F1 seedlings were similar to bothparents in that they commonly exhibited accelerated leaf
chlorosis with epidermal chloroplast defects. F1 plant
phenotypes at the reproductive stage were all wild typelike. Therefore, EGY1 was deemed to be the main causal
gene for the impaired chloroplast phenotypes in Ar50-33pg1.
References

1) Y. Kazama et al., The Plant J. 92, 1020 (2017).
2) G. Chen et al., Plant J. 41, 364 (2005).
3) T. Hirano et al., Mutat. Res. 735, 19 (2012).

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1

III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Eﬀect of heavy-ion irradiation on survival rate of Torenia fournieri
A. Matsuta,∗1 M. Hatashita,∗2 K. Takagi,∗2 Y. Hayashi,∗3 T. Abe,∗3 K. Murai,∗1 and Y. Kazama∗1,∗3
A heavy-ion beam is a powerful mutagen that has
high linear energy transfer (LET). We previously demonstrated that the value of LET aﬀects the size and typeof the induced mutations in a model plant Arabidopsis
thaliana; a C-ion beam with an LET of 30.0 keV/µm
predominantly induce small mutations that aﬀect almost single genes, while an Ar-ion beam with an LET of
290 keV/µm can induce chromosomal rearrangements including translocation and large inversions or deletions.1)
We focus on the induction of chromosomal rearrangements because they can aﬀect multiple genes resulting
in the induction of new phenotypic traits that have notbeen ever observed by single gene mutations.
To investigate such a broad spectrum of phenotypes,
we aim at observing the ﬂoral phenotypes of Torenia
fournieri after the irradiation of heavy-ion beams withhigh LET, because its simple ﬂoral structure with colorful petals allows us to observe the change in the phenotypes with high visibility.2) Moreover, T. fournieri isa useful plant for genetic analysis and molecular biology
because of its small genome size (2n = 18, 171 Mb), andbecause of the transformation techniques established.3,4)
Once an interesting mutant is isolated, mutations including rearrangements responsible for its phenotype can be
determined by whole-genome resequencing. Dry seedirradiation and screening of seed propagated mutants
needs to be conducted using an inbred strain, to eﬃciently perform the investigation of the phenotypic mutation spectrum followed by whole-genome resequencing.
In this study, prior to performing mutant screening, dose
dependence on survival was examined and the eﬀect of
LETs on survival was compared.
The inbred line ‘Zairai murasaki’ was kindly provided
by Dr. Nishijima of the National Institute of Floricultural Science. Dry seeds of ‘Zairai murasaki’ were irradiated with Ar ions with LETs of 184 keV/µm and
290 keV/µm, respectively, at a dose range of 25–200 Gy
100

Survival rate (%)

80
60
40

Ar (184 keV/µm)
Ar (290 keV/µm)

200C (50 keV/µm)
0

50

100

150

200

250

300

350

400

450

500

Dose (Gy)Fig. 1. LET-dependent eﬀect on survival rate in T. fournieri.
∗1
∗2
∗3

Department of Bioscience and Biotechnology, Fukui Prefectural University
Res. and Develop. Dept., The Wakasa Wan Energy ResearchCenter
RIKEN Nishina Center

Fig. 2. Photographs of wild-type ﬂower (A); a mutant ﬂower
with a rough-edged pistil and petals (B), and a mutant
ﬂower without the yellow spot (C). Bars: 1 cm for wholephotos, 1 mm for the photos of pistils.

in the RIKEN RI-beam factory. C-ion beam irradiation with an LET of 50 keV/µm was carried out by
the Wakasa Wan Multi-purpose Accelerator with Synchrotron and Tandem at the Wakasa Wan Energy Research Center at a dose range of 100–500 Gy. IrradiatedM1 seeds were surface-sterilized and incubated on 0.7%
agar containing 1/2 MS medium supplemented with 3%
sucrose at 25◦ C under long-day conditions (16 h light,
8 h dark). About 30–50 seeds were sown for each irradiation treatment. After 1.5 months, the survival rate (thenumber of plants having true leaves per total number ofgerminated plants) was determined.
In any LET, survival rates were decreased as the irradiation dose increased (Fig. 1). The eﬀect on survival
rate diﬀered among LET values; it increased as LET
values increased. The Ar ion beam with the LET of
290 keV/µm was the most eﬀective for the reductionof the survival rates, although the eﬀect of higher values of LET will need to be tested. Based on the ruleof thumb that a dose showing around 90% survival is
the most eﬀective in mutation induction, the most eﬀective doses on mutation induction were estimated fromthe current results; 300 Gy, 75 Gy, and 50 Gy for the
C ion (50 keV/µm), Ar ion (184 keV/µm), and Ar ion(290 keV/µm), respectively.
Mutant screening is carried out in the M2 generation
because a phenotype caused by recessive mutation is expressed in the M2 generation. However, we identiﬁed
two mutants from 30 and 16 M1 plants after irradiation
with LETs of 290 keV/µm and 184 keV/µm, respectively.
The former has jagged pistil and petals (Fig. 2B), andthe latter has no yellow spot (Fig. 2C). These phenotypes were observed in all ﬂowers produced on the samebranch. The detection of mutations responsible for these
phenotypes is in progress.
References

1) Y. Kazama et al., Plant J. 92, 1020 (2017).
2) K. Sasaki et al., Plant Biotechnol. 25, 81 (2008).
3) S. Kikuchi et al., Chromosome Res. 14, 665 (2006).
4) R. Aida et al., Plant Sci. 153, 33 (2000).

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III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Behaviors of the Saprophytic Tricholoma matsutake Mutants G1 andAr 59 In Vitro Substrate Cultivation: the former exhibited
Morphological Changes while the latter did not†H. Murata,∗1 T. Yamanaka,∗1 T. Shimokawa,∗1 T. Abe,∗2 H. Ichida,∗2 Y. Hayashi,∗2 and A. Ohta∗1
Tricholoma matsutake produces a specialty mushroom“matsutake” only in a symbiotic association with live
trees in the wild, unlike cultivated mushrooms based onwood-decaying fungi. Another ectomycorrhizal mushroom Lyophyllum shimeji is commercially cultivated to
produce the gourmet mushroom “shimeji” using spawn
substrates comprising barley and saw dust for a few
decades.1) The key to successful L. shimeji fruiting isthat the isolates that can grow as spawn without hostplants and easily produce fruiting bodies using a protocol similar to that used for cultivated mushrooms.1)
We previously reported T. matsutake mutants G1 andAr 59; the former was isolated after irradiating the wildtype NBRC 33136 (a.k.a., Y1) with γ-rays, and the latter was isolated after irradiating the wild-type with anargon-ion beam.2) Both mutants exhibited signiﬁcantly
higher amylase and cellulase activities compared withthe wild-type; however, G1 gained more saprophytic
traits, and it became lethal rather than symbiotic to Pinus densiflora seedlings, whereas Ar 59 remained symbiotic. Because of such phenotypic conversions, we examined if these mutants could exhibit some morphologicalchanges relevant to fruiting body production.

Fig. 1. Morphological changes in T. matsutake G1 after substrate cultivation at 23◦ C for 3 months followed by 16◦ C
for 6 months. (A–C) Lumps arising from the spawn are
indicated by arrows. (D) Cross-section of lump indicatestissue diﬀerentiation. Scale bars 5 mm.
†∗1∗2

Condensed partly from the article in Bulletin of FFPRI 19, 2
153 (2020)
Forest Research and Management Organization
RIKEN Nishina Center

Fig. 2. Mycelial growth of T. matsutake NBRC 33136 (=Y1), Ar 59, and G1 after the substrate cultivation forca. 1 month. Scale bars 10 mm.

The T. matsutake mutants G1 and Ar 59 and theirwild-type NBRC 33136 were separately cultivated witha modiﬁed barley-based substrate. G1 developed several tiny (∼5–7 mmϕ) lumps arising from the spawn(Fig. 1A–C). Cross-sections of the lumps indicated thatthey were not simple aggregates of aerial hyphae but
tissue-like, although some uncertainty remains as towhether the lumps are related to fruiting bodies suchas a remnant of the inner veil around the pileal margin.
The lumps occurred in the G1 spawn in three consecutive independent experiments did not grow into fruiting
bodies. Like G1, Ar 59 grew better in the substrate than
the wild-type (Fig. 2); however unlike G1, it did not exhibit any morphological changes as observed in NBRC
33136.
The lumps developed in the G1 spawn consecutively inthe three independent experiments, and they developed
sporadically for nearly 2 years, while other traits of G1
that characterize this mutant, including colony morphology on agar plates, increased degrading enzymatic activities, and harmful eﬀects on plants, were maintained.2)
Morphological changes associated with sexual reproduction requires an environment desirable for such vital
life cycle events including nutrient availability, temperature, and moisture ﬂuctuations. In the habitat of T.
matsutake, such moisture and temperature ﬂuctuations
occur in the soil and in the atmosphere, even within asingle day. To resolve this problem, we are currently
inducing mutations in T. matsutake G1 by irradiatingwith heavy-ion beams so that we can obtain mutants
that can easily enter the sexual reproduction stage andfruit in artiﬁcial cultivation only with substrates. Thisline of irradiation breeding can eventually yield cultivarsof T. matsutake.
References

1) A. Ohta, Mycoscience 35, 147 (1994).
2) H. Murata et al., Botany 97, 463 (2019).

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IV. OPERATION RECORDS

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Program Advisory Committee meetings for nuclear physics and formaterials and life sciences
H. Ueno,∗1 K. Yoneda,∗1 K. Ishida,∗1 H. Yamazaki,∗1 N. Imai,∗2 Y. X. Watanabe,∗3 K. Yako,∗2 Y. Hirayama,∗3
and M. Iwasaki∗1
There are two Program Advisory Committees(PACs) that are responsible for reviewing submitted
proposals in the fields of nuclear physics (NP-PAC)
and materials and life science (ML-PAC). The NPPAC is co-organized by the RIKEN Nishina Center(RNC), the Center for Nuclear Study (CNS), the University of Tokyo, and the Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies(IPNS), KEK. The NP-PAC reviews experimental programs at RI Beam Factory (RIBF), whereas the MLPAC reviews those at the Rutherford Appleton Laboratory (RAL) and RIBF.

reviewed. As with the NP-PAC, a face-to-face meeting was avoided, and in consideration of the number ofapplications, the review was conducted through email.
For experimental proposals using RIBF, the same evaluation grade as for NP-PAC was adopted. The outcome of the meeting is summarized in Table 2.
The members of the 20th ML-PAC meetingwere A. D. Hillier (Chair, RAL-ISIS), T. Takayanagi(Saitama Univ.) Y. Kobayashi (Univ. of ElectroCommunications) Z. Qin (CAS-IMP), and Y. Miyazawa(Yamagata Univ.).

NP-PAC

Table 1. Summary of the outcome of the 21st NP-PAC
meeting. The sum of the proposals ranked with S and
A is listed in the “approval” columns.

The 21st NP-PAC meeting was held online on December 14–16, 2020 at 9:00 p.m.–2:00 a.m. JST,1)
where 30 proposals were received and reviewed. This
was the first online meeting conducted owing to thetravel restrictions imposed by COVID-19. The PAC
members watched the presentation videos prepared by
the applicants in advance, and only conducting a question and answer session with the applicants on the dayof the meeting, thus streamlining the meeting. Proposals were evaluated on the basis of five grades: S,
A, B, C, and D. Those with a grade of B or higher
were approved, of which those with a rating of S or A
will be given priority for beamtime allocation. Table 1
summarizes the outcome of the 21st NP-PAC meeting.
The members of the 21st NP-PAC meeting were
R. V. F. Janssens (Chair, Univ. of North Carolina), D. Ackermann (GANIL), N. Aoi (Osaka
Univ.), M. J. G. Borge (CSIC, Madrid), R. Charity (Washington Univ. in St. Louis), A. O. Macchiavelli (LBNL), G. Martinez-Pinedo (GSI/TU Darmstadt), I. Moore (Univ. of Jyväskylä) D. J. Morrissey(MSU), H. Nakada (Chiba Univ.), A. Obertelli (TU
Darmstadt), T. Saito (RIKEN), K. Sekiguchi (Tohoku
Univ.), P. J. Woods (Univ. of Edinburgh), A. Vitturi(Univ. of Padova), and X. Zhou (IMP).

21st NP-PAC (December 14–16, 2020)
beam time (days)
proposal number
request∗1∗2∗3

requestapproval

RILAC (GARIS, ...)AVF (CRIB, ...)RRC (KISS, ...)BigRIPS/ZD
SHARAQ/OEDO
SAMURAI
Rare RI Ring

5
7
2
7
1
9
1

2
4
1
3
0
4
0

61.5
85.5
12.5
56.5
7.5
81.5
12

15
51
6
16
0
32.5
0

( BigRIPS-related
Total

18
32

7
14

157.5
317

48.5 )
120.5

Table 2. Summary of the outcome of the 20th ML-PAC
meeting. For the RIBF proposals, the sum of the proposals ranked with S and A is listed in the “approval”
columns.
20th ML-PAC (January 2021)
beam time (days)
proposal number
request

ML-PACThe 20th ML-PAC meeting was held in January
2021.2) At this meeting, only proposals for the use of
the RIBF were solicited, and not proposals for the useof muon beams at RAL owing to the RAL-ISIS long
shutdown. All the five submitted RIBF proposals wereapproval

RAL
RIBF

5

Total

5

approval

requestapproval—no call for proposals—
5
20
5

20

17
17

References

1) http://www.nishina.riken.jp/RIBF/NP-PAC/ .
2) http://www.nishina.riken.jp/RIBF/ML-PAC/ .

RIKEN Nishina Center
Center for Nuclear Study, the University of Tokyo
Wako Nuclear Science Center (WNSC), IPNS, KEK- 181 -

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Electric power status of RIKEN Nishina Center in 2020
E. Ikezawa,∗1 M. Kidera,∗1 Y. Watanabe,∗1 H. Yamasawa,∗1 and O. Kamigaito∗1
The average hourly electrical power consumption of
the RIKEN Nishina Center (RNC) for each day in 2020is shown in Fig. 1. The total electrical power consumption by RNC in 2020 was 56,549 MWh, which
was 1% lower than that in 2019. When the experiment using an argon (40 Ar) beam accelerated by the
AVF + RRC + IRC was conducted on July 1, 2020, themaximum commercial electrical power supply to the
RIKEN Wako campus reached 20.4 MW with a cogeneration system (CGS) output of 6.0 MW. When RI
Beam Factory (RIBF) experiments using an uranium(238 U) beam were conducted on October 23, 2020,
the maximum electrical power consumption of RNC
reached 17.5 MW.

Fig. 1. Average hourly electrical power consumption of RNC for each day in 2020.

∗1

RIKEN Nishina Center- 182 -

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

RILAC operation
K. Oyamada,∗2 E. Ikezawa,∗1 M. Kase,∗1 T. Nakagawa,∗1 N. Sakamoto,∗1 H. Okuno,∗1 N. Fukunishi,∗1
Y. Watanabe,∗1 M. Komiyama,∗1 A. Uchiyama,∗1 T. Maie,∗1 M. Nagase,∗1 M. Fujimaki,∗1 T. Watanabe,∗1
H. Hasebe,∗1 H. Imao,∗1 K. Ozeki,∗1 K. Suda,∗1 Y. Higurashi,∗1 K. Yamada,∗1 S. Watanabe,∗1 M. Kidera,∗1
T. Nagatomo,∗1 K. Kumagai,∗1 T. Nishi,∗1 T. Ohki,∗2 H. Yamauchi,∗2 M. Tamura,∗2 A. Yusa,∗2 K. Kaneko,∗2
and O. Kamigaito∗1
The RILAC saw the commissioning of a superconducting RILAC (SRILAC) from January to March
2020. Some statistics regarding the operation of RILAC from January 1 to December 31, 2020 are presented in Table 1. Table 2 lists the beam service times
in the standalone mode of RILAC in 2020. The details
are described elsewhere in this progress report.
We performed the following maintenance works during the reporting period.

We faced the following mechanical problems during
the reporting period.
(1) The cooling parts of drift tubes in RILAC cavities No. 2, No. 4, and No. 5 had a coolant leak.
We repaired the parts with a repair material.
(2) The plate DC power supply for a tetrode(SIEMENS-RS2012CJ) in the rf amplifier of RILAC No. 5 malfunctioned. It was fixed by replacing the electric parts.
(3) Water was found to have splashed in the rf power
feeder of RILAC cavity No. 1 because of leakage
from a cooling pipe for the coaxial conductor.
We replaced it with new ones.
(4) The water cooling pipe of the RFQ cavity had awater leak. We repaired the cooling pipe with arepair material.
(5) A section of the air-pressure pipe for the contact
fingers of the rf shorting plate in RILAC cavity
No. 6 had a vacuum leak because of a deteriorated O-ring. We replaced it with a new one.

(1) In the radio-frequency(rf) systems, DC highvoltage power supplies were subjected to annual
inspection. The major components with mechanical parts were subjected to simple inspection.
(2) The water pumps were subjected to simple inspection. All cooling towers were subjected tomonthly inspection.
(3) All turbomolecular pumps were subjected tosimple inspection. Cryogenic pumps used forcavities No. 1, No. 2, A1, and A2 were overhauled.
(4) All magnet power supplies were subjected tosimple inspection.
Table 1. Statistics of RILAC operation from January 1 to
December 31, 2020.
Operation time of RILAC

2878.3 h

Beam course

Total time (h)%Mechanical problem

161.3 he11997.37

50.6

Standalone RILAC

1970.6 he2

973.23

49.4

Injection into RRC

0.0 h

Total

1970.60

100.0

Total beam service time of RILAC∗1∗2

Table 2. Beam service times of RILAC in the standalone
mode in 2020.

1970.6 h

RIKEN Nishina Center
SHI Accelerator Service Ltd.

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1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Operation report on the ring cyclotrons in the RIBF accelerator
complex
S. Ishikawa,∗1 K. Suda,∗2 T. Dantsuka,∗2 M. Fujimaki,∗2 T. Fujinawa,∗2 N. Fukunishi,∗2 S. Fukuzawa,∗1
M. Hamanaka,∗1 H. Hasebe,∗2 Y. Higurashi,∗2 E. Ikezawa,∗2 H. Imao,∗2 O. Kamigaito,∗2 Y. Kanai,∗2 M. Kase,∗2
M. Kidera,∗2 K. Kobayashi,∗1 M. Komiyama,∗2 R. Koyama,∗1 K. Kumagai,∗2 T. Maie,∗2 T. Nagatomo,∗2
T. Nakagawa,∗2 M. Nakamura,∗2 T. Nakamura,∗1 M. Nishida,∗1 M. Nishimura,∗1 J. Ohnishi,∗2 H. Okuno,∗2
K. Ozeki,∗2 N. Sakamoto,∗2 J. Shibata,∗1 N. Tsukiori,∗1 A. Uchiyama,∗2 S. Watanabe,∗2 T. Watanabe,∗2
Y. Watanabe,∗2 K. Yamada,∗2 K. Yadomi,∗1 and H. Yamasawa∗2
The operation report of the ring cyclotrons in the
RIBF accelerator complex from Jan. to Dec. 2020 is presented. Table 1 presents a summary of the beams accelerated by these cyclotrons. The availability is defined as
the ratio of the actual beam service time to the scheduled beam service time, which is an index of the stable
Operation of accelerators. In calculating each availability, for beam service times that were completed earlier
than scheduled, the scheduled times are identified withthe actual times. Multiple experiments supplying identical beams are treated as one and presented in a row. The
total actual beam service time was 1639.1 h. The ratioof the beam service times between the experiments conducted in the old facility (RARF) and the new facility(RIBF) was 54:46.
In the RARF, the actual beam service time was884.5 h, and the availability was 95.7%. In the RIBF, twobeam services were carried out. The actual beam service
time was 754.6 h, and the availability was 89.8%. Due tothe declaration of a state of emergency in relation to the
COVID-19 infection, experiments were cancelled for twomonths from April. Vacuum leak occurred at the RRC
resonator No.1 in May, and weld repair was carried out.
Due to the repair, all the beam service times scheduledin June were cancelled.
In the 238 U beam supply for eight experiments, weachieved a maximum beam intensity of 116 particle nA,
which is 1.2 times higher than that of the previous beamservice in Nov. 2019. The highest record was obtained
due to the upgrade of the RRC resonators1,2) and thechange in gap spacing of the RRC-EDC in 2018, andthe relocation of the fRC-EIC in 2020. The beam supply
was stopped for 8 days due to the repair of the SRC-EDC
and SRC-Resonator 2 (RES2). A septum electrode of the
EDC was damaged by a loss of the high intensity beams.
After the exchange of the EDC, a beam intensity was
reduced to 70 particle nA to prevent EDC damage again.
RES2 could not be excited because the contact fingers
for the coarse tuning plate was partially burned out by ahigh RF input power. The damaged contact fingers were
exchanged. The beam service time was 510.5 h, and theavailability was 81.8%.
In the 70 Zn beam supply for three experiments, werecorded the highest beam intensity of 782 particle nA,
which is 3.1 times higher than that of the previous beamservice in May 2017. The increase of beam intensity wasachieved due to the improvement of the oven in the ion
source and of the beam tuning based on the beam supply parameters obtained by a scaling of that for 238 U.
The beam service time was 244.2 h, and the availability
was 113.1% because the tuning time was shorter thanplanned and the experiment was started ahead of schedule.
References

1) K. Yamada et al., RIKEN Accel. Prog. Rep. 52, 13 (2019).
2) K. Yamada et al., J. Part. Accel. Soc. Jpn. 17, 159 (2020).

Table 1. Summary of the accelerated beams in 2020.
Energy Acceleration
Beam
particle (MeV/nucleon)
mode
C
N
20
Ne
22
Ne
40
Ar
56
Fe
84
Kr
4
He
12
14

RARF

136
40
70

RIBF

∗1
∗2

135
135
135
70
95
90
70
7.25

Xe 10.75

Ar
Zn

160
345

U

345

238

AVF-RRCRILAC2-RRC
AVF-RRC-IRC
RILAC2-RRC-fRC-IRC-SRC

Beam intensity(particle nA)
Requested Actual
E5B (Biology)
1450.0
E3B (RI production)
500
571.0
ESB (Biology)1
270.0
E6 (Material)
250
300.0
E5A (Material)
1
26.5
ESB (Biology)
1
3.5
E5A (Material)
1
9.7
A10 (MS)
18300
590.0
E2B (KEK/KISS)
250
325.0
/E3A (Material)
E5B (Biology)
1
23.3
BigRIPS/ZD
>600
782.0
BigRIPS/ZD
>60
116.3
/Rare-RI Ring
Total
Beam course

Beam service
Availability
time (h)(%)
Scheduled Actual
27.5
9.2
100.0
48.0
49.5
103.2
4.0
2.6
100.0
108.0
107.9
99.9
84.0
86.1
102.5
6.0
2.1
100.0
240.0
205.8
85.6
33.6
33.6
100.0
381.0

371.5

97.5

23.5
216.0

16.2
244.2

100.0
113.1

624.0

510.5

81.8

1795.6

1639.1

92.9

SHI Accelerator Service Ltd.
RIKEN Nishina Center- 184 -

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Operation report on the RIKEN AVF cyclotron for 2020
M. Nishida,∗1 K. Ozeki,∗2 M. Fujimaki,∗2 N. Fukunishi,∗2 S. Fukuzawa,∗1 A. Goto,∗2 H. Hasebe,∗2
M. Hamanaka,∗1 Y. Higurashi,∗2 E. Ikezawa,∗2 H. Imao,∗2 S. Ishikawa,∗1 K. Kamakura,∗3 O. Kamigaito,∗2
M. Kase,∗2 M. Kidera,∗2 K. kobayashi,∗1 M. Komiyama,∗2 Y. Kotaka,∗3 R. Koyama,∗1 K. Kumagai,∗2 T. Maie,∗2
T. Nagatomo,∗2 T. Nakagawa,∗2 T. Nakamura,∗1 M. Nishimura,∗1 J. Ohnishi,∗2 H. Okuno,∗2 Y. Oshiro,∗3
N. Sakamoto,∗2 J. Shibata,∗1 K. Suda,∗2 N. Tsukiori,∗1 A. Uchiyama,∗2 S. Watanabe,∗2 T. Watanabe,∗2
Y. Watanabe,∗2 K. Yadomi,∗1 and K. Yamada∗2
The yearly report on the operation of the RIKEN
AVF cyclotron (denoted as AVF hereafter) for the period January-December 2020 is presented. AVF delivered beams to five courses for stand-alone operations:
C01 (machine study), C03 (radioactive isotope (RI) production), C12 (CNS, RI production), E7A (CRIB), andE7B (RI production, student experiment). On the other
hand, when AVF was used as an injector of the RIKEN
Ring Cyclotron (RRC), beams were delivered to two
courses: RRC-RARF and RRC-IRC-E5. Figure 1 showsthe experimental apparatuses around AVF.
Thus far, AVF was equipped with three ion sources
to deliver various ion beams: the superconducting electron cyclotron resonance ion source (SC ECRIS), HyperECRIS, and polarized ion source (PIS, only used for polarized deuterons). However, a GM refrigerator used forcooling the superconducting mirror coils in SC ECRIS
had become too old. Therefore, SC ECRIS was replacedwith the 18 GHz ECRIS that had been used at RILAC,
and beam deliveries from the 18 GHz ECRIS commenced
in January.
The yearly operation statistics are presented in Tables 1 and 2. In a total operation time of 2702 h, 1520 h
was spent for stand-alone operation, and 1182 h wasspent for injection to RRC. Because of the declaration ofa state of emergency due to the COVID-19 outbreak, allbeam times scheduled for April and May were canceled.

This is a main reason why the operation time for standalone operation in this year is considerably less than thatin the previous year. In addition, an RI production experiment using 30-MeV protons was conducted for the
first time in June.
Table 1. Comparison of AVF operation statistics with thatin the previous year.
AVF stand-alone operation
Tuning of AVF[h]Trouble of AVF [h]C01 M. S.
[h]C03 exp.
[h]
C12 exp.
[h]
E7A exp.
[h]
E7B exp.
[h]
Sub total[h]
AVF operation as injector of RRC
Tuning of AVF[h]Trouble of AVF [h]RRC-RARF exp. [h]RRC-RIBF exp. [h]Sub total
[h]
Total
[h]

2019
1314
0
0
873
36
789
152
3166
2019
117
0
320
0
437
3603

2020
744
1
12
631
18
12
101
1520
2020
178
5
999
0
1182
2702

Table 2. AVF beam list in 2020.
Energy(MeV/nucleon)
Stand-alone operation
Particle

Course

p
12.00
C03
p
19.00
C12
p
30.00
C01, C03
d
12.00
C03
α
6.50
E7B
α
7.25
C03, E7B
α
12.50
C03
7
Li
6.00
C03
16
O
6.80
E7A
18
O
7.00
C12
19
F
6.30
C03
Operation as injector of RRC
C
N
20
Ne
22
Ne
40
Ar
40
Ar
56
Fe
84
Kr
12
14

Fig. 1. Overview of the AVF cyclotron with ion sources, eachexperimental course, and beam transport line to RRC.
∗1
∗2
∗3

SHI Accelerator Service Ltd.
RIKEN Nishina Center
Center for Nuclear Study, the University of Tokyo- 185 -

7.00
7.00
7.00
3.97
3.80
5.20
5.00
3.97

RRC-RARF
RRC-RARF
RRC-RARF
RRC-RARF
RRC-IRC-RARF
RRC-RARF
RRC-RARF
RRC-RARF

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Present status of liquid-helium supply and recovery system
T. Dantsuka,∗1 H. Okuno,∗1 M. Nakamura,∗1 S. Tsuruma,∗1 M. Takahashi,∗1 M. Kuroiwa,∗1 M. Ohshima,∗2
H. Miura,∗2 H. Shiraki,∗2 H. Hirai,∗2 K. Kimura,∗2 M. Haneda,∗2 A. Mikami,∗2 M. Nagano,∗2 and H. Hazama∗2
The liquid-helium supply and recovery system,1)
which can produce liquid helium at a liquefaction rateof 200 L/h from pure helium gas, has been under stable
operation since the beginning of April 2001. However,as operation failure due to deterioration over time has
increased in recent years, duplication of the liqueﬁer
was conducted in 2017. The new liqueﬁer can produce
liquid helium at a liquefaction rate of 220 L/h frompure helium gas. Although the older helium liqueﬁer
has been failing since the summer of 2018, with the
new helium liqueﬁer, a constant supply of liquid helium can be enabled. The older helium liqueﬁer was
repaired in February 2020.
The volumes of liquid helium supplied each year
from 2001 to 2019 are illustrated in Fig. 1. From 2001
to 2013, there was a gradual increase in the supplied
volume, with two declines observed in 2009 and 2011.
In 2014, the supplied volume decreased owing to a system malfunction. However, in 2015, the supplied volume returned to its original value. In 2016, the supplied volume decreased but slightly increased in 2017.
In 2018, the supply volume increased signiﬁcantly. In
2019, we supplied approximately 140,000 L of liquid
200000180000160000Liquid Helium (L)140000120000100000helium despite the high price of helium gas.
However, the purity of helium gas recovered fromthe laboratories gradually deteriorated. At present,
the impurity concentration in the recovered gas is approximately 1000 ppm. The impurity concentration
does not aﬀect the liquefaction operation, but is necessary to observe the progress.
Furthermore, the volume of helium gas recoveredfrom each building in the Wako campus as well as thevolume transported to the liquid helium supply and recovery system were measured. The recovery eﬃciency,
which is deﬁned as the ratio of the amount of recovered
helium gas to the amount of supplied liquid helium,
was calculated. The recovery eﬃciency for the buildings on the south side of the Wako campus, namely the
Cooperation Center building of the Advanced Device
Laboratory, Chemistry and Material Physics building,and Nanoscience Joint Laboratory building, increased
to approximately 95%.
Reference

1) K. Ikegami et al., RIKEN Accel. Prog. Rep. 34, 349(2001).

Magne�c Materials Laboratory
Low Temperature Physics Laboratory
Advanced Device Laboratory
Condensed Molecular Materials Laboratory
Molecular Characteriza�on Team
Surface and Interface Science Laboratory
Surface Chemistry Laboratory
Radioac�ve IsotopePhysics Laboratory
Exploratory Materials Team
Quantum Func�onal System Research Group
Emergent Phenomena Measurement Research Team
Other laboratories

80000
60000
40000
20000
0

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

Fiscal Year
Fig. 1.
∗1∗2

Volumes of liquid helium supplied to the various laboratories for each fiscal year from 2001 to 2019.

RIKEN Nishina Center
Nippon Air Conditioning Service K.K- 186 -

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Operation of the BigRIPS cryogenic plant
K. Kusaka,∗1 M. Ohtake,∗1 K. Yoshida,∗1 M. Ohshima,∗2 A. Mikami,∗2 H. Hazama,∗2 H. Miura,∗2 H. Shiraki,∗2
H. Hirai,∗2 K. Kimura,∗2 M. Nagano,∗2 H. Shiba,∗2 and S. Okada∗2
We operated the BigRIPS cryogenic plant for only
2,838 h in 2020 because the spring beam time was cancelled due to the declaration of state of emergency over
COVID-19. The operation periods were from March 4
to April 24 and from September 25 to December 21. After the long shutdown of the RIBF facility, we started
cooling down the warmed-up superconducting triplet
quadrupole (STQ) magnets on October 2.
After successful cooldown operation, we excited STQ1
magnet with stepwise ramping. The STQ1 magnet isan air-core-type superconducting magnet and consistsof three quadrupole coils, P1, P2, and P3, and one
hexapole coil, SX.1) In contrast to the other STQ’s case,
we excite the coils P1, P2, and P3 separately after cooling down. Before simultaneous excitation of all coils, thecoils P1, P3, and SX coils were excited up to their nominal current of 740 A, 628 A, and 32.5 A, respectively.
However, when we ramped P2 from 610 A to 620 A, it
quenched with a current of 620 A, which is 8 A less than
the nominal current. This was the fourth quench of P2,
and we consider that it a training quench.
Except for the quenching of P2, we operated the cryogenic system without any trouble. We measured thevibrations of the compressor unit and observed low oil
contamination in helium gas during operations. The total operation time of the compressor unit was 75,060 h.
Figure 1 shows the vibration acceleration in the vertical and horizontal directions as a function of the total operation time. We have been measuring the vibrations of the compressor at the high-pressure and lowpressure sides since 2015. Two rapid increases of the vibration acceleration at operation times of 59,000 h and71,000 h are indicated by arrows. They were causedby the damage of the bearing unit in December 20162)
and June 2019.3) The vibration acceleration mostly remained below 8 m/s2 during the operation period. We

Fig. 1. Vibration acceleration of the compressor unit. The
operation period in 2020 is indicated.
∗1∗2

RIKEN Nishina Center
Nippon Air Conditioning Services Co., Ltd.

Fig. 2. Oil contamination at the entrance of the third coalescer vessel.

consider that the exceptionally large value of 10.3 m/s2
at 74,883 h in the vertical direction at the high-pressure
side is due to measurement error.
We measured the operation interval of the drain valvesof the coalescer vessels in the compressor unit in order toevaluate the oil contamination level. We have replaced
coalescer ﬁlter elements 5 times since 2008. The operation periods of the replaced ﬁlter elements were from
August 2008 to July 2010, from September 2010 to July
2012, from September 2012 to July 2014, from September 2014 to July 2016, and from September 2016 to June
2019. Figure 2 shows an estimate of the oil contamination level at the entrance of the third coalescer vessel
as a function of the coalescer ﬁlter operation time. The
navy-blue, green, and yellow diamonds represent the estimates for the ﬁrst, second, and third elements, respectively. The fourth and the ﬁfth elements are shown withpink and red diamonds, respectively. The oil contamination values measured using the oil check kit are also
shown. The open triangles, squares, and circles represent the results for the ﬁrst, second, and third elements,
respectively. The results for the fourth and the ﬁfth elements are indicated by the open diamonds and circles,
respectively. The drain valve of the coalescer vessel operated only once in 2020 after the last maintenance in
2019. The operation time and the estimate of the oil
contamination level for the current coalescer are 3550 h
and 0.05 wt.ppm, respectively, as shown by the brown
diamond in Fig. 2.
Both estimations of the oil contamination level areconsistent with each other, and the performance eﬃciency of the ﬁfth set of ﬁlter elements seems to be better
than that of the others.
References

1) K. Kusaka et al., IEEE Trans. Appl. Supercond. 18, 240(2008).
2) K. Kusaka et al., RIKEN Accel. Prog. Rep. 50, 285 (2017).
3) K. Kusaka et al., RIKEN Accel. Prog. Rep. 53, 222 (2019).

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IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Radiation safety management at RIBF
K. Tanaka,∗1 Y. Uwamino,∗1,∗2 H. Sakamoto,∗1 R. Hirunuma-Higurashi,∗1 H. Mukai,∗3 A. Akashio,∗1
T. Okayasu,∗1 R. Suzuki,∗4 M. Takekoshi,∗4 T. Sato,∗4 K. Igarashi,∗1 S. Iizuka,∗1 N. Usudate,∗1 and Y. Shioda∗1
The results of radiation monitoring at RIBF, carried out at the border of the facility and the radiationcontrolled area are reported. The residual doses along
the accelerator setups are also presented. In 2020,
a 238 U beam of approximately 345 MeV/nucleon wasprovided at an intensity of 70 particle nA in Octoberand November. Subsequently, a 70 Zn beam of approximately 345 MeV/nucleon of 800 particle nA was usedin November and December.
The dose rates at the boundary of the radiationcontrolled area were monitored. Neutron and γ-ray
monitors were used at three locations: the roofs of theRRC, IRC, and BigRIPS. Figure 1 shows the annual
neutron dose at these positions. In 2020, even the highest annual dose of 9 µSv/y at the IRC roof was lower
than the legal limit of 5.2 mSv/y. The dose at the
IRC roof sensitive to IRC and SRC operation time. In
2020, these operated for only three months. Therefore,
the annual dose of the IRC roof was small.
The dose rates at the site boundary, where the legal
limit is 1 mSv/y, were monitored by neutron and γ-ray
monitors. The detection limits of the neutron monitor
were 2 µSv/y and 0.01 µSv/h. The annual dose in 2020
was 3.6 µSv of neutron but less than the hourly detection limits any time after the background correction.
The detection limit of the γ-ray monitor was 8 µSv/y.
The annual dose of the γ-ray was lower than the limit,
which is considerably lower than the legal limit.
The residual radioactivity at the deflectors of the cy-

Fig. 1. Radiation dose at the boundary of the radiationcontrolled area.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Japan Radioisotope Association
Japan Environment Research Corporation
Daiwa Atomic Engineering Corporation

Fig. 2. Dose rates of residual radioactivity at the deflectorsof 5 cyclotrons.

clotrons was measured just before maintenance work.
The residual dose depends on factors such as thebeam intensity, accelerator operation time, and cooling time. The data were obtained from the cyclotrons
maintenance works, when the deflectors were accessible. Therefore, the cooling times have not been constant. The dose rates from 1986 are shown in Fig. 2.
The dose rates for fRC, IRC, and SRC are shown forthe years after 2006, when the RIBF operation started.
For AVF, the dose rate increased in 2006 because theradioisotope production was started and the beam intensity increased.
The residual radioactivity along the beam lines wasmeasured after almost every experiment. Figure 3
shows the locations of the measurement points wherehigh residual doses were observed. Table 1 lists thedose rates, beam conditions, and cooling time at
the measurement points. The maximum dose was
46 mSv/h at point 23, which is in the vicinity of thebeam dump of BigRIPS.
Although the radioactivity in the closed cooling system at BigRIPS is reported annually, it is omitted because the radioactivity was not measured in 2020.
The E-learning module, which can be accessed anytime and from anywhere (even from outside RIKEN),
has been used for the re-training of the radiation workers at RIBF. Approximately 580 radiation workers
have completed the training in 2020. This is lower than
the number in recent years because of the COVID-19
restriction of immigration and etc.
As described above, radiation management to comply with lows and to keep radiation levels as low as
possible has been carried out successfully.

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IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

Table 1. Dose rates measured at beam lines in 2020.
Points 1–24 indicate the locations where measurements
were taken as shown in Fig. 3.

Point

Dose
rate
(µSv/h)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

Fig. 3. Layout of the beam lines at RIBF. The measurement locations listed in Table 1 are indicated.

2- 189 -

100
139
250
100
188
4000
2500
110
200
7000
14000
120
150
581
110
130
3300
6000
30000
530
280
230

Date
(M/D)

8/12
8/12
8/12
12/28
8/12
12/24
12/24
8/12
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24
12/24

Particle
α
α
α
α
C-12
Zn-70
Zn-70
Ar-40
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70
Zn-70

Energy Intensity(A MeV)

(pnA)

7.3
7.3
7.3
6.5
135
50
50
66
114
345
345
345
345
345
345
345
345
345
345
345
345
345

10000
10000
10000
10
2
990
990
24
800
760
760
760
760
760
760
760
760
760
760
760
760
760

Cooling
time
(h)

554
554
554
281
882
270
270
979
270
271
271
270
270
270
270
271
271
271
271
271
271
271

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Operation of the Pelletron tandem accelerator
T. Ikeda,∗1 M. Hamagaki,∗1 and H. Sato∗1
Ion beams with an energy range of MeV are available
from the tandem accelerator (Pelletron 5SDH-2, 1.7 MVmax.) in the Nishina R&D Building, which is managed
by the Detector Team of RNC. This accelerator is also
registered as joint-use equipment in Wako campus formaterial analysis. As shown in the configuration of theaccelerator and beam lines (Fig. 1), two ion sources areavailable. One is the RF charge-exchange ion source,called Alphatross, for experiments using He ion beams.
The other is the Source of Negative Ions by Cesium Sputtering (SNICS), which can generate almost all other ions.
Thus far, ion species of H, He, Li, B, C, N, O, Si, Ti, Ni,
Cu, and Au have been accelerated at 0.5–1.7 MV.
There are four beam lines named BL-E/Wnn (nn denotes the bending angle). In 2020, BL-E15 was restarted
for a user group in the field of material science to perform the analysis of Rutherford backscattering (RBS)
spectrometry. In the west side, BL-W15 (multipurposeline) was used for a micrometer-sized ion beam based on
glass capillary optics with an end window. This was forhorizontal microbeam irradiation experiments. The irradiation port was developed to have a simple connection
to the BL-W15 line. It took a few hours to mount the
microbeam port, including the vacuum pumping. At theend of 2020, BL-W30 was under construction for new
microbeam irradiation studies of the biological samples
in air or solution.
From January 1 to December 31, 2020, the total machine time (MT) including a machine study was only

Fig. 1. Pelletron tandem accelerator and beam lines in the
Nishina R&D Building.

Fig. 2. (a) Apparatus for the RBS spectrometry connectedto the Pelletron accelerator. (b) Online analysis.
∗1

RIKEN Nishina Center

Table 1. Beam conditions and experiments conducted in thetandem accelerator.
Ion

Energy
[MeV]

H+
He2+

2.0–3.0
2.28

14Beam current
Operation
Experiment time [days]
[pnA]
1–120
0.25–5

Irradiation
RBS

8
4

Table 2. Approved conditions at the RIKEN Pelletron.
Ion

Maximum Energy

Ion

Maximum Energy

H
He
Li/Be

3.5 MeV
5.1 MeV
6.8 MeV

B
C
other

10.2 MeV
12 MeV
0.6 MeV/nucleon

12 days, where the condition test of the ion sources is
not included. In addition to the total MT, development
activities were suppressed in 2020.
The ion species accelerated in this year were the lightions H+ and He2+ with energies ranging from 2.0 to
3.0 MeV, as summarized in Table 1. The RBS experiments always used the energy of 2.28 MeV, following
convention. Points 1–6 below list the studies that used
the beam lines, along with the number of days of MT.
All the studies, including those with zero days of MT,
were routine experiments before 2020.
(1) Microbeam performance study with H ions using
glass capillaries at BL-W15 and W301,2) (7 days)(2) Microbeam (He ion) irradiation for single cells at
BL-W303) (0 days)(3) RBS/ERDA experiments using carbon ions (4days)(4) Educational experiment of proton capture by carbon/boron nucleus for Nishina School (0 days)(5) Development of charged-particle/gamma-ray detector to be used for RIBF experiments (0 days)(6) Other development using protons (1 day)
The maximum energies of accelerated ions are summarized in Table 2. Since 2019, the regulation of the maximum energy of carbon ions was changed from 7.2 MeV
to 11.9 MeV, where 12 C6+ is accelerated with the fullvoltage of 1.7 MV.
A commercial RBS apparatus (Charles Evans and Associates Model RBS-400) is shown in Fig. 2(a). A goniometer to rotate the sample is fixed inside the chamber,which is in a vacuum level of the order of 10−7 Torr. The
He2+ beam intensity was less than 10 nA. Improvementsin the vacuum level and beam intensity are in progress.
References

1) T. Ikeda et al., Nucl. Instrum. Methods Phys. Res. B 470,
42 (2020).
2) T. Ikeda, Quantum Beam Sci. 4, 22 (2020).
3) T. Ikeda et al., RIKEN Accel. Prog. Rep. 53, 215 (2020).

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IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Fee-based activities of the Industrial Application Research TeamA. Yoshida,∗1 T. Kambara,∗1 H. Haba,∗1 A. Nambu,∗1 and D. Mori∗1
The fee-based activities of the Industrial Application
Research Team in 2020, which are the utilization ofheavy-ion beams in the industry and the distributionof radioisotopes, are summarized below.
RIKEN Nishina Center allows the use of the AVF
cyclotron, RILAC, and RIKEN Ring Cyclotron (RRC)
by private companies in Japan for a fee.1) At present,
the main users are semiconductor companies that irradiate space-use semiconductor devices with Ar, Kr,
and Xe ions from the RRC to simulate single-event
eﬀects due to the heavy-ion components of cosmic radiation. Proposals for beam utilization are reviewed
by a program advisory committee dedicated to industrial use (InPAC). In July 2020, InPAC reviewed andapproved via e-mail three proposals that were in continuation to previously approved proposals and held its
10th meeting online, where it reviewed and approved
two new proposals. In 2020, six companies executed
eleven fee-based beamtimes, seven of which utilized a
Kr beam with a total beam time of 153 h and four
utilized an Ar beam with a total beam time of 73 h.
In response to the users’ demand, we are preparing to
supply C ions and considering the supply of Xe ionswith higher energies.
Since 2007, RIKEN has distributed radioisotopes(RIs) to users in Japan for a fee in collaboration with
the Japan Radioisotope Association2) (JRIA). The nuclides are 65 Zn (T1/2 = 244 days), 109 Cd (T1/2 = 463
days), 88 Y (T1/2 = 107 days), 85 Sr (T1/2 = 65 days),and 67 Cu (T1/2 = 61.8 hours) produced at the AVF cyclotron by the Nuclear Chemistry Research Team. According to a material transfer agreement (MTA) drawn
between JRIA and RIKEN, JRIA mediates the transaction of the RIs and distributes them to users. 65 Zn
and 109 Cd are delivered approximately two weeks after
the acceptance of an order. 85 Sr, 88 Y, and 67 Cu, whichhave short half-lives, are not stocked like 65 Zn and109
Cd but are instead produced in a scheduled beamtime after an order is accepted. Therefore, they aredelivered two months or more after an order. Details
can be found in the online ordering system J-RAM3)of JRIA.
In 2020, we delivered one shipment of 109 Cd with anactivity of 10 MBq, three of 65 Zn with a total activityof 12 MBq, two of 88 Y with a total activity of 2 MBq,
and two of 85 Sr with a total activity of 3 MBq. The
ﬁnal recipients of the RIs were four universities, one
private company, and one medical research center.
Figure 1 shows the yearly trends in the number oforders and the amounts of distributed RIs. Comparedwith 2019, the amounts of distributed 109 Cd, 65 Zn, and∗1

Sr increased, that of distributed 67 Cu decreased, andthat of distributed 88 Y remained the same. During
the past 10 years, the demand for long-lived RIs has
drastically decreased, whereas that for short-lived RIs
is increasing.

85

Fig. 1. Number of orders (upper) and amounts (lower) of
the RIs distributed yearly from 2007 to 2020. The distribution of 88 Y started in 2010, that of 85 Sr in 2015,
and that of 67 Cu in 2018.

References

1) http://ribf.riken.jp/sisetu-kyoyo/ (Japanese).
2) http://www.jrias.or.jp/ (Japanese),
http://www.jrias.or.jp/e/ (English).
3) https://j-ram.org (Japanese).

RIKEN Nishina Center- 191 -

1

IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Activity report of the second-term (2014–2021) RIBF Theory Forum
T. Abe,∗1 Y. Aritomo,∗2 W. Horiuchi,∗3 M. Kimura,∗3 H. -Z. Liang,∗4 T. Matsumoto,∗5 F. Minato,∗6
K. Nakazato,∗7 N. Nishimura,∗8 and K. Yoshida∗9
Preface
Recent advancements in radioactive-isotope (RI)
beam technology have opened up the research ﬁeld of
the physics of exotic nuclei. Since the RIBF started operation in 2007, our experimental capabilities have beensigniﬁcantly expanded, including neutron- and protonrich nuclei as well as superheavies. With increasing
experimental data for a vast mass region of the nuclear
chart, nuclear structure and reaction theories are expected to play a more important role in interpretingthe data and in profoundly understanding atomic nuclei. A mission of the second-term Theory Forum (TF2)
is to discuss physics in the future of RIBF. Taking overthe discussions in the ﬁrst-term Theory Forum (TF1)(2006–2014), we have been working through various activities. Although most of the members were renewed,
Dr. Y. Utsuno, Dr. K. Ogata, and Dr. S. Wanajo acted
as mediators to bridge the activities of TF1 and TF2.
We would like to express our gratitude to them. This report summarizes our activities over the last seven years
to facilitate handover to the third-term Theory Forum.
Because of the limited space in this progress report, details about our activities are provided on a web page.1)
Short reports from WGs
TF2 was divided into several working groups (WGs)
to discuss physics cases intensively. We also had intergroup discussions regularly. Here, we present shortsummaries of these activities, which are categorized into
three subjects: nuclear astrophysics, the physics of superheavy elements, and the physics of nuclear manybody problems. More details on each subject can befound on the website.
Nuclear astrophysics: r-process, EOS, and nuclear matterIn the ﬁeld of nuclear astrophysics, discussions werestarted with two WGs. The primary purpose of the
r-process WG was to improve the current theoretical
calculations of nuclear properties, including the masses,
decay half-lives, neutron-capture reaction rates, and nuclear ﬁssion rates for the r-process nucleosynthesis cal∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9

RIKEN Nishina Center
Kindai University
Department of Physics, Hokkaido University
Department of Physics, the University of Tokyo
Department of Physics, Kyushu University
JAEA
Faculty of Arts and Science, Kyushu University
Astrophysical Big Bang Laboratory, RIKEN
Department of Physics, Kyoto University

culations. The possibility of updating these rates usedin the nucleosynthesis community was discussed, particularly to reﬂect the latest results from nuclear theory
groups in Japan. A novel mass model based on theBayesian neural-network method was proposed to assess the model uncertainty and to evaluate the impact
of new measurements on the prediction. The signiﬁcance of direct reaction on the neutron capture rates
was investigated through a microscopic approach. Furthermore, we found a compelling diﬀerence between
the phenomenological ﬁssion distributions widely usedin the nucleosynthesis calculations and the results obtained using a dynamical model based on the Langevinmodel in the neutron-rich r-process region. This shows
the necessity of considering dynamical ﬁssion in thedata on systematic ﬁssion yields for better r-process
calculation.
The equation of state (EOS) and nuclear matter WG
aimed to determine the nuclear-physics constraints on
the nuclear EOS. The connection between the astrophysical observations and the nuclear properties revealed at RIBF has been explored. We found that we
can construct a model that can account for the indication of GW170817 if the symmetry energy at twice
the saturation density of nuclear matter is 40–60 MeV.
The symmetry energy in this density region can be constrained from the collision experiment of neutron-richheavy ions measured by the SAMURAI spectrometer
at RIBF.
In addition to these activities focusing speciﬁcallyon theoretical nuclear physics, we organized a series ofworkshops to bring together nuclear physicists and astrophysicists motivated by the discovery of an r-process
event (kilonova) associated with the gravitational-wave
detection by the Advanced LIGO–Advanced Virgo frommerging neutron stars. The workshops were held at
RNC (June 2018), YITP Kyoto University (May 2019),
and NAOJ (October 2020).
Superheavy elements
The main purpose of the superheavy element andﬁssion WG (SHE/Fission WS) was to give theoretical suggestions and make proposals for experiments on
new superheavy elements conducted at RIBF. A primary interest in the physics of superheavy elements isto synthesize new elements exceeding Z = 118, and to
produce nuclei at the center of the island of stability
located around Z = 114 and N = 184. For the former,
heavier projectiles and stable actinide targets are being
promoted. For the latter, there is no available set ofstable projectiles and targets because the center of theisland of stability is located in the neutron-rich region.

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IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

It is thus desirable to estimate the possibility of newelement synthesis based on the theoretical calculationand to propose new experiments.
To synthesize superheavy elements, we proposed the
optimum incident energy and the combination of a target and projectile based on the calculated evaporationresidue cross section. We also calculated the propertiesof new superheavy elements: lifetime, deformation, nuclear structure, ﬁssion barrier height, decay proprieties,
etc. We then suggested a new approach to the synthesisof superheavy nuclei.
We (co)organized the RIBF ULIC mini-WS in August 2016 as a kick-oﬀ meeting and subsequently held a
WS entitled “New developments in superheavy element
research” at Kyushu University in July 2018.
Nuclear structure, collective motion, many-body correlations, and halo
The nuclear systems under extreme conditions are
expected to reveal new facets associated with the correlations among nucleons. A uniqueness of drip-line
nuclei was discussed in view of the nuclear interactions
and the strong correlations in a dilute system, such as
the multi-neutron halo and its condensation. A possibility of measuring the many-body correlations was
also discussed through the nuclear responses and reactions. The connections between the nuclear responses
and the EOS of nuclear matter or the reaction (decay)
rates relevant to the r-process were investigated.
The true pleasure in nuclear physics is the diversityof research topics. Thus, we realized the importanceof oﬀering an opportunity to young colleagues, particularly students and post-docs, where we can frankly
discuss nascent plans of physics research. To provide
such an environment and to explore important physics
for future experiments at RIBF in a variety of researchsubjects covered in the WG, we decided to organize“Hodan-kai” meetings. In contrast to the style of an ordinary workshop, the Hodan-kai aims to facilitate theexchange of unmatured ideas among young researchers.
To concentrate on physics discussions, the venue was a
relatively isolated place, and the presentation ﬁles are
not open to the public.
The ﬁrst Hodan-kai was held from July 31 to August
2, 2017 and focused mainly on the latest theoretical research on nuclear physics. The second and third meetings were held in February 2019 and 2020, respectively.
The topics discussed were extended in the second andthird meetings, as listed in Table 1. In the third meeting, in addition to talks given in the regular Hodan-kai
style, two “panel discussion” sections consisting of introductory talks by organizers and 5–7 short talks byinvited panelists were newly organized to facilitate interaction among the participants. The program andsummary of the Hodan-kai are shared on their respective websites.2–4)

2Table 1. Number of talks by theoretical and experimental
nuclear physicists and researchers from other fields, aswell as participants in the successive Hodan-kai meetings.

1st
2nd
3rd

Date
Aug 2017
Feb 2019
Feb 2020

Theor.
22
6
6

Exp.
1
7
7

Other
0
12
4

Participants
49
42
43

Collaboration and Perspective
In addition to the collaborations among the TF2
members, collaborative works with other researchers
have been conducted, and further collaborations are expected in the near future. We have already co-authored4 papers on the experiments performed at RIBF, 2 proposals to the RIBF PAC, 24 papers on the theoreticalanalysis of the RIBF data, and 30 papers on the physics
expected in the future RI beam facilities. Furthermore,
30+ invited talks on the physics of RI beams have beendelivered by the TF2 members during this term.
We have been discussing nuclear ﬁssion with experimentalists of the Japan Atomic Energy Agency(JAEA). The measurement of nuclear ﬁssion processes
and the formation of nuclei in the actinide region using the multinucleon transfer reaction have been intensively studied at the tandem facility of JAEA. Throughjoint research between JAEA and Kindai University, we
have published a number of co-authored papers thathave advanced the analysis of experimental data andthe interpretation of experimental data. Students ofKindai University attended the summer training schoolat JAEA. These young students are expected to leadthe physics of exotic nuclei in the future. This activity
will thus be a starting point for further collaborative
research in the physics of superheavy nuclei and ﬁssion.
The JSPS-NRF-NSFC A3 Foresight Program “Nuclear Physics in the 21st Century” started in 2019. A
microscopic understanding of the r-process is one of themain projects, and theoretical collaboration among theA3 countries is key to success. The activities in TF2
would set a foundation for the extended collaboration.
A plan for the construction of a microscopic nuclear
data library based on nuclear density-functional theory
is described in Ref. 5).
References

1) https://www.nishina.riken.jp/RIBF/TheoForum/index.
html .
2) 1st Hodan-kai, https://indico2.riken.jp/event/2509/ .
3) 2nd Hodan-kai, https://indico2.riken.jp/event/2864/ .
4) 3rd Hodan-kai, https://indico2.riken.jp/event/3157/ .
5) K. Yoshida, in this report.

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V. EVENTSRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Symposium on Nuclear Data 2020
H. Otsu on behalf of the SND2020 Local Organizing Committee∗1
The Symposium on Nuclear Data 2020 (SND2020)
was held on November 26–27, 2020 at the RIBF conference room as an on-site venue, combined with online connections. This symposium originated from theﬁrst conference1) held in 1978 under the auspices of theJapan Atomic Energy Research Institute (JAERI) andJapanese Nuclear Data Committee (Sigma ResearchCommittee) and has been held almost every year since.
The Nuclear Data Division (NDD) of the Atomic Energy Society of Japan (AESJ) took over the organization of this symposium in 2006. Since then, the symposium has been organized by an executive committeeof the Nuclear Data Division. In practice, it has been
hosted in turn by JAEA, domestic universities, or otherresearch institutes every ﬁscal year.
In 2020, RIKEN Nishina Center hosted the symposium for the ﬁrst time, in order to plant the seeds forcross-disciplinary research, to promote new collaborations, and to expand the possibility of collaborations.
For the eﬀective functioning of the symposium, CNS(U-Tokyo), WSNC (KEK), and the University of Tokyo
were asked to co-host the event, and these institutes
formed the local organizing committee.
The symposium consisted of 16 invited talks, 2 tutorial lectures, and 26 poster presentations, followedby an RIBF facility tour. The full program and abstracts of the symposium are available on the SND2020
webpage.2) The invited talks covered recent topics andprogress in nuclear data activities and consisted of ﬁve
sessions: 1) accelerator facilities and nuclear data, 2)
ﬁssion and heavy-ion nuclear spectroscopy, 3) nuclear
reaction, 4) nuclear medicine and pharmacology, and
5) deep learning or machine learning, and its application to nuclear physics and nuclear data. A feature ofthis year’s symposium was the inclusion of a session onmachine learning. Machine learning is expected to play
an important role in the next decade for nuclear physics
and nuclear data, where multiple variables are handled
and analyzed from raw or processed data. An introduction to the fundamentals of deep learning was provided
including its origins, history of development, and relationship with computing power, The session carefully
examined the capabilities of deep learning, examples ofcommon pitfalls, and expectations for the future.
The two tutorial lectures were dedicated to the basic
theory and actual operation of nuclear reactors. The
lectures aimed to explain how nuclear reactors are established as macroscopic systems, so that even nuclear
physics researchers, who usually understand physicalphenomena from a microscopic perspective, could understand them. It is uncertain whether the aims were∗1

RIKEN Nishina Center

Fig. 1. Symposium photo of on-site participants in front andon-line participants on screen.

fully achieved, but such eﬀorts are believed to be worthwhile.
Poster presentations were held using the break-out
room function of the Zoom web meeting tool. This
was necessary to prevent cluster outbreaks of COVID19 that can potentially be introduced by face-to-face
discussions. Therefore, not only on-site participants
but also online participants presented their posters remotely. The posters themselves were located on thewall at the on-site conference room. Therefore, the onsite participants were able to examine the posters not
only during the poster session, but also during coﬀee
breaks.
Figure 1 shows a group photograph of both on-siteand online participants of the symposium. Despite the
COVID-19 pandemic, which restricted public access,62 on-site participants visited RIKEN Wako campus.
Together with 59 online participants, a total of 121
researchers and students joined the symposium. The
Zoom web meeting tool was utilized not only for theposter session but also for several oral presentations.
The on-site presentations were distributed via Zoom,
and the remote presentations were shown on the screen
at the conference room. Therefore, this conference washeld in the hybrid model of on-site and remote participation. This model will be followed in the future
as well. The next year’s symposium will be hosted by
J-PARC.
References

1) Proc. the 1978 Seminar on Nuclear Data, https://inis.iaea.org/collection/NCLCollectionStore/_Pub
lic/11/537/11537325.pdf .
2) https://indico2.riken.jp/e/snd2020 .

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V. EVENTSRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

The 8th Asia-Pacific Conference on Few-Body Problems in Physics(APFB2020)
E. Hiyama,∗1,∗2 A. Tamii,∗3 and S. Ishikawa4
The 72th Yamada Conference: The 8th AsiaPaciﬁc Conference on Few-Body Problems in Physics(APFB2020) was held in Kanazawa, Japan on March
1–5, 2021. The purpose of the APFB conference is toencourage PhD students and young researchers in Asian
countries to study few-body problems in various physics
ﬁelds. The 1st APFB conference was held in Tokyo in
1999. Subsequently, we held the following APFB conferences: 2nd APFB, Shanghai, China in 2002; 3rd APFB,
Nakhon Ratchasima, Thailand in 2005; 4th APFB, Depok, Indonesia in 2008; 5th APFB, Seoul, Korea in 2011;
6th APFB, Adelaide, Australia in 2014; and 7th APFB,
Guilin, China in 2017. The 8th APFB was planned tobe conducted in August 2020. However, because of the
COVID-19 pandemic, we postponed it to March 1–5,
2021. As the pandemic situation continued well into
2021, we organized the conference in a hybrid format,
that is, with participation both online and on-site. The
venue for the on-site part of the conference was Bunka
hall in Kanazawa, where one large room was prepared forthe plenary session and two smaller rooms were preparedfor parallel sessions. While maintaining social distancing, we prepared desks and chairs for 60 persons in theplenary-session room and for approximately 20 persons
in the other rooms. Moreover, on-site participants wererequested to wear masks during the conference, and theconsumption of food and drinks was prohibited.
The following topics were covered in APFB2020: fewhadron systems and their interactions, hadron structure and quantum chromodynamics, structure of lightnuclei and hypernuclei, relativistic aspects of few-bodysystems near stability and their interactions, symmetries and symmetry breaking, electroweak interactions

Fig. 1. Conference photograph from the on-site venue.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Department of Physics, Tohoku University
RCNP, Osaka University
Science Research Center, Hosei University

Fig. 2. Opening address at the on-site venue.

in few-hadron systems, atomic and molecular systems,
exotic few-body systems and astrophysics, and methods
in few-body systems
This hybrid conference had approximately 300 participants in total, of which 50 participants attended onsite and approximately 250 attended online. We had
160 domestic participants, about 80 participants fromother Asian countries, 40 from Europe, and 15 fromthe U.S.A. All participants from abroad attended online. APFB2020 featured 36 plenary talks, 10 invited
talks in parallel sessions, and 90 contributed talks. The
most diﬃcult tasks in the hybrid-style conference was toorganize a scientiﬁc program and to solve network problems. We also needed to address the diﬀerences in timezone among Asian countries, Europe, and the U.S.A.
Therefore, we split the plenary session into the morning(for the US time zone) and evening (for the European
time zone). The parallel sessions were conducted late in
the morning and in the early afternoon. In addition, we
carefully prepared a reliable network connection, which
was expensive. However, we were concerned about poor
network connections from presenters. To avoid this difﬁculty, we asked them to provide recoded talks in advance. As expected, we had to use some of the recodedtalks during the conference because of poor connections.
The next international Conference on few-body problems in physics will be held in Beijing, China in 2022.
We hope that the conference will be conducted entirely
on-site as it would be more eﬃcient to conduct discussions on physics in that manner.
Finally, we would like to acknowledge RIKEN Nishina
Center, RCNP, RIKEN iTHEMS, Kyushu University,
and Tohoku University as co-host institutes and universities. Furthermore, the conference was hosted by the
Yamada Science Foundation through a Grant-in-Aid for
Scientiﬁc Research on Innovative Areas, titled “Clustering as windows on the hierarchical structure of quantum
systems.”- 196 -

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V. EVENTSRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Domestic Workshop on Spin Physics
Y. Goto,∗1 for the Local Organizing Committee
24th International Symposium on Spin Physics wasscheduled to be held in Matsue City in September 2020
as SPIN2020, but it was postponed to October 2021
because of COVID-19 pandemic and will be held as
SPIN2021. Prior to SPIN2021, we held a domestic
workshop on spin physics as a satellite workshop of
SPIN2021 on February 23rd and 24th, 2021 to discuss
future themes of spin physics and related ﬁelds, activities of various groups, and prospects for development
in Japan, as well as to provide a platform for presentations by young researchers. The workshop language
was Japanese.
In the workshop, topics related to spin phenomena inparticle and nuclear physics and related ﬁelds were discussed. In accordance with the topics to be discussed
in SPIN2021, the following topics were reviewed:• proton radius for the nucleon structure• RHIC and COMPASS results, three-dimensional
parton distribution, and QCD spin physics for the
spin structure of hadrons• physics of the Electron-Ion Collider for future facilities and experiments• theoretical and experimental reviews for fundamental symmetries and physics beyond the standard model• polarized electron sources and solid polarized targets• physics at LEPS for spin physics research using
photon, lepton, and hadron probes• low-energy spin physics in nuclear reactions andnuclei• applications of spin physics

The workshop also included presentations by young
researchers on the understanding of the single-spin
asymmetry, nucleon structure studies based on the lattice ﬁeld theory, theory of the electric-dipole moment,
spin-spin correlation in K-pp decay, polarized targetof COMPASS, study of three-body nucleon force usinga polarized target, and structure analysis of materials
by neutron scattering. The presentations and discussions will be published and distributed as conference
proceedings.
SPIN2021 is planned to be held in October as a hybrid conference combining on-site and online sessions.
The domestic workshop was held at the same venue
as that for SPIN2021, the Kunibiki Messe Convention Center in Matsue City. Together with the venue
staﬀ, we discussed ideas for the success of the hybrid
conference and held the domestic workshop as a test
run of SPIN2021. Considering the current situation∗1

Fig. 1. Setup of the venue for the hybrid conference.

of COVID-19, only the organizing committee participated on-site this time, while the others participatedonline. The number of on-site participants in the workshop was 7, and the number of online participants was
45.
The on-site portion of the workshop was in the format of a regular research meeting in a conference room,
which was distributed via Zoom so that people could
participate online. The system shown in Fig. 1 was
prepared so that the online participants could participate in the question and answer session in the same
way as on-site participants. Some speakers and chairpersons spoke on-site, while others presented online.
The speakers at the venue displayed their slides on the
projector as in a normal conference, and the operator
distributed a split line to Zoom. The online speakers
also displayed their slides via Zoom screen sharing.
The workshop was held with ﬁnancial support fromthe RIKEN Nishina Center and with great help fromthe venue staﬀ. The hybrid conference method allowed us to integrate on-site and online discussions
and conduct an active workshop. We would like tobuild on the success of this experience to organize alarger SPIN2021 International Symposium with parallel sessions in addition to the plenary session, welcoming more on-site and online participants from abroad.

RIKEN Nishina Center- 197 -

1

VI. ORGANIZATION AND ACTIVITIESOF RIKEN NISHINA CENTER(Activities, Members, Publications & Presentations)VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

1. Organization
1.1 Organization Chart as of March 31, 2021 （End of FY2020）- 199 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

1.2 Topics in FY2020
Year

Date

Topics in Management

2020

Apr. 1

Newly appointed:
RNC Director: Hiroyoshi SAKURAI

2020

Oct. 1

Newly appointed:
Team Leader of Plant Genome Evolution Research Team: Hiroyuki ICHIDA

2020

Oct. 1

Newly appointed:
Team Leader of Infrastructure Management Team: Masanori KIDERA

2. Finances
A transition of the RNC budget for the past four years is shown in following graph.
Million Yen

3. Staffing
At the start of FY 2019, there were 142 personnel affiliated with RNC and 419 researchers visiting RNC for research purpose. The following
graphs show a breakdown of personnel into six categories as of April 1, 2019, and a transition of the number of each category.

Permanent Researcher
Contract Researcher
Technical staff
Special Postdoctoral Researcher
Junior Research Associate
External researcher- 200 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

4. Research publication
The number of papers published annually from RNC is shown graphically using the data obtained from Clarivate Analytics’ Web of Science
Documents.
350

Source Documents

300
250
200
150
100
50
0

2017

2018

2019

2020

Publication Year

Citation analysis for the past four years
As of April 2021
Year
Indicators
Total number of papers

2017

2018

2019

2020

298

286

301

300

Percentage of papers in top 10%

16.78

20.63

9.63

1.33

Percentage of papers in top 1%

2.68

4.20

1.00

12.67

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

5. Management
Headed by the RNC Director Hiroyoshi SAKURAI, the RIKEN Nishina Center for Accelerator-Based Science (RNC) consists of:

9 Laboratories
10 Groups with 27 Teams
2 overseas research centers with 3 Groups

as of the end of FY2020. There are also two 'Partner Institutes' which conduct research in the laboratories set up in RNC. RNC is managed
by its Director who takes into consideration the majority decision of the RNC Coordination Committee. The management of RNC is supportedby the following committees:Program Advisory Committee
Safety Review Committee
RIBF Machine Time Committee
Public Relations Committee

There are also committees to support the President of RIKEN and/or the Director of RNC such as:

Nishina Center Advisory Council with three subcommittees:
・RBRC Scientific Review Committee (SRC)・International Advisory Committee for the RIKEN-RAL Muon Facility
・RBRC Management Steering Committee (MSC)

Nishina Center for Accelerator-based Science
Executive Members (as of March 31, 2021)
Hiroyoshi SAKURAI
Director
Osamu KAMIGAITO
Deputy Director (Research Facility Development Division)
Tomoko ABE
Deputy Director (Accelerator Application Division)
Masahiro IWASAKI
Deputy Director (Subnuclear System Research Division)
Yasushige YANO
Senior Advisor
Tohru MOTOBAYASHI
Senior Advisor

RNC Coordination Committee
The following subjects relevant to the RNC management are deliberated under the chairmanship of the RNC Director:






Establishment of the new organization or reorganization in RNC
Personnel management of RNC researchers
Research themes and research budget
Approval of the Partner Institutes
Evaluation of the management of RNC and the response to the recommendations by external evaluation

The RNC Coordination Committee is held monthly.
Members (as of March 31, 2021)
Hiroyoshi SAKURAI
Osamu KAMIGAITO
Tomoko ABE
Masahiko IWASAKI
Yasushige YANO
Tohru MOTOBAYASHI
Tomohiro UESAKA
Hideki UENO
Toru TAMAGAWA
Emiko HIYAMAYuko MOTIZUKI
Kosuke MORITA
Hiroki OKUNO
Nobuhisa FUKUNISHI
Masanori WAKASUGIHiromitsu HABA

Director, RNC; Director, Radioactive Isotope Physics Laboratory and Nuclear Transmutation Data Research Group;
Team Leader, Muon Date Team
Deputy Director, RNC; Director, Accelerator Group and High-Intensity Accelerator R&D Group; Team Leader,
Infrastructure Management Team
Deputy Director, RNC; Director, Beam Mutagenesis Group; Team Leader, Ion Beam Breeding Team
Deputy Director, RNC; Director, Meson Science Laboratory
Senior Advisor, RNC
Senior Advisor, RNC
Director, Spin Isospin Laboratory and Research Instruments Group
Director, Nuclear Spectroscopy Laboratory and User Liaison Group; Team Leader, Outreach Team
Director, High Energy Astrophysics Laboratory
Director, Strangeness Nuclear Physics Laboratory
Director, Astro-Glaciology Research Group
Director, Superheavy Element Research Group
Deputy Group Director, Accelerator Group; Team Leader, Accelerator R&D Team, Cryogenic Technology Team, andHigh-Power Target R&D Team
Deputy Group Director, Accelerator Group; Team Leader, Beam Dynamics & Diagnostics Team
Director, Instrumentation Development Group; Team Leader, Rare RI-Ring Team and SCRIT Team
Director, RI Application Research Group; Team Leader, RI Application Team and Superheavy Element Production- 202 -

VI. RNC ACTIVITIESKanenobu TANAKA
Eiji IKEZAWA
Hideaki OTSU
Naruhiko SAKAMOTO
Hiromi SATO
Toshiyuki SUMIKAMA
Takahide NAKAGAWA
Koji MORIMOTO
Atsushi YOSHIDA
Koichi YOSHIDA
Ken-ichiro YONEDA
Hironobu ISHIYAMA
Hidetada BABA
Hiroyuki Ichida
Masanori Kidera
Tsukasa TADA
Yasushi WATANABE
Yutaka WATANABE
Hideto EN'YO
Yasuyuki AKIBA
Taku IZUBUCHI
Toshiyuki HASHIMOTO

RIKEN Accel. Prog. Rep. 54 (2021)
Team
Director, Safety Management GroupTeam Leader, RILAC Team
Team Leader, SAMURAI Team and Fast RI Data Team
Team Leader, Cyclotron Team and High-Gradient Cavity R&D Team
Team Leader, Detector Team
Team Leader, Slow RI Data Team
Team Leader, Ion Source Team
Team Leader, Superheavy Element Device Development Team
Team Leader, Industrial Application Research Team
Team Leader, BigRIPS Team
Team Leader, RIBF User Liaison Team
Team Leader, SLOWRI Team
Team Leader, Computing and Network Team
Team Leader, Plant Genome Evolution Research Team
Team Leader, Infrastructure Management Team
Vice Chief Scientist, Quantum Hadron Physics Laboratory
Deputy Team Leader, RIBF User Liaison Team
Deputy Team Leader, Infrastructure Management Team
Director, RIKEN BNL Research Center; Director, Radiation Laboratory
Group Leader, Experimental Group, RIKEN BNL Research Center
Group Leader, Computing Group, RIKEN BNL Research Center
Director, Nishina Center and iTHEMS Promotion Office

Program Advisory Committee
The Program Advisory Committee reviews experimental proposals submitted by researchers and reports the approval/disapproval of the
proposals to the RNC Director. The Committee also reports to the RNC Director the available days of operation at RIBF or the Muon
Facility at RAL allocated to researchers. The Committee is divided into three categories according to the research field.


Nuclear Physics Experiments at RIBF (NP-PAC): academic research in nuclear physics
Materials and Life Science Researches at RNC (ML-PAC): academic research in materials science and life science
Industrial Program Advisory Committee (In-PAC): non-academic research

Program Advisory Committee for Nuclear Physics Experiments at RI Beam Factory (NP-PAC)
The 21st NP-PAC was held on December 14−16, 2020 at RIBF.
Members (as of March 31, 2021)
Robert V.F. JANSSENS (Chair)
Dieter ACKERMANN
Nori AOIMaria J.G. BORGE
Robert CHARITY
Augusto O. MACCHIAVELLI
Gabriel MARTINEZ-PINEDO
Iain MOOREDavid J. MORRISSEY
Hitoshi NAKADA
Alexandre OBERTELLITakehiko SAITO
Kimiko SEKIGUCHI
Philip J. WOODS
Andrea VITTURI
Xiaohong ZHOU

University of North Carolina at Chapel Hill
GANIL
Osaka University
Consejo Superior de Investigaciones Científicas
Washington University in St. Louis
Lawrence Berkeley National Laboratory
Technische Universität Darmstadt, GSI Helmholtzzentrum für Schwerionenforschung
University of Jyväskylä
Michigan State University
Chiba University
Technische Universität Darmstadt
RIKEN Cluster for Pioneering Research
Tohoku University
University of Edinburgh
Universita' di Padova
Institute of Modern Physics, CAS

Program Advisory Committee for Materials and Life Science Researches at RIKEN Nishina Center (ML-PAC)
The ML-PAC of FY2020 was held between January 13 and 20, 2021 via e-mail.
Members (as of March 31, 2021)
Adrian HILLIER (Chair)
Zhi QIN
Toshiyuki Takayanagi
Yoshio Kobayashi
Yutaka Miyazawa

ISIS, RAL (UK)Institute of Modern Physics, CAS
Saitama University
The University of Electro-Communications
Yamagata University

Industrial Program Advisory Committee (In-PAC)- 203 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

The 10th In-PAC was held on July 30, 2020 via Web meeting.

Safety Review Committee
The Safety Review Committee is composed of two sub committees, the Safety Review Committee for Accelerator Experiments and the HotLab Safety Review Committee. These Committees review the safety regarding the usage of radiation generating equipment based on the
proposal submitted to the RNC Director from the spokesperson of the approved experiment.
Safety Review Committee for Accelerator Experiments
Members (as of March 31, 2021)
Hiromi SATO (Chair)
Kouji MORIMOTO
Eiji IKEZAWA
Hiromitsu HABA
Atsushi YOSHIDA
Koichi YOSHIDA
Naoki FUKUDA
Naruhiko SAKAMOTO
Daisuke SUZUKI
Masaki SASANO
Yuichi ICHIKAWA

Team Leader, Detector Team
Team Leader, Superheavy Element Device Development Team
Team Leader, RILAC Team
Team Leader, RI Application Team
Team Leader, Industrial Cooperation Team
Team Leader, BigRIPS TeamTechnical Scientis, BigRIPS Team
Team Leader, Cyclotron Team
Research Scientist, Radioactive Isotope Physics Laboratory
Senior Research Scientist, Spin Isospin Laboratory
Senior Research Scientist, Nuclear Spectroscopy Laboratory

External members
Shinichiro MICHIMASA
Hidetoshi YAMAGUCHI
Yutaka WATANABE

Assistant Professor, Center for Nuclear Study, University of Tokyo
Lecturer, Center for Nuclear Study, University of Tokyo
Associate Professor, High Energy Accelerator Research Organization, KEK

Ex officio members
Kanenobu TANAKA
Hisao SAKAMOTO

Director, Safety Management Group
Technical Scientist, Safety Management Group

Hot-Lab Safety Review Committee
Members (as of March 31, 2020)
Tetsuya OHNISHI (Chair)
Kanenobu TANAKA
Hisao SAKAMOTO
Hiroki MUKAI
Eriko HIGURASHI
Hiromitsu HABA
Kazuya TAKAHASHI

Senior Research Scientist, SCRIT Team
Director, Safety Management Group
Technical Scientist, Safety Management Group
Technical Staff I, Safety Management Group
Technical Scientist, Safety Management GroupTeam Leader, RI Application Team
Senior Research Scientist, Nuclear Chemistry Research TeamRIBF Machine Time Committee
Upon request of the RNC Director, the RIBF Machine Time Committee deliberates on the machine time schedule of RIBF and reports theresults to the Director.
Members (as of March 31, 2021)
Hideki UENO (Chair)
Osamu KAMIGAITO
Masanori WAKASUGITomohiro UESAKA
Nobuhisa FUKUNISHI
Hiroki OKUNO
Shunji Nishimura
Tomoko ABE
Hiromitsu HABA
Kanenobu TANAKA
Ken-ichiro YONEDA
Kouji MORIMOTO
Koichi YOSHIDA

Director, User Liaison Group and Nuclear Spectroscopy Laboratory
Director, Accelerator Group
Director, Instrumentation Development Group
Director, Research Instruments Group and Spin Isospin Laboratory
Deputy Group Director, Accelerator Group
Deputy Group Director, Accelerator Group
Senior Research Scientist, Radioactive Isotope Physics Laboratory
Director, Beam Mutagenesis Group
Director, RI Application Research Group
Director, Safety Management GroupTeam Leader, RIBF User Liaison Team
Team Leader, Superheavy Element Research Device Development Team
Team Leader, BigRIPS Team

External members- 204 -

VI. RNC ACTIVITIES
Kentaro YAKO
Hidetoshi YAMAGUCHI
Yutaka WATANABE
Observers
Hiroyoshi SAKURAI
Hideto EN'YO
Susumu SHIMOURA
Michiharu WADA
Hiroari Miyatake
Daisuke Suzuki
Kosuke MORITA
Hideaki OTSU
Atsushi YOSHIDA
Tohru MOTOBAYASHI
Hideyuki SAKAI
Yasuhiro SAKEMI
Hironobu Ishiyama
Toshiyuki Hashimoto
Kazushige FUKUSHIMA

RIKEN Accel. Prog. Rep. 54 (2021)
Associate Professor, Center for Nuclear Study, University of Tokyo
Lecturer, Center for Nuclear Study, University of Tokyo
Associate Professor, High Energy Accelerator Research Organization, KEK
Director, RNC; Director, Radioactive Isotope Physics Laboratory and Nuclear Transmutation Data Research Group;
Team Leader, Muon Date Team
Director, RIKEN BNL Research Center; Director, Radiation Laboratory
Director, Center for Nuclear Study, University of Tokyo
Director, KEK Wako Nuclear Science Center
Professor, High Energy Accelerator Research Organization, KEK
Chair, The RIBF Users Executive Committee (RIBF-UEC), Research Scientist, Radioactive Isotope Physics
Laboratory)
Director, Superheavy Element Research GroupTeam Leader, SAMURAI Team
Team Leader, Industrial Cooperation Team
Senior Advisor, RNC
Senior Advisor, RNC
Professor, Center for Nuclear Study, University of Tokyo
Team Leader, SLOWRI Team
Director, Nishina Center and iTHEMS Promotion Office
Manager, Nishina Center and iTHEMS Promotion OfficePublic Relations Committee
Upon request of the RNC Director, the Public Relations Committee deliberates and coordinates the following matters:Creating public relations system for RNC
Prioritization of the public relations activities for RNC
Other general and important matters concerning the public relations of RNC

Members (as of March 31, 2021)
Toshiyuki HASHIMOTO (Chair) Director, Nishina Center and iTHEMS Promotion OfficeOsamu KAMIGAITO
Deputy Director, RNC; Director, Accelerator Group
Tomoko ABE
Deputy Director, RNC; Director, Beam Mutagenesis Group
Masahiko IWASAKI
Deputy Director, RNC; Director, Meson Science Laboratory
Tomohiro UESAKA
Director, Spin Isospin Laboratory and Research Instruments Group
Hideki UENO
Director, Nuclear Spectroscopy Laboratory and User Liaison GroupToru TAMAGAWA
Director, High Energy Astrophysics Laboratory
Emiko HIYAMA
Director, Strangeness Nuclear Physics Laboratory
Kosuke MORITA
Director, Superheavy Element Research Group
Hideto EN'YO
Director, RIKEN BNL Research Center; Director, Radiation Laboratory

RBRC Management Steering Committee (MSC)
RBRC MSC is set up according to the Memorandum of Understanding between RIKEN and BNL concerning the collaboration on the Spin
Physics Program at the Relativistic Heavy Ion Collider (RHIC). The 26th and 27th MSC was held on July 16 and August 20, 2019,respectively.
Members (as of March 31, 2021)
Shigeo Koyasu
Hiroyoshi Sakurai
Shoji NAGAMIYA
Robert TRIBBLE
Dmitori DENISOV
Berndt MUELLER

Executive Director, RIKEN
Director, RNC; Director, Radioactive Isotope Physics Laboratory and Nuclear Transmutation Data Research Group;
Team Leader, Muon Date Team
Senior Visiting Scientist, RNC
Deputy Director for Science and Technology, BNL
Deputy Associate Laboratory Director for High Energy Physics, BNL
Associate Laboratory Director for Nuclear and Particle Physics, BNL- 205 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

6. International Collaboration

Country

Partner InstituteObjects

RNC contact person

Austria

Stefan Meyer Institute forSubatomic Physics

Framework

Masahiko IWASAKI, Director, Meson Science
Laboratory

China

China Nuclear Physics Society

Creation of the council for China -Japan
research collaboration on nuclear physics

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

Peking University

Nuclear Science

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

Institute of Modern Physics,
Chinese Academy of Science

Physics of heavy ions

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

School of Nuclear Science andTechnology, Lanzhou University

Framework

Masahiko IWASAKI, Director, Meson Science
Laboratory

School of Physics, Nanjing
University

Framework

Emiko HIYAMA, Director, Strangeness Nuclear
Physics Laboratory

Department of Physics, Faculty of
Science, The University of Hong
Kong

Experimental and educational researchcollaboration in experimental nuclear physics

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

School of physics, Nankai
University

Framework

Emiko HIYAMA, Director, Strangeness Nuclear
Physics Laboratory

School of Physical Sciences,
USTC,

Framework

Masahiko IWASAKI, Director, Meson Science
Laboratory

Finland

University of Jyvaskyla

Basic nuclear physics and related
instrumentation

Hironobu ISHIYAMA, Team Leader, SLOWRITeamFranceNational Institute of Nuclear
Physics and Particle Physics(IN2P3)

Physics of heavy ions

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Normandy University

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Commissariat à l'énergie
atomique et aux énergies
alternatives (CEA, French
Alternative Energies and Atomic
Energy Commission)・Direction
des Sciences de la Matière”(DSM)

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

GSI

Physics of heavy ions and accelerator

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

Department of Physics,
Technische Universität Darmstadt

Framework

Emiko HIYAMA, Director, Strangeness Nuclear
Physics Laboratory

Hungary

The Institute of Nuclear Researchof the Hungarian Academy of
Sciences (ATOMKI)

Nuclear physics, Atomic Physics

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Indonesia

ITB, UNPAD, ITS, UGM, UI

Material science using muons at the RIKENRAL muon facility

Masahiko IWASAKI, Director, Meson Science
Laboratory

Hasanuddin University

Agricultural science and related fields
involving heavy-ion beam mutagenesis using
Indonesian crops

Tomoko ABE, Director, Beam Mutagenesis Group

Applied Physics Division,
National Institute for New
Technologies, Energy andEnvironment (ENEA)

Framework

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

European Center for Theoretical
Studies in Nuclear Physics andRelated Areas (ECT*)

Theoretical physics

Tetsuo HATSUDA, Director, Quantum Hadron
Physics Laboratory

Istituto Nazionale di Fisica
Nucleare (INFN)

Physics of heavy ions

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

GermanyItaly- 206 -

VI. RNC ACTIVITIESCountry
Korea

RIKEN Accel. Prog. Rep. 54 (2021)

Partner InstituteObjects

Seoul National University

RNC contact person
Nishina School

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

College of Natural Science, Ewha
Women’s University

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

College of Natural Sciences,
INHA University

Framework

Emiko HIYAMA, Director, Strangeness Nuclear
Physics Laboratory

Malaysia

Universiti Sains Malaysia

Muon Science

Masahiko IWASAKI, Director, Meson Science
Laboratory

NorwayFaculty of Mathematics andNatural Science, University ofOslo（UiO MN）

Framework

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

PolandThe Henryk Niewodniczanski
Institute of Nuclear
Physics, Polish Academy of
Sciences(IFPAN)

Framework

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

Romania“Horia Hulubei” National
Institute of Physics and Nuclear
Engineering Bucharest-Magurele,
Romania

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

University of Bucharest

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Joint Institute for Nuclear
Research (JINR)

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Russian Research Center“Kurchatov Institute”

Framework

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

Switzerland

Paul Scherrer InstituteImprove the performance and reliability ofaccelerator systems

Osamu KAMIGAITO, Director, Accelerator GroupUSA

Columbia University

The development of QCDCQ

Hideto EN’YO, Director, Radiation Laboratory

Michigan State University

Comprehensive
The use of TPC (Time Projection Chamber)

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

Framework

Hiroyoshi SAKURAI, Director, Radioactive Isotope
Physics Laboratory

RussiaVietnamVietnamAtomicCommission

EnergyEuropeEuropean Nuclear Science andApplication
Research2

Framework

Tomohiro UESAKA, Director, Spin Isospin
Laboratory

The European Organization for
Nuclear Research (CERN)

R&D and application of micro-pattern gas
detectors (MPGD) technology (RD51
Collaboration)

Hideto EN’YO, Director, Radiation Laboratory

The European Organization for
Nuclear Research (CERN)

Collaboration in the ALICE Experiment

Hideto EN’YO, Director, Radiation Laboratory

7. Awards
Awardee, Laboratory / TeamAward

Organization

Date

Tomoki KIMURA, Visiting Scientist at the High Energy
Astrophysics Laboratory

The Young Scientists' Prize, theCommendation for Science andTechnology for FY2020

Japan Minister of Education, Culture,
Sports, Science and Technology

Apr. 7

Masaki NISHIMURA, Student Trainee at Nuclear
Spectroscopy Laboratory

The Student Presentation Award of the
Physical Society of Japan in the fieldof experimental/theoretical nuclear
physics

The Physical Society of Japan

May. 16

Takashi ICHIHARA, Special Temporary Research
Scientist at the Radioactive Isotope Physics Laboratory

The 2020JPCERT/CC Certificate of
Gratitude

JPCERT Coordination Center

Aug. 19- 207 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Atsumi. SAITO, Student Trainee at the Spin Isospin
Laboratory

The A3F-CNSSS Young Scientist
AwardsThe Center for Nuclear Study, The
University of Tokyo (CNS)

Aug. 21

Guo YIXIN, Student Trainee at the Quantum Hadron
Physics Laboratory

The A3F-CNSSS Young Scientist
AwardsThe Center for Nuclear Study, The
University of Tokyo (CNS)

Aug. 21Huang SIWEI, IPA at the Spin Isospin Laboratory

The A3F-CNSSS Young Scientist
AwardsThe Center for Nuclear Study, The
University of Tokyo (CNS)

Aug. 21

Junki TANAKA, Postdoctoral Researcher at the Spin
Isospin Laboratory

The A3F-CNSSS Young Scientist
AwardsThe Center for Nuclear Study, The
University of Tokyo (CNS)

Aug. 21

Tomoya NAITO, Student Trainee at the Hadron Quantum
Hadron Physics Laboratory

The A3F-CNSSS Young Scientist
AwardsThe Center for Nuclear Study, The
University of Tokyo (CNS)

Aug. 21

Takahiro NISHI, Postdoctoral Researcher at the
Accelerator GroupThe 17th Annual Meeting Award (the9th)

The Particle Accelerator Society ofJapan

Sep. 2Kazuma NAKAZAWA, Visiting Scientist at theStrangeness Nuclear Physics Laboratory

The 66th Nishina Memorial Prize for
FY2020

Nishina Memorial Foundation

Dec. 4- 208 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

8. Brief overview of the RI Beam Factory
Intensity of Primary Beams

Beamtime for experiments- 209 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Activities of the Center Director
Meeting Attendance as Ex Oﬃcio
International Meetings[NuPECC associate member]
Online Meeting, October 15–16, 2020. A report of “News from Nishina Center” was given.
Online Meeting, March 5, 2020.

[IUPAP WG9]
No meeting was organized because of COVID-19 pandemic.

Domestic Meetings[核物理委員会]
仁科センター報告, オンライン開催, 2020 年 6 月 28 日.
仁科センター報告, オンライン開催, 2020 年 9 月 15 日.
仁科センター報告, オンライン開催, 2021 年 1 月 10 日.
仁科センター報告, オンライン開催, 2021 年 3 月 13 日.

[日本原子力産業協会量子放射線利用普及連絡協議会]
第 32 回会合, オンライン開催, 2020 年 11 月 24 日.

List of Publications & Presentations
Publications[Review Articles]
櫻井博儀他, 「新時代を拓く加速器の『これから』」, Isotope News, 特別号 No. 5 (2021 年 1 月号).

Presentations[Domestic Conferences/Workshops]
土井琢身, 馬場秀忠, 櫻井博儀（招待講演）, 「理研の物理学研究における研究データ戦略とその事例 ～原子核物理学を中心とした
データ利活用の拡大に挑戦～」, 理研ハッカソン オープンシンポジウム —理研が進めるオープンサイエンスの実践—, オンライン開催, 2021 年 3 月 22 日.

Outreach Activities
櫻井博儀, 「RI ビームファクトリーで進展する元素変換科学」, 核物理委員会×ナレッジキャピタル 超学校 ONLINE スペシャル「21 世紀原子核物理の展望～トップ研究者が語る最前線～」, 2020 年 9 月 27 日.
櫻井博儀, 「『魔法数』の謎を解く」, 理研ニュース 474 (2020 年 12 月).
櫻井博儀, 「有馬朗人先生を偲んで」, 理研ニュース 477 (2021 年 3 月).

Others[テレビ番組出演]「ノーベル賞の源流, 仁科芳雄博士」, OHK 岡山放送, 2020 年 12 月 5 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Radioactive Isotope Physics Laboratory
1. Abstract

This Laboratory works as one of core research groups conducting programs at the world-premiere heavy-ion accelerator facilityof RIKEN “RI Beam Factory (RIBF).” The Laboratory explores exotic nuclear structures and dynamics in exotic nuclei that havenever been investigated before, such as those with largely imbalanced proton and neutron numbers. Our aim is to develop new
experimental techniques utilizing fast radioactive isotope (RI) beams at RIBF, to discover new phenomena and properties in exotic
nuclei. The Laboratory is focusing three major subjects; shell evolution of very neutron-rich nuclei, the r-process path and equationof-state in asymmetric nuclear matter. The Laboratory has initiated international collaborations for in-beam gamma spectroscopy,
decay spectroscopy and heavy-ion induced reactions, and has formed a discussion forum for next generation gamma-ray detectors.

2. Major Research Subjects(1) Study of structure and dynamics of exotic nuclei through developments of new tools in terms of reaction- and technique-based
methodology(2) Research on EOS in asymmetric nuclear matter via heavy-ion induced reactions(3) Detector developments for spectroscopy and reaction studies

3. Summary of Research Activity(1) In-beam gamma spectroscopy
In the medium and heavy mass region explored at RIBF, collective natures of nuclei are one of important subjects, which are
obtained through production and observation of high excited and high spin states. To populate such states, heavy-ion induced reactions
such as fragmentation, fission are useful. So far, we have developed two-step fragmentation method as an eﬃcient method to identify
and populate excited states, and lifetime measurements to deduce transition strength.
Devices utilized for the in-beam gamma spectroscopy are ZeroDegree Spectrometer (ZDS) and a NaI array DALI2. Since the endof 2008, the first spectroscopy on nuclei island-of-inversion region was performed, we have explored step-by-step new and unknown
regions in the nuclear chart. The second campaign in 2009 was organized to study background components originating from atomic
processes in a heavy target. Neutron-rich nuclei at N = 20 to 28 were studied in 2010. In 2011–2013, we conducted experiment
programs for Ca-54, Ni-78, neutron-rich nuclei at N = 82 and neutron-deficient nuclei at Z = 50.
A multitude of data obtained with inelastic, nucleon knock-out, fragmentation channels have been analyzed and published. In
2011–2013, collective natures of Mg-36, 38 and Si-42 were both published in PRL. Excited states firstly observed in Ca-54 werereported in Nature to demonstrate a new nuclear magic number of 34. Fragmentation reaction has been found eﬃcient for nuclei
with A > 100 and low-lying excited state in Pd-126 has been successfully observed and reported in PRC. In 2019, results of the first
spectrosocpy of 40 Mg was published in PRL, to demonstrate the exotic structure which is very diﬀerent from in other neutron-rich Mg
isotopes.
To further strengthen the in-beam gamma spectroscopy at RIBF, we have proposed a new setup of MINOS + DALI2 to search
for the 1st excited states in even-even neutron-rich nuclei with Z ∼ 20 to 40. The program was submitted to the PAC 2013 as a
new category of proposal, “proposal for scientific program” and was S-ranked. A dedicated collaboration “SEASTAR” has been
established as a subset of in-beam gamma collaboration “SUNFLOWER.” The three campaigns were organized in 2014, 2015 and2017 to study very neutron-rich isotopes, and were very productive to access very neutron-rich nuclei such as Ar-52, Ca-56, Ni-78,
Kr-100, Zr-110. In 2019, the result of the first spectroscopy of Ni-78 was published in Nature.
A new project of high resolution gamma spectroscopy with fast beams “HiCARI” has been proposed at PAC 2018. MINIBALL
and several Ge tracking detectors from Japan, Europe, the USA and Korea are being combined to form an array of germanium
detectors. The new setup aims to accelerate researches of the nuclear structure by observing gamma-lines in even-odd nuclei andmeasuring lifetimes of excited states. The two workshops were organized in 2019, and the machine time of 43.5 days in total wasapproved at PAC 2019. A part of the HiCARI programs was successfully conducted in 2020. The other HiCARI programs will be
performed in 2021.
Concerning a next generation detector, a discussion forum has been established to write up a white paper on tracking germanium
detectors and high-eﬃcient crystal detectors such LaBr3 and GAGG.
(2) Decay spectroscopy
Beta- and isomer-spectroscopy is an eﬃcient method for studying nuclear structure, especially for non-yrast levels. We had
accumulated experimental techniques at the RIPS facility to investigate nuclear structure in light mass region via beta-gamma andbeta-p coincidence. Concerning the medium and heavy mass region available at RIBF, we have developed two position-sensitive
active-stoppers, strip-silicon detectors and a cylindrical active stopper called CAITEN, to achieve a low-background measurement by
taking correlation between heavy ion stop position and beta-ray emission position. A site of decay-spectroscopy at the new facility of
RIBF is the final focal plane of ZDS, where high precision of TOF in particle identification is obtained due to a long flight path fromBigRIPS to ZDS.
At the end of 2009, the first decay spectroscopy was organized with a minimum setup of four clover gamma detectors and silicon
strip detectors, to study neutron-rich nuclei with A ∼ 110. The first campaign was found successful and eﬃcient to publish four

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

letter articles in 2011, two PRL’s and two PLB’s. One of the PRL papers is associated to the r-process path where half-lives for 18
neutron-rich nuclei were determined for the first time. The other PRL paper reported a finding of deformed magic number 64 in the
Zr isotopes.
The success of the first decay-spectroscopy campaign stimulated to form a new large-scale collaboration “EURICA,” where a
twelve Euroball cluster array is coupled with the silicon-strip detectors to enhance gamma eﬃciency by a factor of 10. A construction
proposal of “EURICA” was approved in the PAC 2011, and the commissioning was successfully organized in spring 2012. Since
then, physics runs had been conducted for programs approved to survey nuclei of interest as many as possible, such as Ni-78, Pd-128,
Sn-100. The EURICA collaboration finished its physics programs in summer 2016. So far, 54 papers including 14 PRL’s and 13
PLB’s were published. One of the highlights is discovery of a seniority isomer in Pd-128, of which cascade gamma decay gives theenergy of first excited state and robustness of N = 82 magic number, and the other is a half-life measurement for 110 neutron-richnuclei across the N = 82 shell gap, which shows implications for the mechanism and universality of the r-process path.
Beta-delayed neutron emission probability of medium and heavy neutron-rich nuclei is important to understand nuclear structure
and the r-process path. In 2013, a new collaboration “BRIKEN” has been established to form a He-3 detector array. A present
design of the array has neutron eﬃciency as high as 70% up to 3 MeV. The array was coupled with the AIDA silicon strip system. A
construction proposal was approved at the PAC 2013 and three physics proposals have been approved. The commissioning run was
conducted in autumn 2016. The major physics runs were conducted in 2017–2020.
The CAITEN detector was successfully tested with fragments produced with a Ca-48 beam in 2010.
(3) Equation-of-state via heavy-ion central collisions
Equation-of-state in asymmetric nuclear matter is one of major subjects in physics of exotic nuclei. Pi-plus and pi-minus yields
in central heavy ion collisions at the RIBF energy are considered as one of EOS sensitive observables at the RIBF energy. To observecharged pions, a TPC for the SAMURAI spectrometer is being constructed under an international collaboration “SπRIT,” Construction
proposal was submitted at the PAC 2012, and physics proposals were approved at the PAC 2012 and 2013. The physics runs weresuccessfully conducted in spring 2016. The data analysis is in progress to produce the first physics results. The first physics paper has
been published in 2020.
An international symposium “NuSYM” on nuclear symmetry energy was organized at RIKEN July 2010 to invite researchers
in three sub-fields, nuclear structure, nuclear reaction and nuclear astrophysics, and to discuss nuclear symmetry energy together.
Since then, the symposium series have been held every year and been useful to encourage theoretical works and to strengthen thecollaboration.
(4) Nucleon correlation and cluster in nuclei
Nucleon correlation and cluster in nuclei are matters of central focus in a “beyond mean-field” picture. The relevant programswith in-beam gamma and missing-mass techniques are to depict nucleon condensations and correlations in nuclear media as a functionof density as well as temperature. Neutron-halo and –skin nuclei are objects to study dilute neutron matter at the surface. By changing
excitation energies in neutron-rich nuclei, clustering phenomena and role of neutrons are to be investigated.
In 2013, two programs were conducted at the SAMURAI spectrometer. One is related to proton-neutron correlation in the C-12
nucleus via p-n knockout reaction with a carbon target. The other is to search for a cluster state in C-16, which was populated via
inelastic alpha scattering. The data is being analyzed.
In 2018, a new project based on missing mass spectroscopy was launched to investigate an exotic cluster state in a very protonrich nucleus. The experiment was organized at GANIL with combination of RIKEN liquid hydrogen target CRYPTA and the MUST2
detector array in 2018.

Members
Director
Hiroyoshi SAKURAI
Research/Technical Scientists
Pieter Christiaan DOORNENBAL (Senior Research Scientist)
Tadaaki ISOBE (Senior Research Scientist)
Akihisa KOHAMA (Senior Research Scientist)

Yoichi NAKAI (Senior Research Scientist)
Shunji NISHIMURA (Senior Research Scientist)
Daisuke SUZUKI (Research Scientist)

Special Postdoctoral Researcher
Browne FRANK
Junior Research Associates
Hideki SHIMIZU (Univ. of Tokyo)

Takuma KOIWAI (Univ. of Tokyo)

International Program Associates
Juan SAIZ LOMAS (Univ. of York)

Xiaohui SUN (Peking Univ.)

Special Temporary Research Scientist- 214 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Takashi ICHIHARA
Research Consultants
Akitsu IKEDA
Masayasu ISHIHARA

Kenichi MATSUYANAGI
Hiroyuki MURAKAMI

Senior Visiting Scientists
Koichiro ASAHI (Tokyo Tech)
Shigeru KUBONO (Univ. of Tokyo)

Kengo OGAWA (Chiba Univ.)

Visiting Scientists
Nori AOI (Osaka Univ.)
Giordano CERIZZA (Michigan State Univ.)
Jin-hee CHANG (Michigan State Univ.)
Silvio CHERUBINI (Univ. of Catania)
Martha Liliana CORTES SUA (INFN)
Mitsunori FUKUDA (Osaka Univ.)
Byungsik HONG (Korea Univ.)
Kazuo IEKI (Rikkyo Univ.)
Kei IIDA (Kochi Univ.)
Natsumi IKENO (Tottori Univ.)
Takuji IZUMIKAWA (Niigata Univ.)
Takashi KISHIDA (Aoyama Gakuin Univ.)
Gabor KISS (ATOMKI)
Khiem LE (Vietnam Academy of Sci. and Tech.)
Hiu Ching LEE (The Univ. of Hong Kong)
Giuseppe LORUSSO (Nat’l Phys. Lab.)
Alan MCINTOSH (Texas A & M Univ.)
Yoshiharu MORI (Kyoto Univ.)
Tetsuya MURAKAMI (Kyoto Univ.)

Megumi NIIKURA (Univ. of Tokyo)
Evgueni NIKOLSKI (Kurchatov Inst.)
Daiki NISHIMURA (Tokyo City Univ.)
Takashi OHTSUBO (Niigata Univ.)
Hooi Jin ONG (Osaka Univ.)
Akira ONO (Tohoku Univ.)
Naohiko OTSUKA (IAEA)
Kazuhiro OYAMATSU (Aichi Shukutoku Univ.)
Clementine Angelique Marie-Th SANTAMARIA (Berkeley
Lab)
Paer-Anders SOEDERSTROEM (TU Darmstadt)
Maya TAKECHI (Niigata Univ.)
Ryo TANIUCHI (Univ. of York)Rensheng WANG (Soochow Univ.)
Hiroshi WATANABE (Beihang Univ.)
Kathrin WIMMER (Inst.o de Estructura de la Materia, Consejo
Superior de Investigaciones Cientias, CSIC)
Jin WU (Argonne Nat’l Lab.)
Yasutaka YAMAMOTO (Osaka Univ.)

Visiting Technicians
Jorge AGRAMUNT ROS (Valencia city hall)
Hilde DE WITTE (KU Leuven)

Herbert E. HESS (Univ. of Cologne)
Ivan KOJOUHAROV (GSI)

Visiting Researchers
Alejandro ALGORA (JSPS)
Benoit J. C. MAUSS (JSPS)

Byul MOON (Nat’l Res. Foundation)

Student Trainees
Takamichi AOKI (Univ. of Tokyo)
Takumi AOKI (Univ. of Tokyo)
Yusei BANDO (Univ. of Tokyo)
Jonathan BARNEY (Michigan State Univ.)
Linh BUI (Vietnam Atomic Energy Inst.)
Justin B. ESTEE (Michigan State Univ.)
Hiroaki FUKUSHIMA (Rikkyo Univ.)
Shinnosuke KANAYA (Osaka Univ.)
Masanori KANEKO (Kyoto Univ.)
Jiseok KIM (Korea Univ.)
Asahi KOHDA (Osaka Univ.)

Kei KOKUBUN (Univ. of Tokyo)
Shunpei KOYAMA (Univ. of Tokyo)
Jung Woo LEE (Korea Univ.)
Thomas G. PARRY (Univ. of Surrey)
Takeshi SAITO (Univ. of Tokyo)
Hidaka TANABE (Tsukuba Univ.)
Chun Yuen TSANG (Michigan State Univ.)
Phong VI (VNU Univ. of Sci.)
Ryo WAKABAYASHI (Osaka Univ.)
Tik Tsun YEUNG (The Univ. of Hong Kong)
Naoya YOSHIDA (Univ. of Tokyo)

Part-time Workers
Kiyomi ARAI (Research Part-time Worker I)
Mie DOI (Research Part-time Worker I)
Masanori KANEKO (Research Part-time Worker I)
Miki KANOU (Research Part-time Worker I)

Noriko OKAYASU (Research Part-time Worker I)
Tsuneyo SUZUKI (Research Part-time Worker I)
Misuzu KANOU (Research Part-time Worker II)
Eiko MIZUMOTO (Research Part-time Worker II)- 215 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

List of Publications & Presentations
Publications[Original Papers]
B. Moon, A. Jungclaus, H. Naı̈dja, A. Gargano, R. Lozeva, C. -B. Moon, A. Odahara, G. S. Simpson, S. Nishimura, F. Browne, P. Doornenbal, G. Gey, J. Keatings, G. Lorusso, Z. Patel, S. Rice, M. Si, L. Sinclair, P. -A. Sd̈erström, T. Sumikama, J. Taprogge, H. Watanabe,
J. Wu, Z. Y. Xu, A. Yagi, D. S. Ahn, H. Baba, F. L. Bello Garrote, S. Bönig, R. Daido, J. M. Daugas, F. Didierjean, F. Drouet, Y. Fang,
N. Fukuda, R. Gernhäuser, B. Hong, E. Ideguchi, S. Ilieva, N. Inabe, T. Ishigaki, T. Isobe, H. S. Jung, D. Kameda, I. Kojouharov,
T. Komatsubara, T. Kröll, T. Kubo, N. Kurz, Y. K. Kwon, C. S. Lee, P. Lee, Z. Li, A. Montaner-Pizá, S. Morimoto, K. Moschner,
D. Mücher, D. Murai, M. Niikura, H. Nishibata, I. Nishizuka, R. Orlandi, H. Sakurai, H. Schaﬀner, Y. Shimizu, K. Steiger, H. Suzuki,
H. Takeda, K. Tshoo, Z. Vajta, A. Wendt, R. Yokoyama, and K. Yoshinaga, “Nuclear structure of Te isotopes beyond neutron magic
number N = 82,”Phys. Rev. C 103, 034320 (2021).
M. Juhász, Z. Elekes, D. Sohler, Y. Utsuno, K. Yoshida, T. Otsuka, K. Ogata, P. Doornenbal, A. Obertelli, H. Baba, F. Browne, D. Calvet,
F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, J. -M. Gheller, A. Giganon, A. Gillibert, C. Hilaire, T. Isobe,
T. Kobayashi, Y. Kubota, V. Lapoux, T. Motobayashi, I. Murray, H. Otsu, V. Panin, N. Paul, W. Rodriguez, H. Sakurai, M. Sasano,
D. Steppenbeck, L. Stuhl, Y. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, N. Achouri, O. Aktas, T. Aumann, L. Chung,Z. Dombrádi, F. Flavigny, S. Franchoo, I. Gašparić, R. -B. Gerst, J. Gibelin, K. Hahn, D. Kim, T. Koiwai, Y. Kondo, P. Koseoglou, J. Lee,
C. Lehr, B. Linh, H. Liu, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Park, D. Rossi, E. Sahin, P. -A. Söderström,
S. Takeuchi, H. Törnqvist, V. Vaquero, V. Wagner, S. Wang, V. Werner, X. Xu, H. Yamada, D. Yan, Z. Yang, M. Yasuda, and L. Zanetti,“First spectroscopic study of 51 Ar by the (p, 2p) reaction,” Phys. Lett. B 814, 136108 (2021).
Y. L. Sun, T. Nakamura, Y. Kondo, Y. Satou, J. Lee, T. Matsumoto, K. Ogata, Y. Kikuchi, N. Aoi, Y. Ichikawa, K. Ieki, M. Ishihara,
T. Kobayshi, T. Motobayashi, H. Otsu, H. Sakurai, T. Shimamura, S. Shimoura, T. Shinohara, T. Sugimoto, S. Takeuchi, Y. Togano,and K. Yoneda, “Three-body breakup of 6 He and its halo structure,” Phys. Lett. B 814, 136072 (2021).
K. Wimmer, W. Korten, P. Doornenbal, T. Arici, P. Aguilera, A. Algora, T. Ando, H. Baba, B. Blank, A. Boso, S. Chen, A. Corsi,
P. Davies, J. P. Delaroche, G. de. Angelis, G. de. France, D. T. Doherty, J. Gerl, R. Gernhäuser, T. Goigoux, M. Girod, D. Jenkins,
G. Kiss, S. Koyama, T. Motobayashi, S. Nagamine, M. Niikura, S. Nishimura, A. Obertelli, J. Libert, D. Lubos, T. R. Rodriguez,
V. H. Phong, B. Rubio, E. Sahin, T. Y. Saito, H. Sakurai, L. Sinclair, D. Steppenbeck, R. Taniuchi, V. Vaquero, R. Wadsworth, J. Wu,
and M. Zielinska, “Shape changes in the mirror nuclei 70 Kr and 70 Se,” Phys. Rev. Lett. 126, 072501 (2021).
G. Jhang, J. Estee, J. Barney, G. Cerizza, M. Kaneko, J. W. Lee, W. G. Lynch, T. Isobe, M. Kurata-Nishimura, T. Murakami, C. Y. Tsang,
M. B. Tsang, R. Wang, D. S. Ahn, L. Atar, T. Aumann, H. Baba, K. Boretzky, J. Brzychczyk, N. Chiga, N. Fukuda, I. Gasparic,
B. Hong, A. Horvat, K. Ieki, N. Inabe, Y. J. Kim, T. Kobayashi, Y. Kondo, P. Lasko, H. S. Lee, Y. Leifels, J. Lukasik, J. Manfredi,A. B. McIntosh, P. Morfouace, T. Nakamura, N. Nakatsuka, S. Nishimura, R. Olsen, H. Otsu, P. Pawfowski, K. Pelczar, D. Rossi,
H. Sakurai, C. Santamaria, H. Sato, H. Scheit, R. Shane, Y. Shimizu, H. Simon, A. Snoch, A. Sochocka, Z. Sosin, T. Sumikama,
H. Suzuki, D. Suzuki, H. Takeda, S. Tangwancharoen, H. Toernqvist, Y. Togano, Z. G. Xiao, S. J. Yennello, J. Yurkon, Y. Zhang, theSπRIT Collaboration M. Colonna, D. Cozma, P. Danielewicz, H. Elfner, N. Ikeno, C. MingKo, J. Mohs, D. Oliinychenko, A. Ono,
J. Suae, Y. J. Wang, H. Wolter, J. Xu, Y. X. Zhang, and Z. Zhang, the TMEP Collaboration, “Symmetry energy investigation with pion
production from Sn + Sn systems,” Phys. Lett. B 813, 136016 (2021).
S. E. A. Orrigo, B. Rubio, W. Gelletly, P. Aguilera, A. Algora, A. I. Morales, J. Agramunt, D. S. Ahn, P. Ascher, B. Blank, C. Borcea,
A. Boso, R. B. Cakirli, J. Chiba, G. De. Angelis, G. De. France, F. Diel, P. Doornenbal, Y. Fujita, N. Fukuda, E. Ganioglu, M. Gerbaux,
J. Giovinazzo, S. Go, T. Goigoux, S. Grevy, V. Guadilla, N. Inabe, G. G. Kiss, T. Kubo, S. Kubono, T. Kurtukian-Nieto, D. Lubos,
C. Magron, F. Molina, A. Montaner-Piza, D. Napoli, D. Nishimura, S. Nishimura, H. Oikawa, V. H. Phong, H. Sakurai, Y. Shimizu,
C. Sidong, P. -A. Söderström, T. Sumikama, H. Suzuki, H. Takeda, Y. Takei, M. Tanaka, J. Wu, and S. Yagi, “β Decay of the very
neutron-deficient 60 Ge and 62 Ge nuclei,” Phys. Rev. C 103, 014324 (2021).
T. Sumikama, N. Fukuda, N. Inabe, D. Kameda, T. Kubo, Y. Shimizu, H. Suzuki, H. Takeda, K. Yoshida, H. Baba, F. Browne, A. M. Bruce,
R. Carroll, N. Chiga, R. Daido, F. Didierjean, P. Doornenbal, Y. Fang, G. Gey, E. Ideguchi, T. Isobe, S. Lalkovski, Z. Li, G. Lorusso,
R. Lozeva, H. Nishibata, S. Nishimura, I. Nishizuka, A. Odahara, Z. Patel, Z. Podolyák, P. H. Regan, S. Rice, O. J. Roberts, H. Sakurai,
G. S. Simpson, L. Sinclair, P. -A. Söderström, M. Tanaka, J. Taprogge, H. Watanabe, V. Werner, O. Wieland, J. Wu, Z. Y. Xu, andA. Yagi, “Observation of new neutron-rich isotopes in the vicinity of 110 Zr,” Phys. Rev. C 103, 014614 (2021).
T. Sumikama, D. S. Ahn, N. Fukuda, Y. Shimizu, H. Suzuki, H. Takeda, H. Wang, K. Yoshida, J. Amano, N. Chiga, K. Chikaato,
A. Hirayama, N. Inabe, S. Kawase, S. Kubono, M. Matsushita, S. Michimasa, K. Nakano, H. Otsu, H. Sakurai, A. Saito, S. Shimoura,
J. Suwa, M. Takechi, S. Takeuchi, Y. Togano, T. Tomai, and Y. Watanabe, “Energy-control and novel particle-identification methods
combined with range in a multi-sampling ionization chamber for experiments using slowed-down RI beams,” Nucl. Instrum. Methods
Phys. Res. A 986, 164687 (2021).
M. L. Cortés, W. Rodriguez, P. Doornenbal, A. Obertelli, J. D. Holt, J. Menéndez, K. Ogata, A. Schwenk, N. Shimizu, J. Simonis,
Y. Utsuno, K. Yoshida, L. Achouri, H. Baba, F. Browne, D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, A. Delbart, J. -M. Gheller,
A. Giganon, A. Gillibert, C. Hilaire, T. Isobe, T. Kobayashi, Y. Kubota, V. Lapoux, H. N. Liu, T. Motobayashi, I. Murray, H. Otsu,
V. Panin, N. Paul, H. Sakurai, M. Sasano, D. Steppenbeck, L. Stuhl, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, O. Aktas,
T. Aumann, L. X. Chung, F. Flavigny, S. Franchoo, I. Gašparı́c, R. -B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, T. Koiwai, Y. Kondo,
P. Koseoglou, J. Lee, C. Lehr, B. D. Linh, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi, E. Sahin,
P. -A. Söderström, D. Sohler, S. Takeuchi, H. Toernqvist, V. Vaquero, V. Wagner, S. Wang, V. Werner, X. Xu, H. Yamada, D. Yan,
Z. Yang, M. Yasuda, and L. Zanetti, “N = 32 shell closure below calcium: Low-lying structure of 50 Ar,” Phys. Rev. C 102, 064320(2020).
A. Jungclaus, J. M. Keatings, G. S. Simpson, H. Naı̈dja, A. Gargano, S. Nishimura, P. Doornenbal, G. Gey, G. Lorusso, P. -A. Söderström,- 216 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

T. Sumikama, J. Taprogge, Z. Y. Xu, H. Baba, F. Browne, N. Fukuda, N. Inabe, T. Isobe, H. S. Jung, D. Kameda, G. D. Kim, Y. -K. Kim,
I. Kojouharov, T. Kubo, N. Kurz, Y. K. Kwon, Z. Li, H. Sakurai, H. Schaﬀner, Y. Shimizu, H. Suzuki, H. Takeda, Z. Vajta, H. Watanabe,
J. Wu, A. Yagi, K. Yoshinaga, S. Bönig, J. -M. Daugas, R. Gernhäuser, S. Ilieva, T. Kröll, A. Montaner-Piza, K. Moschner, D. Mücher,
H. Nishibata, A. Odahara, R. Orlandi, M. Scheck, K. Steiger, and A. Wendt, “Evolution of proton single-particle states in neutron-rich
Sb isotopes beyond N = 82,” Phys. Rev. C 102, 034324 (2020).
A. Gottardo, G. de Angelis, P. Doornenbal, L. Coraggio, A. Gargano, N. Itaco, K. Kaneko, P. Van Isacker, T. Furumoto, G. Benzoni,
J. Lee, H .Liu, M. Matsushita, D. Mengoni, V. Modamio-Hoybjor, S. Momiyama, T. Motobayashi, D. R. Napoli, M. Niikura, E. Sahin,
Y. Shiga, H. Sakurai, R. Taniuchi, S. Takeuchi, H. Wang, J. J. Valiente-Dobon, R. Avigo, H. Baba, N. Blasi, F. L. Bello Garrote,
F. Browne, F. C. L. Crespi, S. Ceruti, R .Daido, M. -C. Delattre, D. Fang, Zs. Dombradi, T. Isobe, I. Kuti, G. Lorusso, K. Matsui,
B. Melon, T. Miyazaki, S. Nishimura, R. Orlandi, Z. Patel, S. Rice, L. Sinclair, P. A. Soderstrom, D .Sohler, T. Sumikama, J. Taprogge,
Zs. Vajta, H. Watanabe, O. Wieland, J. Wu, Z. Y. Xu, M. Yalcinkaya, and R. Yokoyama, “Transition strengths in the neutron-rich
73, 74, 75
Ni isotopes,” Phys. Rev. C 102, 014323 (2020).
J. J. Liu, J. Lee, H. Watanabe, S. Nishimura, G. X. Zhang, J. Wu, P. M. Walker, P. H. Regan, P. -A. Söderström, H. Kanaoka, Z. Korkulu,
P. S. Lee, A. Yagi, A. C. Dai, F. R. Xu, D. S. Ahn, T. Alharbi, H. Baba, F. Browne, A. M. Bruce, R. J. Carroll, K. Y. Chae, Zs. Dombradi,
P. Doornenbal, A. Estrade, N. Fukuda, C. Griﬃn, E. Ideguchi, N. Inabe, T. Isobe, S. Kanaya, I. Kojouharov, F. G. Kondev, T. Kubo,
S. Kubono, N. Kurz, I. Kuti, S. Lalkovski, G. J. Lane, C. S. Lee, E. J. Lee, G. Lorusso, G. Lotay, C. B. Moon, I. Nishizuka, C. R. Nita,
A. Odahara, Z. Patel, V. H. Phong, Zs. Podolyak, O. J. Roberts, H. Sakurai, H. Schaﬀner, C. M. Shand, Y. Shimizu, T. Sumikama,
H. Suzuki, H. Takeda, S. Terashima, Zs. Vajta, J. J. Valiente-Dobon, and Z. Y. Xu, “Isomeric and β-decay spectroscopy of decay of173, 174
Ho,” Phys. Rev. C 102, 024301 (2020).
F. L. Bello Garrote, E. Sahin, Y. Tsunoda, T. Otsuka, A. Görgen, M. Niikura, S. Nishimura, G. de Angelis, G. Benzoni, A. I. Morales,
V. Modamio, Z. Y. Xu, H. Baba, F. Browne, A. M. Bruce, S. Ceruti, F. C. L. Crespi, R. Daido, M. -C. Delattre, P. Doornenbal,
Z. Dombradi, Y. Fang, S. Franchoo, G. Gey, A. Gottardo, K. Hadynska-Klek, T. Isobe, P. R. John, H. S. Jung, I. Kojouharov, T. Kubo,
N. Kurz, I. Kuti, Z. Li, G. Lorusso, I. Matea, K. Matsui, D. Mengoni, T. Miyazaki, S. Momiyama, P. Morfouace, D. R. Napoli,
F. Naqvi, H. Nishibata, A. Odahara, R. Orlandi, Z. Patel, S. Rice, H. Sakurai, H. Schaﬀner, L. Sinclair, P. -A. Söderström, D. Sohler,
I. G. Stefan, T. Sumikama, D. Suzuki, R. Taniuchi, J. Taprogge, Z. Vajta, J. J. Valiente-Dobón, H. Watanabe, V. Werner, J. Wu, A. Yagi,
M. Yalcinkaya, R. Yokoyama, and K. Yoshinaga, “β Decay of 75 Ni and the systematics of the low-lying level structure of neutron-rich
odd-A Cu isotopes,” Phys. Rev. C 102, 034314 (2020).
J. Park, R. Krücken, A. Blazhev, D. Lubos, R. Gernhäuser, M. Lewitowicz, S. Nishimura, D. S. Ahn, H. Baba, B. Blank, P. Boutachkov,
F. Frowne, I. Čeliković, G.de France, P. Doornenbal, T. Faestermann, Y. Fang, N. Fukuda, J. Giovinazzo, N. Goel, M. Górska,
H. Grawe, S. Ilieva, N. Inabe, T. Isobe, A. Jungclaus, D. Kameda, G. D. Kim, Y. -K. Kim, I. Kojouharov, T. Kubo, N. Kurz, Y. K. Kwon,
G. Lorusso, K. Moschner, D. Murai, I. Nishizuka, Z. Patel, M. M. Rajabali, S. Rice, H. Sakurai, H. Schaﬀner, Y. Shimizu, L. Sinclair,
P. -A. Söderström, K. Steiger, T. Sumikama, H. Suzuki, H. Takeda, Z. Wang, H. Watanabe, J. Wu, and Z. Y. Xu, “Spectroscopy of 99 Cd
and 101 In from β decay of 99 In and 101 Sn,” Phys. Rev. C 102, 014304 (2020).
A. Frotscher, M. Gómez-Ramos, A. Obertelli, P. Doornenbal, G. Authelet, H. Baba, D. Calvet, F. Château, S. Chen, A. Corsi, A. Delbart,
J. -M. Gheller, A. Giganon, A. Gillibert, T. Isobe, V. Lapoux, M. Matsushita, S. Momiyama, T. Motobayashi, M. Niikura, H. Otsu,
N. Paul, C. Péron, A. Peyaud, E. C. Pollacco, J. -Y. Roussé, H. Sakurai, C. Santamaria, M. Sasano, Y. Shiga, N. Shimizu, D. Steppenbeck, S. Takeuchi, R. Taniuchi, T. Uesaka, H. Wang, K. Yoneda, T. Ando, T. Arici, A. Blazhev, F. Browne, A. M. Bruce, R. Carroll,
L. X. Chung, M. L. Cortés, M. Dewald, B. Ding, Z. Dombradi, F. Flavigny, S. Franchoo, F. Giacoppo, M. Górska, A. Gottardo,
K. Hadynska-Klek, Z. Korkulu, S. Koyama, Y. Kubota, A. Jungclaus, J. Lee, M. Lettmann, B. D. Linh, J. Liu, Z. Liu, C. Lizarazo,
C. Louchart, R. Lozeva, K. Matsui, T. Miyazaki, K. Moschner, S. Nagamine, N. Nakatsuka, C. Nita, S. Nishimura, C. R. Nobs,
L. Olivier, S. Ota, Z. Patel, Z. Podolyák, M. Rudigier, E. Sahin, T. Y. Saito, C. Shand, P. -A. Söderström, I. G. Stefan, T. Sumikama,
D. Suzuki, R. Orlandi, V. Vaquero, Z. Vajta, V. Werner, K. Wimmer, J. Wu, and Z. Xu, “Sequential nature of (p, 3p) two-proton
knockout from neutron-rich nuclei,” Phys. Rev. Lett. 125, 012501 (2020).
X. H. Sun, H. Wang, H. Otsu, H. Sakurai, D. S. Ahn, M. Aikawa, N. Fukuda, T. Isobe, S. Kawakami, S. Koyama, T. Kubo, S. Kubono,
G. Lorusso, Y. Maeda, A. Makinaga, S Momiyama, K. Nakano, S. Nakayama, M. Niikura, Y. Shiga, P. -A. Soderstrom, H. Suzuki,
H. Takeda, S. Takeuchi, R. Taniuchi, Ya. Watanabe, Yu. Watanabe, H. Yamasaki, X. F. Yang, Y. L. Ye, and K. Yoshida, “Spallationand fragmentation cross sections for 168 MeV/nucleon 136 Xe ions on proton, deuteron, and carbon targets,” Phys. Rev. C 101, 064623(2020).
J. W. Lee, G. Jhang, G. Cerizza, J. Barney, J. Estee, T. Isobe, M. Kaneko, M. Kurata-Nishimura, W. G. Lynch, T. Murakami, C. Y. Tsang,
M. B. Tsang, R. Wang, B. Hong, A. B. McIntosh, H. Sakurai, C. Santamaria, R. Shane, S. Tangwancharoen, S. J. Yennello, Y. Zhang,
For the SπRIT Collaboration “Charged particle track reconstruction with SπRIT time projection chamber,” Nucl. Instrum. Methods
Phys. Res. A 965, 163840 (2020).
S. Bagchi, R. Kanungo, Y. K. Tanaka, H. Geissel, P. Doornenbal, W. Horiuchi, G. Hagen, T. Suzuki, N. Tsunoda, D. S. Ahn, H. Baba,
K. Behr, F. Browne, S. Chen, M. L. Cortés, A. Estradé, N. Fukuda, M. Holl, K. Itahashi, N. Iwasa, G. R. Jansen, W. G. Jiang, S. Kaur,A. O. Macchiavelli, S. Y. Matsumoto, S. Momiyama, I. Murray, T. Nakamura, S. J. Novario, H. J. Ong, T. Otsuka, T. Papenbrock,
S. Paschalis, A. Prochazka, C. Scheidenberger, P. Schrock, Y. Shimizu, D. Steppenbeck, H. Sakurai, D. Suzuki, H. Suzuki, M. Takechi,
H. Takeda, S. Takeuchi, R. Taniuchi, K. Wimmer, and K. Yoshida, “Two-neutron halo is unveiled in 29 F,” Phys. Rev. Lett. 124 222504(2020).
K. Wimmer, T. Arici, W. Korten, P. Doornenbal, J. -P. Delaroche, M. Girod, J. Libert, T. R. Rodrigue, P. Aguilera, A. Algora, T. Ando,
H. Baba, B. Blank, A. Boso, S. Chen, A. Corsi, P. Davies, G. de. Angelis, G. de. France, D. T. Doherty, J. Gerl, R. Gernhäuser,
T. Goigoux, D. Jenkins, G. Kiss, S. Koyama, T. Motobayashi, S. Nagamine, M. Niikura, S. Nishimura, A. Obertelli, D. Lubos,
V. H. Phong, B. Rubio, E. Sahin, T. Y. Saito, H. Sakurai, L. Sinclair, D. Steppenbeck, R. Taniuchi, V. Vaquero, R. Wadsworth, J. Wu,
and M. Zielinska, “Shape coexistence revealed in the N = Z isotope 72 Kr through inelastic scattering.” Eur. Phys. J. A 56.6, 1–12
(2020).

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C. Lizarazo, P. -A. Söderström, V. Werner, N. Pietralla, P. M. Walker, G. X. Dong, F. R. Xu, T. R. Rodrı́guez, F. Browne, P. Doornenbal,
S. Nishimura, C. R. Nita, A. Obertelli, T. Ando, T. Arici, G. Authelet, H. Baba, A. Blazhev, A. M. Bruce, D. Calvet, R. J. Caroll,F. Château, S. Chen, L. X. Chung, A. Corsi, M. L. Cortés, A. Delbart, M. Dewald, B. Ding, F. Flavigny, S. Franchoo, J. Gerl, J. M. Gheller, A. Giganon, A. Gillibert, M. Górska, A. Gottardo, I. Kojouharov, N. Kurz, V. Lapoux, J. Lee, M. Lettmann, B. D. Linh,
J. J. Liu, Z. Liu, S. Momiyama, K. Moschner, T. Motobayashi, S. Nagamine, N. Nakatsuka, M. Niikura, C. Nobs, L. Olivier, Z. Patel,
N. Paul, Z. Podolyák, J. -Y. Roussé, M. Rudigier, T. Y. Saito, H. Sakurai, C. Santamaria, H. Schaﬀner, C. Shand, I. Stefan, D. Steppenbeck, R. Taniuchi, T. Uesaka, V. Vaquero, K. Wimmer, and Z. Xu, “Metastable states of 92, 94Se: Identification of an oblate K isomerof 94 Se and the ground-state shape transition between N = 58 and 60,” Phys. Rev. Lett. 124, 222502 (2020).
J. Wu, S. Nishimura, P. Möller, M. R. Mumpower, R. Lozeva, C. B. Moon, A. Odahara, H. Baba, F. Browne, R. Daido, P. Doornenbal, Y. F. Fang, M. Haroon, T. Isobe, H. S. Jung, G. Lorusso, B. Moon, Z. Patel, S. Rice, H. Sakurai, Y. Shimizu, L. Sinclair,
P. -A. Söderström, T. Sumikama, H. Watanabe, Z. Y. Xu, A. Yagi, R. Yokoyama, D. S. Ahn, F. L. Bello Garrote, J. M. Daugas, F. Didierjean, N. Fukuda, N. Inabe, T. Ishigaki, D. Kameda, I. Kojouharov, T. Komatsubara, T. Kubo, N. Kurz, K. Y. Kwon, S. Morimoto,D. Murai, H. Nishibata, H. Schaﬀner, T. M. Sprouse, H. Suzuki, H. Takeda, M. Tanaka, K. Tshoo, and Y. Wakabayashi, “β-Decay
half-lives of 55 neutron-rich isotopes beyond the N = 82 shell gap,” Phys. Rev. C 101, 042801 (R) (2020).
J. Ha, T. Sumikama, F. Browne, N. Hinohara, A. M. Bruce, S. Choi, I. Nishizuka, S. Nishimura, P. Doornenbal, G. Lorusso, P. A. Söderström, H. Watanabe, R. Daido, Z. Patel, S. Rice, L. Sinclair, J. Wu, Z. Y. Xu, A. Yagi, H. Baba, N. Chiga, R. Carroll,F. Didierjean, Y. Fang, N. Fukuda, G. Gey, E. Ideguchi, N. Inabe, T. Isobe, D. Kameda, I. Kojouharov, N. Kurz, T. Kubo, S. Lalkovski,
Z. Li, R. Lozeva, H. Nishibata, A. Odahara, Z. Podolyák, P. H. Regan, O. J. Roberts, H. Sakurai, H. Schaﬀner, G. S. Simpson, H. Suzuki,
H. Takeda, M. Tanaka, J. Taprogge, V. Werner, and O. Wieland, “Shape evolution of neutron-rich 106, 108, 110 Mo isotopes in the triaxial
degree of freedom,” Phys. Rev. C 101, 044311 (2020).
H. Watanabe, Y. X. Wanatabe, Y. Hirayama, A. N. Andreyev, T. Hashimoto, F. G. Kondev, G. J. Lane, Yu.A. Litinov, J. J. Liu, H. Miyatake,J. Y. Moon, A. I. Morales, M. Mukai, S. Nishimura, T. Niwase, M. Rosenbusch, P. Schury, Y. Shi, M. Wada, and P. M. Walker, “Betadecay of the axially asymmetric ground state of 192 Re,” Phys. Lett. B 814, 136088 (2021).
C. Y. Tsang, J. Estee, R. Wang, J. Barney, G. Jhang, W. G. Lynch, Z. Q. Zhang, G. Cerizza, T. Isobe, M. Kaneko, M. Kurata-Nishimura,J. W. Lee, T. Murakami, and M. B. Tsang, the SπRIT Collaboration, “Space charge eﬀects in the SπRIT time projection chamber,”Nucl. Instrum. Methods Phys. Res. A 959, 163477 (2020).
X. Pereira-Lopez, B. Fernandez-Dominguez, F. Delaunay, N. L. Achouri, N. A. Orr, W. N. Catford, M. Assie, S. Bailey, B. Bastin,
Y. Blumenfeld, R. Borcea, M. Caamano, L. Caceres, E. Clement, A. Corsi, N. Curtis, Q. Deshayes, F. Farget, M. Fisichella, G. de
France, S. Franchoo, M. Freer, J. Gibelin, A. Gillibert, G. F. Grinyer, F. Hammache, O. Kamalou, A. Knapton, T. Kokalova, V. Lapoux,
J. A. Lay, B. Le Crom, S. Leblond, J. Lois-Fuentes, F. M. Marques, A. Matta, P. Morfouace, A. M. Moro, T. Otsuka, J. Pancin, L. Perrot,
J. Piot, E. Pollacco, D. Ramos, C. Rodriguez-Tajes, T. Roger, F. Rotaru, M. Senoville, N. de Sereville, R. Smith, O. Sorlin, M. Stanoiu,
I. Stefan, C. Stodel, D. Suzuki, T. Suzuki, J. C. Thomas, N. Timofeyuk, M. Vandebrouck, J. Walshe, and C. Wheldon, “Low-lying
single-particle structure of 17 C and the N = 14 sub-shell closure,” Phys. Lett. B 811, 135939 (2020).
K. Makiguchi, W. Horiuchi, and A. Kohama, “Utility of antiproton-nucleus scattering for probing nuclear surface density distributions,”
Phys. Rev. C 102, 034614 (2020).
N. T. Zhang, X. Y. Wang, D. Tudor, B. Bucher, I. Burducea, H. Chen, Z. J. Chen, D. Chesneanu, A. I. Chilug, L. R. Gasques, D. G. Ghita,
C. Gomoiu, K. Hagino, S. Kubono, Y. J. Li, C. J. Lin, W. P. Lin, R. Margineanu, A. Pantelica, I. C. Stefanescu, M. Straticiuc,
X. D. Tang, L. Trache, A. S. Umar, W. Y. Xin, S. W. Xu, and Y. Xu, “Constraining the 12 C + 12 C astrophysical S -factors with the12
C + 13 C measurements at very low energies,” Phys. Lett. B 801, 135170 (2020).
N. Iwasa, S. Ishikawa, S. Kubono, T. Sakakibara, K. Kominato, K. Nishio, M. Matsuda, K. Hirose, H. Makii, R. Orlandi, K. Asada,
D. Guru, S. Nishimura, S. Hayakawa, and T. Kawabata, “Experimental study of the Γ p1 /Γ p0 ratios of resonance states in 8 Be fordeducing the 7 Be(n, p1 )7 Li∗ reaction rate relevant to the cosmological lithium problem,” Phys. Rev. C 103, 015801 (2021).

[Review Articles]
H. Yamaguchi, D. Kahl, and S. Kubono, “CRIB: The low energy in-flight RI beam separator,” Nuclear Physics News (NUPECC) 30, 21(2020).

[Proceedings]
K. Nakano, Y. Watanabe, S. Kawase, H. Wang, H. Otsu, H. Sakurai, N. Chiga, J. Suwa, T. Sumikama, S. Takeuchi, T. Nakamura,
K. Chikaato, M. Takechi, S. Koyama, D. S. Ahn, H. Baba, S. Chen, M. L. Cortes, P. Doornenbal, N. Fukuda, A. Hirayama, R. Hosoda,
T. Isobe, S. Kawakami, Y. Kondo, S. Kubono, Y. Maeda, S. Masuoka, S. Michimasa, I. Murray, R. Nakajima, M. Niikura, T. Ozaki,
A. Saito, T. Saito, H. Sato, Y. Shimizu, S. Shimoura, Y. Soudo, P. A. Soderstrom, X. Sun, D. Suzuki, H. Suzuki, H. Takeda, Y.vTogano,
T. Tomai, H. Yamada, M. Yasuda, and K. Yoshida, “Isotope-production cross sections of residual nuclei in proton- and deuteron-induced
reactions on 93 Zr at 50 MeV/u,” Proc. Intern. Conf. Nuclear Data for Science and Technology (ND2019), Beijing, China, May 19–24,
2019, Z. Ge et al., Eds., p. 20006 (2020).
J. Giovinazzo, T. Goigoux, B. Blank, P. Ascher, M. Gerbaux, S. Grevy, T. Kurtukian-Nieto, C. Magron, P. Doornenbal, N. Fukuda,
N. Inabe, G. Kiss, T. Kubo, S. Kubono, S. Nishimura, H. Sakurai, Y. Shimizu, C. Sidong, P. Soderstrom, T. Sumikama, H. Suzuki,
H. Takeda, P. Vi, J. Wu, D. Ahn, J. Agramunt, A. Algora, V. Guadilla, A. Montaner-Piza, A. Morales, S. Orrigo, B. Rubio, Y. Fujita,
M. Tanaka, W. Gelletly, P. Aguilera, F. Molina, F. Diel, D. Lubos, G. de Angelis, D. Napoli, C. Borcea, A. Boso, R. Cakirli, E. Ganioglu,
J. Chiba, D. Nishimura, H. Oikawa, Y. Takei, S. Yagi, K. Wimmer, G. de France, S Go, and B. Brown, “Two-proton radioactivity: theinteresting case of 67 Kr and further studies,” Acta Phys. Pol. B 51, 577 (2020).

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Presentations[International Conferences/Workshops]
H. Sakurai (invited), “Highlights and future directions of RIBF,” Yamada Conference LXXII: The 8th Asia-Pacific Conference on FewBody Problems in Physics, Kanazawa, Japan, March 1–5, 2021.
H. Sakurai (invited), “Physics of exotic nuclei in a 10-year perspective,” Workshop on Frontiers of Nuclear Structure and Nuclear Astrophysics and Toward PKU-UT Joint Research Center on Nuclear Physics, Fragrant Hill Hotel and Online, Beijing, October 14–16,
2020.
P. Doornenbal (invited), “High-resolution in-beam gamma-ray spectroscopy at the RIBF with HiCARI,” NUSTAR Annual Meeting 2021,
Online, February 22–26, 2021.
D. Suzuki (invited), “Two neutron transfer resonances via alpha scattering,” International mini-workshop on physics in resonant reaction
induced by low-energy RI beam, Japan, February 22, 2021.
D. Suzuki (invited), “Spectroscopy of light exotic nuclei beyond the proton drip line,” Yamada Conference LXXII: The 8th Asia-PacificConference on Few-Body Problems in Physics, Kanazawa, Japan, March 1–5, 2021.
K. Asahi (invited), “Electric dipole moment of diamagnetic atom 129 Xe as a probe for new physics,” Fundamental Sciences and Quantum
Technologies using Atomic Systems (FSQT2020) (on-line), Physical Research Laboratory, Navrangpura, Ahmedabad, India, September 28–October 1, 2020.
S. Kubono (invited), “Challenge to explosive hydrogen burning in nuclear physics—study of rp-process and νp-process,” NAOJ Workshop
on Stellar Alchemy to Galactic Archeology, October 26–29, 2020.

[Domestic Conferences/Workshops]
櫻井博儀（招待講演）, 「不安定核ビームが開拓するエキゾチック原子核の物理」, シンポジウム「大強度不安定核ビームが拓く新領域」, 日本物理学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
S. Nishimura (invited), “Frontier of experimental activities relevant to r-process nucleosynthesis at RIBF,” KEK Workshop: Beta decay,r process and related weak interaction processes, February 19, 2021.
S. Nishimura (invited), 「不安定核から探るランタノイド元素合成の謎」, NAOJ Workshop: Stellar Alchemy to Galactic Archeology,
October 26–29, 2020.
槇口雄仁, 堀内渉, 小濱洋央（口頭発表）, 「原子核密度分布に対する反陽子-原子核散乱の有用性」, 日本物理学会 2020 年秋季大会,
オンライン開催, 2020 年 9 月 14–17 日.
F. Browne (oral), “Single-particle energies and strengths around 55 Sc,” FY2020 SPDR Presentation Session, Wako, Japan, January 18,
2021.

[Seminars]
H. Sakurai, “Overview of research activities and plans at RIBF,” The C2R2 (CENS, CENuM, RUA, RULIC) Seminar, on-line, CENS,IBS, Korea, October 22, 2020.
K. Asahi, “Electric dipole moment of diamagnetic atom 129 Xe as a probe for new physics,” ISOLDE Physics Group Seminar, on-line &CERN, Geneva, Switzerland, November 19, 2020.
T. Isobe, 「理研不安定核ビームで探る中性子星の状態方程式」, Physics Seminar, Nara Women’s University, Nara, Japan, July 21, 2020.

AwardsPress Releases「フッ素-29 が「2 中性子ハロー原子核」であることを発見—魔法数 20 の消失と中性子ハロー構造の出現—」, 2020 年 8 月 21 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Spin isospin Laboratory
1. Abstract

The Spin Isospin Laboratory pursues research activities putting primary focus on interplay of spin and isospin in exotic nuclei.
Understanding nucleosyntheses in the universe, especially those in r- and rp-processes is another big goal of our laboratory.
Investigations on isospin dependences of nuclear equation of state, spin-isospin responses of exotic nuclei, occurrence of various
correlations at low-densities, evolution of spin-orbit coupling are main subjects along the line. We are leading a mass measurement
project with the Rare RI Ring project, too. Through the experimental studies, we will be able to elucidate a variety of nuclear
phenomena in terms of interplay of spin and isospin, which will in turn, lead us to better understanding of our universe.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

Direct reaction studies of neutron-matter equation of state
Study of spin-isospin responses with RI-beams
R-process nucleosynthesis study with heavy-ion storage ring
Application of spin-polarization technique to RI-beam experiments and other fields
Development of special targets for RI-beam experiments

3. Summary of Research Activity(1) Direct reaction studies of neutron matter equation of state
Direct reactions induced by light-ions serve as powerful tools to investigate various aspects of nuclei. We are advancing experimental programs to explore equation of state of neutron matter, via light-ion induced reactions with RI-beams.
(1-1) Determination of a neutron skin thickness by proton elastic scattering
A neutron skin thickness is known to have strong relevance to asymmetry terms of nuclear equation of state, especially to aterm proportional to density. The ESPRI project aims at determining density distributions in exotic nuclei precisely by proton elastic
scattering at 200–300 MeV/nucleon. An experiment for 132 Sn that is a flagship in this project has been successfully performed.
(1-2) Asymmetry terms in nuclear incompressibility
Nuclear incompressibility represents stiﬀness of nuclear matter. Incompressibility of symmetric nuclear matter is determined
to be 230 ± 20 MeV, but its isospin dependence still has a large uncertainty at present. A direct approach to the incompressibilityof asymmetric nuclear matter is an experimental determination of energies of isoscalar giant monopole resonances (GMR) in heavy
nuclei. We have developed, in close collaboration with Center for Nuclear Study (CNS) of University of Tokyo, an active gas target
for deuteron inelastic scattering experiments to determine GMR energies. The active gas target has been already tested with oxygen
and xenon beams at HIMAC and finally has been applied to a 132 Sn experiment at RIBF.
(1-3) Multi-neutron and α-cluster correlations at low densities
Occurrences of multi-neutron and α-cluster correlations are other interesting aspects of nuclear matter and define its low-density
behavior. The multi-neutron and α-cluster correlations can be investigated with the large-acceptance SAMURAI spectrometer. The
SAMURAI has been already applied to experiments to explore light neutron-rich nuclei close to the dripline. We plan to reinforce
experimental capabilities of the SAMURAI by introducing advanced devices such as MINOS (Saclay) and NeuLAND (GSI).
(1-4) Fission barrier heights in neutron-rich heavy nuclei
The symmetry energy has a strong influence on fission barrier heights in neutron-rich nuclei. Knowledge on the fission barrierheights, which is quite poor at present, is quite important for our proper understanding on termination of the r-process. We are planningto perform, in collaboration with the TU Munich group, (p, 2p)-delayed fission experiments at the SAMURAI to determine the fission
barrier heights in neutron-rich nuclei in Pb region.
(2) Study of spin-isospin responses with RI-beams
The study of spin-isospin responses in nuclei forms one of the important cores of nuclear physics. A variety of collective states,for example isovector giant dipole resonances, isobaric analogue states, Gamow-Teller resonances, have been extensively studied byuse of electromagnetic and hadronic reactions from stable targets.
The research opportunities can be largely enhanced with light of availabilities of radioactive isotope (RI) beams and of physics of
unstable nuclei. There are three possible directions to proceed. The first direction is studies of spin-isospin responses of unstable nuclei
via inverse-kinematics charge exchange reactions. A neutron-detector array WINDS has been constructed, under a collaboration of
CNS, Tokyo and RIKEN, for inverse kinematics (p, n) experiments at the RI Beam Factory. We have already applied WINDS to the(p, n) experiments for 12 Be, 132 Sn and plan to extend this kind of study to other exotic nuclei.
The second direction is studies with RI-beam induced charge exchange reaction. RI-beam induced reactions have unique properties which are missing in stable-beam induced reactions and can be used to reach the yet-to-be-discovered states. We have constructed
the SHARAQ spectrometer and the high-resolution beam-line at the RI Beam Factory to pursue the capabilities of RI-beam induced
reactions as new probes to nuclei. One of the highlights is an observation of β+ type isovector spin monopole resonances (IVSMR) in
208
Pb and 90 Zr via the (t, 3 He) reaction at 300 MeV/nucleon.
The third direction is studies of neutron- and proton-rich nuclei via stable-beam induced charge exchange reactions, which is
conducted under collaboration with Research Center for Nuclear Physics (RCNP), Osaka University. We have performed the double- 220 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

charge exchange 12 C(18 O,18 Ne) 12 Be reaction at 80 MeV/nucleon to investigate structure of a neutron-rich 12 Be nucleus. Peaks corresponding to ground and excited levels in 12 Be have been clearly observed. Another double charge exchange reaction, (12 C,12 Be(0+2 ))are being used to search for double Gamow-Teller resonances.
(3) R-process nucleosynthesis study with heavy-ion storage ring
Most of the r-process nuclei become within reach of experimental studies for the first time at RI Beam Factory at RIKEN. The
Rare RI Ring at RIBF is the unique facility with which we can perform mass measurements of r-process nuclei. Construction of theRare RI Ring started in FY2012 in collaboration with Tsukuba and Saitama Universities. A major part of the ring has been completed
and the commissioning run is planned in FY2014.
We are planning to start precise mass measurements of r-process nuclei soon. A series of experiments will start with nuclei in the
A = 80 region and will be extended to heavier region.
(4) Application of spin-polarization technique to RI-beam experiments and other fields
A technique to produce nuclear polarization by means of electron polarization in photo-excited triplet states of aromatic molecules
can open new applications. The technique is called “Tripletd-DNP.” A distinguished feature of Triplet-DNP is that it works under alow magnetic field of 0.1–0.7 T and temperature higher than 100 K, which exhibits a striking contrast to standard dynamic nuclear
polarization (DNP) techniques working in extreme conditions of several Tesla and sub-Kelvin.
We have constructed a polarized proton target system for use in RI-beam experiments. Recent experimental and theoretical studies
have revealed that spin degrees of freedom play a vital role in exotic nuclei. Tensor force eﬀects on the evolution of shell and possible
occurrence of p-n pairing in the proton-rich region are good examples of manifestations of spin degrees of freedom. Experimentswith the target system allow us to explore the spin eﬀects in exotic nuclei. It should be noted that we have recently achieved a proton
polarization of 40% at room temperature in a pentacene-d14 doped p-terphenyl crystal.
Another interesting application of Triplet-DNP is sensitivity enhancement in NMR spectroscopy of biomolecules. We started a
new project to apply the Triplet-DNP technique to study protein-protein interaction via two-dimensional NMR spectroscopy, in close
collaboration with biologists and chemists.
(5) Development of special targets for RI-beam experiments
For the research activities shown above, we are developing and hosting special targets for RI-beam experiments listed below:(a) Polarized proton target (described in (4))(b) Thin solid hydrogen target(c) MINOS (developed at Saclay and hosted by the Spin Isospin Laboratory)

Members
Director
Tomohiro UESAKA
Research/Technical Scientists
Masaki SASANO (Senior Research Scientist)
Ken-ichiro YONEDA (Senior Research Scientist)

Sarah NAIMI (Research Scientist)

Research & Development Scientist
Yohei SHIMIZU
Contract Researchers
Takeshi INOUE

Kenichiro TATEISHI

Postdoctoral Researcher
Junki TANAKA
Research Associate
Akane SAKAUE
Junior Research Associates
Tomoya HARADA

Shoichiro MASUOKAInternational Program Associates
Siwei HUANG (Peking Univ.)
Alexandra-Ionela STEFANESCU (Univ. of Bucharest)

Ionut-Catalin STEFANESCU (Univ. of Bucharest)- 221 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Consultants
Harutaka SAKAGUCHI (Osaka Univ.)
Yasuyuki SUZUKI

Kazuko TANABE

Senior Visiting Scientists
Hiroyuki SAGAWA (Univ. of Aizu)
Satoshi ADACHI (Osaka Univ.)
Hidetoshi AKIMUNE (Konan Univ.)
Didier BEAUMEL (Inst. de Phys.Nucl.)
Konstanze BORETZKY (GSI)
Christoph CAESAR (GSI)
Anna CORSI (CEA Saclay)
Zsolt DOMBRADI (ATOMKI)
Zoltan ELEKES (ATOMKI)
Zsolt FULOP (ATOMKI)
Tatsuya FURUNO (Osaka Univ.)
Igor GASPARIC (Rudjer Boskovic Inst.)
Zhuang GE (IMP, CAS)
Alain GILLIBERT (CEA Saclay)
Valdir GUIMARAES (Inst.o de Fisica da Univ. de Sao Paulo)
Zoltan HALASZ (ATOMKI)
Matthias HOLL (TRIUMF)
Kaori KAKI (Shizuoka Univ.)
KAWABATA (Osaka Univ.)
KIKUCHI (NIT, Tokuyama College)
Yosuke KONDO (Tokyo Tech)
Zeren KORKULU (ATOMKI)
Attila KRASZNAHORKAY (ATOMKI)
Dorottya KUNNE SOHLER (ATOMKI)
Istvan KUTI (ATOMKI)
Valerie LAPOUX (Inst.ion CEA-Saclay)

Yury LITVINOV (GSI)
Hongna LIU (TU Darmstadt)
Yohei MATSUDA (Tohoku Univ.)
Kenjiro MIKI (Tohoku Univ.)
Tetsuaki MORIGUCHI (Tsukuba Univ.)
Takashi NAKAMURA (Tokyo Tech)Alexandre OBERTELLI (TU Darmstadt)
Kazuyuki OGATA (Osaka Univ.)
Emanuel POLLACCO (CEA Saclay)
Kimiko SEKIGUCHI (Tohoku Univ.)
Haik SIMON (GSI)
Laszlo STUHL (ATOMKI)
Baohua SUN (Beihang Univ.)
Shinji SUZUKI (Chinese Academy of Sci.)
Satoru TERASHIMA (Beihang Univ.)
Hans Toshihide TOERNQVIST (TU Darmstadt)
Yasuhiro TOGANO (Rikkyo Univ.)
Takashi WAKUI (QST)
He WANG (Tokyo Tech)
Atomu WATANABE (Tohoku Univ.)
Takayuki YAMAGUCHI (Saitama Univ.)
Nobuhiro YANAI (Kyushu Univ.)
Zaihong YANG (Osaka Univ.)
Juzo ZENIHIRO (Kyoto Univ.)
Yuhu ZHANG (IMP, CAS)

Visiting Technicians
Gilles AUTHELET (CEA)
Denis CALVET (CEA)
Alain DELBART (CEA/CE Saclay)
Jean-Marc GHELLER (CEA)
Arnaud GIGANON (CEA/CE Saclay)

Clement HILAIRE (CEA Saclay)
Daniel KOERPER (GSI)
Cedric PERON (CEA Saclay)
Jean-Yves ROUSSE (CEA)
Olivier TELLIER (CEA Saclay)

Student Trainees
Tomoki ADACHI (Kyushu Univ.)
Paul E. ANDRE (CEA Saclay)
Wenbo DOU (Saitama Univ.)
Naoki EBINA (Tokyo Tech)
Shiyo EN’YO (Kyoto Univ.)
Yuki FUJIKAWA (Kyoto Univ.)
Saiya FUJIWARA (Kyushu Univ.)
Jian GAO (Peking Univ.)
Daiki HAMAKAWA (Saitama Univ.)
Yuya HAMANO (Kyushu Univ.)
Sakumi HARAYAMA (Saitama Univ.)
Mika HAYASHI (Tsukuba Univ.)
Yuto HIJIKATA (Kyoto Univ.)
Kouta HORIKAWA (Tokyo Tech)
Kento INABA (Kyoto Univ.)
Minami INOUE (Tohoku Univ.)
Daisuke KAJIKI (Saitama Univ.)
Koki KAMEYA (Tohoku Univ.)
Naoto KANAME (Tsukuba Univ.)
Masanori KANDA (Saitama Univ.)
Yusuke KAWASHIMA (Kyushu Univ.)
Sho KITAYAMA (Tohoku Univ.)

Shuhei KIYOTAKE (Univ. of Miyazaki)
Taishi KUBO (Kyushu Univ.)
Hayato KUROSAWA (Tohoku Univ.)
Hongfu LI (IMP, CAS)
Pengjie LI (The Univ. of Hong Kong)
Ryu MAEDA (Tohoku Univ.)
Yoshiki MARUTA (Tohoku Univ.)
Tomoki MATSUI (Tokyo Tech)
Riku MATSUMURA (Saitama Univ.)
Shinnosuke NAKAI (Tohoku Univ.)
Mio NISHIMURA (Rikkyo Univ.)
Kotaro NONAKA (Univ. of Miyazaki)
Kyoko NOSAKA (Tohoku Univ.)
Shintaro OKAMOTO (Kyoto Univ.)
Misaki OTSU (Saitama Univ.)
Atsumi SAITO (Tokyo Tech)
Yuko SAITO (Tohoku Univ.)
Shigehito SAKAKI (Kyushu Univ.)
Kosuke SAKANASHI (Osaka Univ.)
Hibiki SEKI (Saitama Univ.)
Naru SHINOZAKI (Saitama Univ.)
Kohei TAKAHASHI (Tokyo Tech)- 222 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Keisuke TOMITA (Tsukuba Univ.)
Ryotaro TSUJI (Kyoto Univ.)
Yuta UTSUKI (Tohoku Univ.)
Kohei YAMAMOTO (Tohoku Univ.)

Asahi YANO (Tsukuba Univ.)
Akira YASUDA (Tokyo Tech)
Chieko YONEMURA (Kyushu Univ.)
Yuuki YOSHITOME (Tokyo Tech)

Interns
Maruf ALI (Univ. of Surrey)

George W.G.W. HUDSON-CHANG (Univ. of Surrey)

Assistants
Emiko ISOGAI
Asako TAKAHASHI

Yuri TSUBURAI

List of Publications & Presentations
Publications[Original Papers]
Y. Kubota, A. Corsi, G. Authelet, H. Baba, C. Caesar, D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin,
A. Giganon, A. Gillibert, K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kikuchi, Y. Kiyokawa, M. Kobayashi,
N. Kobayashi, T. Kobayashi, Y. Kondo, Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marques, T. Motobayashi, T. Miyazaki,
T. Nakamura, N. Nakatsuka, Y. Nishio, A. Obertelli, K. Ogata, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis,
E. C. Pollacco, S. Reichert, J. -Y. Rousse, A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata,Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama, Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, Z. H. Yang, J. Yasuda, K. Yoneda,
J. Zenihiro, and T. Uesaka, “Surface localization of the dineutron in 11 Li,” Phys. Rev. Lett. 125, 252501 (2020).
A. Revel, O. Sorlin, F. M. Marqués, Y. Kondo, J. Kahlbow, T. Nakamura, N. A. Orr, F. Nowacki, J. A. Tostevin, C. X. Yuan, N. L. Achouri,
H. Al Falou, L. Atar, T. Aumann, H. Baba, K. Boretzky, C. Caesar, D. Calvet, H. Chae, N. Chiga, A. Corsi, H. L. Crawford, F. Delaunay, A. Delbart, Q. Deshayes, Z. Dombrádi, C. A. Douma, Z. Elekes, P. Fallon, I. Gašparić, J. -M. Gheller, J. Gibelin, A. Gillibert,
M. N. Harakeh, W. He, A. Hirayama, C. R. Hoﬀman, M. Holl, A. Horvat, Á. Horváth, J. W. Hwang, T. Isobe, N. Kalantar-Nayestanaki,
S. Kawase, S. Kim, K. Kisamori, T. Kobayashi, D. Körper, S. Koyama, I. Kuti, V. Lapoux, S. Lindberg, S. Masuoka, J. Mayer, K. Miki,
T. Murakami, M. Najafi, K. Nakano, N. Nakatsuka, T. Nilsson, A. Obertelli, F. de Oliveira Santos, H. Otsu, T. Ozaki, V. Panin,
S. Paschalis, D. Rossi, A. T. Saito, T. Saito, M. Sasano, H. Sato, Y. Satou, H. Scheit, F. Schindler, P. Schrock, M. Shikata, Y. Shimizu,
H. Simon, D. Sohler, L. Stuhl, S. Takeuchi, M. Tanaka, M. Thoennessen, H. Törnqvist, Y. Togano, T. Tomai, J. Tscheuschner, J. Tsubota, T. Uesaka, Z. Yang, M. Yasuda, and K. Yoneda, “Extending the southern shore of the island of inversion to 28 F,” Phys. Rev. Lett.
124, 15, 152502 (2020).
M. Dozono, T. Uesaka, N. Fukuda, M. Ichimura, N. Inabe, S. Kawase, K. Kisamori, Y. Kiyokawa, K. Kobayashi, M. Kobayashi, T. Kubo,
Y. Kubota, C. S. Lee, M. Matsushita, S. Michimasa, H. Miya, A. Ohkura, S. Ota, H. Sagawa, S. Sakaguchi, H. Sakai, M. Sasano,S. Shimoura, Y. Shindo, L. Stuhl, H. Suzuki, H. Tabata, M. Takaki, H. Takeda, H. Tokieda, T. Wakasa, K. Yako, Y. Yanagisawa,
J. Yasuda, R. Yokoyama, K. Yoshida, and J. Zenihiro, “The parity-transfer (16 O, 16 F(0− , g.s.)) reaction as a probe of isovector 0− statesin nuclei,” Nucl. Phys. B 962, 115236 (2021).
N. Itagaki, T. Fukui, J. Tanaka, and Y. Kikuchi, “8 He and 9 Li cluster structures in light nuclei,” Phys. Rev. C 102, 024332 (2020).
X. Roca-Maza, G. Colo, and H. Sagawa, “Isobaric analog state energy in deformed nuclei: a toy model,” Phys. Rev. C 102, 064303-1–
8 (2020).
T. Aumann, C. Barbieri, D. Bazin, C. A. Bertulani, A. Bonaccorso, W. H. Dickhoﬀ, A. Gade, M. Gomez-Ramos, B. P. Kay, A. M. Moro,T. Nakamura, A. Obertelli, K. Ogata, S. Paschalis, and T. Uesaka, “Quenching of single-particle strength from direct reactions withstable and rare-isotope beams,” Prog. Part. Nucl. Phys. 118, 103847 (2021).
S. Yoshida, H. Sagawa, J. Zenihiro, and T. Uesaka, “Trajectory in 2D-plot of isoscalar and isovector densities of 48 Ca and 208 Pb, andsymmetry energy,” Phys. Rev. C 102, 064307-1–12 (2020).
M. Patsyuk, J. Kahlbow, G. Laskaris, M. Duer, V. Lenivenko, E. P. Segarra, T. Atovullaev, G. Johansson, T. Aumann, A. Corsi,
O. Hen, M. Kapishin, V. Panin, E. Piasetzky, Kh. Abraamyan, S. Afanasiev, G. Agakishiev, P. Alekseev, E. Atkin, T. Aushev,
V. Babkin, V. Balandin, D. Baranov, N. Barbashina, P. Batyuk, S. Bazylev, A. Beck, C. A. Bertulani, D. Blaschke, D. Blau, D. Bogoslovsky, A. Bolozdynya, K. Boretzky, V. Burtsev, M. Buryakov, S. Buzin, A. Chebotov, J. Chen, A. Ciszewski, R. Cruz-Torres,
B. Dabrowska, D. Dabrowski, A. Dmitriev, A. Dryablov, P. Dulov, D. Egorov, A. Fediunin, I. Filippov, K. Filippov, D. Finogeev,
I. Gabdrakhmanov, A. Galavanov, I. Gasparic, O. Gavrischuk, K. Gertsenberger, V. Golovatyuk, M. Golubeva, F. Guber, Yu. Ivanova,
A. Ivashkin, A. Izvestnyy, S. Kakurin, V. Karjavin, N. Karpushkin, R. Kattabekov, V. Kekelidze, S. Khabarov, Yu. Kiryushin, A. Kisiel,
V. Kolesnikov, A. Kolozhvari, Yu. Kopylov, I. Korover, L. Kovachev, A. Kovalenko, Yu. Kovalev, A. Kugler, S. Kuklin, E. Kulish, A. Kuznetsov, E. Ladygin, N. Lashmanov, E. Litvinenko, S. Lobastov, B. Löher, Y. -G. Ma, A. Makankin, A. Maksymchyuk,
A. Malakhov, I. Mardor, S. Merts, A. Morozov, S. Morozov, G. Musulmanbekov, R. Nagdasev, D. Nikitin, V. Palchik, D. Peresunko, M. Peryt, O. Petukhov, Yu. Petukhov, S. Piyadin, V. Plotnikov, G. Pokatashkin, Yu. Potrebenikov, O. Rogachevsky, V. Rogov,
K. Rosłon, D. Rossi, I. Rufanov, P. Rukoyatkin, M. Rumyantsev, D. Sakulin, V. Samsonov, H. Scheit, A. Schmidt, S. Sedykh, I. Selyuzhenkov, P. Senger, S. Sergeev, A. Shchipunov, A. Sheremeteva, M. Shitenkov, V. Shumikhin, A. Shutov, V. Shutov, H. Simon,
I. Slepnev, V. Slepnev, I. Slepov, A. Sorin, V. Sosnovtsev, V. Spaskov, T. Starecki, A. Stavinskiy, E. Streletskaya, O. Streltsova,
M. Strikhanov, N. Sukhov, D. Suvarieva, J. Tanaka, A. Taranenko, N. Tarasov, O. Tarasov, V. Tarasov, A. Terletsky, O. Teryaev,
V. Tcholakov, V. Tikhomirov, A. Timoshenko, N. Topilin, B. Topko, H. Törnqvist, I. Tyapkin, V. Vasendina, A. Vishnevsky,
N. Voytishin, V. Wagner, O. Warmusz, I. Yaron, V. Yurevich, N. Zamiatin, Song Zhang, E. Zherebtsova, V. Zhezher, N. Zhigareva,- 223 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

A. Zinchenko, E. Zubarev, and M. Zuev, “Unperturbed inverse kinematics nucleon knockout measurements with a carbon beam,” Nat.
Phys. 1-7 (2021).
Z. H. Yang, Y. Kubota A. Corsi, K. Yoshida, X. -X. Sun, J. G. Li, M. Kimura, N. Michel, K. Ogata, C. X. Yuan, Q. Yuan, G. Authelet,
H. Baba, C. Caesar,D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin, A. Giganon, A. Gillibert,
K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kiyokawa, M. Kobayashi, N. Kobayashi, T. Kobayashi, Y. Kondo,
Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marques, T. Motobayashi, T. Miyazaki, T. Nakamura, N. Nakatsuka, Y. Nishio,
A. Obertelli, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis, E. C. Pollacco, S. Reichert, J. -Y. Rousse,
A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata, Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama,
Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, F. R. Xu, J. Yasuda, K. Yoneda, J. Zenihiro, S. -G. Zhou, W. Zuo, and T. Uesaka,“Quasi-free neutron knockout reaction reveals a smalls-orbital component in the borromean nucleus 17 B,” Phys. Rev. Lett. 126, 082501(2021).
M. Sasano, H. Sagawa, T. Suzuki, and M. Honma, “Energy-weighted sum rule for Gamow-Teller giant resonances in high spin isomericstates of N = Z nuclei,” Phys. Rev. C 103, 014308-1–10 (2021).
J. Tanaka, Z. Yang, S. Typel, S. Adachi, S. Bai, P. van Beek, D. Beaumel, Y. Fujikawa, J. Han, S. Heil, S. Huang, A. Inoue, Y. Jiang,
M. Knösel, N. Kobayashi Y. Kubota, W. Liu, J. Lou, Y. Maeda, Y. Matsuda, K. Miki, S. Nakamura, K. Ogata, V. Panin, H. Scheit,
F. Schindler, P. Schrock, D. Symochko, A. Tamii, T. Uesaka, V. Wagner, K. Yoshida, J. Zenihiro, and T. Aumann, “Formation of α
clusters in dilute neutron-rich matter,” Science 371, 260–264 (2021).
J. Zenihiro, T. Uesaka, S. Yoshida, and H. Sagawa, “Proton density polarization of the doubly magic 40 Ca core in 48 Ca and EoS parameters,” Prog. Theor. Exp. Phys. 2021, 023D05 (2021).
S. Takada, K. Tateishi, Y. Wakabayashi, Y. Ikeda, T. Yoshioka, Y. Otake, and T. Uesaka, “Polarized proton spin filter for epithermal
neutrons based on dynamic nuclear polarization using photo-excited triplet electron spins PTEP 2020,” Prog. Theor. Exp. Phys. 2020,
123G01 (2020).
D. Wu, C. L. Bai, H. Sagawa, and H. Q. Zhang, “Study of charge radii with neural networks,” Phys. Rev. C 102, 054323-1–7 (2020).
C. Lizarazo, P. -A. Söderström, V. Werner, N. Pietralla, P. M. Walker, G. X. Dong, F. R. Xu, T. R. Rodrı́guez, F. Browne, P. Doornenbal,
S. Nishimura, C. R. Niţǎ, A. Obertelli, T. Ando, T. Arici, G. Authelet, H. Baba, A. Blazhev, A. M. Bruce, D. Calvet, R. J. Caroll, F. Château, S. Chen, L. X. Chung, A. Corsi, M. L. Cortes, A. Delbart, M. Dewald, B. Ding, F. Flavigny, S. Franchoo, J. Gerl,
J. -M. Gheller, A. Giganon, A. Gillibert, M. Górska, A. Gottardo, I. Kojouharov, N. Kurz, V. Lapoux, J. Lee, M. Lettmann, B. D. Linh,
J. J. Liu, Z. Liu, S. Momiyama, K. Moschner, T. Motobayashi, S. Nagamine, N. Nakatsuka, M. Niikura, C. Nobs, L. Olivier, Z. Patel,
N. Paul, Zs. Podolyák, J. -Y. Rousse, M. Rudigier, T. Y. Saito, H. Sakurai, C. Santamaria, H. Schaﬀner, C. Shand, I. Stefan, D. Steppenbeck, R. Taniuchi, T. Uesaka, V. Vaquero, K. Wimmer, and Z. Xu, “Metastable states of 92, 94 Se: identification of an oblate K isomerof 94 Se and the ground-state shape transition between N = 58 and 60,” Phys. Rev. Lett. 124, 22, 222501 (2020).
A. Frotscher, M. Gómez-Ramos, A. Obertelli, P. Doornenbal, G. Authelet, H. Baba, D. Calvet, F. Château, S. Chen, A. Corsi, A. Delbart,
J. -M. Gheller, A. Giganon, A. Gillibert, T. Isobe, V. Lapoux, M. Matsushita, S. Momiyama, T. Motobayashi, M. Niikura, H. Otsu,
N. Paul, C. Peron, A. Peyaud, E. C. Pollacco, J. -Y. Rousse, H. Sakurai, C. Santamaria, M. Sasano, Y. Shiga, N. Shimizu, D. Steppenbeck, S. Takeuchi, R. Taniuchi, T. Uesaka, H. Wang, K. Yoneda, T. Ando, T. Arici, A. Blazhev, F. Browne, A. M. Bruce, R. Carroll,
L. X. Chung, M. L. Cortes, M. Dewald, B. Ding, Zs. Dombradi, F. Flavigny, S. Franchoo, F. Giacoppo, M. Górska, A. Gottardo,
K. Hadyńska-Klȩk, Z. Korkulu, S. Koyama, Y. Kubota, A. Jungclaus, J. Lee, M. Lettmann, B. D. Linh, J. Liu, Z. Liu, C. Lizarazo,
C. Louchart, R. Lozeva, K. Matsui, T. Miyazaki, K. Moschner, S. Nagamine, N. Nakatsuka, C. Nita, S. Nishimura, C. R. Nobs,
L. Olivier, S. Ota, Z. Patel, Zs. Podolyák, M. Rudigier, E. Sahin, T. Y. Saito, C. Shand, P. -A. Söderström, I. G. Stefan, T. Sumikama,
D. Suzuki, R. Orlandi, V. Vaquero, Zs. Vajta, V. Werner, K. Wimmer, J. Wu, and Z. Xu, “Sequential nature of (p, 3p) two-proton
knockout from neutron-rich nuclei,” Phys. Rev. Lett. 1251, 012501 (2020).
M. M. Juhász, Z. Elekes, D. Sohler, Y. Utsuno, K. Yoshida, T. Otsuka, K. Ogata, P. Doornenbal, A. Obertelli, H. Baba, F. Browne,
D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, J. -M. Gheller, A. Giganon, A. Gillibert, C. Hilaire,
T. Isobe, T. Kobayashi, Y. Kubotan, V. Lapoux,T. Motobayashi, I. Murray, H. Otsu, V. Panin, N. Paul, W. Rodriguez, H. Sakurai,
M. Sasano, D. Steppenbeck, L. Stuhlo, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, N. L. Achouri, O. Aktasu, T. Aumann,
L. X. Chung, Zs. Dombrádi, F. Flavign, S. Franchoo, I. Gašparic, R. -B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, T. Koiwa, Y. Kondo,
P. Koseoglo, J. Lee, C. Lehr, B. D. Linh, H. N. Liu, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi,
E. Sahina, P. -A. Söderström, S. Takeuchia, H. Törnqvist, V. Vaqueroa, V. Wagner, S. Wanga, V. Werner, X. Xu, H. Yamada, D. Yana,
Z. Yang, and M. Yasuda, “First spectroscopic study of 51 Ar by the (p, 2p) reaction,” Phys. Lett. B 814, 136108 (2021).
W. J. Huang, M. Wang, F. G. Kondev, G. Audi, and S. Naimi, “The AME 2020 atomic mass evaluation (I). Evaluation of input data,
andadjustment procedures,” Chin. Phys. C 45, 030002 (2021).
W. J. Huang, M. Wang, F. G. Kondev, G. Audi, and S. Naimi, “The AME 2020 atomic mass evaluation (II). Tables, graphs and references,”
Chin. Phys. C 45, 3, 030003 (2021).
N. Itagaki, T. Fukui, J. Tanaka, and Y. Kikuchi, “8 He and 9 Li cluster structures in light nuclei,” Phys. Rev. C 102, 024332 (2020).
T. L. Tang, T. Uesaka, S. Kawase, D. Beaumel, M. Dozono, T. Fujii, N. Fukuda, T. Fukunaga, A. Galindo-Uribarri, S. H. Hwang, N. Inabe,
D. Kameda, T. Kawahara, W. Kim, K. Kisamori, M. Kobayashi, T. Kubo, Y. Kubota, K. Kusaka, C. S. Lee, Y. Maeda, H. Matsubara,
S. Michimasa, H. Miya, T. Noro, A. Obertelli, K. Ogata, S. Ota, E. Padilla-Rodal, S. Sakaguchi, H. Sakai, M. Sasano, S. Shimoura,
S. S. Stepanyan, H. Suzuki, M. Takaki, H. Takeda, H. Tokieda, T. Wakasa, T. Wakui, K. Yako, Y. Yanagisawa, J. Yasuda, R. Yokoyama,
K. Yoshida, K. Yoshida, and J. Zenihiro, “How diﬀerent is the core of 25 F from 24 Og.s. ?” Phys. Rev. Lett. 124, 212502 (2020).
W. Horiuchi, Y. Suzuki, T. Uesaka, and M. Miwa, “Total reaction cross section on a deuteron target and the eclipse eﬀect of the constituent
neutron and proton,” Phys. Rev. C 102, 054601 (2020).
M. L. Cortés, W. Rodriguez, P. Doornenbal, A. Obertelli, J. D. Holt, J. Menéndez, K. Ogata, A. Schwenk, N. Shimizu, J. Simonis,
Y. Utsuno, K. Yoshida, L. Achouri, H. Baba, F. Browne, D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, A. Delbart, J-M. Gheller,- 224 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

A. Giganon, A. Gillibert, C. Hilaire, T. Isobe, T. Kobayashi, Y. Kubota, V. Lapoux, H. N. Liu, T. Motobayashi, I. Murray, H. Otsu,
V. Panin, N. Paul, H. Sakurai, M. Sasano, D. Steppenbeck, L. Stuhl, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, O. Aktas,
T. Aumann, L. X. Chung, F. Flavigny, S. Franchoo, I. Gašparić, R. -B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, T Koiwai, Y. Kondo,
P. Koseoglou, J. Lee, C. Lehr, B. D. Linh, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi, E. Sahin,
P. -A. Söderström, D. Sohler, S. Takeuchi, H. Toernqvist, V. Vaquero, V. Wagner, S. Wang, V. Werner, X. Xu, H. Yamada, D. Yan,
Z. Yang, M. Yasuda, and L. Zanetti, “N = 32 shell closure below calcium: Low-lying structure of 50 Ar,” Phys. Rev. C 102, 064320(2020).
D. Nagae, Y. Abe, S. Okada, S. Omika, K. Wakayama, S. Hosoi, S. Suzuki, T. Moriguchi, M. Amano, D. Kamioka, Z. Ge, S. Naimi,
F. Suzaki, N. Tadano, R. Igosawa, K. Inomata, H. Arakawa, K. Nishimuro, T. Fujii, T. Mitsui, Y. Yanagisawa, H. Baba, S. Michimasa,
S. Ota, G. Lorusso, Yu. A. Litvinov, A. Ozawa, T. Uesaka, T. Yamaguchi, Y. Yamaguchi, and M. Wakasugi, “Development andoperation of an electrostatic time-of-flight detector for the Rare RI storage Ring,” Nucl. Instrum. Methods Phys. Res. A 986, 164713(2021).
Y. Zhang, H. Sagawa, and E. Hiyama, “Hyperon halo structure of C and B Isotopes,” Phys. Rev. C 103, 03432-1–9 (2021).
S. Michimasa, M. Kobayashi, Y. Kiyokawa, S. Ota, R. Yokoyama, D. Nishimura, D. S. Ahn, H. Baba, G. P. A. Berg, M. Dozono,
N. Fukuda, T. Furuno, E. Ideguchi, N. Inabe, T. Kawabata, S. Kawase, K. Kisamori, K. Kobayashi, T. Kubo, Y. Kubota, C. S. Lee,
M. Matsushita, H. Miya, A. Mizukami, H. Nagakura, H. Oikawa, H. Sakai, Y. Shimizu, A. Stolz, H. Suzuki, M. Takaki, H. Takeda,
S. Takeuchi, H. Tokieda, T. Uesaka, K. Yako, Y. Yamaguchi, Y. Yanagisawa, K. Yoshida, and S. Shimoura, “Mapping of a new
deformation region around 62 Ti,” Phys. Rev. Lett. 125, 12, 122501 (2020).
C. Y. Fu, Y. H. Zhang, M. Wang X. H. Zhou Yu. A. Litvinov, K. Blaum, H. S. Xu, X. Xu, P. Shuai, Y. H. Lam, R. J. Chen, X. L. Yan,
X. C. Chen, J. J. He, S. Kubono, M. Z. Sun, X. L. Tu, Y. M. Xing, Q. Zeng, X. Zhou, W. L. Zhan, S. Litvinov, G. Audi, T. Uesaka,
T. Yamaguchi, A. Ozawa, B. H. Sun, Y. Sun, and F. R. Xu, “Mass measurements for the T z = −2 fp nuclei 40 Ti, 44 Cr, 46 Mn, 48 Fe, 50 Co,
and 52 Ni,” Phys. Rev. C 102, 5, 054311 (2020).
S. Takada, K. Tateishi, Y. Wakabayashi, Y. Ikeda, T. Yoshioka, Y. Otake, and T. Uesaka, “Polarized proton spin filter for epithermal neutron
based on dynamic nuclear polarization using photo-excited triplet electron spins,” Prog. Theo. Exp. Phys. 2020, 123G01 (2020).

[Review Articles]
K. Nishimura, H. Kouno, Y. Kawashima, K. Orihashi, S. Fujiwara, K. Tateishi, T. Uesaka, N. Kimizuka, and N. Yanai, “Materials
chemistry of triplet dynamic nuclear polarization,” Chem. Commum. 56, 7217–7232 (2020).

[Proceedings]
S. W. Huang, Z. H. Yang, F. M. Marqués, N. L. Achouri, D. S. Ahn, T. Aumann, H. Baba, D. Beaumel, M. Böhmer, K. Boretzky,
M. Caamaño, S. Chen, N. Chiga, M. L. Cortés, D. Cortina, P. Doornenbal, C. A. Douma, F. Dufter, J. Feng, B. Fernández-Domı́nguez,
Z. Elekes, U. Forsberg, T. Fujino, N. Fukuda, I. Gašparić, Z. Ge, R. Gernhäuser, J. M. Gheller, J. Gibelin, A. Gillibert, B. M. Godoy,
Z. Halász, T. Harada, M. N. Harakeh, A. Hirayama, N. Inabe, T. Isobe, J. Kahlbow, N. Kalantar-Nayestanaki, D. Kim, S. Kim,
M. A. Knösel, T. Kobayashi, Y. Kondo, P. Koseoglou, Y. Kubota, I. Kuti, C. Lehr, P. J. Li, Y. Liu, Y. Maeda, S. Masuoka, M. Matsumoto,
J. Mayer, H. Miki, M. Miwa, I. Murray, T. Nakamura, A. Obertelli, N. Orr, H. Otsu, V. Panin, S. Park, M. Parlog, S. Paschalis, M. Potlog,
S. Reichert, A. Revel, D. Rossi, A. Saito, M. Sasano, H. Sato, H. Scheit, F. Schindler, T. Shimada, Y. Shimizu, S. Shimoura, I. Stefan,
S. Storck, L. Stuhl, H. Suzuki, D. Symochko, H. Takeda, S. Takeuchi, J. Tanaka, Y. Togano, T. Tomai, H. T. Törnqvsit, J. Tscheuschner,
T. Uesaka, V. Wagner, K. Wimmer, H. Yamada, B. Yang, L. Yang, Y. Yasuda, K. Yoneda, L. Zanetti, J. Zenihiro, T. Elidiano, andC. Lenain, “Experimental study of 4n with 8 He(p, 2p) reaction,” J. Phys. Conf. Ser. 1643, 012090 (2020).
V. P. Ladygin, A. V. Averyanov, E. V. Chernykh, Y. V. Gurchin, A. Y. Isupov, D. O. Krivenkov, P. K. Kurilkin, N. B. Ladygina, A. N. Livanov, S. M. Piyadin, S. G. Reznikov, Y. T. Skhomenko, A. A. Terekhin, A. V. Tishevsky, and T. Uesaka, “Angular and energy
dependence of Ay , Ayy and A xx analyzing powers in dp elastic scattering and dp breakup reaction investigation,” Proc. Sci. LC2019,048 (2020).
Z. Yang, J. Tanaka, S. Type, T. Aumann, J. Zenihiro, S. Adachi, S. Bai, P. van Beek, D. Beaumel, Y. Fujikawa, J. Han, S. Heil, S. Huang,
A. Inoue, Y. Jia, M. Knösel, N. Kobayashi, Y. Kubota, W. Liu, J. Lou, Y. Maeda, Y. Matsuda, K. Miki, S. Nakamura, K. Ogata, V. Panin,
H. Scheit, F. Schindler, P. Schrock, D. Symochko, A. Tamii, T. Uesaka, V. Wagner, and K. Yoshida, “α-Clustering at the surface of Tin
isotopes 112–124 Sn studied with (p, pα) reaction,” JPS Conf. Proc. 31, 011019 (2020).
P. Koseoglou, V. Werner, N. Pietralla, P. -A. Söderström, P. Doornenbal, A. Obertelli, N. Achouri, H. Baba, F. Browne, D. Calvet,
F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, J-M. Gheller, A. Giganon, A. Gillibert, C. Hilaire, T. Isobe,
T. Kobayashi, Y. Kubota, V. Lapoux, H. Liu, T. Motobayashi, I. Murray, H. Otsu, V. Panin, N. Paul, W. Rodriguez, H. Sakurai,
M. Sasano, D. Steppenbeck, L. Stuhl, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, O. Aktas, T. Auman, L. X. Chung,F. Flavigny, S. Franchoo, I. Gasparic, R. -B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, T. Koiwai, Y. Kondo, J. Lee, C. Lehr, M. Lettmann,
B. D. Linh, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi, E. Sahin, D. Sohler, S. Takeuchi, H. Toernqvist, V. Vaquero, V. Wagner, S. Wang, X. Xu, H. Yamada, D. Yan, Z. Yang, M. Yasuda, and L. Zanetti, “Spectroscopy of neutron-richscandium isotopes,” J. Phys. Conf. Ser. 1555, 012026 (2020).
R. Matsumura, H. Otsu, H. Wang, N. Chiga, S. Kawase, K. Nakano, H. Sakurai, M. Shikata, S. Takeuchi, Y. Togano, and for the ImPACTRIBF Collaboration, “Research for nuclear transmutation of high-radiotoxic nuclide 90Sr via proton- and deuteron-induced reactions,”
JAEA-Conf. 2021-001(2021).

Presentations[International Conferences/Workshops]
R. Matsumura, H. Otsu, H. Wang, N. Chiga, S. Kawase, K. Nakano, H. Sakurai, M. Shikata, S. Takeuchi, Y. Togano, and for the ImPACTRIBF Collaboration, “Nuclear transmutation of high-radiotoxic nuclide 90 Sr via proton- and deuteron-induced reactions in inverse- 225 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

kinematics,” A3F-CNS Summer School 2020, オンライン開催, 2020 年 8 月 17–21 日.
K. Nishimura, H. Kouno, Y. Kawashima, K. Orihashi, S. Fujiwara, K. Tateishi, T. Uesaka, N. Kimizuka, and N. Yanai, “Materials
chemistry of triplet dynamic nuclear polarization,” Chem. Commum. 56, 7217–7232 (2020).

[Domestic Conferences/Workshops]
松村理久, 大津秀暁, 王赫, 千賀信幸, 川瀬頌一郎, 中野敬太, 櫻井博儀, 四方瑞紀, 武内聡, 栂野泰宏, ImPACT-RIBF Collaboration, 「高放射性核種 90 Sr の陽子及び重陽子誘起反応による核変換に向けた研究」, Symposium on Nuclear Data 2020, 埼玉県和光市 (理研
仁科センター), 2020 年 11 月 26–27 日.

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Nuclear Science and Transmutation Research Division
Nuclear Spectroscopy Laborarory
1. Abstract

The research group has conducted nuclear-physics studies utilizing stopped/slowed-down radioactive-isotope (RI) beams mainly
at the RIBF facility. These studies are based on the technique of nuclear spectroscopy such as β-ray-detected NMR (β-NMR), γPAD (Perturbed Angular Distribution), laser, and Mössbauer among other methods that takes advantage of intrinsic nuclear properties
such as nuclear spins, electromagnetic moments, and decay modes. In particular, techniques and devices for the production of spincontrolled RI beams have been developed and combined to the spectroscopic studies, which enable high-sensitivity measurements ofspin precessions/resonances through a change in the angular distribution of radiations. Anomalous nuclear structures and propertiesof far unstable nuclei are investigated from thus determined spin-related observables. The group also aims to apply such techniques tointerdisciplinary fields such as fundamental physics and materials science by exploiting nuclear probes.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Nuclear spectroscopy utilizing spin-oriented fast RI beams
Nuclear/Atomic laser spectroscopy & SLOWRI R&DApplication of RI probes to materials science
Fundamental physics: Study of symmetry

3. Summary of Research Activity(1) Nuclear spectroscopy utilizing spin-oriented fast RI beams
Measurements of static electromagnetic nuclear moments over a substantial region of the nuclear chart have been conducted forstructure studies on the nuclei far from the β-decay stability. Utilizing nuclear spin orientation phenomena of RIs created in the
projectile-fragmentation reaction, ground- and excited-state electromagnetic nuclear moments been determined by means of the βray-detected nuclear magnetic resonance (β-NMR) and the γ-ray time diﬀerential perturbed angular distribution (γ-TDPAD) methods.
In particular, a new method developed for controlling spin in a system of rare RIs, taking advantage of the mechanism of the two-step
projectile fragmentation reaction combined with the momentum-dispersion matching technique, has been developed and employedmaking fully use of world’s highest intensity rare RIBs delivered from BigRIPS for rare isotopes.
(2) Nuclear/Atomic laser spectroscopy & SLOWRI R&D
The group has been conducting system development for nuclear laser spectroscopy from the following two approaches in orderto realize experiments for rare isotopes at RIBF. One is collinear laser spectroscopy for a large variety of elements using sloweddown RI beams produced via a projectile-fragmentation reaction, which can be achieved only by the universal low-energy RI-beamdelivery system, SLOWRI, under installation in collaboration with the SLOWRI Team. This slowed-down RI-beam scheme enables
to perform high-precision laser spectroscopy even with fast-fragmentation-based RIBs without the elemental limitation problematicin the ISOL-based RIBs.
The other approach is a new method utilizing superfluid helium (He II) as a stopping medium of energetic RI beams, in which thecharacteristic atomic properties of ions surrounded by superfluid helium enables us to perform unique nuclear laser spectroscopy. RIions trapped in He II are known to exhibit a characteristic excitation spectrum significantly blue-shifted compared with the emission
one. Consequently, the background derived from the excitation-laser stray light, which often causes serious problems in measurements,
can be drastically reduced.
(3) Application of RI probes to materials science
The application of RI and heavy ion beams as a probe for condensed matter studies is also conducted by the group. The microscopic material dynamics and properties have been investigated through the deduced internal local fields and the spin relaxation of
RI probes based on various spectroscopies utilizing RI probes such as β-NMR/NQR spectroscopy, Mössbauer spectroscopy, the γ-ray
time diﬀerential perturbed angular correlation (γ-TDPAC) spectroscopy. Furthermore, studies on the control of electrical conductivityof diamond by boron and nitrogen implantation are ongoing.
Provided that highly spin-polarized RI probes are produced independently of their element properties and doped into a substanceas an impurity, the constituent particle of the substance can be substituted by the same element RI probe without changing the material
structure. This scheme provides a new opportunity for materials-science researches, but a key technology, production of elementindependent highly spin-polarized RI beams, has not yet been achieved. In this subject, the group has conducted R&D studies torealize an ultra-slow & highly-spin-polarized RI beams, based on the technique of the atomic beam resonance.
(4) Fundamental physics: Study of symmetry
The nuclear spins of stable and unstable isotopes sometimes play important roles in fundamental physics research. New experimental methods and devices have been developed for studies of the violation of time reversal symmetry (T-violation) using spinpolarized nuclei. These experiments aim to detect the small frequency shift in the spin precession arising from new mechanisms
beyond the Standard Model.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Members
Director
Hideki UENO
Research/Technical Scientists
Hiroki YAMAZAKI (Senior Research Scientist)
Aiko TAKAMINE (Research Scientist)

Isao WATANABE (Senior Research Scientist)

Research & Development Scientist
Tetsu SONODA
Contract Researcher
Takashi ABE
Special Postdoctoral Researcher
Momo MUKAI
Postdoctoral Researchers
Minori TAJIMA

Kei IMAMURA (CPR)

Research Associate
Aleksey GLADKOV
Senior Visiting Scientists
Yukari MATSUO (Hosei Univ.)

Takaharu OTSUKA (Univ. of Tokyo)

Visiting Scientists
Dimiter L. BALABANSKI (IFIN-HH)
Georgi GEORGIEV (CNRS-IN2P3)
Yuichi ICHIKAWA (Kyushu Univ.)
Yoshio KOBAYASHI (Univ. of Electro-Commun.)
Kenya KUBO (Int’l Christian Univ.)
Kensaku MATSUTA (Osaka Univ.)
Jun MIYAZAKI (Tokyo Denki Univ.)
Takamasa MOMOSE (The Univ. of British Columbia)
Jiro MURATA (Rikkyo Univ.)

Jin NAKAMURA (Univ. of Electro-Commun.)
Hiroki NISHIBATA (Kyushu Univ.)
Tomoya SATO (Tokyo Tech)
Wataru SATO (Kanazawa Univ.)
Andrew E. STUCHBERY (The Australian Nat’l Univ.)
Satoshi TSUTSUI (Japan Synchrotron Radiation Res. Inst.)
Yasuhiro YAMADA (Tokyo Univ. Sci)
Deyan T. YORDANOV (CNRS-IN2P3)
Akihiro YOSHIMI (Okayama Univ.)

Student Trainees
Sai AKIMOTO (Hosei Univ.)
Miru DOI (Hosei Univ.)
Timothy J. GRAY (The Australian Nat’l Univ.)
Kentaro HAMANO (Univ. of Electro-Commun.)
Manami ITO (Hosei Univ.)
Kyouichi IZUOKA (Tokyo Univ. Sci)
Masato KIJI (Univ. of Electro-Commun.)

Masaki NISHIMURA (Hosei Univ.)
Shinichi OKAMURA (Univ. of Ferrara)
Yuika TAKEUCHI (Hosei Univ.)
Satoshi TANAKA (Hosei Univ.)
Kenta TSUBURA (Hosei Univ.)
Takumi YAMAMOTO (Hosei Univ.)
Mio YOSHIDA (Univ. of Electro-Commun.)Temporary Staﬃng
Emiko SUGISAKI

Naoko YUASA

AssistantIzumi YOSHIDA

List of Publications & Presentations
Publications[Original Papers]
M. Tajima, A. Takamine, M. Wada, and H. Ueno, “Oﬄine ion source for laser spectroscopy of RI at the SLOWRI,” Nucl. Instrum.
Methods Phys. Res. B 486, 48–54 (2021).
N. Tsunoda, T. Otsuka, K. Takayanagi, N. Shimizu, T. Suzuki, Y. Utsuno, S. Yoshida, and H. Ueno, “The impact of nuclear shape on theemergence of the neutron dripline,” Nature 587, 66–71 (2020).
M. Mukai, Y. Hirayama, Y. X. Watanabe, S. Schiﬀmann, J. Ekman, M. Godefroid, P. Schury, Y. Kakiguchi, M. Oyaizu, M. Wada,
S. C. Jeong, J. Y. Moon, J. H. Park, H. Ishiyama, S. Kimura, H. Ueno, M. Ahmed, A. Ozawa, H. Watanabe, S. Kanaya, and H. Miyatake,“In-gas-cell laser resonance ionization spectroscopy of 196, 197, 198 Ir,” Phys. Rev. C 102, 054307 (2020).

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H. Suzuki, K. Yoshida, N. Fukuda, H. Takeda, Y. Shimizu, D. S. Ahn, T. Sumikama, N. Inabe, T. Komatsubara, H. Sato, Z. Korkulu,
K. Kusaka, Y. Yanagisawa, M. Ohtake, H. Ueno, T. Kubo, S. Michimasa, N. Kitamura, K. Kawata, N. Imai, O. B. Tarasov, D. Bazin,
J. Nolen, and W. F. Henning, “Experimental studies of the two-step scheme with an intense radioactive 132 Sn beam for next-generation
production of very neutron-rich nuclei,” Phys. Rev. C 102, 064615 (2020).
Y. Sakemi, T. Aoki, R. Calabrese, H. Haba, K. Harada, T. Hayamizu, Y. Ichikawa, K. Jungmann, A. Kastberg, Y. Kotaka, Y. Matsuda,
Y. Matsuo, H. Nagahama, K. Nakamura, M. Otsuka, N. Ozawa1, K. S. Tanaka, A. Uchiyama, H. Ueno, and L. Willmann, “Fundamental
physics with cold radioactive atoms,” AIP Conf. Proc. 2319, 080020-1–6 (2021).
H. Watanabe, Y. X. Watanabe, Y. Hirayama, A. N. Andreyev, T. Hashimoto, F. G. Kondev, G. J. Lane, Yu. A. Litvinov, J. J. Liu, H. Miyatake, J. Y. Moon, A. I. Morales, M. Mukai, S. Nishimur, T. Niwase, M. Rosenbusch, P. Schury, Y. Shi, M. Wada, and P. M. Walker,“Beta decay of the axially asymmetric ground state of 192 Re,” Phys. Lett. B 814, 136088-1–6 (2020).
P. M. Walker, Y. Hirayama, G. J. Lane, H. Watanabe, G. D. Dracoulis, M. Ahmed, M. Brunet, T. Hashimoto, S. Ishizawa, F. G. Kondev,
Yu. A. Litvinov, H. Miyatake, J. Y. Moon, M. Mukai, T. Niwase, J. H. Park, Zs. Podolyák, M. Rosenbusch, P. Schury, M. Wada,
X. Y. Watanabe, W. Y. Liang, and F. R. Xu, “Properties of 187 Ta revealed through isomeric decay,” Phys. Rev. Lett. 125, 192505-1–5(2020).
Y. X. Watanabe, M. Ahmed, Y. Hirayama, M. Mukai, J. H. Park, P. Schury, Y. Kakiguchi, S. Kimura, A. Ozawa, M. Oyaizu, M. Wada,
H. Miyatake, “Deexcitation γ-ray transitions from the long-lived I π = 13/2+ metastable state in 195 Os,” Phys. Rev. C 101, 041305(2020).
Y. Hirayama, P. Schury, M. Mukai, H. Choi, S. Imamura, X. Y. Watanabe, M. Wada, H. Watanabe, and H. Miyatake, “Three-dimensional
tracking multi-segmented proportional gas counter for β-decay spectroscopy of unstable nuclei,” Nucl. Instrum. Methods Phys. Res.
A 997, 165152-1–10 (2021).
Y. Ichikawa, “Nuclear-moment measurements of exotic nuclei using spin-oriented RI beams at RIBF,” AIP Conf. Proc. 2319, 080021(2021).
Y. Ichikawa, H. Nishibata, Y. Tsunoda, A. Takamine, K. Imamura, T. Fujita, T. Sato, S. Momiyama, Y. Shimizu, D. S. Ahn, K. Asahi,
H. Baba, D. L. Balabanski, F. Boulay, J. M. Daugas, T. Egami, N. Fukuda, C. Funayama, T. Furukawa, G. Georgiev, A. Gladkov,
N. Inabe, Y. Ishibashi, Y. Kobayashi, S. Kojima, A. Kusoglu, T. Kawaguchi, T. Kawamura, I. Mukul, M. Niikura, T. Nishizaka,
A. Odahara, Y. Ohtomo, T. Otsuka, D. Ralet, G. S. Simpson, T. Sumikama, H. Suzuki, H. Takeda, L. C. Tao, Y. Togano, D. Tomonaga,
H. Ueno, H. Yamazaki, and X. F. Yang, “Magnetic moment of the isomeric state of 75 Cu measured with a highly spin-aligned beam,”
JPS Conf. Proc. 32, 010047-1–4 (2020).
S. Bagchi, R. Kanungo, Y. K. Tanaka, H. Geissel, P. Doornenbal, W. Horiuchi, G. Hagen T. Suzuki, N. Tsunoda, D. S. Ahn, H. Baba,
K. Behr, F. Browne, S. Chen, M. L. Cortés, A. Estradé, N. Fukuda, M. Holl, K. Itahashi, N. Iwasa, G. R. Jansen, W. G. Jiang, S. Kaur,A. O. Macchiavelli, S. Y. Matsumoto, S. Momiyama, I. Murray, T. Nakamura, S. J. Novario, H. J. Ong, T. Otsuka, T. Papenbrock,
S. Paschalis, A. Prochazka, C. Scheidenberger, P. Schrock, Y. Shimizu, D. Steppenbeck, H. Sakurai, D. Suzuki, H. Suzuki, M. Takechi,
H. Takeda, S. Takeuchi, R. Taniuchi, K. Wimmer, and K. Yoshida, “Two-neutron halo is unveiled in 29 F,” Phys. Rev. Lett. 124,
22250-1–7 (2020).
N. Mărginean, D. Little, Y. Tsunoda, S. Leoni, R. V. F. Janssens, B. Fornal, T. Otsuka, C. Michelagnoli, L. Stan, F. C. L. Crespi,
C. Costache, R. Lica, M. Sferrazza, A. Turturica, A. D. Ayangeakaa, K. Auranen, M. Barani, P. C. Bender, S. Bottoni, M. Boromiza,
A. Bracco, S. Călinescu, C. M. Campbell, M. P. Carpenter, P. Chowdhnury, M. Ciemała, N. Cieplicka-Oryǹczak, D. Cline, C. Clisu,
H. L. Crawford, I. E. Dinescu, J. Dudouet, D. Filipescu, N. Florea, A. M. Forney, S. Fracassetti, A. Gade, I. Gheorghe, A. B. Hayes,
I. Harca, J. Henderson, A. Ionescu, Ł. W. Iskra, M. Jentschel, F. Kandzia, Y. H. Kim, F. G. Kondev, G. Korschinek, U. Köster,
Krishichayan, M. Krzysiek, T. Lauritsen, J. Li, R. Mărginean, E. A. Maugeri, C. Mihai, R. E. Mihai, A. Mitu, P. Mutti, A. Negret,
C. R. Niţă, A. Olăcel, A. Oprea, S. Pascu, C. Petrone, C. Porzio, D. Rhodes, D. Seweryniak, D. Schumann, C. Sotty, S. M. Stolze,
R. Şuvăilă, S. Toma, S. Ujeniuc, W. B. Walters, C. Y. Wu, J. Wu, S. Zhu, and S. Ziliani, “Shape coexistence at zero spin in 64 Ni driven
by the monopole tensor interaction,” Phys. Rev. Lett. 125, 102502-1–7 (2020).
M. M. Juhász, Z. Elekes, D. Sohler, Y. Utsuno, K. Yoshida, T. Otsuka, K. Ogata, P. Doornenbal, A. Obertelli, H. Baba, F. Browne,
D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, and L. Zanetti, “First spectroscopic study of 51 Ar by the(p, 2p) reaction,” Phys. Lett. B 814, 136108-1–8 (2021).
C. Porzio, C. Michelagnoli, N. Cieplicka-Oryǹczak, M. Sferrazza, S. Leoni, B. Fornal, Y. Tsunoda, T. Otsuka, S. Bottoni, C. Costache,
F. C. L. Crespi, Ł. W. Iskra, M. Jentschel, F. Kandzia, Y. -H. Kim, U. Köster, N. Mărginean, C. Mihai, P. Mutti, and A. Turturică,“Detailed low-spin spectroscopy of 65 Ni via neutron capture reaction,” Phys. Rev. C 102, 064310-1–13 (2020).
N. Shimizu, Y. Tsunoda, Y. Utsuno, and T. Otsuka, “Variational approach with the superposition of the symmetry-restored quasiparticlevacua for nuclear shell-model calculations,” Phys. Rev. C 103, 014312-1–11 (2021).
F. L. Bello Garrote, E. Sahin, Y. Tsunoda, T. Otsuka, A. Görgen, M. Niikura, S. Nishimura, G. de Angelis, G. Benzoni, A. I. Morales,
V. Modamio, Z. Y. Xu, H. Baba, F. Browne, A. M. Bruce, S. Ceruti, F. C. L. Crespi, R. Daido, M. -C. Delattre, P. Doornenbal,
Zs. Dombradi, Y. Fang, S. Franchoo, G. Gey, A. Gottardo, K. Hadyńska-Klȩk, T. Isobe, P. R. John, H. S. Jung, I. Kojouharov, T. Kubo,
N. Kurz, I. Kuti, Z. Li, G. Lorusso, I. Matea, K. Matsui, D. Mengoni, T. Miyazaki, S. Momiyama, P. Morfouace, D. R. Napoli,
F. Naqvi, H. Nishibata, A. Odahara, R. Orlandi, Z. Patel, S. Rice, H. Sakurai, H. Schaﬀner, L. Sinclair, P. -A. Söderström, D. Sohler,
I. G. Stefan, T. Sumikama, D. Suzuki, R. Taniuchi, J. Taprogge, Zs. Vajta, J. J. Valiente-Dobón, H. Watanabe, V. Werner, J. Wu, A. Yagi,
M. Yalcinkaya, R. Yokoyama, and K. Yoshinaga, “β Decay of 75 Ni and the systematics of the low-lying level structure of neutron-rich
odd-A Cu isotopes,” Phys. Rev. C 102, 034314-1–13 (2020).
Y. Tsunoda and T. Otsuka, “Triaxial rigidity of 166 Er and its Bohr-model realization,” Phys. Rev. C 103, L021303-1–6 (2021).
S. Leoni, B. Fornal, N. Marginean, C. Michelagnoli, J. Wilson, M. Sferrazza, Y. Tsunoda, and T. Otsuka, “Shape-coexistence studies in
the ni isotopic chain by using the selectivity of diﬀerent reaction mechanisms,” Acta Phys. Pol. B 51, 807–815 (2020).
P. -A. Söderström, L. Capponi, E. Açıksöz, T. Otsuka, N. Tsoneva, Y. Tsunoda, D. L. Balabanski, N. Pietralla, G. L. Guardo, D. Lattuada,- 229 -

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H. Lenske, C. Matei, D. Nichita, A. Pappalardo, and T. Petruse, “Electromagnetic character of the competitive γγ/γ-decay from 137m Ba,”
Nat. Commun. 11, 3242-1–8 (2020).
Y. Sato, Y. Yamada, Y. Kobayashi, M. K. Kubo, M. Mihara, W. Sato, J. Miyazaki, T. Nagatomo, T. Ando, N. Takahama, K. Some, M. Sato,S. Sato, and A. Kitagawa, “In-beam Mössbauer spectra of 57 Mn implanted into lithium aluminium hydride,” Appl. Radiat. Isot. 170,
109582-1–7 (2021).
Y. Yamada, Y. Sato, Y. Kobayashi, T. Ando, N. Takahama, K. Some, M. Sato, M. Mihara, M. K. Kubo, W. Sato, J. Miyazaki, T. Nagatomo,
J. Kobayashi, A. Okazawa, S. Sato, A. Kitagawa, “In-beam Mössbauer spectra for 57 Mn implanted sulfur hexafluoride,” Hyperfine
Interact. 241, 15-1–6 (2020).

Presentations[International Conferences/Workshops]
A. Takamine (invited), “SLOWRI rf gas catcher development toward symbiotic mass measurement at F11,” RIBF User Meeting 2020,
online, September 2–10, 2020.
M. Mukai, “In-gas-jet laser spectroscopy of 199–202 Pt, 195–198 Ir, 193–198 Os,” SSRI-PNS Collaboration Meeting 2020, online, Japan, September
3, 2020.
H. Ueno (invited), “Nuclear spectroscopy with spin-polarized RI beams,” The International School for Strangeness Nuclear Physics 2020
(SNP School 2020), online & J-PARC, Ibaraki, Japan, December 2–5, 2020.

[Domestic Conferences/Workshops]
上野秀樹 (依頼講演), 「高偏極 RI ビームの生成と核・物質科学研究への応用」, 新学術領域研究「宇宙観測検出器と量子ビームの出会い。新たな応用への架け橋。」第 2 回領域研究会, オンライン開催, 2020 年 7 月 27–28 日.
今村慧 (口頭発表), 「RI 原子線磁気共鳴に向けた中性化装置開発」，新学術領域「宇宙観測検出器と量子ビームの出会い．新たな応用への架け橋．」第 2 回領域全体会議，オンライン開催, 2020 年 7 月 27–28 日.
飯村俊, 高峰愛子, M. Rosenbusch, 和田道治, S. Chen, J. Liu, W. Xian, D. Hou, S. Yan, P. Schury, 園田哲, 小島隆夫, 渡辺裕,
小田原厚子, 石山博恒, 「理研 BigRIPS SLOWRI における RF カーペットガスセルの開発」, 日本物学会 2020 年秋季大会,
オンライン開催, 2021 年 9 月 14–17 日.
三原基嗣, 松多健策, 福田光順, 若林諒, 沖本直哉, 福留美樹, 泉川卓司, 野口法秀, 生越瑞揮, 大坪隆, 西村太樹, 髙橋弘幸, 菅原奏来,
Aleksey Gladkov, 北川敦志, 佐藤眞二, 「短寿命酸素 NMR プローブ核 19 O の物質科学利用」, 日本物学会 2020 年秋季大会, オンライン開催, 2021 年 9 月 14–17 日.
角田佑介, 大塚孝治, 清水則孝, 本間道雄, 宇都野穣, 「モンテカルロ殻模型による Z = 28 近傍の核構造の研究」, 日本物学会 2020年秋季大会, オンライン開催, 2021 年 9 月 14–17 日.
阿部喬 (口頭発表), “Ab initio description of light nuclei from no-core Monte Carlo shell model,” 第 5 回クラスター階層領域研究会, オンライン開催, 2020 年 9 月 24–25 日.
上野秀樹 (依頼講演), 「RI・重イオンビームの学際的利用に向けた研究開発」, 新領域開拓課題 物質階層原理 & ヘテロ界面研究合
同年次成果報告会, オンライン開催, 2021 年 2 月 8–9 日.
市川雄一 (招待講演), 「低エネルギースピン物理」, 日本のスピン物理学の展望研究会, 島根県松江市, オンライン開催, 2021 年 2 月
23–24 日.
田島美典, 高峰愛子, 飯村秀紀, 和田道治, H. A. Schuessler, 上野秀樹, 「コリニアレーザー分光による四重極変形度測定を通した原子核構造研究にむけた開発 II」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
小澤直也, 長濱弘季, 早水友洋, 中村圭佑, 佐藤幹, 永瀬慎太郎, 小高康照, 鎌倉恵太, 田中香津生, 大塚未来, 青木貴稔, 市川雄一,
高峰愛子, 羽場宏光, 上野秀樹, 酒見泰寛, 「フランシウム原子の電気双極子能率探索のための表面電離イオン源の開発」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
飯村俊, 高峰愛子, M. Rosenbusch, 和田道治, S. Chen, D. Hou, J. Liu, W. Xian, S. Yan, P. Schury, 木村創大, 庭瀬暁隆, 伊藤由太,
園田哲, 小島隆夫, 渡辺裕, N. Sara, 道正新一郎, 西村俊二, 小田原厚子, 石山博恒, 「理研 BigRIPS SLOWRI における RF カーペッ
トガスセルの開発—オンライン実験と質量測定—」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
大谷優里花, 三原基嗣, 松多健策, 福田光順, 若林諒, 沖本直哉, 福留美樹, 木村容子, 高山元, 泉川卓司, 野口法秀, 生越瑞揮, 佐藤弥紗,
高津和哉, 大坪隆, 西村太樹, 髙橋弘幸, 菅原奏来, Aleksey Gladkov, 北川敦志, 佐藤眞二, 百田佐多生, 奥村寛之, 森口哲朗, 小沢顕,
「19 O の偏極ビーム生成と固体燃料電池研究への応用」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
清水則孝, 角田佑介, 宇都野穣, 大塚孝治, 「準粒子真空基底によるモンテカルロ殻模型の拡張」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
大塚孝治, 角田佑介, 角田直文, 阿部喬, 清水則孝, P. Van Duppen, 高柳和雄, 鈴木俊夫, 宇都野穣, 上野秀樹, 「原子核物理の再出発」,
KEK 理論センター研究会「原子核・ハドロン物理 2020」, オンライン開催, 2020 年 10 月 6 日.
大塚孝治, 「原子核物理の再出発」, ELPH 研究会 C028「電子散乱による原子核研究—原子核の電荷密度・陽子・ 中性子の分布と半径—」, オンライン開催, 2021 年 3 月 18–19 日.
高峰愛子 (招待講演), “Isotope shift measurement project at the SLOWRI facility,” ELPH 研究会 C028「電子散乱による原子核研究—
原子核の電荷密度・陽子・中性子の分布と半径—」, オンライン開催, 2021 年 3 月 18–19 日.
大塚孝治, 角田直文, 高柳和雄, 清水則孝, 鈴木俊夫, 宇都野穣, 上野秀樹, 「原子核物理の再出発」, “Neutron driplines and shapeevolution of atomic nuclei,” 第 3 回クラスター階層領域研究会, オンライン開催, 2020 年 5 月 18 日.

[University Lectures]
H. Ueno, “Applied Radiation Engineering,” Department of Nuclear Engineering and Management, Graduate School of Engineering, the- 230 -

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University of Tokyo.
H. Yamazaki, “Physics in Daily Life (in Japanese),” General Education Course, Otsuma Women’s University.
A. Takamine, “Exercises in Basic Physics I (in Japanese),” Department of Advanced Sciences, Faculty of Science and Engineering, Hosei
University.
A. Takamine, “Exercises in Basic Physics II (in Japanese),” Department of Advanced Sciences, Faculty of Science and Engineering, Hosei
University.

Press Releases
新聞等掲載: 「中性子過剰ジルコニウム同位体の励起状態での変形」, フジサンケイビジネスアイ, 2020 年 5 月 22 日.
プレスリリース: 東京大学, 理化学研究所, 日本原子力研究開発機構, 上智大学, 日本大学, 宇都宮大学共同記者発表, 「原子核の存在限界（中性子ドリップライン）の新たなメカニズム －中性子は原子核にいくつ入るか－」, 2020 年 11 月 5 日.
新聞等掲載: 「原子核の最大中性子数決定 －新たなメカニズム提唱－」, 科学新聞, 2020 年 11 月 27 日.

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Nuclear Science and Transmutation Research DivisionHigh Energy Astrophysics Laborarory
1. Abstract

In the immediate aftermath of the Big Bang, the beginning of our universe, only hydrogen and helium existed. However, nuclear
fusion in the interior of stars and the explosion of supernovae in the universe over 13.8 billion years led to the evolution of a world
brimming with the many diﬀerent elements we have today. By using scientific satellites or balloons to observe X-rays and gamma-rays
emitted from celestial objects, we are observing the synthesis of the elements at their actual source. Our goal is to comprehensively
elucidate the scenarios for the formation of the elements in the universe, together with our research on sub-atomic physics through theuse of an accelerator.

2. Major Research Subjects
(1)
(2)
(3)
(4)

History of nucleosynthesis in the universe
Physics in extreme conditions in the universe
Research and development of innovative radiation detectors
Apply radiation technology for human to live in space

3. Summary of Research Activity

High Energy Astrophysics Laboratory started in April 2010. The goal of our research is to reveal the mechanism of nucleosynthesis and the evolution of elements in the universe, and to observe/discover exotic physical phenomena in extremely strong magnetic
and/or gravitational fields. We have observed supernova remnants, strongly magnetized neutron stars, pulsars, black holes and galaxies
with X-ray astronomical satellites, balloons and ground-based telescopes.
(1) Nucleosynthesis in the universe(1-1) XRISM
We have contributed to the XRISM (X-ray imaging and spectroscopy mission) mission for the launch in FY2022. XRISM is therecovery mission of the ASTRO-H/Hitomi satellite, which was launched in February 2016 but lost by an accident one month after thelaunch. Hitomi carried four X-ray and gamma-ray detectors covering the 0.3–600 keV energy range. We, in collaboration with JAXA
(Japan Aerospace Exploration Agency), Tokyo Metropolitan University, Kanazawa University, Saitama University, NASA/GSFC etc.,
contributed to the soft X-ray spectrometer (SXS), which achieves unprecedented energy resolution (<7 eV) in the 0.3–12 keV energy
band with a low temperature micro calorimeter. We hoped to use SXS to discover many previously-unknown elemental lines in theuniverse and to measure the abundance of these elements, but this was not possible with Hitomi. The XRISM satellite carries almost
identical X-ray detectors as the Hitomi satellite, and is expected to carry out scientific observations that were not done with the Hitomi
mission.
(1-2) MAXI
From April 2018, High Energy Astrophysics Laboratory hosts MAXI (Monitor of All-sky X-ray Image) onboard International
Space Station (ISS), which was attached on ISS in 2009. MAXI is a RIKEN-lead project collaborating with JAXA and other universities. Since MAXI scans X-ray all-sky in 90 minutes, many transient objects including neutron star or blackhole binaries are found.
All of the data are going to public soon after they are taken, and almost all of the groups in high-energy phenomena rely on the MAXI
data. Until the end of 2020, we issued 362 alerts as ATEL (Astronomer’s Telegram). To detect counterparts of neutron star merger
events (i.e. gravitational wave events), we have prepared an automatic searching system and keep watching all-sky.
(2) Extremely strong magnetism and gravity(2-1) IXPE
We have contributed to the NASA’s world-first X-ray polarimeter mission IXPE (Imaging X-ray Polarimeter Explorer). HighEnergy Astrophysics Laboratory is responsible for providing the gas electron multipliers (GEMs) to the IXPE mission: the GEM is a
key device of the X-ray polarimeter and produced based on our patent for space use. The IXPE satellite is scheduled to launched in
the second half of 2021. We have already provided the flight qualified GEMs to the project in FY2018, and have contributed to thedetector calibrations in FY2019.
By using the IXPE satellite, we aim to proof the strong magnetism of Magnetars, which are one of the species of neutron stars
which have ultra-strong magnetic field B > 1011 T. In such ultra-strong magnetic field, higher-order diagrams, O(eB/m2 ), O(eB/m2 )2
etc., never ignored in the QED perturbation theory. As the results, we observe newly-emerging phenomenon such as vacuum polarization, vacuum birefringence, etc. If such exotic phenomena are detected, we sure that Magnetars have really ultra-strong magnetic field.
In FY2020, we performed a simulation of scientific observations of Magnetars, which are neutron stars with ultra-strong magnetic
fields.
(2-2) Astrophysical data analysis
In parallel with the mission development/operations, we are studying gamma-ray binary systems, which are one of the mostimportant astrophysical targets in the MeV gamma-ray band. To reveal a long-standing question of the physical mechanism of eﬃcientparticle acceleration in these systems, we focused on the characteristic object LS 5039 and performed the timing analysis in the X-ray
band. It resulted in hints of pulsation signals with an about 9-sec period. Though further confirmations are needed considering the- 232 -

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signal detection level, this result suggests that it harbors a strongly magnetized neutron star (magnetar). We proposed a new possibility
that the particle acceleration could be related to the strong magnetic field of the magnetar, and have published a paper.
(3) Innovative breakthrough in astrophysics with a small satellite
We are developing technology and acquiring know-how to make space observation, which requires a lot of money, possible withsmall satellites at low cost. NASA and other space agencies around the world have realized the importance of this opportunities andhave started space observation activities using small satellites. NinjaSat is a micro-satellite mission (6U CubeSat; 30 × 20 × 10 cm3 )led by RIKEN in collaboration with universities. NinjaSat will be deployed from the ISS in 2022. Although several science missions
have recently been conducted using micro-satellites, NinjaSat is the world’s first general purpose CubeSat mission to observe X-ray
sources. NinjaSat carries two Xe-filled gas detectors with 2-degree-wide collimators and performs spectroscopy between 2–50 keV
and timing obervation with a timing resolution of about 120 µs. Since the eﬀective area is not large (∼40 cm2 at 6 keV), the targetof the NinjaSat is a long-term monitoring of bright X-ray sources which are discovered by MAXI etc. In general, bright objects are
diﬃcult to observe and a continuous observations for long period is impossible with large satellite missions. The aim of NinjaSat is
to perform observations that are diﬃcult to perform on larger missions. For example, NinjaSat observes the time variability of binary
neutron stars and binary black holes in conjunction with the ground-based optical, radio and gravitational telescopes. We developed
and tested an engineering model of the X-ray detectors in 2020.
(4) Future X-ray and gamma-ray detectors
In collaboration with NASA Goddard Space Flight Center, we have developed and tested a hard X-ray polarimeter with a Time
Projection Chamber technique. This TPC polarimeter is one of candidates of the future satellite XPP (X-ray polarimeter Probe
mission) planned with an international consortium.
As an successor of the MAXI mission, we are also verifying the principle of a new concept, multiplexing lobster-eye (MuLE)
optics, to monitor the entire sky with a wide field-of-view for detecting and immediate reporting transient objects such as a neutronstar merger. We puslished a peper on the conceptual design of MuLE, and proved the concept by a simple experiment in 2020.
To explore the MeV gamma-ray sky in the Universe, we are proceeding with the GRAMS project. It utilizes a large-scale liquidargon time projection chamber as a gamma-ray imager and aims to improve the sensitivity in the MeV band, by more than an order ofmagnitude than before. In a large-scale detector, MeV gamma rays are easily Compton-scattered multiple times and they sometimes
escape from the detector before they deposit all energies. Thus, one of the key techniques for the above goal is to establish an algorithm
that can reconstruct the incoming gamma-ray energy and direction from such a complex scattering event. We have proposed a newevent reconstruction algorithm based on the maximum likelihood, by formulating physical processes in MeV gamma-ray telescopes.
It is one of the first algorithms that can also estimate the escape gamma-ray energy. We have confirmed that it works successfully forthe multiple scattering events using Geant4 simulations, and have demonstrated a proof of concept of the GRAMS project.

Members
Director
Toru TAMAGAWA
Research/Technical Scientist
Tatehiro MIHARA (Senior Research Scientist)
Special Postdoctoral Researcher
Hiroki YONEDA
Visiting Scientists
Aya BAMBA (Univ. of Tokyo)
Naohisa INADA (NIT, Nara College)
Satoru KATSUDA (Saitama Univ.)
Tomoki KIMURA (Tohoku Univ.)
Kazuki KOMIYA (Tokyo Metropolitan Industrial Tech. Res.
Inst.)
Toru MISAWA (Shinshu Univ.)
Ikuyuki MITSUISHI (Nagoya Univ.)
Yujin NAKAGAWA (JAMSTEC)
Toshio NAKANO (JTEC Corporation)

Hirofumi NODA (Osaka Univ.)
Hirokazu ODAKA (Univ. of Tokyo)
Yuki OKURA (NAOJ/Nat’l Inst. of Natural Sci.)
Rohta TAKAHASHI (NIT, Tomakomai College)
Yoko TAKEUCHI (Tokyo Metropolitan Industrial Tech. Res.
Inst.)
Yukikatsu TERADA (Saitama Univ.)
Masaki WAKABAYASHI (Jakulin Commercial Company LC)
Shinya YAMADA (Rikkyo Univ.)

Student Trainees
Syoki HAYASHI (Tokyo Univ. Sci)
Naoyuki OTA (Tokyo Univ. Sci)
Tomoshi TAKEDA (Tokyo Univ. Sci)

Marina TSUTSUMI (Tokyo Univ. Sci)
Keisuke UCHIYAMA (Tokyo Univ. Sci)
Yuto YOSHIDA (Tokyo Univ. Sci)

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List of Publications & Presentations
Publications[Original Papers]
Q. Abarr, H. Awaki, M. G. Baring, R. Bose, G. De Geronimo, P. Dowkontt, et al., “XL-Calibur—a second-generation balloon-borne hard
X-ray polarimetry mission,” Astropart. Phys. 126, 102529 (2021).
S. Yamada, Y. Ichinohe, H. Tatsuno, R. Hayakawa, T. Ohashi, Y. Ishisaki, et al., “Broadband high-energy resolution hard X-ray spectroscopy using transition edge sensors at SPring-8,” Rev. of Sci. Instrum. 92, 013103 (2021).
T. Kasuga, H. Odaka, K. Hatauchi, S. Takashima, T. Tamba, Y. Aizawa, et al., “Artifact-less coded aperture imaging in the X-ray bandwith multiple diﬀerent random patterns,” J. Astron. Telesc. Instrum. Syst. 6, 035002 (2020).
T. Ebisuzaki, H. Katori, J. Makino, A. Noda, H. Shinkai, T. Tamagawa, “INO: Interplanetary network of optical lattice clocks,” Int. J.
Mod. Phys. D 29, 1940002 (2020).
R. Sasaki, Y. Tsuboi, W. Iwakiri, S. Nakahira, Y. Maeda, K. Gendreau, et al., “The RS CVn-type star GT mus shows most energetic X-ray
flares throughout the 2010s,” Astrophys. J. 910, 25 (2020).
Y. L. Tuo, L. Ji, S. S. Tsygankov, T. Mihara, L. M. Song, M. Y. Ge, et al., “Insight-HXMT insight into switch of the accretion mode: Thecase of the X-ray pulsar 4U 1901+03,” J. High Energy Astrophys. 27, 38 (2020).
M. Tominaga, S. Nakahira, M. Shidatsu, M. Oeda, K. Ebisawa, “Discovery of the black hole X-ray binary transient MAXI J1348-630,”
Astrophys. J. Lett. 899, L20 (2020).
M. Sugizaki, M. Oeda, N. Kawai, T. Mihara, K. Makishima, and M. Nakajima, “X-ray emission evolution of the galactic ultraluminous
X-ray pulsar swift J0243.6 + 6124 during the 2017–2018 outburst observed by the MAXI GSC,” Astrophys. J. 896, 124 (2020).
T. Tamagawa, K. Uchiyama, R. Otsubo, T. Yuasa, Y. Zhou, T. Mihara, et al., “Multiplexing lobster-eye optics: a concept for wide-field
X-ray monitoring,” J. Astron. Telesc. Instrum. Syst. 6, 025003 (2020).

[Proceedings]
Y. Maeda, Q. Abarr, H. Awaki, M. Baring, R. Bose, D. Braun, et al., “XL-Calibur: the next-generation balloon-borne hard X-ray polarimeter,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114442X (2021).
K. Uchiyama, T. Tamagawa, T. Mihara, Y. Zhou, Y. Ezoe, M. Numazawa, et al., “Source position determination method of multiplexing
lobster-eye optics,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114447E (2020).
P. Soﬃtta, P. Attina, L. Baldini, M. Barbanera, W. H. Baumgartner, R. Bellazzini, et al., “The imaging X-ray polarimetry explorer (IXPE):
technical overview III,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 1144462 (2020).
T. Takeda, K. Black, T. Enoto, A. Hayato, J. Hill, W. Iwakiri, et al., “Development and performance verification of a TPC polarimeter forhigh energy X-rays,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114445Y (2020).
K. Hattori, H. Matsumoto, Q. Abarr, H. Awaki, R. Bose, D. Braun, et al., “Current status of the X-ray mirror for the XL-Calibur
experiment,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114445W (2020).
D. Yonetoku, T. Mihara, A. Doi, T. Sakamoto, K. Tsumura, K. Ioka, et al., “High-redshift gamma-ray burst for unraveling the darkages mission: HiZ-GUNDAM,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114442Z(2020).
M. Tashiro, H. Maejima, K. Toda, R. Kelley, L. Reichenthal, L. Hartz, et al., “Status of X-ray imaging and spectroscopy mission(XRISM),” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 1144422 (2020).
T. Enoto, T. Tamagawa, T. Kitaguchi, W. Iwakiri, Y. Kato, M. Numazawa, et al., “NinjaSat: an agile CubeSat approach for monitoring ofbright X-ray compact objects,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 114441V(2020).
Y. Takeuchi, K. Komiya, T. Tamagawa, Y. Zhou, “Development and properties of 100 mm-square size LTCC-GEM,” J. Phys. Conf. Ser.
1498, 012011 (2020).
J. Li, T. Sakamoto, M. Serino, D. Yonetoku, T. Sawano, I. Mitsuish, et al., “X-ray performance and simulation study of lobster eye optics,”
Proc. of SPIE 11444, 114447C (2020).
T. Sawano, D. Yonetoku, M. Arimoto, J. Li, T. Mihara, N. Ogino, “A detection algorithm for faint sources based on 1-d projection fora lobster-eye X-ray imaging system,” Proc. SPIE 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray,
114445K (2020).

Presentations[International Conferences/Workshops]
T. Enoto (oral), T. Tamagawa, T. Kitaguchi, W. Iwakiri, Y. Kato, M. Numazawa, et al., “NinjaSat: an agile CubeSat approach formonitoring of bright X-ray compact objects,” SPIE Astronomical Telescopes + Instrummentation 2020, Online, December 14–18,
2020.
Y. Maeda (oral), Q. Abarr, H. Awaki, M. Baring, R. Bose, D. Braun, et al., “XL-Calibur: the next-generation balloon-borne hard X-ray
polarimeter,” SPIE Astronomical Telescopes + Instrummentation 2020, Online, December 14–18, 2020.
D. Yonetoku (oral), T. Mihara, A. Doi, T. Sakamoto, K. Tsumura, K. Ioka, et al., “High-redshift gamma-ray burst for unraveling the Dark
Ages Mission: HiZ-GUNDAM,” SPIE Astronomical Telescopes + Instrummentation 2020, Online, December 14–18, 2020.
T. Takeda (poster), K. Black, T. Enoto, A. Hayato, J. Hill, W. Iwakiri, et al., “Development and performance verification of a TPC
polarimeter for high energy X-rays,” SPIE Astronomical Telescopes + Instrummentation 2020, Online, December 14–18, 2020.

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K. Uchiyama (poster), T. Tamagawa, T. Mihara, Y. Zhou, Y. Ezoe, M. Numazawa, et al., “Source position determination method ofmultiplexing lobster-eye optics,” SPIE Astronomical Telescopes + Instrummentation 2020, Online, December 14–18, 2020.
T. Tamagawa (Oral), K. Uchiyama, R. Otsubo, T. Yuasa, Y. Zhou, T. Mihara, et al., “New concept for wide-field X-ray monitoring withmultiplexing Lobster-eye optics,” 43rd COSPAR Scientific Assembly, Online, January 28–February 4, 2021.

[Domestic Conferences/Workshops]
玉川徹 (口頭発表), 北口貴雄, 榎戸輝揚, 内山慶祐, 三石郁之, 山口友洋, 柏倉一斗, 田原譲, 郡司修一, 渡邉瑛里, 寺島政伸, 斎藤耀,
深沢泰司, 水野恒史, 高橋弘充, 内田和海, 山本龍哉, 岩切渉, 林田清, 朝倉一統, Martin Weisskopf, Brian Ramsey, Stephen O’Dell,
Paolo Soﬃtta, Luca Baldini ほか IXPE 衛星チーム, 「X 線偏光観測衛星 IXPE への参加現状 (6)」, 日本天文学会 2021 年春季年会,
オンライン, 2021 年 3 月 16–19 日.
三石郁之 (口頭発表), 山口友洋, 柏倉一斗, 瀧川歩, 志村拓馬, 田原譲, 大西崇文, 立花一志, 宮田喜久子, 田村啓輔, 玉川徹, 立花正満,
村島健介, 「X 線偏光観測衛星 IXPE 搭載 X 線望遠鏡用受動型熱制御素子サーマルシールドの開発 (8)」, 日本天文学会 2021 年
春季年会, オンライン, 2021 年 3 月 16–19 日.
Y. Ishisaki (口頭発表), R. L. Kelley, H. Akamatsu, H. Awaki, T. G. Bialas, G. V. Brown, M. P. Chiao, E. Costantini, J.-W. den Herder,
M. J. Dipirro, M. E. Eckart, Y. Ezoe, C. Ferrigno, R. Fujimoto, A. Furuzawa, S. M. Graham, M. Grim, T. Hayashi, T. Horiuchi,
A. Hoshino, Y. Ichinohe, R. Iizuka, M. Ishida, K. Ishikawa, C. A. Kilbourne, S. Kitamoto, M. A. Leutenegger, Y. Maeda, D. McCammon, I. Mitsuishi, M. Mizumoto, T. Ohashi, T. Okajima, S. Paltani, F. S. Porter, K. Sato, T. Sato, M. Sawada, H. Seta, P. J. Shirron,
G. A. Sneiderman, Y. Soong, A. E. Szymkowiak, Y. Takei, T. Tamagawa, M. Tsujimoto, Y. Uchida, C. P. de Vries, S. Yamada, N. Y. Yamasaki, S. Yasuda, and N. Yoshioka, 「X 線分光撮像衛星 XRISM 搭載 Resolve の開発の現状 VI」, 日本天文学会 2021 年春季年会,
オンライン, 2021 年 3 月 16–19 日.
前田良知 (口頭発表), 石田学, 斎藤芳隆, Abarr Quin, Bose R., Braun D., Dowkontt P., Errando M., Gau E., Guarino V., Hossen A.,
Lisalda L., Krawczynski H., Pastrani I., Rauch B., Simburger G., West A., 粟木久光, 今村竜太, Baring M., de Geronimo G., Elliot J.,
Gadson T., Hall K., Harmon K., Heatwole S., Kotsifakis D., Lanzi J., 岡島崇, Peterson Z., Purdy C., Snow C., Stuchlik D., 田村啓輔,
Shreeves C., Vincent B., 榎戸輝揚, 北口貴雄, 玉川徹, 眞武寛人, 深沢泰司, 今里郁弥, 今澤遼, 水野恒史, Poon H., 高橋弘充, 内田和海,
内田悠介, 山本龍哉, 楊冲, 古澤彰浩, 郡司修一, 朝倉一統, 服部兼吾, 袴田知宏, 花岡真帆, 林田清, 石倉彩美, 井出峻太郎, 鴨川航,
松本浩典, 松下友亮, 峯田大 晴, 野田博文, 岡崎貴樹, 大出優一, 佐久間翔太郎, 澤上拳明, 常深博米山友景, 善本真梨那, 石橋和紀,
Iyer Nirmal K., Mozsi K., Ryde F., Stana T.-A., Pearce M., Kislat F., 宮本明日香, 中庭望, 鈴木瞳, 武尾舞, Spooner S., 宮澤拓也,
武田朋志, 内山慶祐, 吉田勇登, Wulf E.,「硬 X 線偏光観測実験 XL-Calibur 気球実験計画」, 日本天文学会 2021 年春季年会, オンライン, 2021 年 3 月 16–19 日.
沼澤正樹 (口頭発表), 榎戸輝揚, 玉川徹, 北口貴雄, 加藤陽, 三原建弘, 内山慶祐, 武田朋志, 吉田勇登, 大田尚享, 林昇輝, 佐藤宏樹,
岩切渉, 内山秀樹, Chin-Ping Hu, 高橋弘充, 小高裕和, 丹波翼, 「明るい X 線源の柔軟な観測を狙う超小型 X 線衛星 NinjaSat」, 日
本天文学会 2021 年春季年会, オンライン, 2021 年 3 月 16–19 日.
武田朋志 (口頭発表), 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘, 岩切渉, 内山秀樹, 内山慶祐, 吉田勇登, 大田尚享,
林昇輝, 佐藤宏樹, Chin-Ping Hu, 高橋弘充, 小高裕和, 丹波翼, 「超小型 X 線衛星 NinjaSat に搭載のガス X 線検出器の開発 (2)」,
日本天文学会 2021 年春季年会, オンライン, 2021 年 3 月 16–19 日.
吉田勇登 (口頭発表), 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘, 岩切渉, 内山秀樹, 内山慶祐, 武田朋志, 大田尚享,
林昇輝, 佐藤宏樹, Chin-Ping Hu, 高橋弘充, 小高裕和, 丹波翼, 「超小型 X 線衛星 NinjaSat 搭載の高電圧印加/アナロク信号処理基板の開発 (2)」, 日本天文学会 2021 年春季年会, オンライン, 2021 年 3 月 16–19 日.
岩切渉 (口頭発表), 戸枝純哉, 芳野史弥, 井上諒太, 長谷川航平, 坪井陽子, 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘,
内山慶祐, 武田朋志, 吉田勇登, 大田尚享, 林昇輝, 佐藤宏樹, 内山秀樹, Chin-Ping Hu, 高橋弘充, 小高裕和, 丹波翼, 「超小型 X
線衛星 NinjaSat に搭載する小型て軽量な X 線コリメーターの開発」, 日本天文学会 2021 年春季年会, オンライン, 2021 年 3 月
16–19 日.
佐々木亮 (口頭発表), 坪井陽子, 岩切渉, 岡本豊, 北古賀智紀, 河合広樹, 三原建弘, 根來均, 他 MAXI チーム, 「全天 X 線監視装置
MAXI を用いた巨大恒星フレアの統計的研究」, 日本天文学会 2021 年春季年会, オンライン, 2021 年 3 月 16–19 日.
根來均 (口頭発表), 中島基樹, 芹野素子, 三原建弘, 岩切渉, 安達稜, 河合誠之, 小川翔司, 中平聡志, 松岡勝 他 MAXI チーム,
「MAXI/GSC か検出した 2020 年度後半の突発現象—ミニアウトバーストの検出—」, 日本天文学会 2021 年春季年会, オンライ
ン, 2021 年 3 月 16–19 日.
玉川徹 (口頭発表), 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘, 武田朋志, 吉田勇登, 大田尚亨, 林昇輝, 内山慶祐, 岩切渉,
内山秀樹, 佐藤宏樹, Chin-Ping Hu, 高橋弘充, 小高裕和, 丹波翼, 「超小型 X 線天体観測衛星 NinjaSat」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
高橋弘充 (口頭発表), Quin Abarr, 朝倉一統, 粟木久光, Matthew G. Baring, Richard Bose, Dana Braun, Gianluigi de Geronimo,Paul Dowkontt, John Elliot, 榎戸輝揚, Manel Errando, 深沢泰司, 古澤彰浩, Thomas Gadson, Epharaim Gau, Victor Guarino, 郡司修一,
袴田知宏, Kenny Hall, 花岡真帆, Keon Harmon, 服部憲吾, 林田清, L, Scott Heatwole, Arman Hossen, 井出峻太郎, 今里郁弥, 今澤遼,
石橋和紀, 石田学, 石倉彩美, Nirmal Kumar Iyer, Fabian Kislat, Mozsi Kiss, 鴨川航, 北口貴雄, David Kotsifakis, Henric Krawczynski,
James Lanzi, Lindsey Lisalda, 前田良知, 松下友亮, 眞武寛人, 松本浩典, 峯田大晴, 宮本明日香, 宮澤拓也, 水野恒史, 中庭望,野田博文, 大出優一, 岡島崇, 岡崎貴樹, Izabella Pastrani, Mark Pearce, N, Zachary Peterson, Helen Poon, Chris Purdy, Brian Rauch,
Felix Ryde, 斎藤芳隆, 佐久間翔太郎, 澤上拳明, Chris Shreeves, Garry Simburger, Carl Snow, Sean Spooner, Theodor-Adrian Stana,David Stuchlik, 鈴木瞳, 武田朋志, 武尾舞, 玉川徹, 田村啓輔, 常深博, 内田和海, 内田悠介, 内山慶祐, Brett Vincent, Andrew West,
Eric Wulf, 山本龍哉, 楊冲, 米山友景, 吉田勇登, 善本真梨那, XL-Calibur チーム, 「硬 X 線偏光観測実験 XL-Calibur 気球実験計
画の 2022 年フライトへ向けた準備状況」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
郡司修一 (口頭発表), 寺島政伸, 渡邉瑛里, 斎藤耀, 水野恒史, 内田和海, 山本龍哉, 深沢泰司, 高橋弘充, 玉川徹, 北口貴雄, 榎戸輝揚,
内山慶祐, 三石郁之, 山口友洋, 柏倉一斗, 田原譲, 林田清, 朝倉一統, 岩切渉, Martin Weisskopf, Brian Ramsey, Stephen O’Dell,
Paolo Soﬃtta, Luca Baldini ほか IXPE 衛星チーム, 「X 線偏光衛星 IXPE の開発の現状」, 日本物理学会第 76 回年次大会, オンラ- 235 -

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イン, 2021 年 3 月 12–15 日.
寺島政伸 (口頭発表), 郡司修一, 渡邉瑛里, 斎藤耀, 水野恒史, 内田和海, 山本龍哉, 深沢泰司, 高橋弘充, 玉川徹, 北口貴雄, 榎戸輝揚,
内山慶祐, 三石郁之, 山口友洋, 柏倉一斗, 田原譲, 林田清, 朝倉一統, 岩切渉, Martin Weisskopf, Brian Ramsey, Stephen O’Dell,
Paolo Soﬃtta, Luca Baldini ほか IXPE 衛星チーム, 「IXPE 衛星による GRB afterglow の偏光観測シミュレーション」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
山本あゆ美 (口頭発表), 坂本貴紀, 芹野素子, 李晋, 盛顯捷, 天谷友亮, 米徳大輔, 澤野達哉, 三原建弘, 三石郁之, 「X 線ビームラインを用いたロブスターアイ光学系の性能評価試験」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
米田浩基 (口頭発表), 高嶋聡, 小高裕和, 井上芳幸, 辻直美, 一戸悠人, Georgia Karagiorgi, Reshmi Mukherjee, Tsuguo Aramaki,
Jonathan Asaadi, Kerstin Perez, GRAMS コラボレーション, 「GRAMS 実験 3: 全体報告・イベント再構成アルゴリズムの開発」,
日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
高嶋聡 (口頭発表), 小高裕和, 馬場彩, 米田浩基, 木村眞人, 田中雅士, 寄田浩平, GRAMS コラボレーション, 「GRAMS 実験 4: 液体アルゴン検出器のエネルギー測定性能と宇宙線バックグラウンドの研究」, 日本物理学会第 76 回年次大会, オンライン, 2021
年 3 月 12–15 日.
石崎欣尚 (ポスター発表), Richard L. Kelley, 赤松弘規, 粟木久光, Thomas G. Bialas, Gregory V. Brown, Meng P. Chao, Elisa Costantini,
Jan-Willem den Herder, Michael J. Dipirro, Megan E. Ekart, 江副祐一郎, Carlo Ferrigno, 藤本龍一, 古澤彰浩, Steven M. Graham, Martin Grim, 林多佳由, 堀内貴史, 星野晶夫, 一戸悠人, 飯塚亮, 石田学, 石川久美, Caroline A. Kilbourne, 北本俊二, Maurice A. Leutenegger, 三石郁之, 水本岬希, 森英之, 大橋隆哉, 岡島崇, Stephane Paltani, F. Scott Porter, 佐藤浩介, 澤田真理, 瀬田弘美, Peter J. Shirron,
Gary J. Sneiderman, Yang Soong, Andrew E. Szymkowiak, 竹井洋, 玉川徹, 辻本匡弘, 内田悠介, Cor P. de Vries, 山田真也, 山崎典子, 安田進, 吉岡奈紗, 「X 線分光撮像衛星 (XRISM) 搭載 Resolve の開発状況」, 第 21 回宇宙科学シンポジウム, オンライン, 2021
年 1 月 6–7 日.
玉川徹,(ポスター発表) 北口貴雄, 榎戸輝揚, 内山慶祐, 三石郁之, 山口友洋, 柏倉一斗, 田原譲, 郡司修一, 渡邉瑛里, 寺島政伸, 斎藤耀,
深沢泰司, 水野恒史, 高橋弘充, 内田和海, 山本龍哉, 岩切渉, 林田清, 朝倉一統, Martin Weisskopf, Brian Ramsey, Stephen O’Dell,
Paolo Soﬃtta, Luca Baldini ほか IXPE 衛星チーム, 「X 線偏光観測衛星 IXPE 開発の現状」, 第 21 回宇宙科学シンポジウム, オン
ライン, 2021 年 1 月 6–7 日.
三石郁之 (ポスター発表), 山口友洋, 柏倉一斗, 瀧川歩, 田村啓輔, 宮田喜久子, 田原譲, 玉川徹, 大西崇文, 立花一志, 立花正満,
村島健介, 「X 線偏光観測衛星 IXPE 搭載に向けた望遠鏡用サーマルシールドの開発 (2)」, 第 21 回宇宙科学シンポジウム, オン
ライン, 2021 年 1 月 6–7 日.
郡司修一 (ポスター発表), 寺島政伸, 渡邉瑛里, 斎藤耀, 水野恒史, 内田和海, 山本龍哉, 深沢泰司, 高橋弘充, 玉川徹, 北口貴雄, 榎戸輝揚,
内山慶祐, 三石郁之, 山口友洋, 柏倉一斗, 田原譲, 林田清, 朝倉一統, 岩切渉, Martin Weisskopf, Brian Ramsey, Stephen O’Dell,
Paolo Soﬃtta, Luca Baldini ほか IXPE 衛星チーム, 「日本チームによる IXPE 衛星の偏光観測シミュレーションの現状」, 第 21回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
三原建弘 (ポスター発表), 根来均, 中平聡志ほか MAXI チーム, 「MAXI の現状」
, 第 21 回宇宙科学シンポジウム, オンライン, 2021
年 1 月 6–7 日.
根来均 (ポスター発表), 中島基樹, 芹野素子, 三原建弘, 上野史郎, 冨田洋, 中平聡志, 菅原泰晴, 河合誠之, 吉田篤正, 坂本貴紀,
杉田聡司, 上田佳宏, 坪井陽子, 岩切渉, 山内誠, 山岡和貴, 川室太希, 志達めぐみ, 杉崎睦, 松岡勝, 「2020 年に MAXI が発見した新天体と突発現象」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
富永愛侑 (ポスター発表), 中平聡志, 志達めぐみ, 大枝幹, 海老沢研, 菅原泰晴, 根来均, 河合誠之, 杉崎睦, 上田佳宏, 三原建弘ほか
MAXI チーム, 「ブラックホール X 線新星 MAXI J1348-630 の発見」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月
6–7 日.
三原建弘 (ポスター発表) (理研) ほか MAXI チーム, 「MAXI 後期運用 (3) 期間中 (2018-2020) の MAXI の成果: 論文, リンクと概説」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
米徳大輔 (口頭発表), 三原建弘, 土居明広, 坂本貴紀, 津村耕司, HiZ-GUNDAM WG, 「ガンマ線バーストを用いた初期宇宙・極限
時空探査計画 HiZ-GUNDAM」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
李晋 (ポスター発表), 坂本貴紀, 芹野素子, 澤野達哉, 米徳大輔, 三石郁之, 三原建弘, 「ロブスターアイ光学系の地上試験及びシミュレータによる性能評価」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
荻野直樹 (ポスター発表), 有元誠, 澤野達哉, 米徳大輔, 平賀純子, 坂本貴紀, 盛顯捷, 谷津陽一, 「HiZ-GUNDAM に向けた CMOS イ
メージセンサの高速読み出しシステムの開発」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
澤野達哉 (ポスター発表),, 米徳大輔, 有元誠, 李晋, 三原建弘, 荻野直樹, 坂本貴紀, 芹野素子「ロブスターアイ光学系による X 線突
発天体検出アルゴリズムの研究」, 第 21 回宇宙科学シンポジウム, オンライン, 2021 年 1 月 6–7 日.
武田朋志 (口頭発表)(理科大/理研), 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘 (理研), 岩切渉 (中央大), 内山秀樹 (静岡大), 内山慶祐, 吉田勇登 (理科大/理研), 佐藤宏樹 (芝浦工大/理研), Chin-Ping Hu (京都大), 高橋弘充 (広島大), 小高裕和, 「超小型 X 線衛星 NinjaSat に搭載のガス X 線検出器の開発」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
吉田勇登 (理科大/理研), 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘 (理研), 岩切渉 (中央大), 内山秀樹 (静岡大),内山慶祐, 武田朋志 (理科大/理研), 佐藤宏樹 (芝浦工大/理研), Chin-Ping Hu(京都大), 高橋弘充 (広島大), 小高裕和 (東京大) 「超小型 X 線衛星 NinjaSat に搭載の高電圧印加・アナロク信号処理ボードの開発」, 日本天文学会 2020 年秋季年会, オンライン,
2020 年 9 月 8–10 日.
佐藤宏樹 (芝浦工大/理研), 玉川徹, 榎戸輝揚, 北口貴雄, 加藤陽, 沼澤正樹, 三原建弘 (理研), 岩切渉 (中央大), 内山秀樹 (静岡大),内山慶祐, 武田朋志, 吉田勇登 (理科大/理研), Chin-Ping Hu (京都大), 高橋弘充 (広島大), 小高裕和 (東大) 「超小型 X 線衛星
Ninjasat に搭載の X 線背景放射減衰シールドの最適化」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
畠内康輔, 春日知明, 丹波翼, 高嶋聡, 鈴木寛大, 渡邊泰平, 南木宙斗, 谷本敦, 小高裕和, 馬場彩 (東大), 周圓輝 (理科大/理研), 玉川徹(理研), 長澤俊作, 峰海里, 高橋忠幸 (東大 Kavli IPMU), 成影典之 (国立天文台), 佐久間翔太郎, 朝倉一統, 林田清 (阪大) 「CMOS
イメージセンサを用いた硬 X 線撮像偏光計の開発 III」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.

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高橋弘充, 内田和海, 内田悠介, 深沢泰司, 水野恒史 (広島大学), 林田清, 松本浩典, 常深博 (大阪大学), 前田良知, 石田学, 斎藤芳
隆 (宇宙科学研究所), 宮澤拓也 (沖縄科学技術大学院大学), 粟木久光 (愛媛大学), 石橋和紀 (名古屋大学), 北口貴雄, 玉川徹, 榎
戸輝揚 (理化学研究所), 内山慶祐, 武田朋志, 吉田勇登 (東京理科大学), 郡司修一 (山形大学), Henric Krawczynski(ワシントン大学), Fabian Kislat(ニューハンプシャー大学), 岡島崇, 田村啓輔, 林多佳由 (NASA), Mark Pearce(スウェーデン王立工科大学),
XL-Calibur チーム「硬 X 線偏光観測実験 XL-Calibur 気球の 2022 年フライトへ向けた準備状況」, 日本天文学会 2020 年秋季年
会, オンライン, 2020 年 9 月 8–10 日.
山本龍哉, 水野恒史, 深沢泰司, 高橋弘充, 内田和海 (広島大), 玉川徹, 北口貴雄, 榎戸輝揚 (理研), 三石郁之, 山口友洋, 柏倉一斗,
田原譲 (名古屋大), 郡司修一, 渡邊瑛理, 寺島政伸, 斎藤耀 (山形大), 林田清, 朝倉一統 (大阪大), 内山慶祐 (東理大/理研), 岩切渉 (中央大), Martin Weisskopf, Brian Ramsey, Stephen O ’Dell(NASA/MSFC), Paolo Soﬃtta(IAPS), Luca Baldini(INFN), 他 IXPE チーム「シミュレーションを用いた IXPE 衛星による広がった天体の軟 X 線偏光解析手法の研究」, 日本天文学会 2020 年秋季年会, オ
ンライン, 2020 年 9 月 8–10 日.
山口友洋, 瀧川歩, 柏倉一斗, 三石郁之, 田原譲, 大西崇文, 立花一志 (名古屋大学), 宮田喜久子 (名城大学), 田村啓輔 (NASA/GSFC,
UMBC), 玉川徹 (理研), 立花正満, 村島健介 (株式会社カネカ) 「X 線偏光観測衛星 IXPE 搭載 X 線望遠鏡用受動型熱制御素子
サーマルシールドの開発 (7)」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
小高裕和, 高嶋聡 (東京大学), 井上芳幸, 米田浩基, 辻直美 (理研), 一戸悠人 (立教大学), Georgia Kara- giorgi, Reshmi Mukherjee(Columbia 大学), Tsuguo Aramaki (Northeastern 大学/SLAC), GRAMS コラボレーション「GRAMS 計画 1: MeV ガンマ線観測・
ダーククマター探索気球実験」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
根來均, 中島基樹, 青木真凜 (日大), 三原建弘, 松岡勝 (理研), 岩切渉, 北古賀智紀, 岡本豊 (中央大), 志達めぐみ (愛媛大), 菅原泰晴
(JAXA), 庭野聖史, 河合誠之 (東工大) 他 MAXI チーム「MAXI/GSC が検出した 2020 年度前半の突発現象: X 線連星系の短期長期活動と増光する矮新星 SS Cyg の検出」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
米田浩基 (理研), 牧島一夫 (Kavli IPMU/東大理/理研), 榎戸輝揚 (理研), Dmitry Khangulyan(立教大), 峰海里 (東大理/Kavli IPMU),
水野恒史 (広島大), 高橋忠幸 (Kavli IPMU/東大理) 「ガンマ線連星 LS 5039 の, NuSTAR 衛星と Fermi 衛星を用いた広帯域スペ
クトル解析」, 日本天文学会 2020 年秋季年会, オンライン, 2020 年 9 月 8–10 日.
内田悠介 (口頭発表), Quin Abarr, 粟木久光, Richard Bose, Dana Braun, Gialuigi de Geronimo, Paul Dowkontt, 榎戸輝揚, Manel Errando, 深沢泰司, Tom Gadson, Victor Guarino, 郡司修一, Keon Harmon, 林田清, Scott Heatwole, 石田学, Fabian Kislat, Mozsi
Kiss, 北口貴雄, Henric Krawczynski, Nirmal Kumar Iyer, Rakhee Kushwah, James Lanzi, Shaorui Li, Lindsey Lisalda, 前田良知,
松本浩典, 宮澤拓也, 水野恒史, 岡島崇, Mark Pearce, Zachary Peterson, Brian Rauch, Felix Ryde, 斎藤芳隆, Theodor-Adrian Stana,David Stuchlik, 高橋弘充, 武田朋志, 玉川徹, 田村啓輔, 常深博, 内田和海, 内山慶祐, Andrew West, Eric A. Wulf, 吉田勇登, XLCalibur チーム, 「硬 X 線集光偏光系 XL-Calibur 気球実験の準備状況と 0.8 mm 厚 CZT 検出器の性能」, 日本物理学会 2020 年
秋季大会, オンライン, 2020 年 9 月 14–17 日.
小高裕和 (口頭発表), 畠内康輔, 春日知明, 渡邊泰平, 丹波翼, 鈴木寛大, 高嶋聡, 南木宙斗, 谷本敦, 馬場彩, 周圓輝, 玉川徹, 長澤俊作,
峰海里, 高橋忠幸, 成影典之, 佐久間翔太郎, 朝倉一統, 林田清, 「CMOS イメージャを用いた X 線偏光撮像システムの開発 V: 開発と性能評価の現状」, 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.
米田浩基 (口頭発表), 牧島一夫, 榎戸輝揚, Dmitry Khangulyan, 峰海里, 水野恒史, 高橋忠幸, 「ガンマ線連星 LS 5039 の MeV ガン
マ線放射の起源と, マグネター連星の可能性」, 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.
小高裕和 (口頭発表), 高嶋聡, 井上芳幸, 米田浩基, 辻直美, 一戸悠人, Georgia Karagiorgi, Reshmi Mukherjee, Tsuguo Aramaki, GRAMS
コラボレーション, 「GRAMS 実験 1: MeV ガンマ線観測・ダークマター探索気球実験ミッション概要」, 日本物理学会 2020 年
秋季大会, オンライン, 2020 年 9 月 14–17 日.
高嶋聡 (口頭発表), 小高裕和, 馬場彩, 米田浩基, 木村眞人, 田中雅士, 寄田浩平, GRAMS コラボレーション,「GRAMS 実験 2: 液体ア
ルゴン検出器における多重コンプトン散乱イベントの解析」, 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.
米田浩基, 「ガンマ線連星 LS 5039 の MeV ガンマ線放射と, マグネター連星系の可能性」, Pulsar Bi-Monthly Meeting, オンライン,
2020 年 12 月.

[Seminars]
米田浩基, 「ガンマ線連星 LS 5039 のマグネター連星系の可能性: 硬 X 線パルスの兆候と強い MeV ガンマ線放射」, 高エネルギー
宇宙物理学研究会 2020, 東京大学宇宙線研, 2020 年 12 月.
Hiroki Yoneda, “Mystery of the strong MeV gamma-ray emission from gamma-ray binary systems—magnetic reconnection close tomagnetars in binaries? —,” 知の共有ゼミ, 理研, 2020 年 6 月.
Hiroki Yoneda, “The mystery of the MeV gamma-ray emission from gamma-ray binary systems,” , ICRR Seminar, オンライン, 2020 年
12 月.

Outreach Activities
三原建弘ほか, 「ISS 20 年, 日本の挑戦の軌跡」, NHK コズミックフロントネクスト 2020 年 12 月 17 日放送.

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Nuclear Science and Transmutation Research Division
Superheavy Element Research Group
1. Abstract

The elements with their atomic number Z > 103 are called as trans-actinide or superheavy elements. This group has been studying
the physical and chemical properties of superheavy elements. They must be produced by artificially for the scientific study utilizing
the accelerators in RIBF. Two teams lead the study of the superheavy elements. Superheavy Element Production Team studies various
methods of eﬃcient production of the superheavy elements and their physical and chemical properties. Superheavy Element Device
Development Team develops the main experimental device, i.e., the gas-filled recoil ion separator, GARIS.
The synthesis of elements having atomic numbers over 119 will be attempted with the aim of establishing nuclear synthesis
technology that reaches the “island of stability” where the lifetime of atomic nuclei is expected be prolonged significantly. With theaim of constructing an ultimate nuclear model, maximum utilization will be made of key experimental devices which become fully
operational in order to conduct research for the syntheses of element 119 and 120.

2. Major Research Subjects

Superheavy Element Production Team
(1) Searching for new elements(2) Spectroscopic study of the nucleus of heavy elements(3) Chemistry of superheavy elements(4) Study of a reaction mechanism for fusion process Superheavy Element Device Development Team
(5) Maintenance of GARIS, GARIS-II and development of new gas-filled recoil ion separator GARIS-III(6) Maintenance and development of detector and DAQ system for GARIS, GARIS-II and GARIS-III(7) Maintenance and development of target system for GARIS, GARIS-II and GARIS-III

3. Summary of Research Activity(1) Searching for new elements
To expand the periodic table of elements and the nuclear chart, we will search for new elements.
(2) Spectroscopic study of the nucleus of heavy elements
Using the high sensitivity system for detecting the heaviest element, we plan to perform a spectroscopic study of nuclei of theheavy elements.
(3) Chemistry of superheavy elements
Study of chemistry of the trans-actinide (superheavy element) has just started world-wide, making it a new frontier in the field ofchemistry. Relativistic eﬀects in chemical property are predicted by many theoretical studies. We will try to develop this new field.
(4) Study of a reaction mechanism for fusion process
Superheavy elements have been produced by complete fusion reaction of two heavy nuclei. However, the reaction mechanism of
the fusion process is still not well understood theoretically. When we design an experiment to synthesize nuclei of the superheavy
elements, we need to determine a beam-target combination and the most appropriate reaction energy. This is when the theory becomes
important. We will try to develop a reaction theory useful in designing an experiment by collaborating with the theorists.
(5) Research highlight
The discovery of a new element is one of the exciting topics both for nuclear physicists and nuclear chemists. The elements with
their atomic number Z > 103 are called as trans-actinides or superheavy elements. The chemical properties of those elements have notyet been studied in detail. Since those elements do not exist in nature, they must be produced by artificially, by using nuclear reactions
for the study of those elements. Because the production rate of atoms of those elements is extremely small, an eﬃcient production andcollection are key issues of the superheavy research. In our laboratory, we have been trying to produce new elements, studying thephysical and chemical properties of the superheavy elements utilizing the accelerators in RIKEN.
Although the Research Group for Superheavy element has started at April 2013, the Group is a renewal of the Superheay Element
Laboratory started at April 2006, based on a research group which belonged to the RIKEN accelerator research facility (RARF), andhad studied the productions of the heaviest elements. The main experimental apparatus is a gas-filled recoil ion separator GARIS. The
heaviest elements with their atomic numbers, 107 (Bohrium), 108 (Hassium), 109 (Meitnerium), 110 (Darmstadtium), 111 (Roentogenium), and 112 (Copernicium) were discovered as new elements at Helmholtzzentrum fur Schwerionenforschung GmbH (GSI),
Germany by using 208 Pb or 209 Bi based complete fusion reactions, so called “cold fusion” reactions. We have made independentconfirmations of the productions of isotopes of 108th, 110th, 111th, and 112th elements by using the same reactions performed at GSI.
After these work, we observed an isotope of the 113th element, 278 113, in July 2004, in April, 2005, and in August 2012. The isotope,
278
113, has both the largest atomic number, (Z = 113) and atomic mass number (A = 278) which have determined experimentally
among the isotopes which have been produced by cold fusion reactions. We could show the world highest sensitivity for production
and detection of the superheavy elements by these observations. Our results that related to 278 113 has been recognized as a discoveryof new element by a Joint Working Party of the International Union of Pure and Applied Chemistry (IUPAC) and International Union- 238 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

of Pure and Applied Physics (IUPAP). Finally, we named the 113th element as “Nihonium.”
We decided to make one more recoil separator GARIS-II, which has an acceptance twice as large as existing GARIS, in order torealize higher sensitivity. The design of GARIS-II has finished in 2008. All fabrication of the separator will be finished at the end of
fiscal year 2008. It has been ready for operation after some commissioning works.
Preparatory work for the study of the chemical properties of the superheavy elements has started by using the gas-jet transportsystem coupled to GARIS. The experiment was quite successful. The background radioactivity of unwanted reaction products has beenhighly suppressed. Without using the recoil separator upstream the gas-jet transport system, large amount of unwanted radioactivity
strongly prevents the unique identification of the event of our interest. This new technique makes clean and clear studies of chemistryof the heaviest elements promising.
The spectroscopic study of the heaviest elements has started by using alpha spectrometry. New isotope, 263 Hs (Z = 108), which
has the smallest atomic mass number ever observed among the Hassium isotopes, had discovered in the study. New spectroscopic
information for 264 Hs and its daughters have obtained also. The spectroscopic study of Rutherfordium isotope 261 Rf (Z = 104) has
done and 1.9-s isomeric state has directly produced for the first time.
Preparatory works for the study of the new superheavy elements with atomic number 119 and 120 have started in 2013. We
measured the reaction products of the 248 Cm (48 Ca, xn)296−x Lv (Z = 116) previously studied by Frelov Laboratory of Nuclear Reaction,
Russia, and GSI. We observed 5 isotopes in total which tentatively assigned to 293 Lv, and 292 Lv.

MemberDirector
Kosuke MORITA- 239 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Superheavy Element Research Group
Superheavy Element Production Team
1. Abstract

The elements with atomic number Z ≥ 104 are called as trans-actinide or superheavy elements (SHEs). Superheavy Element
Production Team investigates synthesis mechanisms of SHEs, nuclear properties of SHE nuclei, and chemical properties of SHEs
mainly in collaboration with Superheavy Element Devise Development Team and Nuclear Chemistry Research Team of RIKEN
Nishina Center.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Search for new superheavy elements
Decay spectroscopy of the heaviest nuclei
Study of reaction mechanisms for production of the heaviest nuclei
Study of chemical properties of the heaviest elements

3. Summary of Research Activity(1) Search for new superheavy elements
In November, 2016, the 7th period of the periodic table was completed with the oﬃcial approval of four new elements, nihonium(Nh, atomic number Z = 113), moscovium (Mc, Z = 115), tennessine (Ts, Z = 117), and oganesson (Og, Z = 118) by International
Union of Pure and Applied Chemistry. We have started to search for new elements to expand the chart of the nuclides toward to theisland of stability and the periodic table of the elements toward the 8th period. In January, 2020, RIKEN heavy-ion Linear ACcelerator(RILAC) was upgraded as Superconducting RIKEN heavy-ion Linear ACcelerator (SRILAC). We developed the new gas-filled recoil
ion separator GARIS III on the beam line of SRILAC. In June and July, 2020, we conducted the commissioning of the SRILAC +GARIS III setup in the 169 Tm + 40 Ar, 208 Pb + 40 Ar, and 208 Pb + 51 V reactions. Then, we started to search for new element, element
119 in the 248 Cm + 51 V reaction in October, 2020.
(2) Decay spectroscopy of the heaviest nuclei
In collaboration with KEK, we developed a multi-refection time-of-fight mass spectrograph (MRTOF-MS) equipped with an
α-TOF detector on the focal plane of GARIS-II at RRC for decay-correlated mass measurements of low-yield and short-lived SHE
isotopes. By correlating measured time-of-flight signals with decay events, it can suppress background events and obtain accurate,high-precision mass and half-life values even in cases of very low event rates. The performance of the system was investigated using
the Ra isotopes produced in the 159 Tb + 51 V reaction.
(3) Study of reaction mechanisms for production of the heaviest nuclei
SHE nuclei have been produced by complete fusion reactions of two heavy nuclei. However, the reaction mechanism of thefusion process is still not well understood both theoretically and experimentally. We measured excitation functions for the quasielastic
scattering of the 248 Cm + 51 V reaction using GARIS III at SRILAC. The result can be utilized to estimate the optimal incident beamenergy for production of isotopes of new element 119.
(4) Study of chemical properties of the heaviest elements
Chemical characterization of newly-discovered SHEs is an extremely interesting and challenging subject in modern nuclear andradiochemistry. In collaboration with Nuclear Chemistry Research Team of RIKEN Nishina Center, we are developing SHE production systems as well as rapid single-atom chemistry apparatuses for chemistry studies of SHEs. We installed a gas-jet transportsystem to the focal plane of GARIS at RILAC. This system is a promising approach for exploring new frontiers in SHE chemistry: thebackground radiations from unwanted products are strongly suppressed, the intense primary heavy-ion beam is absent in the gas-jet
chamber, and hence the high gas-jet extraction yield is attained. Furthermore, the beam-free conditions make it possible to investigate
new chemical systems. In 2020, we continued to develop an ultra-rapid gas-chromatograph apparatus at the focal plane of GARIS forthe gas chemistry of SHEs. This apparatus consists of an RF carpet gas cell and a cryo-gas-chromatograph column with a Si detector array. For the aqueous chemistry, we developed a flow solvent extraction apparatus which consisted of a continuous dissolution
apparatus Membrane DeGasser (MDG), a Flow Solvent Extractor (FSE), and a liquid scintillation detector for α/SF-spectrometry.

Members
Team Leader
Hiromitsu HABA

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research & Development Scientist
Daiya KAJI
Special Postdoctoral Researcher
Tomohiro HAYAMIZU
Visiting Scientists
Marc ASFARI (Inst. Pluridisciplinaire Hubert Curien / Strasbourg Univ.)
Mahananda DASGUPTA (Australian Nat’l Univ.)
Olivier DORVAUX (Strasbourg Univ.)
Benoit Jean-Paul GALL (Strasbourg Univ. / Inst. Pluridisciplinaire Hubert Curien)
Zaiguo GAN (Chinese Academy of Sci.)
Shintaro GO (Kyushu Univ.)
David HINDE (The Australian Nat’l Univ.)
Student Trainees
Masato HIGASHI (Kyushu Univ.)
Tamito KAI (Kyushu Univ.)
Kieran KESSACI (IPHC Strasbourg/Strasbourg Univ.)
Ikuto MURAKAMI (Kyushu Univ.)
Taiga MUTO (Kyushu Univ.)

Minghui HUANG (IMP, CAS)
Hiroyuki KOURA (JAEA)
Daisuke NAGAE (Kyushu Univ.)
Satoshi SAKAGUCHI (Kyushu Univ.)
Mirei TAKEYAMA (Yamagata Univ.)
Masaomi TANAKA (Kyushu Univ.)
Taiki TANAKA (The Australian Nat’l Univ.)
Huabin YANG (IMP, CAS)
Zhiyuan ZHANG (IMP, CAS)
Yuto NAGATA (Kyushu Univ.)
Natsuki NAITO (Kyushu Univ.)
Mako OSADA (Kyushu Univ.)
Taro TOMIMATSU (Kyushu Univ.)

List of Publications & Presentations
Publications[Original Papers]
H. Haba, F. Fan, D. Kaji, Y. Kasamatsu, H. Kikunaga, Y. Komori, N. Kondo, H. Kudo, K. Morimoto, K. Morita, M. Murakami, K. Nishio,
J. P. Omtvedt, K. Ooe, Z. Qin, D. Sato, N. Sato, T. K. Sato, Y. Shigekawa, A. Shinohara, M. Takeyama, T. Tanaka, A. Toyoshima,
K. Tsukada, Y. Wakabayashi, Y. Wang, S. Wulﬀ, S. Yamaki, S. Yano, Y. Yasuda, and T. Yokokita, “Production of 266 Bh in the
248
Cm(23 Na, 5n)266 Bh reaction and its decay properties,” Phys. Rev. C 102, 024625 (2020).
Y. Kasamatsu, K. Toyomura, H. Haba, T. Yokokita, Y. Shigekawa, A. Kino, Y. Yasuda, Y. Komori, J. Kanaya, M. Huang, M. Murakami,
H. Kikunaga, E. Watanabe, T. Yoshimura, K. Morita, T. Mitsugashira, K. Takamiya, T. Ohtsuki, and A. Shinohara, “Co-precipitation
behaviour of single atoms of rutherfordium in basic solutions,” Nat. Chem. 13, 226 (2021).

[Review Articles]
羽場宏光, 「元素周期表の新時代 119 番以降の新元素を求めて」, 現代化学 9 月号, No. 594, 43 (2020).
羽場宏光, 「スタニズラオ・カニッツァーロ」, 和光純薬時報, Vol. 88, No. 4, 28 (2020). Vol. 27, pp. 11–14 (2020).

[Proceedings]
T. Niwase, K. Fujita, Y. Yamano, K. Watanabe, D. Kaji, K. Morimoto, H. Haba, T. Hirano, S. Mitsuoka, and K. Morita, “Measurementof fusion barrier distribution in 51 V+208 Pb system,” Proc. 13th Int. Conf. on Nucleus-Nucleus Collisions, JPS Conf. Proc. 32, 010022(2020).
Y. Sakemi, T. Aoki, R. Calabrese, H. Haba, K. Harada, T. Hayamizu, Y. Ichikawa, K. Jungmann, A. Kastberg, Y. Kotaka, Y. Matsuda,
Y. Matsuo, H. Nagahama, K. Nakamura, M. Otsuka, N. Ozawa, K. Tanaka, A. Uchiyama, H. Ueno, and L. Willmann, “Fundamental
physics with cold radioactive atoms,” Proc. 14th Asia-Pacific Phys. Conf., AIP Conf. Proc. 2319, 080020 (2021).

Presentations[International Conferences/Workshops]
H. Haba (invited), “Production and applications of radioisotopes at RIKEN RI beam factory—Search for new elements through diagnosis
and therapy of cancer—,” Symposium on Nuclear Data 2020, Wako, Japan, November 26–27, 2020.
Y. Komori (poster), H. Haba, M. Aikawa, M. Saito, S. Takács, and F. Ditrói, “Production cross sections of 175 Hf in the nat Lu(p,xn) andnat
Lu(d,xn) reactions,” Symposium on Nuclear Data 2020, Wako, Japan, November 26–27, 2020.
T. Hayamizu (oral), H. Haba, K. Nakamura, T. Aoki, H. Nagahama, K. Tanaka, N. Ozawa, M. Ohtsuka, and Y. Sakemi, “Development of
ultracold francium atomic sources towards the permanent EDM search,” Yamada Conference LXXII: The 8th Asia-Pacific Conference
on Few-Body Problems in Physics (APFB2020), Kanazawa, Japan, March 1–5, 2021.

[Domestic Conferences/Workshops]
羽場宏光 (招待講演), 「ラジオアイソトープの製造と応用～新元素の探索からがん治療まで～」, 第 17 回日本加速器学会年会, オ
ンライン, 2020 年 9 月 2–4 日.
寺西翔 (口頭発表), 森田涼雅, 早川優太, 坂口綾, 中島朗久, 小森有希子, 横北卓也, 森大輝, 羽場宏光, 横山明彦, 「232 Th+7 Li 反応のNp 合成系における不完全融合反応の影響」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

森田涼雅 (口頭発表), 寺西翔, 早川優太, 坂口綾, 中島朗久, 小森有希子, 横北卓也, 森大輝, 羽場宏光, 横山明彦 , 「232 Th+7 Li 反応における反跳率補正による核分裂断面積測定法の確立」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
庭瀬暁隆 (口頭発表), P. Schury, 和田道治, P. Brionnet, S. Chen, 橋本尚志, 羽場宏光, 平山賀一, D. S. Hou, 飯村俊, 石山博恒, 石澤倫,
伊藤由太, 加治大哉, 木村創大, 小浦寛之, J. J. Liu, 宮武宇也, J. Y. Moon, 森本幸司, 森田浩介, 長江大輔, M. Rosenbusch, 高峰愛子,
渡辺裕, H. Wollnik, W. Xian, S. X. Yan, 「MRTOF+α-TOF による 257 Db の直接質量測定」, 日本放射化学会第 64 回討論会 (2020),
オンライン, 2020 年 9 月 9–11 日.
重河優大 (口頭発表), 山口敦史, 佐藤望, 高峰愛子, 和田道治, 羽場宏光, 「核化学研究用高周波イオン収集システムの開発」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
加藤瑞穂 (口頭発表), 安達サディア, 豊嶋厚史, 塚田和明, 浅井雅人, 羽場宏光, 横北卓也, 小森有希子, 重河優大, Yang Wang, 森大輝,
柏原歩那, 床井健運, 中島朗久, 鈴木雄介, 西塚魁人, 末木啓介, 「HF/HNO3 系における Db の陰イオン交換挙動」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
横北卓也 (口頭発表), 笠松良崇, 渡邉瑛介, 小森有希子, 重河優大, 森大輝, 王洋, 二宮秀美, 速水翔, 東内克馬, ゴーシュコースタブ,
篠原厚, 羽場宏光, 「硫酸系における Rf の陰イオン交換: 分配係数の硫酸濃度依存性」, 日本放射化学会第 64 回討論会 (2020), オ
ンライン, 2020 年 9 月 9–11 日.
小森有希子 (ポスター発表), 羽場宏光, 「Calix[4]arene-bis(benzocrown-6) を用いた Fr と Cs の溶媒抽出」, 日本放射化学会第 64 回
討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
小森有希子 (ポスター発表), 羽場宏光, 合川正幸, 斎藤萌美, Sándor Takács, Ferenc Ditrói, 「nat Lu(p,xn) および nat Lu(d,xn) 反応による 175 Hf の生成断面積の測定」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
渡邉瑛介 (ポスター発表), 笠松良崇, 横北卓也, 速水翔, 東内克馬, 重河優大, 羽場宏光, 篠原厚, 「Rf の化学研究に向けた 89m Zr の硝酸系でのオンライン陰イオン交換実験」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
小澤直也 (口頭発表), 長濱弘季, 早水友洋, 中村圭佑, 佐藤幹, 永瀬慎太郎, 小高康照, 鎌倉恵太, 田中香津生, 大塚未来, 青木貴稔,
市川雄一, 高峰愛子, 羽場宏光, 上野秀樹, 酒見泰寛, 「フランシウム原子の電気双極子能率探索のための表面電離イオン源の開発」, 日本物理学会第 76 回年次大会（2021 年）, オンライン, 2021 年 3 月 12–15 日.

[Seminars]
早水友洋, Emily Altiere, Eric R. Miller, David J. Jones, Kirk W. Madison, 百瀬孝昌, 「キセノンの 5p5 6p ← 5p6 遷移の高分解能 2 光
子分光」, 第 6 回精密計測を元に科学技術に変革をもたらす回路技術調査専門委員会, オンライン, 2021 年 3 月 23 日.

Press Releases
原子 1 つの沈殿を調べる! —超重元素ラザホージウムの共沈挙動の実験的観測—, 理化学研究所, 2021 年 2 月 18 日. https://www.riken.jp/press/2021/20210218_1 .

Outreach Activities
羽場宏光, 「原子の仕組みとラジオアイソトープの応用～新元素の探索からがんの治療まで～」, 令和 2 年度（2020 年度）八王子市生涯学習センター主催市民自由講座, 八王子, 2021 年 3 月 9 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Superheavy Element Research Group
Superheavy Element Device Development Team
1. Abstract

A gas-filled recoil ion separator has been used as a main experimental device for the study of superheavy elements. This teamis in charge of maintaining, improving, developing, and operating the separators and related devices. In the RIBF facility, three gasfilled recoil ion separators are installed at RILAC and RRC facility. One is GARIS that is designed for a symmetric reaction such as
coldfusion reaction, and the other two are developed for an asymmetric reaction such as hot-fusion reaction, GARIS-II and GARIS-III.
New elements 278 113 were produced by 70 Zn + 209 Bi reaction using GARIS. Further the new element search is currently in progressby using GARIS-II and GARIS-III.

2. Major Research Subjects(1) Maintenance of GARIS, GARIS-II and development of new separator GARIS-III(2) Maintenance and development of detector and DAQ system for superheavy element research(3) Maintenance and development of target system for GARIS, GARIS-II and GARIS-III

3. Summary of Research Activity

The GARIS-II and III are newly developed which has an acceptance twice as large as existing GARIS, in order to realize higher
transmission. A new element search program aiming to element 119 was started using GARIS-II. And new separator GARIS-III wasdeveloped and installed into the RILAC experimental hall. After the some commissioning works of GARIS-III, new 119th element
search has been started. We will also oﬀer user-support if a researcher wishes to use the devices for his/her own research program.

Members
Team Leader
Kouji MORIMOTO
Research/Technical Scientists
Masaki FUJIMAKI (Senior Technical Scientist)

Daiya KAJI (Technical Scientist)

Postdoctoral Researcher
Pierre BRIONNET
Postdoctoral Researcher
Sota KIMURA
Junior Research Associate
Toshitaka NIWASE
Visiting Scientists
Shin-ichi GOTO (Niigata Univ.)
Eiji IDEGUCHI (Osaka Univ.)
Yuta ITO (JAEA)

Katsuhisa NISHIO (JAEA)
Fuyuki TOKANAI (Yamagata Univ.)

Student Trainees
Satoshi ISHIZAWA (Yamagata Univ.)
Yoshiki TAKAHASHI (Niigata Univ.)

Hiroki TSUNODA (Niigata Univ.)

List of Publications & Presentations
Publications[Original Papers]
S. Hofmann, S. N. Dmitriev, C. Fahlander, J. M. Gates, J. B. Roberto, and H. Sakai, “On the discovery of new elements (IUPAC/IUPAP
Report), —Report of the 2017 Joint Working Group of IUPAC and IUPAP—,” Pure Appl. Chem. 92, 1387 (2020).

[Review Articles]
庭瀬暁隆, 「MRTOF+α-TOF による 257 Db の直接質量測定」, 放射化学 43, 31 (2021 年 3 月).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Presentations[International Conferences/Workshops]
K. Morimoto (oral), “Present status and plans of GARIS, GARIS-II and GARIS-III,” SSRI-PNS Collaboration Meeting 2020, online,
September 3, 2020.

[Domestic Conferences/Workshops]
庭瀬暁隆 (口頭), P. Schury, 和田道治, P. Brionnet, S. Chen, 橋本尚志, 羽場宏光, 平山賀一, D. S. Hou, 飯村俊, 石山博恒, 石澤倫,
伊藤由太, 加治大哉, 木村創大, 小浦寛之, J. Liu, 宮武宇也, J. Y. Moon, 森田浩介, 森本幸司, 長江大輔, M. Rosenbusch, 高峰愛子,
渡辺裕, W. Xian, S. X. Yan, H. Wollnik, 「MRTOF + α-TOF による 257 Db の直接質量測定」, 日本放射化学会第 64 回討論会 (2020),
オンライン, 2020 年 9 月 9 日–11 日.
庭瀬暁隆 (口頭), 「MRTOF + α-TOF 検出器による（超）重核の精密質量と α 崩壊の相関測定」, 2020 重元素核化学ワークショッ
プ, オンライン, 2021 年 3 月 30 日.

Awards
庭瀬暁隆, 若手優秀発表賞, 日本放射化学会第 64 回討論会 (2020), 令和 2 年度 理研桜舞賞, 理化学研究所.

Others
石澤 倫, 「超重元素探索に用いられる TOF 検出器の検出率向上に関する研究」, 山形大学大学院理工学研究科博士学位論文 (2021).
Toshitaka Niwase, “First direct mass measurement of superheavy nuclide via MRTOF mass spectrograph equipped with an α-TOF detector,” Department of Physics, Kyushu University, Doctoral Thesis (2021).
内藤夏樹, 「後方準弾性散乱測定による 51 V + 248 Cm/208 Pb 系の融合障壁分布の 研究」, 九州大学大学院理学研究院修士論文 (2021).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Astro-Glaciology Research Group
1. Summary of Research Activities

Our Astro-Glaciology Research Group promotes both experimental and theoretical studies to open up the new interdisciplinary
research field of astro-glaciology, which combines astrophysics, astrochemistry, glaciology, and climate science.
On the experimental side, we measure isotopic and ionic concentrations in ice cores drilled at Dome Fuji station, Antarctica,
in collaboration with the National Institute of Polar Research (NIPR, Tokyo). Here, the ice cores are time capsules which preserve
atmospheric information of the past. In particular, the ice cores obtained around the Dome Fuji site are very unique, because they
contain much more information on the stratosphere than any other ice cores obtained from elsewhere on Earth. This means that
we have significant advantages in using Dome Fuji ice cores if we wish to study the Universe, since UV photons, gamma-rays, andhighenergy protons emitted by astronomical phenomena aﬀect the stratosphere. Our principal aim is thus to acquire and interpret
information preserved in ice cores regarding:• Signatures of past volcanic eruptions and solar cycles;• Relationships between climate change and volcanic activity, and climate change and solar activity as well;• Traces of past supernovae in our galaxy, in order to understand better the rate of galactic supernova explosions.

Moreover, we are promoting experimental projects on:• Development of an automated laser melting sampler for analyzing ice cores with high depth resolution;• Development of precise analytical techniques of high sensitivity for analyzing ice cores;• The evolution of molecules in space.
• The application of analytical methods for measuring isotopes in ice cores to archaeological artifacts;

On the theoretical side, we are simulating numerically:• Chemical eﬀects of giant solar flares and supernovae on the Earth’s atmosphere;• The explosive and the r-process nucleosynthesis in core-collapse supernovae.

Combining our experimental evidence and theoretical simulations, we are promoting the researches mentioned above. These all willcontribute to understanding relationships between the Universe and Earth. In particular, climate change is the most critical issue facing
the world in the 21st century. It is also emphasized that the frequency of supernova explosions in our galaxy has not yet been fully
understood, and it is the key to understand the r-process nucleosynthesis.

Members
Director
Yuko MOTIZUKI
Special Temporary Research Scientist
Kazuya TAKAHASHI
Senior Research Scientist
Yoichi NAKAI
Technical Staﬀ I
Yu Vin SAHOO
Senior Visiting Scientists
Yasushige YANO

Kunihiko KODERA

Visiting Scientists
Hideharu AKIYOSHI (Nat’l Inst. for Environmental Studies)
Hisashi HAYAKAWA (Nagoya Univ.)
Akira HORI (Kitami Inst. of Tech.)
Kazuho HORIUCHI (Hirosaki Univ.)

Yoshinori IIZUKA (Hokkaido Univ.)
Naoyuki KURITA (Nagoya Univ.)
Hideki MADOKORO (Mitsubushi Heavy Industries, Ltd.)
Hideaki MOTOYAMA (Nat’l Inst. of Polar Res.)

Visiting Technicians
Junya HIROSE (Fusion Tech. Co., Ltd.)

Yuma HASEBE (Denryoku Comp. Ctr., Ltd.)

AssistantKeiko SUZUKI
Part-time Workers- 245 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Satomi NEGISHI (Research Part-time Worker I)

Kanako FUJITA (Administrative Part-time Worker I)

List of Publications & Presentations
Publications[Original Papers]
S. Katsuda, H. Fujiwara, Y. Ishisaki, Y. Maeda, K. Mori, Y. Motizuki, K. Sato, M. S. Tashiro, and Y. Terada, “New measurement of
the vertical atmospheric density profile from occultations of the crab nebula with X-Ray astronomy satellites Suzaku and Hitomi,” J.
Geophys. Res. (Space Physics) 126, (4) e28886, doi:10.1029/2020JA028886 (2021).
E. Tsantini, T. Minami, M. A. C. Ontiveros, K. Takahashi, and J. C. Melgarejo, “Sulfur isotope analysis to examine the provenance of
cinnabar used in wall paintings in the Roman domus Avinyó (Barcelona),” Minerals 11, (1) 6 (2021).
K. Kitajima, Y. Nakai, W. M. C. Sameera, M. Tsuge, A. Miyazaki, H. Hidaka, A. Kouchi, and N. Watanabe, “Delivery of electrons byproton-hole transfer in ice at 10 K: Role of surface OH radicals,” J. Phys. Chem. Lett. 12, 704 (2021).
A. Miyazaki, N. Watanabe, W. M. C. Sameera, Y. Nakai, M. Tsuge, T. Hama, H. Hidaka, and A. Kouchi, “Photostimulated desorptionof OH radicals from amorphous solid water: Evidence for the interaction of visible light with an OH-ice complex,” Phys. Rev. A 102,052822 (2020).

[Books]
望月優子, 佐藤勝彦, 「シリーズ現代の天文学第 1 巻 人類の住む宇宙 第 2 版」
（第 2 刷観測進展にあわせ改訂）, pp. 99–144（「第 3章 元素の起源」）岡村定矩他編, 日本評論社, 2020 年 4 月.
望月優子, 佐藤勝彦, 「天文学辞典（インターネット版）」, 「r 過程」（部分執筆）, https://astro-dic.jp/r-process/, 日本天文学会, 2020 年 10 月.
望月優子, 佐藤勝彦, 「天文学辞典（インターネット版）」, 「s 過程」（部分執筆）, https://astro-dic.jp/s-process/, 日本天文学会, 2020 年 10 月.

[Proceedings]
南武志, 高橋和也, 「与呂木古墳から出土した頭蓋骨付着朱の硫黄同位体比分析」, 三木市文化研究資料第 35 集 「与呂木古墳・与呂木 12 号墳—与呂木青葉台団地造成に伴う発掘調査報告書」, 三木市教育委員会, 35–39 (2021).
高橋和也, 南武志, 藤田淳, 池田征弘,「硫黄同位体比分析による兵庫県の遺跡出土朱の産地推定」, 兵庫県立考古博物館 研究紀要 13,
53-–58 (2020).

Presentations[International Conferences/Workshops]
Y. Motizuki (e-poster), Y. Nakai, K. Takahashi, J. Hirose, Y. V. Sahoo, Y. Yano, M. Yumoto, M. Maruyama, M. Sakashita, K. Kase, andS. Wada, “A novel laser-melting ice-core sampler with high depth resolution and high throughput for discrete ice core analyses,” The11th International Symposium on Polar Science, Online event, November 16-–December 18, 2020.

[Domestic Conferences/Workshops]
中井陽一, 日高宏, 渡部直樹, 「低エネルギーイオンと低温氷表面との反応実験装置開発の現状 2」, 日本物理学会第 76 回年次大会,
オンライン発表, 2021 年 3 月 12–15 日.
北島謙生, 中井陽一, W. M. C. Sameera, 宮﨑彩音, 柘植雅士, 日髙宏, 香内晃, 渡部直樹, 「極低温アモルファス氷への紫外光・電子
線同時照射による負の氷透過電流生成」, 原子衝突学会第 45 回年会, オンライン発表, 2020 年 12 月 8–10 日.
高橋和也, 中井陽一, 本山秀明, 望月優子, 「高感度硫黄同位体比分析法を用いた南極ドームふじ基地氷床コアから得られた試料の分析」, 日本分析化学会第 69 回年会, オンライン開催, 2020 年 9 月 16–18 日.
菅澤佳世, 三宅芙沙, 多田悠馬, 堀内一穂, 大谷昴, 笹公和, 高橋努, 松村万寿美, 落合悠太, 高野健太, 望月優子, 高橋和也, 中井陽一,
本山秀明, 松崎浩之, 「約 100 年分のドームふじアイスコア中 10 Be と 36 Cl の高分解能測定による BC5480 年宇宙線イベントの調査」, 第 81 回応用物理学会秋季学術講演会, オンライン開催, 2020 年 9 月 8–11 日.

Press Releases
Kazuya Takahashi and Yuko Motizuki, “Sticky tape: A key ingredient for mapping artifact origins,” March 9, 2020. https://www.
riken.jp/en/news_pubs/research_news/pr/2019/20191126_2/- 246 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Nuclear Transmutation Data Research Group
1. Abstract

The nuclear waste problem is an inevitable subject in nuclear physics and nuclear engineering communities. Since the Chicago
Pile was established in 1942, nuclear energy has become one of major sources of energy. However, nowadays the nuclear waste
produced at nuclear power plants has caused social problems. Minor actinide components of the waste have been studied well as a fuelin fast breeder reactors or ADS. Long-lived fission products (LLFP) in waste, on the other hand, have not been studied extensively. A
deep geological disposal has been a policy of several governments, but it is diﬃcult to find out location of the disposal station in termsof security, sociology and politics. To solve the social problem, a scientific eﬀort is necessary for nuclear physics community to findout eﬃcient methods for reduction of nuclear waste radioactivity. In the world-wide situation above, our Group aims to obtain reaction
data of LLFP at RIBF and other muon facilities for muon capture data. These data are necessary to design an accelerator-based system
for transmutation, and also may lead to a new discovery and invention for peaceful use of nuclear power and the welfare of humanity.

2. Major Research Subjects

The Group is formed by three research teams. The first two Teams, “Fast RI Data Team” and “Slow RI Data Team,” are in
charge of proton- and deuteron-induced reaction data of LLFP in inverse kinematics at RIBF. The third Team “Muon Data Team” isto obtain muon capture data of LLFP at muon facilities. All of the teams are focusing to obtain high-quality data which are essentiallynecessary to establish reliable reaction models. Each team has its own subjects and promotes LLFP reaction programs based on theirlarge experiences, techniques and skills.

3. Summary of Research Activity

In 2014, all the teams polished up experimental strategies, formed collaboration and prepared experiments. Physics runs forspallation reaction were successfully organized at RIBF in 2015–2017. The muon program started at RCNP, Osaka University inspring 2016 and the data for Pd isotopes were successfully obtained in 2017–2019 via in-beam method with DC beams at RCNP, andvia activation method with pulsed beams at J-PARC and ISIS-RAL/RIKEN facilities.
The reaction data obtained with both fast and energy-degraded beams at RIBF encouraged the nuclear data group of JAEA, anda new database called “JENDLE/ImPACT-2018” has been released. The new database has been generated by a newly developed
reaction model “DEURACS” which treats deuteron-induced reactions. DEURACS reproduces very well cross section data, and muchbetter than other reaction models. A simulation code “PHITS” has been re-coordianted to use the database information.
In December 2018, the Team leader, Hideaki Otsu, was invited to join Technical Meeting of IAEA, entitled “Novel Multidisciplinary Applications with Unstable Ion Beams and Complementary Techniques.” Our activity has been demonstrated and recognizedinternationally. In November 2020, Hideaki Otsu organized a domestic conference entitled “RIKEN Sympoium on Nuclear Data
2020”.

MemberDirector
Hiroyoshi SAKURAI

List of Publications & Presentations
Presentations[Domestic Conferences/Workshops]
櫻井博儀（招待講演）,「仁科センターの核データ活動」, 理研シンポジウム「2020 年度核データ研究会」, 和光市, 2020 年 11 月
26–27 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Nuclear Transmutation Data Research Group
Fast RI Data Team
1. Abstract

Fast RI team aims at obtaining and accumulating the cross section data for long lived fission products (LLFPs) in order to explore
the possibility of using accelerator for nuclear transmutation.
LLFPs as nuclear waste have been generated continuously in nuclear power plants for wealth for human lives, while people
noticed the way of disposal has not necessarily been established, especially after the Fukushima Daiichi power plant disaster. One of
the ways to reduce the amount of LLFP or to recover them as recycled resources is nuclear transmutation technique.
RIBF facility has a property to generate such LLFP as a secondary beam and the beam species are identified by event by event.
Utilizing the property, absolute values of the cross section of various reactions on LLFPs are measured and accumulated as a database.

2. Major Research Subjects(1) Measurement of reaction products by the interaction of LLFPs with proton, deuteron, and photon to explore candidate reactions for the transmutation of LLFPs.
(2) Evaluation of the cross section data for the neutron induced reactions from the obtained data.

3. Summary of Research Activity
(1)
(2)
(3)
(4)

Acting as a collaboration hub on many groups which plan to take data using fast RI beams in RIBF facility.
Concentrating on taking data for proton and deuteron induced spallation reactions with inverse kinematics.
Accumulating the cross section data and evaluating them as evaluated nuclear data.
Evaluating cross section of neutron induced reaction on LLFP by collaborating with the nuclear model calculation and evaluation group.

Members
Team Leader
Hideaki OTSU (Concurrent: Team Leader, SAMURAI Team)
Visiting Scientist
Takashi TERANISHI (Kyushu Univ.)
Student Trainee
Koichi GOTO (Kyushu Univ.)

List of Publications & Presentations
Publications[Original Papers]
X. H. Sun, H. Wang, H. Otsu, H. Sakurai, et al., “Spallation and fragmentation cross sections for 168 MeV/nucleon 136 Xe ions on proton,
deuteron, and carbon targets,” Phys. Rev. C 101, 064623 (2020).

[Proceedings]
H. Wang, H. Otsu, H. Sakurai, et al., “Spallation reaction study for long-lived fission products in nuclear waste,” EPJ Web Conf. 239,
06003 (2020) (Proc. International Conference on Nuclear Data for Science and Technology (ND2019), Beijing, China, May 19–24,
2019).
K. Nakano, Y. Watanabe, S. Kawase, et al., “Isotope-production cross sections of residual nuclei in proton- and deuteron-induced reactions
on 93 Zr at 50 MeV/nucleon,” EPJ Web Conf. 239, 20006 (2020) (Proc. International Conference on Nuclear Data for Science andTechnology (ND2019), Beijing, China, May 19–24, 2019).
X. Sun, H. Wang, H. Otsu, H. Sakurai, et al., “Cross-section measurement in the reactions of 136 Xe on proton, deuteron and carbon” EPJ
Web Conf. 239, 01037 (2020) (Proc. International Conference on Nuclear Data for Science and Technology (ND2019), Beijing, China,
May 19–24, 2019).

Presentations[International Conferences/Workshops]
R. Matsumura, H. Otsu, H. Wang, N. Chiga, et al., “Nuclear transmutation of high-radiotoxic nuclide 90 Sr via proton- and deuteroninduced reactions in inverse kinematics,” A3F-CNS Summer School 2020, online, August 17–21, 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

松村理久, 大津秀暁, 王赫, 千賀信幸, 他 ImPACT-RIBF Collaboration, 「核分裂生成核種 90 Sr の陽子及び重陽子誘起反応に関する研究」, 日本物理学会第 75 回年次大会, 愛知県名古屋市 (名古屋大学現地開催中止), 2020 年 3 月 16–19 日.
松村理久, 大津秀暁, 王赫, 千賀信幸, 他 ImPACT-RIBF Collaboration, 「高放射性核種 90 Sr の陽子及び重陽子誘起反応による核変換に向けた研究」, Symposium on Nuclear Data 2020, 埼玉県和光市, 2020 年 11 月 26–27 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Nuclear Transmutation Data Research Group
Slow RI Data Team
1. Abstract

This team is in charge of the development of low-energy RI beams of long-lived fission fragments (LLFP) from the 238 U by meansof degrading the energy of beams produced by the BigRIPS fragment separator.

2. Major Research Subjects

Studies of the slowing down and purification of RI beams are the main subjects of the team. Developments of devices used forthe slowing down of RI beams are also an important subject.
(1) Study and development of the slowed-down methods for LLFP.
(2) Development of the devices used for the slowing down.
(3) Operation of the BigRIPS separator and supply the low energy LLFP beam to the experiment in which the cross sections of
LLFP are measured at the low energy.
(4) Development of the framework to seamlessly handle device, detector, DAQ, and analysis for the easy control of the complicate
slowed-down RI beam production and its development.

3. Summary of Research Activity

A new OEDO beam line, designed for the slowed-down RI beams, was constructed under the collaboration with CNS, the University of Tokyo. Our group was responsible for the construction of the infrastructure such as the cooling water and the electricalequipment, and the movement and alignment of existing vacuum chambers, quadrupole magnets. The power supply for the Superconducting Triplet Quadrupoles (STQ) was made, which had a stability also under the low current condition.
Slowed-down 93 Zr beams with 20 or 50 MeV/nucleon were successfully developed at June 2016 for the first time. The methods
to obtain the narrow energy, position, and angle distribution were developed. The methods of the energy adjustment and the particle
identification at 50 MeV/nucleon were developed. The 93 Zr and 107 Pd beams with 50 MeV/nucleon were produced for the nucleartransmutation experiments using proton or deuteron targets at October 2016. The commissioning experiment of the OEDO beamline was successfully performed at June 2017. The first transmutation experiments using OEDO beam line were performed with 93 Zr,
107
Pd, and 79 Se around 20 MeV/nucleon.
With our developments, the slowed-down RI beams became ready for the transmutation experiments. On the other hand, theprocedure to make the slowed-down RI beams became highly specialized. In order to easily produce the slowed-down RI beam, theframework is under the development to seamlessly handle the device, detector, DAQ, and analysis. The procedure of the RI-beamenergy control was implemented in the web application.

Members
Team Leader
Toshiyuki SUMIKAMA
Student Trainees
SungHan BAE (Seoul Nat’l Univ.)
Hiroya FUKUDA (Kyushu Univ.)

Misaki SAITSU (Kyushu Univ.)

List of Publications & Presentations
Publications[Original Papers]
T. Sumikama, D. S. Ahn, N. Fukuda, Y. Shimizu, H. Suzuki, H. Takeda, H. Wang, K. Yoshida, J. Amano, N. Chiga, K. Chikaato,
A. Hirayama, N. Inabe, S. Kawase, S. Kubono, M. Matsushita, S. Michimasa, K. Nakano, H. Otsu, and H. Sakurai, “Energy-control
and novel particle-identification methods combined with range in a multi-sampling ionization chamber for experiments using sloweddown RI beams,” Nucl. Instrum. Methods Phys. Res. A 986, 164687 (2021).
K. Nakano, Y. Watanabe, S. Kawase, H. Wang, H. Otsu, H. Sakurai, N. Chiga, J. Suwa, T. Sumikama, S. Takeuchi, T. Nakamura,
K. Chikaato, M. Takechi, S. Koyama, D. S. Ahn, H. Baba, S. Chen, M. L. Cortes, P. Doornenbal, N. Fukuda, A. Hirayama, R. Hosoda,
T. Isobe, S. Kawakami, Y. Kondo, S. Kubono, Y. Maeda, S. Masuoka, S. Michimasa, I. Murray, R. Nakajima, M. Niikura, T. Ozaki,
A. Saito, T. Saito, H. Sato, Y. Shimizu, S. Shimoura, Y. Soudo, P. -A. Söderström, X. Sun, D. Suzuki, H. Suzuki, H. Takeda, Y. Togano,
T. Tomai, H. Yamada, M. Yasuda, and K. Yoshida, “Isotope-production cross sections of residual nuclei in proton- and deuteron-induced
reactions on 93 Zr at 50 MeV/nucleon,” EPJ Web Conf. 239, 20006 (2020).
H. Wang, H. Otsu, H. Sakurai, D. S. Ahn, M. Aikawa, T. Ando, S. Araki, S. Chen, N. Chiga, P. Doornenbal, N. Fukuda, T. Isobe,
S. Kawakami, S. Kawase, T. Kin, Y. Kondo, S. Koyama, S. Kubono, Y. Maeda, A. Makinaga, M. Matsushita, T. Matsuzaki, S. Michimasa, S. Momiyama, S. Nagamine, T. Nakamura, K. Nakano, M. Niikura, T. Ozaki, A. Saito, T. Saito, Y. Shiga, M. Shikata, Y. Shimizu,- 250 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

S. Shimoura, T. Sumikama, P. -A. Söderstrom, H. Suzuki, H. Takeda, S. Takeuchi, R. Taniuchi, Y. Togano, J. Tsubota, M. Uesaka,
Y. Watanabe, Y. Watanabe, K. Wimmer, T. Yamamoto, and K. Yoshida, “Spallation reaction study for long-lived fission products innuclear waste,” EPJ Web Conf. 239, 06003 (2020).
J. Ha, T. Sumikama, F. Browne, N. Hinohara, A. M. Bruce, S. Choi, I. Nishizuka, S. Nishimura, P. Doornenbal, G. Lorusso,
P. -A. Söderström, H. Watanabe, R. Daido, Z. Patel, S. Rice, L. Sinclair, J. Wu, Z. Y. Xu, A. Yagi, H. Baba, N. Chiga, R. Carroll,F. Didierjean, Y. Fang, N. Fukuda, G. Gey, E. Ideguchi, N. Inabe, T. Isobe, D. Kameda, I. Kojouharov, N. Kurz, T. Kubo, S. Lalkovski,
Z. Li, R. Lozeva, H. Nishibata, A. Odahara, Zs. Podolyák, P. H. Regan, O. J. Roberts, H. Sakurai, H. Schaﬀner, G. S. Simpson,
H. Suzuki, H. Takeda, M. Tanaka, J. Taprogge, V. Werner, and O. Wieland, “Shape evolution of neutron-rich 106, 108, 110 Mo isotopes inthe triaxial degree of freedom,” Phys. Rev. C 101, 044311 (2020).
T. Sumikama, N. Fukuda, N. Inabe, D. Kameda, T. Kubo, Y. Shimizu, H. Suzuki, H. Takeda, K. Yoshida, H. Baba, F. Browne, A. M. Bruce,
R. Carroll, N. Chiga, R. Daido, F. Didierjean, P. Doornenba, Y. Fang, G. Gey, E. Ideguchi, T. Isobe, S. Lalkovski, Z. Li, G. Lorusso,
R. Lozeva, H. Nishibata, S. Nishimura, I. Nishizuka, A. Odahara, Z. Patel, Zs. Podolyák, P. H. Regan, S. Rice, O. J. Roberts, H. Sakurai,
G. S. Simpson, L. Sinclair, P. -A. Söderström, M. Tanaka, J. Taprogge, H. Watanabe, V. Werner, O. Wieland, J. Wu, Z. Y. Xu, andA. Yagi, “Observation of new neutron-rich isotopes in the vicinity of 110 Zr,” Phys. Rev. C 103, 014614 (2021).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
Nuclear Transmutation Data Research Group
Muon Data Team
1. Abstract

Dr. Yoshio Nishina observed muons in cosmic rays in 1937. The muon is an elementary particle similar to electron and classified
to lepton group. The muon has positive or negative electric charge, and the lifetime is 2.2 µsec. The negative muon (µ− ) is 207 times
heavier than the electron and behaves as a “heavy electron” in materials. The negative muon is captured by atomic orbits of nuclei
to form a muonic atom and cascades down to the 1 s orbit to make muon nuclear capture. The muon is combined with a proton in
the nucleus to convert to a neutron and a neutrino. The muon nuclear capture reaction on a nucleus (ZA N) with the atomic number Z
A−xN(x = 0, 1, 2, 3, 4) by emitting some neutrons in the reaction. The phenomenon isand mass number A generates the isotopes of Z−1
A−x
N reactions (x = 0, 1, 2, 3, 4) is one of importantcalled “muon nuclear transmutation.” The reaction branching ratio of ZA N(µ− , xnν)Z−1
factors toward various applications with nuclear transmutation technique. From a viewpoint of the nuclear physic, the muon nuclear
capture reaction is very unique and interesting. A high-energy compound nuclear state is suddenly generated in the nuclei associatedwith a weak conversion process of proton to neutron and neutrino. Many experimental results have been so far reported, however, thereaction mechanism itself is not well clarified. The research team aims at obtaining the experimental data to investigate the reaction
mechanism of muon nuclear capture, and also at theoretical understanding on the nuclear capture reaction.

2. Major Research Subjects(1) Experimental clarification on the mechanism of nuclear muon capture reaction(2) Theoretical understanding on the nuclear muon capture reaction(3) Interdisciplinary applications with the nuclear transmutation technique

3. Summary of Research Activity

There are two experimental methods to study the muon nuclear capture reaction. The first one is “muon in-beam spectroscopy
A−x
N nuclei are prompt events and are observed by the “muonmethod.” The neutron and γ-ray emissions from the excited states of Z−1
in-beam spectroscopy method” with a DC muon beam. The reaction branching ratio is directly determined by measuring the neutron
multiplicity in the reaction. The DC muon beam is available at the MuSIC (Muon Science Innovative Channel) muon facility in the
Research Center for Nuclear Physics (RCNP) at Osaka University. The second one is “muon activation method” with the pulsed
A−x
N make β+/− decays. The γ-rays associated with β+/− decays to the daughter nuclei aremuon beam. The produced unstable nuclei Z−1
observed in the experiment. The build-up curve of γ-ray yield at muon beam-on and the decay curve at beam-oﬀ are measured. Since
A−x
N nuclei are determined
the half-lives and decay branching ratios of β+/− -γ decays are known, the reaction branching ratios to the Z−1
by the γ-ray yield curves. The pulsed muon beam is available at the RIKEN-RAL Muon Facility in the UK and J-PARC muon facility.
Muon nuclear capture reactions are studied on five isotope-enriched palladium targets (104, 105, 106, 108, 110 Pd) and five isotopeenriched zirconium targets (90, 91, 92, 94, 96 Zr) employing two experimental methods. By obtaining the experimental data on the Pd and Zr
targets, the reaction mechanism is investigated experimentally, and the results are compared with appropriate theoretical calculations.
The 107 Pd is classified to a long-lived fission product (LLFP) and is contained in a spent nuclear fuel. The study of muon nuclear
capture on the Pd and Zr targets is aiming at exploring a possible reaction path to make the nuclear transmutation of the Pd and Zr
metal extracted from the spent nuclear fuel without an isotope separation process. This research was funded by the ImPACT Programof Council for Science, Technology and Innovation (Cabinet Oﬃce, Government of Japan).
(1) Experiments with “muon in-beam spectroscopy method”
Muon nuclear capture reactions were investigated on five palladium targets (104, 105, 106, 108, 110 Pd) by employing the DC muon
beam at MuSIC. The γ-ray and neutron in the muon nuclear capture reaction were measured with the time information relative toA−x
Rh reactions, wheremuon beam arrival. The measured neutron multiplicity gives the reaction branching ratio of 46A Pd(µ− , xnν)45
A = 104, 105, 106, 108, 110 and x = 0, 1, 2, 3, 4.
Employing a newly built neutron spectrometer, the neutron was measured to obtain the reaction branching ratios of muon capture
reactions on the Pd targets. We have constructed a neutron spectrometer named “Seamine”: Scintillator Enclosure Array for Muon
Induced Neutron Emission. The spectrometer consists of 21 liquid scintillation counters, 2 Ge γ-ray detectors, 7 BaF2 counters. The
Pd target, muon beam counters and muon degraders are placed at the center of spectrometer. The neutron counter is a BC-501A
liquid scintillation counter with 20 cm diameter and 5 cm depth and is connected to a 5” photo multiplication tube (H4144-01). The
total neuron detection eﬃciency is estimated 5%, where the distance is 4 cm from the target to neutron counters. The Ge γ-ray
detectors are placed at 10 cm form the target, and the typical detection eﬃciency is 0.5% for 200 keV γ-ray. The BaF2 counters arelocated beneath the target to detect fast γ-rays emitted from the compound nucleus formed in the reactions. Signals from the liquid
scintillation counters are processed in a CAEN V1730B waveform digitizer (16 channel, 14 bit, 500 M samplings/sec.). The neuron-γ
discrimination is performed on-line during the experiment, and the detailed data analysis is conducted oﬀ-line after the experiment.
The neutron energy spectrum is constructed in the digitizer. Signals from Ge detectors are also processed in the digitizer to obtain theenergy and time spectrum of γ-rays associated with the reaction. Signals from the BaF2 counters and muon beam counters are sent to
the digitizer to make the fast timing signals.
We have established the muon in-beam spectroscopy method employing the “Seamine” spectrometer. The neutron data analysis- 252 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

is in progress to obtain the multiplicity, the energy and the TOF spectrum using start signals given by γ-rays detected in the BaF2
counters. The γ-ray data gives the energy spectrum of prompt γ-rays and muonic X-rays originated from the 104, 105, 106, 108, 110 Pdtargets.
(2) Experiments with “muon activation method” at the RIKEN-RAL Muon Facility
We conducted the experiments on the muon nuclear capture employing the muon activation method at the RIKEN-RAL Muon
Facility in the UK. The pulsed muon beam was irradiated on the 104, 105, 106, 108, 110 Pd targets. The γ-rays were detected by a Ge detector
located at the downstream of the Pd targets to maximize the detection eﬃciency. The build-up and decay curves of γ-ray intensities
were measured associated with β+/− decays of produced unstable nuclei to daughter nuclei. The γ-ray-yield curves give the absolute
A−x
Rh reactions. The
radiation activity produced by the reaction, and the reaction branching ratios are determined for 46A Pd(µ− , xnν)45
decay curves of γ-rays from the produced nuclei with long half-lives were measured under low γ-ray background at an experimental
apparatus built in a separated room. The detailed oﬀ-line data analysis is in progress.
(3) Experiments with “muon activation method” at J-PARC muon facility
The experiments employing the muon activation method were performed at J-PARC muon facility. The five isotope-enriched Pdtargets (104, 105, 106, 108, 110 Pd) were irradiated by the pulsed muon beam, and the build-up and decay curves of γ-ray intensities were
measured.
In addition to the Pd targets, the experiments on five isotope-enriched Zr target (90, 91, 92, 94, 96 Zr) were conducted to obtain theA−x
Y reactions, where A = 90, 91, 92, 94, 96. The obtained reaction branching ratios on thereaction branching ratios of 40A Zr(µ− , xnν)39
Pd and Zr targets are important to understand the reaction mechanism of muon nuclear capture. The 93 Zr is one of the LLFP and iscontained in a spent nuclear fuel. The experiment on the Zr targets is to explore a possibility to realize the nuclear transmutation of
the Zr metal extracted from the spent nuclear fuel.
−107−x
Rh reactions, the muon activation experiment was performed
In order to obtain the reaction branching ratio of 107
46 Pd(µ , xnν)45
107
employing a Pd target containing Pd of 15.3%. The γ-ray intensities associated with β+/− decays of produced unstable nuclei were
measured to obtain the build-up and decay curves. Once the branching ratios of the reactions on the 104, 105, 106, 108, 110 Pd targets are
obtained, these contributions are extracted from the branching-ratio data obtained for the Pd target with 107 Pd. The reaction branching−107−x
Rh reactions is finally determined. The detailed oﬀ-line data analysis is in progress.
ratio of 107
46 Pd(µ , xnν)45(4) Comparison with theory
The muon activation method gives the reaction branching ratios. The muon in-beam spectroscopy method gives the neutron
multiplicity and the neutron energy spectrum. These experimental results are important to understand the compound nuclear state andneutron emission mechanism. The reaction branching ratios obtained by the muon activation method are compared with the results ofneutron multiplicity measurements. The neutron energy spectrum is considered to be reflected by the energy distribution of compound
nuclear state and neutron emission mechanism. The experimental results are compared with the appropriate calculations employing theneutron emission mechanisms due to an evaporation, a cascade and a direct emission processes with assuming the energy distribution
at compound nuclear state.

Members
Team Leader
Hiroyoshi SAKURAI
Contract Researcher
Teiichiro MATSUZAKI
Part-time Worker
Takeshi SAITO (Research Part-time Worker I)

List of Publications & Presentations
Presentations[Domestic Conferences/Workshops]
齋藤岳志（招待講演）, 「ミューオン原子 X 線分光による原子核の荷電分布・荷電半径測定」, ELPH 研究会 C028「電子散乱による原子核研究—原子核の電荷密度・陽子・中性子の分布と半径—」, オンライン, 2021 年 3 月 18–19 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
High-Intensity Accelerator R&D Group
1. Abstract

The High-Intensity Accelerator R&D group, consisting of two teams, develops elemental technology of high-power acceleratorsand high-power targets, aiming at future applications to nuclear transmutations of long-lived fission product into short-lived nuclides.
The research subjects are superconducting rf cavities for low-velocity ions, design of high-power accelerators, high-power target
systems and related technologies.
Nuclear transmutation with high-intensity accelerators is expected to reduce the high-level radioactive wastes and to recycle
the precious resources such as rare-earth materials in future. This method is one of the important applications of the ion-accelerator
technologies that have been developed at RIKEN for a long time. Under the framework of ImPACT Fujita Program, we have conducted
R&D of elemental technology related to the high-power accelerators and high-power targets, from FY2014 to FY2018. We gained alot of experiences in these R&Ds. Among them, the development of a superconducting rf cavity has become the basis of the upgrade
program of the RILAC facility which started in 2016.

2. Major Research Subjects(1) R&D of elemental technology of high-power accelerators and high-power targets.

3. Summary of Research Activity(1) A high-gradient rf cavity has been constructed and tested based on the superconducting rf technology.
(2) Several candidates for the high-power target have been proposed and their prototypes have been tested.
(3) A high-current deuteron RFQ has been designed.

Members
Director
Osamu KAMIGAITO (concurrent: Group Director, Accelerator Group)- 254 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
High-Intensity Accelerator R&D Group
High-Gradient Cavity R&D Team
1. Abstract

We develop new components for accelerators dedicated for low-beta-ions with very high intensity. Specifically, we are designingand constructing a cryomodule for superconducting linac eﬃcient for acceleration of low-beta-ions. In parallel, we try to optimize an
rf acceleration system by making computer simulations for acceleration of very high intensity beams.

2. Major Research Subjects(1) Development of high-gradient cavites for low beta ions
(2) Development of power saving cryomodules

3. Summary of Research Activity• Development of highly eﬃcient superconducting accelerator modules

Members
Team Leader
Naruhiko SAKAMOTO
Research/Technical Scientists
Kazunari YAMADA
Yutaka WATANABE

Kazutaka OZEKI

Research & Development Scientist
Kenji SUDA

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Nuclear Science and Transmutation Research Division
High-Intensity Accelerator R&D Group
High-Power Target R&D Team
1. Abstract

The subjects of this team cover R&D studies with respect to target technology for the transmutation of the LLFPs.

2. Major Research Subjects(1) Liquid lithium target for production of neutron or muon
(2) Beam window without solid structure

3. Summary of Research Activity(1) Liquid lithium target for production of neutron or muon (H. Okuno)(2) Beam window with solid structure (H. Okuno)

Members
Team Leader
Hiroki OKUNO
Special Postdoctoral Researcher
Yasuto MIYAKE- 256 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator Group
1. Abstract

The Accelerator Group, consisting of seven teams, pursues various upgrade programs on the world-leading heavy-ion accelerator
facility, RI Beam Factory (RIBF), to enhance the accelerator performance and operation eﬃciency. The programs include the R&D of
superconducting ECR ion source, charge stripping systems, beam diagnostic devices, radio-frequency systems, control systems, andbeam simulation studies. We are also maintaining the large infrastructure to realize eﬀective operation of the RIBF. Moreover, we are
actively promoting the applications of the facility to various research fields.
Our primary mission is to supply intense, stable heavy-ion beams for the users through eﬀective operation, maintenance, andupgrade of the RIBF accelerators and related infrastructure. The director members govern the development programs that are not dealt
with by a single team, such as intensity upgrade and eﬀective operation. We also discuss the future plans of RIBF along with otherlaboratories belonging to the RIBF research division.
Various improvements and developments have been carried out for the RIBF accelerators in order to upgrade the beam intensities
and stability. Owing to the eﬀorts, for example, we succeeded in accelerating the uranium beam of 117 pnA through SRC in October
2020. This surpassed the long-standing target of 100 pnA, and also means that one of goals of the current mid-term plan of RNC has
been achieved. The beam intensity of 70 Zn increased to 788 pnA in December 2020, corresponding to the beam power of 19.0 kW.
On the other hand, at the new RILAC facility, which was commissioned at the end of FY2019 with the superconducting booster
linac (SRILAC), a superheavy element synthesis experiment was started after the closure of RIKEN due to COVID-19. Despite aproblem in one of the superconducting cavities, a high-intensity vanadium beam is being supplied to the users. Construction of a newbeam line for the R&D of mass production method of 211 At has been also started at the RILAC facility.
An upgrade plan of RIBF for further increasing uranium beam has been continuously discussed. The plan is based on the idea of“charge-stripper ring (CSR),” which is used to improve the overall stripping eﬃciency of the uranium beam. This device recirculates
and re-injects the uranium ions into the charge stripper until the ions have the charge state required for the succeeding acceleration,
while the bunch structure is kept with its isometric orbit lengths for all the charge states. We are planning to install two CSRs in the
RIBF accelerator chain and the ultimate goal of the uranium beam intensity is 2,000 pnA at the exit of SRC. Initial design study of thefirst CSR (CSR1) has been almost completed. A pair of quadrupole magnets, that will be used in CSR1, is under fabrication, in orderto study the magnetic field in and around the magnets.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Intensity upgrade of RIBF accelerators (Okuno)
Eﬀective and stable operation of RIBF accelerators (Fukunishi)
Stable operation of the upgraded RILAC facility
Promotion of the future plan

3. Summary of Research Activity(1) The maximum intensity of the uranium beam reached 117 pnA at 345 MeV/nucleon, which corresponds to the beam powerof 9.6 kW.
(2) The maximum intensity of zinc beam reached 788 pnA, corresponding to 19.0 kW.
(3) The overall beam availability for the RIBF experiments was 90% in 2020.
(4) The new RILAC facility, which was commissioned at the end of FY2019 with the superconducting booster linac (SRILAC),
started supplying high-intensity vanadium beam for a superheavy element synthesis experiment.
(5) The large infrastructure was properly maintained based on a well-organized cooperation among the related sections in RIKEN.
(6) An intensity-upgrade plan of the RIBF has been further investigated. Elemental R&D of the first charge-stripper ring (CSR1)
is under progress.

Members
Director
Osamu KAMIGAITO
Deputy Directors
Hiroki OKUNO (for intensity upgrade)

Nobuhisa FUKUNISHI (for stable and eﬃcient operation)

Junior Research Associate
Kaori NAKAMURA- 257 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Part-time Worker I
Akira GOTO

Masayuki KASE

Research Consultants
Tadashi FUJINAWA

Toshiyuki HATTORI (Tokyo Tech)

Visiting Scientists
Eiji KAKO (KEK)
Hirotaka NAKAI (KEK)
Kensei UMEMORI (KEK)
Hiroshi SAKAI (KEK)

Taro KONOMI (KEK)
Noboru SASAO (Okayama Univ.)
Yasutaka IMAI (Okayama Univ.)

Assistant
Karen SAKUMA
Administrative Part-time Worker II
Ryoko UMEZAKI

List of Publications & Presentations
Publications[Original Papers]
O. Kamigaito, “Circuit-model formulas for external-Q factor of resonant cavities with capacitive and inductive coupling,”
arXiv:2005.05843 (2020).

Presentations[International Conferences/Workshops]
O. Kamigaito (invited), “Commissioning of superconducting linac booster for heavy-ion linac at RIKEN,” 30th Linear Accelerator Conference (LINAC20), Liverpool, United Kingdom (ONLINE), September 1–4, 2020.

Outreach Activities“First beam acceleration test successfully performed at SRILAC,” RIKEN NEWS No. 470 (8) 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator Group
Accelerator R&D Team
1. Abstract

We are developing the key hardware in upgrading the RIBF accelerator complex. Our primary focus and research is charge
stripper which plays an essential role in the RIBF accelerator complex. Charge strippers remove many electrons in ions and realizeeﬃcient acceleration of heavy ions by greatly enhancing charge state. The intensity of uranium beams is limited by the lifetime of the
carbon foil stripper conventionally installed in the acceleration chain. The improvement of stripper lifetimes is essential to increase
beam power towards the final goal of RIBF in the future. We are developing the low-Z gas stripper. In general gas stripper is free fromthe lifetime related problems but gives low equilibrium charge state because of the lack of density eﬀect. Low-Z gas stripper, however,can give as high equilibrium charge state as that in carbon foil because of the suppression of the electron capture process. Another our
focus is the upgrade of the world’s first superconducting ring cyclotron.

2. Major Research Subjects(1) Development of charge strippers for high power beams (highly oriented graphite film, low-Z gas)
(2) Upgrade of the superconducting ring cyclotron(3) Maintenance and R&D of the electrostatic deflection/inflection channels for the beam extraction/injection

3. Summary of Research Activity(1) Development of charge strippers for high power beams (foil, low-Z gas)
(H. Hasebe, H. Imao, H. Okuno)
We are developing the charge strippers for high intensity heavy ion beams. We are focusing on the developments on highlyoriented carbon graphite films and gas strippers including He gas stripper.
(2) Upgrade of the superconducting ring cyclotron(J. Ohnishi, H. Okuno)
We are focusing on the upgrade of the superconducting ring cyclotron.
(3) Maintenance and R&D of the electrostatic deflection/inflection channels for the beam extraction/injection(J. Ohnishi, H. Okuno)
We are developing high-performance electrostatic channels for high power beam injection and extraction.

Members
Team Leader
Hiroki OKUNO
Research/Technical Scientists
Hiroshi IMAO (Senior Research Scientist)

Hiroo HASEBE (Technical Scientist)

Special Temporary Technical Scientist
Jun-ichi OHNISHI
Visiting Scientists
Andreas ADELMANN (Paul Sherrer Inst.)

HAYASHIZAKI (Tokyo Tech)

Part-time Worker
Yoshiki SHIKUMA (Research Part-time Worker II)

List of Publications & Presentations
Publications[Original Papers]
H. Imao, “Charge stripper ring for RIKEN RI beam factory,” J. Instrum. 15, P12036 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator GroupIon Source Team
1. Abstract

Our aim is to operate and develop the ECR ion sources for the accelerator-complex system of the RI Beam Factory. We focus on
further upgrading the performance of the RI Beam Factory through the design and fabrication of a superconducting ECR ion sourcefor production of high-intensity heavy ions.

2. Major Research Subjects(1) Operation and development of the ECR ion sources(2) Development of a superconducting ECR heavy-ion source for production of high-intensity heavy ion beams

3. Summary of Research Activity(1) Operation and development of ECR ion sources(T. Nakagawa, M. Kidera, Y. Higurashi, T. Nagatomo, Y. Kanai, and H. Haba)
We routinely produce and supply various kinds of heavy ions such as zinc and calcium ions for the super-heavy element searchexperiment as well as uranium ions for RIBF experiments. We also perform R&D’s to meet the requirements for stable supply ofhigh-intensity heavy ion beams.
(2) Development of a superconducting ECR ion source for use in production of a high-intensity heavy ion beam
(T. Nakagawa, J. Ohnishi, M. Kidera, Y. Higurashi, and T. Nagatomo)
The RIBF is required to supply heavy ion beams with very high intensity so as to produce RI’s and for super-heavy element searchexperiment. We have designed and are fabricating an ECR ion source with high magnetic field and high microwave- frequency, since
the existing ECR ion sources have their limits in beam intensity. The coils of this ion source are designed to be superconducting for the
production of high magnetic field. We are also designing the low-energy beam transport line of the superconducting ECR ion source.

Members
Team Leader
Takahide NAKAGAWA
Research/Technical Scientists
Takashi NAGATOMO (Senior Technical Scientist)

Yoshihide HIGURASHI (Technical Scientist)

Special Temporary Research Scientist
Yasuyuki KANAI

List of Publications & Presentations
Presentations[International Conferences/Workshops]
T. Nagatomo (poster), “High intense vanadium-beam production to search for new super-heavy element with Z = 119,” 24th International
Workshop on ECR Ion Sources (ECRIS2020), East Lansing, USA, September 28–30, 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator GroupRILAC Team
1. Abstract

The operation and maintenance of the RIKEN Heavy-ion Linac (RILAC) have been carried out. There are two operation modes:
one is the stand-alone mode operation and the other is the injection mode operation. The RILAC has been used especially as an
injector for the RIKEN RI- Beam Factory accelerator complex. The RILAC is composed of the 28 GHz SC ECR ion source, thefrequency-variable RFQ linac, the frequency-variable main linac, and the SC booster linac (SRILAC).

2. Major Research Subjects(1) The long-term high stability of the RILAC operation.
(2) Improvement of high eﬃciency of the RILAC operation.

3. Summary of Research Activity

The RILAC was started to supply ion beams for experiments in 1981. Thousands hours are spent in a year for delivering manykinds of heavy-ion beams to various experiments.
The RILAC has two operation modes: one is the stand-alone mode operation delivering low-energy beams directly to experiments
and the other is the injection mode operation injecting beams into the RRC. In the first mode, the RILAC supplies a very important
beam to the nuclear physics experiment of “the research of super heavy elements.” In the second mode, the RILAC plays a very
important role as upstream end of the RIBF accelerator complex.
The maintenance of these devices is extremely important in order to keep the log-term high stability and high eﬃciency of the
RILAC beams. Therefore, improvements are always carried out for the purpose of more stable and more eﬃcient operation.

Members
Team Leader
Eiji IKEZAWA
Research/Technical Scientist
Yutaka WATANABE (Senior Technical Scientist)

List of Publications & Presentations
Publications[Proceedings]
K. Oyamada, E. Ikezawa, T. Ohki, H. Yamauchi, M. Tamura, A. Yusa, K. Kaneko, H. Imao, A. Uchiyama, K. Ozeki, T. Nishi,
N. Sakamoto, K. Suda, T. Nagatomo, M. Fujimaki, K. Yamada, T. Watanabe, Y. Watanabe, and O. Kamigaito, “Present status of
RILAC,” Proceedings of the 17th Annual Meeting of Particle Accelerator Society of Japan, PASJ2020 FRSP06.

Presentations[Domestic Conferences/Workshops]
小山田和幸, 池沢英二, 大木智則, 山内啓資, 田村匡史, 遊佐陽, 金子健太, 今尾浩士, 内山暁仁, 大関和貴, 西隆博, 坂本成彦, 須田健嗣,
長友傑, 藤巻正樹, 山田一成, 渡邉環, 渡邉裕, 上垣外修一「理研重イオンリニアックの現状報告」, 第 17 回日本加速器学会年会,
PASJ2020 FRSP06.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator Group
Cyclotron Team
1. Abstract

Together with other teams of Nishina Center accelerator division, maintaining and improving the RIBF cyclotron complex. The
accelerator provides high intensity heavy ions. Our mission is to have stable operation of cyclotrons for high power beam operation.
Recently stabilization of the rf system is a key issue to provide 10 kW heavy ion beam.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

RF technology for Cyclotrons
Operation of RIBF cyclotron complex
Maintenance and improvement of RIBF cyclotrons
Single turn operation for polarized deuteron beams
Development of superconducting linac

3. Summary of Research Activity• Development of the rf system for a reliable operation• Development of highly stabilized low level rf system• Development of superconducting linac• Development of the intermediate-energy polarized deuteron beams.

Members
Team Leader
Naruhiko SAKAMOTO
Research/Technical Scientists
Kazutaka OZEKI (Senior Technical Scientist)

Kenji SUDA (Technical Scientist)

List of Publications & Presentations
Publications[Proceedings]
西隆博, 内山暁仁, 上垣外修一, 坂本成彦, 長友傑, 福西暢尚, 藤巻正樹, 渡邉環, 渡邉裕, 「理研超伝導線形加速器ビームラインのためのエミッタンス測定及び光学系調整」Proc. PASJ2020, online meeting, THOO08, 116–119 (2020).
N. Sakamoto, M. Fujimaki, E. Ikezawa, H. Imao, O. Kamigaito, T. Nagatomo, T. Nishi, K. Ozeki, K. Suda, A. Uchiyama, T. Watanabe,
Y. Watanabe, and K. Yamada, “Commissioning of superconducting-linac booster for RIKEN heavy-ion linac,” Proc. PASJ2020, online
meeting, FRPP05, 679–683 (2020).

Presentations[International Conferences/Workshops]
K. Suda, O. Kamigaito, K. Ozeki, N. Sakamoto, K. Yamada, E. Kako, H. Nakai, K. Umemori, H. Hara, A. Miyamoto, K. Sennyyu,
and T. Yanagaisawa, ““Compact tuner designed to minimize the intervals of QWRs for RIKEN heavy-ion linac,” Tesla Technology
Collaboration Meeting 2020 (TTC 2020), Geneva (CERN), Switzerland, February 4–7, 2020.
K. Yamada, “Cryomodule design, assembly and installation utilizing “KOACH” system,” Tesla Technology Collaboration Meeting 2020
(TTC 2020), Geneva (CERN), Switzerland, February 4–7, 2020.
N. Sakamoto, K. Yamada, K. Suda, K. Ozeki, O. Kamigaito, Y. Watanabe, H. Imao, T. Nagatomo, E. Ikezawa, K. Kumagai, S. Dantsuka,
E. Kako, H. Nakai, and K. Umemori, “Commissioning and operation of RIKEN heavy ion superconducting linac,” Tesla Technology
Collaboration Meeting 2021 (TTC 2021), online (Hosted by DESY), January 19–21, 2021.
K. Ozeki, “Power coupler issues in CM operation from RIKEN,” Tesla Technology Collaboration Meeting 2021 (TTC 2021), online(Hosted by DESY), January 19–21, 2021.

[Domestic Conferences/Workshops]
西隆博, 内山暁仁, 上垣外修一, 坂本成彦, 長友傑, 福西暢尚, 藤巻正樹, 渡邉環, 渡邉裕, 「理研超伝導線形加速器ビームラインのためのエミッタンス測定及び光学系調整」(THOO08), 第 17 回日本加速器学会年会, オンライン開催, 2020 年 9 月 2–4 日.

Others
坂本成彦, 「理研 RIBF における低速重イオン用超伝導線形加速器の開発」, 「加速器」17, 70–80 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator GroupBeam Dynamics & Diagnostics Team
1. Abstract

Aiming at stable and eﬃcient operation of the RIBF cascaded cyclotron system, Beam Dynamics and Diagnostics Team developes
power supplies, beam instrumentation, computer control and beam dynamic studies. We have successfully increased the beam availability for user experiments to more than 90%. We have also established small-beam-loss operations. The latter strongly contributes
to recent high-power operations at RIBF.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

More eﬃcient and stable operations of the RIBF cascaded cyclotron system
Maintenance and developments of the beam instrumentation
Developments of computer control system for more intelligent and eﬃcient operations
Maintenance and improvements of the magnet power supplies for more stable operations
Upgrade of the existing beam interlock system for high-power beams with few tens of kW

3. Summary of Research Activity(1) High-intensity heavy-ion beams such as 117-pnA uranium, 173-pnA xenon, 486-pnA krypton, 788-pnA Zinc and 740-pnA
calcium beams have been obtained.
(2) The world-first high-T c SQUID beam current monitor has been developed.
(3) The bending power of the fixed-frequency Ring Cyclotron has been upgraded to 700 MeV.
(4) The world-most-intense V beams are stably supplied to super-heavy-element-search experiments.
(5) The RIBF control system has been operated stably by replacing legacy hardware controllers carried over from our old facility
with new ones. Several useful operation tools are also developed.
(6) The dated power supplies exciting the main coils of RIKEN Ring Cyclotron has been upgraded to a new one having a betterlong-term stability than the old ones.
(7) Developments of automatic beam tuning methods based on recent machine-learning technology and adaptive control are in
progress.

Members
Team Leader
Nobuhisa FUKUNISHI
Research/Technical Scientists
Masaki FUJIMAKI (Senior Technical Scientist)
Keiko KUMAGAI (Senior Technical Scientist)

Tamaki WATANABE (Senior Technical Scientist)
Kazunari YAMADA (Senior Technical Scientist)

Technical Scientist
Akito UCHIYAMA (Technical Scientist)
Expert Technician
Misaki KOMIYAMA
Postdoctoral Researcher
Takahiro NISHI
Research Associate
Hiroki FUJII
Visiting Scientists
Shin-ichiro HAYASHI (Hiroshima Int’l Univ.)
Atsushi KAMOSHIDA (Nat’l Instruments Japan Corporation)

Takuya MAEYAMA (Kitasato Univ.)

List of Publications & Presentations
Publications[Review Articles]
K. Yamada, “Upgrade of the rf system for RIKEN Ring Cyclotron,” J. Part. Accel. Soc. Jpn. 17, 159–168 (2020).
N. Fukunishi, “Performance upgrade and present status of RI Beam Factory accelerator complex,” J. Part. Accel. Soc. Jpn. 17, 236–246(2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)[Proceedings]
N. Fukunishi, “Beam intensity upgrade of RIKEN RI Beam Factory,” Proceedings of 17th Annual Meeting of Particle Accelerator Societyof Japan, 7–12 (2020).
T. Nishi, A. Uchiyama, O. Kamigaito, N. Sakamoto, T. Nagatomo, N. Fukunishi, M. Fujimaki, T. Watanabe, and Y. Watanabe, “Emittancemeasurement and ion optics tuning for SRILAC beam line,” Proceedings of 17th Annual Meeting of Particle Accelerator Society ofJapan, 116–119 (2020).
T. Watanabe, T. Toyama, K. Hanamura, H. Imao, A. Uchiyama, K. Ozeki, O. Kamigaito, N. Sakamoto, T. Nishi, N. Fukunishi, K. Yamada,
Y. Watanabe, R. Koyama, and A. Kamoshida, “Commissioning of the beam energy and position monitor system for the superconducting
RIKEN heavy-ion linac,” Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan, 718–723 (2020).
A. Uchiyama and M. Komiyama, “Introduction of archiver appliance to RILAC control system,” Proceedings of 17th Annual Meeting ofParticle Accelerator Society of Japan, 739–742 (2020).
T. Watanabe, N. Fukunishi, H. Imao, O. Kamigaito, T. Nishi, T. Ozeki, N. Sakamoto, A. Uchiyama, Y. Watanabe, K. Yamada, T. Toyama,
A. Kamoshida, K. Hanamura, and R. Koyama, “Commissioning of the beam energy position monitoring system for the superconducting
RIKEN heavy-ion linac,” Proceedings of 9th International Beam Instrumentation Conference, 295–302, ISBN:978-3-95450-222-6(2020).

Presentations[International Conferences/Workshops]
T. Watanabe (invited), N. Fukunishi, H. Imao, O. Kamigaito, T. Nishi, T. Ozeki, N. Sakamoto, A. Uchiyama, Y. Watanabe, K. Yamada, T. Toyama, A. Kamoshida, K. Hanamura, and R. Koyama, “Commissioning of the beam energy position monitoring system forthe superconducting RIKEN heavy-ion linac,” 9th International Beam Instrumentation Conference, FRAO04, Santos, Brazil (online),
September 14–18, 2020.

[Domestic Conferences/Workshops]
N. Fukunishi (invited), “Beam intensity upgrade of RIKEN RI Beam Factory,” 17th Annual Meeting of Particle Accelerator Society ofJapan, WEOOP02, Online, September 2–4, 2020.
T. Nishi (oral), A. Uchiyama, O. Kamigaito, N. Sakamoto, T. Nagatomo, N. Fukunishi, M. Fujimaki, T. Watanabe, and Y. Watanabe,“Emittance measurement and ion optics tuning for SRILAC beam line,” 17th Annual Meeting of Particle Accelerator Society of Japan,
THOO08, Online, September 2–4, 2020.
T. Watanabe (poster), T. Toyama, K. Hanamura, H. Imao, A. Uchiyama, K. Ozeki, O. Kamigaito, N. Sakamoto, T. Nishi, N. Fukunishi,
K. Yamada, Y. Watanabe, R. Koyama, and A. Kamoshida, “Commissioning of the beam energy and position monitor system for thesuperconducting RIKEN heavy-ion linac,” 17th Annual Meeting of Particle Accelerator Society of Japan, FRPP20, Online, September
2–4, 2020.
A. Uchiyama (poster) and M. Komiyama, “Introduction of archiver appliance to RILAC control system,” 17th Annual Meeting of Particle
Accelerator Society of Japan, FRPP26, Online, September 2–4, 2020.
T. Watanabe (invited), “Construction of beam energy position monitoring system using PXI digitizers for the superconducting RIKEN
heavy-ion linac,” LabVIEW User’s Particle Accelerator Community 2020.12.16 Online Conference, Online, December 16, 2020.

AwardsT. Nishi, “Emittance measurement and ion optics tuning for SRILAC beam line,” Oral Presentation Awards of 17th Annual Meeting ofParticle Accelerator Society of Japan (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator Group
Cryogenic Technology Team
1. Abstract

We are operating the cryogenic system for the superconducting ring cyclotron in RIBF. We are operating the helium cryogenic
system in the south area of RIKEN Wako campus and delivering the liquid helium to users in RIKEN. We are trying to collecteﬃciently gas helium after usage of liquid helium.

2. Major Research Subjects(1) Operation of the cryogenic system for the superconducting ring cyclotron in RIBF.
(2) Operation of the helium cryogenic plant in the south area of Wako campus and delivering the liquid helium to users in Wako
campus.

3. Summary of Research Activity(1) Operation of the cryogenic system for the superconducting ring cyclotron in RIBF (H. Okuno, T. Dantsuka, M. Nakamura,
T. Maie).
(2) Operation of the helium cryogenic plant in the south area of Wako campus and delivering the liquid helium to users in Wako
campus. (T. Dantsuka, S. Tsuruma, M. Kuroiwa, M. Takahashi, H. Okuno).

Members
Team Leader
Hiroki OKUNO
Research/Technical Scientist
NAKAMURA (Senior Technical Scientist)
Expert Technicians
Tomoyuki DANTSUKA

Takeshi MAIE

Part-time Workers
Mamoru TAKAHASHI (Research Part-time Worker I)
Shizuho TSURUMA (Administrative Part-time Worker I)

Mayumi KUROIWA (Administrative Part-time Worker II)- 265 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Accelerator Group
Infrastructure Management Team
1. Abstract

Our team is in charge of the design, operation, and maintenance of the large-scale infrastructure for the entire RI Beam Factory(RIBF), including cooling water, air conditioning, and electrical equipment, as well as the research and development of their advanced
management. In order to operate the RIBF eﬃciently, it is very important to ensure the sound operation of these infrastructures thatlead to the stable functioning of various devices. Another important mission is to coordinate the scheduling of major construction andrepair work related to the RIBF so that beamtime runs smoothly.
The recent issue is the aging of infrastructure equipment. In line with these measures, we are making modifications that contributeto the stability of accelerator equipment and energy saving. In addition, infrastructure equipment has many sensors for management,
and a huge amount of measurement data from these sensors is archived. We are planning to use this data to build a more advanced
management system.

2. Major Research Subjects(1) Operation, maintenance and monitoring of infrastructure of RI Beam Factory.
(2) Development of advanced management of infrastructure that contributes to accelerator and beam stability.
(3) Coordination of large construction work and modification related to RI Beam Factory.

Members
Team Leader
Masanori KIDERA
Deputy Team Leader
Yutaka WATANABE
Special Temporary Technical Scientist
Shu WATANABE
Special Temporary Employee
Hideyuki YAMASAWA

List of Publications & Presentations
Publications[Proceedings]
西田稔, 大関和貴, 後藤彰, 大西純一, 大城幸光, 福澤聖児, 濱仲誠, 石川盛, 小林清志, 小山亮, 仲村武志, 西村誠, 柴田順翔, 月居憲俊,
矢冨一慎, 藤巻正樹, 福西暢尚, 長谷部裕雄, 日暮祥英, 今尾浩士, 上垣外修一, 加瀬昌之, 木寺正憲, 込山美咲, 熊谷桂子, 真家武士,
長友傑, 中川孝秀, 奥野広樹, 坂本成彦, 須田健嗣, 内山暁仁, 渡部秀, 渡邉環, 渡邉裕, 山田一成, 鎌倉恵太, 小高康照, 「理研 AVF
サイクロトロン運転の現状報告」, “Status report on the operation of RIKEN AVF Cyclotron,” Proc. 17th Annu. Meet. Part. Accel.
Soc. Jpn., p. 921, 2020 年 10 月 23 日.
石川盛, 須田健嗣, 福澤聖児, 濱仲誠, 小林清志, 小山亮, 仲村武志, 西田稔, 西村誠, 柴田順翔, 月居憲俊, 矢冨一慎, 段塚知志, 藤巻正樹,
藤縄雅, 福西暢尚, 長谷部裕雄, 日暮祥英, 池沢英二, 今尾浩士, 上垣外修一, 金井保之, 加瀬昌之, 木寺正憲, 込山美咲, 熊谷桂子,
真家武士, 長友傑, 中川孝秀, 中村仁音, 大西純一, 奥野広樹, 大関和貴, 坂本成彦, 内山暁仁, 渡部秀, 渡邉環, 渡邉裕, 山田一成,
山澤秀行,「理研 RIBF におけるリングサイクロトロンの運転報告」, “Status report of the operation of RIBF ring cyclotrons,” 第 17 回
日本加速器学会年会プロシーディングス, web 公開のみ, 2020 年 10 月 21 日. https://www.pasj.jp/web_publish/pasj2020/
proceedings/PDF/WESP/WESP03.pdf .
坂本成彦, 藤巻正樹, 池沢英二, 今尾浩士, 上垣外修一, 長友傑, 西隆博, 大関和貴, 須田健嗣, 内山暁仁, 渡邉環, 渡邉裕, 山田一成, 「理研超伝導線型加速器 SRILAC のコミッショニング」, “Commissioning of superconducting-linac booster for RIKEN heavy-ion linac,”
第 17 回日本加速器学会年会プロシーディングス, web 公開のみ, 2020 年 10 月 21 日. https://www.pasj.jp/web_publish/pasj2020/proceedings/PDF/WESP/WESP03.pdf .
渡邉環, 福西暢尚, 今尾浩士, 上垣外修一, 西隆博, 大関和貴, 坂本成彦, 内山暁, 渡邉裕, 山田一成, 外山毅, 鴨志田敦史, 花村幸篤, 小山亮,
「理研超伝導重イオンリニアック用ビームエネルギー・位置モニターシステムのコミッショニング」, “Commissioning of the beamenergy position monitoring system for the superconducting RIKEN Heavy-ion LINAC,” Proc. 9th International Beam Instrumentation
Conference (IBIC 2020), pp. 295–302 October 30, 2020. http://accelconf.web.cern.ch/ibic2020/papers/frao04.pdf .
渡邉環, 外山毅, 花村幸篤, 今尾浩士, 内山暁, 大関和貴, 上垣外修一, 坂本成彦, 西隆博, 福西暢尚, 山田一成, 渡邉裕, 小山亮, 鴨志田敦史,「理研超伝導リニアック用ビームエネルギー・位置モニターのコミッショニング」, “Commissioning of the beam energy and position
monitor system for the superconducting RIKEN Heavy-ion Linac,” 第 17 回日本加速器学会年会, PASJ2020 FRPP20, pp. 718–723,
2020 年 10 月 23 日. https://www.pasj.jp/web_publish/pasj2020/proceedings/PDF/FRPP/FRPP20.pdf- 266 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

H. Imao, O. Kamigaito, N. Sakamoto, T. Watanabe, Y. Watanabe, K. Yamada, K. Oyamada, “Non-evaporative getter-based diﬀerential
pumping system for SRILAC at RIBF,” Proc. 19th International Conference on RF Superconductivity (SRF 2019), web 公開のみ,
2019 年 11 月. http://accelconf.web.cern.ch/srf2019/papers/tup013.pdf .

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Instrumentation Development Group
1. Abstract

This group develops core experimental installations at the RI Beam factory. Three projects are currently going on. SLOWRI is anexperimental installations under testing and a common element enabling multiple-use. This will stop high-energy RI beams in a gascatcher system and re-accelerates up to several-tenth keV, and the high-quality cold RI beam will be delivered to the users. SCRIT is
the world first facility for an electron scattering oﬀ unstable nuclei, and has been constructed independently of the RIBF main facility.
The first physic result was demonstrated in 2017, and the facility is now under upgrading of the electron beam power driving the RI
beam production. Rare-RI Ring is an event-by-event operated heavy-ion storage ring aiming at the precision mass measurement for
extremely rare exotic nuclei. This is now open for an experimental proposal application, and has already performed PAC-approved
experiments, and an improvement for higher precise mass measurement is now going on. A small size heavy-ion storage ring,
RUNBA, is R&D machine for technical development of beam recycling aiming at nuclear reaction study for rarely produced isotopes.
This is under preparing for construction and the technical development for some key components in the ring are now going on. All
instrumentations were designed to maximize the research potential of the world’s most intense RI beams, and the exclusive equipment
available at the RI Beam Factory makes experimental challenges possible. Technologies and experiences accumulated in this groupwill be able to provide opportunities of new experimental challenges and the foundation for future developments of RIBF.

2. Major Research Subjects
(1)
(2)
(3)
(4)

SCRIT Project
SLOWRI Project
Rear RI Ring Project
RUNBA project (Beam recycling development)

3. Summary of Research Activity

We are developing beam manipulation technology in carrying out above listed project. They are the high-quality slow RI beam
production (SCRIT and SLOWRI), the beam cooling and stopping (SCRIT and SLOWRI), and the beam accumulation technology(Rare RI Ring and RUNBA) in a storage ring. The technological knowhow accumulated in our projects will play a significant rolein the next generation RIBF. Status and future plan for each project is described in subsections. The electron scattering from 132 Xe
isotopes has been successfully measured and the nuclear charge density distribution has been obtained in SCRIT. We are upgrading
the power of electron beam from RTM, which is the driver for RI production, for going to world-first electron scattering oﬀ unstable
nuclei. Performance of Rare RI Ring has already been evaluated and successfully started mass-measurements for unknown-massnuclei in the experiments approved by PAC. Recently, we succeeded in measurement of masses of 74, 76 Ni, 122 Rh, 123, 124 Pd, and 125 Ag
for the first time. Since expected performances on a mass resolution and an eﬃciency has slightly been unachieved, the fast kicker
system and the optics tuning system are under improvement. SLOWRI is now under test experiments to establish a slow RI beam
production using two types of gas cells. PALIS has been commissioned from 2015, and basic functions such as, for instance, the
RI-beam stopping in Ar gas cell and the extraction from the gas cell have beam evaluated. RF carpet gas cell (RFGC) combinedwith multi-reflection time-of-flight device is now working as a movable mass spectrograph at some facility such as ZeroDegree and
GARIS. Detail status and future plans for these projects are described in subsections.
According to the future plans of the Nishina Center, we have started development of a beam re-cycling technique. A circulationof an RI beam in a storage ring equipped by a thin internal target is maintained until that some nuclear reaction occur at the target.
In order to establish a beam re-cycling technique, the energy loss has to be compensated and growth of the energy-spread and theemittance have to be corrected by using a re-acceleration system and a beam-cooling or a fast feedback system, respectively. A beam
re-cycling technique is supposed to greatly enhance an RI use eﬃciency in a nuclear physics study. For the development of thesenovel technique, we will construct a relatively small size of heavy-ion storage ring (RUNBA) connected to ISOL (ERIS) in the SCRIT
facility. This is equipped by acceleration devices and beam-cooling devices necessary in our R&D study. It was originally constructed
as a beam cooler ring (sLSR) at the Institute for Chemical Research (ICR), Kyoto University more than ten years ago. This ringis re-cycled at RIBF and it has been already moved to RIBF. Technical development for key devices required in RUNBA such as acharge breeder (CB), an energy-dispersion corrector (EDC), angular diﬀusion corrector (ADC), and an internal target system havebeen already started under the research cooperation agreement with ICR Kyoto University.

Members
Director
Masanori WAKASUGIContract Researcher
Ryo OGAWARA- 268 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Visiting Scientists
Yasushi ABE (Nat’l Inst. of Radiological Sci.)
Akira OZAWA (Tsukuba Univ.)

Fumi SUZAKI (JAEA)
Kyo TSUKADA (Kyoto Univ.)

Part-time Worker
Midori TAKEMON (Administrative Part-time Worker I)

List of Publications & Presentations
Publications and presentations are listed in subsections.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Instrumentation Development GroupSLOWRI Team
1. Abstract

SLOWRI is a universal low-energy RI-beam facility at RIBF that provides a wide variety of short-lived nuclei as high-purity andlow-emittance ion beams or stored ions in a trap, including a parasitic operation mode. The SLOWRI team develops and manages thefacility and performs high-precision spectroscopy experiments. The construction of the SLOWRI facility began in FY2013 and commissioning work is ongoing. From FY2019, SLOWRI has been started to be co-operated under RNC and WNSC/KEK collaboration.
High-energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large He gas catcher cell
(RFGC) or in a small Ar gas catcher cell (PALIS cell). From these gas cells, the low-energy ion beams will be delivered via mass
separators and switchyards to various devices: such as an ion trap, a collinear fast beam apparatus, and a multi-reflection time of flightmass spectrograph. A multi-reflection time-of-flight mass spectrograph (MRTOF) has been also developed.
Two mass measurement projects using MRTOF mass spectrographs have been started: one is for trans uranium elements at
the GARIS facility and the other is for r-process nuclides at SLOWRI facility. At GARIS-II, we installed second prototype RFCG
combined with MRTOF, which is a medium-sized cryogenic RF-carpet He gas cell. Using second prototype RFGC, more than
80 nuclear masses have been measured including first mass measurements of Md and Es isotopes. In FY2020, we have started massmeasurements for neutron rich unstable nuclei using a fission source installed in the second prototype RFGC. At SLOWRI facility, third
prototype RFGC has been installed at F11, the downstream of ZeroDegree spectrometer, which is a 50-cm-long RF-carpet-type He
gas cell combined with MRTOF. In November and December of FY2020, we have successfully performed the on-line commissioning,
symbiotically by using RIs provided for HiCARI campaign. The extraction eﬃciency in total has been achieved at 1% in maximum
and the masses on more than 70 nuclei have been measured using RIs provided with BigRIPS.
Parallelly, the on-line commissioning for PALIS has been continuously performed at F2 of BigRIPS. In FY2020, the extractionof I-emitter Bi Isotopes by the gas flow without a laser ionization has been confirmed from PALIS gas cell.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Construction of the stopped and low-energy RI-beam facility, SLOWRI.
Development of a multi-reflection time-of-flight mass spectrograph for precision mass measurements of short-lived nuclei.
Development of collinear laser spectroscopy apparatus.
Development of a parasitic slow RI-beam production method using resonance laser ionization.

3. Summary of Research Activity(1) Construction of stopped and low-energy RI-beam facility (SLOWRI)SLOWRI consists of two gas catchers (RF carpet gas cell and PALIS gas cell), mass separators a 50-m-long beam transport line,
a beam cooler-buncher, an isobar separator, and a laser system. The RF carpet gas cell (RFGC) will be installed at the exit of the D5
dipole magnet of BigRIPS. The gas catcher contains a large cryogenic He gas cell with a large traveling wave rf-carpet. The PALIS
gas cell is installed in the vicinity of the second focal plane slit of BigRIPS. It will provide parasitic RI-beams from those ions lost in
the slits during other experiments. In this gas catcher, thermalized RI ions quickly become neutral and will be re-ionized by resonant
laser radiations. Oﬀ- and on-line commissioning is underway.
Based on test experiments with the prototype setups, the RF-carpet gas cell contains a three stage rf-carpet structure: a gutter rf
carpet (1st carpet) for the collection thermal ions in the cell into a small slit, a narrow (about 10 mm) traveling-wave rf-carpet (2ndcarpet) for collection of ions from the gutter carpet and for transporting the ions towards the exit, and a small rf carpet for extraction
from the gas cell. The oﬀ-line test has been completed in FY2019.
A 50-cm-long RFGC, which is a prototype for final version RFGC with 1.5 m length, has been installed at F11 of ZeroDegreee
spectrometer of BigRIPS in FY2020. In November and December of 2020, the on-line commissioning has been successfully performed
symbiotically using RIs provided with BigRIPS during HiCARI campaign. The extraction eﬃciency in total has been achieved at 1%
in maximum.
(2) Development of a multi-reflection TOF mass spectrograph for short-lived nuclei
The atomic mass is one of the most important quantities of a nucleus and has been studied in various methods since the early daysof modern physics. From among many methods we have chosen a multi-reflection time-of-flight (MRTOF) mass spectrometer. Slow
RI beams extracted from the RF ion-guide are bunched and injected into the spectrometer with a repetition rate of ∼100 Hz. A massresolving power of 170,000 has been obtained with a 2 ms flight time for 40 K and 40 Ca isobaric doublet. This mass-resolving powershould allow us to determine ion masses with an accuracy of ≤10−7 . A new MRTOF has been assembled in FY2019 to be coupledwith the third prototype of RFGC and has been installed at F11 of BigRIPS in FY2020. Mass measurements using RIs provided withBigRIPS during HiCARI campaign have been symbiotically performed. As the result, atomic masses on more than 70 nuclei havebeen successfully measured. Among them, 11 isotope masses improve the present uncertainty significantly and 3 isotope masses havebeen measured for the first time.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)(3) Development of collinear fast beam apparatus for nuclear charge radii measurements
The root-mean-square charge radii of unstable nuclei have been determined exclusively by isotope shift measurements of the
optical transitions of singly charged ions or neutral atoms by laser spectroscopy. Many isotopes of alkali, alkali-earth, and noble-gas
elements in addition to several other elements have been measured by collinear laser spectroscopy since these ions all have good
optical transitions and are available at conventional ISOL facilities. However, isotopes of other elements, especially refractory andshort-lived ones, have not been investigated so far.
In SLOWRI, isotopes of all atomic elements will be provided as well collimated, mono-energetic ion beams. This should expand
the range of nuclides available for laser spectroscopy. An oﬀ-line mass separator and a collinear fast beam apparatus with a largesolid-angle fluorescence detector was built previously. A 617-nm transition of the metastable Ar+ ion at 20 keV was measured withboth collinear and anti-collinear geometry, which allowed determination of the absolute resonant frequency of the transition at restwith a relative accuracy better than 10−8 . A new setup is under preparation at the SLOWRI experiment area in collaboration with the
Nuclear Spectroscopy Laboratory.
(4) Development of parasitic slow RI-beam production scheme using resonance laser ionization
More than 99.9% of RI ions produced in projectile fission or fragmentation are simply dumped in the first dipole magnet and theslits. A new scheme, named PALIS, meant to rescue such precious RI using a compact gas catcher cell and resonance laser ionization,
was proposed as a part of SLOWRI. The thermalized RI ions in a cell filled with Ar gas can be quickly neutralized and transported tothe exit of the cell by gas flow. Irradiation of resonance lasers at the exit ionizes neutral RI atoms eﬃciently and selectively. PALIS
has been installed at F2 at the downstream of BigRIPS. and oﬀ- and on-line commissioning is under progress.
At F2, due to high radiation from a beam dump, it is not easy to handle ions using electric ion guides. Therefore, a 70-cm-long gas
pipe from the Ar gas cell was newly installed to transport RIs to relatively low radiation area thanks for the Ar gas flow. In FY2020, we
have confirmed the transportation of RIs through the gas pipe to the relatively low radiation area using -emitting Bi isotopes provided
with BigRIPS. In FY2021, an on-line test for resonant laser ionization is planned using α-emitting Bi isotopes.

Members
Team Leader
Hironobu ISHIYAMA
Research/Technical Scientists
Takao KOJIMA (Senior Research Scientist)
Aiko TAKAMINE (Research Scientist)

Tetsu SONODA (Technical Scientist)

Expert Technician
Takeshi MAIE
Junior Research Associate
Shun IIMURA
Visiting Scientists
Hideki IIMURA (JAEA)
Kunihiro OKADA (Sophia Univ.)
Mikael REPONEN (Univ. of Jyvaskyla)
Hans SCHUESSLER (Texas A&M Univ.)

Volker SONNENSCHEIN (Nagoya Univ.)
Minoru TANIGAKI (Kyoto Univ.)
Hideki TOMITA (Nagoya Univ.)
Hermann WOLLNIK (Univ. of Giessen)

List of Publications & Presentations
Publications[Original Papers]
Y. Hirayama, P. Schury, M. Mukasi, H. Choi, S. Iimura, Y. X. Watanabe, M. Wada, H. Watanabe, and H. Miyatake, “Three-dimentional
tracking multi-segmented proportional gas counter for beta-decay spectroscopy of unstable nuclei,” Nucl. Instrum. Methods Phys. Res.
A 997, 165152 (2020).
M. Rosenbusch, P. Schury, M. Wada, S. Iimura, Y. Ito, and H. Wollnik, “Accurately accounting for eﬀects on times-of-flight causedby finite field-transition times during the ejection of ions from a storage trap: A study for single-reference TOF and MRTOF mass
spectrometry,” International Journal of Mass Spectrometry 456, 116346 (2020).
M. Mukai, Y. Hirayama, P. Schury, Y. X. Watanabe, M. Ahmed, H. Haba, H. Ishiyama, S. C. Jeong, Y. Kakiguchi, S. Kimura, J. Y. Moon,
M. Oyaizu, A. Ozawa, J. H. Park, H. Ueno, M. Wada, and H. Miyatake, “Development of a multi-segmented proportional gas counterfor β-decay spectroscopy at KISS,” Nucl. Instrum. Methods Phys. Res. B 463, 423–424 (2020).
Y. Hirayama, Y. X. Watanabe, M. Mukai, P. Schury, M. Ahmed, H. Ishiyama, S. C. Jeong, Y. Kakiguchi, S. Kimura, J. Y. Moon,
M. Oyaizu, J. H. Park, M. Wada, and H. Miyatake, “Nuclear spectroscopy of r-process nuclei using KEK isotope separation system,”Nucl. Instrum. Methods Phys. Res. B463, 425–430 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

M. Mukai, Y. Hirayama, Y. X. Watanabe, S. Schiﬀmann, J. Ekman, M. Godefroid, P. Schury, Y. Kakiguchi, M. Oyaizu, M. Wada,
S. C. Jeong, J. Y. Moon, J. H. Park, H. Ishiyama, S. Kimura, H. Ueno, M. Ahmed, A. Ozawa, H. Watanabe, S. Kanaya, and H. Miyatake,“In-gas-cell laser resonance ionization spectroscopy of 196, 197, 198 Ir,” Phys. Rev. C 102, 054307 (2020).
M. Rosenbusch, M. Wada, P. Schury, Y. Ito, H. Ishiyama, S. Ishizawa, Y. Hirayama, S. Kimura, T. M. Kojima, H. Miyatake, J. Y. Moon,
T. Niwase, T. Sonoda, A. Takamine, Y. X. Watanabe, and H. Wollnik, “A new multi-reflection time-of-flight mass spectrograph for the
SLOWRI facility,” Nucl. Instrum. Methods Phys. Res. B 463, 184–188 (2020).

Presentations[International Conferences/Workshops]
A. Takamine (invited), “SLOWRI rf gas catcher development toward symbiotic mass measurement,” RIBF Users Meeting 2020, on-line,
Wako, Japan, September 8–10, 2020.
H. Ishiyama (invited), “Present status of SLOWRI,” SSRI-PNS collaboration meeting, on-line, Wako, Japan, September 3, 2020.

[Domestic Conferences/Workshops]
飯村俊, 高峰愛子, M. Rosenbusch, 和田道治, S. Chen, J. Liu, W. Xian, D. Hou, S. Yan, P. Schury, 園田哲, 小島隆夫, 渡辺裕, 小田原厚子,
石山博恒, 「理研 BigRIPS SLOWRI における RF カーペットガスセルの開発～オンライン試験と質量測定」, 日本物理学会第 76
回年次大会, on-line, 2021 年 3 月 12 日.
M. Rosenbush, M. Wada, P. Schury, Y. Hirayama, H. Miyatake, Y. X. Watanabe, S. Iimura, H. Ishiyama, T. Kojima, T. Sonoda, M. Mukai,
S. Nishimura, S. Naimi, T. Niwase, A. Takamine, Y. Ito, D. S. Hou, J. Liu, S. Chen, J. Lee, and W. Xian, “New mass measurements of
exotic nuclides by the first MRTOF setup at BigRIPS/RIKEN,” 日本物理学会第 76 回年次大会, on-line, 2021 年 3 月 12 日.
飯村俊, 高峰愛子, M. Rosenbusch, 和田道治, S. Chen, J. Liu, W. Xian, D. Hou, S. Yan, P. Schury, 園田哲, 小島隆夫, 渡辺裕,
小田原厚子, 石山博恒, 「理研 BigRIPS SLOWRI における RF カーペットガスセルの開発」, 日本物理学会 2020 年秋季大会, 2020
年 9 月 8–11 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Instrumentation Development Group
Rare RI-ring Team
1. Abstract

The aim of Rare-RI Ring (R3) is to measure the masses of short-lived unstable nuclei far from the beta-stability line. In particular,a high-precision mass measurement for nuclei located around the r-process pass (rare-RI) is required in nucleosynthesis point ofview. The R3 completed the construction at the end of 2014, and has been performed commissioning experiments several times by
2017. Through the commissioning experiments, we confirmed the high ability of R3 as a storage ring capable of handling one event,and demonstrated that it is possible to perform the time-of-flight Isochronous Mass Spectrometry (IMS) in shorter than 1 ms. We
have acquired an adequate eﬃciency to conduct the mass measurement experiments in the end of 2017. In 2020, a machine study
was conducted using upgraded kicker system. We succeeded in extracting all injected nuclides in a single extraction and then theexperimental eﬃciency became at least twice better than that achieved using the previous method, where diﬀerent extraction timings
were needed to extract all nuclides. Furthermore, the systematic uncertainty caused by diﬀerent kick angles has been eliminated.
The open question of the first mass measurement experiment in 2018 will be solved by performing mass measurement experiments
utilizing the upgraded kicker system in 2021.

2. Major Research Subjects(1) Further improvement of experimental eﬃciency and mass measurement precision(2) Precision mass measurement for rarely produced isotopes related to r-process

3. Summary of Research Activity

In the commissioning experiments up to 2017, we confirmed the unique performances of R3 and demonstrated the time-of-flightisochronous mass measurement method. The ring structure of R3 was designed with a similar concept of a separate-sector ring
cyclotron. It consists of six sectors and straight sections, and each sector consists of four rectangular bending magnets. Two magnets
at both ends of each sector are additionally equipped with ten trim coils to form a precise isochronous field. We have realized informing the precise isochronous field of 5 ppm with wide momentum range of ∆p/p = ±0.5%. Another performance required forR3 is to eﬃciently seize hold of an opportunity of the mass measurement for rare-RIs produced unpredictably. It was realized byconstructing the Isotope-Selectable Self-trigger Injection (ISSI) scheme which pre-identified rare-RI itself triggers the injection kicker
magnets. Key device was an ultra-fast response kicker system that has been successfully developed. Full activation of the kicker
magnetic field can be completed within the flight time of the rare-RI from an originating point (F3 focal point in BigRIPS) of thetrigger signal to the kicker position in R3.
Since R3 accumulates, in principle, only one event, we fabricated high-sensitive beam diagnostic devices in the ring. They should
be applicable even for one event circulation. One of them is a cavity type of Schottky pick-up installed in a straight section of R3.
The Schottky pick-up successfully monitored a single 78 Kr36+ ion circulation with the measurement time of less than 10 ms in the firstcommissioning experiment. We also confirmed that it is useful for fine tuning of the isochronous field. Another is a timing monitor,
which detects secondary electrons emitted from thin carbon foil placed on the circulation orbit. The thickness of the foil is 50 µg/cm2 .
This timing monitor is working well to observe first several tens turns for injected event.
We performed mass measurement in the third commissioning experiment by using unstable nuclei which masses are well-known.
The masses of 79 As, 77 Ga, 76 Zn, and 75 Cu relative to 78 Ge were derived with the accuracy of less than 10 ppm. In addition, we have
improved the extraction eﬃciency to 2% by considering the matching condition between the emittance of injection events and theacceptance of R3. This extraction eﬃciency was suﬃcient to conduct the accepted two proposals: mass measurements of Ni isotopes
and mass measurements of Sn region.
In the beginning of 2018, we examined the feasibility of these two proposals in detail and decided to proceed with two proposals
at the same period. In the beginning of November 2018, we have conducted the first experiment using R3 to measure the masses for
74, 76
Ni in 4 days. After that, we also measured the masses for 122 Rh, 123, 124 Pd, and 125 Ag in 4.5 days at the end of November 2018.
These nuclei were successfully extracted from R3 with the eﬃciency of 1–2%. However, unexpected deviation from the evaluatedvalues of literature remains in the masses obtained by detailed analysis. This open question is thought to be due to the following two
reasons. One is that the TOF at R3 is mistaken because the target nuclei were extracted at a slope part of kicker field distribution. The
other is that the absolute value of beta or magnetic rigidity determined for each extracted event is incorrect. In order to eliminate theformer concern and verify the latter, we have improved the kicker system. This improvement achieves a flat-top of 100 ns for injection
and a long flat-top of 350 ns or more for extraction.
A machine study was conducted using the upgraded kicker system in November 2020. We succeeded in extracting all events with
diﬀerent revolution times at once by realizing a long flat-top. Experimental eﬃciency became at least twice better than that achieved
using the previous method, where diﬀerent extraction timings were needed to extract all nuclides. In addition, it was confirmed that
there is a risk that an incorrect mass will be derived when extracted events at a slope part of kicker field distribution, depending on an
isochronous condition. On the other hand, the masses could be derived with the expected accuracy when extracted events at a flat-top
part of kicker field distribution. Since each proposal mentioned above still has a machine time of several days, we will conduct massmeasurement experiments using the upgraded kicker system in 2021 and solve the open question.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Members
Team Leader
Masanori WAKASUGITechnical Scientist
Yoshitaka YAMAGUCHI (Technical Scientist)
Expert Technician
Takeshi MAIE

List of Publications & Presentations
Publications[Original Papers]
D. Nagae, Y. Abe, S. Okada, S. Omika, K. Wakayama, S. Hosoi, S. Suzuki, T. Moriguchi, M. Amano, D. Kamioka, Z. Ge, S. Naimi,
F. Suzaki, N. Tadano, R. Igosawa, K. Inomata, H. Arakawa, K. Nishimuro, T. Fujii, T. Mitsui, Y. Yanagisawa, H. Baba, S. Michimasa,
S. Ota, G. Lorusso, Yu. A. Litvinov, A. Ozawa, T. Uesaka, T. Yamaguchi, Y. Ymaguchi, and M. Wakasugi, “Development and operationof an electrostatic time-of-flight detector for the Rare RI storage Ring,” Nucl. Instrum. Methods Phys. Res. A 986, 164713-1–7 (2020).
S. Suzuki, A. Ozawa, D. Kamioka, Y. Abe, M. Amano, H. Arakawa, Z. Ge, K. Hiraishi, Y. Ichikawa, K. Inomata, A. Kitagawa,
T. Kobayashi, H. F. Li, T. Matsumoto, T. Moriguchi, M. Mukai, D. Nagae, S. Naimi, S. Omika, S. Sato, Y. Tajiri, K. Wakayama,
and T. Yamaguchi, “Eﬃciency and timing performance of time-of-flight detector utilizing thin foils and crossed static electric andmagnetic fields for mass measurements with Rare-RI Ring facility,” Nucl. Instrum. Methods Phys. Res. A 965, 163807-1–14 (2020).
C. Y. Fu, Y. H. Zhang, M. Wang, X. H. Zhou, Yu. A. Litvinov, K. Blaum, H. S. Xu, X. Xu, P. Shuai, Y. H. Lam, R. J. Chen, X. L. Yan,
X. C. Chen, J. J. He, S. Kubono, M. Z. Sun, X. L. Tu, Y. M. Xing, Q. Zeng, X. Zhou, W. L. Zhan, S. Litvinov, G. Audi, T. Uesaka,
T. Yamaguchi, A. Ozawa, B. H. Sun, Y. Sun, and F. R. Xu, “Mass measurements for the T z = −2 fp-shell nuclei 40 Ti, 44 Cr, 46 Mn, 48 Fe,
50
Co, and 52 Ni,” Phys. Rev. C 102, 054311-1–11 (2020).

[Proceedings]
S. Naimi, H. F. Li, Y. Abe, Y. Yamaguchi, D. Nagae, F. Suzaki, M. Wakasugi, H. Arakawa, W. Dou, D. Hamakawa, S. Hosoi, Y. Inada,
K. Inomata, D. Kajiki, T. Kobayashi, M. Sakaue, K. Yokota, T. Yamaguchi, R. Kagesawa, D. Kamioka, T. Moriguchi, M. Mukai,
A. Ozawa, S. Ota, N. Kitamura, S. Masuoka, D. S. Ahn, H. Baba, N. Fukuda, Y. Shimizu, H. Suzuki, H. Takeda, C. Y. Fu, Z. Ge,
Q. Wang, M. Wang, Yu. A. Litvinov, G. Lorusso, and T. Uesaka, “Experimental challenges of the first mass measurement campaign at
the Rare-RI Ring,” J. Phys. Conf. Ser. 1643, 012058-1–6 (2020).
S. Omika, T. Yamaguchi, N. Tadano, Y. Abe, M. Amano, Z. Ge, D. Kamioka, T. Morigushi, D. Nagae, S. Naimi, A. Ozawa, F. Suzaki,
S. Suzuki, T. Suzuki, T. Uesaka, M. Wakasugi, K. Wakayama, and Y. Yamaguchi, “Development of a new in-ring beam monitor in the
Rare-RI Ring,” Nucl. Instrum. Methods Phys. Res. B 463, 241–243 (2020).
J. H. Liu, X. Xu, P. Zhang, P. Shuai, X. L. Yan, Y. H. Zhang, M. Wang, Yu. A. Litvinov, H. S. Xu, K. Blaum, T. Bao, H. Chen, X. C. Chen,
R. J. Chen, C. Y. Fu, D. W. Liu, W. W. Ge, R. S. Mao, X. W. Ma, M. Z. Sun, X. L. Tu, Y. M. Xing, J. C. Yang, Y. J. Yuan, Q. Zeng,
X. Zhou, X. H. Zhou, W. L. Zhan, S. Litvinov, T. Uesaka, Y. Yamaguchi, T. Yamaguchi, A. Ozawa, and B. H. Sun, “Improving theresolving power of isochronous mass spectrometry by employing an in-ring mechanical slit,” Nucl. Instrum. Methods Phys. Res. B
463, 138–142 (2020).
Yu. A. Litvinov, Th. Stoehlker, X. W. Ma, Y. H. Zhang, and T. Yamaguchi, “Nuclear physics research at heavy ion accelerators: Precision
studies with stored and cooled exotic nuclei,” J. Phys. Conf. Ser. 1401, 012001-1–9 (2020).

Presentations[International Conferences/Workshops]
S. Naimi (invited), “Status of R3 and new in-ring detectors,” NucAR Workshop, Online, December 7–10, 2020.
S. Naimi (invited), “Development of a large-area position-sensitive detector for the Rare-RI Ring at Riken,” TCHoU Workshop, Online,
March 29, 2021.

[Domestic Conferences/Workshops]
濱川大貴（口頭発表）, 「稀少 RI リングのためのプラスチックシンチレータを用いた位置検出器の開発」, 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.
梶木大輔（口頭発表）, 「稀少 RI リングにおける周回周期の測定のためのデルタ線検出器の性能評価」, 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.

[Seminars]
Yu. A. Litvinov (oral), “Heavy-ion storage rings and their use for precision nuclear structure and astrophysics experiments,” Seminar on
Precision Physics and Fundamental Symmetries, Online, July 2, 2020.
Yu. A. Litvinov (oral), “Combining atomic and nuclear physics in ion storage rings,” Online Lectures of the Matter and Cosmos Section(SMuK), Online, March 11, 2021.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Instrumentation Development GroupSCRIT Team
1. Abstract

The SCRIT Electron Scattering Facility has been constructed at RIKEN RIBF. This aims at investigation of internal nuclear structure for short-lived unstable nuclei by means of electron scattering. SCRIT (Self-Confining RI Ion Target) is a novel method to form
internal targets in an electron storage ring. This is a unique method for making electron scattering experiments for unstable nuclei possible. Construction of the facility has been started in 2009. This facility consists of an electron accelerator (RTM), a SCRITequipped
electron storage ring (SR2), an electron-beam-driven RI separator (ERIS), and a window-frame spectrometer for electron scattering(WiSES) which consists of a large window-frame dipole magnet, drift chambers and trigger scintillators. Installation of all components in the facility was completed in 2015. After the comprehensive test and tuning, the luminosity was reached to 3 × 1027 /(cm2 s)
with the number of injected ions of 3 × 108 . In 2016, we successfully completed a measurement of diﬀraction of scattered electrons
from 132 Xe nuclei and determined the charge density distribution for the first time. The facility is now under setting up to move thefirst experiment for unstable nuclei.

2. Major Research Subjects

Development of SCRIT electron scattering technique and measurement of the nuclear charge density distributions of unstable
nuclei.

3. Summary of Research Activity

SCRIT is a novel technique to form internal target in an electron storage ring. Positive ions are three dimensionally confined in theelectron beam axis by transverse focusing force given by the circulating electron beam and applied electrostatic longitudinal mirror
potential. The created ion cloud composed of RI ions injected from outside works as a target for electron scattering. Constructionof the SCRIT electron scattering facility has been started in 2009. The electron accelerators RTM and the storage ring SR2 weresuccessfully commissioned in 2010. Typical accumulation current in SR2 is 250–300 mA at the energy range of 120–300 MeV that isrequired energy range in electron scattering experiment. The SCRIT device was inserted in the straight section of SR2 and connected
to an ISOL named ERIS (Electron-beam-driven RI separator for SCRIT) by 20-m long low energy ion transport line. A buncher
system based on RFQ linear trap named FRAC (Fringing-RF-field-Activated dc-to-pulse converter) was inserted in the transport line
to convert the continuous beam from ERIS to pulsed beam, which is acceptable for SCRIT. The detector system WiSES consisting ofa high-resolution magnetic spectrometer, drift chambers and trigger scintillators, was constructed, and it has a solid angle of 100 msr,
energy resolution of 10−3 , and the scattering angle coverage of 25–55 degrees. A wide range of momentum transfer, 80–300 MeV/c,
is covered by changing the electron beam energy from 150 to 300 MeV.
We successfully measured a diﬀraction pattern in the angular distribution of scattered electron from 132 Xe isotope at the electron
beam energy of 150 MeV, 200 MeV, and 300 MeV, and derived the nuclear charge distribution by assuming two-parameters Fermi
model for the first time. At this time, luminosity was reached to 3 × 1027 /(cm2 s) at maximum and the averaged value was 1.2 ×1027 /(cm2 s) with the number of injected target ions of 3 × 108 .
We are now under preparation for going to the experiments for unstable nuclei. There are some key issues for that. They are
increasing the intensity of the RI beams from ERIS, eﬃcient DC-to-pulse conversion at FRAC, improving the transmission eﬃciency
from FRAC to SCRIT, and eﬀective suppression of the background in measurement of scattered electrons. RI beam intensity will be
improved by upgrading the electron beam power from 10 W to 60 W, increasing the contained amount of U in the target ion source,and some modifications in mechanical structure in the ion source. For upgrading the electron beam power, the RF system of RTM
has been maintained intensively, and we will continue the development of RTM. For eﬃcient DC-to-pulse conversion, we establishedthe two-step bunching method, which is time compression at FRAC in combination with pre-bunching at the ion source using gridaction. Furthermore, we will improve the conversion eﬃciency and the transmission eﬃciency from FRAC to the SCRIT device bycooling the trapped ions using minuscule amounts of a buﬀer gas. These improvements on FRAC were already confirmed in oﬀ-line
test. Since one of significant contribution to the background for scattered electron is scattering from massive structural objects aroundthe trapping region originated from halo components of the electron beam, we remodeled the SCRIT electrodes. The vacuum pumpsystem at the SCRIT device has been upgraded to reduce the contribution of residual gases. Luminosity for radioactive Xe isotopes is
expected to be more than 1026 /(cm2 s) after these improvements. Then, we will be able to start experiments for unstable nuclei. Whenfurther upgrading in the RTM power planed to be 3 kW will be achieved, we can extend the measurements to more exotic nuclei.
In 2018, we developed several instruments. One is the introduction of the surface-ionization type ion source at ERIS in order
to increase kinds of radioactive beam and to produce high intensity beam. Another development is the upgrading of the drift chamber located in front of the magnetic spectrometer of WiSES to improve the momentum resolution and angular acceptance. Thesedevelopments help us to realize experiments for unstable nuclei.
In 2019, we installed a newly designed SCRIT electrodes. The main purpose of the replacement was to lower the background
during the measurement due to the electron scattering from the SCRIT electrodes itself but not from the ion targets for the experiment.
For that purpose, we employed thin metal wires to construct the electrodes rather than metal plates nor blocks. In addition, we
modified the inside structure of the SCRIT chamber to symmetrize the electric ground potential aﬀecting the potential curve inside theelectrodes.

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In 2020, we tested accelerators RTM and SR2 if they bear for long term experiment for 24 hours. Currently, we are adjusting theSR2 accelerator and ion source ERIS to be ready for the real electron scattering measurement of unstable nuclei.

Members
Team Leader
Masanori WAKASUGI
Research/Technical Scientists
Masamitsu WATANABE (Senior Research Scientist)

Tetsuya OHNISHI (Senior Technical Scientist)

Expert Technician
Takeshi MAIE
Junior Research Associate
Hikari WAUKE
Research Consultants
Takashi EMOTO
Masahiro HARA

Toshitada HORI (Hiroshima Univ.)
Shinichi ICHIKAWA

Visiting Scientists
Akitomo ENOKIZONO (Rikkyo Univ.)
Yuki HONDA (Tohoku Univ.)

Toshimi SUDA (Tohoku Univ.)
Shuo WANG (Shandong Univ. (Weihai)

Student Trainees
Taihei AOYAGI (Tohoku Univ.)
Taiga GOKE (Tohoku Univ.)
Kazushi ISHIZAKI (Tohoku Univ.)

Clement V. LEGRIS (Tohoku Univ.)
Daisuke TAKI (Tohoku Univ.)

List of Publications & Presentations
Publications[Original Papers]
T. Suda, “Electron scattering for exotic nuclei,” J. Phys. 1643, 012159 (2020).
H. Kurasawa, T. Suda, and T. Suzuki, “The mean square radius of the neutron distribution and the skin thickness derived from electron
scattering,” Prog. Theor. Exp. Phys. 2021, 013D02 (2021).

Presentations[International Conferences/Workshops]
H. Wauke (oral), A. Enokizono, T. Suda, T. Tamae, K. Tsukada, T. Ohnishi, M. Wakasugi, and M. Watanabe, “Study of internal structureof unstable nuclei by electron scattering,” International School for Strangeness Nuclear Physics 2020, KEK, Tsukuba, Japan, December
3–5, 2020.

[Domestic Conferences/Workshops]
須田利美 (申請代表者), 「シンポジウム: 軽中重核の電弱励起・崩壊と宇宙物理」, 日本物理学会 2020 年秋季大会, オンライン, 2020
年 9 月 14–17 日.
和宇慶ひかり (口頭発表), 石崎一志, 榎園昭智, 大西哲哉, 栗田和好, Clement Legris, 郷家大雅, 須田利美, 高木周, 瀧大祐 玉江忠明,
塚田 暁, 本多佑記, 若杉昌徳, 渡邊正満, 「電子散乱による核内中性子分布半径測定のための前方検出器の開発」, 日本物理学会
2020 年秋季大会, オンライン, 2020 年 9 月 14–17 日.
須田利美 (招待講演), “Electron scattering for structure studies of proton and exotic nuclei,” 筑波大学原子核理論セミナー, 2020 年 10月 23 日.
須田利美 (招待講演), 「陽子のサイズがおかしい？」, 埼玉大学原子核グループセミナー, 埼玉県さいたま市 (埼玉大学), 2021 年 2
月 16 日.
須田利美 (招待講演), 「陽子半径」, 日本のスピン物理学の展望, 島根県松江市, 2021 年 2 月 23–24 日.

Outreach Activities
須田利美 (特別講義), 「陽子のサイズがおかしい？」, 非常勤講師 (対象: 理系６クラス, 講義３コマ), 埼玉県熊谷市 (埼玉県熊谷高校), 2020 年 12 月 15 日.
須田利美 (集中講義), 「電子散乱による原子核研究」, 埼玉県さいたま市 (埼玉大学理学部物理), 2021 年 2 月 15–17 日.

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Research Facility Development Division
Research Instruments Group
1. Abstract

The Research Instruments Group is the driving force at RI Beam Factory (RIBF) for continuous enhancement of activities andcompetitiveness of experimental research. Consisting of four teams, we are in charge of the operation, maintenance, and improvementof the core research instruments at RIBF, such as the BigRIPS in-flight RI separator, ZeroDegree spectrometer and SAMURAI spectrometer, and the related infrastructure and equipment. We are also in charge of the production and delivery of RI beams using the
BigRIPS separator. The group also conducts related experimental research as well as R&D studies on the research instruments.

2. Major Research Subjects

Design, construction, operation, maintenance, and improvement of the core research instruments at RIBF and related R&D studies.
Experimental studies on exotic nuclei.

3. Summary of Research Activity

The current research subjects are summarized as follows:(1) Production and delivery of RI beams and related research(2) Design, construction, operation, maintenance, and improvement of the core research instruments at RIBF and their related
infrastructure and equipment(3) R&D studies on the core research instruments and their related equipment at RIBF
(4) Experimental research on exotic nuclei using the core research instruments at RIBF

Members
Director
Tomohiro UESAKA
Contract Researcher
Toshiyuki KUBO
Junior Research Associate
Rieko TSUNODA
Senior Visiting Scientist
Toshio KOBAYASHI (Tohoku Univ.)
Student Trainees
Fumitaka ENDO (Tohoku Univ.)
Kosuke ICHIMURA (Tohoku Univ.)

Keisuke SAKUMA (Tohoku Univ.)- 277 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Research Instruments GroupBigRIPS Team
1. Abstract

This team is in charge of design, construction, development and operation of BigRIPS in-flight separator and its related research
instruments at RI beam factory (RIBF). They are employed not only for the production of RI beams but also the experimental studies
using RI beams.

2. Major Research Subjects

Design, construction, development and operation of BigRIPS in-flight separator, RI-beam transport lines, and their related research
instruments.

3. Summary of Research Activity

This team is in charge of design, construction, development and operation of BigRIPS in-flight separator, RI-beam transport lines,
and their related research instruments such as ZeroDegree spectrometer at RI beam factory (RIBF). They are employed not only forthe production of RI beams but also various kinds of experimental studies using RI beams. The research subjects may be summarized
as follows:(1) General studies on RI-beam production using in-flight scheme.
(2) Studies on ion-optics of in-flight separators, including particle identification of RI beams.
(3) Simulation and optimization of RI-beam production.
(4) Development of beam-line detectors and their data acquisition system.
(5) Experimental studies on production reactions and unstable nuclei.
(6) Experimental studies of the limits of nuclear binding.
(7) Development of superconducting magnets and their helium cryogenic systems.
(8) Development of a high-power production target system.
(9) Development of a high-power beam dump system.
(10) Development of a remote maintenance and remote handling systems.
(11) Operation, maintenance and improvement of BigRIPS separator system, RI-beam transport lines, and their related research
instruments such as ZeroDegree spectrometer and so on.
(12) Experimental research using RI beams.

Members
Team Leader
Koichi YOSHIDA
Research/Technical Scientists
Yoshiyuki YANAGISAWA (Senior Research Scientist)
Naohito INABE (Senior Technical Scientist)
Kensuke KUSAKA (Senior Technical Scientist)
Masao OHTAKE (Senior Technical Scientist)

Naoki FUKUDA (Technical Scientist)
Yohei SHIMIZU (Technical Scientist)
Hiroshi SUZUKI (Technical Scientist)
Hiroyuki TAKEDA (Technical Scientist)

Postdoctoral Researcher
Masahiro YOSHIMOTO
Visiting Scientists
Deuk Soon AHN (Korea Basic Sci. Inst.)
Alan Matthew AMTHOR (Bucknell Univ.)
Daniel P. BAZIN (Michigan State Univ.)
Alfredo ESTRADE VAZ (Central Michigan Univ.)
Michael FAMIANO (Western Michigan State Univ.)
Hans GEISSEL (GSI)
Tuomas Arne Santeri GRAHN (Univ. of Jyvaskyla)
Kazuo IEKI (Rikkyo Univ.)

Naohito IWASA (Tohoku Univ.)
Yutaka MIZOI (Univ. of Electro-Commun.)
Sadao MOMOTA (Kochi Univ. Tech.)David MORRISSEY (Michigan State Univ.)
Mauricio PORTILLO (Michigan State Univ.)
Bradley M. SHERRILL (Michigan State Univ.)
Oleg TARASOV (Michigan State Univ.)

Student Trainee
Shunki ISHIKAWA (Tohoku Univ.)- 278 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

List of Publications & Presentations
Publications[Original Papers]
V. Vaquero, A. Jungclaus, T. Aumann, J. Tscheuschner, E. V. Litvinova, J. A. Tostevin, H. Baba, D. S. Ahn, R. Avigo, K. Boretzky,
A. Bracco, C. Caesar, F. Camera, S. Chen, V. Derya, P. Doornenbal, J. Endres, N. Fukuda, U. Garg, A. Giaz, M. N. Harakeh, M. Heil,
A. Horvat, K. Ieki1, N. Imai, N. Inabe, N. Kalantar-Nayestanaki, N. Kobayashi, Y. Kondo, S. Koyama, T. Kubo, I. Martel, M. Matsushita, B. Million, T. Motobayashi, T. Nakamura, N. Nakatsuka, M. Nishimura, S. Nishimura, S. Ota, H. Otsu, T. Ozaki, M. Petri,
R. Reifarth, J. L. Rodrı́guez-Sánchez, D. Rossi, A. T. Saito, H. Sakurai, D. Savran, H. Scheit, F. Schindler, P. Schrock, D. Semmler, Y. Shiga, M. Shikata, Y. Shimizu, H. Simon, D. Steppenbeck, H. Suzuki, T. Sumikama, D. Symochko, I. Syndikus, H. Takeda,
S. Takeuchi, R. Taniuchi1, Y. Togano1, J. Tsubota, H. Wang, O. Wieland, K. Yoneda, J. Zenihiro, and A. Zilges, “Fragmentation of
single-particle strength around the doubly magic nucleus 132 Sn and the position of the 0 f5/2 proton-hole state in 131 In,” Phys. Rev. Lett.
124, 022501 (2020).
M. Tanaka, M. Takechi, A. Homma, M. Fukuda, D. Nishimura, T. Suzuki, Y. Tanaka, T. Moriguchi, D. S. Ahn, A. Aimaganbetov,
M. Amano, H. Arakawa, S. Bagchi, K. -H. Behr, N. Burtebayev, K. Chikaato, H. Du, S. Ebata, T. Fujii, N. Fukuda, H. Geissel, T. Hori,
W. Horiuchi, S. Hoshino, R. Igosawa, A. Ikeda, N. Inabe, K. Inomata, K. Itahashi, T. Izumikawa, D. Kamioka, N. Kanda, I. Kato,
I. Kenzhina, Z. Korkulu, Y. Kuk, K. Kusaka, K. Matsuta, M. Mihara, E. Miyata, D. Nagae, S. Nakamura, M. Nassurlla, K. Nishimuro,
K. Nishizuka, K. Ohnishi, M. Ohtake, T. Ohtsubo, S. Omika, H. J. Ong, A. Ozawa, A. Prochazka, H. Sakurai, C. Scheidenberger,
Y. Shimizu, T. Sugihara, T. Sumikama, H. Suzuki, S. Suzuki, H. Takeda, Y. K. Tanaka, I. Tanihata, T. Wada, K. Wakayama, S. Yagi,
T. Yamaguchi, R. Yanagihara, Y. Yanagisawa, K. Yoshida, and T. K. Zholdybayev, “Swelling of doubly magic 48 Ca core in Ca isotopes
beyond N = 28,” Phys. Rev. Lett. 124, 102501 (2020).
F. Boulay, G. S. Simpson, Y. Ichikawa, S. Kisyov, D. Bucurescu, A. Takamine, D. S. Ahn, K. Asahi, H. Baba, D. L. Balabanski,
T. Egami, T. Fujita, N. Fukuda, C. Funayama, T. Furukawa, G. Georgiev, A. Gladkov, M. Hass, K. Imamura, N. Inabe, Y. Ishibashi,
T. Kawaguchi, T. Kawamura, W. Kim, Y. Kobayashi, S. Kojima, A. Kusoglu, R. Lozeva, S. Momiyama, I. Mukul, M. Niikura, H. Nishibata, T. Nishizaka, A. Odahara, Y. Ohtomo, D. Ralet, T. Sato, Y. Shimizu, T. Sumikama, H. Suzuki, H. Takeda, L. C. Tao, Y. Togano,
D. Tominaga, H. Ueno, H. Yamazaki, X. F. Yang, and J. M. Daugas, “g Factor of the 99 Zr (7/2+ ) isomer: monopole evolution in the
shape-coexisting region,” Phys. Rev. Lett. 124, 112501 (2020).
T. L. Tang, T. Uesaka, S. Kawase, D. Beaumel, M. Dozono, T. Fujii, N. Fukuda, T. Fukunaga, A. Galindo-Uribarri, S. H. Hwang, N. Inabe,
D. Kameda, T. Kawahara, W. Kim, K. Kisamori, M. Kobayashi, T. Kubo, Y. Kubota, K. Kusaka, C. S. Lee, Y. Maeda, H. Matsubara,
S. Michimasa, H. Miya, T. Noro, A. Obertelli, K. Ogata, S. Ota, E. Padilla-Rodal, S. Sakaguchi, H. Sakai, M. Sasano, S. Shimoura,
S. S. Stepanyan, H. Suzuki, M. Takaki, H. Takeda, H. Tokieda, T. Wakasa, T. Wakui, K. Yako, Y. Yanagisawa, J. Yasuda, R. Yokoyama,
K. Yoshida, K. Yoshida, and J. Zenihiro, “How diﬀerent is the core of 25 F from 24 Og.s. ?” Phys. Rev. Lett. 124, 212502 (2020).
K. J. Cook, T. Nakamura, Y. Kondo, K. Hagino, K. Ogata, A. T. Saito, N. L. Achouri, T. Aumann, H. Baba, F. Delaunay, Q. Deshayes,
P. Doornenbal, N. Fukuda, J. Gibelin, J. W. Hwang, N. Inabe, T. Isobe, D. Kameda, D. Kanno, S. Kim, N. Kobayashi, T. Kobayashi,
T. Kubo, S. Leblond, J. Lee, F. M. Marqués, R. Minakata, T. Motobayashi, K. Muto, T. Murakami, D. Murai, T. Nakashima, N. Nakatsuka, A. Navin, S. Nishi, S. Ogoshi, N. A. Orr, H. Otsu, H. Sato, Y. Satou, Y. Shimizu, H. Suzuki, K. Takahashi, H. Takeda,
S. Takeuchi,1, R. Tanaka, Y. Togano, J. Tsubota, A. G. Tuﬀ, M. Vandebrouck, and K. Yoneda, “Halo structure of the neutron-dripline
nucleus 19 B,” Phys. Rev. Lett. 124, 212503 (2020).
S. Bagchi, R. Kanungo, Y. K. Tanaka, H. Geissel, P. Doornenbal, W. Horiuchi, G. Hagen, T. Suzuki, N. Tsunoda, D. S. Ahn, H. Baba,
K. Behr, F. Browne, S. Chen, M. L. Cortés, A. Estradé, N. Fukuda, M. Holl, K. Itahashi, N. Iwasa, G. R. Jansen, W. G. Jiang, S. Kaur,A. O. Macchiavelli, S. Y. Matsumoto, S. Momiyama, I. Murray, T. Nakamura1, S. J. Novario, H. J. Ong, T. Otsuka, T. Papenbrock,
S. Paschalis, A. Prochazka, C. Scheidenberger, P. Schrock, Y. Shimizu, D. Steppenbeck, H. Sakurai, D. Suzuki, H. Suzuki, M. Takechi,
H. Takeda, S. Takeuchi, R. Taniuchi, K. Wimmer, and K. Yoshida, “Two-neutron halo is unveiled in 29 F,” Phys. Rev. Lett. 124, 222504(2020).
S. Michimasa, M. Kobayashi, Y. Kiyokawa, S. Ota, R. Yokoyama, D. Nishimura, D. S. Ahn, H. Baba, G. P. A. Berg, M. Dozono,
N. Fukuda, T. Furuno, E. Ideguchi, N. Inabe, T. Kawabata, S. Kawase, K. Kisamori, K. Kobayashi, T. Kubo, Y. Kubota, C. S. Lee1,
M. Matsushita, H. Miya, A. Mizukami, H. Nagakura, H. Oikawa, H. Sakai, Y. Shimizu, A. Stolz, H. Suzuki, M. Takaki, H. Takeda,
S. Takeuchi, H. Tokieda, T. Uesaka, K. Yako, Y. Yamaguchi, Y. Yanagisawa, K. Yoshida, and S. Shimoura, “Mapping of a new
deformation region around 62 Ti,” Phys. Rev. Lett. 125, 122501 (2020).
G. Jhang, J. Estee, J. Barney, G. Cerizza, M. Kaneko, J. W. Lee, W. G. Lynch, T. Isobe, M. Kurata-Nishimura, T. Murakami, C. Y. Tsang,
M. B. Tsang, R. Wang, D. S. Ahn, L. Atar, T. Aumann, H. Baba, K. Boretzky, J. Brzychczyk, N. Chiga, N. Fukuda, I. Gasparic,
B. Hong, A. Horvat, K. Ieki, N. Inabe, Y. J. Kim, T. Kobayashi, Y. Kondo, P. Lasko, H. S. Lee, Y. Leifels, J. Łukasik, J. Manfredi,A. B. McIntosh, P. Morfouace, T. Nakamura, N. Nakatsuka, S. Nishimura, R. Olsen, H. Otsu, P. Pawłowski, K. Pelczar, D. Rossi,
H. Sakurai, C. Santamaria, H. Sato, H. Scheit, R. Shane, Y. Shimizu, H. Simon, A. Snoch, A. Sochocka, Z. Sosin, T. Sumikama,
H. Suzuki, D. Suzuki, H. Takeda, S. Tangwancharoen, H. Toernqvist, Y. Togano, Z. G. Xiao, S. J. Yennello, J. Yurkon, Y. Zhang, theSπRIT Collaboration, M. Colonna, D. Cozma, P. Danielewicz, H. Elfner, N. Ikeno, C. M. Koo, J. Mohs, D. Oliinychenko, A. Ono, J. Su,
Y. J. Wang, H. Wolter, J. Xu, Y. -X. Zhang, Z. Zhang, the TMEP collaboration, “Symmetry energy investigation with pion production
from Sn + Sn systems,” Phys. Lett. B 813, 136016 (2020).
J. Wu, S. Nishimura, P. Möller, M. R. Mumpower, R. Lozeva, C. B. Moon, A. Odahara, H. Baba, F. Browne, R. Daido, P. Doornenbal, Y. F. Fang, M. Haroon, T. Isobe, H. S. Jung, G. Lorusso, B. Moon, Z. Patel, S. Rice, H. Sakurai, Y. Shimizu, L. Sinclair,
P. -A. Söderström, T. Sumikama, H. Watanabe, Z. Y. Xu, A. Yagi, R. Yokoyama, D. S. Ahn, F. L. Bello Garrote, J. M. Daugas, F. Didierjean, N. Fukuda, N. Inabe, T. Ishigaki, D. Kameda, I. Kojouharov, T. Komatsubara, T. Kubo, N. Kurz, K. Y. Kwon, S. Morimoto,D. Murai, H. Nishibata, H. Schaﬀner, T. M. Sprouse, H. Suzuki, H. Takeda, M. Tanaka, K. Tshoo, and Y. Wakabayashi, “β-Decay
half-lives of 55 neutron-rich isotopes beyond the N = 82 shell gap,” Phys. Rev. C 101, 042801(R) (2020).

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J. Ha, T. Sumikama, F. Browne, N. Hinohara, A. M. Bruce, S. Choi, I. Nishizuka, S. Nishimura, P. Doornenbal, G. Lorusso,
P. -A. Söderström, H. Watanabe, R. Daido, Z. Patel, S. Rice, L. Sinclair, J. Wu, Z. Y. Xu, A. Yagi, H. Baba, N. Chiga, R. Carrol,
F. Didierjean, Y. Fang, N. Fukuda, G. Gey, E. Ideguchi, N. Inabe, T. Isobe, D. Kameda, I. Kojouharov, N. Kurz, T. Kubo, S. Lalkovski,
Z. Li, R. Lozeva, H. Nishibata, A. Odahara, Zs. Podolyák, P. H. Regan, O. J. Roberts, H. Sakurai, H. Schaﬀner, G. S. Simpson,
H. Suzuki, H. Takeda, M. Tanaka, J. Taprogge, V. Werner, and O. Wieland, “Shape evolution of neutron-rich 106, 108, 110 Mo isotopes inthe triaxial degree of freedom,” Phys. Rev. C 101, 044311 (2020).
X. H. Sun, H. Wang, H. Otsu, H. Sakurai, D. S. Ahn, M. Aikawa, N. Fukuda, T. Isobe, S. Kawakami, S. Koyama, T. Kubo, S. Kubono,
G. Lorusso, Y. Maeda, A. Makinaga, S. Momiyama, K. Nakano, S. Nakayama, M. Niikura, Y. Shiga, P. -A. Söderström, H. Suzuki,
H. Takeda, S. Takeuchi, R. Taniuchi, Ya. Watanabe, Yu. Watanabe, H. Yamasaki, X. F. Yang, Y. L. Ye, and K. Yoshida, “Spallationand fragmentation cross sections for 168 MeV/nucleon 136 Xe ions on proton, deuteron, and carbon targets,” Phys. Rev. C 101, 064623(2020).
J. Park, R. Krücken, A. Blazhev, D. Lubos, R. Gernhäuser, M. Lewitowicz, S. Nishimura, D. S. Ahn, H. Baba, B. Blank, P. Boutachkov,
F. Browne, I. Čeliković, G. de France, P. Doornenbal, T. Faestermann, Y. Fang, N. Fukuda, J. Giovinazzo, N. Goel, M. Górska,
H. Grawe, S. Ilieva, N. Inabe, T. Isobe, A. Jungclaus, D. Kameda, G. D. Kim, Y. -K. Kim, I. Kojouharov, T. Kubo, N. Kurz, Y. K. Kwon,
G. Lorusso, K. Moschner, D. Murai, I. Nishizuka, Z. Pate, M. M. Rajabali, S. Rice, H. Sakurai, H. Schaﬀner, Y. Shimizu, L. Sinclair,
P. -A. Söderström, and K. Steiger, “Spectroscopy of 99 Cd and 101 In from β decays of 99 In and 101 Sn,” Phys. Rev. C 102, 014304 (2020).
J. J. Liu, J. Lee, H. Watanabe, S. Nishimura, G. X. Zhang, J. Wu, P. M. Walker, P. H. Regan, P. -A. Söderström, H. Kanaoka, Z. Korkulu,
P. S. Lee, A. Yagi, A. C. Dai, F. R. Xu, D. S. Ahn, T. Alharbi, H. Baba, F. Browne, A. M. Bruce, R. J. Carroll, K. Y. Chae, Zs. Dombradi,
P. Doornenbal, A. Estrade1, N. Fukuda, C. Griﬃn, E. Ideguchi, N. Inabe, T. Isobe, S. Kanaya, I. Kojouharov, F. G. Kondev, T. Kubo,
S. Kubono, N. Kurz, I. Kuti, S. Lalkovski, G. J. Lane, C. S. Lee, E. J. Lee, G. Lorusso, G. Lotay, C. -B. Moon, I. Nishizuka, C. R. Nita,
A. Odahara, Z. Patel, V. H. Phong, Zs. Podolyák, O. J. Roberts, H. Sakurai, H. Schaﬀner, C. M. Shand, Y. Shimizu, T. Sumikama,
H. Suzuki, H. Takeda, S. Terashima, Zs. Vajta, J. J. Valiente-Dobón, and Z. Y. Xu, “Isomeric and β-decay spectroscopy of 173, 174 Ho,”
Phys. Rev. C 102, 024301 (2020).
A. Jungclaus, J. M. Keatings, G. S. Simpson, H. Naı̈dja, A. Gargano, S. Nishimura, P. Doornenbal, G. Gey, G. Lorusso, P. -A. Söderström,
T. Sumikama, J. Taprogge, Z. Y. Xu, H. Baba, F. Browne, N. Fukuda, N. Inabe, T. Isobe, H. S. Jung, D. Kameda, G. D. Kim,
Y. -K. Kim, I. Kojouharov, T. Kubo, N. Kurz, Y. K. Kwon, Z. Li1, H. Sakurai, H. Schaﬀner, Y. Shimizu, H. Suzuki, H. Takeda,
Z. Vajta1, H. Watanabe, J. Wu1, A. Yagi, K. Yoshinaga, S. Bönig, J. -M. Daugas, R. Gernhäuser, S. Ilieva, T. Kröll, A. MontanerPiza, K. Moschner, D. Mücher, H. Nishibata, A. Odahara1, R. Orlandi, M. Scheck, K. Steiger, and A. Wendt, “Evolution of proton
single-particle states in neutron-rich Sb isotopes beyond N = 82,” Phys. Rev. C 102, 034324 (2020).
H. Suzuki, K. Yoshida, N. Fukuda, H. Takeda, Y. Shimizu, D. S. Ahn, T. Sumikama, N. Inabe, T. Komatsubara, H. Sato, Z. Korkulu,
K. Kusaka, Y. Yanagisawa, M. Ohtake, H. Ueno, T. Kubo, S. Michimasa, N. Kitamura, K. Kawata, N. Imai, O. B. Tarasov, D. Bazin,
J. Nolen, and W. F. Henning, “Experimental studies of the two-step scheme with an intense radioactive 132 Sn beam for next-generation
production of very neutron-rich nuclei,” Phys. Rev. C 102, 064615 (2020).
J. Giovinazzo, T. Goigoux, B. Blank, P. Ascher, M. Gerbauxa, S. Grévy, T. Kurtukian-Nieto, C. Magron, P. Doornenbal, N. Fukuda,
N. Inabe, G. G. Kiss, T. Kubo, S. Kubono, S. Nishimura, H. Sakurai, Y. Shimizu, C. Sidong, P. -A. Söderström, T. Sumikama,
H. Suzuki, H. Takeda, P. Vi, J. Wu, D. S. Ahn, J. Agramunt, A. Algora, V. Guadilla, A. Montaner-Piza, A. I. Morales, S. E. A. Orrigo,
B. Rubio, Y. Fujita, M. Tanaka, W. Gelletly, P. Aguilera, F. Molina, F. Diel, D. Lubos, G. de Angelis, D. Napoli, C. Borcea, A. Boso,
R. B. Cakirli, E. Ganioglu, J. Chiba, D. Nishimura, H. Oikawa, Y. Takei, S. Yagi, K. Wimmer, G. de France, S. Go, and B. A. Brown,“Two-proton radioactivity: the interesting case of 67 Kr and further studies,” Acta Physica Polonica B 51, 577 (2020).
A. Vitéz-Sveiczer, A. Algora, A. I. Morales, B. Rubio, G. G. Kiss, G. de Angelis, F. Recchia, S. Nishimura, J. Agramunt, V. Guadilla,
A. Montaner-Pizá, S. E. A. Orrigo, A. Horváth, D. Napoli, S. Lenzi, A. Boso, V. H. Phong, J. Wu, P. -A. Söderström, T. Sumikama,
H. Suzuki, H. Takeda, D. S. Ahn, H. Baba, P. Doornenbal, N. Fukuda, N. Inabe, T. Isobe, T. Kubo, S. Kubono, H. Sakurai, Y. Shimizu,
S. Chen, B. Blank, P. Ascher, M. Gerbaux, T. Goigoux, J. Giovinazzo, S. Grévy, T. Kurtukián Nieto, C. Magron, W. Gelletly,
Zs. Dombrádi, Y. Fujita, M. Tanaka, P. Aguilera, F. Molina, J. Eberth, F. Diell, D. Lubos, C. Borcea, E. Ganioglu, D. Nishimura,
H. Oikawa, Y. Takei, S. Yagi, W. Korten, G. de France, P. Davies, J. Liu, J. Lee, T. Lokotko, I. Kojouharov, N. Kurz, and H. Shaﬀner,“Studying the exotic decay 70 Kr → 70 Br,” Acta Physica Polonica B 51, 587 (2020).

[Proceedings]

K. Kusaka, “Long term operation of the superconducting triplet quadrupoles with cryocoolers,” J. Phys. Conf. Ser. 1559, 012071 (2020).

Presentations[International Conferences/Workshops]
N. Fukuda, “Present status of the BigRIPS separator and recent development of RI-beam production,” RIBF Users Meeting 2020, Virtual
Conference (Zoom), September 09, 2020.
H. Takeda, “RI beam production in RIBF from the perspective of nuclear reaction,” JSPS/NRF/NSFC A3 Foresight Program “Nuclear
physics in the 21st century” Joint Annual Meeting, Online Conference, November 18, 2020.
N. Fukuda (invited), “Particle identification at BigRIPS separator,” Workshop on Techniques and Detectors for Heavy-ion Charge-State
Identification in High-acceptance Spectrometers, Virtual Conference (Zoom), December 16–17, 2020.

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Research Facility Development Division
Research Instruments GroupSAMURAI Team
1. Abstract

In collaboration with research groups in and outside RIKEN, the team designs, develops and constructs the SAMURAI spectrometer and relevant equipment that are and will be used for reaction experiments using RI beams at RI Beam Factory. The SAMURAI
spectrometer consists of a large superconducting dipole magnet and a variety of detectors to measure charged particles and neutrons.
After the commissioning experiment in March 2012, the team prepared and conducted, in collaboration with researchers in individual experimental groups, the first series of experiments with SAMURAI in May 2012. Then, several numbers of experiments were
well performed until now utilizing the property of SAMURAI. The team also provides a basis for research activities by, for example,
organizing collaboration workshops by researchers who are interested in studies or plan to perform experiments with the SAMURAI
spectrometer.

2. Major Research Subjects

Design, operation, maintenance and improvement of the SAMURAI spectrometer and its related research instruments. Supportand management for SAMURAI-based research programs. Generate future plans for next generation instruments for nuclear reaction
studies.

3. Summary of Research Activity

The current research subjects are summarized as follows:(1) Operation, maintenance and improvement of a large superconducting dipole magnet that is the main component of the SAMURAI spectrometer.
(2) Design, development and construction of various detectors that are used for nuclear reaction experiments using the SAMURAI
spectrometer.
(3) Preparation for planning experiments using SAMURAI spectrometer.
(4) Maintenance and improvement of the SAMURAI beam line.
(5) Formation of a collaboration platform called SAMURAI collaboration.
(6) Preparation for next generation spectrometer for nuclear reaction studies.

Members
Team Leader
Hideaki OTSU
Research & Development Scientist
Mizuki NISHIMURA
Junior Research Associate
Takato TOMAI

List of Publications & Presentations
Publications[Original Papers]
M. M. Juhasz, Z. Elekes, D. Sohler, et al., “First spectroscopic study of 51 Ar by the (p, 2p) reaction,” Phys. Lett. B 814, 136108 (2021).
Y. L. Sun, T. Nakamura, Y. Kondo, et al., “Three-body breakup of 6 He and its halo structure,” Phys. Lett. B 814, 136072 (2021).
Z. H. Yang, Y. Kubota, A. Corsi, et al., “Quasifree neutron knockout reaction reveals a small s-orbital component in the Borromean
nucleus 17 B,” Phys. Rev. Lett. 126, 082501 (2021).
M. L. Cortes, W. Rodriguez, P. Doornenbal, et al., “N = 32 shell closure below calcium: Low-lying structure of 50 Ar,” Phys. Rev. C 102,
064320 (2020).
A. Frotscher, M. Gomez-Ramos, A. Obertelli, et al., “Sequential nature of (p, 3p) two-proton knockout from neutron-rich nuclei,” Phys.
Rev. Lett. 125, 012501 (2020).
Y. Kubota, A. Corsi, G. Authelet, et al., “Surface localization of the dineutron in 11 Li,” Phys. Rev. Lett. 125, 252501 (2020).
T. Lokotko, S. Leblond, J. Lee, et al., “Shell structure of the neutron-rich isotopes 69, 71, 73 Co,” Phys. Rev. C 101, 034314 (2020).
A. Revel, O. Sorlin, F. M. Marqués, et al., “Extending the southern shore of the island of inversion to 28 F,” Phys. Rev. Lett. 124, 152502(2020).
K. J. Cook, T. Nakamura, Y. Kondo, et al., “Halo structure of the neutron-dripline nucleus 19 B,” Phys. Rev. Lett. 124, 212503 (2020).
M. L. Cortes, W. Rodriguez, P. Doornenbal, et al., “Shell evolution of N = 40 isotones towards 60 Ca: First spectroscopy of 62 Ti,” Phys.
Lett. B 800, 135071 (2020).

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Y. L. Sun, A. Obertelli, P. Doornenbal, et al., “Restoration of the natural E(1/2+1 )-E(3/2+1 ) energy splitting in odd-K isotopes towards
N = 40,” Phys. Lett. B 802, 135215 (2020).

Presentations[International Conferences/Workshops]
Y. Togano, “Current status and future perspective of SAMURAI at RIBF,” RIBF Users Meeting 2020, Online, September 8–10, 2020.
T. Nakamura, “Exploring the extreme of nuclear landscape using radioactive beams,” IIT Guwahati and Tokyo Tech-2nd Joint Workshop
on Topics in Condensed Matter Physics, High-Energy Physics, Cosmology & Astrophysics, Online, December 15, 17–18, 2020.
T. Nakamura, “Dineutron correlation in neutron-rich nuclei,” Tokyo Tech-Uppsala Univ. Joint Symposium, Online, November 16–17,
2020.
SAMURAI International Collaboration Workshop 2020, Online, September 1–4, 2020 (https://indico2.riken.jp/e/
SAMURAIICW2020).

[Domestic Conferences/Workshops]
中村隆司, 「ダイニュートロンから多中性子クラスターへ」, 日本物学会第 76 回年次大会 シンポジウム「量子クラスターで読み解
く物質の階層構造」, , オンライン開催, 2021 年 3 月 12–15 日.
吉留勇起, 「25 O の不変質量核分光」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
齊藤敦美, 「クーロンおよび核力分解による 6 He の 3 体崩壊」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
海老名直樹, 「陽子準弾性散乱による多中性子クラスター探索実験のための反跳陽子検出器の開発」, 日本物学会第 76 回年次大会,
オンライン開催, 2021 年 3 月 12–15 日.
高橋康平, 「中性子過剰核における近距離相関した陽子中性子対探索実験に向けた検出器系の開発」, 日本物学会第 76 回年次大会,
オンライン開催, 2021 年 3 月 12–15 日.
栂野泰宏, 「52 Ca の電気双極子応答」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
西村未生, 「中性子過剰核の陽子準自由散乱反応測定に向けた CsI(Na) シンチレータの性能評価」, 日本物学会第 76 回年次大会, オ
ンライン開催, 2021 年 3 月 12–15 日.
高橋康平, 「ダイニュートロン相関探索に向けた高分解能中性子検出器 HIME の開発」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020 年 9 月 14–17 日.
王赫, “Development of the detector systems for the recoil protons from the quasi-free scattering of neutron-rich nuclei at SAMURAI at
RIBF-I,” 日本物理学会 2020 年秋季大会, オンライン開催, 2020 年 9 月 14–17 日.
海老名直樹, 「中性子過剰核の準弾性散乱散乱測定用陽子検出器の開発 II」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020
年 9 月 14–17 日.
齊藤敦美, 「中性子過剰ヘリウム同位体のクーロンおよび核力分解反応」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020 年
9 月 14–17 日.
齊藤敦美, “Coulomb and nuclear breakup of halo nuclei 6 He,” 第 5 回クラスター階層領域研究会, オンライン, 2020 年 9 月 24–25 日.
大津秀暁, “Cluster structure study on neutron rich nuclei,” 第 5 回クラスター階層領域研究会, オンライン, 2020 年 9 月 24–25 日.
堀川晃太 (poster), 「中性子過剰核における短距離相関実験のための反跳陽子検出器の開発」, 日本物学会第 76 回年次大会, オンラ
イン開催, 2021 年 3 月 12–15 日.
松井智輝 (poster), 「多中性子クラスター探索実験のための陽子全エネルギー検出器の開発」, 日本物学会第 76 回年次大会, オンラ
イン開催, 2021 年 3 月 12–15 日.

[Seminars]
T. Nakamura, “Dineutron correlation of exotic nuclei along the neutron drip line,” Seminar at Hokkaido University, November 25, 2020.

AwardsA. Saito, A3F-CNSSS20 Award for Young Scientist, 2020.

Doctor Thesis
Atsumi Saito, “Coulomb and nuclear breakup of the Borromean nucleus 6 He,” Tokyo Institute of Technology, February 2021.

Master Thesis
吉留勇起, 「25 O の不変質量核分光」, 東京工業大学理学院.
安田聖, 「ダイニュートロン相関探索実験のための高精細中性子検出器 HIME の開発」, 東京工業大学理学院.
西村未生, 「質量欠損法による中性子過剰核の構造研究に向けた CsI(Na) シンチレータのエネルギー分解能測定」, 立教大学理学研
究科.

Bachelor Thesis
堀川晃太, 「中性子過剰核における短距離相関探索実験のための反跳陽子検出器の開発」, 東京工業大学理学院物理学系.
松井智輝, 「多中性子クラスター探索実験のための陽子全エネルギー検出器の開発」, 東京工業大学理学院物理学系.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Research Instruments Group
Computing and Network Team
1. Abstract

This team is in charge of development, management and operation of the computing and network environment, mail and information servers and data acquisition system and management of the information security of the RIKEN Nishina Center.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

Development, management and operation of the general computing servers
Development, management and operation of the mail and information servers
Development, management and operation of the data acquisition system
Development, management and operation of the network environment
Management of the information security

3. Summary of Research Activity

This team is in charge of development, management and operation of the computing and network environment, mail and information servers and data acquisition system and management of the information security. The details are described elsewhere in thisprogress report.
(1) Development, management and operation of the general computing servers
We are operating Linux/Unix NIS/NFS cluster system for the data analysis of the experiments and general computing. This
cluster system consists of eight computing servers with 64 CPU cores and totally 200 TB RAID of highly-reliable Fibre-channelinterconnection. There are approximately 300 active user accounts on this cluster system (a total of about 800 accounts were registeredso far). We are adopting the latest version of the Scientific Linux (X86 64) as the primary operating system, which is widely used in
the accelerator research facilities, nuclear physics and high-energy physics communities in the world.
(2) Development, management and operation of the mail and information servers
We are operating RIBF.RIKEN.JP server as a mail/NFS/NIS server. This server is a core server of RIBF Linux cluster system.
Postfix has been used for mail transport software and dovecot has been used for imap and pop services. These software packages
enable secure and reliable mail delivery. Sophos Email Security and Control (PMX) installed on the mail front-end servers whichtags spam mails and isolates virus-infected mails. The probability to identify the spam is approximately 95–99%. We are operating
several information servers such as Web servers, Integrated Digital Conference (INDICO) server, Wiki servers, Groupware servers,
Wowza streaming servers. We have been operating approximately 70 units of wireless LAN access points in RNC. Almost the entire
radiation-controlled area of the East Area of RIKEN Wako campus is covered by wireless LAN for the convenience of experiments
and daily work.
(3) Development, management and operation of the data acquisition system
We have developed the standard data-acquisition system named as RIBFDAQ. This system can process up to 40 MB/s data. By
using crate-parallel readout from front-end systems such as CAMAC and VME, the dead time could be minimized. To synchronize theindependent DAQ systems, the time stamping system has been developed. The resolution and depth of the time stamp are 10 ns and48 bits, respectively. This time stamping system is very useful for beta decay experiments such as EURICA, BRIKEN and VANDLE
projects. One of the important tasks is the DAQ coupling, because detector systems with dedicated DAQ systems are transported to
RIBF from foreign facilities. In case of SAMURAI Silicon (NSCL/TUM/WUSTL), the readout system is integrated into RIBFDAQ.
The projects of MUST2 (GANIL), MINOS (CEA Saclay), NeuLAND (GSI) and TRB3 (TUM) cases, data from their DAQ systems
are transferred to RIBFDAQ and merged online. For SPIRIT (RIKEN/GANIL/CEA Saclay/NSCL), RIBFDAQ is controlled fromthe NARVAL-GET system that is a large-scale signal processing system for the time projection chamber. EURICA (GSI), BRIKEN(GSI/Univ. Liverpool/IFIC), VANDLE (UTK) and OTPC (U. Warsaw) projects, we adopt the time stamping system to apply individual
trigger for each detector system. In this case, data are merged in oﬄine. In addition, we are developing intelligent circuits based on
FPGA. General Trigger Operator (GTO) is an intelligent triggering NIM module. Functions of “common trigger management,” “gateand delay generator,” “scaler” are successfully implemented. The trigger system in BigRIPS DAQ is managed by 5 GTO modules. To
improve the data readout speed of VME system, we have successfully developed the MPV system which is a parallel readout extensionof the VME system. Data readout sequence is completely parallelized that helps to improve the DAQ deadtime. Thanks to the MPV
system, now the DAQ system in RIBF is 10 times faster than in 2007. Toward to the next generation DAQ system, I have started todevelop a real-time data processing unit based on Xilinx RFSoC that includes FPGA and 4 GHz FADC.
(4) Development, management and operation of the network environment
We have been managing the network environment collaborating with Information Systems Division in RIKEN. All the Ethernet
ports of the information wall sockets are capable of the Gigabit Ethernet connection (10/100/1000 BT). In addition, some 10 Gbps
networks port has been introduced to RIBF experimental area. Approximately 100 units of wireless LAN access points have been
installed to cover the almost entire area of Nishina Center.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)(5) Management of the information security
It is essential to take proper information security measures for information assets. We are managing the information security of
Nishina Center collaborating with Information Systems Division in RIKEN.

Members
Team Leader
Hidetada BABA
Research/Technical Scientist
Yasushi WATANABE (Senior Research Scientist)
Special Temporary Research Scientist
Takashi ICHIHARA
Visiting Scientist
Shoichiro KAWASE (Kyushu Univ.)
Student Trainee
Shoko TAKESHIGE (Rikkyo Univ.)

List of Publications & Presentations
Presentations[International Conferences/Workshops]
H.Baba (poster) et al., “MPV—Parallel Readout Architecture for the VME data acquisition system,” 22nd IEEE Real Time Conference,
Virtual, October 12–23, 2020.

[Domestic Conferences/Workshops]
武重祥子 (oral), 馬場秀忠他, 「RFSoC を用いた高帯域波形処理システムの開発」, 日本物理学会第 73 回年次大会, 千葉県野田市 (東京理科大学), 2018 年 3 月 22–25 日.
馬場秀忠 (oral), 「並列化 VME の紹介」, 計測システム研究会 2020@J-PARC, 茨城県東海村 (KEK 東海キャンパス) & オンライン
開催, 2020 年 11 月 26–27 日.

Awards
市原卓, 2020 年 JPCERT/CC 感謝, JPCERT コーディネーションセンター, 2020 年 8 月 19 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Research Facility Development Division
Research Instruments Group
Detector Team
1. Abstract

This team is in charge of development, fabrication, and operation of various detectors used for nuclear physics experiments at
RIBF. Our current main mission is maintenance and improvement of detectors which are used at BigRIPS separator and its succeeding
beam lines for beam diagnosis and particle identification of RI beams. We are also engaged in R&D of new detectors that can be used
for higher-intensity RI beams. In addition, we are doing the R&D which uses the pelletron accelerator together with other groups.

2. Major Research Subjects

Development, fabrication, and operation of various detectors for nuclear physics experiments, including beam-line detectors which
are used for the production and delivery of RI beams (beam diagnosis and particle identification). R&D which uses the pelletron
accelerator.

3. Summary of Research Activity

The current research subjects are summarized as follows:(1) Maintenance and improvement of the beam-line detectors which are used at BigRIPS separator and its succeeding beam lines.
(2) Development of new beam-line detectors with radiation hardness and tolerance for higher counting rates.
(3) Management of the pelletron accelerator and R&D which uses the pelletron.

Members
Team Leader
Hiromi SATO
Research/Technical Scientist
Tokihiro IKEDA (Senior Research Scientist)
Research Consultant
Manabu HAMAGAKIVisiting Scientist
Takeshi KOIKE (Tohoku University)
Student Trainees
Yuka HIKIMA (Toho University)
Mitsumasa MORI (Toho University)

Keito SANGU (Toho University)

List of Publications & Presentations
Publications[Original Papers]
A. Revel, O. Sorlin, F. M. Marqués, Y. Kondo, J. Kahlbow, T. Nakamura, N. A. Orr, F. Nowacki, J. A. Tostevin, C. X. Yuan, N. L. Achouri,
H. Al Falou, L. Atar, T. Aumann, H. Baba, K. Boretzky, C. Caesar, D. Calvet, H. Chae, N. Chiga, A. Corsi, H. L. Crawford, F. Delaunay, A. Delbart, Q. Deshayes, Z. Dombrádi, C. A. Douma, Z. Elekes, P. Fallon, I. Gašparić, J. -M. Gheller, J. Gibelin, A. Gillibert,
M. N. Harakeh, W. He, A. Hirayama, C. R. Hoﬀman, M. Holl, A. Horvat, Á. Horváth, J. W. Hwang, T. Isobe, N. Kalantar-Nayestanaki,
S. Kawase, S. Kim, K. Kisamori, T. Kobayashi, D. Körper, S. Koyama, I. Kuti, V. Lapoux, S. Lindberg, S. Masuoka, J. Mayer, K. Miki,
T. Murakami, M. Najafi, K. Nakano, N. Nakatsuka, T. Nilsson, A. Obertelli, F. de Oliveira Santos, H. Otsu, T. Ozaki, V. Panin,
S. Paschalis, D. Rossi, A. T. Saito, T. Saito, M. Sasano, H. Sato, Y. Satou, H. Scheit, F. Schindler, P. Schrock, M. Shikata, Y. Shimizu,
H. Simon, D. Sohler, L. Stuhl, S. Takeuchi, M. Tanaka, M. Thoennessen, H. Törnqvist, Y. Togano, T. Tomai, J. Tscheuschner, J. Tsubota, T. Uesaka, Z. Yang, M. Yasuda, and K. Yoneda, “Extending the southern shore of the island of inversion to 28 F,” Phys. Rev. Lett.
124, 152502 (2020).
K. J. Cook, T. Nakamura, Y. Kondo, K. Hagino, K. Ogata, A. T. Saito, N. L. Achouri T. Aumann, H. Baba, F. Delaunay, Q. Deshayes,
P. Doornenbal N. Fukuda, J. Gibelin, J. W. Hwang, N. Inabe, T. Isobe, D. Kameda, D. Kanno, S. Kim, N. Kobayashi, T. Kobayashi,
T. Kubo, S. Leblond, J. Lee, F. M. Marqués, R. Minakata, T. Motobayashi, K. Muto, T. Murakami, D. Murai, T. Nakashima, N. Nakatsuka, A. Navin, S. Nishi, S. Ogoshi, N. A. Orr, H. Otsu, H. Sato, Y. Satou, Y. Shimizu, H. Suzuki, K. Takahashi, H. Takeda, S. Takeuchi,
R. Tanaka, Y. Togano, J. Tsubota, A. G. Tuﬀ, M. Vandebrouck, and K. Yoneda, “Halo structure of the neutron-dripline nucleus 19 B,”
Phys. Rev. Lett. 124, 212503 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

G. Jhang, J. Estee, J. Barney, G. Cerizza, M. Kaneko, J. W. Lee, W. G. Lynch, T. Isobe, M. Kurata-Nishimura, T. Murakami, C. Y. Tsang,
M. B. Tsang, R. Wang, D. S. Ahn, L. Atar, T. Aumann, H. Baba, K. Boretzky, J. Brzychczyk, N. Chiga, N. Fukuda, I. Gasparic,
B. Hong, A. Horvat, K. Ieki, N. Inabe, Y. J. Kim, T. Kobayashi, Y. Kondo, P. Lasko, H. S. Lee, Y. Leifels, J. Lukasik, J. Manfredi,A. B. McIntosh, P. Morfouace, T. Nakamura, N. Nakatsuka, S. Nishimura, R. Olsen, H. Otsu, P. Pawlowski, K. Pelczar, D. Rossi,
H. Sakurai, C. Santamaria, H. Sato, H. Scheit, R. Shane, Y. Shimizu, H. Simon, A. Snoch, A. Sochocka, Z. Sosin, T. Sumikama,
H. Suzuki, D. Suzuki, H. Takeda, S. Tangwancharoen, H. Toernqvist, Y. Togano, Z. G. Xiao, S. J. Yennello, J. Yurkon, Y. Zhang, theSπRIT Collaboration, M. Colonna, D. Cozma, P. Danielewicz, H. Elfner, N. Ikeno, C. M. Ko, J. Mohs, D. Oliinychenko, A. Ono,
J. Suae, Y. J. Wang, H. Wolter, J. Xu, Y. -X. Zhang, Z. Zhang, the TMEP collaboration, “Symmetry energy investigation with pion
production from Sn + Sn systems,” Phys. Lett. B 813, 136016 (2021).
Y. Kubota, A. Corsi, G. Authelet, H. Baba, C. Caesar, D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin,
A. Giganon, A. Gillibert, K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kikuchi, Y. Kiyokawa, M. Kobayashi,
N. Kobayashi, T. Kobayashi, Y. Kondo, Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marqués, T. Motobayashi, T. Miyazaki,
T. Nakamura, N. Nakatsuka, Y. Nishio, A. Obertelli, K. Ogata, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis,
E. C. Pollacco, S. Reichert, J. -Y. Roussé, A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata,Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama, Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, Z. H. Yang, J. Yasuda, K. Yoneda,
J. Zenihiro, and T. Uesaka, “Surface localization of the dineutron in 11 Li,” Phys. Rev. Lett. 125, 252501 (2020).
H. Suzuki, K. Yoshida, N. Fukuda, H. Takeda, Y. Shimizu, D. S. Ahn, T. Sumikama, N. Inabe, T. Komatsubara, H. Sato, Z. Korkulu,
K. Kusaka, Y. Yanagisawa, M. Ohtake, H. Ueno, T. Kubo, S. Michimasa, N. Kitamura, K. Kawata, N. Imai, O. B. Tarasov, D. Bazin,
J. Nolen, and W. F. Henning, “Experimental studies of the two-step scheme with an intense radioactive 132 Sn beam for next-generation
production of very neutron-rich nuclei,” Phys. Rev. C 102, 064615 (2020).
Z. H. Yang, Y. Kubota, A. Corsi, K. Yoshida, X. -X. Sun, J. G. Li, M. Kimura, N. Michel, K. Ogata, C. X. Yuan, Q. Yuan, G. Authelet,
H. Baba, C. Caesar, D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin, A. Giganon, A. Gillibert,
K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kiyokawa, M. Kobayashi, N. Kobayashi, T. Kobayashi, Y. Kondo,
Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marqués, T. Motobayashi, T. Miyazaki, T. Nakamura, N. Nakatsuka, Y. Nishio,
A. Obertelli, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis, E. C. Pollacco, S. Reichert, J. -Y. Roussé,A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata, Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama,
Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, F. R. Xu, J. Yasuda, K. Yoneda, J. Zenihiro, S. -G. Zhou, W. Zuo, and T. Uesaka, “Quasifree
neutron knockout reaction reveals a small s-orbital component in the Borromean nucleus 17 B,” Phys. Rev. Lett. 126, 082501 (2021).
T. Ikeda, “Applications of microbeams produced by tapered glass capillary optics,” Quantum Beam Sci. 4(2), 22 (2020).
S. Kawamura, T. Ikeda, and W. -G. Jin, “Transmission characteristic of ultraviolet-laser microbeam with tapered glass capillary optics,”
J. Phys. Soc. Jpn. 89, 055002 (2020).

Presentations[Domestic Conferences/Workshops]
高橋弘幸, 西村太樹, 菅原奏来, 延與紫世, 福田直樹, 原田知也, 土方佑斗, 松村理久, 佐藤広海, 清水陽平, 鈴木宏, 竹田浩之, 田中純貴,
上坂友洋, 宇根千晶, 吉田光一, 銭廣十三 (口頭発表), 「Th ビームの開発に向けたイオンチェンバーの性能評価」, 日本物理学会
第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
土方佑斗, 銭廣十三, 上坂友洋, 延與紫世, 大田晋輔, 坂口治隆, 佐藤広海, 清水陽平, 菅原奏来, 鈴木宏, 高橋弘幸, 武重祥子, 竹田浩之,
田中純貴, 辻崚太朗, 寺嶋知, 堂園昌伯, 西村俊二, 西村太樹, 馬場秀忠, 原田知也, G, 福田直樹, 松田洋平, 道正新一郎, 山村周,
吉田光一 (口頭発表), 「大強度かつ極めて重い不安定核ビームの粒子識別に向けた Xe ガスシンチレータの開発」, 日本物理学会
第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
吉留勇起, 近藤洋介, 中村隆司, Nadia Lynda Achouri, Thomas Aumann, 馬場秀忠, Franck Delaunay, Pieter Doornenbal, 福田直樹, Julien
Gibelin, Jongwon Hwang, 稲辺尚人, 磯部忠昭, 亀田大輔, 簡野大輝, Sunji Kim, 小林信之, 小林俊雄, 久保敏幸, Sylvain Leblond,
Jenny Lee, Miguel Marques, 本林透, 村井大地, 村上哲也, 武藤琴美, 中嶋丈嘉, 中塚徳継, Alahari Navin, 西征爾郎, Nigel Andrew
Orr, 大津秀暁, 佐藤広海, 佐藤義輝, 清水陽平, 鈴木宏, 高橋賢人, 竹田浩之, 栂野泰宏, Adam Garry Tuﬀ, Marine Vandebrouck, 米田
健一郎 (口頭発表), 「25 O の不変質量核分光」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
池田時浩 (口頭発表), 「Applications of MeV-ion microbeams produced by tapered glass capillary optics」, 第 21 回「イオンビームによる表面・界面の解析と改質」特別研究会, 京都大学宇治キャンパス&オンライン, 京都, 2020 年 12 月 4–5 日.
引間宥花, 池田時浩, 森光正, 金衛国 (招待講演), 「生物照射のためのガラスキャピラリーマイクロビーム法とスポット径解析」, 原子衝突学会第 45 回年会, オンライン, 2020 年 12 月 8–10 日.
引間宥花, 池田時浩, 森光正, 金衛国 (ポスター), 「生物照射のためのガラスキャピラリーマイクロビーム法とスポット径解析」, 原子衝突学会第 45 回年会, オンライン, 2020 年 12 月 8–10 日.
引間宥花, 池田時浩, 森光正, 金衛国 (口頭発表), 「ガラスキャピラリーによる H+ マイクロビームの大気中微小標的への照射距離の評価」, 第 63 回放射線化学討論会, オンライン, 2020 年 12 月 12–14 日.
三宮圭人, 池田時浩, 森光正, 引間宥花, 田山優雅, 福田彩実, 山口航平, 金衛国 (口頭発表), 「ガラスキャピラリーにおけるパルス
レーザーマイクロビームの透過特性」, 第 63 回放射線化学討論会, オンライン, 2020 年 12 月 12–14 日.

Awards引間宥花, 「生物照射のためのガラスキャピラリーマイクロビーム法とスポット径解析」, 原子衝突学会第 45 回年会ホットトピッ
ク公演.

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Accelerator Applications Research Division
Beam Mutagenesis Group
1. Abstract

This group promotes biological applications of ion beams from RI Beam Factory (RIBF). Ion Beam Breeding Team studies
various biological eﬀects of fast heavy ions and develops new technology to breed plants and microbes by heavy-ion irradiations.
Plant Genome Evolution Research Team studies the eﬀect of chromosomal rearrangements on plant genomes and phenotypes.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Biological eﬀects of fast heavy ions
Molecular nature of DNA alterations induced by heavy-ion irradiation
Research and development of heavy-ion breeding
Study on the eﬀect of chromosomal rearrangements on plant genomes and phenotypes

3. Summary of Research Activity

Summary of research activities of the two teams are given in the sections of each team.

Members
Director
Tomoko ABE
Team Leaders
Tomoko ABE

Hiroyuki ICHIDA- 287 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Accelerator Applications Research Division
Beam Mutagenesis GroupIon Beam Breeding Team
1. Abstract

Ion beam breeding team studies various biological eﬀects of fast heavy ions. It also develops new technique to breed plants andmicrobes by heavy-ion irradiations. Fast heavy ions can produce dense and localized ionizations in matters along their tracks, incontrast to photons (X rays and gamma rays) which produce randomly distributed isolated ionizations. These localized and dense ionization can cause double-strand breaks of DNA which are not easily repaired and result in mutation more eﬀectively than singlestrand
breaks. A unique feature of our experimental facility at the RIKEN Ring Cyclotron (RRC) is that we can irradiate living tissues inatmosphere since the delivered heavy-ion beams have energies high enough to penetrate deep in matter. This team utilizes a dedicatedbeam line (E5B) of the RRC to irradiate microbes, plants and animals with beams ranging from carbon to iron. Its research subjects
cover study of ion-beam radiation mutagenesis, genome-wide analyses of mutation, and development of new plants and microbial
varieties by heavy-ion irradiation. Thirty-five new varieties have already been brought to the market.

2. Major Research Subjects(1) Study on the biological eﬀects by heavy-ion irradiation(2) Study on the molecular nature of DNA alterations induced by heavy-ion irradiation(3) Innovative applications of heavy-ion beams

3. Summary of Research Activity

We study biological eﬀects of fast heavy ions from the RRC using 135 A MeV C, N, Ne ions, 95 A MeV Ar ions, 90 A MeV Fe
ions and from the IRC using 160 A MeV Ar ions. We also develop breeding technology of microbes and plants. Main subjects are:(1) Study on the biological eﬀects by heavy-ion irradiation
Heavy-ion beam deposits a concentrated amount of dose at just before stop with severely changing the linear energy transfer(LET). The peak of LET is achieved at the stopping point and known at the Bragg peak (BP). Adjusting the BP to target malignant
cells is well known to be eﬀective for cancer therapy. On the other hand, a uniform dose distribution is a key to the systematic study
for heavy-ion mutagenesis, thus to the improvement of the mutation eﬃciency. Plants and microbes therefore, are irradiated using ionswith stable LET. We investigated the eﬀect of LET ranging from 23 to 640 keV/µm, on mutation induction using dry seeds of the model
plants Arabidopsis thaliana and rice (Oryza sativa L.). The most eﬀective LET (LETmax) was 30 keV/µm in Arabidopsis. LETmax
irradiations showed the same mutation rate as that by chemical mutagens, which typically cause high mutation rate. The LETmax
was 23–39 keV/µm in buckwheat, 23–50 keV/µm in rice and 50–70 keV/µm in wheat. By contrast, when LET was 290 keV/µm, themutation rate was low and the survival rate was greatly reduced in plants. In the case of microbe, filamentous fungus (Neurospora
crassa), the Ar ions at 290 keV/µm demonstrated higher mutagenic activity than the Fe-ions at 640 keV/µm. Thus, the LET is an
important factor to be considered in heavy-ion mutagenesis.
(2) Study on the molecular nature of DNA alterations induced by heavy-ion irradiation
A whole-genome analysis with high-throughput sequencing is a powerful tool used to characterize the nature of induced mutations.
We have been using whole genome sequencing to analyze DNA mutations in Arabidopsis and rice genomes. C ions with LETmax
mainly induced single nucleotide variants (SNVs) and small insertions and deletions (InDels), while the number of large deletions
and chromosomal rearrangements was low. However, 290-keV/µm Ar ions showed a diﬀerent mutation spectrum: SNVs and numberof small InDels was low, while the number of large deletions (≧100 bp) and chromosomal rearrangements was high. Number ofmutated gene induced by C-ion and Ar-ion irradiation is less than 10, relatively small, and often only 1 mutation is found near the
mapped location. Thus, irradiation with these ions can eﬃciently generate knockout mutants of a target gene and can be applied
to reverse genetics. Mutants of the causative gene of Arabidopsis induced by ion beam irradiation were compared at 30 keV/µm
and 290 keV/µm with two typical LETs. The most mutations irradiated with C ion at 30 keV/µm were small deletions (<100 bp).
Irradiation with 290-keV/µm C-ion and Ar-ion resulted in the most large-deletions and chromosomal rearrangements, and decreased
small deletions.
(3) Innovative application of heavy-ion beams
In 1999, we formed a consortium for ion-beam breeding consisting of 24 groups. In 2020, the consortium grew to 184 groups
from Japan and 20 from overseas. Previously, the ion-beam breeding procedures were carried out using mainly flowers and ornamental
plants. We have recently put a new non-pungent and tearless onion, ‘Smile ball,’ on the market along with ‘Kiku Meigetsu,’ anedible late flowering chrysanthemum. In addition, a new project was launched to expand the cultivation area of this variety ofchrysanthemum in Yamagata prefecture. Beneficial variants have been grown for various plant species, such as high yield sea weeds,
lipids hyperaccumulating unicellular alga, medicinal plant with high productivity of medicinal ingredient, peanuts without major
allergens, oranges with delayed coloring and one-month late harvest, and lettuce with a low browning property as a cut vegetable. As
a result of a collaborative study with the University of Hasanuddin, we have selected five useful aromatic rice mutants and increased
the percentage of fertile grains from 32% control to over 52%. By broadening the target of heavy-ion breeding extending from flowers- 288 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

to crops such as grains, the technology will contribute to solving the global problems of food shortage and environmental destruction.

Members
Team Leader
Tomoko ABE
Research/Technical Scientists
Tokihiro IKEDA (Senior Research Scientist)
Masako IZUMI (Senior Research Scientist)
Teruyo TSUKADA (Senior Research Scientist)

Kazuhide TSUNEIZUMI (Senior Research Scientist)
Ryouhei MORITA (Technical Scientist)

Research & Development Scientists
Hiroyuki ICHIDA
Technical Staﬀ I
Yoriko HAYASHI

Yuki SHIRAKAWA

Technical Staﬀ II
Sumie OHBU

Mieko YAMADASpecial Temporary Technical Scientists
Hiroshi ABE

Katsunori ICHINOSE

Research Consultant
Masahiro MII (Chiba Univ.)
Visiting Scientists
Ayumi DEGUCHI (Chiba Univ.)
Makoto FUJIWARA (Sophia Univ.)
Eitaro FUKATSU (Forestry and Forest Products Res. Inst.)
Tomonari HIRANO (Univ. of Miyazaki)
Akiko HOKURA (Tokyo Denki Univ.)
Yutaka MIYAZAWA (Yamagata Univ.)
Kazumitsu MIYOSHI (Chiba Univ.)
Toshikazu MORISHITA (Nat’l Agriculture and Food Res.
Org.)
Koji MURAI (Fukui Prefectural Univ.)

Kyosuke NIWA (Tokyo Univ. of Marine Sci. and Tech.)
Norihiro OHTSUBO (Kyoto Prefectural Univ.)
Tadashi SATO (Tohoku Univ.)
Yoichi SATO (Riken Food Co., Ltd.)
Kenichi SUZUKI (Suntory Flowers Co., Ltd.)
Hinako TAKEHISA (Nat’l Agriculture and Food Res. Org.)
Masanori TOMITA (Central Res. Inst. of Electric Power Industry)
Masao WATANABE (Tohoku Univ.)
Takeshi YAMAKI (Riken Vitamin Co., Ltd.)

Visiting Technicians
Yukiko KANAZAWA (Nippon Beet Sugar Manufacturing Co.,
Ltd.)
Norihide KISHINO (Sanwa Norin Co. Ltd.)

Miho MOGAMIYA (Riken Food Co., Ltd.)
Daisuke SAITO (Riken Food Co., Ltd.)
Takuji YOSHIDA (Takii & Co., Ltd)

Research Fellow
Hironari UCHIDA (Saitama Agricultural Tech. Res. Center)

List of Publications & Presentations
Publications[Original Papers]
T. Hirano, Y. Sato, K. Ichinose, M. Yamada, Y. Hayashi, N. Fukunishi, and T. Abe, “Mutant induction in gametophytes of Undaria
pinnatifida (Phaeophyceae) by heavy ion beam irradiation,” Phycol. Res. 68, 63–69 (2019).
N. Fukuda, N. Kitajim, Y. Terada, T. Abe, I. Nakai, and A. Hokura, “Visible cellular distribution of cadmium and zinc in the hyperaccumulator Arabidopsis halleri ssp. gemmifera determined by 2-D X-ray fluorescence imaging using high-energy synchrotron radiation,”
Metallomics 12, 193–203 (2019).
Y. Oono, H. Ichida, R. Morita, S. Nozawa, K. Satoh, A. Shimizu, T. Abe, H. Kato, and Y. Hase, “Genome sequencing of ion-beam-induced
mutants facilitates detection of candidate genes responsible for phenotypes of mutants in rice,” Mutat. Res. Fund. Mol. Mech. Mutagen.
(2020).
R. Tabassum, T. Dosaka, H. Ichida, R. Morita, Y. Ding, T. Abe, and T. Katsube-Tanaka, “FLOURY ENDOSPERM11-2 encodes plastid
HSP70-2 involved with the temperature-dependent chalkiness of rice (Oryza sativa L.) grains,” Plant J. 103, 604–616 (2020).
K. Kaya, Y. Kazama, T. Abe, and F. Shiraishi, “Influence of medium components and pH on the production of odd-carbon fatty acids by
Aurantiochytrium sp. SA-96,” J. Appl. Phycol. 32, 1597–1606 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

S. Muramatsu, K. Atsuji, K. Yamada, K. Ozasa, H. Suzuki, T. Takeuchi, Y. Hashimoto-Marukawa, Y. Kazama, T. Abe, K. Suzuki, andO. Iwata, “Isolation and characterization of a motility-defective mutant of Euglena gracilis,” Peer J 8, e10002 (2020).
H. Murata, S. Nakano, T. Yamanaka, T. Shimokawa, T. Abe, H. Ichida, Y. Hayashi, and K. Tahara, “Argon-ion beam induced mutantsof the ectomycorrhizal agaricomycete Tricholoma matsutake defective in β-1,4-endoglucanase activity promote the seedling growth ofPinus densiflora in vitro,” Botany, 99(3), DOI:10.1139/cjb-2020-0076 (2020).

[Proceedings]
A. M. Okasa, M. Riadi, K. Toriyama, K. Ishii, Y. Hayashi, T. Sato, T. Abe, Trisnawaty, N. J. Panga, and R. Sjahril, “Mutation breeding
for improvement of aromatic rice mutant by using ion beam irradiation,” IOP Conf. Ser. Earth Environ. Sci. 486, 012091 (2020).

Presentations[International Conferences/Workshops]
T. Kashiwabara, N. Kitajima, R. Onuma, N. Fukuda, S. Endo, Y. Terada, T. Abe, A. Hokura, and I. Nakai, “Synchrotron micro-X-ray
fluorescence imaging of arsenic in frozen-hydrated sections of a root of Pteris vittate,” Goldschmidt2020: Global Virtual Conference,
online, June 21–26, (2020).
T. Abe (invited), “Development for ion-beam breeding technology over the last two decades in Japan,” Virtual Meeting on FAO/IAEA
Mutation Breeding Network (MBN) for Asia Pacific Region, online, November 12–13, (2020).

[Domestic Conferences/Workshops]
常泉和秀, 山田美恵子, 一瀬勝紀, 市田裕之, 金禧珍, 萩原篤志, 川田実季, 片山貴士, 﨑山一孝, 手塚信弘, 小磯雅彦, 阿部知子, 「シオミズツボワムシの高増殖・大型変異系統の樹立」, 日本農芸化学会 2020 年度大会, 福岡県福岡市 (九州大学), 2020 年 3 月 26 日.
市田裕之, 阿部知子, 「オープンソースな変異タイピング手法の開発とイネをモデルとした概念実証」, 日本育種学会 第 137 回講演会, 東京都文京区 (東京大学), 2020 年 3 月 28 日.
渡邊遙, 大部澄江, 阿部知子, 風間裕介, 「ゲノム編集によるシロイヌナズナへの 758 kb の逆位の導入」, 同上.
A. M. Okasa, M. Riadi, 佐藤雅志, 鳥山欽哉, 石井公太郎, 林依子, 阿部知子, R. Sjahril, “An approach toward isolating early-heading
mutants from Tana Toraja local aromatic rice ‘Pare Bau’ irradiated with heavy ion-beam,” 同上.
橋本佳澄, 西浦愛子, 上田純平, 風間裕介, 阿部知子, 市田裕之, 村井耕二, 「2 倍体ヒトツブコムギにおける重イオンビーム照射による超極早生変異体 extra early-flowering 4 の原因遺伝子の同定」, 同上.
森田竜平, 市田裕之, 石井公太郎, 林依子, 安部弘, 白川侑希, 一瀬勝紀, 常泉和秀, 風間智彦, 鳥山欽哉, 佐藤雅志, 阿部知子, 「イネ長粒変異体 lin1 の単離および原因遺伝子同定」, 同上.
石井公太郎, 大部澄江, 白川侑希, 阿部知子, 「全ゲノム変異解析による重イオンビームの高頻度な変異誘発線量区の推定」, 同上.
村井耕二, 風間裕介, 阿部知子, 「2 倍体ヒトツブコムギにおける重イオンビーム突然変異体作出のための最適処理条件」, 同上.
Y. Ding(口頭発表), T. Katsube-Tanaka, H. Ichida, R. Morita, and T. Abe, “Studies on chalkiness of the rice cultivar ‘Kinmaze’under heatstress,” 日本作物学会第 250 回講演会, オンライン開催, 2020 年 9 月 3–4 日.
蝶野真喜子 (ポスター発表), 藤田雅也, 神山紀子, 松中仁, 氷見英子, 市田裕之, 阿部知子, 川上直人, 「粒の赤みが弱い新規コムギ変異体の農業特性」, 日本育種学会 第 138 回講演会, オンライン開催, 2020 年 10 月 10–11 日.
藤田悠生 (ポスター発表), 市田裕之, 風間智彦, 阿部知子, 鳥山欽哉, 「インディカイネ品種 Lebed に由来する雄性不稔遺伝子とその抑制遺伝子の解析」, 同上.
石井公太郎 (口頭発表), 風間裕介, 浅野円花, 阿部知子, 河野重行, 「Ar・Fe イオンビーム照射によって生じるクロレラ染色体の断片化と染色体再編成」, 同上.
南壮次郎 (口頭発表), 渡邊遥, 大部澄江, 阿部知子, 風間裕介, 「ゲノム編集を用いたシロイヌナズナへの染色体再編成の導入」, 同上.
野村文希 (ポスター発表), 風間裕介, 阿部知子, 村井耕二, 「イオンビーム照射により作出された Ppd-1 欠失『農林 61 号』変異系統の解析」, 第 15 回ムギ類研究会, オンライン開催, 2020 年 12 月 26 日.
橋本佳澄 (ポスター発表), 西浦愛子, 風間裕介, 市田裕之, 阿部知子, 村井耕二, 「重イオンビーム照射によって作出された超極早生
コムギ変異体 extra early-flowering 4（exe4）の花成関連遺伝子の発現解析」, 同上.

Awards
佐藤陽一, 斎藤大輔, 最上谷美穂, 令和 2 年度（第 21 回）民間部門農林水産研究開発功績者表彰（農林水産技術会議会長賞民間部門）, 「わかめ養殖種苗の優良系統開発と生産条件最適化による普及実用化」, 農林水産会議, 2020 年 11 月 12 日.

Patents
石井重久, 阿部知子, 林依子, サクラ「真和」, 品種登録出願番号 34356, 出願日 2019 年 11 月 27 日.
石井重久, 阿部知子, 林依子, サクラ「真理」, 品種登録出願番号 34356, 出願日 2019 年 11 月 27 日.
石井重久, 阿部知子, 林依子, サクラ「真星」, 品種登録出願番号 34356, 出願日 2020 年 4 月 14 日.

Outreach Activities
We established the “Asagao (morning glory) club” to deepen the understanding of our technology of mutation breeding. The club
distributes the morning glory seeds irradiated with C-ion on request, and collects and compiles the observation reports of their growth.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Accelerator Applications Research Division
Beam Mutagenesis Group
Plant Genome Evolution Research Team
1. Abstract

Established in May 2018 and succeed in October 2020, the plant genome evolution research team studies the eﬀect of heavyion induced mutations on plant and microbial phenotypes. Chromosome rearrangements including translocations, inversions, anddeletions are thought to play an important role in evolution and have a greater potential to achieve large phenotypic changes. However,this potential has not been fully investigated due to the lack of an eﬀective method to induce and analyze complexed mutations.
We employ the population genomics approach with robust molecular biology and bioinformatics techniques to characterize genomic
mutations in model and non-model plant and microbial species, and create the future of mutation breeding.

2. Major Research Subjects(1) Study on the eﬀect of chromosomal rearrangements on plant genomes and phenotypes(2) Genomics-based approach to revolutionize the mutagenesis in model and non-model plants and microbes

3. Summary of Research Activity(1) Study on the eﬀect of chromosomal rearrangements on plant genomes and phenotypes
We have established an eﬃcient bioinformatics pipeline named AMAP, an automated mutation analysis pipeline, and have used
it for genome-wide analysis of chromosome rearrangements and other mutations in various organisms. In Arabidopsis, we isolated ashort-petiole mutant, Ar55-as1, from Ar-beam irradiated population at a dose of 50 Gy with an LET of 290 keV/µm. We showed that
this mutant has no typical base substitutions, deletions, and insertions that were linked to the mutant’s phenotype, but has chromosomal
rearrangements in the genome. Genetic linkage analysis showed that the short-petiole phenotype and the presence or absence of theinversion on chromosome 2 was completely linked in M3 generation, indicating that this inversion is responsible for the phenotype.
The Ar55-as1 mutant will serve as a good model to investigate the eﬀects on gene expressions by chromosomal rearrangements.
We previously isolated a high oil-production mutant of Parachlorella kessleri, a starch and oil-producing unicellular green algae,by C-beam irradiations. The eﬀect on chromosomal rearrangements by Ar- and Fe-beams was quantitatively evaluated by cytologicalobservations and high-throughput sequencing. As the result, Fe-beam irradiation at a dose of 75 Gy caused dramatic increase offragmented chromosomes: 14 percent of the population had more than 30 chromosomes right after the irradiation and three percent of
the population still remained more than 20 chromosomes after four consecutive cultures, although the wild-type P. kessleri cells have
only seven A- and three B-chromosomes. We performed whole-genome sequencing in two mutants, and the results indicated that one
mutant, Fe75-1-3H had chromosomal rearrangements with 10 junction regions, and the other, Ar75-1-2C, had a novel chromosomal
terminus by the result from a translocation.
(2) Genomics-based approach to revolutionize the mutagenesis in model and non-model plants and microbes
Recent advances in genome sequencing and bioinformatics technology enabled us to obtain a genome-wide view of the induced
mutations in unselected populations. We chose baker’s yeast and a legume Lotus japonicus as model systems, irradiated diﬀerent dosesof carbon-ion beams to these organisms, and determined the dose-survival correlation. We isolated a semi-dwarf L. japonicus mutant,identified the responsible mutation by whole-genome sequencing, and started to characterize the phenotypic traits of this mutant. The
semi-dwarf L. japonicus mutant is suitable for high-density cultivation in laboratory environment and may serve as an eﬃcient model
platform for legume-Rhizobium symbiosis.

Members
Team Leader
Tomoko ABE (～2020.09)

Hiroyuki ICHIDA (2020.10～)

Contract Researcher
Kotaro ISHII
Visiting Scientists
Ali FERJANI (Tokyo Gakugei Univ.)

Yusuke KAZAMA (Fukui Prefectural Univ.)

Part-time Worker
Yusaku NISHIMIYA (Administrative Part-time Worker II)

List of Publications & Presentations
Publications[Original Papers]- 291 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Y. Oono, H. Ichida, R. Morita, S. Nozawa, K. Satoh, A. Shimizu, T. Abe, H. Kato, and Y. Hase, “Genome sequencing of ion-beaminduced mutants facilitates detection of candidate genes responsible for phenotypes of mutants in rice,” Mutat. Res. Fund. Mol. Mech.
Mutagen.821, 111691 (2020).
R. Tabassum, T. Dosaka, H. Ichida, R. Morita, Y. Ding, T. Abe, and T. Katsube-Tanaka, “FLOURY ENDOSPERM11-2 encodes plastid
HSP70-2 involved with the temperature-dependent chalkiness of rice (Oryza sativa L.) grains,” Plant J. 103, 604–616 (2020).
H. Murata, S. Nakano, T. Yamanaka, T. Shimokawa, T. Abe, H. Ichida, Y. Hayashi, and K. Tahara, “Argon-ion beam induced mutantsof the ectomycorrhizal agaricomycete Tricholoma matsutake defective in β-1,4-endoglucanase activity promote the seedling growth ofPinus densiflora in vitro,” Botany 99, 139–149 (2020). DOI:10.1139/cjb-2020-0076 .

Presentations[Domestic Conferences/Workshops]
市田裕之, 阿部知子, 「オープンソースな変異タイピング手法の開発とイネをモデルとした概念実証」, 日本育種学会 第 137 回講演会, 東京都文京区 (東京大学), 2020 年 3 月 28 日.
橋本佳澄, 西浦愛子, 上田純平, 風間裕介, 阿部知子, 市田裕之, 村井耕二, 「2 倍体ヒトツブコムギにおける重イオンビーム照射による超極早生変異体 extra early-flowering 4 の原因遺伝子の同定」, 同上.
森田竜平, 市田裕之, 石井公太郎, 林依子, 安部弘, 白川侑希, 一瀬勝紀, 常泉和秀, 風間智彦, 鳥山欽哉, 佐藤雅志, 阿部知子, 「イネ長粒変異体 lin1 の単離および原因遺伝子同定」, 同上.
石井公太郎, 大部澄江, 白川侑希, 阿部知子, 「全ゲノム変異解析による重イオンビームの高頻度な変異誘発線量区の推定」, 同上.
Y. Ding (口頭発表), T. Katsube-Tanaka, H. Ichida, R. Morita, and T. Abe, “Studies on chalkiness of the rice cultivar ‘Kinmaze’ underheat stress,” 日本作物学会第 250 回講演会, オンライン開催, 2020 年 9 月 3–4 日.
蝶野真喜子 (ポスター発表), 藤田雅也, 神山紀子, 松中仁, 氷見英子, 市田裕之, 阿部知子, 川上直人, 「粒の赤みが弱い新規コムギ変異体の農業特性」, 日本育種学会 第 138 回講演会, オンライン開催, 2020 年 10 月 10–11 日.
藤田悠生 (ポスター発表), 市田裕之, 風間智彦, 阿部知子, 鳥山欽哉, 「インディカイネ品種 Lebed に由来する雄性不稔遺伝子とその抑制遺伝子の解析」, 同上.
石井公太郎 (口頭発表), 風間裕介, 浅野円花, 阿部知子, 河野重行, 「Ar・Fe イオンビーム照射によって生じるクロレラ染色体の断片化と染色体再編成」, 同上.
橋本佳澄 (ポスター発表), 西浦愛子, 風間裕介, 市田裕之, 阿部知子, 村井耕二, 「重イオンビーム照射によって作出された超極早生
コムギ変異体 extra early-flowering 4（exe4）の花成関連遺伝子の発現解析」, 第 15 回ムギ類研究会, オンライン開催, 2020 年 12月 26 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Accelerator Applications Research Division
RI Application Research Group
1. Abstract

RI Application Research Group promotes industrial applications of radioisotopes (RIs) and ion beams at RIKEN RI Beam Factory(RIBF). Nuclear Chemistry Research Team develops production technologies of useful RIs for application studies in nuclear andradiochemistry. The team also develops technologies of mass spectrometry for trace-element and isotope analyses and apply themto the research fields such as cosmochemistry, environmental science, archaeology, and so on. Industrial Application Research Team
promotes industrial applications of the accelerator facility and its related technologies.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)

Research and development of RI production technologies at RIBF
RI application researches
Distribution of RIs produced at RIBF
Development of trace element analyses using accelerator techniques and their applications to geoscience and archaeologicalresearch fields
Development of chemical materials for ECR ion sources of the RIBF accelerators
Development of technologies on industrial utilization and novel industrial applications of RIBF
Support of industrial utilization of the heavy-ion beams at RIBF
Support of materials science experiments

3. Summary of Research Activity

See the subsections of Nuclear Chemistry Research Team and Industrial Application Research Team.

MemberDirector
Hiromitsu HABA

List of Publications & Presentations
See the subsections of Nuclear Chemistry Research Team and Industrial Application Research Team.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Accelerator Applications Research Division
RI Application Research Group
Nuclear Chemistry Research Team
1. Abstract

The Nuclear Chemistry Research Team develops production technologies of unique radioisotopes (RIs) at RIKEN RI Beam
Factory (RIBF) and applies them in the research fields of physics, chemistry, biology, engineering, medicine, pharmaceutical andenvironmental sciences. The purified RIs such as 65 Zn, 67 Cu, 85 Sr, 88 Y, and 109 Cd are delivered to universities and institutes throughJapan Radioisotope Association. We also develop new technologies of mass spectrometry for the trace-element analyses using accelerator techniques and apply them to the research fields such as cosmochemistry, environmental science, archaeology, and so on. We
perform various isotopic analyses on the elements such as S, Pd, and Pb using ICP-MS, TIMS, and IRMS. We also develop chemicalmaterials such as metallic 238 U, 238 UO2 , and 48 CaO for ECR ion sources of the heavy-ion accelerators at RIBF.

2. Major Research Subjects(1) Research and development of RI production technologies at RIBF
(2) RI application researches(3) Development of trace element analyses using accelerator techniques and their applications to geoscience and archaeologicalresearch fields(4) Development of chemical materials for ECR ion sources of the heavy-ion accelerators at RIBF

3. Summary of Research Activity(1) Research and development of RI production technologies at RIBF and RI application researches
Due to its high sensitivity, the radioactive tracer technique has been successfully applied for investigations of the behavior ofelements in the fields of chemistry, biology, engineering, medicine, pharmaceutical and environmental sciences. We have been developing production technologies of useful radioisotopes (RIs) at RIBF and conducting their application studies in collaboration withmany researchers in various fields. With 30-MeV proton, 24-MeV deuteron, and 50-MeV alpha beams from the AVF cyclotron, we
presently produce about 100 RIs from 7 Be to 211 At. Among them, 65 Zn, 67 Cu, 85 Sr, 88 Y, and 109 Cd are delivered to Japan Radioisotope
Association for fee-based distribution to the general public in Japan. Our RIs are also distributed to researchers under the Supply
Platform of Short-lived Radioisotopes for Fundamental Research, supported by MEXT KAKENHI in FY2016–2021. On the other
hand, RIs of a large number of elements are simultaneously produced from metallic targets such as nat Ti, nat Ag, nat Hf, 197 Au, and 232 Th
irradiated with a 135-MeV nucl.−1 14 N beam from the RIKEN Ring Cyclotron. These multitracers are also supplied to universities
and institutes as collaborative researches.
In 2020, we developed production technologies of RIs such as 7 Be, 28 Mg, 43 K, 44m Sc, 44 Ti, 48 Cr, 186 Re, 211 At, 212 Pb, 224 Ra,
225
Ac, and 229 Pa which were strongly demanded but lack supply sources in Japan. We also investigated the excitation functions forthe nat V(d, x), nat Gd(d, x), 141 Pr(d, x), and nat Nd(α, x) reactions to quantitatively produce useful RIs. We used radiotracers of 28 Mg,
211
At, 212 Pb, 224 Ra, and 229 Pa for application studies in chemistry, 44m Sc, 67 Cu, 186 Re, 211 At, and 225 Ac in nuclear medicine, and 43 K,
48
Cr, 186 Re, and 211 At in engineering. We also produced 65 Zn, 85 Sr, 88 Y, and 109 Cd for our scientific researches on a regular scheduleand supplied the surpluses through Japan Radioisotope Association to the general public. In 2020, we accepted 6 orders of 65 Zn witha total activity of 33 MBq, 5 orders of 85 Sr with 9.7 MBq, 1 order of 88 Y with 1 MBq, and 1 order of 109 Cd with 10 MBq. We also
distributed 7 Be (0.45 MBq × 1), 88 Zr (1 MBq × 2), 95 Nb (1 MBq × 1 and 2 MBq × 1), 121m Te (2 MBq × 1), 175 Hf (1 MBq × 2), and211
At (5 MBq × 6, 10 MBq × 1, 18 MBq × 2, 50 MBq × 1, 80 MBq × 1, and 100 MBq × 16) under the Supply Platform of Short-lived
Radioisotopes for Fundamental Research.
(2) Superheavy element chemistry
Chemical characterization of newly-discovered superheavy elements (SHEs, atomic number Z ≥ 104) is an extremely interesting and challenging subject in modern nuclear and radiochemistry. We are developing SHE production systems as well as rapid
single-atom chemistry apparatuses at RIBF. Using heavy-ion beams from RILAC and AVF, 261 Rf (Z = 104), 262 Db (Z = 105),265
Sg (Z = 106), and 266 Bh (Z = 107) are produced in the 248 Cm(18 O, 5n)261 Rf, 248 Cm(19 F, 5n)262 Db, 248 Cm(22 Ne, 5n)265 Sg, and248
Cm(23 Na, 5n)266 Bh reactions, respectively, and their chemical properties are investigated.
We installed a gas-jet transport system to the focal plane of the gas-filled recoil ion separator GARIS at RILAC. This system isa promising approach for exploring new frontiers in SHE chemistry: the background radiations from unwanted products are strongly
suppressed, the intense primary heavy-ion beam is absent in the gas-jet chamber, and hence the high gas-jet extraction yield is attained.
Furthermore, the beam-free condition makes it possible to investigate new chemical systems. To realize aqueous chemistry studies of
Sg and Bh, we have been developing a continuous and rapid solvent extraction apparatus which consists of a continuous dissolution
apparatus Membrane DeGasser (MDG), a Flow Solvent Extractor (FSE), and a liquid scintillation detector for α/SF-spectrometry. On
the other hand, we produced radiotracers of 88, 89m Zr, 95 Nb, 175 Hf, and 177, 179 Ta at the AVF cyclotron and conducted model experiments
for aqueous chemistry studies on Rf and Db. We also developed a cryogenic RF-carpet gas cell, which will be placed on the focal
plane of GARIS and connected to a gas chromatographic apparatus, for the future gas-phase chemistry of the short-lived SHEs (<3 s).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)(3) Development of trace element analyses using accelerator techniques and their applications to geoscience and archaeologicalresearch fields
We have been developing the ECR Ion Source Mass Spectrometer (ECRIS-MS) for trace element analyses. We renovated thedetection system of ECRIS-MS and evaluated its sensitivity and mass resolution power. We equipped a laser-ablation system with an
ion source and a pre-concentration system to achieve high-resolution analyses for noble gases such as Kr and Xe.
Using the conventional ICP-MS, TIMS, IRMS, and so on, we studied Pb and S isotope ratios on cinnabar and asphalt samples
from ancient ruins in Japan to elucidate the distribution of goods in the archaic society and to reveal the establishment of the Yamato
dynasty in the period from Jomon to Tumulus. We established a sampling technique for pigment without any damages on the artifacts
or wall paintings, using a S-free adhesive tape. Then, we applied the technique to the analyses of the pigment from Roman ruins(Avinyó in Barcelona, Spain). We also applied the technique to the analyses of the red-color substances on the artifacts such as
Kyoden remains (Izumo-city, Shimane prefecture), Renpeijou-ato (Zentsuji-City, Kagawa prefecture) and so on. We also establishedthe method to identify the source mine of vermilion, using sulfur, mercury and lead isotopic analyses, and we applied this method toinvestigation of vermilion from three representative tombs (Kofunperiod in Japan)(4) Development of chemical materials for ECR ion sources of the heavy-ion accelerators at RIBF
In 2020, we prepared 238 UO2 on a regular schedule for 238 U-ion accelerations with the 28-GHz ECR of RILAC II.

Members
Team Leader
Hiromitsu HABA
Research & Development Scientist
Hiroo HASEBE
Contract Researchers
Katsumasa FUJIKI

Yukiko KOMORISpecial Postdoctoral Researcher
Yudai SHIGEKAWA
Postdoctoral Researchers
Yang WANG
Xiaojie YIN

Takuya YOKOKITA

Technical Staﬀ I
Akihiro NAMBU
Special Temporary Research Scientist
Kazuya TAKAHASHI
Research Consultant
Hisaaki KUDO (Niigata Univ.)
Visiting Scientists
Msayuki AIKAWA (Hokkaido Univ.)
Kazuhiko AKIYAMA (Tokyo Metropolitan Univ.)
Takatoshi AOKI (Univ. of Tokyo)
Masato ASAI (JAEA)
Ferenc DITRÓI (ATOMKI)
Osuke FUJIMOTO (Fujifilm Toyama Chemical Co., Ltd.)
Takahiro HIRAKI (Okayama Univ.)
Hayato IKEDA (Tohoku Univ.)
Noriko ISHIOKA (QST)
Masamichi KAJITA (Fujifilm Toyama Chemical Co., Ltd.)
Yoshitaka KASAMATSU (Osaka Univ.)
Hiroshi KATO (Fujifilm Toyama Chemical Co., Ltd.)
Mayeen U. KHANDAKER (Sunway Univ.)
Hidetoshi KIKUNAGA (Tohoku Univ.)
Yoshikatsu KOGA (Nat’l Cancer Center)
Shoko KUBOTA (Fujifilm Toyama Chemical Co., Ltd.)
Takumi KUBOTA (Kyoto Univ.)
Susanta Kumar LAHIRI (Saha Inst. of Nucl. Phys. India)

Takahiko MASUDA (Okayama Univ.)
Toshimitsu MOMOSE (Int’l Univ. of Health and Welfare)Eri NAKAMURA (Fujifilm Toyama Chemical Co., Ltd.)
Kenichiro OGANE (Int’l Univ. of Health and Welfare)
Miki OHTSUKA (Waseda Univ.)
Kazuhiro OOE (Osaka Univ.)
Shinobu OSHIKIRI (Fujifilm Toyama Chemical Co., Ltd.)
Yasutaka SAITO (Fujifilm Toyama Chemical Co., Ltd.)Aya SAKAGUCHI (Tsukuba Univ.)
Miho SATAKE (Fujifilm Toyama Chemical Co., Ltd.)
Tetsuya SATO (JAEA)
Yuki SATO (Fujifilm Toyama Chemical Co., Ltd.)
Kenji SHIMAZOE (Univ. of Tokyo)
Keisuke SUEKI (Tsukuba Univ.)
Kentaro SUZUKI (Fujifilm Toyama Chemical Co., Ltd.)
Zoltán SZŰCS (ATOMKI)
Sándor TAKÁCS (ATOMKI)
Hiroyuki TAKAHASHI (Univ. of Tokyo)- 295 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Miho TAKAHASHI (Tokyo Univ. of Marine Sci. and Tech.)
Miwako TAKAHASHI (QST)
Yuichi TAKAKU (Inst. for Environmental Sci.)
Hiroki TAKASHIMA (Nat’l Cancer Center)
Kazuo TANAKA (Tohoku Univ.)
Masayoshi TODA (Tokyo Univ. of Marine Sci. and Tech.)Atsushi TOYOSHIMA (Osaka Univ.)
Kazuaki TSUKADA (JAEA)
Naoyuki UKON (Fukushima Medical Univ.)

Ahmed R. USMAN (Umaru Musa Yar’adua Univ.)
Shigeki WATANABE (QST)
Takahiro YAMADA (Kindai Univ.)
Chunli YANG (Inst. of Modern Phys./Chinese Academy ofSci.)
Akihiko YOKOYAMA (Kanazawa Univ.)
Zenko YOSHIDA (ATOX Co., Ltd.)
Koji YOSHIMURA (Okayama Univ.)

Visiting Technicians
Hideyuki ARAI (Metal Tech. Co. Ltd.)
Hiroshi ARATA (Metal Tech. Co. Ltd.)
Mai FUKUMORI (ATOX Co., Ltd.)
Hidehiro HASHIMOTO (Metal Tech. Co. Ltd.)
Yoshiyuki IIZUKA (ATOX Co., Ltd.)
Akimitsu KANDA (Japan Radioisotope Association)
Shota KIMURA (Japan Radioisotope Association)
Yukiyoshi KON (Osaka Univ.)
Takashi KURIHARA (Metal Tech. Co. Ltd.)

Takahiro MIKAMOTO (Japan Radioisotope Association)
Shingo NAKAMURA (Metal Tech. Co. Ltd.)
Hiroki SHIBAHARA (ATOX Co., Ltd.)
Yuki TAKEMURA (ATOX Co., Ltd.)
Yasutaka TAKEUCHI (ATOX Co., Ltd.)
Shusaku TAZAWA (ATOX Co., Ltd.)
Yuichirou WAKITANI (Japan Radioisotope Association)
Mami YUKI (ATOX Co., Ltd.)

Student Trainees
Kjeld A.A.G. BEEKS (Vienna Univ. of Tech.)
Desheng CHEN (Univ. of Chinese Academy of Sci.)
Shunsuke FUJINO (Kindai Univ.)
Sena HAMAGAMI (Kindai Univ.)
Yukina HANADA (Hokkaido Univ.)
Sho HAYAMI (Osaka Univ.)
Mariko HISAMATSU (Osaka Univ.)
Xuan HOU (Univ. of Tokyo)
Mizuho KATO (Tsukuba Univ.)
Cheonghun KIM (Univ. of Tokyo)
Mizuki KITAJIMA (Univ. of Tokyo)
Takuto MAEHASHI (Hokkaido Univ.)
Kenichi MORI (Kindai Univ.)
Ryoga MORITA (Kanazawa Univ.)
Ayumu NAGAI (Kanazawa Univ.)
Akihisa NAKAJIMA (Tsukuba Univ.)
Ryohei NAKANISHI (Osaka Univ.)

Teruhito NAKASHITA (Univ. of Tokyo)
Koichi OKAI (Okayama Univ.)
Michiya SAKAGUCHI (Hokkaido Univ.)
Motoki SATO (Univ. of Tokyo)
Kei SAWAMURA (Osaka Univ.)
Fumiki SENSUI (Univ. of Tokyo)
Ayano SETO (Kanazawa Univ.)
Kaori SHIRAI (Niigata Univ.)
Hayato SUZUKI (Ibaraki Univ.)
Kakeru TERANISHI (Kanazawa Univ.)
Katsuyuki TOKOI (Osaka Univ.)
Mizuki UENOMACHI (Univ. of Tokyo)
Eisuke WATANABE (Osaka Univ.)
Kazeki YAMANE (Univ. of Tokyo)
Yuki YASUDA (Osaka Univ.)
Zhihong ZHONG (Univ. of Tokyo)

Part-time Workers
Michiko KITAGAWA (Research Part-time Worker I)
Nozomi SATO (Research Part-time Worker I)

Sachiko USUDA (Research Part-time Worker I)
Minako OSANAI (Research Part-time Worker II)

List of Publications & Presentations
Publications[Original Papers]
A. R. Usman, M. U. Khandaker, H. Haba, N. Otuka, and M. Murakami, “Production cross sections of thulium radioisotopes for alphaparticle induced reactions on holmium,” Nucl. Instrum. Methods Phys. Res. B 469, 42 (2020).
M. U. Khandaker, H. Haba, Y. Komori, and N. Otuka, “Excitation functions of deuteron-induced nuclear reactions on erbium in the energy
range of 4–24 MeV,” Nucl. Instrum. Methods Phys. Res. B 470, 1 (2020).
Z. Tsoodol, M. Aikawa, I. Dagvadorj, T. Khishigjargal, N. Javkhlantugs, Y. Komori, and H. Haba, “Production cross sections of 68 Ga andradioactive by-products in deuteron-induced reactions on natural zinc,” Appl. Radiat. Isot. 159, 109095 (2020).
M. Saito, M. Aikawa, T. Murata, Y. Komori, H. Haba, S. Takács, F. Ditrói, and Z. Szűcs, “Production cross sections of 169 Yb by the
proton-induced reaction on 169 Tm,” Nucl. Instrum. Methods Phys. Res. B 471, 13 (2020).
M. Sakaguchi, M. Aikawa, M. Saito, N. Ukon, Y. Komori, and H. Haba, “Activation cross section measurement of the deuteron-induced
reaction on yttrium-89 for zirconium-89 production,” Nucl. Instrum. Methods Phys. Res. B 472, 59 (2020).
J. Grund, M. Asai, K. Blaum, M. Block, S. Chenmarev, Ch. E. Düllmann, K. Eberhardt, S. Lohse, Y. Nagame, Sz. Nagy, P. Naubereit,
J. J. W. van de Laar, F. Schneider, T. K. Sato, N. Sato, D. Simonovski, K. Tsukada, and K. Wendt, “First online operation of TRIGATRAP,” Nucl. Instrum. Methods Phys. Res. A 972, 164013 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Y. Shigekawa, Y. Kasamatsu, Y. Yamakita, Y. Yasuda, E. Watanabe, N. Kondo, H. Haba, and A. Shinohara, “Development of a retardingfield type magnetic bottle spectrometer for studying the internal-conversion process of 235m U,” Nucl. Instrum. Methods Phys. Res. A
976, 164207 (2020).
S. Takács, M. Aikawa, H. Haba, Y. Komori, F. Ditrói, Z. Szűcs, M. Saito, T. Murata, M. Sakaguchi, and N. Ukon, “Cross sections ofalpha-particle induced reactions on nat Ni: Production of 67 Cu,” Nucl. Instrum. Methods Phys. Res. B 479, 125 (2020).
H. Haba, F. Fan, D. Kaji, Y. Kasamatsu, H. Kikunaga, Y. Komori, N. Kondo, H. Kudo, K. Morimoto, K. Morita, M. Murakami, K. Nishio,
J. P. Omtvedt, K. Ooe, Z. Qin, D. Sato, N. Sato, T. K. Sato, Y. Shigekawa, A. Shinohara, M. Takeyama, T. Tanaka, A. Toyoshima,
K. Tsukada, Y. Wakabayashi, Y. Wang, S. Wulﬀ, S. Yamaki, S. Yano, Y. Yasuda, and T. Yokokita, “Production of 266 Bh in the
248
Cm(23 Na, 5n)266 Bh reaction and its decay properties,” Phys. Rev. C 102, 024625 (2020).
Y. Ohshima, H. Suzuki, H. Hanaoka, I. Sasaki, S. Watanabe, H. Haba, Y. Arano, Y. Tsushima, and N. S. Ishioka, “Preclinical evaluationof new α-radionuclide therapy targeting LAT1: 2-[211 At]astato-α-methyl-L-phenylalanine in tumor-bearing model,” Nucl. Med. Biol.
90–91, 15 (2020).
C. Xu, Y. Wang, T. Zhu, H. Wang, Y. Su, J. Zuo, and J. Han, “Experimental study of tritium activity concentration in cooling water of
Heavy Ion Research Facility in Lanzhou,” Nucl. Technol. Radiat. Prot. 35, 304 (2020).
Z. Tsoodol, M. Aikawa, D. Ichinkhorloo, T. Khishigjargal, E. Norov, Y. Komori, H. Haba, S. Takács, F. Ditrói, and Z. Szűcs, “Production
cross sections of 45 Ti in the deuteron-induced reaction on 45 Sc up to 24 MeV,” Appl. Radiat. Isot. 168, 109448 (2021).
Y. Kasamatsu, K. Toyomura, H. Haba, T. Yokokita, Y. Shigekawa, A. Kino, Y. Yasuda, Y. Komori, J. Kanaya, M. Huang, M. Murakami,
H. Kikunaga, E. Watanabe, T. Yoshimura, K. Morita, T. Mitsugashira, K. Takamiya, T. Ohtsuki, and A. Shinohara, “Co-precipitation
behaviour of single atoms of rutherfordium in basic solutions,” Nat. Chem. 13, 226 (2021).
H. Takashima, Y. Koga, S. Manabe, K. Ohnuki, R. Tsumura, T. Anzai, N. Iwata, Y. Wang, T. Yokokita, Y. Komori, D. Mori, S. Usuda,
H. Haba, H. Fujii, Y. Matsumura, and M. Yasunaga, “Radioimmunotherapy with an 211 At-labeled anti-tissue factor antibody protectedby sodium ascorbate,” Cancer Sci. 112, 1975 (2021).
T. Fukuchi, M. Shigeta, H. Haba, D. Mori, T. Yokokita, Y. Komori, S. Yamamoto, and Y. Watanabe, “Image reconstruction method for
multiple-isotope positron emission tomography,” J. Instrum. 16, P01035 (2021).
M. Aikawa, T. Maehashi, D. Ichinkhorloo, S. Ebata, Y. Komori, and H. Haba, “Activation cross sections of deuteron-induced reactions on
praseodymium up to 24 MeV,” Nucl. Instrum. Methods Phys. Res. B 498, 23 (2021).
D. Ichinkhorloo, M. Aikawa, Z. Tsoodol, T. Murata, M. Sakaguchi, Y. Komori, T. Yokokita, and H. Haba, “Production cross sectionsof dysprosium, terbium and gadolinium radioisotopes from the alpha-induced reactions on natural gadolinium up to 50 MeV,” Nucl.
Instrum. Methods Phys. Res. B 499, 46 (2021).
E. Tsantini, T. Minami, M. Ángel C. Ontiveros, K. Takahashi, and J. C. Melgarejo, “Sulfur isotope analysis to examine the provenance of
cinnabar used in wall paintings in the Roman domus Avinyó (Barcelona),” Mineral. 11, 6 (2021).
M. K. A. Patwary, T. Kin, K. Aoki, K. Yoshinami, M. Yamaguchi, Y. Watanabe, K. Tsukada, N. Sato, M. Asai, T. K. Sato, Y. Hatsukawa,and S. Nakayama, “Measurement of double-diﬀerential thick-target neutron yields of the C(d,n) reaction at 12, 20, and 30 MeV,”
J. Nucl. Sci. Technol. 58, 252 (2021).
T. Masuda, T. Watanabe, K. Beeks, H. Fujimoto, T. Hiraki, H. Kaino, S. Kitao, Y. Miyamoto, K. Okai, N. Sasao, M. Seto, T. Schumm,
Y. Shigekawa, K. Tamasaku, S. Uetake, A. Yamaguchi, Y. Yoda, A. Yoshimi, and K. Yoshimura, “Absolute x-ray energy measurement
using a high-accuracy angle encoder,” J. Synchrotron Radiat. 28, 111 (2021).
藤井博史, 大貫和信, 羽場宏光, 吉本光喜, 安永正浩, 高島大輝, 「生物医学研究施設におけるアルファ線放出核種の放射能測定」, Jpn.
Soc. Mol. Imaging (JSMI) Rep. 14, 3 (2021).
南武志, 高橋和也,「与呂木古墳から出土した頭蓋骨付着朱の硫黄同位体比分析」, 三木市文化研究資料第 35 集「与呂木古墳・与呂木 12 号墳—与呂木青葉台団地造成に伴う発掘調査報告書—」, pp. 35–39, (2021).

[Review Articles]
海野弘行, 笠松良崇, 重河優大, 羽場宏光, 平木貴宏, 増田孝彦, 山口敦史, 横北卓也, 吉見彰洋, 吉村浩司, 「高輝度 X 線を用いた核共鳴散乱技術による原子核 229 Th アイソマー状態の人工生成」, Isotope News No. 768, 2 (2020).
羽場宏光, 「元素周期表の新時代 119 番以降の新元素を求めて」, 現代化学 9 月号, No. 594, 43 (2020).
羽場宏光, 「スタニズラオ・カニッツァーロ」, 和光純薬時報, Vol. 88, No. 4, 28 (2020).
南武志, 高橋和也, 「清水風遺跡の朱」, 唐古・鍵考古学ミュージアム展示図録, Vol.27, pp. 11–14 (2020).

[Proceedings]
T. Niwase, K. Fujita, Y. Yamano, K. Watanabe, D. Kaji, K. Morimoto, H. Haba, T. Hirano, S. Mitsuoka, and K. Morita, “Measurementof fusion barrier distribution in 51 V+208 Pb system,” Proc. 13th Int. Conf. on Nucleus-Nucleus Collisions, JPS Conf. Proc. 32, 010022(2020).
A. R. Usman, M. U. Khandaker, and H. Haba, “Eﬀect of target density uncertainties on extracted experimental cross sections for thenatTi(α,x)51 Cr,46 Sc reactions,” Proc. Int. Conf. Nucl. Data Sci. Technol. (ND2019), EPJ Web Conf. 239, 01011 (2020).
Y. Sakemi, T. Aoki, R. Calabrese, H. Haba, K. Harada, T. Hayamizu, Y. Ichikawa, K. Jungmann, A. Kastberg, Y. Kotaka, Y. Matsuda,
Y. Matsuo, H. Nagahama, K. Nakamura, M. Otsuka, N. Ozawa, K. Tanaka, A. Uchiyama, H. Ueno, and L. Willmann, “Fundamental
physics with cold radioactive atoms,” Proc. 14th Asia-Pacific Phys. Conf., AIP Conf. Proc. 2319, 080020 (2021).
T. Zolbadral, M. Aikawa, D. Ichinkhorloo, K. Tegshjargal, Y. Komori, H. Haba, S. Takács, F. Ditrói, and Z. Szűcs, “Production crosssections of 45 Ti via deuteron-induced reaction on 45 Sc,” Proc. 2019 Symp. Nucl. Data, JAEA-Conf 2020-001, 75 (2020).
M. Saito, M. Aikawa, T. Murata, Y. Komori, H. Haba, S. Takács, F. Ditorói, and Z. Szűcs, “Production of 169 Yb by the proton-induced
reaction on 169 Tm,” Proc. 2019 Symp. Nucl. Data, JAEA-Conf 2020-001, 79 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Presentations[International Conferences/Workshops]
H. Takashima (poster), Y. Koga, K. Onuki, S. Manabe, R. Tsumura, T. Anzai, N. Iwata, M. Yasunaga, W. Yang, T. Yokokita, Y. Komori,D. Mori, H. Haba, H. Fujii, and Y. Matsumura, “Preclinical evaluation of astatine-211-conjugated anti-tissue factor antibody,” American
Association for Cancer Research (AACR) Virtual Annual Meeting II, online, June 22–24, 2020.
K. Ooe (poster), T. Watabe, Y. Shirakami, D. Mori, T. Yokokita, Y. Komori, H. Haba, and J. Hatazawa, “Production and separation oftheranostic radionuclide Ag-111 from Pd target,” Society of Nuclear Medicine and Molecular Imaging (SNMMI) Annual Meeting
2020, online, July 11–14, 2020.
H. Haba (invited), “Production and applications of radioisotopes at RIKEN RI Beam Factory—Search for new elements through diagnosis
and therapy of cancer—,” Symposium on Nuclear Data 2020, Wako, Japan, November 26–27, 2020.
Y. Komori (poster), H. Haba, M. Aikawa, M. Saito, S. Takács, and F Ditrói, “Production cross sections of 175 Hf in the nat Lu(p,xn) andnat
Lu(d,xn) reactions,” Symposium on Nuclear Data 2020, Wako, Japan, November 26–27, 2020.
T. Hayamizu (oral), H. Haba, K. Nakamura, T. Aoki, H. Nagahama, K. Tanaka, N. Ozawa, M. Ohtsuka, and Y. Sakemi, “Development of
ultracold francium atomic sources towards the permanent EDM search,” Yamada Conference LXXII: The 8th Asia-Pacific Conference
on Few-Body Problems in Physics (APFB2020), Kanazawa, Japan, March 1–5, 2021.

[Domestic Conferences/Workshops]
高島大輝 (ポスター発表), 古賀宣勝, 大貫和信, 津村遼, 岩田望, 眞鍋史乃, 羽場宏光, 藤井博史, 安永正浩, 松村保広, 「アルファ線放出核種アスタチン—211 結合抗組織因子抗体の開発」, 第 36 回日本 DDS 学会学術集会, 神戸, 2020 年 8 月 28–29 日.
羽場宏光 (招待講演), 「ラジオアイソトープの製造と応用～新元素の探索からがん治療まで～」, 第 17 回日本加速器学会年会, オ
ンライン, 2020 年 9 月 2–4 日.
中島朗久 (口頭発表), 坂口綾, 早川優太, 羽場宏光, 松村夏紀, 寺西翔, 森田涼雅, 横北卓也, 小森有希子, Yang Wang, 森大輝, Karin
Hain, 山崎信哉, Jian Zheng, 末木啓介, 横山明彦, 「U+p 及び Th+Li 反応による Np 同位体励起関数の作成」, 日本放射化学会第64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
寺西翔 (口頭発表), 森田涼雅, 早川優太, 坂口綾, 中島朗久, 小森有希子, 横北卓也, 森大輝, 羽場宏光, 横山明彦, 「232 Th+7 Li 反応のNp 合成系における不完全融合反応の影響」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
森田涼雅 (口頭発表), 寺西翔, 早川優太, 坂口綾, 中島朗久, 小森有希子, 横北卓也, 森大輝, 羽場宏光, 横山明彦, 「232 Th+7 Li 反応における反跳率補正による核分裂断面積測定法の確立」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
Xiaojie Yin (口頭発表), 南部明弘, 小森有希子, 森大輝, 羽場宏光, 「Production of 225 Ac in the 232 Th(14 N,xnyp)225 Ac reaction」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
庭瀬暁隆 (口頭発表), P. Schury, 和田道治, P. Brionnet, S. Chen, 橋本尚志, 羽場宏光, 平山賀一, D. S. Hou, 飯村俊, 石山博恒, 石澤倫,
伊藤由太, 加治大哉, 木村創大, 小浦寛之, J. J. Liu, 宮武宇也, J. Y. Moon, 森本幸司, 森田浩介, 長江大輔, M. Rosenbusch, 高峰愛子,
渡辺裕, H. Wollnik, W. Xian, S. X. Y an, 「MRTOF+α-TOF による 257 Db の直接質量測定」, 日本放射化学会第 64 回討論会 (2020),
オンライン, 2020 年 9 月 9–11 日.
重河優大 (口頭発表), 山口敦史, 佐藤望, 高峰愛子, 和田道治, 羽場宏光, 「核化学研究用高周波イオン収集システムの開発」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
重河優大 (口頭発表), 山口敦史, 鈴木健太, 羽場宏光, 平木貴宏, 菊永英寿, 増田孝彦, 西村俊二, 笹尾登, 吉見彰洋, 吉村浩司, 「U-233の α-γ 同時計数測定による Th-229 の原子核励起状態の半減期の決定」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020
年 9 月 9–11 日.
加藤瑞穂 (口頭発表), 安達サディア, 豊嶋厚史, 塚田和明, 浅井雅人, 羽場宏光, 横北卓也, 小森有希子, 重河優大, Yang Wang, 森大輝,
柏原歩那, 床井健運, 中島朗久, 鈴木雄介, 西塚魁人, 末木啓介, 「HF/HNO3 系における Db の陰イオン交換挙動」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
横北卓也 (口頭発表), 笠松良崇, 渡邉瑛介, 小森有希子, 重河優大, 森大輝, 王洋, 二宮秀美, 速水翔, 東内克馬, ゴーシュコースタブ,
篠原厚, 羽場宏光, 「硫酸系における Rf の陰イオン交換：分配係数の硫酸濃度依存性」, 日本放射化学会第 64 回討論会 (2020),
オンライン, 2020 年 9 月 9–11 日.
濱野健太郎 (口頭発表), 小林義男, 羽場宏光, 上野秀樹, 「ナトリウム電池電極材料 Na2 Ru1-x Fex O3 のメスバウアースペクトル」,日
本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
大江一弘 (口頭発表), 渡部直史, 白神宜史, 森大輝, 横北卓也, 小森有希子, 羽場宏光, 畑澤順, 「核医学利用に向けた Ag-111 の加速器による製造と分離精製」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
青井景都 (口頭発表), 新裕貴, 川﨑康平, 丸山峻平, 鷲山幸信, 西中一朗, 羽場宏光, 森大輝, Yang Wang, 横山明彦, 「211 Rn/211 At ジェ
ネレータシステムに必要な 207 Po 除去の条件の最適化」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
丸山峻平 (口頭発表), 川崎康平, 青井景都, 東美里, 西中一朗, 鷲山幸信, 羽場宏光, 森大輝, 横山明彦, 「薄層クロマトグラフィーを利用したアスタチン化学種同定による溶媒抽出の最適化」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
小森有希子 (ポスター発表), 羽場宏光, 「Calix[4]arene-bis(benzocrown-6) を用いた Fr と Cs の溶媒抽出」, 日本放射化学会第 64 回
討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
小森有希子 (ポスター発表), 羽場宏光, 合川正幸, 斎藤萌美, Sándor Takács, Ferenc Ditrói, 「nat Lu(p,xn) および nat Lu(d,xn) 反応による 175 Hf の生成断面積の測定」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
渡邉瑛介 (ポスター発表), 笠松良崇, 横北卓也, 速水翔, 東内克馬, 重河優大, 羽場宏光, 篠原厚, 「Rf の化学研究に向けた 89m Zr の硝酸系でのオンライン陰イオン交換実験」, 日本放射化学会第 64 回討論会 (2020), オンライン, 2020 年 9 月 9–11 日.
Z. Tsoodol (口頭発表), M. Aikawa, D. Ichinkhorloo, T. Khishigjargal, E. Norov, Y. Komori, H. Haba, S. Takács, F. Ditrói, and Z. Szűcs,“Production cross sections of the medically interesting radionuclide 45 Ti in the deuteron-induced reaction on 45 Sc,” 日本原子力学会- 298 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

2020 年秋の大会, オンライン, 2020 年 9 月 16 日–18 日.
高橋浩之 (口頭発表), 島添健次, 鎌田圭, 羽場宏光, 百瀬敏光, 「多光子ガンマ線時間・空間相関型イメージング法の開発 1 (概要)」,
2021 年第 68 回応用物理学会春季学術講演会, オンライン, 2021 年 3 月 16–19 日.
鎌田圭 (口頭発表), 金敬鎭, 吉野将生, 島添健次, 高橋美和子, 羽場宏光, 百瀬敏光, 高橋浩之, 吉川彰, 「多光子ガンマ線時間・空間
相関型イメージング法の研究 2 (シンチレータ開発)」, 2021 年第 68 回応用物理学会春季学術講演会, オンライン, 2021 年 3 月
16–19 日.
羽場宏光 (口頭発表), 横北卓也, 王洋, 南部明弘, 臼田祥子, 高橋浩之, 島添健次, 鎌田圭, 百瀬敏光, 高橋美和子, 「多光子ガンマ線
時間・空間相関型イメージング法の開発 (3) 多光子放出核種生成」, 2021 年第 68 回応用物理学会春季学術講演会, オンライン,
2021 年 3 月 16–19 日.
島添健次 (口頭発表), 上ノ町水紀, 大鐘健一朗, 高橋浩之, 鎌田圭, 吉川彰, 羽場宏光, 百瀬敏光, 高橋美和子, 「多光子ガンマ線時間・空間相関型イメージング法の開発 (システム開発)」, 2021 年第 68 回応用物理学会春季学術講演会, オンライン, 2021 年 3 月
16–19 日.
藤澤豊 (口頭発表), 森大輝, 羽場宏光, 間賀田泰寛, 飯田靖彦, 「Cu-67 標識新規ソマトスタチン誘導体を用いた神経内分泌腫瘍に対する腫瘍抑制効果の評価」, 第 60 回日本核医学会学術総会, 神戸, 2020 年 11 月 12–14 日.
竹村友紀 (口頭発表), 横北卓也, 結城真美, 田沢周作, 羽場宏光, 「TAT のための 228 Th/224 Ra/212 Pb ジェネレータシステム開発に関する基礎検討」, 第 60 回日本核医学会学術総会, 神戸, 2020 年 11 月 12–14 日.
大江一弘 (口頭発表), 渡部直史, 白神宜史, 森大輝, 横北卓也, 小森有希子, 羽場宏光, 畑澤順, 「治療用核種 Ag-111 の Pd 標的からの加速器製造と分離精製」, 第 60 回日本核医学会学術総会, 神戸, 2020 年 11 月 12–14 日.
髙島大輝 (ポスター発表), 古賀宣勝, 大貫和信, 津村遼, 岩田望, 眞鍋史乃, 羽場宏光, 藤井博史, 松村保広, 安永正浩, 「アルファ線放出核種アスタチン-211 結合抗組織因子抗体の前臨床試験」, 第 27 回次世代医工学研究会, オンライン, 2020 年 12 月 7 日.
羽場宏光 (口頭発表), 「ケミカルプローブに利用できる理研 RI」, Chemical Probe 第三回合同セミナー, オンライン, 2020 年 12 月
14 日.
Yin Xiaojie (口頭発表), 「Production of 225 Ac in the 232 Th(14 N,xnyp)225 Ac reaction」, Chemical Probe 第三回合同セミナー, オンライ
ン, 2020 年 12 月 14 日.
羽場宏光 (招待講演), 「多光子ガンマ線放出核種の製造」, 科学研究費基盤研究 (S) 「多光子ガンマ線時間/空間相関型断層撮像法の研究」ワークショップ「多光子ガンマ線検出技術の新展開」, オンライン, 2020 年 12 月 21 日.
岡井晃一 (口頭発表), Kjeld Beeks, 藤本弘之, 羽場宏光, 原秀明, 海野弘之, 笠松良崇, 北尾真司, 小早川大貴, 小無健司, 増田孝彦,
宮本祐樹, 平木貴宏, 笹尾登, Thorsten Schumm, 瀬戸誠, 重河優大, Simon Stellmer, 玉作賢治, 植竹智, 渡部信, 渡部司, 山口敦史,
安田勇輝, 依田芳卓, 吉見彰洋, 吉村浩司, 吉村太彦, 「トリウム 229 アイソマー状態からの真空紫外光観測に向けた Th:CaF2 結
晶の光学特性評価」, 日本物理学会第 76 回年次大会（2021 年）, オンライン, 2021 年 3 月 12–15 日.
小澤直也 (口頭発表), 長濱弘季, 早水友洋, 中村圭佑, 佐藤幹, 永瀬慎太郎, 小高康照, 鎌倉恵太, 田中香津生, 大塚未来, 青木貴稔,
市川雄一, 高峰愛子, 羽場宏光, 上野秀樹, 酒見泰寛, 「フランシウム原子の電気双極子能率探索のための表面電離イオン源の開発」, 日本物理学会第 76 回年次大会（2021 年）, オンライン, 2021 年 3 月 12–15 日.
羽場宏光 (招待講演), 「理研における At-211 の製造分離状況と将来計画」, 放射線科学基盤機構シンポジウム「核医学セラノスティ
クス：基盤技術から臨床応用まで/Theranostics from radioisotope production technology to clinical application」, オンライン, 2021
年 3 月 18 日.
重河優大 (口頭発表), 「Pa-229 を利用した Th-229m の真空紫外光観測実験の現状」, 2020 重元素核化学ワークショップ, オンライ
ン, 2021 年 3 月 30 日.

Press Releases
原子 1 つの沈殿を調べる! —超重元素ラザホージウムの共沈挙動の実験的観測—, 理化学研究所, 2021 年 2 月 18 日. https://www.riken.jp/press/2021/20210218_1 .

Patents
田沢周作, 竹村友紀, 結城真美, 竹内康隆, 芝原裕規, 羽場宏光, 横北卓也, 「目的核種の生成方法」, 特願 2021-037814.

Outreach Activities
羽場宏光, 「原子の仕組みとラジオアイソトープの応用～新元素の探索からがんの治療まで～」, 令和 2 年度（2020 年度）八王子市生涯学習センター主催市民自由講座, 八王子, 2021 年 3 月 9 日.

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Accelerator Applications Research Division
RI Application Research Group
Industrial Application Research Team
1. Abstract

Industrial application research team handles non-academic activities at RIBF corresponding mainly to industries.

2. Major Research Subjects(1) Support of industrial utilization of the RIBF accelerator beam.
(2) Fee-based distribution of radioisotopes produced at RIKEN AVF Cyclotron.

3. Summary of Research Activity(1) Support of Industrial Utilization of RIBF
RNC promote facility-sharing program “Promotion of applications of high-energy heavy ions and RI beams.” In this program,
RNC opens a part of the RIBF facility, which includes the AVF cyclotron, RILAC, RIKEN Ring Cyclotron and experimental instruments, to non-academic proposals from users including private companies. The proposals are reviewed by a program advisorycommittee, industrial PAC (In-PAC). The proposals which have been approved by the In-PAC are allocated with beam times and theusers pay RIKEN the beam time fee. The intellectual properties obtained by the use of RIBF belong to the users. In order to encourage
the use of RIBF by those who are not familiar with utilization of ion beams, the first two beam times of each proposal can be assigned
to trial uses which are free of beam time fee.
In July 2020, the In-PAC met and approved fee-based proposals from private companies; two proposals from new companies andthree proposals from continuously using companies. In January 2021, the In-PAC held a mail review and approved three fee-based
proposals from continuous users. In 2020, six companies executed eleven fee-based beamtimes, seven of which utilized a Kr beamwith a total beam time of 153 h and four utilized, an Ar beam with a total beam time of 73 h.
(2) Fee-based distribution of radioisotopes produced at RIKEN AVF Cyclotron
We have been handling fee-based distribution of radioisotopes since 2007. The radionuclides are 65 Zn (T 1/2 = 244 days), 109 Cd(463 days), 88 Y (107 days), 85 Sr (65 days) and 67 Cu (2.58 days) which are produced at the AVF cyclotron by the Nuclear Chemistry
Research Team. According to a material transfer agreement (MTA) drawn between Japan Radioisotope Association (JRIA) and
RIKEN, JRIA mediates the transaction of the RIs and distributes them to users. Details can be found on the online ordering system
J-RAM home page of JRIA.
In 2020, we delivered one shipment of 109 Cd with an activity of 10 MBq, three of 65 Zn with a total activity of 12 MBq, two of 88 Y
with a total activity of 2 MBq, and two of 85 Sr with a total activity of 3 MBq. The final recipients of the RIs were four universities,
one private company, and one medical research center.

Members
Team Leader
Atsushi YOSHIDA
Contract Researcher
Tadashi KAMBARA
Technical Staﬀ I
Akihiro NAMBU

List of Publications & Presentations
OthersFee-based beamtimes for private companies: Kr beam 153 h, Ar beam 73 h.

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Subnuclear System Research Division
Quantum Hadron Physics Laboratory
1. Abstract

Atomic nuclei are made of protons and neutrons bound by the exchange of pion and other mesons. Also, protons and neutrons
are made of quarks bound by the exchange of gluons. These strong interactions are governed by the non-Abelian gauge theory
called the quantum chromodynamics (QCD). On the basis of theoretical and numerical analyses of QCD, we study the interactions
between the nucleons, properties of the dense quark matter realized at the center of neutron stars, and properties of the hot quark-gluon
plasma realized in the early Universe. Strong correlations common in QCD and cold atoms are also studied theoretically to unravel
the universal features of the strongly interacting many-body systems. Developing perturbative and non-perturbative techniques inquantum field theory and string theory are of great importance not only to solve gauge theories such as QED and QCD, but also to findthe theories beyond the standard model of elementary particles. Various theoretical approaches along this line have been attempted.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

Perturbative and non-perturbative methods in quantum field theories
Quantum computing
Lattice gauge theory
QCD under extreme conditions
Nuclear and atomic many-body problems

3. Summary of Research Activity(1) Perturbative and non-perturbative methods in quantum field theories(1-1) Theory of the anomalous magnetic moment of the electron
The anomalous magnetic moment of the electron ae measured in a Penning trap occupies a unique position among high precision
measurements of physical constants in the sense that it can be compared directly with the theoretical calculation based on the renormalized quantum electrodynamics (QED) to high orders of perturbation expansion in the fine structure constant α, with an eﬀective
parameter α/π. Both numerical and analytic evaluations of ae up to (α/π)4 were firmly established. The coeﬃcient of (α/π)5 has
been obtained recently by an extensive numerical integration. The contributions of hadronic and weak interactions have also been
estimated. The sum of all these terms leads to ae (theory) = 1 159 652 181.606 (11)(12)(229) × 10−12 , where the first two uncertainties
are from the tenth-order QED term and the hadronic term, respectively. The third and largest uncertainty comes from the current bestvalue of the fine-structure constant derived from the cesium recoil measurement: α−1 (Cs) = 137.035 999 046 (27). The discrepancy
between ae (theory) and ae (experiment) is 2.4σ. Assuming that the standard model is valid so that ae (theory) = ae (experiment)
holds, we obtained α−1 (ae ) = 137.035 999 1496 (13)(14)(330), which is nearly as accurate as α−1 (Cs). The uncertainties are from thetenth-order QED term, hadronic term, and the best measurement of ae , in this order.
(1-2) Transport theory of chiral fermions under external gravity and fluid field
We formulated the kinetic theory of chiral matter in external gravitational fields, based on quantum field theory. The resulting
kinetic theory reveals that the Riemann curvature induces non-dissipative transport phenomena of chiral fermions. In particular, wefound that the spin-gravity coupling results in the antiparallel flow of the charge current and energy current of fermions, which is never
explained in the classical picture. These novel framework and phenomena takes place not only in cosmological systems involving
neutrinos but also in chiral matter aﬀected by background fluid, such as quark-gluon plasma, graphene and Dirac/Weyl semimetals.
We demonstrated that a temperature gradient and fluid vorticity induce a pressure correction and charge and energy flow in Dirac/Weylsemimetals.
(1-3) Spin transport of massive fermion
We derived the spin kinetic theory under external electromagnetic and gravitational fields. We derived the global equilibrium
conditions from the kinetic equations and find that the finite Riemann curvature or an external electromagnetic field is necessary to
determine the spin-thermal vorticity coupling. Solving the equation of motion of axial vector part of the Wigner transformed fermion
propagator, we evaluated the Pauli-Lubanski vector, which expresses the spin polarization of massive fermions, at the local equilibriumand out of equilibrium. This formula is potentially important of the Λ polarization puzzle found in heavy-ion collisions, which cannot
be understood in the calculations based on global equilibrium assumption.
(1-4) Chiral vortical eﬀect in condensed matter systems
We revisited the chiral vortical eﬀect in condensed matter physics, by using the semiclassical wave-packet theory. In high-energy
physics, the chiral vortical current is conventionally defined as the Noether current. Such a definition is however improper in thecontext of condensed matter systems since there potentially exists the contributions of the magnetization current. Indeed we showedthat the chiral vortical current is compensated by the magnetization current. Hence the chiral vortical eﬀect cannot be observed inpseudo-relativistic condensed matter systems, such as Dirac/Weyl semimetals. Instead, we demonstrated that the chiral vortical eﬀect
is an observable in several nonrelativistic matter, and suggested possible table-top experimental setups.
(1-5) Lorentzian conformal field theories through sine-square deformation
In quantum field theories, symmetry plays an essential and exceptional role. Focusing on some proper symmetry and delving
into its meaning have been proven to be one of the most fruitful strategies. We reexamined two-dimensional Lorentzian conformal
field theory using the formalism previously developed in a study of sine-square deformation of Euclidean conformal field theory. We- 301 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

construct three types of Virasoro algebra. One of them reproduces the result by Luscher and Mack, while another type exhibits thedivergence in the central charge term. The other leads the continuous spectrum and contains no closed time-like curve in the system.
(2) Quantum computing(2-1) Hybrid quantum annealing via molecular dynamics
A novel quantum-classical hybrid scheme was proposed to eﬃciently solve large-scale combinatorial optimization problems. The
key concept is to introduce a Hamiltonian dynamics of the classical flux variables associated with the quantum spins of the transversefield Ising model. Molecular dynamics of the classical fluxes can be used as a powerful preconditioner to sort out the frozen andambivalent spins for quantum annealers. It was demonstrated that the performance and accuracy of our smooth hybridization are
better in comparison to the standard classical algorithms (the tabu search and the simulated annealing) by employing the MAX-CUTand Ising spin-glass problems.
(3) Lattice gauge theory(3-1) Most charming dibaryon near unitarity
The interaction between Ωccc –Ωccc in the S -wave and spin-0 channel was studied from the (2 + 1)-flavor lattice QCD with nearly
physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The time-dependent HAL
QCD method was employed to extract the Ωccc Ωccc potential from the lattice QCD data of two-baryon spatial correlation, and thescattering observables were calculated. The potential was found to be attractive at mid-range and weakly repulsive at short-range.
Taking into account the Coulomb repulsion with the charge form factor of Ωccc as well, the scattering length aC0 ∼= 19 fm and theCC∼= 0.45 fm were obtained. The ratio reﬀ/aC0 ∼= −0.024, whose magnitude is considerably smaller than that of theeﬀective range reﬀ
dineutron (−0.149), indicates that Ωccc Ωccc is located in the unitary region.
(3-2) d∗ (2380) dibaryon from lattice QCD
The ∆∆ dibaryon resonance d∗ (2380) with (J π , I) = (3+ , 0) was studied from the 3-flavor lattice QCD with heavy pion masses (mπ= 0.68, 0.84, 1.02 GeV). The central ∆∆ potential in 7 S3 channel obtained by HAL QCD method shows a strong short-range attraction,
so that a quasi-bound state corresponding to d*(2380) is formed with the binding energy 25–40 MeV below the ∆∆ threshold for theheavy pion masses. The tensor part of the transition potential from ∆∆ to NN was also extracted. Although the obtained transition
potential is strong at short distances, the decay width of d∗ (2380) to NN in the D-wave was found to be kinematically suppressed.
(3-3) Stress tensor around static quark-anti-quark from Yang-Mills gradient flow
The spatial distribution of the stress tensor around the quark-anti-quark pair in SU(3) lattice gauge theory was studied. The
YangMills gradient flow plays a crucial role to make the stress tensor well-defined and derivable from the numerical simulations on
the lattice. The resultant stress tensor with a decomposition into local principal axes shows, for the first time, the detailed structureof the flux tube along the longitudinal and transverse directions in a gauge invariant manner. The linear confining behavior of thepotential at long distances is derived directly from the integral of the local stress tensor.
(4) QCD under extreme conditions(4-1) Finite density QCD based on complex Langevin method
The complex Langevin method (CLM) is one of a promising approach to overcome the sign problem. The central idea of thisapproach is that the stochastic quantization does not require the probabilistic interpretation of the Boltzmann weight e−S even when theaction takes complex values. Although the equivalence between CLM and the familiar path integral quantization is quite nontrivial, it
is pointed out that the probability distribution of the drift term can judge the correctness of the CLM. This enable us to perform latticesimulation of QCD based on CLM in the finite density region in a self-contained manner. We discussed the applicability of the CLM
with four-flavor staggered fermions on a 83 × 16 lattice with quark mass m = 0.01. In particular, we focus on the behavior of theeigenvalue distribution of the fermion mass matrix which is closely related to the appearance of the singular drift problem.
(4-2) Non-equilibrium quantum transport of chiral fluids from kinetic theory
We introduced the quantum-field-theory (QFT) derivation of chiral kinetic theory (CKT) from the Wigner-function approach,which manifests side jumps and non-scalar distribution functions associated with Lorentz covariance and incorporates both background fields and collisions. The formalism is utilized to investigate second-order responses of chiral fluids near local equilibrium. Such nonequilibrium anomalous transport is dissipative and aﬀected by interactions. Contributions from both quantum corrections in anomalous hydrodynamic equations (EOM) of motion and those from the CKT and Wigner functions (WF) are considered in a relaxation-time approximation (RTA). Anomalous charged Hall currents engendered by background electric fields andtemperature/chemical-potential gradients are obtained. Furthermore, chiral magnetic/vortical eﬀects (CME/CVE) receive viscous corrections as non-equilibrium modifications stemming from the interplay between side jumps, magnetic-moment coupling, and chiralanomaly.
(4-3) Hadron-quark crossover in cold and hot neutron stars
We presented a much improved equation of state for neutron star matter, QHC19, with a smooth crossover from the hadronic
regime at lower densities to the quark regime at higher densities. We now use the Togashi et al. equation of state, a generalization of
the Akmal-Pandharipande-Ravenhall equation of state of uniform nuclear matter, in the entire hadronic regime; the Togashi equation ofstate consistently describes nonuniform as well as uniform matter, and matter at beta equilibrium without the need for an interpolation
between pure neutron and symmetric nuclear matter. We describe the quark matter regime at higher densities with the NambuJonaLasinio model, now identifying tight constraints on the phenomenological universal vector repulsion between quarks and thepairing interaction between quarks arising from the requirements of thermodynamic stability and causal propagation of sound. The
resultant neutron star properties agree very well with the inferences of the LIGO/Virgo collaboration, from GW170817, of the pressure- 302 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

versus baryon density, neutron star radii, and tidal deformabilities. The maximum neutron star mass allowed by QHC19 is 2.35 MS,
consistent with all neutron star mass determinations.
(4-4) Gluonic energy and momentum distribution at finite temperature
We studied the energy-momentum distribution of the gluons around a static quark at finite temperature on the basis of theeﬀective field theory (EFT) of thermal QCD. Spatial correlations between the Polyakov loop and the energy-momentum tensor
were calculated up to the next-to-leading order in EFT. The results were compared with the recent quenched lattice QCD calculation
obtained by using the gradient flow formalism. The EFT results and the lattice QCD data agree quite well without any fitting
parameters at high temperature above deconfinement. On the other hand, there is a substantial diﬀerence near the critical temperatureespecially in the distribution of the energy density, which indicates some non-perturbative eﬀect.
(5) Nuclear and atomic many-body problems(5-1) Density functional theory for nuclear structure
The atomic nuclei are composed of protons and neutrons interacting via the nuclear and Coulomb interactions. The density
functional theory (DFT) is widely used to calculate the ground-state properties. Nevertheless, because of the lack of knowledge of
nuclear interaction in medium (eﬀective interaction), the eﬀective interaction is fitted to experimental data, and it has been attained todevelop a high-accuracy one. In contrast, the nucleons have finite charge distributions, while this is not considered in DFT calculation.
Because it is indispensable to treat the Coulomb interaction more accurately to achieve high-accuracy nuclear eﬀective interaction, we
consider such finite-size eﬀects to nuclear DFT, and we reveal that such eﬀects give a non-negligible contribution to nuclear binding
energies. In nuclear structure calculation, both non-relativistic and relativistic schemes of DFT are used, while the connection between
them, especially in terms of the eﬀective interaction, is not understood well. To reveal it, we also develop the eﬃcient non-relativistic
reduction of the many-body systems.
(5-2) Fundamental problems of density functional theory
The density functional theory (DFT) is one of the powerful methods to calculate ground-state properties of the quantum manybody problems, including atomic nuclei, atoms, molecules, and solids. The accuracy of the DFT depends on the energy density
functional (EDF), which contains information on the interaction. We develop a method to calculate EDF for electronic systems
purely microscopically using the functional renormalization group. In this method, energy density for so many various densities canbe calculated, and eventually, DFT calculation can be performed without fitting energy density to some functional forms. We also
develop the relativistic DFT in which the finite-light-speed correction to the Coulomb interaction is also considered to calculate theground-state properties of super-heavy elements.
(5-3) One-dimensional Bose and Fermi gases with contact interactions
We investigate local quantum field theories for one-dimensional (1D) Bose and Fermi gases with contact interactions, which
are closely connected with each other by Girardeau’s Bose-Fermi mapping. While the Lagrangian for bosons includes only a twobody interaction, a marginally relevant three-body interaction term is found to be necessary for fermions. Because of this three-bodycoupling, the three-body contact characterizing a local triad correlation appears in the energy relation for fermions, which is one of thesum rules for a momentum distribution. In addition, we apply in both systems the operator product expansion to derive large-energy
and momentum asymptotics of a dynamic structure factor and a single-particle spectral density. These behaviors are universal in thesense that they hold for any 1D scattering length at any temperature. The asymptotics for the Tonks-Girardeau gas, which is a Bosegas with a hardcore repulsion, as well as the Bose-Fermi correspondence in the presence of three-body attractions are also discussed.
(5-4) Mesoscopic spin transport between strongly interacting Fermi gases
We investigate a mesoscopic spin current for strongly interacting Fermi gases through a quantum point contact. Under thesituation where spin polarizations in left and right reservoirs are same in magnitude but opposite in sign, we calculate the contributionof quasiparticles to the current by means of the linear response theory and many-body T -matrix approximation. For a small spin-bias
regime, the current in the vicinity of the superfluid transition temperature is strongly suppressed due to the formation of pseudogaps.
For a large spin-bias regime where the gases become highly polarized, on the other hand, the current is aﬀected by the enhancement ofa minority density of states due to Fermi polarons. We also discuss the broadening of a quasiparticle peak associated with an attractive
polaron at a large momentum, which is relevant to the enhancement(5-5) Optical spin conductivity in ultracold quantum gases
Measurement of frequency-resolved spin transport is a subject of much interest in condensed matter physics. Here we show thatthe optical spin conductivity, which is a small AC response of a spin current, can be measured with existing methods in ultracold atom
experiments. We point out that once interatomic interactions are turned on, the optical spin conductivity becomes nontrivial even inclean ultracold atomic gases and thereby can be a probe of generic quantum states of matter. This is a sharp contrast to the optical massconductivity which becomes trivial in typical cold-atom systems without disorder and lattice potential. For systems with arbitrary spin
degrees of freedom, we construct a general formalism of the optical spin conductivity and derive the f -sum rule. To demonstrate
the availability of the optical spin conductivity, our formalism is applied to a spin-1/2 Fermi superfluid and a spin-1 Bose-Einsteincondensate. It turns out that both superfluids show nontrivial responses that cannot be captured with the Drude conductivity. The
application of our proposed method to generic ultracold atomic gases with spin degrees of freedom is feasible.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Members
Director
Masahiko IWASAKI
Vice Chief Scientist
Tsukasa TADA
Research/Technical Scientist
Takumi DOI (Senior Research Scientist)
Senior Scientist
Makiko NIO
Contract Researcher
Dang NGUYEN DINH
Special Postdoctoral Researchers
Matthias W.G. BERWEIN
Kazuya MAMEDA

Shoichiro TSUTSUI

Research Consultant
Takeo INAMI (Inst. of Phys. Vietnamese Academy of Sci. andTech.)
Visiting Scientists
Shinya AOKI (Kyoto Univ.)
Tatsumi AOYAMA (KEK)
Gergely P. FEJOS (Eotvos Lorand Univ.)
Kenji FUKUSHIMA (Univ. of Tokyo)
Hideki HAMAGAKI (Nagasaki Inst. of Applied Sci.)
Koji HASHIMOTO (Osaka Univ.)
Masashi HAYAKAWA (Nagoya Univ.)
Tomoya HAYATA (Keio Univ.)
Takashi INOUE (Nihon Univ.)
Noriyoshi ISHII (Osaka Univ.)
Yuki KAMIYA (Chinese Academy of Sci.)
Yoichi KAZAMA (Univ. of Tokyo)
Phuc T. LE (Inst. of Fundamental and Applied Sci. Duy Tan
Univ.)
Haozhao LIANG (Univ. of Tokyo)
Takaya MIYAMOTO (NEC Corporation)

Kenji MORITA (QST)
Masaki MURATA (Japan Univ. of Economics)
Atsushi NAKAMURA (Osaka Univ.)
Takashi NAKATSUKASA (Tsukuba Univ.)
Hung NGUYEN (Duy Tan Univ.)
Yoji OHASHI (Keio Univ.)
RHINE KUMAR ARAYAKKANDI KEECH (Cochin Univ. ofSci. and Tech.)
Shoichi SASAKI (Tohoku Univ.)
Kenji SASAKI (Kyoto Univ.)
Hiroshi SUZUKI (Kyushu Univ.)
Motoi TACHIBANA (Saga Univ.)
Sachiko TAKEUCHI (The Social Work Research Institute)
Hiroshi TOKI (Osaka Univ.)
Di-Lun YANG (Keio Univ.)

Visiting Researcher
Yuta SEKINO (JSPS)
Student Trainees
Yutaro AKAHOSHI (Kyoto Univ.)
Asahi CHIKAOKA (Univ. of Tokyo)
Yixin GUO (Univ. of Tokyo)
Akira HIRAYAMA (Saitama Univ.)
Xun LIU (Univ. of Tokyo)

Yan LYU (Peking Univ.)
Kotaro MURAKAMI (Kyoto Univ.)
Tomoya NAITO (Univ. of Tokyo)
Hui TONG (Peking Univ.)
Tingyu ZHANG (Univ. of Sci. and Tech. of China)

List of Publications & Presentations
Publications[Original Papers]
G. Accorto, T. Naito, H. Liang, T. Niksic, and D. Vretenar, “Nuclear energy density functionals from empirical ground-state densities,”
Phys. Rev. C 103, 044304 (2021).
T. Hayata, Y. Hidaka, and K. Mameda, “Second order chiral kinetic theory under gravity and antiparallel charge-energy flow,” J. HighEnergy Phys. 2021, 23 (2021).
N. Itagaki and T. Naito, “Consistent description for cluster dynamics and single-particle correlation,” Phys. Rev. C 103, 044303 (2021).
T. Yokota and T. Naito, “Ab initio construction of the energy density functional for electron systems with the functional-renormalizationgroup-aided density functional theory,” Phys. Rev. Res. 3, L012015 (2021).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Y. Sekino, H. Tajima, and S. Uchino, “Optical spin transport in ultracold quantum gases,” arXiv:2103.02418 [cond-mat.quant-gas] (2021).
Y. Lyu, H. Tong, T. Sugiura, S. Aoki, T. Doi, T. Hatsuda, J. Meng, and T. Miyamoto, “Most charming dibaryon near unitarity,”
arXiv:2102.00181 [hep-lat] (2021).
T. Naito, G. Colò, H. Liang, and X. Roca-Maza, “Second and fourth moments of the charge density and neutron-skin thickness of atomic
nuclei,” arXiv:2101.07680 [nucl-th] (2021).
Z. Wang, T. Naito, H. Liang, and W. H. Long, “Exploring eﬀects of tensor force and its strength via neutron drops,” arXiv:2101.04860[nucl-th] (2021).
Y. Tanabe, Y. Ito, K. Sugawara, M. Koshino, S. Kimura, T. Naito, I. Johnson, T. Takahashi, and M. Chen, “Dirac Fermion kinetics inthree-dimensionally curved graphene,” Adv. Mater. 32, 202005838 (2020).
X. Liu and T. Tada, “Analysis for Lorentzian conformal field theories through sine-square deformation,” Prog. Theor. Exp. Phys. 2020,
061B01225 (2020).
Z. Wang, T. Naito, and H. Liang, “Tensor eﬀects on shell-structure evolution in N = 82 isotones and Z = 50 isotopes in the relativistic
Hartree-Fock theory,” arXiv:2012.13143 [nucl-th] (2020).
Y. Sekino and Y. Nishida, “Field theoretical aspects of one-dimensional Bose and Fermi gases with contact interactions,” Phys. Rev. A
103, 043307 (2021).
T. Naito, S. Endo, K. Hagino, and Y. Tanimura, “Are atoms spherical?” arXiv:2009.05955 [physics.atom-ph] (2020).
K. Murakami, Y. Akahoshi, and S. Aoki, “S-wave kaon-nucleon potentials with all-to-all propagators in the HAL QCD method,” Prog.
Theor. Exp. Phys. 2020, 093B03 (2020).
H. Irie, H. Liang, T. Doi, S. Gongyo, and T. Hatsuda, “Hybrid quantum annealing via molecular dynamics,” Sci. Rep. 11, 8426 (2021)
Y. Akahoshi, S. Aoki, T. Aoyama, T. Doi, T. Miyamoto, and K. Sasaki, “The HAL QCD potential in I = 1 ππ system with the ρ mesonbound state,” (2020). Prog. Theor. Exp. Phys. 2020, 073B07 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
Strangeness Nuclear Physics Laboratory
1. Abstract

We proposed accurate calculation method called ‘Gaussian Expansion Method using infinitesimally shifted Gaussian lobe basis
function.’ When one proceeds to four-body systems, calculation of the Hamiltonian matrix elements becomes much laborious. In orderto make the four-body calculation tractable even for complicated interactions, the infinitesimally-shifted Gaussian lobe basis function
has been proposed. The GEM with the technique of infinitesimally-shifted Gaussians has been applied to various three-, four- andfive-body calculations in hypernuclei, the four-nucleon systems, and cold-atom systems. As results, we succeeded in extracting newunderstandings in various fields.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Structure of Hypernuclei and neutron-rich nuclei from the view point of few-body problem
Structure of exotic hadron system
quantum atomic system and ultra cold atomic system
Equation of state for neutron star

3. Summary of Research Activity(1) We study Λ hypernuclei of C and B isotopes. We calculated Λ binding energies of these Λ hypernuclei and found halo
structure in the Λ 1p state with extended wave functions. In addition, we propose to measure electric-dipole transition
between Λ 1p and 1s states to see evidence for this hyperon halo structure.
(2) Bound states of double-heavy tetraquark systems are studied in a constituent quark model. We have two bound states for
T = 0, J π = 1+ in bbu-bar u-bar system. One is deeply bound state and the other is a shallow bound state. The former state isin good agreement with the result by lattice QCD.
(3) We investigate the miscibility of two kinds of bosons with repulsive interactions. In addition to the known miscible andimmiscible phases, we predict a partially miscible phase due to quantum fluctuations. It leads to the formation of mixed
bubbles that are similar to quantum liquid droplets found in attractive mixtures and could be observed in experiments.

Members
Director
Emiko HIYAMA
Research/Technical Scientist
Pascal NAIDON (Senior Research Scientist)
Special Postdoctoral Researcher
Tokuro FUKUIPostdoctoral Researcher
Christiane H. SCHMICKLER
Senior Visiting Scientist
Makoto OKA (JAEA)
Visiting Scientists
Masayuki ASAKAWA (Osaka Univ.)
Kadir Utku CAN (The Univ. of Adelaide)
Jaume CARBONELL (CNRS-IN2P3)
Lorenzo CONTESSI (Hebrew Univ. of Jerusalem)
Jiwei CUI (Xidian Univ.)
Akinobu DOTE (KEK)
Shimpei ENDO (Tohoku Univ.)
Tomokazu FUKUDA (Univ. of Electro-Commun.)
Yasuro FUNAKI (Kanto Gakuin Univ.)
Takenori FURUMOTO (Yokohama Nat’l Univ.)
Philipp GUBLER (JAEA)
Satoru HIRENZAKI (Nara Women’s Univ.)
Atsushi HOSAKA (Osaka Univ.)
Jinniu HU (Nankai Univ.)
Tetsuo HYODO (Tokyo Metropolitan Univ.)

Kiyomi IKEDA (Niigata Univ.)
Yoichi IKEDA (Kyushu Univ.)
Masahiro ISAKA (Hosei Univ.)
Souichi ISHIKAWA (Hosei Univ.)
Daisuke JIDO (Tokyo Tech)
Hyun-Chul KIM (Inha Univ.)
Kei KOTAKE (Fukuoka Univ.)
Toshio MOTOBA (Univ. of Electro-Commun.)Takayuki MYO (Osaka Inst. of Tech.)
Satoshi NAKAMURA (Tohoku Univ.)
Kazuma NAKAZAWA (Gifu Univ.)
Hidekatsu NEMURA (Osaka Univ.)
Jean-Marc RICHARD (Lyon Univ.)
Thomas RIJKEN (Univ. Of Nijmegen)Shoichi SASAKI (Tohoku Univ.)- 306 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Hans-Josef SCHULZE (INFN)
Shoji SHINMURA(Gifu Univ.)
Jirina STONE (Univ. of Tennessee)
Tingting SUN (Zhengzhou Univ.)
Hiroyuki TAJIMA (Univ. of Tokyo)
Hajime TOGASHI (Tohoku Univ.)
Atsushi UMEYA (Nippon Inst. of Tech.)
Shin WATANABE (NIT, Gifu College )Wolfram WEISE (TU Munich)Chengjun XIA (Zhejiang Univ.)
Masanobu YAHIRO (Kyushu Univ.)
Ulugbek YAKHSHIEV (Inha Univ.)
Taiichi YAMADA (Kanto Gakuin Univ.)
Yasuo YAMAMOTO (Tsuru Univ.)
Nodoka YAMANAKA (Kennesaw State Univ.)
Takuma YAMASHITA (Tohoku Univ.)
Ying ZHANG (Tianjin Univ.)
Xian-Rong ZHOU (East China Normal Univ.)

Student Trainees
Kongyi HU (Nankai Univ.)
Dongwook LEE (Kyushu Univ.)
Jie LIU (Nanjing Univ.)

Qi MENG (Nanjing Univ.)
Qian WU (Nanjing Univ.)

Part-time Worker
Yoko FUJITA (Administrative Part-time Worker I)

List of Publications & Presentations
Publications[Original Papers]
Y. Kim, E. Hiyama, M. Oka, and K. Suzuki, “Spectrum of singly heavy baryons from a chiral eﬀective theory of diquarks,” Phys. Rev. D
102, 014004 (2020).
T. -W. Wu, M. -Z. Liu, L. -S. Geng, E. Hiyama, M. P. Valderrama, and W. -L. Wang, “Quadruply charmed dibaryons as heavy quark
symmetry partners of the DDK bound state,” Eur. Phys. J. 80, 901 (2020).
Q. Wu, Y. Funaki, E. Hiyama, and H. Zong, “Resonant states of 9Λ Be with α + α + Λ three-body cluster model,” Phys. Rev. C 102, 054303(2020).
A. Nay L. Nyaw, K. Nakazawa, et al., “Observation of double-strangeness nuclei using nuclear-emulsion technology,” Bull. Soc. Photogr.
Imag. Jpn. 30, 2 22–25 (2020).
T. Yamashita, Y. Kino, E. Hiyama, S. Jonsell, and P. Froelich, “Near-threshold production of antihydrogen positive ion in positroniumantihydrogen collision,” New J. Phys. 23, 012001 (2021).
S. H. Hayakawa, K. Nakazawa, et al. (J-PARC E07 Collaboration), “Observation of coulomb-assisted nuclear bound state of Ξ− -14 N
system,” Phys. Rev. Lett. 126, 062501 (2021).
J. Yoshida, K. Nakazawa, et al., “CNN-based event classification of alpha-decay events in nuclear emulsion,” Nucl. Instrum. Methods
Phys. Res. A 989, 16430 (2021).
N. Yamanaka and E. Hiyama, “Weinberg operator contribution to the nucleon electric dipole moment in the quark model,” Phys. Rev. D
103, 035023 (2021).
Q. Meng, E. Hiyama, A. Hosaka, M. Oka, P. Gubler, K. U. Can, T. T. Takahashi, and H. S. Zong, “Stable double-heavy tetraquarks:
Spectrum and structure,” Phys. Lett. B 814, 136095 (2021).
P. Naidon and D. S. Petrov, “Mixed bubbles in Bose-Bose mixtures,” Phys. Rev. Lett. 126, 115301 (2021).

[Proceedings]
J. Carbonell, E. Hiyama, R. Lazauskas, and F. M. Marques, “19 B isotope as a 17 B-n-n three-body cluster close to unitary limit,” J. Phys.
Conf. Ser. 1643, 012120 (2020).

Presentations[International Conferences/Workshops]
P. Naidon (invited), “A partial mixing of quantum gases,” Yamada Conference LXXII: The 8th Asia-Pacific Conference on Few-Body
Problems (APFB2020), Kanazawa, Japan, March 1–5, 2021.
P. Naidon (invited), “Mixed bubbles in repulsive Bose-Bose mixtures,” The 5th Symposium on Clustering as a Window on the Hierarchical
Structure of Quantum Systems, September 24, 2020.
T. Fukui (oral), “Chiral three-body force and shell evolution,” Yamada Conference LXXII: The 8th Asia-Pacific Conference on Few-Body
Problems in Physics (APFB2020), Kanazawa, Japan, March 1–5, 2021.
C. Schmickler, “Origin of the three-body parameter of the Kartavtsev-Malykh crossover trimer,” Yamada Conference LXXII: The 8th
Asia-Pacific Conference on Few-Body Problems in Physics (APFB2020), Kamazawa, Japan, March 1–5, 2021.

[Domestic Conferences/Workshops]
P. Naidon (poster), “A new kind of bubble,” The 22nd RIKEN Interdisciplinary Exchange Evening, September 25, 2020.
福井徳朗 (口頭発表), 「カイラル相互作用による軽い核のクラスター構造の理解に向けて」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)[Seminars & Lectures]
P. Naidon (invited), “Universal few-body physics,” 4-Part Lecture at Hokkaido University Nuclear Theory Group, February 16, 2021.
P. Naidon (invited), “Mixed bubbles in repulsive Bose-Bose mixtures,” Kindai University, December 16, 2020.
P. Naidon (invited), “Universal few-body physics,” 2-Part Lecture at Strange Nuclear Physics School 2020, December 2–5, 2020.
P. Naidon (invited), “QCD-like phase diagram of resonantly interacting SU(3) Fermi gases,” Kyushu University, July 10, 2020.

Press Releases「極低温での新しい量子相 “混合バブル” を予言—混和性・非混和性の中間に存在する部分混和性の発見—」, 2021 年 3 月 22 日.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
Radiation Laboratory
1. Abstract

Nucleons, such as protons and neutrons, are a bound state of constituent quarks glued together with gluons. The detail structureof nucleons, however, is not well understood yet. Especially the mechanism to build up the spin of proton, which is 1/2, is a major
problem in physics of the strong force. The research goal of Radiation Laboratory is to solve this fundamental question using the world
first polarized-proton collider, realized at RHIC in Brookhaven National Laboratory (BNL) in USA. RHIC stands for Relativistic
Heavy Ion Collider, aiming also to create Quark Gluon Plasma, the state of Universe just after the Big Bang, and study its property.
RIKEN-BNL Research Center (RBRC) also directed by H. En’yo carries our core team at BNL for those exciting researches using thePHENIX detector and its upgraded sPHENIX detector in preparation. We have observed that the proton spin carried by gluons is finite
and indeed sizable. We also identified W bosons in the electron/positron decay channel and in the muon decay channel, with which we
showed how much anti-quarks carry the proton spin. Other than the activities at RHIC we are preparing and starting new experiments
at J-PARC and Fermilab to study the nature of hadron and preparing for the electron-ion collider (EIC). We are also performing
technical developments such as novel ion sources, fine-pitch silicon pixel detectors and high-performance trigger electronics.

2. Major Research Subjects(1) Spin physics with relativistic polarized-proton collisions at RHIC
(2) Study of nuclear matter at high temperature and/or at high density(3) Technical developments on radiation detectors and accelerators

3. Summary of Research Activity(1) Experimental study of spin structure of proton using RHIC polarized proton collider[See also RIKEN-BNL Research Center Experimental Group for the activities at BNL]
The previously published central rapidity neutral and charged pion double spin asymmetries at the highest collision energies at
RHIC of 510 GeV have been augmented with the world’s first preliminary direct photon results. The direct photon probe also restricts
the initial, hard interaction to be predominantly between a quark and a gluon thus further increasing the sensitivity to the gluon spin.
It has therefore been considered the golden channel to access the gluon spin, albeit the statistics are limited. Also, the first preliminary
jet results have been extracted by PHENIX. The jet measurement is in principle a cleaner probe since no fragmentation functions are
involved as in the pion results. All these results will be included in future global fits of all the existing experimental data in the world
and will improve the sensitivity of quark and gluon spin contributions to the total spin of the nucleon.
While orbital angular momentum cannot be directly accessed at RHIC, several transverse spin phenomena have been observed
which relate to orbital angular momentum and the three-dimensional structure of the nucleon. These phenomena by themselves havebecome a major field of research as the dynamics of the strong interaction can be studies with these functions. Various single spin
asymmetry measurements have been obtained for various rapidities. When moving to central rapidities, these left-right asymmetries
are known to be very small for neutral pions. Since then, they have been confirmed to be small also for eta mesons. A substantially
improved data set with significantly reduced uncertainties has been recently published in PRD for both final states. For the first time
also direct photon single spin asymmetries have been extracted at RHIC. The direct photon asymmetries are again very important here
as they are only sensitive to the transverse spin eﬀects in the initial state and not the fragmentation-related eﬀects. Furthermore, it
provides sensitivity to a gluon correlation function that is not accessible in other processes. The direct photon results have also been
submitted for publication in PRL.
In June of 2017, an electro-magnetic calorimeter was installed in the most forward area of the STAR experiment and took polarized
proton collision data for neutral particle production (neutron, photon, neutral pion). The cross-section measurement will give us new
inputs to develop high-energy particle-collision models which are essential to understand air-shower from ultra-high energy cosmic
rays. The asymmetry measurement will improve the understanding of hadronic collisions at small scales. An unexpectedly large
neutral pion asymmetry has been found using this data that may connect to the large pion asymmetries at smaller rapidities and higher
transverse momenta. The results have been published in PRL.
At similar rapidities also neutron asymmetries have been observed in the past. While previously only their general magnitude
was obtained, using unfolding techniques it was possible to extract the first asymmetries as a function of the neutron transverse
moment for proton-proton collisions. These results have been published in PRD and correlated asymmetries, as well as asymmetries
in proton-nucleus collisions are being prepared.
Some of us are participating in the Fermilab SeaQuest experiment as a pilot measurement of muon pairs from Drell-Yan processusing a 120-GeV unpolarized proton at Fermilab. After finishing unpolarized measurements in 2017 to study the quark spin-orbit
eﬀect, a new measurement with a polarized proton target will start in 2021 to study the sea-quark orbit eﬀect of the polarized proton in
the target. The first result from the SeaQuest experiment on the asymmetry of the antimatter in the proton has been recently publishedin Nature.
For many jet related measurements fragmentation functions are necessary to gain spin and or flavor sensitivity. Those are currently
extracted by some of us using the KEK-Belle data. In addition to using the fragmentation results with RHIC measurements, they will
also provide the basis for most of the key measurements to be performed at the electron-ion collider. In 2020, in improved result for
single and di-hadron fragmentation in diﬀerent event topologies was published in PRD. These measurements are essential to nearly- 309 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

all nucleon structure measurements at RHIC, semi-inclusive DIS and the EIC.
As the Electron-Ion Collider is becoming a reality, many of us are participating in the various community eﬀorts to define thephysics goals of the EIC and how they inform on the choices of collisions energies, luminosities, and detector components. While theaccelerator eﬀorts are naturally led by the two main nuclear physics laboratories in the US, BNL and JLAB, a large EIC user group of
more than 1200 members from all around the world is working on making the EIC a reality. Within this group, we are participatingin various functions from the steering committee, the conference and talks committee to various physics or detector related topicalgroups. During 2020 the community eﬀort leading to the so-called Yellow Report studied and summarized these physics and detector
requirements in detail and the Yellow Report has since been made public on the arXiv.
(2) Experimental study of quark-gluon plasma using RHIC heavy ion collider[See also RIKEN-BNL Research Center Experimental Group for the activities at BNL]
We have completed several key measurements in the study of quark-gluon plasma at RHIC. As the top of them, we lead theanalysis of the first thermal photon measurement in heavy ion collisions. The measurement indicates that the initial temperaturereached in the central Au + Au collision at 200 GeV is about 350 MeV, far above the expected transition temperature T c ∼ 170 MeV,
from hadronic phase to quark-gluon plasma. This work was rewarded by Nishina Memorial Prize given to Y. Akiba in 2011. We alsomeasured direct photons in d + Au and direct photon flow strength ν2 and ν3 in Au + Au
We led measurement of heavy quark (charm and bottom) using VTX, a 4-layer silicon vertex tracker which we jointly constructedwith US DOE. The detector was installed in PHENIX in 2011. PHENIX recorded approximately 10 times more data of Au + Au
collisions in the 2014 run than the 2011 run. PHENIX recorded high statistics p + p and p + A data in 2015, and the doubled the
Au + Au in 2016. PHENIX concluded its data taking in the 2016 run.
The results of the 2011 run were published in Physical Review C (Phys. Rev. C 93, 034904 (2016)). This is the first publicationfrom VTX. The result showed that the electrons from bottom quark decay is suppressed for pT > 4 GeV/c, but the suppression factor
is smaller than that of charm decay electrons for 3 < pT < 4 GeV/c. This is the first observation of bottom electron suppression inheavy ion collisions, and the first result that shows the bottom and charm suppression is diﬀerent. The results of b → e and c → emeasurement in the 2015 p + p run has been published in Physical Review D99, 092003 (2019). The centrality dependence of the
suppression b → e and c → e from the 2014 Au + Au data is in preparation. The 2016 run is the final data taking run of PHENIX, andthis run doubled the dataset for heavy-flavor measurement with VTX. This year we completed the VTX geometry calibration of the2016 run.
PHENIX published measurements of flow strength in p + Au, d + Au, and 3 He + Au (Nat. Phys. 15, 214 (2019)). The results
provide strong evidence for formation of small droplet of quark gluon plasma in collisions of small systems at RHIC.
In Wako we are operating a cluster computer system (CCJ) specialized to analyze huge data sets taken with the PHENIX detector.
It consists of 28 nodes (18 old nodes and 10 new nodes) each of which has two CPUs and 10 sets of local disks for data repository(old node: quad-core CPU, 1 TB disk, new node: six-core CPU, 2 TB disk). There are 264 CPU cores and 380 TB disks in total.
This configuration ensures the fastest disk I/O when each job is assigned to the node where the required data sets are stored. It is also
important that this scheme does not require an expensive RAID system and network. Through this development we have establisheda fast and cost-eﬀective solution in analyzing massive data.
The data of 0.9 PByte obtained by the PHENIX experiment is stored in a hierarchical storage system which is a part of HOKUSAI
BigWaterfall/SailingShip supercomputer systems operated by the Head Oﬃce for Information Systems and Cybersecurity. In addition,
we operate a dedicated server for the RHICf group and two servers for the J-PARC E16 group, to keep their dedicated compilationand library environments, and some data.
(3) Study of properties of mesons and exotic hadrons with domestic accelerators
Preparation of the experiment E16 at J-PARC Hadron experimental facility is underway with several Grant-in-Aids. This experiment aims to perform a systematic study of the spectral modification of low-mass vector mesons in nuclei to explore the physics ofchiral symmetry breaking and restoration in dense nuclear matter, namely, the mechanism proposed by Nambu to generate most of
hadron masses.
The Gas Electron Multiplier (GEM) technology is adopted for the two key detectors, GEM Tracker (GTR) and Hadron-blind
Cherenkov detector (HBD). To improve electron-identification performance, lead-glass calorimeters (LG) are used in combination
with HBD. We are in the production phase. Read-out electronics and trigger logic modules are also installed and tested. We have beena member of the CERN-RD51 collaboration to acquire the read-out technology for GEM. The MoU for RD51 was extended for theperiod of 2019–2023.
Due to the budgetary limitation, we aim to install a part of the detectors at the beginning of the experiment, eight modules of aset of GTR, HBD and LG, out of 26 modules in the full installation. J-PARC PAC (Program Advisory Committee) gave us a stage-2
approval in July 2017 to perform commissioning runs (Run 0). Although there is a significant delay from the originally planned dateof March 2016, the construction of the beam line by KEK was completed finally in early 2020 to perform this experiment.
We performed the 1st half of commissioning run (Run-0a) in June 2020 successfully, using a primary proton beam with anintensity of 1 × 1010 protons per 2-sec duration of beam spill. This intensity is a designed full intensity of the beam line. The 2ndhalf, which started in February 2021, was suspended due to the malfunction of the J-PARC MR accelerator and a compensation beamtime is allocated in June 2021. Eight modules of GTR, six modules of HBD and six modules of LG are assembled and installed in theE16 spectrometer magnet in January 2021 for this beam time. First physics run is planned in JFY2022, after two more HBDs and two
more LG modules are installed.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)(4) Detector development for PHENIX experiment
The PHENIX experiment proposes substantial detector upgrades to go along the expected accelerator improvements, including
the future electron-ion collider “EIC.” The present PHENIX detector is repurposed to the sPHENIX (super PHENIX) detector whichreuses the Babar solenoid magnet at SLAC and is covered by the hadronic calorimeter which was not available in the previous RHIC
experiments. The sPHENIX was approved for the Project Decision-2/3 (corresponds to DOE’s Critical Decision-2/3) in May 2019.
We RIKEN group have been developing the one of the tracking devices of sPHENIX detector, so called intermediate tracker (INTT)
since 2015. The INTT provides the best timing resolution among the sPHENIX tracking system, in conjunction with a time projection
chamber and a MAPS based vertex detectors. The prototype detectors demonstrated satisfactory performance in the eﬃciency andposition resolutions as designed in the last two beam tests at the Fermilab Test Beam Facility (FTBF) using 120 GeV proton beam in
March 2018 and June 2019. The production of silicon ladder assembly has been proceeded both in Taiwan Silicon Detector Facility(TSiDF) and BNL since Spring 2021. The INTT barrel assembly will be started in this Summer.
We have been planning to build a forward spectrometer to be added to the sPHENIX detector. With this addition, the detector
called fsPHENIX will have hadronic and electromagnetic calorimetry as well as tracking capability in the forward rapidity region.
This upgrade makes it possible to study forward jets and hadrons in jets which are of vital importance for the cold QCD program inpolarized p + p and p + A collisions at RHIC. The fsPHENIX detector can be further upgraded to the ePHENIX detector to be used
for electron-ion collisions at EIC. We are preparing test bench to perform R&D for the forward hadron calorimeter.
As the further investigation of the neutral pion production asymmetry discovered in the RHICf experiment, we started preparation
for the next phase of the experiment, namely RHICf-II. The target year of physics data taking is 2024 as a part of either STASR orsPHENIX experiments. The highlight of the upgraded experiment is to adopt a larger acceptance with higher position resolution for thezero-degree calorimeter (ZDC). The detector technology developed for the FoCAL upgrade project of the ALICE experiment at LHC
well satisfies the RHICf-II performance requirement. We thus resumed the associated membership of the ALICE collaboration, andthe RHICf-II detectors are to be developed together with the ALICE FoCAL collaboration. This new detector technology development
is also a part of an essential R&D programs for a ZDC detector for EIC.

Members
Director
Hideto EN’YO
Research/Technical Scientists
Yuji GOTO (Senior Research Scientist)
Itaru NAKAGAWA (Senior Research Scientist)
Seidl RALF (Senior Research Scientist)

Yasushi WATANABE (Senior Research Scientist)
Satoshi YOKKAICHI (Senior Research Scientist)

Contract Researcher
Tomonori TAKAHASHI
Special Postdoctoral Researcher
Koki KANNO
Research Associate
Wataru NAKAIInternational Program Associate
Benard MULILO (Korea Univ.)
Senior Visiting Scientist
Toshiaki SHIBATA (Nihon Univ.)
Visiting Scientists
Kazuya AOKI (KEK)
Tatsuya CHUJO (Tsukuba Univ.)
Se Young HAN (Korea Univ.)
Shoichi HASEGAWA (JAEA)
Shunzo KUMANO (KEK)
Tsutomu MIBE (KEK)
Yuhei MORINO (KEK)

Ken-ichi NAKANO (Tokyo Tech)
Megumi NARUKI (Kyoto Univ.)
Kyoichiro OZAWA (KEK)
Susumu SATO (JAEA)
Kenta SHIGAKI (Hiroshima Univ.)
Maya SHIMOMURA (Nara Women’s Univ.)
Kiyoshi TANIDA (JAEA)

Student Trainees
Daichi ARIMIZU (Kyoto Univ.)
Sakiko ASHIKAGA (Kyoto Univ.)
Takehito KONDO (Hiroshima Univ.)
Shono KYAN (Tsukuba Univ.)

Miu MORITA (Nara Women’s Univ.)
Tomoki MURAKAMI (Univ. of Tokyo)
Satomi NAKASUGA (Kyoto Univ.)
Naoki OGATA (Kyoto Univ.)- 311 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Kenta SATO (Nagoya Univ.)
Mika SHIBATA (Nara Women’s Univ.)
Yudai TAKAURA (Kyoto Univ.)

Kosuke TSUKUI (Tsukuba Univ.)
Yosuke UEDA (Hiroshima Univ.)

Interns
Daisuke IMAGAWA (Rikkyo Univ.)

Hikaru IMAI (Rikkyo Univ.)

AssistantKeiko SUZUKI

List of Publications & Presentations
Publications[Original Papers]
0
U. A. Acharya et√ al. (PHENIX Collaboration), “Transverse single-spin asymmetries of midrapidity π and η mesons in polarized p + p
collisions at s = 200 GeV,” Phys. Rev. D 103, 5, 052009 (2021).
U. A. Acharya et al. (PHENIX Collaboration),“Transverse momentum dependent forward neutron single spin asymmetries in transversely√
polarized p + p collisions at s = 200 GeV,” Phys. Rev. D 103, 3, 032007 (2021).
U. √A. Acharya et al. (PHENIX Collaboration), “Polarization and cross section of midrapidity J/ψ production in p + p collisions at
s = 510 GeV,” Phys. Rev. D 102, 7, 072008 (2020).
√
U. A. Acharya et al. (PHENIX Collaboration), “Production of bb̄ at forward rapidity in p + p collisions at s = 510 GeV,” Phys. Rev. D
102, 9, 092002 (2020).
U. A. Acharya et al. (PHENIX Collaboration), “Measurement of jet-medium interactions via direct photon-hadron correlations in Au + Au√
and d + Au collisions at sNN = 200 GeV,” Phys. Rev. C 102, 5, 054910 (2020).
U. A. Acharya et al. (PHENIX √Collaboration), “Measurement of charged pion double spin asymmetries at midrapidity in longitudinallypolarized p + p collisions at s = 510 GeV,” Phys. Rev. D 102, 3, 032001 (2020).
L. Gamberg, Z. Kang, D. Pitonyak, A. Prokudin, N. Sato, and R. Seidl, “Electron-Ion Collider impact study on the tensor charge of thenucleon,” Phys. Lett. B 816, 136255 (2021).
R. Seidl, et al. (Belle Collaboration), “Update of inclusive cross sections of single and pairs of identified light charged hadrons,” Phys.
Rev. D 101, 092004 (2020).
J. Dove, Y. Goto, et al., “The asymmetry of antimatter in the proton,” Nature 590, 561–565 (2021).

Presentations[International Conferences/Workshops]
K. Kanno (invited), “Experimental study of spectral change of vector mesons in nuclear medium at J-PARC,” YITP international workshop
on Hadron in Nucleus (HIN2020), Kyoto (YITP), Japan & Online, March 8–10, 2021.
T. N. Takahashi (poster), “Data acquisition system in Run0 of the J-PARC E16 experiment,” 22nd IEEE Real Time Conference (RT2020),
Online, October 12–23, 2020.
R. Seidl (invited), “PHENIX highlights,” RHIC AGS Users Meeting 2020, October 23, 2020.
R. Seidl (invited), “Fragmentation related measurements at Belle,” 40th International Conference on High Energy Physics (ICHEP 2020),
Prague, July 31, 2020.
Y. Goto, “Physics and detector requirements at zero degree of EIC,” Contribution to: Workshop of QCD and Forward Physics at the FutureElectron Ion Collider and Cosmic Ray Physics, 59–64 (2020).
K. Sato, Y. Goto, √I. Nakagawa, R. Seidl, J. S. Park, M. H. Kim, et al., “The energy spectrum of forward photons measured by the RHICf
experiment in s = 510 GeV proton-proton collisions,” PoS ICRC2019, 413 (2021).
Benard Mulilo, “Transverse momentum dependent forward neutron single spin asymmetry in p + p collisions at 200 GeV,” International
Workshop on Forward Physics and QCD with LHC, EIC and Cosmic Rays, held at JLAB January 20–23, 2021.
√
Benard Mulilo, “PHENIX preliminary results of forward neutron transverse single spin asymmetry in p↑ + p collisions at s = 200 GeV,”IWHSS2020 Conference, Trieste-Italy, November 16, 2020.

[Domestic Conferences/Workshops]
四日市悟 (招待講演), 「DAQ and circuit in the J-PARC E16 experiment」, 計測システム研究会 2020, 茨城県東海村/オンライン開催,
2020 年 11 月 26–27 日.
中須賀さとみ (口頭発表), 「J-PARC E16 実験のための電子識別検出器の性能評価 II」, 日本物理学会 2020 年 秋季大会, オンライン
開催, 2020 年 9 月 14–17 日.
近藤丈仁 (口頭発表), 「J-PARC E16 実験 GEM 飛跡検出器トリガ用信号読出回路の対放電保護」, 日本物理学会 第 76 回 年次大会,
オンライン開催, 2021 年 3 月 12–15 日.
村上智紀 (口頭発表), 「J-PARC E16 実験における GEM 飛跡検出器の建設及び実機の性能評価」, 日本物理学会 第 76 回 年次大会,
オンライン開催, 2021 年 3 月 12–15 日.
Ralf Seidl (invited), “RHIC and COMPASS results,” 「日本のスピン物理学の展望」研究会, 島根県松江市, 2021 年 2 月 23–24 日.

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Ralf Seidl (invited), “The electron ion collider as a next generation facility for the study of QCD,” KEK 研究会「素粒子・原子核コライ
ダー物理の交点」, オンライン開催, 2020 年 8 月 31 日.
Y. Goto (invited), “FoCal, RHICf-II and EIC,” TCHoU Workshop, Online Meeting, March 30, 2021.
後藤雄二（口頭発表）, 「PHENIX 実験での縦スピン非対称度測定の最新の結果」, 日本物理学会第 76 回年次大会, オンライン開催,
2021 年 3 月 13 日.
後藤雄二（招待講演）, 「Electron-Ion Collider の物理」, 「日本のスピン物理学の展望」研究会, 島根県松江市, 2021 年 2 月 23–24 日.
後藤雄二（招待講演）, 「EIC 日本グループの議論」, KEK 研究会「素粒子・原子核コライダー物理の交点」, オンライン開催, 2020
年 8 月 31 日.
√
後藤雄二（口頭発表）, 「 s = 510 GeV での縦偏極陽子衝突による荷電パイ中間子の二重スピン非対称度の測定」, 日本物理学会
75 回年次大会, 愛知県名古屋市 (現地開催中止), 2020 年 3 月 17 日.

[Seminars]
Ralf Seidl (invited), “Fragmentation function measurements in Belle,” Hiroshima University Nuclear and Particle Physics Seminar,
September 3, 2020.

Press Releases「陽子の中の反物質が持つ大きな非対称性の発見—反クォークの生成過程により物質の成り立ちを探る—」, 東京工業大学, 高エ
ネルギー加速器研究機構, 山形大学, 理化学研究所, 2021 年 2 月 25 日.

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Subnuclear System Research Division
Meson Science Laboratory
1. Abstract

Particles like muons, pions, and kaons have finite life times, so they do not exist in natural nuclei or matters. By implanting theseparticles into nuclei/matters, exotic phenomena in various objects can be studied from new point of view.
For example, kaon is the second lightest meson, which has strange quark as a constituent quark. It is expected that if one embeds
mesons into nuclei, the sizes of the nuclei become smaller and one can form a high-density object beyond the normal nuclear density.
Study of this object could lead to better understanding of the origin of the mass of the matter, and may reveal the quark degree of
freedom beyond the quark-confinement. The other example is the weak interaction in nuclear matter. It can only be studied by the
weak decay of hypernuclei, which have Lambda particle in the nuclei.
Muon provides even wider scope of studies, covering condensed matter physics as well as nuclear and atomic physics, and weare trying to extend the application field further into chemical and biological studies. For instance, stopping positively charged muonin a material, we obtain information on the magnetic properties or the local field at the muon trapped site (µSR). Injecting negatively
charged muon to hydrogen gas, muonic hydrogen atom (µp) is formed. We are planning to measure µp hyperfine splitting energy tomeasure proton magnetic radius, which is complementary quantity to the proton charge radius and its puzzle. We are also interested
in precision measurement of muon property itself, such as muon anomalous magnetic moment (g − 2).
In our research, we introduce diﬀerent kind of impurities into nuclei/matters, and study new states of matter, new phenomena, or
the object properties.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)

Study of meson property and interaction in nuclei
Origin of matter mass/quark degree of freedom in nuclei
Condensed matter and material studies with muon
Nuclear and particle physics studies via muonic hydrogen
Development of ultra cold muon beam, and its application from material science to particle physics

3. Summary of Research Activity(1) Hadron physics at J-PARC, RIKEN-RIBF, GSI and SPring-8
Kaon and pion will shed a new insight to the nuclear physics. The recent discovery of deeply bound pionic atom enables us toinvestigate the properties of mesons in nuclear matter. At RIKEN-RIBF, we are preparing precise experimental study of the pionicatom. Very lately, we succeeded to discover kaonic nuclear bound state, “K − pp,” at J-PARC. The yield dependence on momentumtransfer shows that observed system is unexpectedly small. We extended our study on Λ(1405) that could be K-p bound state. By theseexperiments, we are studying the KN − interaction, and clarify the nature of kaon in nuclei. At Spring-8 and at GSI, we are planning tostudy omega and η′ nuclei. By these experiments, we aim to be a world-leading scientific research group using these light meta-stableparticles.
(1-1) Deeply bound kaonic nuclei
J-PARC E15 experiment had been performed to explore the simplest kaonic nuclear bound state, “K − pp.” Because of the strong
attraction between KN − , the K − in nuclei may attract surrounding nucleons, resulting in forming a deeply bound and extremely dense
object. Measurement of the kaon properties at such a high-density medium will provide precious information on the origin of hadron
masses, if the standard scenario of the hadron-mass-generation mechanism, in which the hadron masses are depends on matter densityand energy, is correct. Namely, one may study the chiral symmetry breaking of the universe and its partial restoration in nuclear
medium.
The E15 experiment was completed to observe the “K − pp” bound state by the in-flight 3 He(K − , n) reaction, which allows us
the formation via the invariant-mass spectroscopy by detecting decay particles from “K − pp.” For the experiment, we constructed a
dedicated spectrometer system at the secondary beam-line, K1.8BR, in the hadron hall of J-PARC.
With the Λpn final states obtained in the first stage experiment, we observed a kinematic anomaly in the Λp invariant mass
near the mass threshold of M(K − pp) (total mass of kaon and two protons) at the lower momentum transfer q region. We conducteda successive experiment to examine the nature of the observed kinematical anomaly in the Λpn final state, and we confirmed theexistence of the bound state below the mass threshold of M(K − pp) at as deep as the binding energy of 40 MeV. The momentum
transfer q naturally prefers lower momentum for the bound state formation, but the observed event concentration extended having theform-factor parameter ∼400 MeV/c. Based on the PWIA calculation, the data indicated that the “K − pp” system could be as small as∼0.6 fm. It is astonishingly compact in contrast to the mean nucleon distance ∼1.8 fm.
This observed signal shows that a meson (qq− ) forms a quantum state where baryons (qqq) exist as nuclear medium, i.e., ahighly excited novel form of nucleus with a kaon, in which the mesonic degree-of-freedom still holds. This is totally new form of
nuclear system, which never been observed before.
(1-2) Precision X-ray measurement of kaonic atom
To study the KN − interaction at zero energy from the atomic state level shift and width of kaon, we have performed an X-ray
spectroscopy of atomic 3d → 2p transition of negatively charged K-mesons captured by helium atoms. However, our first experimentis insuﬃcient in energy resolution to see the K − -nucleus potential. Aiming to provide a breakthrough from atomic level observation,- 314 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

we introduce a novel X-ray detector, namely superconducting transition-edge-sensor (TES) microcalorimeter oﬀering unprecedented
high energy resolution, being more than one order of magnitude better than that achieved in the past experiments using conventional
semiconductor detectors. The experiment J-PARC E62 aims to determine 2p-level strong interaction shifts of kaonic 3 He and 4 He
atoms by measuring the atomic 3d → 2p transition X-rays using TES detector with 240 pixels having about 23 mm2 eﬀective area
and the average energy resolution of 7 eV (FWHM) at 6 keV. We carried out the experiment at J-PARC in June 2018 and successfully
observed distinct X-ray peaks from both atoms. The data analysis is now ongoing.
Another important X-ray measurement of kaonic atom would be 2p → 1s transition of kaonic deuteron (K − -d). We have measured
same transition of kaonic hydrogen (K − -p), but the width and shift from electro-magnetic (EM) value reflect only isospin average ofthe KN interaction. We can resolve isospin dependence of the strong interaction by the measurements both for K − -p and K − -d. The
experiment J-PARC E57 aims at pioneering measurement of the X-rays from K − -d atoms. Prior to full (stage-2) approval of the E57
proposal, we performed a pilot run with hydrogen target in March 2019.
(1-3) Deeply bound pionic atoms and η′ mesonic nuclei
We have been working on precision spectroscopy of pionic atoms systematically, which leads to understanding of the non-trivial
structure of the vacuum and the origin of hadron masses. The precision data set stringent constraints on the chiral condensate at
nuclear medium. We are presently preparing for the precision systematic measurements at RIBF. A pilot experiment performed in2010 showed a unprecedented results of pionic atom formation spectra with finite reaction angles. The measurement of pionic 121 Sn
performed in 2014 showed a very good performance of the system. We have been finalizing the data analysis to achieve informationon the pion-nucleus interaction based on the pionic atom spectroscopy. At the same time we have been working on a systematic highprecision spectroscopy of pionic tin isotopes.
We are also working on spectroscopy of η′ mesonic nuclei in GSI/FAIR. Theoretically, peculiarly large mass of η′ is attributed
to UA(1) symmetry and chiral symmetry breaking. As a result, large binding energy is expected for η′ meson bound states in nuclei(η′ -mesonic nuclei). From the measurement, we can access information about gluon dynamics in the vacuum via the binding energy
and decay width of η′ -nuclear bound state. We are preparing for a new experiment using a large solid angle detectors at GSI.
(1-4) 3Λ H lifetime puzzle and our approach
Three recent heavy ion experiments (HypHI, STAR, and ALICE) announced surprisingly short lifetime for 3Λ H hyper-nucleus’s
Mesonic Weak Decay (MWD), which seems to be inconsistent with the fact that the 3Λ H is a very loosely bound system. It is very
interesting to study this with a diﬀerent experimental approach. We proposed a direct measurement of 3Λ H MWD lifetime with ∼20%
resolution at J-PARC hadron facility by using K − meson beam at 1 GeV/c. As for the feasibility test, we also measure 4Λ H lifetime.
A Cylindrical Detector System (CDS) used in J-PARC E15/E31 experiment is employed to capture the delayed π− as a weak decay
product from 3,Λ4 H a calorimeter is installed in the very forward region to tag fast π0 meson emission at ∼0 degree, which ensures thatthe Λ hyperon production with small recoil momentum. By this selection, we can improve the ratio between 3,Λ4 H and quasi-free Λ andΣ background. A test beam for feasibility study with 4 He target has been conditionally approved by J-PARC PAC. We will conduct
the experiment and to present the data in short.
(2) Muon science at RIKEN-RAL branch
The research area ranges over particle physics, condensed matter studies, chemistry and life science. Our core activities are
based on the RIKEN-RAL Muon Facility located at the Rutherford-Appleton Laboratory (UK), which provides intense pulsed-muonbeams. We have variety of important research activities such as particle/nuclear physics studies with muon’s spin and condensed
matter physics by muon spin rotation/relaxation/resonance (µSR).
(2-1) Condensed matter/materials studies with µSR
We stated to share experimental equipment with those of RAL in order to make organization of RIKEN beam time schedules
easier and to enhance the eﬃciency to carry out RIKEN’s experiments. We use shared cryostats and manpower supports available
from RAL as well we other experimental areas. Both two µSR spectrometers, ARGUS (Port-2) and CHRNUS (Port-4), are working
wel wit maintenance supports provide from RAL. Among our scientific activities on µSR studies from year 2017 to 2020, following
studies are most important subjects of material sciences at the RIKEN-RAL muon facility:(1) Multi magnetic transitions in the Ru-based pyrochlore systems, R2 Ru2 O7 .
(2) Magnetic properties of the nano-cluster gold in the border of macro- and micro- scale.
(3) Novel magnetic and superconducting properties of nano-size La-based high-T c superconducting curates.
(4) Determination of muon positions estimated from density functional theory (DFT) and dipole-field calculations.
(5) Chemical muonic states in DNA molecules.
(2-2) Nuclear and particle physics studies via ultra-cold muon beam and muonic atoms
If we can improve muon beam emittance, timing and energy dispersion (so-called “ultra-cold muon”), then the capability of µSR
studies will be drastically improved. The ultra-cold muon beam can stop in a thin foil, multi-layered materials and artificial lattices, so
one can apply the µSR techniques to surface and interface science. The development of ultra-cold muon beam is also very importantas the source of pencil-like small emittance muon beam for muon g − 2 measurement.
Ultra-cold muon beam has been produced by laser ionization of muoniums in vacuum (bound system of µ+ and electron). We
are developing two key components, high eﬃciency muonium generator at room temperature and high intensity ionization laser. The
study of muonium generator has been done in collaboration with TRIUMF. In 2013, we demonstrated at least 10 times increase of
the muonium emission eﬃciency by fabricating fine laser drill-holes on the surface of silica aerogel. Further study was done in 2017with more than 20 aerogel target having diﬀerent surface conditions. We are analyzing the data to identify which condition mostcontributed to increasing the muonium emission eﬃciency. We also developed a high power Lyman-α laser in collaboration with laser- 315 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

group at RIKEN. In this laser development, we succeeded to synthesize novel laser crystal Nd:YGAG, which has an ideal wavelength
property for laser amplification to generate Lyman-α by four-wave mixing in Kr gas cell. We already achieved 10 times increase of
Lyman-α generation than before. However, in order to increase the intensity by one more order, we need a larger size crystal. So far
we have inhomogeneity problem but we are trying to solve this problem.
A large discrepancy was found recently in the proton charge radius between the new precise value from muonic hydrogen atom at
PSI and the values from normal hydrogen spectroscopy and e-p scattering. We are planning a precise measurement of proton Zemachradius (with charge and magnetic distributions combined) using the laser spectroscopy of hyperfine splitting energy in the muonichydrogen atom. As a key parameter for designing the experiment, we need to know the quench rate of the muonic proton polarization
due to collision with surrounding protons, for which only theoretical estimations are available. We first measured the quench rate ofmuonic deuterium polarization in deuterium gas, which confirmed the long lifetime consistent with the calculation. We also carriedout measurement on muonic proton in low pressure hydrogen gas and the analysis is in progress.

Members
Director
Masahiko IWASAKI
Research Scientists
Kenta ITAHASHI (Senior Research Scientist)
Yue MA (Senior Research Scientist)
Haruhiko OUTA (Senior Research Scientist)

Fuminori SAKUMA (Senior Research Scientist)
Isao WATANABE (Senior Research Scientist)

Contract Researcher
Katsuhiko ISHIDA
Junior Research Associates
Shun SEO (Univ. of Tokyo)

Muhamad D. UMAR (Hokkaido Univ.)

International Program Associates
Muhammad H.B. CHE LAH (Univ. Sains Malaysia)
Harison B. ROZAK (Univ. Sains Malaysia)

Suci WINARSIH (Univ. Indonesia)
Utami WIDYAISWARI (Univ. Indonesia)

Research Consultant
Masayasu KAMIMURA
Senior Visiting Scientists
Hiroyuki NOUMI (Osaka Univ.)

Kazuhiro TANAKA (KEK)

Visiting Scientists
Tadashi ADACHI (Sophia Univ.)
Hiroko ARIGA (Hokkaido Univ.)
Retno ASIH (Inst. Teknologi Sepuluh Nopember)
Fahmi ASTUTI (Inst. Teknologi Sepuluh Nopember)
KwangYong CHOI (Chung-Ang Univ.)
Catalina Oana CURCEANU (INFN)
Zyun EZAWA (Tohoku Univ.)
Hiroyuki FUJIOKA (Tokyo Tech)
Masaki FUJITA (Tohoku Univ.)
Shuhei FUKUOKA (Hokkaido Univ.)
Takayuki GOTO (Sophia Univ.)
Maryam HASSANVAND (Isfahan Univ. of Tech.)
Wataru HIGEMOTO (JAEA)
Ko-ichi HIRAKI (Fukushima Medical Univ.)
Satoru HIRENZAKI (Nara Women’s Univ.)
Koichi ICHIMURA (Hokkaido Univ.)
Yasuyuki ISHII (Shibaura Inst. of Tech.)
Ryosuke KADONO (KEK)
Takayuki KAWAMATA (Tohoku Univ.)
Seiko KAWAMURA (JAEA)
Hikomitsu KIKUCHI (Univ. of Fukui)
Takuya KOBAYASHI (Saitama Univ.)
Yoji KOIKE (Tohoku Univ.)
Seungwon LEE (Univ. of Toyama)

Kenji MATSUDA (Univ. of Toyama)
Hiroyasu MATSUURA (Univ. of Tokyo)
Mototsugu MIHARA (Osaka Univ.)
Takaaki MINAMIDATE (Tokyo Univ. of Sci)
Yasuhiro MIYAKE (KEK)
Mohamed Ismail MOHAMED-IBRAHIM (Univ. Sains
Malaysia)
Takehito NAKANO (Ibaraki Univ.)
Takahiro NAMIKI (Univ. of Toyama)
Katsuhiko NISHIMURA (Univ. of Toyama)
Yasuo NOZUE (Osaka Univ.)
Agustinus NUGROHO (Inst. Teknologi Bandung)
Kazuki OHISHI (Comprehensive Res. Org. for Sci. and Soc.)
Yu OISHI (KEK)
Atsushi OKAZAWA (Univ. of Tokyo)
Dita PUSPITA SARI (Shibaura Inst. of Tech.)Irwan RAMLI (Univ. Cokroaminoto Palopo)
RISDIANA (Padjadjaran Univ.)
Lusi SAFRIANI (Padjadjaran Univ.)
Naohito SAITO (KEK)
Shinichi SHAMOTO (CROSS)
Ichiro SHIRAKI (Univ. of Yamanashi)
Shukri SULAIMAN (Univ. Sains Malaysia)
Ken SUZUKI (Stefan Meyer Inst.)- 316 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Kensuke SUZUKI (Tohoku Univ.)
Takao SUZUKI (Shibaura Inst. of Tech.)
Hiroshi TANIDA (Toyama Prefectural Univ.)
Takanori TANIGUCHI (Tohoku Univ.)
Andrea VACCHI (Udine Univ. (Italy))
Eberhard WIDMANN (Stefan Meyer Inst.)
Zhuan XU (Zhejiang Univ.)
Yasuhiro YAMAGUCHI (JAEA)

Ichihiro YAMAUCHI (Saga Univ.)
Toshimitsu YAMAZAKI (Univ. of Tokyo)
Yukio YASUI (Meiji Univ.)
Masaru YOSOI (Osaka Univ.)
Wan Nurfadhilah B. ZAHARIM (Univ. Sains Malaysia)
Xu-Guang ZHENG (Saga Univ.)
Johann ZMESKAL (Austrian Academy of Sci.)

Student Trainees
Redo Muhammad RAMADHAN (Univ. Indonesia)
Harison B. ROZAK (Univ. Sains Malaysia)
Yuki SAGARA (Shibaura Inst. of Tech.)Ryo SASAKI (Shibaura Inst. of Tech.)
SUCI WINARSIH (Univ. Indonesia)

Assistants
Kumiko TAKAHASHI

Mitsue YAMAMOTO

List of Publications & Presentations
Publications[Original Papers]
J. Sugiyama, O. Kenji Forslund, E. Nocerino, N. Matsubar, K. Papadopoulos, Y. Sassa, Stephen P. Cottrell, Adrian D. Hillier, K. Ishida,
M. Mansson, and J. H. Brewer, “Lithium diﬀusion in LiMnPO4 detected with µ± SR,” Phys. Rev. Research 2, 033161 (2020).
M. Aramini, C. Milanese, Adrian D. Hillier, A. Girella, C. Horstmann, T. Klassen, K. Ishida, M. Dornheim, and C. Pistidda, “Spectroscopic tool for the investigation of the local chemistry of elements,” Nanomaterials 2020, 10, 1260 (2020).
E. Mocchiutti, A. Adamczak, D. Bakalov, G. Baldazzi, R. Benocci, R. Bertoni, M. Bonesini, V. Bonvicini, H. CabreraMorales, F. Chignoli, M. Clemenza, L. Colace, M. Danailov, P. Danev, A. de Bari, C. DeVecchi, M. DeVincenzi, E. Furlanetto, F. Fuschinod,
K. S. Gadedjisso-Tossoua, D. Guﬀantia, K. Ishida, C. Labanti, V. Maggi, R. Mazza, A. Menegolli, G. Morgante, M. Nastasi, J. Niemela,
C. Pizzolotto, A. Pullia, R. Ramponi, L. P. Rignanese, M. Rossella, N. Rossi, M. Stoilov, L. Stoychev, L. Tortora, E. Vallazza, G. Zampa,
and A. Vacchi, “First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen,” Phys.
Lett. A 384, 126667 (2020).
C. Pizzolotto, A. Adamczak, D. Bakalov, G. Baldazzi, M. Baruzzo, R. Benocci, R. Bertoni, M. Bonesini, V. Bonvicini, H. Cabrera,
D. Cirrincione, M. Citossi, F. Chignoli, M. Clemenza, .Colace,. Danailov, P. Danev, A. de Bari, C. De Vecchi, M. de Vincenzi, E. Fasci,
E. Furlanetto,. Fuschino, K. S. Gadedjisso-Tossou, L. Gianfran, D. Guﬀanti, A. D. Hillier, K. Ishida,. J. C. King, C. Labanti, V. Maggi,
R. Mazza, A. Menegolli, E. Mocchiutti, L. Moretti,. Morgante, J. Niemela, B. Patrizi, A. Pirri, A. Pullia, R. Ramponi, L. P. Rignanese,
E. Roman,. Rossella, R. Sarkar, A. Sbrizzi,. Stoilov, L. Stoychev, J. J. Suárez-Vargas, G. Toci, L. Tortora, E. Vallazza, M. Vannini,
C. Xiao, G. Zampa, and A. Vacchi1, “The FAMU experiment: muonic hydrogen high precision spectroscopy studies,” Eur. Phys. J. A
56, 185 (2020).
J. Beare, G. Beer, J. H. Brewer, T. Iijima, K. Ishida, M. Iwasaki, S. Kamal, K. Kanamori, N. Kawamura, R. Kitamura, S. Li, G. M. Luke,
G. M. Marshall, T. Mibe, Y. Miyake, Y. Oishi, K. Olchanski, A. Olin, M. Otani, M. A. Rehman, N. Saito, Y. Sato, K. Shimomura,
K. Suzuki, M. Tabata, and H. Yasuda, “Study of muonium emission from laser-ablated silica aerogel,” Prog. Theor. Exp. Phys. 2020,
123C01 (2020).
H. Yamauchi, D. P. Sari, I. Watanabe, Y. Yasui, L. -J. Chang, K. Kondo, T. U. Ito, M. Ishikado, M. Hahara, M. D. Frontzk, C. Chi,
J. A. Fernandez-Bac, J. S. Lord, A. Berlie, A. Kotani, S. Mori, and S. Shamoto, “High-temperature short-range order in Mn3 RhSi,”
Commun. Matter. 1, 42 (2020).
M. Fujita, K. M. Suzuki, S. Asano, H. Okabe, A. Koda, R. Kadono, and I. Watanabe, “Magnetic behavior of T ’-type Eu2 CuO4 revealed
by muon spin rotation and relaxation measurements,” Phys. Rev. B 102, 045116 (2020).
R. Kitamura, S. Bae, S. Choi, Y. Fukao, H. Iinuma, K. Ishida, N. Kawamura, B. Kim, Y. Kondo, T. Mibe, Y. Miyake, M. Otani, G. P. Razuvaev, N. Saito, K. Shimomura, and P. Strasser, “Development of negative muonium ion source for muon acceleration,” Phys. Rev. Accel.
Beams 24, 033403 (2021).
S. Kanda, Y. Fukao, Y. Ikedo, K. Ishida, M. Iwasaki, D. Kawall, N. Kawamura, K. M. Kojima, N. Kurosawa, Y. Matsuda, T. Mibe,
Y. Miyake, S. Nishimura, N. Saito, Y. Sato, S. Seo, K. Shimomura, P. Strasser, K. S. Tanaka, T. Tanaka, H. A. Torii, A. Toyoda, andY. Ueno, “New precise spectroscopy of the hyperfine structure in muonium with a high-intensity pulsed muon beam,” Phys. Lett. B
815, 136154 (2021).
A. D. Pant, K. Ishida, N. Kawamura, S. Matoba, A. Koda, S. Nishimura, and K. Shimomura, “Study of muonium behavior in n-typesilicon for generation of ultra cold muonium in vacuum,” Physica B 613, 412997 (2021).
T. Yamaga et al., “Observation of a KNN bound state in the 3 He(K − , Λp)n reaction,” Phys. Rev. C 102, 044002 (2020).

[Proceedings]
F. Sakuma et al., “K − pp bound system at J-PARC,” AIP Conference Proceedings 2249, 020005 (2020).
F. Sakuma et al., “K-nuclear bound state at J-PARC,” JPS Conf. Proc. 32, 010088 (2020).
H. Fujioka, K. Itahashi, V. Metag, M. Nanova, and Y. K. Tanaka, “Comment on ‘Search for η′ bound nuclei in the 12 C(γ, p) reaction withsimultaneous detection of decay products’,” Phys. Rev. Lett. 126, 019201 (2021).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

A. Tani, N. Ikeno, D. Jido, H. Nagahiro, H. Fujioka, K. Itahashi, and S. Hirenzaki, “Structure of double pionic atoms,” PTEP 2021, 3,
033D02 (2021).

Presentations[International Conferences/Workshops]
F. Sakuma (plenary), “Recent results and future prospects of kaonic nuclei at J-PARC,” Yamada Conference LXXII: The 8th Asia-PacificConference on Few-Body Problems in Physics (APFB2020), Kanazawa, Japan, March 1–5, 2021.
T. Yamaga (invited), “Observation of the K − pp bound state in J-PARC E15,” Hadron in Nucleus 2020 (HIN20), Kyoto, Japan, March
8–10, 2021.
T. Hashimoto (invited), “Kaonic atom experiments at J-PARC,” Hadron in Nucleus 2020 (HIN20), Kyoto, Japan, March 8–10, 2021.
Y. Ma (invited), “Towards solving the hypertriton lifetime puzzle with direct lifetime measurement: current status of J-PARC E73 experiment,” Hadron in Nucleus 2020 (HIN20), Kyoto, Japan, March 8–10, 2021.

[Domestic Conferences/Workshops]
石田勝彦, 「英国理研 RAL ミュオン施設におけるミュオン利用分析研究の進展」, 第 3 回 文理融合シンポジウム 量子ビームで歴史を探る—加速器が紡ぐ文理融合の地平—, オンライン, 2020 年 9 月 25–26 日.
石田勝彦 (招待講演), 「理研 RAL と J-PARC」, パルス中性子ミュオン発生 40 周年記念シンポジウム, オンライン, 2020 年 12 月
23 日.
石田勝彦, 「理研 RAL での非破壊元素分析」, 第 4 回文理融合シンポジウム 量子ビームで歴史を探る—加速器が紡ぐ文理融合の地平—, オンライン, 2021 年 1 月 28–29 日.
佐久間史典（口頭発表）, 「軽い K 中間子原子核の系統的測定」, 日本物理学会 第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
0

山我拓巳（口頭発表）, 「K − pp のスピン・パリティ測定と K nn の探索」, 日本物理学会第 76 回年次大会, オンライン, 2021 年 3 月
12–15 日.
浅野秀光 （口頭発表）, 「K − d 反応の運動量移行と π± Σ ± 不変質量分布の関係」, 日本物理学会 第 76 回年次大会, オンライン, 2021
年 3 月 12–15 日.
橋本直 （口頭発表）, 「TES マイクロカロリメータを用いた K 中間子ヘリウム原子 X 線精密分光」, 日本物理学会 第 76 回年次大会, オンライン, 2021 年 3 月 12–15 日.
赤石貴也 （口頭発表）, 「K − ビームを用いたハイパートライトンの寿命直接測定の現状」, 日本物理学会 第 76 回年次大会, オンラ
イン, 2021 年 3 月 12–15 日.
赤石貴也 （口頭発表）, 「3Λ H 寿命直接測定のための PbF2 カロリメータの性能評価 (2)」, 日本物理学会 2020 年秋季大会, オンライ
ン, 2021 年 3 月 12–15 日.
山我拓巳 （招待講演）, “Measurement of spin-spin correlation in K − pp decay,” 日本のスピン物理学の展望, オンライン, 2021 年 2 月
23–24 日.
山我拓巳 （招待講演）, 「J-PARC E15 実験における KNN 束縛状態の発見と今後の展望」, ELPH 研究会 C029「様々なフレーバー領域で探るクォーク・ハドロン多体系の分光と構造」, 宮城県仙台市 (東北大学電子光理学研究センター), 2020 年 11 月 4–5 日.

Press Releases
正負のミュオンで捉えたイオンの動き 2020 年 8 月 7 日—Li イオンの動きを, 負ミュオンで確認, 正ミュオンで詳細観察—一般財
団法人総合科学研究機構（CROSS）中性子科学センター杉山 純サイエンスコーディネータ国立研究開発法人理化学研究所（理研）仁科加速器科学研究センター石田勝彦協力研究員.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
RIKEN BNL Research Center
1. Abstract

The RIKEN BNL Research Center was established in April 1997 at Brookhaven National Laboratory with Professor T. D. Lee
of Columbia University as its initial Director. The Center is dedicated to the study of strong interactions, including spin physics,
lattice QCD and RHIC physics through the nurturing of a new generation of young physicists. Professor Lee was succeeded by BNL
Distinguished Scientist, the former BNL director, N. P. Samios, who served until 2013. The other former BNL director, S. H. Aronson
led the Center from 2013. Hideto En’yo succeeded the director position starting from JFY 2017. Support for RBRC was initially forfive years and has been renewed four times, and presently extends to March 2023. Theoretical activities in the RBRC Theory andComputing Groups are closely and intimately related to those of the Nuclear Theory, High Energy Theory and Lattice Gauge Theory
Groups at BNL. The RBRC Experimental Group jointly works with Radiation Laboratory at Wako RIKEN, the RHIC Spin Groupat BNL, the RHIC Spin Physics community, and the PHENIX/sPHENIX collaboration. BNL provides oﬃce space, management,
computing and administrative support. The Deputy Director of RBRC is D. Morrison (BNL). In May 2021 Y. Hatta (BNL) becomes
Theory Group leader, succeeding D. Kharzeev. Y. Akiba (RIKEN) is Experimental Group leader and T. Izubuchi (BNL) is Computing
Group leader.

2. Major Research Subjects

Major research subjects of the theory group are(1) Spin structure of proton(2) Gluon saturation at small-x(3) Physics of quark gluon plasma
Major research subjects of the computing group are(1) Search for new law of physics through tests for Standard Model of particle and nuclear physics(2) Dynamics of QCD and related theories(3) Theoretical and algorithmic development for lattice field theories, QCD machine design
Major research subject of the experimental group are(1) Experimental Studies of the Spin Structure of the Nucleon(2) Study of Quark-Gluon Plasma at RHIC
(3) sPHENIX detector construction

3. Summary of Research Activity

Summary of Research Activities of the three groups of the Center are given in the sections of each group.

Members
Director
Hideto EN’YO
Deputy Director
David P. MORRISON
Administrative Staﬀ
Kazushige FUKUSHIMA (Administration Manager, Nishina
Center and iTHEMS Promotion Oﬃce)
Hiroshi ITO (Deputy Administration Manager, Nishina Centerand iTHEMS Promotion Oﬃce)- 319 -

Keiko IWANO-OKABE (Deputy Administration Manager,
Nishina Center and iTHEMS Promotion Oﬃce)
Pamela ESPOSITO (Administrative Assistant)
Maureen MCNEIL-SHEA (Administrative Assistant)

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
RIKEN BNL Research Center
Theory Group
1. Abstract

The eﬀorts of the RBRC theory group are concentrated on the major topics of interest in High Energy Nuclear Physics, inparticular, the physics explored by the RHIC experiment at Brookhaven National Laboratory (BNL). This includes: understandingof the Quark-Gluon Plasma (QGP); the nature of dense quark matter; the initial state in high energy collisions, the Color Glass
Condensate and its evolution to QGP through a Glasma; QCD spin physics; physics relevant to the future Electron-Ion Collider at
BNL.

2. Major Research Subjects(1) Heavy Ion Collisions, QCD phase diagram(2) Perturbative Quantum Chromo-Dynamics (QCD)(3) Nucleon structure, mass and spin

3. Summary of Research Activity(1) Phase diagram of QCD
The major goal of RHIC heavy-ion program is to map out the QCD phase diagram at finite temperature and density. Together
with collaborations, V. Skokov has determined the location of the Yang-Lee edge singularity in the O(N) model using the functional
renormalization group method. This can be applied to the QCD phase diagram to determine the radius of convergence of the fugacity
expansion and hence the location of the QCD critical point at finite chemical potential.
(2) QCD at small x
The initial condition of heavy-ion collisions at RHIC is governed by the Color Glass Condensate (CGC) which is the universal
form of matter in the high energy (small-x) limit of QCD. The RBRC scientists have made major contributions to this field, andthe eﬀorts continue to date. V. Skokov has worked on various aspects of the CGC and their phenomenological consequences. In
particular, he has calculated the multiplicity and transverse momentum dependence of the elliptic flow parameter ν2 in proton-nucleus(pA) collisions in the dense-dilute framework of CGC. Together with M. Li, he has also computed the first saturation corrections in pA
collisions by solving the real-time classical Yang-Mills equation. Y. Mehtar-Tani and R. Boussarie have proposed a novel formulationof the gluon transverse momentum dependent (TMD) distribution which captures the leading logarithms in both the Bjorken andRegge limits.
(3) Jet and jet quenching
Jets have become an important tool to uncover the transport properties of matter created in heavy-ion collisions and the nontrivial
parton structure in the nucleon. These are important goals of the sPHENIX and EIC experiments. Y. Mehtar-Tani has pushed thecalculation of jet quenching to higher precision, now up to next-to-next-to-leading order (NNLO) in the opacity expansion. Together
with collaborators, he has made concrete prediction of the nuclear modification factor at the LHC based on the state-of-the-art theoryof jet quenching. Y. Hatta and collaborators calculated the impact of soft gluon resummation on the azimuthal angular correlation of
jets. It has been shown that angular correlations of perturbative origin are numerically significant. They could obscure the primordialcorrelation due to the nontrivial parton distribution such as the linearly polarized gluon distribution. Y. Hatta and T. Ueda has calculated
the gap survival probability in dijet production in proton-proton collisions at the LHC, resumming the nonglobal logarithms without
any approximation to the number of colors.
(4) Origin of proton mass
Understanding the origin of proton mass is one of the most important goals of the future Electron-Ion Collider. Y. Hatta and
R. Boussarie has developed an OPE-based approach to calculate the cross section of near-threshold electro-production of heavy
quarkonia at large photon virtuality. The impact of the gluon condensate, related to the proton mass via the trace anomaly, has been
estimated. D. Kharzeev argued that the cross section is dominated by the form factor of the trace of the energy momentum tensor.
Based on this, he has extracted the nucleon “mass radius” from the recent experimental data on J/psi production from the Jeﬀerson
laboratory. Y. Hatta and Y. Zhao have introduced a parton distribution function associated with the gluon condensate and performed a
one-loop calculation with a special attention to the possible zero mode.
(5) Hydrodynamical simulation of heavy-ion collisions
C. Shen has developed a comprehensive dynamical platform to simulate the evolution of fireballs created in heavy-ion collisions
based on numerical codes for the viscous hydrodynamic equation. This can be applied to RHIC experiments with a wide range incenter-of-mass energy, from the top energy (200 GeV per nucleon) to very low energy (7 GeV per nucleon) relevant to the ongoing
Beam Energy Scan II experiment (BES II). This allows him to extract the shear viscosity from the input equation of state and theexperimental data on particle multiplicity, etc. C. Shen has also studied various aspects of heavy-ion collisions such as Lambda
polarization, deutron production and signals of vortex formation.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)(6) Quantum information & computing
RBRC theorists also work on quantum computing and quantum information science. Y. Kikuchi discussed how to recover damaged information from Hawking radiation in Hayden-Preskill thought experiment. D. Kharzeev, Y. Kikuchi, and K. Ikeda have studied
the real-time dynamics of the topological susceptibility near the critical point of massive Schwinger model and observed a sharp
maximum due to critical fluctuations. Their spin Hamiltonian formulation is suitable for future digital quantum simulations.
(7) Beyond the standard model physics in low and high energy nuclear physics
Together with collaborators, J. de Vries has explored possible manifestations of physics beyond the Standard Mode (BSM) in
low energy nuclear physics such as neutrinoless double beta decays and the nucleon electric dipole moment. In particular, his group
has presented a first estimate of the complete amplitude of neutrinoless double beta decay including a contact term necessary for
renormalization in chiral eﬀective theory. J. de Vries also studied the prospect to discover sterile neutrinos at the LHC in the frameworkof neutrino-extended Standard Model Eﬀective Field Theory.
(8) New connection between the nucleon electric dipole moment and QCD spin physics
One of the plausible operators to induce an electric dipole moment (EDM) in nucleons is the Weinberg operator which is adimension-6, purely gluonic operator. Y. Hatta has found a novel relation between the nucleon matrix element of the Weinberg
operator and certain twist-4 corrections in polarized Deep Inelastic Scattering (DIS) experiment. Based on this observation, he has
made a numerical estimate of the EDM which turned out to be smaller than a previous estimate based on the QCD sum rule.

Members
Group Leader
Dmitri KHARZEEV
Deputy Group Leader
Yoshitaka HATTARBRC Researchers
Jordy DE VRIES
Yuta KIKUCHI
Yacine MEHTAR-TANI

Chun SHEN
Vladimir SKOKOV

Visiting Scientists
Hiromichi NISHIMURA (Keio Univ.)

Yuya TANIZAKI (North Carolina State Univ.)

List of Publications & Presentations
Publications[Original Papers]
R. Boussarie and Y. Hatta, “QCD analysis of near-threshold quarkonium leptoproduction at large photon virtualities,” Phys. Rev. D 101,
114004 (2020).
Y. Hatta and Y. Zhao, “Parton distribution function for the gluon condensate,” Phys. Rev. D 102, 034004 (2020).
Y. Hatta, “CP-odd gluonic operators in QCD spin physics,” Phys. Rev. D 102, 094004 (2020).
Y. Hatta, B. Xiao, F. Yuan, and J. Zhou, “Anisotropy in dijet production in exclusive and inclusive processes,” Phys. Rev. Lett. 126, 142001(2021).
Y. Hatta and T. Ueda, “Non-global logarithms in hadron collisions at Nc = 3,” Nucl. Phys. B 962, 115273 (2021).
Y. Hatta, “Nucleon electric dipole moment from polarized deep inelastic scattering,” Phys. Lett. B 814, 136126 (2021).
Y. Hatta and M. Strikman, “ϕ-meson leptoproduction near threshold and the strangeness D-term,” Phys. Lett. B 817, 136295 (2021).
N. Bao and Y. Kikuchi, “Hayden-Preskill decoding from noisy Hawking radiation,” J. High Energy Phys. 2021, 17 (2021).
K. Ikeda, D. Kharzeev, and Y. Kikuchi, “Real-time dynamics of Chern-Simons fluctuations near a critical point,” Phys. Rev. D 103,
L071502 (2021).
L. Gao, S. Kaushik, D. Kharzeev, and E. Philip, “Chiral kinetic theory of anomalous transport induced by torsion,” arXiv.2010.07123[cond-mat], (2020).
D. Kharzeev, “The mass radius of the proton,” arXiv.2102.00110 [hep-ph] (2021).
M. Buzzegoli and D. Kharzeev, “Anomalous gravitomagnetic moment and non-universality of the axial vortical eﬀect at finite temperature,” arXiv.2102.01676 [hep-th] (2021).
D. Kharzeev and E. Levin, “Deep inelastic scattering as a probe of entanglement: confronting experimental data,” arXiv.2102.09773[hep-ph] (2021).
R. Boussarie and Y. Mehtar-Tani, “A novel formulation of the unintegrated gluon distribution for DIS,” arXiv.2006.14569 [hep-ph] (2020).
J. Barata, Y. Mehtar-Tani, and A. Soto-Ontoso, “Revisiting transverse momentum broadening in dense QCD media,” arXiv.2009.13667[hep-ph] (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Y. Mehtar-Tani, D. Pablos, and K. Tywoniuk, “Cone size dependence of jet suppression in heavy-ion collisions,” arXiv.2101.01742 [hepph] (2021).
R. Boussarie and Y. Mehtar-Tani, “Gauge invariance of transverse momentum dependent distributions at small-x,” Phys. Rev. D 103,
094012 (2021).
M. Li and V. Skokov, “First saturation correction in high energy proton-nucleus collisions: I. Time evolution of classical Yang-Mills fields
beyond leading order,” arXiv.2102.01594 (2021).
T. Altinoluk, N. Armesto, A. Kovner, M. Lublinsky, and V. Skokov, “Angular correlations in pA collisions from CGC: multiplicity andmean transverse momentum dependence of ν2 ,” arXiv.2012.01810 [hep-ph] (2020).
A. Behtash, S. Kamata, M. Martinez, A. Schafer, and V. Skokov, “Transasymptotics and hydrodynamization of the Fokker-Planck equation
for gluons,” Phys. Rev. D 103, 056010 (2021).
A. Dumitru and V. Skokov, “An incorrect pre-asymptotic RG flow of scattering amplitudes in QCD towards the unitarity limit,”
arXiv.2010.03015 [hep-ph] (2020).
A. Connelly, G. Johnson, F. Rennecke, and V. Skokov, “Universal location of the Yang-Lee edge singularity in O(N) theories,” Phys. Rev.
Lett. 125, 19 (2020).
C. Cheng and C. Shen, “Exploring theoretical uncertainties in the hydrodynamic description of heavy-ion collisions,” arXiv.2103.09848[nucl-th] (2021).
W. Serenone, J. Barbon, D. Chinellato, M. Lisa, and C. Shen, “Lambda polarization from thermalized jet energy,” arXiv.2102.11919[hep-ph] (2021).
M. Lisa, J. Barbon, D. Chinellato, W. Serenone, C. Shen, J. Takahashi, and G. Torrieri, “Vortex rings from high energy central pA
collisions,” arXiv.2101.10872 [hep-ph] (2021).
W. Zhao, C. Shen, C. Ko, Q. Liu, and H. Song, “Beam-energy dependence of the production of light nuclei in Au + Au collisions,” Phys.
Rev. C 102, 044912 (2020).
√
D. Oliinychenko, C. Shen, and V. Koch, “Deuteron production in AuAu collisions at s = 7–200 GeV via pion catalysis,” Phys. Rev. C
103, 034913 (2021).
G. Giacalone, B. Schenke, and C. Shen, “Observable signature of initial state momentum anisotropies in nuclear collisions,” Phys. Rev.
Lett. 125, 192391 (2020).
B. Schenke, C. Shen, and P. Tribedy, “Running the gamut of high energy nuclear collisions,” Phys. Rev. C 102, 044905 (2020).
B. Schenke, C. Shen, and D. Teaney, “Transverse momentum fluctuations and their correlation with elliptic flow in nuclear collision,”
Phys. Rev. C 102, 034905 (2020).
V. Cirigliano, W. Dekens, J. de Vries, M. Hferichter, and E. Mereghetti, “Towards complete leading-order predictions for neutrinolessdouble β decay,” Phys. Rev. Lett. 126, 172002 (2021).
J. de Vries, H. Dreiner, J. Gunther, Z. Wang, and G. Zhou, “Long-lived sterile neutrinos at the LHC in eﬀective field theory,” J. HighEnergy Phys. 2021, 148 (2021).
J. de Vries, A. Gnech, and S. Shain, “Renormalization of CP-violating nuclear forces,” Phys. Rev. C 103, L012501 (2021).
V. Cirigliano, W. Dekens, J. de Vries, M. Hoferichter, and E. Mereghetti, “Determining the leading-rder contact term in neutrinolessdouble beta decay,” arXiv.2102.03371 [nucl-th] (2021).

[Review Articles]
D. Kharzeev and J. Liao, “Chiral magnetic eﬀect reveals the topology of gauge fields in heavy-ion collisions,” Nat. Rev. Phys. 3, 55(2021).
A. Monnai, B. Schenke, and C. Shen, “QCD equation of state at finite chemical potentials for relativistic nuclear collisions,” Int. J. Mod.
Phys. A 36, 2130007 (2021).
C. Shen and L. Yan, “Recent development of hydrodynamic modeling in heavy-ion collisions,” Nucl. Sci. Tech. 31, 122 (2020).

Presentations[International Conferences/Workshops]
Y. Hatta (invited), “Use of Wigner/GTMD at the EIC,” Jet Observables at the Electron-Ion Collider, RIKEN BNL Center Workshop, BNL,
July 27–29, 2020.
Y. Hatta (invited), “QCD Wigner distribution,” QCD with Electron-Ion Collider, IIT, Bombay, India, January 4–7, 2020.
Y. Hatta (invited), “Quarkonium photo- and lepto-production near threshold,” 3rd Proton Mass Workshop, Argonne National Lab, January
14–16, 2021.
Y. Hatta (invited), “Quarkonium production near threshold,” Open Questions in Photon-Induced Interactions, CFNS Workshop, April
26–28, 2021.
D. Kharzeev (invited), “Chirality: a theoretical overview,” Chirality and Criticality Workshop, INT, Seattle, May 11–22, 2020.
D. Kharzeev (invited), “The Chiral Qubit: quantum computing with Dirac/Weyl semimetals,” APS Users Meeting, ANL, August 27–28,
2020.
D. Kharzeev (invited), “Mass radius of the proton,” Deep Inelastic Scattering Conference, Stony Brook, April 12–16, 2021.
D. Kharzeev (invited), “Semiclassical description of chiral anomaly with real and synthetic gauge fields,” Gravity and Emergent Gauge
Fields Workshop, ITP Mainz, April 12–23, 2021.
C. Shen (invited), “Dynamical modeling of the collectivity in pO and OO collisions,” Opportunities of OO and pO Collisions at the LHC,

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

CERN, Febuary 5, 2021.
V. Skokov (invited), “Universality driven analytic structure of QCD crossover,” International Workshop “FunQCD: from first principles
to eﬀective theories,” March 29–April1, 2021.
V. Skokov (invited), “Universality driven analytic structure of QCD crossover,” XXXII International (online) Workshop on High Energy
Physics, “Hot problems of strong interactions,” November 9–13, 2020.
V. Skokov (invited), “Saturation corrections to dilute-dense particle production in the color glass condensate,” RHIC&AGS User’s Group
Meeting, October 22, 2020.
V. Skokov (invited), “Universality driven analytic structure of QCD crossover: radius of convergence in baryon chemical potential,” Rice
University & University of Illinois at Urbana-Champaign, June 15, 2020.
Y. Kikuchi, “Real-time chiral dynamics from a digital quantum simulation,” The 2020 Fall Meeting of the Division of Nuclear Physics of
the American Physical Society, October 29–November 1, 2020.

[Seminars]
Y. Hatta, “QCD trace anomaly and proton mass problem,” University of Kentucky, October 20, 2020.
Y. Hatta, “Two topics in QCD spin,” Kyoto University, November 20, 2020.
Y. Hatta, “Probing the Wigner distribution at the electron-ion collider,” Tata Institute of Fundamental Research, July 23, 2020.
D. Kharzeev, “Chiral magnetic eﬀect: from quarks to quantum computers,” INT Colloquium, March 18, 2021.
V. Skokov, “Analytic structure of QCD crossover,” Seminar Physics Department, Ben-Gurion University of the Negev, April 19, 2021.
C. Shen, “Dynamical modeling of the initial energy-momentum and baryon charge distributions for heavy-ion collisions,” LBL HIT
Seminar, March 2, 2021.
C. Shen, “Multi-messenger heavy-ion physics,” Invited Physics Colloquium, ASU Theoretical Physics Colloquium, March 31, 2021.
C. Shen, “Observable signature of initial state momentum anisotropies in nuclear collisions,” Nuclear Seminar, the ALICE Collaboration,
December 8, 2020.
C. Shen, “Dynamical modeling of relativistic heavy-ion collision at beam energy scan energies,” The 4th RHIC-BES Theory and Experiment Online Seminar, August 25, 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
RIKEN BNL Research Center
Experimental Group
1. Abstract

RIKEN BNL Research Center (RBRC) Experimental Group studies the strong interactions (QCD) using RHIC accelerator at
Brookhaven National Laboratory, the world first heavy ion collider and polarized p + p collider. We have three major activities: Spin
Physics at RHIC, Heavy ion physics at RHIC, and detector upgrades of PHENIX experiment at RHIC.
We study the spin structure of the proton using the polarized proton-proton collisions at RHIC. This program has been promoted
by RIKEN’s leadership. The first focus of the research is to measure the gluon spin contribution to the proton spin. Recent resultsfrom PHENIX π0 measurement and STAR jet measurement has shown that gluons in the proton carry about 30% of the proton spin.
This is a major milestone of RHIC spin program. The second goal of the spin program is to measure the polarization of anti-quarks
in the proton using W → e and W → µ decays. The results of W → e measurement was published in 2016. The final results of W → µ
was published in 2018.
The aim of Heavy ion physics at RHIC is to re-create Quark Gluon Plasma (QGP), the state of Universe just after the Big Bang.
Two important discoveries, jet quenching eﬀect and strong elliptic flows, have established that new state of dense matter is indeed
produced in heavy ion collisions at RHIC. We are now studying the property of the matter. Recently, we have measured direct photons
in Au + Au collisions for 1 < pT < 3 GeV/c, where thermal radiation from hot QGP is expected to dominate. The comparison between
the data and theory calculations indicates that the initial temperature of 300 MeV to 600 MeV is achieved. These values are well above
the transition temperature to QGP, which is calculated to be approximately 160 MeV by lattice QCD calculations.
We had major roles in detector upgrades of PHENIX experiment, namely, the silicon vertex tracker (VTX) and muon trigger
upgrades. Both of the upgrade is now complete. The VTX is the main device to measure heavy quark (charm and bottom) production
and the muon trigger is essential for W → µ measurement. The results from the first run with VTX detector in 2011 was published.
The results show that electrons from bottom quark decay is strongly suppressed at high pT , but the suppression is weaker than that ofcharm decay electron for 3 < pT < 4 GeV/c. We have recorded 10 times as much Au + Au collisions data in each of the 2014 run and2016 run. The large dataset will produce definitive results on heavy quark production at RHIC.
PHENIX completed its data taking in 2016. We are now working on R&D of intermediate silicon tracker INTT for sPHENIX, a
new experiment at RHIC that will be installed in the PHENIX IR.

2. Major Research Subjects(1) Experimental Studies of the Spin Structure of the Nucleon(2) Study of Quark-Gluon Plasma at RHIC
(3) sPHENIX INTT detector

3. Summary of Research Activity

We study the strong interactions (QCD) using the RHIC accelerator at Brookhaven National Laboratory, the world first heavy ion
collider and polarized p + p collider. We have three major activities: Spin Physics at RHIC, Heavy ion physics at RHIC, and detector
upgrades of PHENIX experiment. From 2016, Y. Akiba (Experimental Group Leader) is the Spokesperson of PHENIX experiment.
(1) Experimental study of spin structure of proton using RHIC polarized proton collider
How is the spin of proton formed with 3 quarks and gluons? This is a very fundamental question in Quantum Chromodynamics(QCD), the theory of the strong nuclear forces. The RHIC Spin Project has been established as an international collaboration between
RIKEN and Brookhaven National Laboratory (BNL) to solve this problem by colliding two polarized protons for the first time inhistory. This project also has extended the physics capabilities of RHIC.
The first goal of the Spin Physics program at RHIC is to determine the gluon contribution to proton spin. It is known that the spinof quark accounts for only 25% of proton spin. The remaining 75% should be carried either by the spin of gluons or the orbital angularmomentum of quarks and gluons. One of the main goals of the RHIC spin program has been to determine the gluon spin contribution.
Before the start of RHIC, there was little experimental constraint on the gluon polarization, ∆G.
PHENIX measures the double helicity asymmetry (ALL ) of π0 production to determine the gluon polarization. Our most recent
publication of π0 ALL measurement at 510 GeV shows non-zero value of ALL , indicating that gluons in the proton is polarized. Global
analysis shows that approximately 30% of proton spin is carried by gluons.
Figure 1 and Fig. 2 shows most recent√ spin physics measurement with PHENIX from our group. Figure 1 show the ALL of charged
pions in polarized p + p collisions at s = 510 GeV and Fig. 2 shows AN (pT ) of very forward neutron. These results are published in
Physical Review D.
Members of our group also participate in RHICf experiment, a small experiment at RHIC to measure particle production andsingle spin asymmetry of particles produced at very forward direction. Figure 3 shows AN (xF ) of very forward π0 measured by RHICf
compared with other experiments, published in Physical Review Letters. This is the first published results of RHICf experiment.
(2) Experimental study of Quark-Gluon Plasma using RHIC heavy-ion collider
The goal of high energy heavy ion physics at RHIC is study of QCD in extreme conditions i.e. at very high temperature and at- 324 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Fig. 1. Double spin asymmetry ALL of charged pions in midrapidity in p + p collisions at
QCD. Published in Phys. Rev. D 102, 032001 (2020).

√

5 = 510 GeV compared with theoretical predictions of perturbative

Fig. 2. Pt dependence of single spin asymmetry AN of very forward neutron in p + p. Published in Phys. Rev. D 103, 032007 (2021).

very high energy density. Experimental results from RHIC have established that dense partonic matter is formed in Au + Au collisions
at RHIC. The matter is very dense and opaque, and it has almost no viscosity and behaves like a perfect fluid. These conclusions areprimarily based on the following two discoveries:• Strong suppression of high transverse momentum hadrons in central Au + Au collisions (jet quenching)• Strong elliptic flow
These results are summarized in PHENIX White paper, which has more than 3000 citations to date. The focus of the research inheavy ion physics at RHIC is now to investigate the properties of the matter. RBRC have played the leading roles in some of the most- 325 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Fig. 3. AN (xF ) of very forward π0 measured by RHICf experiment is compared with other data. Published in Phys. Rev. Lett. 124, 252501 (2020).

important results from PHENIX in the study of the matter properties. These include (1) measurements of heavy quark production
from the single electrons from heavy flavor decay (2) measurements of J/Ψ production (3) measurements of di-electron continuumand (4) measurements of direct photons.
Our most important result is the measurement of direct photons for 1 < pT < 5 GeV/c in p + p and Au + Au through their internalconversion to e + e− pairs. If the dense partonic matter formed at RHIC is thermalized, it should emit thermal photons. Observation ofthermal photon is direct evidence of early thermalization, and we can determine the initial temperature of the matter. It is predicted that
thermal photons from QGP phase is the dominant source of direct photons for 1 < pT < 3GeV/c at the RHIC energy. We measured
the direct photon in this pT region from measurements of quasi-real virtual photons that decays into low-mass e + e− pairs. Strong
enhancement of direct photon yield in Au + Au over the scaled p + p data has been observed. Several hydrodynamical models canreproduce the central Au + A data within a factor of two. These models assume formation of a hot system with initial temperature of
T init = 300 MeV to 600 MeV. This is the first measurement of initial temperature of quark gluon plasma formed at RHIC. Y. Akiba
received 2011 Nishina memorial Prize mainly based on this work.
PHENIX experiment recently measured the flow in small collision systems (p + Au, d + Au, and 3 He + Au), and observed strong
flow in all of these systems. Theoretical models that assume formation of small QGP droplets best describe the data. These results are
published in Nature Physics in 2019.
(3) sPHENIX INTT detector
The group had major roles in several PHENIX detector upgrades, namely, the silicon vertex tracker (VTX) and muon trigger
upgrades. VTX is a high precision charged particle tracker made of 4 layers of silicon detectors. It is jointly funded by RIKEN andthe US DOE. The inner two layers are silicon pixel detectors and the outer two layers are silicon strip detectors. Y. Akiba is the project
manager and A. Deshpande is the strip system manager. The VTX detector was completed in November 2010 and subsequently
installed in PHENIX. The detector started taking data in the 2011 run. With the new detector, we measure heavy quark (charm andbottom) production in p + p, A + A collisions to study the properties of quark-gluon plasma. The final result of the 2011 run was
published. The result show that single electrons from bottom quark decay is suppressed, but not as strong as that from charm decay
in low pT region (3 < pT < 4 GeV/c). This is the first measurement of suppression of bottom decay electrons at RHIC and the firstobservation that bottom suppression is smaller than charm. We have recorded 10 times as much Au + Au collisions data in each of the2014 run and 2016 run. The large dataset will produce definitive results on heavy quark production at RHIC. A preliminary results on
the elliptic flow strength ν2 of b → e and c → e has been presented in Quark Matter 2018 conference. The results of bottom/charm ratios
in p + p collisions at 200 GeV from the 2015 run was published (Phys. Rev. D 99 092003 (2019)). A paper reporting measurementsof the nuclear suppression factor RAA of charm and bottom in Au + Au collisions from the 2014 data is in preparation.
PHENIX completed its data taking in 2016. We are now working on construction of intermediate silicon tracker INTT forsPHENIX, a new experiment at RHIC that will start taking data in 2023. Figure 4 shows snapshot of INTT construction work. INTT
consists of 56 ladders of silicon detector. So far approximately 30 ladders are produced. INTT will be completed in JFY2021.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Fig. 4. Left panel shows completed INTT ladders. Right panel shows the test assembly of a half barrel of INTT detector.

Members
Group Leader
Yasuyuki AKIBARBRC Researchers
Jan C. BERNAUER
Megan CONNORS
Yuji GOTO
Takashi HACHIYA
Itaru NAKAGAWA
Genki NUKAZUKA

Ralf SEIDL
Atsushi TAKETANI
Takahito TODOROKIYasushi WATANABE
Satoshi YOKKAICHISpecial Postdoctoral Researcher
Minho KIM
Special Temporary Research Scientist
Takashi ICHIHARA
Visiting Scientists
Stefan BATHE (Baruch College Univ. of New York)
Gaku MITSUKA (KEK)
Rachid NOUICER (BNL)
Masahiro OKAMURA (BNL)

Takao SAKAGUCHI (BNL)
Takashi SAKO (Univ. of Tokyo)
Milan STOJANOVIC (Purdue Univ.)

Visiting Technician
Li-Hsin HSU (Nat’l Central Univ.)
Student Trainees
Kai-Yu CHENG (Nat’l Central Univ.)
Anthony HODGES (Georgia State Univ.)
Han-Sheng LI (Purdue Univ.)
Lihan LIU (Vanderbilt Univ.)

Xiao RUI (Purdue Univ.)
Cheng Wei SHIH (Nat’l Central Univ.)
Cheuk-Ping WONG (Georgia State Univ.)

List of Publications & Presentations
Publications[Original Papers]√
U. A. Acharya et al., “Transverse sngle-spn asymmetries of midrapidty π0 and η mesons in polarized p + p collisions at s = 200 GeV,”
Phys. Rev. D 103, 052009 (2021).
U. A.√Acharya et al., “Transverse momentum dependent forward neutron ssingle spin asymmetries in transversely polarized p+ collisions
at s = 200 GeV,” Phys. Rev. D 103, 032007 (2021).
U. A. Acharya et al., “Nuclear dependence of the transverse single-spin asymmetry in the production of π0 and η mesons in U+U collisions√
at sNN = 192 GeV,” Phys. Rev. C 102, 064905 (2020).
√
A. Adare et al., “Production of bb̄ at forward rapidity in p + p collisions at s = 510 GeV,” Phys. Rev. D 102, 092002 (2020).
√
U. A. Acharya et al., “Polarization and cross section of J/ψ production in p + p collisions at s = 510 GeV,” Phys. Rev. D 102, 072008(2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)√
M. H. Kim et al., “Transverse single-pin aymmetry for very forward neutral pion production in polarized p + p collisions at s =510 GeV,” Phys. Rev. Lett. 124, 252501 (2020).
U. A. Acharya et al., “Measurement of jet-medium nteractinos via direct photon-hadron correlations in Au + Au and d + Au collisions at√
sNN = 200 GeV,” Phys. Rev. C 102, 054910 (2020).
U. A.√Acharya et al., “Measurement of charged pion double spin asymmetries at midrapidity in longitudinally polarized p + p collisions
at s = 510 GeV,” Phys. Rev. D 102, 032001 (2020).
√
U. A. Acharya et al., “J/ψ nd ψ(2S ) production at forward rapidity n p + p collion at s = 510 GeV,” Phys. Rev. D 101, 052006 (2020).
√
U. A. Acharya et al., “Measurement of J/ψ at forward and backward rapidity in p p , p + Al, p + Au and 3 He + Au collisions at sNN =200 GeV,” Phys. Rev. C 101, 014902 (2020).
C. Aidala et al., “Nuclear-modification factor of charged hadrons at forward and backward rapidty in p + Al and p + Au collisions at√
sNN = 200 GeV,” Phys. Rev. C 101, 034910 (2020).

Presentations[International Conferences/Workshops]
M. Connors (poster), “Jets modification with two-particle correlations in Au+Au collisions at PHENIX,” 10th international conference
on Hard and Electromagnetc Probes of High Energy Nuclear Collisions (Hard Probe 2020) (Online) May 31–June 5, 2020.
T. Hachiya (poster), “PHENIX results on quark flavor dependence of low in AuAu colliisions,” 10th international conference on Hard andElectromagnetc Probes of High Energy Nuclear Collisions (Hard Probe 2020) (Online) May 31–June 5, 2020.

Press Releases
New research deepens mystery of particle generation in proton collisions, RIKEN, June 23, 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
RIKEN BNL Research Center
Computing Group
1. Abstract

The computing group founded in 2011 as a part of the RIKEN BNL Research Center established at Brookhaven National Laboratory in New York, USA, and dedicated to conduct researches and developments for large-scale physics computations important forparticle and nuclear physics. The group was forked from the RBRC Theory Group.
The main mission of the group is to provide important numerical information that is indispensable for theoretical interpretationof experimental data from the first principle theories of particle and nuclear physics. Their primary area of research is lattice quantum
chromodynamics (QCD), which describes the sub-atomic structures of hadrons, which allow us the ab-initio investigation for stronglyinteracting quantum field theories beyond perturbative analysis.
The RBRC group and its collaborators have emphasized the necessity and importance of precision calculations, which will precisely check the current understandings of nature, and will have a potential to find a physics beyond the current standard model offundamental physics. We have therefore adopted techniques that aim to control and reduce any systematic errors. This approach has
yielded many reliable results.
The areas of the major activities are R&D for high performance computers, developments for computing algorithms, and researches of particle, nuclear, and lattice theories. Since the inception of RBRC, many breakthroughs and pioneering works has carriedout in computational forefronts. These are the use of the domain-wall fermions, which preserve chiral symmetry, a key symmetry forunderstanding nature of particle nuclear physics, the three generations of QCD devoted supercomputers, pioneering works for QCD
calculation for Cabibbo-Kobayashi-Maskawa theory, QCD + QED simulation for isospin breaking, novel algorithm for error reduction
in general lattice calculation. Now the chiral quark simulation is performed at the physical up, down quark mass, the precision formany basic quantities reached to accuracy of sub-percent, and the group is aiming for further important and challenging calculations,such as the full and complete calculation of CP violating K → ππ decay and ε′ /ε, or hadronic contributions to muon’s anomalous
magnetic moment g − 2. Another focus area is the nucleon’s shape, structures, and the motion of quarks and gluon inside nucleon
called parton distribution, which provide theoretical guidance to physics for sPHENIX and future Electron Ion Collider (EIC), Hyper
Kamiokande, DUNE, or the origin of the current matter rich universe (rather than anti-matter). Towards finite density QCD, they also
explore Quantum Computing to overcome the sign problem. The Machine Learning (ML) and Artificial Intelligence (AI) are the new
topics some of members are enthusiastically studying lately.

2. Major Research Subjects(1) Search for new law of physics through tests for Standard Model of particle and nuclear physics, especially in the frameworkof the Cabibbo-Kobayashi-Maskawa (CKM), hadronic contributions to the muon’s anomalous magnetic moment (g − 2) for
FNAL and J-PARC’s experiments, as well as B physics at Belle II and LHCb.
(2) Nuclear Physics and dynamics of QCD or related theories, including study for the structures of nucleons related to physics
for Electron Ion Collider (EIC or eRHIC), Hyper Kamiokande, T2K, DUNE.
(3) Theoretical and algorithmic development for lattice field theories, QCD machine (co-)design and code optimization.

3. Summary of Research Activity

In 2011, QCD with Chiral Quarks (QCDCQ), a third-generation lattice QCD computer that is a pre-commercial version of IBM’s
Blue Gene/Q, was installed as an in-house computing resource at the RBRC. The computer was developed by collaboration among
RBRC, Columbia University, the University of Edinburgh, and IBM. Two racks of QCDCQ having a peak computing power of 2 × 200
TFLOPS are in operation at the RBRC. In addition to the RBRC machine, one rack of QCDCQ is owned by BNL for wider use forscientific computing. In 2013, 1/2 rack of Blue Gene/Q is also installed by US-wide lattice QCD collaboration, USQCD. The group
has also used the IBM Blue Gene supercomputers located at Argonne National Laboratory and BNL (NY Blue), and Hokusai and
RICC, the super computers at RIKEN (Japan), Fermi National Accelerator Laboratory, the Jeﬀerson Lab, and others. From 2016, thegroup started to use the institutional cluster both GPU and Intel Knight Landing (KNL) clusters installed at BNL and University ofTokyo extensively.
Such computing power enables the group to perform precise calculations using up, down, and strange quark flavors with proper
handling of the important symmetry, called chiral symmetry, that quarks have. The group and its collaborators carried out the first
calculation for the direct breaking of CP (Charge Parity) symmetry in the hadronic K meson decay (K → ππ) amplitudes, ε′ /ε, which
provide a new information to CKM paradigm and its beyond. They also provide the hadronic contribution in muon’s anomalous magnetic moment (g − 2)µ . These calculation for ε′ /ε, hadronic light-by-light of (g − 2), are long waited calculation in theoretical physics
delivered for the first time by the group. The K → ππ result in terms of ε′ /ε currently has a large error, and deviates from experimental
results by 2.1σ. To collect more information to decide whether this deviation is from the unknown new physics or not, the group continues to improve the calculation in various way to reduce their error. Hadronic light-by-light contribution to (g − 2)µ is improved bymore than two order of magnitudes compared to our previous results. As of 2019 summer, their calculation is among the most precise
determination for the g − 2 hadronic vacuum polarization (HVP), and only one calculation in the world for the hadronic light-by-light(HLbL) contribution at physical point. These (g − 2)µ calculations provide the first principle theoretical prediction for on-going newexperiment at FNAL and also for the planned experiment at J-PARC. Other projects including flavor physics in the framework of the- 329 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

aHVP,LO. 1010µ

Magnetic field
ETM-18/19
Mainz/CLS-19
FHM-19PACS-19
RBC/UKQCD-18
BMW-17Mainz/CLS-17
HPQCD-16
ETM-13muon

Hadronic Vacuum Polarization (HVP)(a) V(c) ST

(b) S

(f) F

(d) T

KNT-19DHMZ-19
BDJ-19Jegerlehner-18(e) TdRBC/UKQCD-18
LQCD
Pheno.

(h) D3T(g) D3

No New Physics

Pheno+LQCD(i) D1(j) D1T(k) D1d(l) D1d,T(m) D2(n) D2d

600

650

700

750

Figure 42: Photonic-correction diagrams to order O(↵) with external vector operators. Adapted from Ref. [403].

LO
10 . The filled
Fig. 1. Feynman diagrams for Lattice QCD computationsof Muon’s
anoma- of recent
Fig.results
2. Current
VacuumPolarization(HVP)
con-that are included i
Figure44: Compilation
for aHVP,in unitsofofthe
10 Hadronic
dark blue
circles are lattice
resultsµ summaryworld
average”.
Theaverage,which
isobtainedfroma conservative
averagingprocedurein Sec.
3.5.1,
isAboveindicatedlous magnetic moment (g − 2)µ to take into account for the eﬀects of.
theby a light blue ban
tribution for Muon’s
anomalous
magnetic
moment(g−2)µ
LO
indicates the “no new physics” scenario, where aHVP,
are large enough to bring the SM prediction of aµ int
quark’s electric charges. Each diagram, in which thelight-green
black dotsband
connectupper horizontal line shows µvariousresults
Lattice
QCD determinations of HVP
with experiment. The unfilled dark blue circles are lattice results that are older or superseded by more recent calculations. The red squing the quark propagators (solid curves) are the electric
while
the redresultsinfrom
hadronic
decay
electronpositron
resultscurrent
obtainedemmitfrom the data-driven
methods
reviewed
Sec. 2.
See Table
8 forofmore
information
on scattering
the results included in the pting or absorbing photons (wave curves), representsfrom
a partof [443].
the isospin(R-ratio), the green bands is the experimental results of (g − 2)µ showing
Ref.
Figure 43: SIB-correction diagrams to order O(∆m). The diamonds denote the insertion of a scalar operator. Adapted from Ref. [403].
breaking eﬀects to hadronic vacuum polarization contribution to (g−2)µa 3–4σ discrepancies.
setof diagrams(topplot).coming from the expansion to O(↵) in the QED coupling is shown in Fig. 42. These diagrams can29

be divided into three di↵erent classes: QED corrections to the quark-connected contributions are given by diagrams V,
S , and S T ; diagrams F, D3, and D3T represent corrections to the quark-disconnected contributions; while diagrams T ,D1, D1T , D2 and T d , D1d , D1d,T , D2d account for QED IB e↵ects coming from dynamical sea quarks for the quarkconnected and quark-disconnected contributions (the latter denoted by a subscript d), respectively. Diagrams S T , D1T ,
D3T , D1d,T of Fig. 42, denoted by subscripts T , correspond to the insertions of the tadpole operator. The latter is afeature of lattice discretization and plays a crucial role in order to preserve gauge invariance to O(↵) in the expansionof the quark action. In the calculation performed in Ref. [11] tadpole contributions are absent since insertions of local
vector currents are used. Regularization-specific IB e↵ects associated with the tuning of the quark critical masses in
the presence of QED interactions [389, 393] arise when the lattice fermionic action does not preserve chiral symmetry,
as in the case of Wilson and twisted-mass fermions (see, e.g., Refs. [12, 375]). This requires in addition the evaluationof diagrams with insertions of pseudoscalar densities (i.e., replacing the insertions of a scalar operator in Fig. 43 bypseudoscalar currents). IB corrections due to the expansion in the quark masses are given by the diagrams in Fig. 43.
The ETM [12, 375] and RBC/UKQCD [11] calculations are performed within the so-called electroquenchedapproximation, i.e., by treating sea quarks as neutral particles with respect to electromagnetism. Thus, diagrams where

are not included in the averages.
LO(ud), shown in the u
The lattice results for the dominant light-quark connected contribution aHVP,
µ
HVP,
LO
CKM theory for kaons and B mesons that include
new45,
calculation
b-baryonΛb →p; theelectromagnetic.properties
There is a 2.4 tension
paneltheof Fig.
exhibit a ofsimilarspreaddecay,
in central
valuesas those
for aµof hadrons; the proton’s and neutron’s form factors
and structure
functionincludingelectric
proton[15],decay;
nucleonthe resultswith lowest(ETM-18/19[17, 377])
anddipolehighestmoments;(Mainz/CLS-19
PACS-19[13]) central val
form factors, which are related to the proton spin
problemorneutrino-nucleon
interaction;
Neutron-antineutron
oscillations;
inclusive
BMW-17 [10], RBC/UKQCD-18 [11], FHM-19 [14], and Aubin et al.-19 [16] lie in between. In HPQCD
hadronic decay of τ leptons; nonperturbative studies
for beyond
standard
model suchcomposite
Higgs
or darkmodelsfromthe light-quark
connected
contribution
is notdefined in
the samewaymatteras in thisreview,
as it is evaluateLthe physicalchargedpion mass.
As electromagnetica result it cannot properties;
be directly QCD
comparedto lattice results for aHVP,
strong strongly interacting gauge theories; a few-bodynuclearphysics
and their
thermodynamicsµ
HVP, LO
The use of lattice conserved vector currents at the source and at the sink requires the evaluation of additional diagrams [432].
in finite temperature/density systems such as those
producedin heavy-ion
at the Relativistic
Heavy
Collider;Quantum
is sensitive
to the long-dista
is therefore
omittedfrom Fig.collisions
45. As discussed
in Sec. 3.2,
aµ Ion (ud)77
Euclideantime) behaviorof thevector-current
correlator, which is the region where the correlator su↵ers f
Information, Quantum Computing; and applicationsof Machine
Learning(ML)
in field theories.
It is thepossiblethat thetension ofis related
to thedi↵erent strategies
employed
The RBRC group and its collaborators haveproblem.
emphasizednecessity
andaboveimportance
precision
calculations,which will
provideto control and m
Furthercomparisonsof otherintermediate
quantities with di↵estringent checks for the current understandingsimportantof nature,region.
and willhaveinvestigations,a potential to including
find physics
beyond thecurrent
standard modelof sensitivity
to thethat
shortandtolong-distancewould be useful.
factapproachthat the tension betweeof fundamental physics. We have therefore adopted
techniques
aim
control and contributions,
reduce any systematic
errors.The
This
is larger
individual
errorssub-percent
may be an indicationthat some systematic e↵ects are underestim
has yielded many reliable results, many of basicresults
quantities
arethannowthecomputed
withinaccuracies.
expectthat
thissituationwill
improveinfuturehigh-precision
studies,which willThese
enablemore refined analy
The group also delivers several algorithmic breakthroughs, which speed up generic lattice gauge theory computation.
novel
underlying systematic errors.
technique divides the whole calculation into frequent approximated calculations, and infrequent expensive
and accurate
calculation
LO
LO
The strange- and charm-quark connected contributions aHVP,(s) and aHVP,(c) are shown in the uµµusing lattice symmetries called All Mode Averaging (AMA), or a compression for memory needs by exploiting
the local-coherence
and lower-left panels of Fig. 45 respectively. These quantities are already calculated at close to target
of QCD dynamics. Together with another formalism,
zMobius fermion,
which approximatechiral lattice quark action eﬃciently, theLO
LO
The results for aHVP,(s) and for aHVP,(c) from Refs. [10, 11, 17, 358, 377] are nicely consistent. Hoµµtypical calculation is now improved by a couple of orders of magnitudes,
and more than an order of magnitude less memory needs HVP, LO
HVP, LO(s) is in 1 tension with the other lattice results while for a(c) it is
PACS-19 [13] result for aµcompared to the traditional methods. RBRC groupand its collaborators also provide very eﬃcient and generic code optimized to the µ
2 tension with the rest. The strange- and charm-quark connected contributions, while insensitive to FVE
29state-of-arts CPU or GPU, and also improve how to eﬃciently generate QCD ensemble.

81

Members
Group Leader
Taku IZUBUCHI
Special Postdoctoral Researchers
Akio TOMIYARBRC Researchers- 330 -

in the “latticend, while theto agreement
uares indicate
plot. Adapted

upper-rightn between
lues, while
D-16 [376],
ed there atLO(ud) andance (large
from a StN
model thiserent levels
en di↵erent
mated. We
yses of theupper-right
precision.
owever, thes in almost
Es and StN

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Sergey SYRITSYNLuchang JIN

Visiting Scientists
Thomas BLUM (Univ. of Connecticut)
Chulwoo JUNG (BNL)
Shigemi OHTA (KEK)
Tomomi ISHIKAWA (Shanghai Jiao-Tong Univ.)
Christoph LEHNER (BNL)

Meifeng LIN (BNL)
Robert MAWHINNEY (Columbia Univ.)
Hiroshi OKI (Nara Women’s Univ.)
Christopher KELLY (Columbia Univ.)

List of Publications & Presentations
Publications[Original Papers]
M. Abramczyk, T. Blum, T. Izubuchi, C. Jung, M. Lin, A. Lytle, S. Ohta, E. Shintani, “Nucleon mass and isovector couplings in 2 + 1flavor dynamical domain-wall lattice QCD near physical mass,” Phys. Rev. D 101, no.3, 034510 (2020).
T. Izubuchi, L. Jin, C. Kallidonis, N. Karthik, S. Mukherjee, P. Petreczky, C. Shugert, S. Syritsyn, “Valence parton distribution functionof pion from fine lattice,” Phys. Rev. D 100, 034516 (2019).
N. H. Christ, X. Feng, L. C. Jin, C. T. Sachrajda, “Finite-volume eﬀects in long-distance processes with massless leptonic propagators,”
Phys. Rev. D 103, 014507 (2021).
Y. Li, S. C. Xia, X. Feng, L. C. Jin, C. Liu, “Field sparsening for the construction of the correlation functions in lattice QCD,” Phys. Rev.
D 103, 014514 (2021).
C. Y. Seng, X. Feng, M. Gorchtein, L. C. Jin, U. G. Meißner, “New method for calculating electromagnetic eﬀects in semileptonic
beta-decays of mesons,” J. High Energy Phys. 10, 179 (2020).
X. Gao, L. Jin, C. Kallidonis, N. Karthik, S. Mukherjee, P. Petreczky, C. Shugert, S. Syritsyn, Y. Zhao, “Valence parton distribution of thepion from lattice QCD: Approaching the continuum limit,” Phys. Rev. D 102, 094513 (2020).
HI +HI

X. Feng, L. C. Jin, Z. Y. Wang, Z. Zhang, “Finite-volume formalism in the 2 −−−−−→ 2 transition: An application to the lattice QCD
calculation of double beta decays,” Phys. Rev. D 103, 034508 (2021).
R. Abdul Khalek et al., “Science Requirements and Detector Concepts for the Electron-Ion Collider: EIC Yellow Report,”
arXiv:2103.05419 [physics.ins-det].
X. Gao, N. Karthik, S. Mukherjee, P. Petreczky, S. Syritsyn, Y. Zhao, “Pion form factor and charge radius from Lattice QCD at physicalpoint,” arXiv:2102.06047 [hep-lat].
X. Gao, N. Karthik, S. Mukherjee, P. Petreczky, S. Syritsyn, Y. Zhao, “Towards studying the structural diﬀerences between the pion andits radial excitation,” Phys. Rev. D 103, 094510 (2021).
G. Silvi, S. Paul, C. Alexandrou, S. Krieg, L. Leskovec, et al., “P-wave nucleon-pion scattering amplitude in the ∆(1232) channel fromlattice QCD,” Phys. Rev. D 103, 094508 (2021).
M. Yu. Barabanov, M. A. Bedolla, W. K. Brooks, G. D. Cates, C. Chen, et al., “Diquark correlations in hadron physics: Origin, impact
and evidence,” Prog. Part. Nucl. Phys. 116, 103835 (2021).
M. Engelhardt, J. R. Green, N. Hasan, S. Krieg, S. Meinel, J. Negele, A. Pochinsky, S .Syritsyn, “From Ji to Jaﬀe-Manohar orbital angularmomentum in lattice QCD using a direct derivative method,” Phys. Rev. D 102, 074505 (2020).
G. Rendon, L. Leskovec, S. Meinel, J. Negele, S. Paul, et al., “I = 1/2 S -wave and P-wave Kπ scattering and the κ and K ∗ resonancesfrom lattice QCD,” Phys. Rev. D 102, 114520 (2020).
Z. Fan, X. Gao, R. Li, H. -W. Lin, N. Karthik, et al., “Isovector parton distribution functions of the proton on a superfine lattice,” Phys.
Rev. D 102, 074504 (2020).
H. T. Ding, S. T. Li, Swagato Mukherjee, A. Tomiya, X. D. Wang, Y. Zhang, “Correlated Dirac eigenvalues and axial anomaly in chiralsymmetric QCD,” Phys. Rev. Lett. 126, 082001 (2021).
M. Kawaguchi, S. Matsuzaki, A. Tomiya, “Nonperturbative flavor breaking in topological susceptibility at hot QCD criticality,” Phys.
Lett. B 813, 136044 (2021).
H. -T. Ding, C. Schmidt, A. Tomiya, X. -D. Wang, “Chiral phase structure of three flavor QCD in a background magnetic field,” Phys.
Rev. D 102, 054505 (2020).
B. Chakraborty, M. Honda, T. Izubuchi, Y. Kikuchi and A. Tomiya, “Digital quantum simulation of the Schwinger model with topologicalterm via adiabatic state preparation,” arXiv:2001.00485 [hep-lat].

[Review Articles]
T. Aoyama, N. Asmussen, M. Benayoun, J. Bijnens, T. Blum, M. Bruno, I. Caprini, C. M. Carloni Calame, M. Cè and G. Colangelo, etal., “The anomalous magnetic moment of the muon in the Standard Model,” Phys. Rept. 887, 1–166 (2020).

[Books]Akio Tomiya, “An introduction to machine learning in physics” (in Japanese), Kodansha, March 2021.
K. Hashimoto, A. Tanaka, A. Tomiya, “Deep learning and physics,” Springer, February 2021.

[Proceedings]- 331 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

T. Izubuchi, H. Ohki and S. Syritsyn, “Computing Nucleon Electric Dipole Moment from lattice QCD,” PoS LATTICE2019, 290 (2020).
M. Bruno, T. Izubuchi, C. Lehner and A. S. Meyer, “Exclusive Channel Study of the Muon HVP,” PoS LATTICE2019, 239 (2019)
M. Kawaguchi, S. Matsuzaki, A. Tomiya, “Analysis on nonperturbative flavor violation at chiral crossovercriticality in QCD,”
arXiv:2005.07003 [hep-ph].
A. Tomiya, Y. Nagai, “Gauge covariant neural network for 4 dimensional non-abelian gaugetheory,” arXiv:2103.11965 [hep-lat].
M. Kawaguchi, S. Matsuzaki, A. Tomiya, “A new critical endpoint in thermomagnetic QCD,” arXiv:2102.05294 [hep-ph].
Y. Nagai, A. Tanaka, A. Tomiya, “Self-learning Monte-Carlo for non-abelian gauge theory withdynamical fermions,” arXiv:2010.11900[hep-lat].
H. -T. Ding, S. -T. Li, A. Tomiya, X. -D. Wang, Y. Zhang, “Chiral properties of (2 + 1)-flavor QCD in strong magnetic fields at zerotemperature,” arXiv:2008.00493 [hep-lat].
H. -T. Ding, S. -T. Li, S. Mukherjee, A. Tomiya, X. -D. Wang, “Meson masses in external magnetic fields with HISQ fermions,”
arXiv:2001.05322 [hep-lat].

Presentations[International Conferences/Workshops]
L. Jin (invited), “Lattice calculations in muon g − 2,” The Hadron Mass and Structure Forum, online, April 2021.
L. Jin (invited), “Muon g−2: hadronic light-by-light contribution and lattice QCD,” The Muon g−2 Discussion Forum, Peking University,
online, April 2021.
L. Jin (invited), “Pion electric polarizability,” the χQCD Collaboration Meeting, online, January 2021.
L. Jin (invited), “Lattice calculation of the hadronic light-by-light contribution to the muon magnetic moment,” The Hadron Physics
Online Forum, online, August 2020.
S. Syritsyn (invited), “Nucleon Form Factors at High Momentum Transfer from Lattice QCD,” Nuclear & Particle Theory Seminar,
MIT/CTP, March 9, 2020.
A. Tomiya (oral), “Self-learning Monte-Carlo for non-abelian gauge theory withdynamical fermions,” APS April Meeting 2020, Virtual,
April 18–21, 2020
A. Tomiya (invited), “Self-learning Monte-Carlo for non-abelian gauge theory with dynamical fermions,” Workshop on Non-Equilibrium
Systems and Machine Learning, Virtual, March 30, 2020.
A. Tomiya (oral), “Quantum computing for QCD phase diagram? Finite chemicalpotential and temperature?” Kickoﬀ Meeting of C2QACenter, Virtual (BNL), October 30, 2020.
A. Tomiya (invited), “Machine learning and theoretical physics,” Progress of Particle Physics 2020, Virtual (YITP), September 4, 2020.
A. Tomiya (oral), “Thermal field theory with pure states,” Asia-Pacific Symposium for Lattice Field Theory (APLAT 2020), Virtual(KEK), August 6, 2020 (JST).
A. Tomiya (invited), “Applications of machine learning to computational physics,” A. I. for Nuclear Physics, Virginia (Jeﬀerson Laboratory), U.S.A., March 3, 2020.

[Domestic Conferences/Workshops]
富谷昭夫 (口頭発表), “Gauge covariant neural network for 4 dimensional non-abelian gaugetheory,” 「ゲージ共変なニューラルネットと 4 次元非可換ゲージ理論への応用 (Gauge covariant neural network for 4 dimensional non-abelian gauge theory)」, Deep Learning
and Physics, オンライン開催, 2020 年 4 月 8 日 (JST).
富谷昭夫 (口頭発表), 「動的フェルミオンを含む非可換ゲージ理論のための自己学習モンテカルロ法」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日 (JST).
富谷昭夫 (招待講演), チュートリアル講演「理論物理学における機械学習の応用」, 第 5 回 統計・機械学習若手シンポジウム, オンライン開催, 2020 年 12 月 3–5 日 (JST).
富谷昭夫 (口頭発表), 「ニューラルネットを使った 2 次元イジング模型の相検出」, Deep Learning and Physics 2020, オンライン開催 (大阪大学), 2020 年 11 月 26 日 (JST).

[Seminars]
L. Jin (invited), “Lattice calculations in muon g − 2,” The Theory Seminar at the Department of Physics and Astronomy, University ofCalifornia, Davis, online, May 2021.
L. Jin (invited), “Lattice calculations in muon g − 2,” The Lunch Seminar at the Institute of Theoretical Physics, Chinese Academy of
Sciences, online, April 2021.
L. Jin (invited), “First-principles calculation of electroweak box diagrams from lattice QCD,” The Physics Seminar in Hunan University,
online, December 2020.
L. Jin (invited), “First-principles calculation of electroweak box diagrams from lattice QCD,” The Theory Seminar at the Institute ofModern Physics, Chinese Academy of Sciences, online, July 2020.
L. Jin (invited), “First-principles calculation of electroweak box diagrams from lattice QCD,” The BNL Nuclear Theory Seminar, online,
May 2020.
L. Jin (invited), “Lattice calculation of the hadronic light-by-light contribution to the muon magnetic moment,” The QCD Seminar, online,
May 2020.
S. Syritsyn (invited), “From quarks and gluons to nucleons and nuclei,” Seminar at IACS (Inst. Adv. Comp. Sci), Stony Brook, Oct 8,- 332 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

2020.
A. Tomiya (oral), “Gauge covariant neural network for 4 dimensional non-abelian gaugetheory,” MIT, online, April 29, 2020.
A. Tomiya (oral), “Applications of machine learning on theoretical physics,” Ochanomizu University, online, May 19, 2020.
A. Tomiya (oral), “Gauge covariant neural network for 4 dimensional non-abelian gaugetheory,” RIKEN Center for Computational Science (R-CCS), online, April 28, 2020.
A. Tomiya (oral), “Applications of machine learning for theoretical physics,” J-PARC, online, March 18, 2020.
A. Tomiya (oral), “Self-learning Monte-Carlo for non-abelian gauge theory withdynamical fermions,” Yukawa Institute for Theoretical
Physics (YITP), Kyoto Univeristy, online, December 7, 2020.
A. Tomiya (oral), “Applications of machine learning on theoretical physics,” Shimane University, online, October 29, 2020
A. Tomiya (oral), “Lattice gauge theory with quantum computers,” RIKEN Center for Computational Science (R-CCS), online, June 3,2020.
A. Tomiya (oral), “Lattice gauge theory with quantum computers,” Osaka University, online, May 12, 2020.

Awards
富谷昭夫, 理研基礎科学特別研究員 成果発表会ポスター賞, 2021 年 1 月.

Press Releases
Brookhaven National Laboratory (April 7, 2021), “Background on Brookhaven Lab’s Involvement in the Muon g-2 Experiment,” https://www.bnl.gov/newsroom/news.php?a=218814 .
CERN Courier (April 14, 2021), “An anomalous moment for the muon,” https://cerncourier.com/a/an-anomalous-moment-fo
r-the-muon/ .
UConn Today (May 20, 2021), “UConn Physicists Focus on a Law-Breaking Particle,” https://today.uconn.edu/2021/05/uconnphysicists-focus-on-a-law-breaking-particle/ .

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Subnuclear System Research Division
RIKEN Facility Oﬃce at RAL
1. Abstract

Our core activities are based on the RIKEN-RAL Muon Facility located at the ISIS Neutron & Muon Source at the Rutherford
Appleton Laboratory (UK), which provides intense pulsed-muon beams. The RIKEN-RAL Muon Facility is a significant and longstanding collaboration between RIKEN and RAL in muon science—with 2020 being the 30th years of continuous agreements between
RIKEN and RAL. The Facility enables muon science throughout Japan and other field—it continues to attract proposals from a wide
variety of Japanese universities and institutions (with over 80 groups having now used the facility), and including industrial users suchat Toyota, and has been instrumental in establishing scientific links with other Asian universities.
Muons have their own spins with 100% polarization, and can detect local magnetic fields and their fluctuations at muon stoppingsites very precisely. The method to study the characteristics of materials by observing time dependent changes of muon spin polarization is called “Muon Spin Rotation, Relaxation and Resonance” (µSR method), and is applied to study electro-magnetic properties
of insulating, metallic, magnetic and superconducting systems. Muons reveal static and dynamic properties of the electronic state ofmaterials in the zero-field condition, which is the ideal magnetic condition for research into magnetism. For example, we have carriedout µSR investigations on a wide range of materials including frustrated pyrochlore systems, which have variety of exotic groundstates of magnetic spins, so the magnetism study of this system using muon is quite unique.
The ultra-cold muon beam can be stopped in thin foil, multi-layered materials and artificial lattices, which enables us to apply theaSR techniques to surface and interface science. The development of an ultra-cold muon beam is also very important as a source of
pencil-like small emittance muon beam for muon g − 2/EDM measurement. We have been developing muonium generators to create
more muonium atoms in vacuum even at room temperature to improve beam quality compared with the conventional hot-tungsten
muonium generator. We have demonstrated a strong increase in the muonium emission eﬃciency by fabricating fine laser drill-holeson the surface of silica aerogel. We are also developing a high power Lyman-alpha laser in collaboration with the Advanced Photonics
group at RIKEN. The new laser will ionize muoniums 100 times more eﬃciently for slow muon beam generation.
Over the past 2–3 years, a significant development activity in muon elemental analysis has taken place, proton radius experiments
have continued and been developed, and chip irradiation experiments have also continued.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Materials science by muon-spin-relaxation method and muon site calculation
Development of elemental analysis using pulsed negative muons
Nuclear and particle physics studies via muonic atoms and ultra-cold muon beam
Other muon applications

3. Summary of Research Activity(1) Material science at the RIKEN-RAL muon facility
Muons have their own spins with 100% polarization, and can detect local magnetic fields and their fluctuations at muon stoppingsites very precisely. The µSR method is applied to studies of newly fabricated materials. Muons enable us to conduct (1) material
studies under external zero-field condition, (2) magnetism studies with samples without nuclear spins, and (3) measurements of muon
spin relaxation changes at wide temperature range with same detection sensitivity. The detection time range of local field fluctuations
by µSR is 10−6 to 10−11 second, which is an intermediate region between neutron scattering method (10−10 –10−12 second) and Nuclear
Magnetic Resonance (NMR) (longer than 10−6 second). At Port-2 and 4 of the RIKEN-RAL Muon Facility, we have been performingµSR researches on strong correlated-electron systems, organic molecules, energy related materials and biological samples to study
electron structures, superconductivity, magnetism, molecular structures and crystal structures.
Among our scientific activities on µSR studies from year 2017 to 2020, following subjects of material sciences are most importantachievements at the RIKEN-RAL muon facility:(1) Multi magnetic transitions in the Ru-based pyrochlore systems, R2 Ru2 O7 .
(2) Novel magnetic and superconducting properties of nano-size La-based high-T c superconducting cuprates.
(3) Determination of muon positions estimated from density functional theory (DFT) and dipole-field calculations.
(4) Chemical muonic states in DNA molecules.
Result-1) Doped hole eﬀects on the magnetic properties of corner-shared magnetic moments on pyrochlore systems gave us newinterpretations to understand exotic phenomena, like the quantum criticality of magnetic moments and a quasi-magnetic monopole
state. Result-2) The same nano-size eﬀect was examined on the La-based high-T c superconducting oxide changing the electronic statefrom insulating to superconducting. We confirmed the reduction in the magnetic interaction and the disappearance of the superconducting state leading the increase in the ferromagnetic interaction within the wide-range of the hole concentration. Result-3) Well
known and deeply investigated La2 CuO4 has opened a new scheme of the Cu spin. Taking into account quantum eﬀects to expand
the Cu-spin orbital and muon positions, we have succeeded to explain newly found muon sites and hyperfine fields at those sites.
Result-4) Chemical states of the muon which attaches to DNA molecules were investigated by the avoided level-crossing muon-spin
resonance experiments. In conjunction with DFT calculations, we are trying to reveal the electron motion though the DNA molecule.
We have been continuing to develop muon-science activities in Asian countries. We enhanced international collaborations toorganize new µSR experimental groups and to develop muon-site calculation groups using computational method. We are creating- 334 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

new collaborations with new teams in diﬀerent countries and also continuing collaborations in µSR experiments on strongly correlated
systems with researchers from Taiwan, Indonesia, China, Thailand and Malaysia including graduate students. We are starting tocollaborate with the new Chinese muon group who are developing the Chinese Muon Facility and trying to develop more muon
activities in the Asian area.
(2) Development of elemental analysis using pulsed negative muons
There has been significant development of elemental analysis using negative muons on Port 4 and Port 1 over the past coupleof years. Currently, elemental analysis commonly uses X-ray and electron beams, which accurately measure surfaces. However, asignificant advantage of muonic X-rays over those of electronic X-rays is their higher energy due to the mass of the muon. These highenergy muonic X-rays are emitted from the bulk of the samples without significant photon self-absorption. The penetration depth ofthe muons can be varied by controlling the muon momentum, providing data from a thin slice of sample at a given depth. This can beover a centimetre in iron, silver and gold or over 4 cm in less dense materials such as carbon.
Some techniques for elemental analysis are destructive or require the material under investigation to undergo significant treatment
and some of the techniques are only sensitive to the surface. Therefore, negative muons oﬀer a unique service in which they canmeasure inside, beyond the surface layer and completely non-destructively.
The areas of science that have used negative muons for elemental analysis have been very diverse. The largest area is the cultural
heritage community as the non-destructive ability is particularly important and will become more so. This community have investigated swords from diﬀerent eras, coins (Roman gold and silver, Islamic silver and from the Tudor Warship Mary Rose), miniatureboats from Sardinia, reliefs on Baptist church gate, Bronze Age tools and cannon balls. In addition, energy materials (Li composition
for hydrogen storage), bio-materials (search for iron to potentially help understand Alzheimer’s), engineering alloys (manufacturing
processes for new materials for jet engines), and functional materials (surface eﬀects in piezo electrics) have also been investigated.
The study was extended to see the diﬀerence by isotopes of silver and lead, which may give hint on the source of the material.
(3) Ultra-cold (low energy) muon beam generation and applications
Positive muon beam with thermal energy has been produced by laser ionization of muonium (bound system of µ+ and electron)
emitted from a hot tungsten surface with stopping surface muon beam at Port-3. The method generates a positive muon beam withacceleration energy from several 100 eV to several 10 keV, small beam size (a few mm) and good time resolution (less than 8 nsec). By
stopping the ultra-cold muon beam in thin foil, multi-layered materials and artificial lattices, we can precisely measure local magnetic
field in the materials, and apply the µSR techniques to surface and interface science. In addition, the ultra-cold muon is very importantas the source of pencil-like small emittance muon beam for muon g − 2/EDM measurement. It is essential to increase the slow
muon beam production eﬃciency by 100 times for these applications. There are three key techniques in ultra-cold muon generation:
production of thermal muonium, high intensity Lyman-alpha laser and the ultra-cold muon beam line.
A high-power Lyman-alpha laser was developed in collaboration with the Advanced Photonics group at RIKEN. The new laser
system is used at J-PARC U-line and, upon completion, will ionize muoniums 100 times more eﬃciently for slow muon beam
generation. In this development, we succeeded to synthesize novel ceramic-based Nd:YGAG crystal, which realized a highly eﬃcientand stable laser system. However, larger size crystal than presently available is needed for full design power. We are working hard to
improve the crystal homogeneity including the option of using material with slightly diﬀerent composition.
We also succeeded in developing an eﬃcient muonium generator, laser ablated silica aerogel, which emits more muoniums into
vacuum even at room temperature. Study has been done at TRIUMF utilizing positron tracking method of muon decay position.
We demonstrated in 2013 at least 10 times increase of the muonium emission eﬃciency by fabricating fine laser drill-holes on thesurface of silica aerogel. Further study was carried out in 2017 to find the optimum fabrication that will maximize the muonium
emission. From the analysis, we found the emission has large positive correlation with the laser ablated area rather than with anyother parameters. We also confirmed the muon polarization in vacuum. An alternative detection method for muonium emission using
muonium spin rotation, which will be sensitive even to muoniums near the surface, was tested at RIKEN-RAL in 2018 and was foundsuccessful. The study was further applied to the measurement of the temperature dependence.
In RIKEN-RAL Port 3, the ultra-cold muon beam line, which had been designed with hot tungsten, was completely rebuilt to use
advantage of the new room temperature silica aerogel target. The equipment was tested with surface muon beam and basic data suchas muon stopping in aerogel were taken. A similar target design will be adopted in the ultimate cold muon source planned for muong − 2/EDM at J-PARC.
(4) Other fundamental physics studies
A measurement of the proton radius using 2S -2P transition of muonic hydrogen at PSI revealed that the proton charge radius
is surprisingly smaller than the radius measured using normal hydrogen spectroscopy and e-p scattering by more than 5 times theirexperimental precision. The muonic atom has larger sensitivity to the proton radius because the negative muon orbits closer tothe proton, although there is no reason why these measurements can yield inconsistent results if there exists no exotic physics orunidentified phenomenon behind. The cause of the discrepancy is not understood yet, thus a new measurement with independent
method is much anticipated.
We proposed the measurement of the proton radius by using the hyperfine splitting of the muonic hydrogen ground state. This
hyperfine splitting is sensitive to the Zemach radius, which is a convolution of charge and magnetic-dipole distributions inside proton.
We are planning to re-polarize the muonic hydrogen by a circularly polarized excitation laser (excites one of the F = 1 states andregenerates the muon spin polarization), and detect the recovery of the muon decay-asymmetry along the laser.
Preparation using muon beam is in progress. We measured the muon stopping distribution in low-density hydrogen-gas cell, which- 335 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

gave us consistent results with beam simulation. Another key is the lifetime of the upper hyperfine state of the muonic hydrogen thatwill contribute the polarization. We successfully observed the clear muon spin precession of muonic deuterium atom in 2018 for the
first time in the world. The measurement with muonic protium was carried out in 2019 and the data is being analyzed.
(5) Other topics
RIKEN and ISIS have signed a new collaboration agreement for the period 2018–2023. This is the fourth in a continuous series ofagreements, the first being signed in 1990, resulting in a partnership which will have lasted over 30 years. Under the new agreement,
ownership and operation of the facility was passed to ISIS, a refurbishment programme of the facility has started, a user programme forJapanese scientists continued under the partnership between RIKEN and ISIS. The RIKEN-RAL collaboration is regularly highlighted
as a good example of UK-Japanese science partnership at the UK-Japan Joint Committee on Science and Technology (chaired by the
UK Chief Scientific Advisor to Government and a counterpart from Japan)—for example, Dr. King and Dr. Watanabe presented
RIKEN-RAL at the November 2016 meeting of the Committee. The RIKEN-RAL collaboration has also enabled the developmentof collaborative activity between RIKEN and other Asian universities, e.g. through several MoUs with Indonesian and Malaysian
universities.
It was very unfortunate that the research activity at RIKEN-RAL had severe restriction in FY2020 due to the COVID-19 pandemic. Almost all the access to RIKEN-RAL by external users had to be stopped. Even though, we managed to carry out severalµSR experiments with mailed samples, where the ISIS staﬀ mounted the samples and the external users controlled the experimental
sequence remotely.

Members
Director
Philip KING
Senior Research Scientist
Isao WATANABE
Contract Researcher
Katsuhiko ISHIDA

List of Publications & Presentations
Publications[Original Papers]
R. Kitamura, S. Bae, S. Choi, Y. Fukao, H. Iinuma, K. Ishida, N. Kawamura, B. Kim, Y. Kondo, T. Mibe, Y. Miyake, M. Otani, G. P. Razuvaev, N. Saito, K. Shimomura, and P. Strasser, “Development of negative muonium ion source for muon acceleration,” Phys. Rev. Accel.
Beams 24, 033403 (2021).
S. Kanda, Y. Fukao, Y. Ikedo, K. Ishida, M. Iwasaki, D. Kawall, N. Kawamura, K. M. Kojima, N. Kurosawa, Y. Matsuda, T. Mibe,
Y. Miyake, S. Nishimura, N. Saito, Y. Sato, S. Seo, K. Shimomura, P. Strasser, K. S. Tanaka, T. Tanaka, H. A. Torii, A. Toyoda, andY. Ueno, “New precise spectroscopy of the hyperfine structure in muonium with a high-intensity pulsed muon beam,” Phys. Lett. B
815, 136154 (2021).
A. D. Pant, K. Ishida, N. Kawamura, S. Matoba, A. Koda, S. Nishimura, and K. Shimomura, “Study of muonium behavior in n-typesilicon for generation of ultra cold muonium in vacuum,” Physica B 613, 412997 (2021).
J. Sugiyama, O. K. Forslund, E. Nocerino, N. Matsubar, K. Papadopoulos, Y. Sassa, S. P. Cottrell, A. D. Hillier, K. Ishida, M. Mansson,
and J. H. Brewer, “Lithium diﬀusion in LiMnPO4 detected with µ± SR,” Phys. Rev. Res. 2, 033161 (2020).
M. Aramini, C. Milanese, A. D. Hillier, A. Girella, C. Horstmann, T. Klassen, K. Ishida, M. Dornheim, and C. Pistidda, “Spectroscopic
tool for the investigation of the local chemistry of elements,” Nanomaterials 2020, 10, 1260 (2020).
E. Mocchiutti, A. Adamczak, D. Bakalov, G. Baldazzi, R. Benocci, R. Bertoni, M. Bonesini, V. Bonvicini, H. CabreraMorales, F. Chignoli, M. Clemenza, L. Colace, M. Danailov, P. Danev, A. de Bari, C. DeVecchi, M. DeVincenzi, E. Furlanetto, F. Fuschinod,
K. S. Gadedjisso-Tossoua, D. Guﬀantia, K. Ishida, C. Labanti, V. Maggi, R. Mazza, A. Menegolli, G. Morgante, M. Nastasi, J. Niemela,
C. Pizzolotto, A. Pullia, R. Ramponi, L. P. Rignanese, M. Rossella, N. Rossi, M. Stoilov, L. Stoychev, L. Tortora, E. Vallazza, G. Zampa,
and A. Vacchi, “First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen,” Phys.
Lett. A 384, 126667(2020).
C. Pizzolotto, A. Adamczak, D. Bakalov, G. Baldazzi, M. Baruzzo, R. Benocci, R. Bertoni, M. Bonesini, V. Bonvicini, H. Cabrera,
D. Cirrincione, M. Citossi, F. Chignoli, M. Clemenza, L. Colace, M. Danailov, P. Danev, A. de Bari, C. De Vecchi, M. de Vincenzi,
E. Fasci, E. Furlanetto, F. Fuschino, K. S. Gadedjisso-Tossou, L. Gianfran, D. Guﬀanti, A. D. Hillier, K. Ishida, P. J. C. King, C. Labanti,
V. Maggi, R. Mazza, A. Menegolli, E. Mocchiutti, L. Moretti, G. Morgante, J. Niemela, B. Patrizi, A. Pirri, A. Pullia, R. Ramponi,
L. P. Rignanese, E. Roman, M. Rossella, R. Sarkar, A. Sbrizzi, M. Stoilov, L. Stoychev, J. J. Suárez-Vargas, G. Toci, L. Tortora,
E. Vallazza, M. Vannini, C. Xiao, G. Zampa, and A. Vacchi, “The FAMU experiment: muonic hydrogen high precision spectroscopy
studies,” Eur. Phys. J. A 56, 185 (2020).
J. Beare, G. Beer, J. H. Brewer, T. Iijima, K. Ishida, M. Iwasaki, S. Kamal, K. Kanamori, N. Kawamura, R. Kitamura, S. Li, G. M. Luke,
G. M. Marshall, T. Mibe, Y. Miyake, Y. Oishi, K. Olchanski, A. Olin, M. Otani, M. A. Rehman, N. Saito, Y. Sato, K. Shimomura,- 336 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

K. Suzuki, M. Tabata, and H. Yasuda, “Study of muonium emission from laser-ablated silica aerogel,” Prog. Theor. Exp. Phys. 2020,
123C01 (2020).
H. Yamauchi, D. P. Sari, I. Watanabe, Y. Yasui, L. -J. Chang, K. Kondo, T. U. Ito, M. Ishikado, M. Hahara, M. D. Frontzk, C. Chi,
J. A. Fernandez-Bac, J. S. Lord, A. Berlie, A. Kotani, S. Mori, and S. Shamoto, “High-temperature short-range order in Mn3 RhSi,”
Commun. Matter. 1, 42 (2020).
M. Fujita, K. M. Suzuki, S. Asano, H. Okabe, A. Koda, R. Kadono, and I. Watanabe, “Magnetic behavior of T ’-type Eu2 CuO4 revealed
by muon spin rotation and relaxation measurements,” Phys. Rev. B 102, 045116 (2020).

Presentations[Domestic Conferences/Workshops]
石田勝彦, 「理研 RAL での非破壊元素分析」, 第 4 回文理融合シンポジウム 量子ビームで歴史を探る—加速器が紡ぐ文理融合の地平—, オンライン, 2021 年 1 月 28–29 日.
石田勝彦 (招待講演), 「理研 RAL と J-PARC」, パルス中性子ミュオン発生 40 周年記念シンポジウム, オンライン, 2020 年 12 月
23 日.
石田勝彦, 「英国理研 RAL ミュオン施設におけるミュオン利用分析研究の進展」, 第 3 回 文理融合シンポジウム 量子ビームで歴史を探る—加速器が紡ぐ文理融合の地平—, オンライン, 2020 年 9 月 25–26 日.

Press Releases
正負のミュオンで捉えたイオンの動き 2020 年 8 月 7 日—Li イオンの動きを, 負ミュオンで確認, 正ミュオンで詳細観察— 一般財
団法人総合科学研究機構（CROSS）中性子科学センター・サイエンスコーディネータ 杉山 純国立研究開発法人理化学研究所（理研）仁科加速器科学研究センター・協力研究員石田 勝彦- 337 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Safety Management Group
1. Abstract

The RIKEN Nishina Center for Accelerator-Based Science possesses one of the largest accelerator facilities in the world, which
consists of two heavy-ion linear accelerators and five cyclotrons. This is the only site in Japan where uranium ions are accelerated.
The center also has electron accelerators of microtron and synchrotron storage ring. Our function is to keep the radiation level inand around the facility below the allowable limit and to keep the exposure of workers as low as reasonably achievable. We are also
involved in the safety management of the Radioisotope Center, where many types of experiments are performed with sealed andunsealed radioisotopes.

2. Major Research Subjects(1) Safety management at radiation facilities of Nishina Center for Accelerator-Based Science(2) Safety management at Radioisotope Center(3) Radiation shielding design and development of accelerator safety systems

3. Summary of Research Activity

Our most important task is to keep the personnel exposure as low as reasonably achievable, and to prevent an accident. Therefore,
we daily patrol the facility, measure the ambient dose rates, maintain the survey meters, shield doors and facilities of exhaust air
and wastewater, replenish the protective supplies, and manage the radioactive waste. Advice, supervision and assistance at major
accelerator maintenance works are also our task.
Minor improvements of the radiation safety systems were also done. The old type of computer system unit for the radiation
monitoring system and the old UPS for radiation management system of the RIBF building were replaced. The old exhaust equipmentof hotlabo exhaust system in Nishina building was also replaced.

Members
Director
Kanenobu TANAKA
Research/Technical Scientists
Rieko HIGURASHI (Technical Scientist)

Hisao SAKAMOTO (Technical Scientist)

Expert Technician
Atsuko AKASHIO
Technical Staﬀ I
Hiroki MUKAI
Junior Research Associate
Kenta SUGIHARA
Visiting Scientists
Masayuki HAGIWARA (KEK)
Noriaki NAKAO (Shimizu Corporation)
Toshiya SANAMI (KEK)

Nobuhiro SHIGYO (Kyushu Univ.)
Hiroshi YASHIMA (Kyoto Univ.)

Part-time Workers
Kimie IGARASHI (Administrative Part-time Worker I)
Satomi IIZUKA (Administrative Part-time Worker II)

Yukiko SHIODA (Administrative Part-time Worker II)
Naoko USUDATE (Administrative Part-time Worker II)

Temporary Staﬃng
Ryuji SUZUKI
Assistant
Tomomi OKAYASU

List of Publications & Presentations
Publications[Original Papers]
K. Sugihara, N. Shigyo, E. Lee, T. Sanami, and K. Tanaka, “Measurement of thick target neutron yields from 7 MeV/u α incidence on
209Bi,” Nucl. Instrum. Method Phys. Res. B 470 (2020).

[Proceedings]
K. Sugihara, N. Shigyo, A. Akashio, and K. Tanaka, “Measurement of neutron energy spectra of 345 MeV/u 238 U incidence on a copper
target,” JAEA-Conf 2020-001, 143–147.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Presentations[International Conferences/Workshops]
K. Sugihara (poster), Y. Ikeda, T. Kobayashi, K. Fujita, N. Shigyo, K. Tanaka, and Y. Otake, “Study on characteristics of neutron and
γ-ray fields at compact neutron source RANS-II facility by simulation by the PHITS code,” 2020 Symposium on Nuclear Data, RIKEN
Wako Campus, November 26–27, 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

User Liaison Group
1. Abstract

The User Liaison Group is a group that provides user support, including various procedures required for accelerator use, in orderto promote collaborative-use of the RIBF facilities. The group will provide user support on matters necessary for RIBF experiments,from application to completion. The group will also provide technical support for the dissemination of information on the research
results of the RIBF.
The group consists of two teams. The RIBF User Liaison Team provides various supports to visiting RIBF users through the RIBF
Users Oﬃce. Managing RIBF beam time and organizing the Program Advisory Committee Meetings to review RIBF experimental
proposals are also important mission of the Team in order to enhance collaborative-use of the RIBF. The Outreach Team has createdvarious information materials, such as pamphlets, posters, and homepages, to introduce the research activities in the RNC. On the
homepage, we provide information on usage of the RIBF facility. The team also participate in science introduction events hosted bypublic institutions. In addition, the User Liaison Group also takes care of laboratory tours for RIBF visitors from public. The numbersof visitors usually amounts to 2,300 per year.

Members
Director
Hideki UENO
Assistants
Yu NAYA
Tomomi OKAYASU

Midori YAMAMOTO- 340 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

User Liaison GroupRIBF User Liaison Team
1. Abstract

To enhance synergetic common use of the world-class accelerator facility, the Radioisotope Beam Factory (RIBF), it is necessary
to promote a broad range of applications and to maximize the facility’s importance. The facilitation and promotion of the RIBF are
important missions charged to the team. Important operational activities of the team include: i) the organization of international Program Advisory Committee (PAC) meetings to review experimental proposals submitted by RIBF users, ii) RIBF beam-time operation
management, and iii) promotion of facility use by hosting outside users through the RIBF Independent Users program, which is a
new-user registration program begun in FY2010 at the RIKEN Nishina Center (RNC) to enhance the synergetic common use of the
RIBF. The team opened the RIBF Users Oﬃce in the RIBF building in 2010, which is the main point of contact for Independent Usersand provides a wide range of services and information.

2. Major Research Subjects(1) Facilitation of the use of the RIBF
(2) Promotion of the RIBF to interested researchers

3. Summary of Research Activity(1) Facilitation of the use of the RIBF
The RIBF Users Oﬃce, formed by the team in 2010, is a point of contact for user registration through the RIBF Independent User
program. This activity includes:• registration of users as RIBF Independent Users,• registration of radiation workers at the RIKEN Wako Institute,• provision of an RIBF User Card (a regular entry permit) and an optically stimulated luminescence dosimeter for each RIBF
Independent User, and• provision of safety training for new registrants regarding working around radiation, accelerator use at the RIBF facility, andinformation security, which must be completed before they begin RIBF research. The RIBF Users Oﬃce is also a point ofcontact for users regarding RIBF beam-time-related paperwork, which includes:• contact for beam-time scheduling and safety review of experiments by the In-House Safety Committee, and• maintaining the above information in a beam-time record database.
In addition, the RIBF Users Oﬃce assists RIBF Independent Users with matters related to their visit, such as invitation procedures,visa applications, and the reservation of on-campus accommodation.
(2) Promotion of the RIBF to interested researchers• The team has organized an international PAC for RIBF experiments; it consists of leading scientists worldwide and reviews
proposals in the field of nuclear physics (NP) purely on the basis of their scientific merit and feasibility. The team also assists
another PAC meeting for material and life sciences (ML) organized by the RNC Advanced Meson Laboratory. The NP PAC
meeting is organized once a year regularly, and the ML PAC meetings are organized once or twice a year.
• The team coordinates beam times for PAC-approved experiments and other development activities. It manages the operatingschedule of the RIBF accelerator complex according to the decisions arrived at by the RIBF Machine Time Committee.
• To promote research activities at RIBF, proposals for User Liaison and Industrial Cooperation Group symposia/mini-workshops
are solicited broadly both inside and outside of the RNC. The RIBF Users Oﬃce assists in the related paperwork.
• The team is the point of contact for the RIBF users’ association. It arranges meetings at RNC headquarters for the RIBF User
Executive Committee of the users’ association.
• The Team conducts publicity activities, such as arranging for RIBF tours, development and improvement of the RNC oﬃcial web
site, and delivery of RNC news via email and the web.

Members
Team Leader
Ken-ichiro YONEDA
Contract Researcher
Tadashi KAMBARA- 341 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

User Liaison Group
Outreach Team
1. Abstract

The mission of the Outreach Team is to provide various “intangible” technical support for the dissemination of information on the
research in RNC. For instance, the team creates brochures introducing the RNC and the RIBF accelerator facility, posters of symposia
and the summer school hosted by RNC, the center homepage containing information such as details of RNC and the procedure for theuse of the RIBF facility, and images of equipment and facilities available for researchers inside and outside RIKEN, among the others.
Furthermore, the team also participates in science introduction events hosted by public institutions.

2. Major Work Contents

The major work contents of the Outreach Team is to promote the publicity of RNC, through the creation of various materials suchas brochures, websites, posters, and videos, among the others. The arrangement of tours of the RIBF facility and the exhibition andintroduction of the RIBF facility at science events are also conducted independently or in cooperation with RIKEN Public Relations
Oﬃce.

3. Summary of Work Activity

The specific work contents performed by the team are as follows:• [Website] The Team creates/manages the RNC oﬃcial website (http://www.nishina.riken.jp), which introduces the organization and its research activities. This website plays an important role in providing information to researchers who visit RNC
to conduct his/her own research.
• [Brochures] The Team has produced various brochures introducing the organization and the studies performed at RNC. The
brochures named “Your body is made of star scraps” explaining element synthesis in the universe and “Introduction of RIBF
Facility” in a cartoon style for children are among them.
• [Posters] Conference/Symposium posters connected with RNC were prepared on the request of organizers. For general purpose,a special poster featuring the nuclear chart has been prepared for distribution. In commemoration of the discovery of nihonium,
brochures and posters dedicated to the ceremony were made.
• [RIBF Cyclopedia] In April 2012, the permanent exhibition hall (RIBF Cyclopedia) located at the entrance hall of the RIBF
building was set up in cooperation with RIKEN Public Relations Oﬃce. Explanatory illustrations on nuclear science, research at
RIBF, RIBF history, a 3D nuclear chart built with LEGO blocks, and a 1/6-size GARIS model are displayed to help understanding
through visual means. The Team is also working on updating the exhibits.
• [RIBF facility tour] The Team arranges RIBF facility tour for over 2000 visitors per year. The tour is guided by a researcher.
• [Science event participation] In 2010, 2012, 2013, 2015, and 2016, the sub-team opened an exhibition booth of RNC to introduce
the latest research activities on the occasion of the “Science Agora” organized by Japan Science and Technology Agency (JST).
From time to time, the sub-team was invited to participate in scientific events by MEXT, Wako city, and Nissan global foundation.
One attraction targeting children is the hands-on work of assembling “Iron-beads” to create a nuclear chart or a shape of nihonium.
In addition to the above-noted work contents, the Team conducts a variety of works, such as taking pictures of meetings organized by
RNC, cooperation in the production of a 3D video to explain the accelerators and the research at RIBF, among the others.

Members
Team Leader
Hideki UENO
Deputy Team Leader
Yasushi WATANABE
Technical Staﬀ I
Narumasa MIYAUCHI- 342 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Oﬃce of the Center Director
1. Abstract

This oﬃce is in place from JFY2018 to conduct works that the Center Director deems necessary for the operation of the research
center and the secretarial work related to the research center in general.

2. Major Work Contents• Nishina Center Monthly Meeting
The pupose of the meeting is to share information on activities within the Nishina Center with all of the members. The meetingcovers introduction of new comers, press-released achievements, announcement of events organized by or related to the Nishina
Center, safety issues, and others to be informed to all members. The meeting agenda is distributed to all of the members via
mailing-list.
• Conference Support
Assistant staﬀ members support coherently a large-size conference hosted by the Nishina Center.
• Orientation for new comers to the Nishina Center
The Orientation is organized once a year to the new comers to give instructions for emergency response, safety in research,
computer and network resources and security, and research misconduct prevention.

3. Summary of Work Activity• Nishina Center Monthly Meeting
Noriko Asakawa arranged the agenda and Hidetada Baba supported the on-line video system for the meeting.
– The 157th Meeting on April 2, 2020
(1) Greetings from newly appointed RNC director(2) Introduction of new arrivals and newly appointed members– The 158th Meeting on May 13, 2020
(1) Greetings from the new RNC deputy director (Iwasaki)(2) Introduction of newcomers who joined RNC in April and May(3) “Swelling of doubly magic 48 Ca core in Ca isotopes beyond N = 28” (M. Tanaka)(4) Coronavirus update
RIKEN’s initiative (Sakurai, the RNC director)
Remote work from home: tips and problems, issues to be addressed(5) Other– The 159th Meeting on June 10, 2020
(1) Report from the RNC director
Current events(2) Introduction of a press release“Discovery that a single proton from a fluorine nucleus can have a major eﬀect on the state of the nucleus” (Uesaka)(3) Information exchange on corona update– The 160th Meeting on July 8, 2020
(1) Report from the RNC director
The RNC director reported on the facility visit by M. Ueno, State Minister of MEXT
revision of the RIKEN rules and the coronavirus update.
(2) Situation in BNL and Long Island under the COVID-19 Pandemic (I. Nakagawa)At the beginning of April, the outbreak of COVID-19 hit New York where BNL is located, which then led to a
medical collapse at the epic center, New York City. Living on the outskirts of New York City (nearby BNL), myfamily and I waited for the right timing to returning to Japan by closely monitoring the situation in NY and Tokyo.
With much improvement of the situation in New York lately, we were able to return to Japan safely just recently.
BNL is under the process of gradual reopening.
– The 161st Meeting on September 9, 2020
(1) Report from the RNC director(2) Report from the Nishina Center and iTHEMS Promotion Oﬃce(3) Website featuring RIKEN-RAL Muon Facility’s 30th anniversary(4) FY2019 RIKEN Ohbu Award
Researcher Incentive Award
Research & Industry Partnership Incentive Award(5) Press Release(6) Other– The 162nd Meeting on October 14, 2020
(1) Greetings from the newly appointed Team Leaders
Masanori Kidera (Infrastructure Management Team)- 343 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Hiroyuki Ichida (Plant Genome Evolution Research Team)(2) 2020 JPCERT/CC Certificate of Appreciation
Takashi Ichihara (Radioactive Isotope Physics Laboratory)(3) Topics on the RIKEN information systems (Baba)(4) Report from the RNC director
COVID-19
Facility tour
Lecture Presentation (Organizer: Nuclear Physics Committee)(5) Other– The 163rd Meeting on November 11, 2020
(1) Report on award
A3F-CNSSS20 Award for young scientist
The 9th Annual Award presented by the Particle Accelerator Society of Japan at the 17th Annual Meeting(2) Report from the RNC director
Update on COVID-19
Facility tour
(3) Othere-learning on research ethics (Motobayashi)– The 164th Meeting on December 9, 2020
(1) On passing of Dr. Akito Arima, former RIKEN President(2) Introduction of award recipient (Hiyama)
Recipient of the FY2020 Nishina Memorial Prize: Kazuma Nakazawa (Strangeness Nuclear Physics Laboratory)(3) Report on symposium (Otsu)
SND2020 (Symposium on Nuclear Data) held on November 23–27(4) On Accelerator Progress Report (Ueno)(5) Report from the RNC director
Outstanding matters from the old Nishina Laboratory
COVID-19 situation(6) Other– The 165th Meeting on January 13, 2021
(1) Introduction of a newcomer (Haba)
Yin Xiaojie Post doctorate Researcher (Nuclear Chemistry Research Team)(2) Generation of high intensity Zn beam (Higurashi)(3) Report from the RNC director
New Year’s greetings
COVID-19 situation(4) Other– The 166th Meeting on February 10, 2021
(1) Press Release
Discovery in neutron pair correlation inside the halo nuclei of Lithium-11—Evidence of dineutron at the surfaceof neutron-rich nuclei found (Uesaka)
Filling a crucial gap in aquafarming: ion beam breeding to the rescue (Abe)(2) Report from the RNC director
COVID-19 situation(3) Other– The 167th Meeting on March 10, 2021
(1) Introduction of a newcomer (K. Yoshida)
Masahiro Yoshimoto (Postdoctoral Researcher, BigRIPS Team)(2) Relocation of the third cyclotron (Fukushima)(3) RIKEN Open Day (Tanaka)(4) Report from the RNC director
COVID-19 situation(5) Retirement speech
Eiji Ikezawa (Team Leader, RILAC Team)• Conference Support
No large size conferences hosted by the Nishina Center were organized.
• Orientation for new comers to the Nishina Center
Due to the COVID-19 pandemic, the Orientation was not organized in 2020.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Members
Director
Hiroyoshi SAKURAI
Research Administrator
Narumasa MIYAUCHI
Assistants
Noriko ASAKAWA
Yu NAYA
Karen SAKUMA

Asako TAKAHASHI
Mitsue YAMAMOTO
Izumi YOSHIDA- 345 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Partner Institutions

The RIKEN Nishina Center for Accelerator-Based Science (RNC) has collaborated with universities and research institutes since 2008
under the research partnership agreement. This collaboration framework permits an external institute to develop its own projects at
the RIKEN Wako Campus in equal partnership with the RNC. At present, two institutes—the Center for Nuclear Study (CNS), theUniversity of Tokyo and the Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies (IPNS), High Energy
Accelerator Research Organization (KEK)—are conducting joint research under the research partnership agreement.
The CNS and RNC signed the research partnership agreement in 2008. Until then, the CNS had collaborated in joint programswith RIKEN under the “Research Collaboration Agreement on Heavy Ion Physics” (collaboration agreement) signed in 1998. The
partnership agreement redefines procedures related to the joint programs while keeping the spirit of the collaboration agreement. The
joint programs include experimental nuclear-physics activities using CRIB, SHARAQ, and GRAPE at the RI Beam Factory (RIBF),
accelerator development; and activities at RHIC PHENIX.
The KEK-WNSC and RNC signed a research partnership agreement on “Low-Energy Unstable Nuclear Beam Science” in 2011.
The joint experimental programs are based on the KEK Isotope Separation System (KISS). The KISS has been available for RIBF
users since 2015. The research collaboration agreement for the SLOWRI facility and the multi-reflection time-of-flight (MRTOF)
mass spectrograph was then signed in 2019, based on which the SLOWRI Joint Operation Committee has been established for thecollaborative use and operation of the SLOWRI facility.
Experimental proposals that request the use of the above-noted devices of the CNS and KEK, together with other key devices at
the RIBF, are screened by the Program Advisory Committee for Nuclear Physics experiments at the RIBF (NP-PAC). The NP-PAC
meetings are co-hosted by the CNS and KEK.
Matters necessary for the smooth promotion of joint research based on the research partner agreement are determined at the Collaboration Liaison Council. More specific matters related to the execution of collaborative research are discussed at the Collaboration Liaison
Committee established under the Liaison Council. In order to enhance the eﬀectiveness of coordination and information sharing on
joint research programs, the Joint Researchers Meeting was established in 2020 under the Collaboration Liaison Committee.
Several members of both institutes have also been invited to participate as external members in RNC committees related to theoperation of the RIBF, such as the Machine-Time Committee and the Safety Review Committee.
The activities of the CNS and KEK are reported in the succeeding pages.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Partner Institution
Center for Nuclear Study, Graduate School of Science
The University of Tokyo
1. Abstract

The Center for Nuclear Study (CNS) aims to elucidate the nature of nuclear system by producing the characteristic states where
the Isospin, Spin and Quark degrees of freedom play central roles. These researches in CNS lead to the understanding of the matterbased on common natures of many-body systems in various phases. We also aim at elucidating the explosion phenomena and theevolution of the universe by the direct measurements simulating nuclear reactions in the universe. In order to advance the nuclear
science with heavy-ion reactions, we develop AVF upgrade, CRIB and SHARAQ facilities in the large-scale accelerators laboratories
RIBF. The OEDO facility has been developed as an upgrade of the SHARAQ, where a RF deflector system has been introduced toobtain a good quality of low-energy beam. A new project for fundamental symmetry using heavy RIs has been starting to install new
experimental devices in the RIBF. We promote collaboration programs at RIBF as well as RHIC-PHENIX and ALICE-LHC with
scientists in the world, and host international meetings and conferences. We also provide educational opportunities to young scientists
in the heavy-ion science through the graduate course as a member of the department of physics in the University of Tokyo and throughhosting the international summer school.

2. Major Research Subjects(1) Accelerator Physics(2) Nuclear Astrophysics(3) Nuclear spectroscopy of exotic nuclei(4) Quark physics(5) Nuclear Theory(6) OEDO/SHARAQ project(7) Exotic Nuclear Reaction(8) Low Energy Nuclear Reaction Group(9) Active Target Development(10) Fundamental Physics

3. Summary of Research Activity(1) Accelerator physics
One of the major tasks of the accelerator group is the AVF upgrade project that includes development of ion sources, upgrading the
AVF cyclotron of RIKEN and the beam transport system to CRIB, E7B, and C12 in the E7 experiment room. In 2020, the operatingtime of the HyperECR was 1146 hours. The beam extraction system of the HyperECR is developed to realize a high intensity and low
emittance beam and the study of mixing gas is started for heavy ionization. The calculation model of injection beam orbit of the AVF
cyclotron was completed and the study of the optimization of injection beam orbit was started. For the detailed studies on ion opticsof the beamline to CRIB and experiment device of Fr-EDM measurement from AVF cyclotron, the development of 4-dimensional
emittance monitor for high power ion beams was started. the prototype was completed and evaluated for performance.
(2) Nuclear astrophysics
The main activity of the nuclear astrophysics group is to study astrophysical reactions and special nuclear structure, such as
clusters, using the low-energy RI beam separator CRIB. To produce RI beams at CRIB with higher intensity, a project to improve theheat durability of the cryogenic gas target is in progress. In 2020, we used a high-current oxygen beam to test the heat durability of thegas target. Sealing foils of several materials and copper extention parts were employed in the test, and we found the target can standfor the beam heat much exceeding the previous limit of 2 Watts per foil. The secondary beam development is also on going. A 6 He
RI beam was first produced at CRIB in March 2021, as the lightest RI beam ever created at CRIB. We successfully produced a 6 He
beam at the intensity more than 105 pps, which is to be used for the approved 6 He + p scattering measurement, as well as other future
experiments.
(3) Nuclear structure of exotic nuclei
The NUSPEQ (NUclear SPectroscopy for Extreme Quantum system) group studies exotic structures in high-isospin and/or highspin states in nuclei. The CNS GRAPE (Gamma-Ray detector Array with Position and Energy sensitivity) is a major apparatus forhigh-resolution in-beam gamma-ray spectroscopy. Missing mass spectroscopy using the SHARAQ is used for another approach on
exotic nuclei. The group plays a major role in the OEDO/SHARAQ project described below. In 2020, analysis of a new measurementof the 4 He(8 He, 8 Be)4n reaction for better statistics and better accuracy has been proceeding.
(4) Quark physics
Main goal of the quark physics group is to understand the properties of hot and dense nuclear matter created by colliding heavy
nuclei at relativistic energies. The group has been involved in the PHENIX experiment at Relativistic Heavy Ion Collider (RHIC) at
Brookhaven National Laboratory, and the ALICE experiment at Large Hadron Collider (LHC) at CERN. As for ALICE, the group- 348 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

has involved in the data analyses, which include the measurement of low-mass lepton pairs in Pb-Pb collisions, the measurement oflong range two particle correlations in p-Pb collisions, searches for thermal photons in high multiplicity pp and p-Pb collisions andfor strangeness dibaryons. The group has involved in the ALICE-TPC upgrade using a Gas Electron Multiplier (GEM), where thegroup is very active in the development and benchmarking of the online space-charge distortion corrections using machine learningtechniques running on the Graphical Processing Unit (GPU).
(5) Nuclear theory
The nuclear theory group participates in a project, “Program for Promoting Researches on the Supercomputer Fugaku” andpromotes computational nuclear physics utilizing the Fugaku supercomputer. In FY2020, we proposed a new framework called the“quasi-particle vacua shell model,” which is an extension of the Monte Carlo shell model, and promoted its code developments.
Based on these methodological developments, we investigated the exotic structure of nuclei, especially neutron-rich Mg isotopes,
and discussed the mechanism to determine the neutron drip line. In addition, the nuclear Schiﬀ moments of 129 Xe and 199 Hg weretheoretically evaluated by large-scale shell-model calculations to contribute to the experimental search of time-reversal breaking. In
parallel, we promoted the collaborative researches with experimental groups for investigating the exotic structure of unstable nuclei,
such as 35 S, 30 Mg, 64 Ni, 75 Ni, 112 Sn and 137 Ba.
(6) OEDO/SHARAQ project
The OEDO/SHARAQ group pursues experimental studies of RI beams by using the high-resolution beamline and the SHARAQ
spectrometer. A mass measurement by TOF-Bρ technique for very neutron-rich nuclei successfully reaches titanium isotopes at
N = 40, 62 Ti, of which the report was published in 2020. The experimental study of 0− strength in nuclei using the parity-tansfer
charge exchange (16 O, 16 F) will be reported soon. As for The OEDO beamline, the results of the first and second experiments for
LLFPs will be finalized and reported soon. Since experimental studies using OEDO were newly proposed, we continue developments
to improve the performance for coming these beam times, such as the intensity of low-energy RI beams and the suppression of X raysfrom RF deflector.
(7) Exotic nuclear reaction
The Exotic Nuclear Reaction group studies various exotic reactions induced by beams of unstable nuclei. One subject is inversekinematics (p, n) measurement by using the neutron counter array PANDORA. Candidate nuclei to study are high spin isomers such as
52
Fe(12+ ). Study of the production mechanism of high-spin isomer beams was in progress. Another is search of double Gamow-Teller
resonance by a double charge exchange reaction (12 C, 12 Be). Preparations including the development of MWDCs were ongoing.
(8) Low energy nuclear reaction group
A recoil particle detector for missing mass spectroscopy, named TiNA, had been upgraded under the collaboration with RIKEN
and RCNP. The original TiNA consisted of 6 sector telescopes and 12 CsI (Tl) crystals. Four TTT-type (1024 channels) doubly-sided
silicon detectors and twenty-two CsI(Tl) were added to make a TiNA2 array. The commissioning experiment of the TiNA2 wasconducted at Kyushu University in March 2021. The production cross sections of 178m2 Hf were evaluated for the mass production in
the future and will be reported soon. The digital signal processing devices for the GRAPE are under development. For the SHARAQ11
experiment which uses a tritium-doped titanium target, the safety devices has been developed with Tohoku University.
(9) Active target development
Three gaseous active target TPCs called CAT-S, CAT-M and GEM-MSTPC are developed and used for the missing mass spectroscopies. The CAT’s are employed for the study of equation of state of nuclear matter. The measurement of giant monopole resonancein 132 Sn at RIBF with CAT-S and the data analysis is ongoing. The CAT-M was employed for the measurements of the proton inelastic
scattering on 136 Xe at HIMAC and the proton elastic scattering on 132 Sn. The development for the reduction of space charge due tothe ion backflow and the reduction of delta-ray background is ongoing. The GEM-MSTPC is employed for the nuclear astrophysics
study. The data analysis of (α, p) reaction on 18 Ne and 22 Mg and the β-decay of 16 Ne followed by α emission are ongoing.
(10) Fundamental physics
In order to investigate the origin of matter-antimatter symmetry (CP) violation, we focused on the fact that the permanent electric
dipole moment (EDM) of heavy elements such as Francium (Fr) is greatly enhanced by the relativistic eﬀect and octupole deformationof the nucleus. The development of the laser cooled Fr source is in progress at RIBF. In particular, we have established a technique fora high-intensity Fr source by using the nuclear fusion reaction with a surface ionization ion source using a non-contact heating methodwith an infrared heater. Also the frequency stabilization with an iodine molecule and a high-precision wavemeter are ready at present.
Furthermore, by establishing a coexistence trapping technique for two types of Rb isotopes, we have established a co-magnetometer
for an accurate EDM measurement.

Members
Director
Susumu SHIMOURA- 349 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Scientific Staﬀ
Susumu SHIMOURA (Professor)
Yasuhiro SAKEMI (Professor)
Kentaro YAKO (Associate Professor)
Nobuaki IMAI (Associate Professor)
Taku GUNJI (Associate Professor)

Noritaka SHIMIZU (Project Associate Professor)
Hidetoshi YAMAGUCHI (Lecturer)
Shin’ichiro MICHIMASA (Assistant Professor)
Shinsuke OTA (Assistant Professor)
Hiroki NAGAHAMA (Assistant Professor)

Guest Scientists
Yutaka UTSUNO (Guest Professor)
Daiki NISHIMURA (Guest Associate Professor)

Toshitaka KAJINO (Guest Post Doctoral Associate)
Ikuko HAMAMOTO (Guest Post Doctoral Associate)

Technical Staﬀ
Yasuteru KOTAKA
Techinical Assistant
Masayoshi YAGYU
Project Research Associates
Masanori DOZONO

Seiya HAYAKAWA

Post Doctoral Associates
Daiki SEKIHATA
Keisuke NAKAMURA
Keita KAMAKURA
Nanru MA

Yusuke TSUNODA
Kota YANASE
Thomas William CHILLERY

Assistant Teaching Staﬀ
Yuko SEKIGUCHI
Keita KAWATA

Noritaka KITAMURA
Shumpei KOYAMA

Academic Support Staﬀ
Reiko KOJIMA
Graduate Students
Shoichiro MASUOKA
Hideki SHIMIZU
Rieko TSUNODA
Naoya OZAWA

Shutaro HANAINatsuki SHIMIZU
Shintaro NAGASE
Ryotaro KOHARA

Research Student
Jiatai LI
Administration Staﬀ
Noriko SHIMANE
Ikuko YAMAMOTO
Takako ENDO

Yukino KISHI
Aki KOTAKA

List of Publications & Presentations
Publications[Original Papers]
Z. H. Yang, Y. Kubota, A. Corsi, K. Yoshida, X. -X. Sun, J. G. Li, M. Kimura, N. Michel, K. Ogata, C. X. Yuan, Q. Yuan, G. Authelet,
H. Baba, C. Caesar, D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin, A. Giganon, A. Gillibert,
K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kiyokawa, M. Kobayashi, N. Kobayashi, T. Kobayashi, Y. Kondo,
Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marqúes, T. Motobayashi, T. Miyazaki, T. Nakamura, N. Nakatsuka, Y. Nishio,
A. Obertelli, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis, E. C. Pollacco, S. Reichert, J. -Y. Roussé,A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata, Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama,
Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, F. R. Xu, J. Yasuda, K. Yoneda, J. Zenihiro, S. -G. Zhou, W. Zuo, and T. Uesaka, “Quasifree
neutron knockout reaction reveals a small s-orbital component in the borromean nucleus 17 B,” Phys. Rev. Lett. 126, 082501 (2021).
Y. Kubota, A. Corsi, G. Authelet, H. Baba, C. Caesar, D. Calvet, A. Delbart, M. Dozono, J. Feng, F. Flavigny, J. -M. Gheller, J. Gibelin,
A. Giganon, A. Gillibert, K. Hasegawa, T. Isobe, Y. Kanaya, S. Kawakami, D. Kim, Y. Kikuchi, Y. Kiyokawa, M. Kobayashi,
N. Kobayashi, T. Kobayashi, Y. Kondo, Z. Korkulu, S. Koyama, V. Lapoux, Y. Maeda, F. M. Marqués, T. Motobayashi, T. Miyazaki,
T. Nakamura, N. Nakatsuka, Y. Nishio, A. Obertelli, K. Ogata, A. Ohkura, N. A. Orr, S. Ota, H. Otsu, T. Ozaki, V. Panin, S. Paschalis,
E. C. Pollacco, S. Reichert, J. -Y. Roussé, A. T. Saito, S. Sakaguchi, M. Sako, C. Santamaria, M. Sasano, H. Sato, M. Shikata,Y. Shimizu, Y. Shindo, L. Stuhl, T. Sumikama, Y. L. Sun, M. Tabata, Y. Togano, J. Tsubota, Z. H. Yang, J. Yasuda, K. Yoneda,
J. Zenihiro, and T. Uesaka, “Surface localization of the dineutron in 11 Li,” Phys. Rev. Lett. 125, 252501 (2020).

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N. Kitamura, K. Wimmer, N. Shimizu, V. M. Bader, C. Bancroft, D. Barofsky, T. Baugher, D. Bazin, J. S. Berryman, V. Bildstein, A. Gade,
N. Imai, T. Kröll, C. Langer, J. Lloyd, E. Lunderberg, G. Perdikakis, F. Recchia, T. Redpath, S. Saenz, D. Smalley, S. R. Stroberg,
J. A. Tostevin, N. Tsunoda, Y. Utsuno, D. Weisshaar, and A. Westerberg, “Structure of 30 Mg explored via in-beam γ-ray spectroscopy,”
Phys. Rev. C 102, 054318 (2020).
S. Momiyama, K. Wimmer, D. Bazin, J. Belarge, P. Bender, B. Elman, A. Gade, K. W. Kemper, N. Kitamura, B. Longfellow, E. Lunderberg, M. Niikura, S. Ota, P. Schrock, J. A. Tostevin, and D. Weisshaar, “Shell structure of 43 S and collapse of the N = 28 shell closure,”
Phys. Rev. C 102, 034325 (2020).
T. Noro, T. Wakasa, T. Ishida, Hidetomo P. Yoshida, M. Dozono, H. Fujimura, K. Fujita, K. Hatanaka, T. Ishikawa, M. Itoh, J. Kamiya,
T. Kawabata, Y. Maeda, H. Matsubara, M. Nakamura, H. Sakaguchi, Y. Sakemi, Y. Shimizu, H. Takeda, Y. Tameshige, A. Tamii,
K. Tamura, S. Terashima, M. Uchida, Y. Yasuda, and M. Yosoi, “Experimental study of (p, 2p) reactions at 392 MeV on 12 C, 16 O, 40 Ca
and 208 Pb nuclei leading to low-lying states of residual nuclei,” Prog. Theor. Exp. Phys. 2020, 093D02 (2020).
K. B. Howard, U. Garg, M. Itoh, H. Akimune, M. Fujiwara, T. Furuno, Y. K. Gupta, M. N. Harakeh, K. Inaba, Y. Ishibashi, K. Karasudani,
T. Kawabata, A. Kohda, Y. Matsuda, M. Murata, S. Nakamura, J. Okamoto, S. Ota, J. Piekarewicz, A. Sakaue, M.Şenyiğit, M. Tsumura,and Y. Yang, “Compressional-mode resonances in the molybdenum isotopes: Emergence of softness in open-shell nuclei near A = 90,”
Phys. Lett. B 807, 135608 (2020).
A. Frotscher, M. Gómez-Ramos, A. Obertelli, P. Doornenbal, G. Authelet, H. Baba, D. Calvet, F. Château, S. Chen, A. Corsi, A. Delbart,
J. -M. Gheller, A. Giganon, A. Gillibert, T. Isobe, V. Lapoux, M. Matsushita, S. Momiyama, T. Motobayashi, M. Niikura, H. Otsu,
N. Paul, C. Péron, A. Peyaud, E. C. Pollacco, J. -Y. Roussé, H. Sakurai, C. Santamaria, M. Sasano, Y. Shiga, N. Shimizu, D. Steppenbeck, S. Takeuchi, R. Taniuchi, T. Uesaka, H. Wang, K. Yoneda, T. Ando, T. Arici, A. Blazhev, F. Browne, A. M. Bruce, R. Carroll,
L. X. Chung, M. L. Cortées, M. Dewald, B. Ding, Zs. Dombradi, F. Flavigny, S. Franchoo, F. Giacoppo, M. Górska, A. Gottardo,
K. Hadyńska-Klȩk, Z. Korkulu, S. Koyama, Y. Kubota, A. Jungclaus, J. Lee, M. Lettmann, B. D. Linh, J. Liu, Z. Liu, C. Lizarazo,
C. Louchart, R. Lozeva, K. Matsui, T. Miyazaki, K. Moschner, S. Nagamine, N. Nakatsuka, C. Nita, S. Nishimura, C. R. Nobs,
L. Olivier, S. Ota, Z. Patel, Zs. Podolyák, M. Rudigier, E. Sahin, T. Y. Saito, C. Shand, P. -A. Söderström, I. G. Stefan, T. Sumikama,
D. Suzuki, R. Orlandi, V. Vaquero, Zs. Vajta, V. Werner, K. Wimmer, J. Wu, and Z. Xu, “Sequential nature of (p, 3p) two-proton
knockout from neutron-rich nuclei,” Phys. Rev. Lett. 125 012501 (2020).
A. E. Barzakh, D. Atanasov, A. N. Andreyev, M. Al Monthery, N. A. Althubiti, B. Andel, S. Antalic, K. Blaum, T. E. Cocolios, J. G. Cubiss, P. Van Duppen, T. Day Goodacre, A. de Roubin, G. J. Farooq-Smith, D. V. Fedorov, V. N. Fedosseev, D. A. Fink, L. P. Gaﬀney,
L. Ghys, R. D. Harding, M. Huyse, N. Imai, S. Kreim, D. Lunney, K. M. Lynch, V. Manea, B. A. Marsh, Y. Martinez Palenzuela,
P. L. Molkanov, D. Neidherr, M. Rosenbusch, R. E. Rossel, S. Rothe, L. Schweikhard, M. D. Seliverstov, S. Sels, C. Van Beveren,
E. Verstraelen, A. Welker, F. Wienholtz, R. N. Wolf, and K. Zuber, “Shape coexistence in 187 Au studied by laser spectroscopy,” Phys.
Rev. C 101, 064321 (2020).
R. D. Harding, A. N. Andreyev, A. E. Barzakh, D. Atanasov, J. G. Cubiss, P. Van Duppen, M. Al Monthery, N. A. Althubiti, B. Andel,
S. Antalic, K. Blaum, T. E. Cocolios, T. Day Goodacre, A. de Roubin, G. J. Farooq-Smith, D. V. Fedorov, V. N. Fedosseev, D. A. Fink,
L. P. Gaﬀney, L. Ghys, D. T. Joss, F. Herfurth, M. Huyse, N. Imai, S. Kreim, D. Lunney, K. M. Lynch, V. Manea, B. A. Marsh,
Y. Martinez Palenzuela, P. L. Molkanov, D. Neidherr, R. D. Page, A. Pastore, M. Rosenbusch, R. E. Rossel, S. Rothe, L. Schweikhard,
M. D. Seliverstov, S. Sels, C. Van Beveren, E. Verstraelen, A. Welker, F. Wienholtz, R. N. Wolf, and K. Zuber, “Laser-assisted decay
spectroscopy for the ground states of 180, 182 Au,” Phys. Rev. C 102, 024312 (2020).
J. G. Cubiss, A. N. Andreyev, A. E. Barzakh, V. Manea, M. Al Monthery, N. A. Althubiti, B. Andel, S. Antalic, D. Atanasov, K. Blaum,
T. E. Cocolios, T. Day Goodacre, A. de Roubin, G. J. Farooq-Smith, D. V. Fedorov, V. N. Fedosseev, D. A. Fink, L. P. Gaﬀney, L. Ghys,
R. D. Harding, F. Herfurth, M. Huyse, N. Imai, D. T. Joss, S. Kreim, D. Lunney, K. M. Lynch, B. A. Marsh, Y. Martinez Palenzuela,
P. L. Molkanov, D. Neidherr, G. G. O’Neill, R. D. Page, M. Rosenbusch, R. E. Rossel, S. Rothe, L. Schweikhard, M. D. Seliverstov,S. Sels, A. Stott, C. Van Beveren, P. Van Duppen, E. Verstraelen, A. Welker, F. Wienholtz, R. N. Wolf, and K. Zuber, “Laser-assisted
decay spectroscopy and mass spectrometry of 178 Au,” Phys. Rev. C 102, 044332 (2020).
T. L. Tang, T. Uesaka, S. Kawase, D. Beaumel, M. Dozono, T. Fujii, N. Fukuda, T. Fukunaga, A. Galindo-Uribarri, S. H. Hwang, N. Inabe,
D. Kameda, T. Kawahara, W. Kim, K. Kisamori, M. Kobayashi, T. Kubo, Y. Kubota, K. Kusaka, C. S. Lee, Y. Maeda, H. Matsubara,
S. Michimasa, H. Miya, T. Noro, A. Obertelli, K. Ogata, S. Ota, E. Padilla-Rodal, S. Sakaguchi, H. Sakai, M. Sasano, S. Shimoura,
S. S. Stepanyan, H. Suzuki, M. Takaki, H. Takeda, H. Tokieda, T. Wakasa, T. Wakui, K. Yako, Y. Yanagisawa, J. Yasuda, R. Yokoyama,
K. Yoshida, K. Yoshida, and J. Zenihiro, “How diﬀerent is the core of 25 F from 24 Og.s. ,” Phys. Rev. Lett. 124, 212502 (2020).
S. Michimasa, M. Kobayashi, Y. Kiyokawa, S. Ota, R. Yokoyama, D. Nishimura, D. S. Ahn, H. Baba, G. P. A. Berg, M. Dozono,
N. Fukuda, T. Furuno, E. Ideguchi, N. Inabe, T. Kawabata, S. Kawase, K. Kisamori, K. Kobayashi, T. Kubo, Y. Kubota, C. S. Lee,
M. Matsushita, H. Miya, A. Mizukami, H. Nagakura, H. Oikawa, H. Sakai, Y. Shimizu, A. Stolz, H. Suzuki, M. Takaki, H. Takeda,
S. Takeuchi, H. Tokieda, T. Uesaka, K. Yako, Y. Yamaguchi, Y. Yanagisawa, K. Yoshida, and S. Shimoura, “Mapping of a new
deformation region around 62 Ti,” Phys. Rev. Lett. 125, 122501 (2020).
D. Nagae, Y. Abe, S. Okada, S. Omika, K. Wakayama, S. Hosoi, S. Suzuki, T. Moriguchi M. Amano, D. Kamioka, Z. Ge, S. Naimi,
F. Suzaki, N. Tadano, R. Igosawa, K. Inomata H. Arakawa, K. Nishimuro, T. Fujii, T. Mitsui, Y. Yanagisawa, H. Baba, S. Michimasa,
S. Ota, G. Lorusso, Yu.A. Litvinov, A. Ozawa, T. Uesaka, T. Yamaguchi, Y. Yamaguchi, and M. Wakasugi, “Development and operationof an electrostatic time-of-flight detector for the Rare RI storage Ring,” Nucl. Instrum. Methods Phys. Res. A 986, 164713 (2021).
H. Suzuki, K. Yoshida, N. Fukuda, H. Takeda, Y. Shimizu, D. S. Ahn, T. Sumikama, N. Inabe, T. Komatsubara, H. Sato, Z. Korkulu,
K. Kusaka, Y. Yanagisawa, M. Ohtake, H. Ueno, T. Kubo, S. Michimasa, N. Kitamura, K. Kawata, N. Imai, O. B. Tarasov, D. Bazin,
J. Nolen, and W. F. Henning “Experimental studies of the two-step scheme with an intense radioactive 132 Sn beam for next-generation
production of very neutron-rich nuclei,” Phys. Rev. C 102, 064615 (2020).
T. Sumikama. D. S. Ahn. N. Fukuda, Y. Shimizu, H. Suzuki, H. Takeda, H. Wang, K. Yoshida, J. Amano, N. Chiga, K. Chikaato,
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J. Suwa, M. Takechi, S. Takeuchi, Y. Togano, T. Tomai, and Y. Watanabe, “Energy-control and novel particle-identification methods
combined with range in a multi-sampling ionization chamber for experiments using slowed-down RI beams,” Nucl. Instrum. Methods
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Y. L. Sun, T. Nakamura, Y. Kondo, Y. Satou, J. Lee, T. Matsumoto, K. Ogata, Y. Kikuchi, N. Aoi, Y. Ichikawa, K. Ieki, M. Ishihara,
T. Kobayshi, T. Motobayashi, H. Otsu, H. Sakurai, T. Shimamura, S. Shimoura, T. Shinohara, T. Sugimoto, S. Takeuchi, Y. Togano,and K. Yoneda, “Three-body breakup of 6 He and its halo structure,” Phys. Lett. B 814, 136072 (2021).
S. Go, E. Ideguchi, R. Yokoyama, N. Aoi, F. Azaiez, K. Furutaka, Y. Hatsukawa, A. Kimura, K. Kisamori, M. Kobayashi, F. Kitatani, M. Koizumi, H. Harada, I. Matea, S. Michimasa, H. Miya, S. Nakamura, M. Niikura, H. Nishibata, N. Shimizu, S. Shimoura,
T. Shizuma, M. Sugawara, D. Suzuki, M. Takaki, Y. Toh, Y. Utsuno, D. Verney, and A. Yagi, “High-spin states in 35 S,” Phys. Rev. C
103, 034327 (2021).
G. G. Kiss, M. La Cognata, C. Spitaleri, R. Yarmukhamedov, I. Wiedenhöver, L. T. Baby, S. Cherubini, A. Cvetinović, G. D’Agata,
P. Figuera, G. L. Guardo, M. Gulino, S. Hayakawa, I. Indelicato, L. Lamia, M. Lattuada, F. Mudò, S. Palmerini, R. G. Pizzone,
G. G. Rapisarda, S. Romano, M. L. Sergi, R. Spartà, O. Trippella, A. Tumino, M. Anastasiou, S. A. Kuvin, N. Rijal, B. Schmidt,
S. B. Igamov, S. B. Sakuta, K. I. Tursunmakhatov, Zs. Fülöp, Gy. Gyürky, T. Szücs, Z. Halász, E. Somorjai, Z. Hons, J. Mrázek,
R. E. Tribble, and A. M. Mukhamedzhanov, “Astrophysical S -factor for the 3 He(α, γ)7 Be reaction via the asymptotic normalizationcoeﬃcient (ANC) method,” Phys. Lett. B 807, 135606 (2020).
L. Yang, C. J. Lin, Y. X. Zhang, P. W. Wen, H. M. Jia, D. X. Wang, N. R. Ma, F. Yang, F. P. Zhong, S. H. Zhong, and T. P. Luo, “Bayesiananalysis on interactions of exotic nuclear systems,” Phys. Lett. B 807, 135540 (2020).
L. Yang, C. J. Lin, H. Yamaguchi, J. Lei, P. W. Wen, M. Mazzocco, N. R. Ma, L. J. Sun, D. X. Wang, G. X. Zhang, K. Abe, S. M. Cha,
K. Y. Chae, A. Diaz-Torres, J. L. Ferreira, S. Hayakawa, H. M. Jia, D. Kahl, A. Kim, M. S. Kwag, M. La Commara, R. Navarro Pérez,
C. Parascandolo, D. Pierroutsakou, J. Rangel, Y. Sakaguchi, C. Signorini, E. Strano, X. X. Xu, F. Yang, Y. Y. Yang, G. L. Zhang,
F. P. Zhong, and J. Lubian, “Insight into the reaction dynamics of proton drip-line nuclear system 17 F + 58 Ni at near-barrier energies,”
at near-barrier energies,” Phys. Lett. B 813, 136045 (2021).
N. Iwasa S. Ishikawa, S. Kubono, T. Sakakibara, K. Kominato, K. Nishio, M. Matsuda, K. Hirose, H. Makii, R. Orlandi, K. Asada,
D. Guru, S. Nishimura, S. Hayakawa, and T. Kawabata, “Experimental study of the Γ p1 /Γ p0 ratios of resonance states in 8 Be fordeducing the 7 Be(n, p1 )7 Li∗ reaction rate relevant to the cosmological lithium problem,” Phys. Rev. C 103, 015801 (2021).
D. X. Wang, C. J. Lin, L. Yang, N. R. Ma, L. J. Sun, F. Yang, H. M. Jia, F. P. Zhong, and P. W. Wen, “Compact 16-channel integrated
charge-sensitive preamplifier module for silicon strip detectors,” Nucl. Sci. Tech. 31, 48 (2020).
Y. J. Yao, C. J. Lin, L. Yang, N. R. Ma, D. X. Wang, G. L. Zhang, G. X. Zhang, H. M. Jia, F. Yang, F. P. Zhong, P. W. Wen, X. B. Qin,
and H. M. Zhao, “Relative probabilities of breakup channels in reactions of 6, 7 Li with 209 Bi at energies around and above the Coulomb
barrier,” Chin. Phys. C 45, 054104 (2021).
Y. J. Yao, C. J. Lin, L. Yang, N. R. Ma, D. X. Wang, G. L. Zhang, G. X. Zhang, H. M. Jia, and F. Yang, “The eﬀects of beam drifts onelastic scattering measured by the large solid-angle covered detector array,” Nucl. Sci. Tech. 32, Article number:14 (2021).
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Shreyasi Acharya et al. (ALICE Collaboration), “Centrality dependence of J/ψ and ψ(2S) production and nuclear modification in p-Pb√
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Shreyasi Acharya et al. (ALICE Collaboration), “Global baryon number conservation encoded in net-proton fluctuations measured in√
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Shreyasi Acharya et al. (ALICE Collaboration), “Probing the eﬀects of strong electromagnetic fields with charge-dependent directed flowin Pb-Pb collisions at the LHC,” Phys. Rev. Lett. 125, 022301 (2020).
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pidity in Pb-Pb collisions at sNN = 5.02 TeV,” Phys. Lett. B 805, 135434 (2020).
√
Shreyasi Acharya et al. (ALICE Collaboration), “Measurement of the (anti-)3 He elliptic flow in Pb-Pb collisions at sNN = 5.02 TeV,”
Phys. Lett. B 805, 135414 (2020).
Shreyasi Acharya et al. (ALICE Collaboration), “Coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at√
sNN = 5.02 TeV,” J. High Energy Phys. 2006, 035 (2020).
Shreyasi Acharya et al. (ALICE Collaboration), “Jet-hadron correlations measured relative to the second order event plane in Pb-Pb√
collisions at sNN = 2.76 TeV,” Phys. Rev. C 101, 064901 (2020).
√
Shreyasi Acharya et al. (ALICE Collaboration), “Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at sNN= 5.02 TeV,”J. High Energy Phys. 2005, 085 (2020).
Shreyasi Acharya et al. (ALICE Collaboration), “Longitudinal and azimuthal evolution of two-particle transverse momentum correlations√in Pb-Pb collisions at sNN = 2.76 TeV,”Phys. Lett. B 804, 135375 (2020).
Shreyasi Acharya et al. (ALICE Collaboration), “Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity√
in pp and Pb-Pb collisions at sNN = 5.02 TeV,” Phys. Lett. B 804, 135377 (2020).
Shreyasi Acharya et al. (ALICE Collaboration), “Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp- 353 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)√
collisions at sNN = 5.02 TeV,” Phys. Rev. C 101, 044907 (2020).
√
Shreyasi Acharya et al. (ALICE Collaboration), “Production of (anti-)3 He and (anti-)3 H in p-Pb collisions at sNN = 5.02 TeV,” Phys.
Rev. C 101, 044906 (2020).
√
Shreyasi Acharya et al. (ALICE Collaboration), “Underlying event properties in pp collisions at s = 13 TeV,” J. High Energy Phys.
2004, 192 (2020).
√
Shreyasi Acharya et al. (ALICE Collaboration), “Global polarization of Λ Λ hyperons in Pb-Pb collisions at sNN = 2.76 and 5.02 TeV,”
Phys. Rev. C 101, 044611 (2020).
A. Kastberg, B. K. Sahoo, T. Aoki, Y. Sakemi, and B. P. Das, “Analysis of an optical lattice methodology for detection of atomic parity
nonconservation,” Symmetry 12, 974 (2020).
N. Shimizu, Y. Tsunoda, Y. Utsuno, and T. Otsuka, “The variational approach with the superposition of the symmetry-restored quasiparticle vacua for nuclear shell-model calculaions,” Phys. Rev. C 103, 014312 (2021).
K. Kaneko, N. Shimizu, T. Mizusaki, and Y. Sun, “Triple enhancement of quasi-SU(3) quadrupole collectivity in strontium-zirconium
N Z isotopes,” Phys. Lett. B 817, 136286 (2021).
S. Go, E. Ideguchi, R. Yokoyama, F. Azaiez, N. Aoi, K. Furutaka, Y. Hatsukawa, A. Kimura, K. Kisamori, M. Kobayashi, F. Kitatani, M. Koizumi, H. Harada, I. Matea, S. Michimasa, H. Miya, S. Nakamura, M. Niikura, H. Nishibata, N. Shimizu, S. Shimoura,
T. Shizuma, M. Sugawara, D. Suzuki, M. Takaki, Y. Utsuno, Y. Toh, D. Verney, and A. Yagi, “High-spin states in 35 S,” Phys. Rev. C
103, 034327 (2021).
N. Kitamura, K. Wimmer, N. Shimizu, V. M. Bader, C. Bancroft, D. Barofsky, T. Baugher, D. Bazin, J. S. Berryman, V. Bildstein, A. Gade,
N. Imai, T. Koll, C. Langer, J. Lloyd, E. Lunderberg, G. Perdikakis, F. Recchia, T. Redpath, S. Saenz, D. Smalley, S. R. Stroberg,
J. A. Tostevin, N. Tsunoda, Y. Utsuno, D. Weisshaar, and A. Westerberg “Structure of 30 Mg explored via in-beam γ-ray spectroscopy,”
Phys. Rev. C 102, 054318 (2020).
N. Tsunoda, T. Otsuka, K. Takayanagi, N. Shimizu, T. Suzuki, Y. Utsuno, and H. Ueno, “The impact of nuclear shape on the emergenceof the neutron dripline,” Nature 587, 66 (2020).
K. Kaneko, N. Shimizu, T. Mizusaki, Y. Sun, “Quasi-SU(3) coupling of (1h11/2 , 2 f7/2 ) across the N = 82 shell gap: Enhanced E2collectivity and shape evolution in Nd isotopes,” Phys. Rev. C 103, L021301 (2021).
N. Shimizu, T. Togashi, and Y. Utsuno, “Gamow-Teller transitions of neutron-rich N = 82 and N = 81 nuclei by shell-model calculations,”
Prog. Theor. Exp. Phys. 2021, 033D01 (2021).
K. Yanase and N. Shimizu, “Large-scale shell-model calculations of nuclear Schiﬀ moments of 129 Xe and 199 Hg,” Phys. Rev. C 102,065502 (2020).
K. Yanase, “Screening of nucleon electric dipole moments in atomic systems,” Phys. Rev. C 103, 035501 (2021).
P. A. S0̈derstr0̈m, L. Capponi, E. Açiksöz, T. Otsuka, N. Tsoneva, Y. Tsunoda, D. L. Balabanski, N. Pietralla, G. L. Guardo, D. Lattuada,
H. Lenske, C. Matei, D. Nichita, A. Pappalardo, and T. Petruse, “Electromagnetic character of the competitive γγ/γ-decay from
137m
Ba,”
N. Mărginean, D. Little, Y. Tsunoda, S. Leoni, R. V. F. Janssens, B. Fornal, T. Otsuka, C. Michelagnoli, L. Stan, F. C. L. Crespi,
C. Costache, R. Lica, M. Sferrazza, A. Turturica, A. D. Ayangeakaa, K. Auranen M. Barani, P. C. Bender, S. Bottoni, M. Boromiza,
A. Bracco, S. Călinescu, C. M. Campbell, M. P. Carpenter, P. Chowdhury, M. Ciemala, N. Cieplicka-Oryǹczak, D. Cline, C. Clisu,
H. L. Crawford, I. E. Dinescu, J. Dudouet, D. Filipescu, N. Florea, A. M. Forney, S. Fracassetti, A. Gade, I. Gheorghe, A. B. Hayes,
I. Harca, J. Henderson, A. Ionescu, L. W. Iskra, M. Jentschel, F. Kandzia, Y. H. Kim, F. G. Kondev, G. Korschinek, U. Köster,
Krishichayan, M. Krzysiek, T. Lauritsen, J. Li, R. Mărginean, E. A. Maugeri, C. Mihai, R. E. Mihai, A. Mitu, P. Mutti, A. Negret,
C. R. Niţă, A. Olăcel, A. Oprea, S. Pascu, C. Petrone, C. Porzio, D. Rhodes, D. Seweryniak, D. Schumann, C. Sotty, S. M. Stolze,
R. Şuvăilă, S. Toma, S. Ujeniuc, W. B. Walters, C. Y. Wu, J. Wu, S. Zhu, and S. Ziliani, “Shape coexistence at zero spin in 64Ni driven
by the monopole tensor interaction,” Phys. Rev. Lett. 125, 102502 (2020).
F. L. Bello Garrote, E. Sahin, Y. Tsunoda, T. Otsuka, A. Görgen, M. Niikura, S. Nishimura, G. de Angelis, G. Benzoni, A. I. Morales,
V. Modamio, Z. Y. Xu, H. Baba, F. Browne, A. M. Bruce, S. Ceruti, F. C. L. Crespi, R. Daido, M. -C. Delattre, P. Doornenbal,
Zs. Dombradi, Y. Fang, S. Franchoo, G. Gey, A. Gottardo, K. Hadyńska-Klȩk, T. Isobe, P. R. John, H. S. Jung, I. Kojouharov, T. Kubo,
N. Kurz, I. Kuti, Z. Li, G. Lorusso, I. Matea, K. Matsui, D. Mengoni, T. Miyazaki, S. Momiyama, P. Morfouace, D. R. Napoli,
F. Naqvi, H. Nishibata, A. Odahara, R. Orlandi, Z. Pate, S. Rice, H. Sakurai, H. Schaﬀner, L. Sinclair, P. -A. Söderström, D. Sohler,
I. G. Stefan, T. Sumikama, D. Suzuki, R. Taniuchi, J. Taprogge, Zs. Vajta, J. J. Valiente-Dobón, H. Watanabe, V. Werner, J. Wu, A. Yagi,
M. Yalcinkaya, R. Yokoyama, and K. Yoshinaga, “β decay of 75Ni and the systematics of the low-lying level structure of neutron-rich
odd-A Cu isotopes,” Phys. Rev. C 102, 034314 (2020).
C. Porzio, C. Michelagnoli, N. Cieplicka-Oryńczak, M. Sferrazza, S. Leoni, B. Fornal, Y. Tsunoda, T. Otsuka, S. Bottoni, C. Costache,
F. C. L. Crespi, L. W. Iskra, M. Jentschel, F. Kandzia, Y. -H. Kim, U. Köster, N. Mărginean, C. Mihai, P. Mutti, and A. Turturică,“Detailed low-spin spectroscopy of 65Ni via neutron capture reaction,” Phys. Rev. C 102, 064310 (2020).
Y. Tsunoda and T. Otsuka, “Triaxial rigidity of 166 Er and its Bohr-model realization,” Phys. Rev. C 103, L021303 (2021).
A. Kundu, Md. S. R. Laskar, R. Palit, R. Raut, S. Santra, N. Shimizu, T. Togashi, E. Ideguchi, H. Pai, S. Ali, F. S. Babra, R. Banik,
S. Bhattacharya, B. Das, P. Dey, R. Donthi, A. Goswami, S. Jadhav, G. Mukherjee, B. S. Naidu, L. P. Singh, S. Rajbanshi, H. P. Sharma,
S. S. Tiwary, and A. T. Vazhappilly, “New lifetime measurement for the 2+1 level of 112 Sn by the Doppler shift attenuation method,”Phys. Rev. C 103, 034315 (2021).

[Review Articles]
H. Yamaguchi, D. Kahl, and S. Kubono, “CRIB: the low energy in-flight RI beam separator,” Nuclear Physics News International 30,
No. 2, 21–27 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)[Proceedings]
L. Lamia, R. G. Pizzone, M. Mazzocco, S. Hayakawa, M. La Cognata, C. A. Bertulani, S. Cherubini, G. D’Agata, G. L. Guardo,
M. Gulino, I. Indelicato, G. G. Rapisarda, S. Romano, M. L. Sergi, R. Spartà, C. Spitaleri, and A. Tumino, J. Phys. Conf. Ser. 1643,
012096 (2020).
A. Inoue, A. Tamii, P. Chan, S. Hayakawa, N. Kobayashi, Y. Maeda, K. Nonaka, T. Shima, H. Shimizu, D. T. Tran, X. Wang, H. Yamaguchi, L. Yang, and Z. Yang, J. Phys. Conf. Ser. 1643, 012049 (2020).
H. Yamaguchi, S. Hayakawa, N. Ma, H. Shimizu, L. Yang, D. Kahl, K. Abe, T. Suhara, N. Iwasa, A. Kim, D. Kim, S. Cha, M. Kwag,
J. Lee, E. Lee, K. Chae, Y. Wakabayashi, N. Imai, N. Kitamura, P. Lee, J. Moon, K. Lee, C. Akers, H. Jung, N. Duy, L. Khiem, C. Lee,
S. Cherubini, M. Gulino, C. Spitaleri, G. Rapisarda, L. Cognata, L. Lamia, S. Romano, A. Coc, N. de Sereville, F. Hammache, G. Kiss,
S. Bishop, T. Teranishi, T. Kawabata, Y. Kwon, and D. Binh, J. Phys. Conf. Ser. 1643, 012069 (2020).
M. Mazzocco, N. Keeley, A. Boiano, C. Boiano, M. L. Commara, A. Lagni, C. Manea, C. Parascandolo, D. Pierroutsakou, C. Signorini,
E. Strano, D. Torresi, H. Yamaguchi, D. Kahl, L. Acosta, D. Meo, J. P. Fernandez-Garcia, T. Glodariu, J. Grebosz, A. Guglielmetti,
Y. Hirayama, N. Imai, H. Ishiyama, N. Iwasa, S. C. Jeong, H. M. Jia, Y. H. Kim, S. Kimura, S. Kubono, G. L. Rana, C. J. Lin, P. Lotti,
G. Marquı́nez-Duran, I. Martel, H. Miyatake, M. Mukai, T. Nakao, M. Nicoletto, A. Pakou, K. Rusek, Y. Sakaguchi, A. M. SanchezBenitez, T. Sava, O. Sgouros, V. Soukeras, F. Soramel, E. Stiliaris, L. Stroe, T. Teranishi, N. Toniolo, Y. Wakabayashi, Y. X. Watanabe,
L. Yang, Y. Y. Yang, and H. Q. Zhang, J. Phys. Conf. Ser. 1643, 012096 (2020).
H. Yamaguchi, S. Hayakawa, L. Yang, H. Shimizu, D. Kahl, T. Suhara, N. Iwasa, S. M. Cha, M. S. Kwag, J. H. Lee, E. J. Lee, K. Y. Chae,
A. Kim, D. H. Kim, Y. Wakabayashi, N. Imai, N. Kitamura, P. Lee, J. Y. Moon, K. B. Lee, C. Akers, N. N. Duy, L. H. Khiem, andC. S. Lee, JPS Conf. Proc. 32, 010055 (2020).
S. Hayakawa, L. Lamia, C. Spitaleri, C. A. Bertulani, S. Q. Hou, M. L. Cognata, M. Mazzocco, R. G. Pizzone, D. Pierroutsakou,
S. Romano, M. L. Sergi, and A. Tumino, JPS Conf. Proc. 32, 010058 (2020).
R. G. Pizzone, G. D’Agata, I. Indelicato, M. L. Cognata, P. Figuera, G. L. Guardo, S. Hayakawa, L. Lamia, M. Lattuada, M. Milin,
G. G. Rapisarda, S. Romano, M. L. Sergi, N. Skukan, N. Soic, C. Spitaleri, and A. Tumino, JPS Conf. Proc. 32, 010062 (2020).
A. Tumino, C. Spitaleri, M. L. Cognata, S. Cherubini, G. L. Guardo, M. Gulino, S. Hayakawa, I. Indelicato, L. Lamia, H. Petrascu,
R. G. Pizzone, S. M. R. Puglia, G. G. Rapisarda, S. Romano, M. L. Sergi, R. Sparta, and L. Trache, Proceedings of 13th International
Conference on Nucleus-Nucleus, JPS Conf. Proc. 32, 010059 (2020).
Y. Kotaka, Y. Ohshiro, H. Yamaguchi, N. Imai, Y. Sakemi, S. Shimoura, T. Nagatomo, J. Ohnishi, T. Nakagawa, M. Kase, A. Goto,
K. Hatanaka, and H. Muto, “Development of the calculation method of injection beam trajectory of RIKEN AVF Cyclotron with
4D emittance measured by the developed pepper-pot emittance monitor,” Proceedings of the 8th International Beam Instrumentation
Conference (IBIC2019), JACoW-IBIC2019-TUPP022 (2020).
Y. Sakemi, T. Aoki, R. Calabrese, H. Haba, K. Harada, T. Hayamizu, Y. Ichikawa, K. Jungmann, A. Kastberg, Y. Kotaka, Y. Matsuda,
H. Nagahama, K. Nakamura, M. Otsuka, N. Ozawa, K. S. Tanaka, A. Uchiyama, H. Ueno, and L. Willmann, “Fundamental physics
with cold radioactive atoms,” AIP Conf. Proc. 2319, 080020 (2021).

Presentations[International Conferences/Workshops]
N. Imai (invited), “Preparation status of NP1912-SHARAQ18,” OEDO/SHARAQ Collabotration Meeting 2020, On-line, September 7,
2020.
S. Michimasa (invited), “Mapping background X-rays from OEDO RFD,” OEDO/SHARAQ Collabotration Meeting 2020, On-line,
September 7, 2020.
M. Dozono (invited), “Probing exotic structures of highly excited nuclei: OEDO-SHARAQ activities,” RIBF User Meeting, On-line,
September 8–10, 2020.
S. Michimasa (invited), “Development of energy-degraded RI beam and expansion of nuclear reaction studies,” Symposium of Nuclear
Data 2020 (hybrid), Saitama, Japan, November 26–27, 2020.
S. Ota (invited), “Study of nuclear matter property via nuclear scattering and reactions,” JPS/NRF/NSFC A3 Foresight Program “Nuclear
Physics in the 21st Century” Joint Annual Meeting, Huizhou, China and On-line, November 18–19, 2020.
H. Yamaguchi (oral), “Activities at the low-energy RI beam separator CRIB,” RIBF Users Meeting 2020 (on-line), Saitama, Japan,
Sepember 8–10, 2020.
H. Yamaguchi (oral), “Overview of alpha resonant scattering experiments at CRIB,” International mini-workshop on “Physics in resonant
reaction induced by low-energy RI beam”, Web Meeting Hosted by CNS, the University of Tokyo/IBS Center for Exotic Nuclear
Studies/Department of Pure and Applied Physics, Kansai University/Research Center for Nuclear Physics (RCNP), Osaka, Japan,
February 22, 2021.
N. R. Ma (oral), “Primary result of 14 O + α clustering study at CRIB,” International mini-workshop on “Physics in resonant reaction
induced by low-energy RI beam”, Web Meeting Hosted by CNS, the University of Tokyo/IBS Center for Exotic Nuclear Studies/Department of Pure and Applied Physics, Kansai University/Research Center for Nuclear Physics (RCNP), Osaka, Japan, February
22, 2021.
D. Sekihata (oral) for the ALICE Collaboration, “Low-mass dielectron measurements in pp, p-Pb and Pb-Pb collisions with ALICE at
the LHC,” 10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, Online, June 2020.
T. Hayamizu (oral), “Development of ultracold francium atomic sources towards the permanent EDM search,” Yamada Conference
LXXII: The 8th Asia-Pacific Conference on Few-Body Problems in Physics (APFB2020), Kanazawa, Japan, March 4, 2021.
N. Shimizu (oral), “Data-driven approaches in nuclear shell-model calculations,” Nuclear Data Symposium 2020 (RIKEN Nishina Cen-

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)ter), Saitama, Japan, November 27, 2020.
Y. Tsunoda (invited), “Structure of medium-mass nuclei studied by Monte Carlo shell model calculations,” The RIBF Users Meeting
2020, Online, September 9, 2020.
Y. Tsunoda (oral), “Nuclear shapes and collective motions in the region of Sm,” 12th Symposium on Discovery, Fusion, Creation of New
Knowledge by Multidisciplinary Computational Sciences, Online, October 6, 2020.
K. Yanase (oral), “Large-scale shell-model calculations of nuclear Schiﬀ moments of 129Xe and 199Hg,” Beyond-the-Standard-Model
Physics with Nucleons and Nuclei (INT 20-2b), online, July 23, 2020.

[Domestic Conferences/Workshops]
今井伸明 (招待講演), 「不安定核の中性子捕獲率測定プロジェクト」, 研究会「星の錬金術から銀河考古学へ」, 東京都三鷹市（国立天文台）, 2020 年 10 月 26–29 日.
下浦亨（招待講演）, “Direct reactions as quantum probes of nuclear system,” Symposium on “JPS nuclear physics and physical review
C,” 日本物理学会 2020 年秋季大会, オンライン, 2020 年 9 月 14 日–17 日.
花井周太郎 (口頭発表), 「分割電極型 PPAC(SR-PPAC) における位置較正手法の開発」, 日本物理学会 2020 年秋季大会, on-line, 2020
年 9 月 14 日–17 日.
道正新一郎（口頭発表）, 「中性子過剰 62 Ti 核および近傍核の質量測定」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年
3 月 12–15 日.
堂園昌伯（口頭発表）, 「(4 He, 6 He) 反応による錫同位体の対振動状態の研究」, 日本物理学会 第 76 回年次大会, オンライン講演,
2021 年 3 月 12–15 日.
郡司卓（招待講演）, “ALICE upgrade and physics topics (II),” 第４回クラスター階層領域研究会, オンライン講演, 2020 年 5 月 28 日.
関畑大貴（口頭発表）, 「機械学習を用いた ALICE-TPC 検出器内部の空間電荷効果補正」, MPGD & Active 媒質 TPC 研究会 2020,
兵庫県神戸市（神戸大学+オンライン）, 2020 年 12 月.
関畑大貴 for the ALICE Collaboration（口頭発表）, 「機械学習を用いた ALICE-TPC 検出器内部の空間電荷効果補正」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
関畑大貴（基調講演）, 「核子対あたり重心系エネルギー 5.02 における中性中間子と直接光子測定」(受賞記念企画公演), 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
関口裕子（口頭発表） for the ALICE Collaboration, 「LHC-ALICE 実験を用いた小さな衝突系における方位角異方性の擬ラピディ
ティ依存性測定」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
清水夏樹（口頭発表） for the ALICE Collaboration, 「ALICE 実験における Run2 全統計を用いたエキゾチックハドロン探索」,日
本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
佐藤幹（口頭発表）, 「高効率フランシウム原子線のための吸着防止コーティング材の評価」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
君塚大樹（口頭発表）, 「狭線幅光会合を用いた極低温 Sr2 分子生成のための高安定な光源開発」, 日本物理学会 第 76 回年次大会,
オンライン講演, 2021 年 3 月 12–15 日.
池田英彦（口頭発表）, 「電場の量子センシングに向けた Sr リドベルグ原子の分光」, 日本物理学会 第 76 回年次大会, オンライン
講演, 2021 年 3 月 12–15 日.
小澤直也（口頭発表）, 「フランシウム原子の電気双極子能率探索のための表面電離イオン源の開発」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.
清水則孝（口頭発表）, 「準粒子真空基底によるモンテカルロ殻模型の拡張」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021
年 3 月 12–15 日.
角田佑介（口頭発表）, 「モンテカルロ殻模型による二重ベータ崩壊の核行列要素の計算」, 新学術領域「地下宇宙」2020 年度領域研究会, オンライン講演, 2020 年 6 月 2 日.
角田佑介（口頭発表）, 「モンテカルロ殻模型による二重ベータ崩壊の核行列要素の計算」, 日本物理学会 第 76 回年次大会, オンラ
イン講演, 2021 年 3 月 12–15 日.
柳瀬宏太（口頭発表）, 「原子核殻模型による電気双極子モーメントの精密計算」, 「富岳で加速する素粒子・原子核・宇宙・惑星」
シンポジウム, オンライン講演, 2021 年 1 月 28 日.
柳瀬宏太（口頭発表）, 「清水則孝, 原子核殻模型による電気双極子モーメントの精密計算」, 日本物理学会 第 76 回年次大会, オンライン講演, 2021 年 3 月 12–15 日.

[Seminars]
N. Kitamura (oral), “In-beam spectroscopy of 30 Mg: structural evolution approaching the island of inversion,” CNS Seminar, On-line,
July 29, 2020.
S. Koyama (oral), “Spectroscopy of resonance states in light proton-rich nuclei via missing mass method,” CNS Seminar, On-line, August
7, 2020.
鎌倉惠太 (oral), 「東大 HyperECR イオン源の現状」, 第 19 回 AVF 合同打ち合わせ, 宮城県仙台市（東北大学）, 2021 年 3 月 10 日.
小高康照 (oral), 「理研 AVF のビーム輸送系最適化の現状」, 第 19 回 AVF 合同打ち合わせ, 宮城県仙台市（東北大学）, 2021 年 3
月 10 日.

Awards
関畑大貴, 第 15 回日本物理学会若手奨励賞 (実験核物理領域).
関畑大貴, 第 27 回原子核談話会新人賞.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Press Releases
道正新一郎, 小林幹, 下浦享, 上坂友洋, 井手口栄治, 西村太樹, 「チタン同位体でおこる新たな安定化現象を発見—質量測定で迫る原子核存在限界」, 2020 年 9 月 16 日.
大塚孝治, 角田直文, 高柳和雄, 清水則孝, 鈴木俊夫, 宇都野穣, 吉田聡太, 上野秀樹, 「原子核の存在限界（中性子ドリップライン）の新たなメカニズム」, 2020 年 11 月 5 日, https://www.s.u-tokyo.ac.jp/ja/press/2020/7074/ .

Others[東京大学理学部ニュース]
道正新一郎, 「質量から探る原子核の秩序と存在限界」, 学部生に伝える研究最前線, 東京大学理学部ニュース 2021 年 1 月号.

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Partner Institution
Wako Nuclear Science Center, IPNS (Institute of Particle and Nuclear Studies)
KEK (High Energy Accelerator Research Organization)
1. Abstract

The Wako Nuclear Science Center (WNSC) of KEK aims to promote low-energy nuclear physics and nuclear astrophysics researchand interdisciplinary studies using short-lived radioactive nuclei. WNSC operates the KEK Isotope Separation System (KISS), an
electro-magnetic isotope separator featuring elemental selectivity from resonance laser ionization in a gas catcher. The KISS facility
provides various neutron-rich nuclei via multinucleon transfer reactions. Of particular significance is its provision of nuclei in thevicinity of the neutron magic number N = 126. Optical and β-γ spectroscopy have been applied to these neutron-rich nuclear beams
for nuclear structure and nuclear astrophysical studies. In addition, several new developments—a rotating target, a donut-shaped gas
cell, and an in-jet laser ionization scheme—have been performed to improve the performance of the KISS facility. The WNSC has also
developed multi-reflection time of flight mass spectrographs (MRTOF-MS) for precision mass measurements of short-lived nuclei incollaboration with the RIKEN SLOWRI team and the Institute of Basic Science (IBS), Korea. After successful mass measurements
combined with the GARIS-II at RILAC, the existing MRTOF-MS setup has been renewed for use with the GARIS-II relocated after
the ring cyclotron for high precision mass measurements of superheavy nuclides. Furthermore, additional MRTOF-MS setups havebeen placed at KISS and F11 of the ZeroDegree Spectrometer for comprehensive mass measurement.
The Wako Nuclear Science Center (WNSC) of KEK aims to promote low-energy nuclear physics and nuclear astrophysics research
as well as interdisciplinary studies using short-lived radioactive nuclei. WNSC operates the KEK Isotope Separation System (KISS)
which is an electro-magnetic isotope separator featuring elemental selectivity from the use of resonance laser ionization in a gas
catcher. The KISS facility provides various neutron-rich nuclei via multinucleon transfer reactions. Of particular significance is its
provision of nuclei in the vicinity of the neutron magic number N = 126. Optical and β-γ spectroscopy have been applied to theseneutron-rich nuclear beams, for nuclear structure and nuclear astrophysical studies. Several new developments—a rotating target, adonut-shaped gas cell, and in-jet laser ionization scheme—have been performed to improve the performance of KISS facility. The
WNSC has also developed multi-reflection time of flight mass spectrographs (MRTOF-MS) for precision mass measurements ofshort-lived nuclei in collaboration with the RIKEN SLOWRI team and the Institute of Basic Science (IBS), Korea. After successful
mass measurements in combination with the GARIS-II at RILAC, the existing MRTOF-MS setup has been renewed for use with the
GARIS-II relocated after the ring cyclotron for high precision mass measurements of superheavy nuclides, and additional MRTOF-MS
setups have been placed at KISS and at F11 of the ZeroDegree Spectrometer for comprehensive mass measurements of more than one
thousand nuclides.

2. Major Research Subjects
(1)
(2)
(3)
(4)
(5)
(6)

Production and manipulation of radioactive isotope beams for nuclear experiments.
Explosive nucleosynthesis (r- and rp-process).
Heavy ion reaction mechanism for producing heavy neutron-rich nuclei.
Development of MRTOF mass spectrographs for short-lived nuclei.
Comprehensive mass measurements of short-lived nuclei including superheavy elements.
Development of KISS-II.

3. Summary of Research Activity

The Wako Nuclear Science Center (WNSC) provides low-energy short-lived radioactive ion beams to researchers from universities
using the KEK isotope separator system (KISS). Research activities in RIKEN RIBF were restricted due to the COVID-19 pandemic
for more than half of the JFY2020. During the governmental “stay home” period, the WNSC researchers worked on writing research
papers and technical development at home. Five physics papers were published for the experiments conducted at KISS, including two
experiments right before a national state of emergency was declared. A press release was announced on one of the experiments toadvertise the KISS uniqueness that can provide low-energy neutron-rich isotopes of refractory elements. These nuclides are essential
ones for the study of the origin of gold in the universe.
In late September, a part of the activities was restarted at the laboratory. Modification of the KISS beamline has started toperform decay spectroscopy of pure isobaric or isomeric nuclides by placing the detector array behind a multi-reflection time-of-flight(MRTOF) mass spectrograph. When the modification is completed in JFY2021, simultaneous spectroscopy of multiple species will
be realized thanks to the spectrographic future of the MRTOF device and a gamma-ToF detector that is under development.
The WNSC is conducting a campaign of comprehensive mass measurements of all available nuclides at RIKEN RIBF in collaboration with RIKEN’s SLOWRI team. A new combined gas cell and MRTOF device were installed in front of the beam dump of the
BigRIPS in-flight fragmentation separator. A series of online commissioning experiments were conducted using parasitic beams of
the in-beam gamma-ray spectroscopy experiments (HiCARI campaign) in November–December 2020. The energetic radioactive ion
beams passing through the upstream experiments’ target were guided to the gas cell and converted to trapped ions for precision massmeasurements using the MRTOF mass spectrograph.
The total system eﬃciencies were studied with various elements. While some species were diverse across molecular sidebands(e.g., ScOH), more than 1% eﬃciencies were obtained for heavier nuclides (e.g., Te and Sb). In sum, the commissioning campaign
was highly successful, with more than 70 atomic masses measured with the parasitic beams. The masses of three nuclides (88As,- 358 -

VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

89As, 112Mo) have been measured for the first time, and eleven other nuclear masses improve the present uncertainty significantly.
The WNSC plans to extend the present KISS facility to investigate the nuclides in the neutron-rich region of uranium using themulti-neutron transfer reactions of actinide targets to study the origin of uranium. The primary studies of the future facility are in
progress.

Members
Group Leader
Michiharu WADA
Researchers
Yutaka WATANABEPeter SCHURY
Sunchan JEONG

Yoshikazu HIRAYAMA
Hiroari MIYATAKE
Marco Rosenbusch

Technical Staﬀ
Yutaka KAKIGUCHI

Michihiro OYAIZU

Visiting Researchers
Hermann WOLLNIK (NMSU)
Jun-young MOON (IBS)
Sidong CHEN (HKU)
Wenduo XIAN (HKU)
Hiroshi WATANABE (Beihan University)

Hyun-suk CHOI (Seoul National University)
Jiajian LIU (HKU)
Shuxiong YAN (Jinan University)
Dongsheng HOU (IMP)Student Trainees
Toshitaka NIWASE (PhD. Student, Kyushu Univ.)

Shun IIMURA (PhD. Student, Osaka Univ.)

Assistant
Machiko IZAWA

List of Publications & Presentations
Publications[Original Papers]
H. Watanabe, Y. X. Watanabe, Y. Hirayama, A. N. Andreyev, T. Hashimoto, F. G. Kondev, G. J. Lane, Yu.A. Litvinov, J. J. Liu, H. Miyatake, J. Y. Moon, A. I. Morales, M. Mukai, S. Nishimura, T. Niwase, M. Rosenbusch, P. Schury, Y. Shi, M. Wada, and P. M. Walker,“Beta decay of the axially asymmetric ground state of 192 Re,” Phys. Lett. B, 814, 136088 (2021).
S. Kimura, D. Kaji, Y. Ito, H. Miyatake, K. Morimoto, P. Schury, and M. Wada, “Reduction of contaminations originating from primarybeam by improving the beam stoppers in GARIS-II,” Nucl. Instrum. Methods Phys. Res. A, 164996 (2020).
P. M. Walker, Y. Hirayama, G. J. Lane, H. Watanabe, G. D. Dracoulis, M. Ahmed, M. Brunet, T. Hashimoto, S. Ishizawa, F. G. Kondev,
Yu. A. Litvinov, H. Miyatake, J. Y. Moon, M. Mukai, T. Niwase, J. H. Park, Zs. Podolyák, M. Rosenbusch, P. Schury, M. Wada,
X. Y. Watanabe, W. Y. Liang, and F. R. Xu, “Properties of 187 Ta reveled through isomeric decay,” Phys. Rev. Lett. 125, 192505 (2020).
M. Rosenbusch, P. Schury, M. Wada, S. Iimura, Y. Ito, and H. Wollnik, “Accurately accounting for eﬀects on times-of-flight causedby finite field-transition times during the ejection of ions from a storage trap: A study for single-reference TOF and MRTOF mass
spectrometry,” Int. J. Mass Spectrom. 456, 116346 (2020).
M. Mukai, Y. Hirayama, Y. X. Watanabe, S. Schiﬀmann, J. Ekman, M. Godefroid, P. Schury, Y. Kakiguchi, M. Oyaizu, M. Wada,
S. C. Jeong, J. Y. Moon, J. H. Park, H. Ishiyama, S. Kimura, H. Ueno, M. Ahmed, A. Ozawa, H. Watanabe, S. Kanaya, and H. Miyatake,“In-gas-cell laser resonance ionization spectroscopy of 196, 197, 198 Ir,” Phys. Rev. C 102, 054307 (2020).
H. Choi, Y. Hirayama, S. Choi, T. Hashimoto, S. C. Jeong, H. Miyatake, J. Y. Moon, M. Mukai, T. Niwase, M. Oyaizu, M. Rosenbusch,
P. Schury, A. Taniguchi, Y. X. Watanabe, and M. Wada, “In-gas-cell laser ionization spectroscopy of 194, 196 Os isotopes by using a
multireflection time-of-flight mass spectrograph,” Phys. Rev. C 102, 034309 (2020).
A. V. Chudinov, M. Rosenbusch, V. I. Kozlovskiy, V. V. Raznikov, P. Schury, M. Wada, and H. Wollnik, “Model independent peak fitting
and uncertainty assignment for high-precision time-of-flight mass spectrometry,” Analyst 145, 3401–3406 (2020).
Y. X. Watanabe, M. Ahmed, Y. Hirayama, M. Mukai, J. H. Park, P. Schury, Y. Kakiguchi, S. Kimura, A. Ozawa, M. Oyaizu, M. Wada, and
H. Miyatake, “Deexcitation γ-ray transitions from the long-lived I π = 13/2+ metastable state in 195 Os,” Phys. Rev. C 101, 041305(R)(2020).

[Proceedings]
Y. Hirayama, Y. X. Watanabe, M. Mukai, M. Ahmed, H. Ishiyama, S. C. Jeong, Y. Kakiguchi, S. Kimura, J. Y. Moon, M. Oyaizu,
J. H. Park, P. Schury, M. Wada, and H. Miyatake, “Nuclear spectroscopy of r-process nuclei using KEK isotope separation system,”J. Phys. Conf. Ser. 1643, 012138 (2020).
M. Mazzocco, Y. Hirayama, S. C. Jeong, H. Miyatake, Y. X. Watanabe, et al., “Direct processes for the systems 7 Be, 8 B + 208 Pb at
Coulomb barrier energies,” J. Phys. Conf. Ser. 1643, 012096 (2020).
J. W. Hwang, H. Miyatake, Y. X. Watanabe, et al., “Performance of the OEDO beamline,” J. Phys. Conf. Ser. 1643, 012035 (2020).

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VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 54 (2021)

Presentations[International Conferences/Workshops]
Michiharu Wada (invited), “MRTOF development and status @ RIKEN-RIBF,” NUSTAR Annual Meeting, Online, February 24, 2021.

[Domestic Conferences/Workshops]
Marco Rosenbusch (口頭発表), “New mass measurements of exotic nuclides by the first MRTOF setup at BigRIPS/RIKEN,” 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
飯村俊 (口頭発表), 「理研 BigRIPS SLOWRI における RF カーペットガスセルの開発—オンライン実験と質量測定—」, 日本物学会第 76 回年次大会, オンライン開催, 2021 年 3 月 12–15 日.
渡邉裕 (招待講演), 「KISS, MRTOF を用いた核分光実験の現状」, 令和 2 年度専門研究会「短寿命 RI を用いた核分光と核物性研
究 VII」, オンライン開催, 2021 年 1 月 15 日.
平山賀一, 「KISS での核分光実験/Nuclear spectroscopy at KISS」, 2020 年度核データ研究会, 埼玉県和光市, 2020 年 11 月 26–27 日.
Toshitaka Niwase (口頭発表), “First direct mass measurement of superheavy nuclide via MRTOF-MS +α-TOF,” KEK Student Day,
Online, November 17, 2020.
和田道治 (招待講演), 「何故, 如何に原子質量を測るのか?」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020 年 9 月 14–17 日.
渡邉寛 (口頭発表), 「非軸対称変形核 192 Re の基底状態からのベータ崩壊」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020
年 9 月 14–17 日.
飯村俊 (口頭発表), 「理研 BigRIPS SLOWRI における RF カーペットガスセルの開発」, 日本物理学会 2020 年秋季大会, オンライン開催, 2020 年 9 月 14–17 日.

[Seminars]
Peter Schury (invited), “Use of multi-reflection time-of-flight mass spectrometry to study SHE,” Virtual SHE seminars, Online, January
12, 2021.

Press Releases「中性子過剰なタンタル核異性体で探る原子核形状の多様性—原子核構造の研究から重元素合成の起源天体解明に迫る—」, 2020年 11 月 11 日. https://www.kek.jp/ja/press/ipns_pr20201111-2/ .

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VII. APPENDICESVII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

List of Symposia & Workshops (April 2020―March 2021)
RNC
1

SAMURAI International Collaboration Workshop 2020
https://indico2.riken.jp/event/3429/

onlineSep. 1–4

2

SSRI-PNS Collaboration Meeting 2020
https://indico2.riken.jp/event/3452/

onlineSep. 3–4

3

RIBF Users Meeting 2020
https://indico2.riken.jp/event/3443/

onlineSep. 8–10

4International Technical Safety Forum（ITSF2020）

RIBF Conf. Hall, RIKEN
Wako Campus

Nov. 9–13

5

Symposium on Nuclear Data 2020

RIBF Conf. Hall, RIKEN
Wako Campus

Nov. 26–27

6

第 17 回高エネルギーQCD・核子構造勉強会
https://indico2.riken.jp/event/3623/

onlineFeb. 5

7Spin Symposium

Kunibiki Messe, Shimane

Feb. 23–24

8

The 8th Asia-Pacific Conference on Few-Body Problems in Physics (APFB2020)

Kanazawa Bunka Hall

Mar. 1–5

onlineSep. 3–4

KEK
1

SSRI-PNS Collaboration meeting 2020
https://research.kek.jp/group/wnsc/ssri-pns/

2

第 11 回停止・低速 RI ビームを用いた核分光研究会（京大複合研専門研究会 「短寿命 RI を用いた核分光と核online
物性研究 VI」 同時開催）
http://www.rri.kyoto-u.ac.jp/NBMP/kurpro/R1pro.pdf- 361 -

Jan. 16–17

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

List of Seminars (April 2020―March 2021)
Nuclear Physics Monthly Colloquium
Not held in 2020

RIBF Nuclear Physics Seminar
1

Sidong Chen
(U. Hong Kong)

Structural evolution of neutron-rich calcium isotopes
https://indico2.riken.jp/event/3365/

May 26

2

Junki Tanaka(RIKEN)

Experimental evidence of α clustering in the ground state of stable heavy nuclei
https://indico2.riken.jp/event/3441/

Jul. 28

３

Wataru Horiuchi(Hokkaido University)

Utility of antiproton- and deuteron-scattering for studies of unstable nuclei
https://indico2.riken.jp/event/3639/

Jan. 21

4

Takumi Yamaga(RIKEN)

�NN
Observation of an anti-kaon nuclear bound state, K
https://indico2.riken.jp/event/3650/

5

Masaomi Tanaka(Kyushu U.)

Swelling of doubly magic 48Ca core in Ca isotopes beyond N = 28
https://indico2.riken.jp/event/3640/

Feb. 96

Heather Crawford(Berkeley Lab)First spectroscopy in 40Mg and the implications for structure near the dripline
https://indico2.riken.jp/event/3669/

Feb. 16

Seminar by Each Laboratory
Nuclear Science and Transmutation Research Division1

Jens Lassen(TRIUMF)

Nuclear Spectroscopy Lab. Seminar (Quantum Beam Application Research B03 Seminar)
Radioactive ion beams at TRIUMF using the resonance ionization laser ion source
https://indico2.riken.jp/event/3469/"

Sep. 2

2

Yutaka Shikano(Keio U.)

Nuclear Spectroscopy Lab. Seminar (Quantum Beam Application Research B03 Seminar)
Fundamentals and applications of weak measurement (弱測定の基礎と応用)
https://indico2.riken.jp/event/3662/

Feb. 4High Energy Astrophysics Lab. Seminar → http://astro.riken.jp/wordpress/?page_id=65

Subnuclear System Research Division
1

Eduardo Grossi(SBU)

Nuclear Physics & RIKEN Theory Seminar (virtual)
A mode by mode approach to heavy ion collision

Apr. 102

Debasish Banerjee(PNNL)

Nuclear Physics & RIKEN Theory Seminar (virtual)
The Color Glass Condensate density matrix: Lindblad evolution, entanglement entropy andWigner functional

Apr. 17

3

Jianwei Qiu(Jefferson Lab)

Nuclear Physics & RIKEN Theory Seminar (virtual)
3D tomography of parton motion inside hadrons

Apr. 24

4

Andrea Signori(Jlab)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Transverse momentum distributions: predictive power and flavor structure

May 1

5

R. Loganayagam(ICTS)

Nuclear Physics & RIKEN Theory Seminar (virtual)Open QFTs from holography

May 8

6

Emilie Huffman(Perimeter Inst)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Quantum criticality in fermion-bag inspired Hamiltonian lattice field theories

May 15- 362 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

7

Fabian Rennecke(BNL)

BNL RIKEN Seminar (virtual)
From anomalous correlations to dark matter: the effects of higher topological charge

May 218

Sourendu Gupta(TIFR)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Why is chemical freezeout at the chiral cross over temperature?

May 22

9

Yuta Sekino(RIKEN)

SNP Seminar
Mesoscopic spin transport between strongly interacting Fermi gases

May 2710

Masafumi Fukuma(Kyoto U.)

BNL RIKEN Seminar (virtual)
Sign problem in Monte Carlo simulations and the tempered Lefschetz thimble method

May 28

11

Luchang Jin(U. Conn)

Nuclear Physics & RIKEN Theory Seminar (virtual)First-principles calculation of electroweak box diagrams from lattice QCD

May 2912

Phiala Shanahan(MIT)

BNL RIKEN Seminar (virtual)
From quarks to nuclei: machine learning the structure of matterJun. 413

Alexander Soloviev(Stony Brook U.)

BNL RIKEN Seminar (virtual)
Transport and hydrodynamics in the chiral limit

Jun. 11

14

Gregory Soyez(IPhT)

Nuclear Physics & RIKEN Theory Seminar (virtual)
The quest for precision across scales

Jun. 1215

Shao-Feng Wu(Shanghai U., Yangzhou
U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Deep learning black hole metrics from shear viscosity

Jun. 18

16

Akihiko Monnai(JWU)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Prompt, pre-equilibrium, and thermal photons in relativistic nuclear collisions

Jun. 19

17

Munekazu Horikoshi(Osaka City U.)

SNP Seminar
Ultracold AMO experiment for quantum few-body and many-bodyJun. 22

18

Mamiya Kawaguchi(Fudan U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Nonperturbative quark-flavor breaking at chiral crossover criticality in hot QCD

Jun. 25

19

Lukas Weih
(ITP)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Postmerger gravitational-wave signatures of phase transitions in binary mergers

Jun. 26

20

Chris Greene(Purdue U.)

SNP Seminar
Linking Efimov physics, few-fermion universality, and the 3n and 4n systems

Jul. 1021

Andreas Ipp(TU)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Transverse momentum broadening in the Glasma

Jul. 1022

Asmita Mukherjee
(IIT)

23

Xiang Gao,
(BNL)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Probing Gluon Sivers Function in J/ψ production at the Electron-Ion Collider

24

Gregory Johnson,(NCSU)

25

C.-J. David Lin(National Chiao-Tung U.)

26

Zhangbo Kang
(UCLA)

27

Sinya Aoki
(YITP)

28

29

Nuclear Physics & RIKEN Theory Seminar (virtual)
Parton distribution functions inside hardron from lattice QCD

Nuclear Physics & RIKEN Theory Seminar (virtual)
Universal location of the Yang-Lee edge singularity in O(N) theories

Nuclear Physics & RIKEN Theory Seminar (virtual)
Massive Thirring model in 1+1 dimensions from matrix product states
Nuclear Physics & RIKEN Theory Seminar (virtual)
QCD factorization and resummation in the small-x regime

Jul. 17

Jul. 23

Jul. 24

Jul. 30

Jul. 31

Nuclear Physics & RIKEN Theory Seminar (virtual)
Conserved charges in general relativity and its implication on Oppenheimer-Volkoff equation

Aug. 7

Vincent Cheung(UC Davis)

Nuclear Physics & RIKEN Theory Seminar (virtual）
Quarkonium production and polarization in the color evaporation model

Aug. 13

Mithat Unsal(NCSU)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Strongly coupled QFT dynamics via TQFT coupling

Aug. 21- 363 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

30

Pasi Huovinen(Inst. Physics Belgrade)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Does eta/s depend on EoS?

Aug. 2831

Peng Zhang (Renmin
University, Beijing)

SNP Seminar
Laser control of two-body processes in nuclear and cold-atom systems

Sep. 332

Hans-Werner Hammer(TU Darmstadt)

SNP Seminar
The lifetime of the hypertriton

Sep. 333

Bowen Xiao
(CCNU)

Nuclear Physics & RIKEN Theory Seminar (virtual)
The curious story of the photon

Sep. 434

Vajravelu Ravindran

Nuclear Physics & RIKEN Theory Seminar (virtual)
On next to soft corrections to Inclusive cross sections at the colliders

Sep. 1135

Jesse Stryker(U. Washington)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Loop, string, and hadron dynamics in SU(2) Hamiltonian lattice gauge theories

Sep. 18

36

Christian Bierlich(Lund U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
New applications of dipole Monte Carlo implementations

Sep. 25

37

Tetsuo Hyodo
(TMU)

38

Aleksi Vuorinen(U. Helsinki)

SNP SeminarΛ (1405) as a hadronic molecule39

Sep. 28

Nuclear Physics & RIKEN Theory Seminar (virtual)
Quark matter cores in massive neutron stars

Oct. 2

Yiannis Makris(INFN)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Groomed and energy-energy correlation event shapes in DIS

Oct. 940

Ying Zhang(Tianjin U., RIKEN)SNP Seminar
Farewell seminars of Ying Zhang and Jinniu Hu
Lambda halo structure of C, B and Zr isotopes

Oct. 14

41

Jinniu Hu(Nankai U., RIKEN)SNP Seminar
Farewell seminars of Ying Zhang and Jinniu Hu
The mass limit of a neutron star

Oct. 1442

Chien Yeah Seng
(U. Bon)

Nuclear Physics & RIKEN Theory Seminar (virtual)
The quest for explaining the top-row CKM unitarity deficit

Oct. 16

43

Volker Koch
(LBNL)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Correlations, fluctuations and the QCD phase diagram

Oct. 23

44

Servaas Kokkelmans(TU/e)SNP Seminar
Elastic few-body interactions in dilute Bose gases

Oct. 2745

Isobel Kolbe,(U. Washington)

BNL RIKEN Seminar (virtual)
Matter and radiation in the fragmentation region of heavy-ion collisions

Nov. 546

Dr Xin An(NC State U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Deterministic fluctuating hydrodynamics and relativistic heavy-ion collisions

Nov. 647

Viljami Leino,(TUM)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Heavy quark diffusion constant from the lattice"

Nov. 1348

Heng-Tong DING(CCNU)BNL RIKEN Seminar (virtual)
Correlated Dirac eigenvalues and axial anomaly in chiral symmetric QCD

Nov. 19

49

Thomas Cohen(Maryland U.)

50

Shun Uchino(JAEA)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Surprises in large Nc Thermodynamics

51

Teppei Kitahara(Nagoya U.)

52

Aleksey Cherman
Nuclear Physics & RIKEN Theory Seminar (virtual)(U. Minnesota Twin Cities) Higgs-confinement phase transitions with fundamental representation matter

Nov. 20

SNP Seminar
Atomtronics

Nov. 26

BNL RIKEN Seminar (virtual)
Electroweak effective field theory from massive scattering amplitudes

Dec. 3- 364 -

Dec. 4

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

53

Hidenori Fukaya(Osaka U.)

BNL RIKEN Seminar (virtual)
Study of axial U(1) anomaly at high temperature with lattice chiral fermionsDec. 1054

Shin Inouye(Osaka City U.)

SNP Seminar
Measurement of the variation of electron-to-proton mass ratio using ultracold molecules
produced from laser-cooled atoms

Dec. 11

55

Salazar Wong
(Stony Brook U.)

BNL RIKEN Seminar (virtual)
Gluon imaging using azimuthal correlations in diffractive scattering at the Electron-Ion
ColliderDec. 17

56

Srimoyee Sen(Iowa State U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Quarkyonic model for neutron stars

Dec. 18

57

Yair Mulian(Jyvaskyla U.)

BNL RIKEN Seminar (virtual)
Toward full result for next-to-leading order dijet production in proton-nucleus collisions

Jan. 7

58

Pavel Kovtun(U. Victoria)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Relativistic Navier-Stokes equations

Jan. 859

Heng-Tong DING(CCNU)BNL RIKEN Seminar (virtual)
Correlated Dirac eigenvalues and axial anomaly in chiral symmetric QCD

Jan. 1460

Yuichiro Mori
(KEK)

61

Martin Gonzalez-Alonso(U. Valencia)

BNL RIKEN Seminar (virtual)
Weak value and CP violation measurement

62

Jan. 21High-Energy Physics & RIKEN Theory Seminar (virtual)
EFT constraints from neutrino oscillation data

Jan. 21Tokuro Fukui(Kyoto U.)

SNP Seminar
Many-body effective models with chiral interaction

Jan. 2263

Varun Vaidya(MIT)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Effective Field theory for jet substructure in heavy ion collisions

Jan. 2264

Ian Balitsky(JLab, ODU)

65

James Halverson(Northeastern)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Gauge-invariant TMD factorization for Drell-Yan hadronic tensor at small x

66

Jan. 29

BNL RIKEN Seminar (virtual)
A triangle of influence: Bringing together physics, pure mathematics, and computer scienceFeb. 4

Andrew Hanlon(BNL)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Two-baryon interactions from lattice QCD

Feb. 5

67

Philipp Scior(BNL)

BNL RIKEN Seminar (virtual)
Spectral functions from the real-time functional renormalization groupFeb. 18

68

Michael Ramsey-Musolf(U Mass)

High-Energy Physics & RIKEN Theory Seminar (virtual)Was there an electroweak phase transition?"

Feb. 19

69

Konrad Tywoniuk(U. Bergen)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Energy loss of QCD jets in heavy-ion collisions

Feb. 2470

Shimpei Endo
(Tohoku U.)

SNP Seminar
Are atoms spherical?

Feb. 25

71

Yusuke Tanimura(Tohoku U.)

SNP Seminar
How to visualize nuclear many-body correlations?

Feb. 25

72

Mattia Bruno(CERN)

High-Energy Physics & RIKEN Theory Seminar (virtual)
Variations on the Maiani-Testa approach and the inverse problem

Feb. 25

73

Peter Schweitzer,(Connecticut U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
The D-term and forces inside hadrons

Feb. 26

74

Paul Caucal(BNL)

BNL RIKEN Seminar (virtual)
Pinning down pQCD modifications of in-medium jet evolution with substructure observables

Mar. 475

Andreas von Manteuffel(MSU)

High-Energy Physics & RIKEN Theory Seminar (virtual)
Mixed EW-QCD two-loop amplitudes for Drell-Yan dilepton production

Mar. 4- 365 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

76

Yizhuang Liu(U. Regensburg)

Nuclear Physics & RIKEN Theory Seminar (virtual）
Quantum anomalous energy and proton mass decomposition

Mar. 5

77

Yuber Perez-Gonzalez(Fermilab, Northwestern)

High-Energy Physics & RIKEN Theory Seminar (virtual)
Neutrinos from Primordial Black Holes, an opera in two acts

Mar. 1178

Raoul Rontsch(CERN)

High-Energy Physics & RIKEN Theory Seminar (virtual)
Mixed QCD-electroweak corrections to vector boson production and their impact on the Wmass measurement by Raoul Rontsch (CERN)"

Mar. 18

79

Yukinari Sumino(Tohoku U.)

Nuclear Physics & RIKEN Theory Seminar (virtual)
Understanding heavy quark-antiquark system by perturbative QCD

Mar. 1980

Yifei Niu
(Lanzhou U.)

SNP Seminar
Beyond mean-field description of nuclear weak interaction processes in stars

Mar. 25

QHP Seminar → http://ribf.riken.jp/QHP/seminar.html
SNP Seminar → http://snp.riken.jp/seminar.html
RIKEN/BNL Lunch Time Talk → https://www.bnl.gov/events/- 366 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

Events (April 2020—March 2021)
RNC
Jul. 1–13

The 14th Industrial Program Advisory Committee (In-PAC)

Jul. 16

The 26th RBRC Management Steering Committee (MSC)

Jul. 30

The 15th Industrial Program Advisory Committee (In-PAC)

Aug.20The 27th RBRC Management Steering Committee (MSC)

Dec.14 – 16

The 21st Program Advisory Committee for Nuclear Physics Experiments at RI Beam Factory (NP-PAC)

Dec.19 –Jan.13

The 16th Industrial Program Advisory Committee (In-PAC)

Jan.13 –20

The 20th Program Advisory Committee for Materials and Life Science Researches at RIKEN Nishina Center (ML-PAC)

CNS
Aug. 17–21

19th CNS International Summer School (CNSSS20)
https://indico2.cns.s.u-tokyo.ac.jp/event/102/- 367 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

Press Releases (April 2020−March 2021)
RNC
May. 15

Extending the southern shore of the island of inversion to 28F

T. Uesaka, H. Otsu, Spin isospin Laboratory,
SAMURAI TeamMay. 28“A single proton can make a heck of a difference”—Exploring the limits of existence of neutron-rich nuclei—

T. T. Leung, Spin isospin Laboratory

Jun. 18

Halo structure of the neutron-dripline nucleus 19B

H. Otsu, K. Yoneda, SAMURAI Team, Spin
isospin Laboratory

Jun. 23

Left-right asymmetry of π meson production from proton collisions—New discovery reveals the origin of particle production—

Y. Goto, Radiation Laboratory

Jul. 21High-temperature short-range order in Mn3RhSi

I. Watanabe, Meson Science Laboratory

Aug. 7

Lithum diffusion in LiMnPO4 detected with μ±SR

K. Ishida, Meson Science Laboratory

Aug. 21

Discovery of "two-neutron halo" in fulorine-29—Magicity loss at 20 and emergence of halo structure—

H. Sakurai, P. Doornenbal, Radioactive
Isotope Physics Laboratory

Sep. 16

Mapping of a new deformation region around 62Ti

T. Uesaka, Spin isospin Laboratory

Nov. 5The impact of nuclear shape on the emergence of the neutron dripline

T. Otsuka, H. Ueno, Nuclear Spectroscopy
Laboratory

Nov. 5

Dirac Fermion Kinetics in 3D curved graphene

T. Naito, Quantum Hadron Physics Laboratory

Nov. 11

Properties of 187Ta revealed through isomeric decay

M. Mukai, Nuclear Spectroscopy Laboratory

Dec. 17

A new discovery on dineutron correlation in neutron halo of Lithium-11—Evidence of surface localization of the dineutron found—

T. Uesaka, Spin isospin Laboratory

Jan. 13

Broadband high-energy resolution hard X-ray spectroscopy using transition edge
sensors at Spring-8.

T. Tamagawa, T. Isobe, High Energy
Astrophysics Laboratory, Radioactive
Isotope Physics Laboratory

Jan. 15

Larger-than-usual rotifer fed to juvenile tuna, successfully produced—"Mega-rotifer" created by a heavy ion beam—

T. Abe, K. Tsuneizumi, Ion Beam Breeding
Team

Jan. 21

Alpha particles found at the surface of nuclei of Sn—Unraveling the mystery of the structure of neutron stars and the process of alphadecay—

T. Uesaka, Spin isospin Laboratory

Feb. 18

Co-precipitation behavior of single atoms of rutherfordium in basic solutions

H. Haba, Nuclear Chemistry Research Team

Mar. 22

Prediction of a new quantum phase "mixed bubble" at ultra-low temperatures.
—Discovery of quantum partial miscibility between miscibility and immiscibility—

P. Naidon, Strangeness Nuclear Physics
Laboratory

KEK
Nov. 11

中性子過剰なタンタル核異性体で探る原子核形状の多様性

P. M. Walker, Y. Hirayama—原子核構造の研究から重元素合成の起源天体解明に迫る—
https://www.kek.jp/ja/press/ipns_pr20201111-2/- 368 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

List of Preprints (April 2020―March 2021)
RIKEN NC-NP
Not Applicable

RIKEN NC-AC
Not Applicable

RIKEN MP
Not Applicable

RIKEN QHP
418

Partial wave decomposition on the lattice and its applications to the HAL QCD method

T. Miyamoto et al.

419

Superfluid phase transitions and effects of thermal pairing fluctuations in asymmetric nuclear
matter

H. Tajima et al.

420

Non-relativistic expansion of single-nucleon Dirac equation: Comparison between
Foldy-Wouthuysen transformation and similarity renormalization group

Y. Guo, H. Liang

421

Coulomb energy density functionals for nuclear systems: Recent studies of coulomb exchange
and correlation functionals

T. Naito et al.

422

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy
Y. Yerin et al.
gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

423
424

Probing Ω-Ω and p-Ω dibaryons with femtoscopic correlations in relativistic heavy-ion collisions
How to improve functionals in density functional theory? —Formalism and benchmark
calculation—

K. Morita et al.
T. Naito et al.

425

Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners Y. Yamaguchi et al.

426

Theoretical study of Nb isotope productions by muon capture reaction on 100Mo

M. Ciccarelli et al.

427

Spin-dipole mode in a trapped Fermi gas near unitarity

H. Tajima et al.

428

Relativistic density functional theory with finite-light-speed correction for the Coulombinteraction: a non-relativistic-reduction-based approach

T. Naito et al.

429
430

E. Hiyama et al.

Possible lightest Ξ hypernucleus with modern ΞN interactions

Lattice QCD and baryon-baryon interactions: HAL QCD method

S. Aoki, T. Doi

431

Study of the pion-pion scatterings with a combination of all-to-all propagators and the HAL QCD
Y. Akahosh et al.
method432

Exploring the QCD phase diagram at finite density by the complex Langevim method on a 163 ×
S. Tsutsui
32 lattice433

Emergent discrete 3-form symmetry and domain walls

434

BCS-BEC crossover and pairing fluctuations in a two-band superfluid/superconductor: a T-matrix
H. Tajima et al.
approach

Y. Hidaka et al.

ΛΛ and NΞ interactions from Lattice QCD near the physical point

K. Sasaki et al.

Non-relativistic expansion of Dirac equation with spherical scalar and vector potentials byreconstituted Foldy-Wouthuysen transformation

Y. Guo, H. Liang

437

Collisional dynamics of polaronic clouds immersed in a Fermi sea

H. Tajima et al.

438

Towards an ab initio covariant density functional theory for nuclear structure

S. Shen et al.

435
436

- 369 -

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)
439

Predictions of nuclear beta-decay half-lives with machine learning and their impact on r-process
Z. M. Niu et al.
nucleosynthesis

440

Goldstino spectrum in an ultracold Bose-Fermi mixture with explicitly broken supersymmetry

H. Tajima et al.

441

Quantum kinetic theory for spin transport: general formalism for collisional effects

D.-L. Yang et al.

442

Measurement of the Decays Λc → Σππ at BelleM. Berger et al

443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470

First evidence for cos 2β > 0 and resolution of the Cabibbo-Kobayashi-Maskawa quark-mixing
unitarity triangle ambiguity

Measurement of cos 2β in B0 → D (*)h0 with D → KS0π +π – decays by a combined time-dependent
Dalitz plot analysis of BABAR and Belle data

I. Adachi et al
I. Adachi et al

Search for the rare decay of B+ → ℓ +νℓ γ with improved hadronic tagging

M. Gelbet et al

Measurement of time-dependent CP violation in B 0 → KS0π 0π 0 decays

Y. Yusa et al

Observation of transverse Λ/𝛬𝛬𝛬𝛬̅ hyperon polarization in e + + e – annihilation at BelleY. Guan et al

Search for a light CP-odd Higgs boson and low-mass dark matter at the Belle experiment

I.S. Seong et al,

Search for CP violation with kinematic asymmetries in the D 0 → K +K –π + + π – decay

J. B. Kim et al

Observation of Ξ (1620)0 and evidence for Ξ (1690)0 in 𝛯𝛯𝛯𝛯𝑐𝑐𝑐𝑐+ → 𝛯𝛯𝛯𝛯− 𝜋𝜋𝜋𝜋 + 𝜋𝜋𝜋𝜋 + decays

M. Sumihama et alFirst Measurements of absolute branching fractions of the Ξ c+ baryon at BelleY. B. Li et al

Search for the B → Y (4260)K, Y (4260) → J/ψπ +π – decays

R. Garg et al

Measurements of isospin asymmetry and difference of direct CP asymmetries in inclusive B → Xsγ
S. Watanuki et al
decaysObservation of B + → p𝛬𝛬𝛬𝛬̅K +K – and B + → 𝑝𝑝𝑝𝑝̅ΛK +K +Measurements of branching fraction and direct CP asymmetry in 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵± → 𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝜋𝜋𝜋𝜋 ±±→ 𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝐾𝐾𝐾𝐾 ±P.-C. Lu et al

and a search forA. B. Kaliyar et al
B. Pal et al

Evidence for the decay 𝐵𝐵𝐵𝐵0 → 𝑝𝑝𝑝𝑝̅𝑝𝑝𝑝𝑝𝜋𝜋𝜋𝜋 0Search for 𝛸𝛸𝛸𝛸(3872) and 𝛸𝛸𝛸𝛸(3915) decay into χc1 in B decays at BelleV. Bhardwaj et al

Measurement of branching fraction and final-state asymmetry for the 𝐵𝐵𝐵𝐵�0 → 𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝐾𝐾𝐾𝐾 ∓ 𝜋𝜋𝜋𝜋 ± decay

Y.-T. Lai et al

Search for 𝐵𝐵𝐵𝐵0 → 𝛸𝛸𝛸𝛸(3872)𝛾𝛾𝛾𝛾

P.-C. Chou et al

Search for Ω (2012) → KΞ (1530) → KπΞ at Belle

S. Jia et al

Observation of 𝜏𝜏𝜏𝜏 − → 𝜋𝜋𝜋𝜋 − 𝜈𝜈𝜈𝜈𝜏𝜏𝜏𝜏 𝑒𝑒𝑒𝑒 + 𝑒𝑒𝑒𝑒 − and search for 𝜏𝜏𝜏𝜏 − → 𝜋𝜋𝜋𝜋 − 𝜈𝜈𝜈𝜈𝜏𝜏𝜏𝜏 𝜇𝜇𝜇𝜇+ 𝜇𝜇𝜇𝜇−

Y. Jin et al

Transverse momentum dependent production cross sections of charged pions, kaons and protons
R. Seidl et al
produced in inclusive e+e ‒ annihilation at √𝑠𝑠𝑠𝑠 = 10.58 GeV
Evidence for 𝐵𝐵𝐵𝐵+ → hc𝐾𝐾𝐾𝐾 + and observation of 𝜂𝜂𝜂𝜂𝑐𝑐𝑐𝑐 (2𝑆𝑆𝑆𝑆) → 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝̅ 𝜋𝜋𝜋𝜋 + 𝜋𝜋𝜋𝜋 −K. Chilikin et alFirst measurements of absolute branching fractions of the 𝛯𝛯𝛯𝛯𝑐𝑐𝑐𝑐+ baryon at BelleY. B. Li et al

Measurement of the CKM matrix element |Vcb| from 𝐵𝐵𝐵𝐵0 → 𝐷𝐷𝐷𝐷∗− ℓ+ 𝜈𝜈𝜈𝜈ℓ at BelleE. Waheed et alFirst measurement of the CKM angle φ3 with 𝐵𝐵𝐵𝐵± → 𝐷𝐷𝐷𝐷(𝐾𝐾𝐾𝐾𝑠𝑠𝑠𝑠0 𝜋𝜋𝜋𝜋 + 𝜋𝜋𝜋𝜋 − 𝜋𝜋𝜋𝜋 0 )𝐾𝐾𝐾𝐾 ± decays

P. K. Resmi et al

Observation of a new structure near 10.75 GeV in the energy dependence of the 𝑒𝑒𝑒𝑒 + 𝑒𝑒𝑒𝑒 − →𝛶𝛶𝛶𝛶(𝑛𝑛𝑛𝑛𝑆𝑆𝑆𝑆)𝜋𝜋𝜋𝜋 + 𝜋𝜋𝜋𝜋 − (𝑛𝑛𝑛𝑛 = 1, 2, 3) cross sections
Azimuthal asymmetries of back-to-back 𝜋𝜋𝜋𝜋 ± − (𝜋𝜋𝜋𝜋 0 , 𝜂𝜂𝜂𝜂, 𝜋𝜋𝜋𝜋 ± ) pairs in 𝑒𝑒𝑒𝑒 + 𝑒𝑒𝑒𝑒 − annihilation′0

Measurements of the branching fractions ℬ(𝐵𝐵𝐵𝐵 → 𝛬𝛬𝛬𝛬𝑐𝑐𝑐𝑐̅ 𝛯𝛯𝛯𝛯𝑐𝑐𝑐𝑐 ), ℬ(𝐵𝐵𝐵𝐵 → 𝛬𝛬𝛬𝛬𝑐𝑐𝑐𝑐̅ 𝛯𝛯𝛯𝛯𝑐𝑐𝑐𝑐 (2645) ) and ℬ(𝐵𝐵𝐵𝐵 →𝛬𝛬𝛬𝛬𝑐𝑐𝑐𝑐̅ 𝛯𝛯𝛯𝛯𝑐𝑐𝑐𝑐 (2790)0 )−−0Observation of a vector charmoniumlike state in 𝑒𝑒𝑒𝑒 + 𝑒𝑒𝑒𝑒 − → 𝐷𝐷𝐷𝐷𝑠𝑠𝑠𝑠+ 𝐷𝐷𝐷𝐷𝑠𝑠𝑠𝑠1 (2356)− + 𝑐𝑐𝑐𝑐. 𝑐𝑐𝑐𝑐.

- 370 -−

R. Mizuk et al
H. Li et al
Y. Li et al
S. Jia et al

VII. APPENDICESRIKEN Accel. Prog. Rep. 54 (2021)

471

Measurement of the integrated luminosity of the Phase 2 data of the Belle II experiment

F. Abudinén et al472

Mesoscopic spin transport between strongly interacting Fermi gases

Y. Sekino et al473

Effects of finite nucleon size, vacuum polarization, and electromagnetic spin-orbit interaction on
T. Naito et al
nuclear binding energies and radii in spherical nuclei
The HAL QCD potential in I = 1 ππ system with the ρ meson bound state

Y. Akahoshi et al

Analysis for Lorentzian conformal field theories through sine-square deformation

X. Liu, T. Tada

476

Hybrid quantum annealing via molecular dynamics

H. Irie et al477

S-wave kaon-nucleon potentials with all-to-all propagators in the HAL QCD method

K. Murakami et al478

Low-dimensional fluctuations and pseudogap in Gaudin-Yang Fermi gases

H. Tajima et al479

Complex Langevin calculations in QCD at finite density

Y. Ito et al480

Are atoms spherical?

T. Naito et al

481

Second and fourth moments of the charge density a Consistent description for cluster dynamics
T. Naito et al
and single-particle correlation nd neutron-skin thickness of atomic nuclei

474
475

482

Ab initio construction of the energy density functional for electron systems with thefunctional-renormalization-group-aided density functional theory

T. Yokota, T. Naito

483

Dirac Fermion kinetics in three-dimensionally curved graphene

Y. Tanabe et al

485

Consistent description for cluster dynamics and single-particle correlation

T. Naito et al487

Field theoretical aspects of one-dimensional Bose and Fermi gases with contact interactions

N. Itagaki, T. Naito

488

Second order chiral kinetic theory under gravity and antiparallel charge-energy flow

Y. Sekino, Y. Nishida489

Tensor effects on shell-structure evolution in N = 82 isotones and Z = 50 isotopes in the relativistic
T, Hayata et al
Hartree-Fock theory
Exploring effects of tensor force and its strength via neutron drops

Z. Wang et al491

Most charming dibaryon near unitarity

Z. Wang et al492

Nuclear energy density functionals from empirical ground-state densities

Y. Lyu et al

493

Optical spin transport in ultracold quantum gases

G. Accorto et al490

CNS-REP99

CNS Annual Report 2019

H. Nagahama

Nishina Center Preprint server (not including Partner Institution) can be found at
http://nishina-preprints.riken.jp/- 371 -

理化学研究所
埼玉県 和光市 広沢
RIKEN 2021-45
ISSN 0289-842X