VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 55 (2022)

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 ﬂight
mass 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 atthe 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 FY2021, masses on more than 100
radioactive isotopes from the ﬁssion source have been measured and the analysis is going on. 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 cellcombined with MRTOF. In FY2020, we have successfully performed the on-line commissioning, symbiotically by using RIs providedfor 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. In FY2021, Mass measurement in the vicinity of double magic nucleus of 78 Ni
was successfully performed, which was approved at NP-PAC. As the result, masses of 74 Ni and 75 Ni have been measured for the ﬁrsttime. The analysis is going on.
Parallelly, the on-line commissioning for PALIS has been continuously performed at F2 of BigRIPS. In FY2021, the extraction ofα-emitter Ac Isotopes without a laser ionization has been conﬁrmed after the ion guide from PALIS gas cell. We will try to the laser
ionization in FY2022.

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, and 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. In FY2021,ﬁrst experiment approved in NP-PAC has been performed, which has aimed the mass measurement in the vicinity of the double magicnucleus of 78 Ni. As the result, masses of 74 Ni and 75 Ni have been measured with high precision less than 20 keV for the ﬁrst time.
(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 have- 265 -VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 55 (2022)

been successfully measured. Among them, 11 isotope masses improve the present uncertainty signiﬁcantly and 3 isotope masses havebeen measured for the ﬁrst time. In FY2021, thanks to the ﬁne tuning and the improved data analysis, the mass resolving power has
reached up to ∼1 M in maximum for A/q ∼ 80/1+. Also, to eliminate contaminant ions, a TOF mass ﬁlter has been installed inside theMRTOF, which has been working well.
(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 theoptical 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 theNuclear 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 FY2021,
we have conﬁrmed the transportation of ions of interest at the downstream of an ion guide behind the gas pipe using α-emitting Ac
isotopes provided with BigRIPS. Also, we have found a lot of contaminant ions from the gas cell, which are originated from impurities
in the gas. To reduce the inﬂuence of such contaminant, a quadrupole mass ﬁlter will be installed at the downstream of the ion guide.
In FY2022, an on-line test for resonant laser ionization is planned.

MembersTeam Leader
Hironobu ISHIYAMA
Senior Research Scientist
Takao KOJIMA
Research Scientist
Aiko TAKAMINETechnical Scientist
Tetsu SONODA
Expert Technician
Takeshi MAIE
Junior Research Associate
Shun IIMURA
Visiting Scientists
Hideki IIMURA (JAEA)
Minoru TANIGAKI (Kyoto Univ.)

Hideki TOMITA (Nagoya Univ.)

Student Trainee
Shun IIMURA- 266 -VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 55 (2022)

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).
T. Niwase, M. Wada, P. Schury, P. Brionnet, S. D. Chen, T. Hashimoto, H. Haba, Y. Hirayama, D. S. Hou, S. Iimura, H. Ishiyama,
S. Ishizawa, Y. Ito, D. Kaji, S. Kimura, J. Liu, H. Miyatake, J. Y. Moon, K. Morimoto, K. Morita, D. Nagae, M. Rosenbusch,
A. Takamine, T. Tanaka, Y. X. Watanabe, H. Wollnik, W. Xian, and S. X. Yan, “α-decay-correlated mass measurement of 206, 207g, m Rausing an α-TOF detector equipped multireﬂection time-of-ﬂight mass spectrograph system,” Phys. Rev. C 104, 044617 (2021).
P. Schury, T. Niwase, M. Wada, P. Brionnet, S. Chen, T. Hashimoto, H. Haba, Y. Hirayama, D. S. Hou, S. Iimura, H. Ishiyama, S. Ishizawa,
Y. Ito, D. Kaji, S. Kimura, H. Koura, J. J. Liu, H. Miyatake, J. -Y. Moon, K. Morimoto, K. Morita, D. Nagae, M. Rosenbusch,
A. Takamine, Y. X. Watanabe, H. Wollnik, W. Xian, and S. X. Yan, “First high-precision direct determination of the atomic mass of asuperheavy nuclide,” Phys. Rev. C 104, L021304 (2021).

[Proceeding]
S. Kimura, Y. Ito, D. Kaji, P. Schury, M. Wada, H. Haba, T. Hashimoto, Y. Hirayama, M. MacCormick, H. Miyatake, J. Y. Moon,
K. Morimoto, M. Mukai, I. Murray, A. Ozawa, M. Rosenbusch, H. Schatz, A. Takamine, T. Tanaka, Y. X. Watanabe, and H. Wollnik,“High precision mass measurements of intermediate-mass neutron-deﬁcient nuclei via MRTOF-MS,” JPS Conf. Proc. 35, 011005(2021).

Presentations[International Conferences/Workshops]
S. Iimura (poster), A. Takamine, M. Rosenbusch, M. Wada, S. Chen, D. Hou, J. Liu, W. Xian, S. Yan, P. Schury, S. Kimura, A. Niwase,Y. Ito, S. Sonoda, T. Kojima, Y. Watanabe, S. Naimi, S. Michimasa, S. Nishimura, A. Odahara, and H. Ishiyama, “Mass measurementof neutron rich nuclei of Sc, Ti, and V region using the new ZD-MRTOF system,” The 16th International Symposium on Nuclei in theCosmos (NIC-XVI), Online, China, September 21–25, 2021.
M. Rosenbusch (oral), S. Chen, W. Xian, S. Yan, A. Takamine, D. Hou, S. Iimura, M. Wada, P. Schury, Y. Hirayama, H. Ishiyama, Y. Ito,
S. Kimura, T. M. Kojima, J. Liu, S. Michimasa, H. Miyatake, S. Naimi, S. Nishimura, T. Niwase, T. Sonoda, Y. X. Watanabe, andH. Wollnik, “The new high-precision MR-TOF mass spectrograph at the ZeroDegree spectrometer of BigRIPS,” The 16th International
Symposium on Nuclei in the Cosmos (NIC-XVI), Online, China, September 21–25, 2021.
M. Rosenbusch (invited), “The new high-precision MR-TOF mass spectrograph at the ZeroDegree spectrometer of BigRIPS,” RIBF Users
Meeting 2021, Wako, Japan, Online, September 7–9, 2021.
H. Ishiyama (invited), “Present status of SLOWRI,” SSRI-PNS Collaboration Meeting 2021, Online, September 2–3, 2021.

[Domestic Conferences/Workshops]
富田英生 (口頭発表), V. Sonnenschein, 服部浩也, 山口穂乃花, 井坪暁, 寺林稜平, 島添健次, 園田哲, 石山博恒, K. Wendt, 「理研 RI
ビームファクトリー—低速 RI ビーム施設におけるレーザー共鳴イオン化イオン源の開発」, 日本原子力学会 2022 年春季大会,
オンライン, 2022 年 3 月 16–18 日.
飯村俊 (口頭発表), 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, S. Naimi, 道正新一郎, 西村俊二, 小田原厚子, 石山博恒, “Mass measurement of neutron rich nucleiof Sc, Ti, and V region using the new ZD-MRTOF system,” 日本物理学会 2021 年度秋季大会, オンライン, 2021 年 9 月 14–17 日.
W. Xian (口頭発表), S. Chen, M. Rosenbusch, S. Yan, D. Hou, S. Iimura, A. Takamine, M. Wada, J. Liu, P. Schur, S. Kimura, T. Niwase,Y. Ito, T. Sonoda, T. M. Kojima, Y. X. Watanabe, S. Naimi, S. Michimasa, S. Nishimura, H. Ishiyama, and H. Wollnik, “New massmeasurements of neutron-rich nuclei of Ge, As, and Se, and an accuracy study of the new ZD-MRTOF system,” 日本物理学会 2021
年度秋季大会, オンライン, 2021 年 9 月 14–17 日.
D. Hou (口頭発表), A. Takamine, S. Iimura, M. Rosenbusch, S. Chen, W. Xian, S. Yan, M. Wada, P. Schury, Y. Hirayama, H. Ishiyama,
Y. Ito, S. Kimura, J. Liu, S. Michimasa, H. Miyatake, S. Naimi, S. Nishimura, T. Niwase, Y. X. Watanabe, and H. Wollnik, “Massmeasurement in the neutron-rich Mo region using the new ZD-MRTOF system,” 日本物理学会 2021 年度秋季大会, オンライン, 2021
年 9 月 14–17 日.
M. Rosenbusch (口頭発表), S. Chen, W. Xian, S. Yan, A. Takamine, D. Hou, S. Iimura, M. Wada, P. Schury, Y. Hirayama, H. Ishiyama,Y. Ito, S. Kimura, T. M. Kojima, J. Liu, S. Michimasa, H. Miyatake, S. Naimi, S. Nishimura, T. Niwase, T. Sonoda, Y. X. Watanabe,and H. Wollnik, “New technologies for multi-reﬂection time-of-ﬂight mass spectrometry at BigRIPS,” 日本物理学会 2021 年度秋季大会, オンライン, 2021 年 9 月 14–17 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, 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, and S. X. Yan,「超重核 257 Db の直接質量測定」, 日本物理学会 2021 年度秋季大会, オンライン, 2021 年 9 月
14–17 日.
服部浩也 (口頭発表), V. Sonnenschein, 山口穂乃花, 井坪暁, 寺林稜平, 島添健次, 園田哲, 石山博恒, K. Wendt, 富田英生, 「半導体レーザー直接励起 Ti:Sapphire レーザーを用いた高分解能共鳴イオン化分光法の開発」, 日本物理学会 2021 年度秋季大会, オンライン, 2021 年 9 月 14–17 日.

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