Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

First Spectroscopic study of 56 Ca
S. Chen,∗1,∗2,∗3 F. Browne,∗3 J. Lee,∗2 P. Doornenbal,∗3 A. Obertelli,∗4,∗3,∗5 H. Baba,∗3 D. Calvet,∗4F. Château,∗4 N. Chiga,∗3 A. Corsi,∗4 M. L. Cortés,∗3 A. Delbart,∗4 J-M. Gheller,∗4 A. Giganon,∗4A. Gillibert,∗4 C. Hilaire,∗4 T. Isobe,∗3 T. Kobayashi,∗6 Y. Kubota,∗3,∗7 V. Lapoux,∗4 H. N. Liu,∗4,∗13T. Motobayashi,∗3 I. Murray,∗3,∗8 H. Otsu,∗3 V. Panin,∗3 N. Paul,∗4 W. Rodriguez,∗9 H. Sakurai,∗3,∗10M. Sasano,∗3 D. Steppenbeck,∗3 L. Stuhl,∗7 Y. L. Sun,∗4 Y. Togano,∗11 T. Uesaka,∗3 K. Wimmer,∗10K. Yoneda,∗3 N. Achouri,∗12 O. Aktas,∗13 T. Aumann,∗5 L. X. Chung,∗14 F. Flavigny,∗8 S. Franchoo,∗8I. Gasparic,∗15 R.-B. Gerst,∗16 J. Gibelin,∗12 K. I. Hahn,∗17 D. Kim,∗17 T. Koiwai,∗10 Y. Kondo,∗18
P. Koseoglou,∗5,∗15 C. Lehr,∗5 B. D. Linh,∗14 T. Lokotko,∗2 M. MacCormick,∗8 K. Moschner,∗16T. Nakamura,∗18 S. Y. Park,∗17 D. Rossi,∗15 E. Sahin,∗19 D. Sohler,∗20 P-A. Söderström,∗5 S. Takeuchi,∗18H. Toernqvist,∗15 V. Vaquero,∗21 V. Wagner,∗5 S. Wang,∗22 V. Werner,∗5 X. Xu,∗2 H. Yamada,∗18 D. Yan,∗22Z. Yang,∗3 M. Yasuda,∗18 and L. Zanetti∗5The ﬁrst measurement of low-lying excited states of
Ca was performed as part of the third SEASTAR1)(Shell Evolution And Search for Two-plus energies At
the RIBF) campaign in May 2017. In a simple shellmodel description, this nucleus has two neutrons inthe f5/2 orbital outside the closed (sub)-shell nucleus
54Ca.2) The location of its 2+
1 energy gives a measurement of the diﬀerence between 0+ and 2+ two-bodymatrix elements in ν(f5/2 )2 , which is of importance tounderstand the nature of the very neutron-rich, potential closed (sub)-shell nucleus 60 Ca. Theoretical predictions of this energy level vary from 0.5 to 2 MeV;
therefore, its experimental determination is desirable.
A 70 Zn beam accelerated to 345 MeV/nucleon impinged on a 10-mm thick 9 Be primary target withan average intensity of ∼160 pnA at the entranceof the BigRIPS separator to produce the radioactive
secondary beam. BigRIPS was tuned to select andidentify particles of interest via the measurement ofBρ, ∆E and ToF by using standard beamline detectors. The particle identiﬁcation of BigRIPS is shown inFig. 1. The average production rate of 57 Sc nuclei was
13.6 s−1 . To induce knock-out reactions populating
low-lying states in 56 Ca, the secondary beam impinged

BigRIPS PID

SAMURAI PID

56

2457

2256

ZScZ

2224

20

2018182.66 2.68

2.7

2.72 2.74 2.76 2.78

A/QCa2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85

A/Q

Fig. 1. BigRIPS particle identification (left) and SAMURAI particle identification for 57 Sc secondary beam(right). The 57 Sc(p, 2p)56 Ca channel is selected.

on the 150-mm-length LH2 target of the MINOS device.3) The beam energy in front of the secondary target was measured to be ∼250 MeV/nucleon. The upgraded DALI24) array, which contains 226 NaI(Tl) detectors, was used to measure gamma rays emitted fromthe in-ﬂight particles. The reaction residues were identiﬁed using the SAMURAI spectrometer.5) The identiﬁcation of the residues from the 57 Sc secondary beamis also shown in Fig. 1, from which the 56 Ca isotopes
are selected.
Currently, the gamma-ray spectrum in coincidencewith the 57 Sc(p, 2p)56 Ca reaction channel is underanalysis. This preliminary energy spectrum shows a+candidate peak of the 2+
1 → 01 transition observed at
an energy consistent with the aforementioned range oftheoretical predictions. The spectra coincident withother reaction channels, which produce 56 Ca, are also
under analysis.

∗1School of Physics, Peking University
Department of Physics, The University of Hong Kong
∗3 RIKEN Nishina Center∗4 IRFU, CEA, Université Paris-Saclay∗5 Institut für Kernphysik, Technische Universität Darmstadt∗6 Department of Physics, Tohoku University∗7 Center for Nuclear Study, the University of Tokyo∗8 IPN Orsay, CNRS, Univ. Paris Sud, Univ. Paris Saclay∗9 Universidad Nacional de Colombia∗10 Department of Physics, University of Tokyo∗11 Department of Physics, Rikkyo University∗12 LPC Caen, ENSICAEN, Université de Caen
∗13 Department of Physics, Royal Institute of Technology∗14 Institute for Nuclear Science & Technology, VINATOM∗15 GSI Helmholtzzentrum Darmstadt∗16 Institut für Kernphysik, Universität zu Köln∗17 Ewha Womans University∗18 Department of Physics, Tokyo Institute of Technology∗19 Department of Physics, University of Oslo
∗20 MTA Atomki∗21 Instituto de Estructura de la Materia, CSIC
∗22 Institute of Modern Physics, Chinese Academy of Sciences∗2References
1) P. Doornenbal, A. Obertelli, RIKEN Proposal for Scientific Program (2013).
2) D. Steppenbeck et al., Nature (London) 502, 207(2013).
3) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).
4) I. Murray et al., In this report.
5) T. Kobayashi et al., Nucl. Instrum. Methods B 317, 294(2013).

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