Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 52 (2019)

Interplay between nuclear shell evolution and shape deformation
revealed by magnetic moment of 75 Cu†
Y. Ichikawa,∗1 H. Nishibata,∗1,∗2 Y. Tsunoda,∗3 A. Takamine,∗1 K. Imamura,∗1,∗4 T. Fujita,∗1,∗2 T. Sato,∗1,∗5S. Momiyama,∗6 Y. Shimizu,∗1 D. S. Ahn,∗1 K. Asahi,∗1,∗5 H. Baba,∗1 D. L. Balabanski,∗1,∗7 F. Boulay,∗1,∗8,∗9J. M. Daugas,∗1,∗9 T. Egami,∗10 N. Fukuda,∗1 C. Funayama,∗5 T. Furukawa,∗11 G. Georgiev,∗12A. Gladkov,∗1,∗13 N. Inabe,∗1 Y. Ishibashi,∗1,∗14 T. Kawaguchi,∗10 T. Kawamura,∗2 Y. Kobayashi,∗1,∗15S. Kojima,∗5 A. Kusoglu,∗7,∗12,∗16 I. Mukul,∗17 M. Niikura,∗6 T. Nishizaka,∗10 A. Odahara,∗2 Y. Ohtomo,∗1,∗5T. Otsuka,∗1,∗3,∗6,∗18 D. Ralet,∗12 G. S. Simpson,∗19 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 L. C. Tao,∗1,∗20Y. Togano,∗1,∗5 D. Tominaga,∗10 H. Ueno,∗1 H. Yamazaki,∗1 and X. F. Yang∗183.0

Magnetic moment [ μN ]Exotic nuclei are characterized by a number of excessneutrons (or protons) relative to stable nuclei. Theirshell structure, which represents single-particle motion
in a nucleus, may vary owing to nuclear force andexcess neutrons, in a phenomenon called shell evolution. This eﬀect could be counterbalanced by collectivemodes causing deformations of the nuclear surface. We
studied the interplay between shell evolution and shapedeformation by focusing on the magnetic moment of
an isomeric state of the neutron-rich nucleus 75 Cu,1)
where low-lying states of the Cu isotopes exhibit an
intriguing behavior involving the shell evolution.2–4)
The magnetic moment measurement was carried out
at the BigRIPS at RIBF. Spin alignment as large as
30% was achieved in the isomeric state of 75 Cu by
a scheme of two-step projectile fragmentation with atechnique of momentum-dispersion matching,5) incorporating an angular-momentum selecting proton removal from 76 Zn. The magnetic moment was determined using the time-diﬀerential perturbed angular
distribution (TDPAD) method. Owing to the highspin alignment realized by the reﬁned two-step scheme,
the observed oscillation for the 66.2-keV γ rays in theTDPAD spectrum had a signiﬁcance greater than 5σ.
The magnetic moment of the 66.2-keV isomer with spinparity 3/2− was determined to be µ = 1.40(6) µN for
the ﬁrst time.

μ(π p3/2)
3/2−

2.0μ(π f5/2)

This work
1.00

Exp. 3/2−
Exp. 5/2−
Calc. 3/2−
Calc. 5/2−

5/2−

69

Cu

71

Cu

Cu

7375

Cu

Cu

7779

Cu

Fig. 1. Systematics of magnetic moments for odd-A Cu
isotopes. Filled and open circles represent experimental
data for 3/2− and 5/2− states, respectively. Filled red
circle represents the result obtained in this work. Solidgreen and blue lines represent MCSM calculations for
3/2− and 5/2− states, respectively, with 20 ≤ (N, Z) ≤56 model space.6) µ(πp3/2 ) and µ(πf5/2 ) denote theproton Schmidt values for p3/2 and f5/2 , respectively.

The magnetic moment, thus obtained, demonstrated
a considerable deviation from the Schmidt value, µ =3.05 µN , for the p3/2 orbital. Figure 1 shows the systematics of magnetic moments of the 3/2− and 5/2−states, where deviation from the Schmidt values appears to be maximal at 75 Cu. The analysis of themagnetic moment with the help of Monte Carlo shellmodel (MCSM) calculations6) reveals that the trendof the deviation corresponds to the eﬀect of core excitation and the low-lying states in 75 Cu are, to a large
extent, of a single-particle nature on top of a correlated 74 Ni core, elucidating the crucial role of the shellevolution even in the presence of collective mode.

†Condensed from the letter in Nat. Phys. 15, 321 (2019)
RIKEN Nishina Center∗2 Department of Physics, Osaka University∗3 Center for Nuclear Study, University of Tokyo∗4 Department of Physics, Meiji University∗5 Department of Physics, Tokyo Institute of Technology∗6 Department of Physics, University of Tokyo∗7 ELI-NP, IFIN-HH∗8 GANIL, CEA/DSM-CNRS/IN2P3∗9 CEA, DAM, DIF∗10 Department of Advanced Sciences, Hosei University∗11 Department of Physics, Tokyo Metropolitan University∗12 CSNSM, CNRS/IN2P3, Université Pris-Sud∗13 Department of Physics, Kyungpook National University∗14 Department of Physics, University of Tsukuba∗15 Department of Informatics and Engineering, University ofElectro-Communications∗16 Department of Physics, Istanbul University∗17 Department of Particle Physics, Weizmann Institute∗18 Intsituut voor Kern-en Srralingsfysica, K. U. Leuven∗19 LPSC, Université Grenoble Alpes, CNRS/IN2P3∗20 School of Physics, Peking University∗1References
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3) S. Franchoo et al., Phys. Rev. Lett. 81, 3100 (1998).
4) K. T. Flanagan et al., Phys. Rev. Lett. 103, 142501(2009).
5) Y. Ichikawa et al., Nat. Phys. 8, 918 (2012).
6) Y. Tsunoda et al., Phys. Rev. C 89, 031301(R) (2014).

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