RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

75 75Competition
betweenshapeandshell
clariﬁed
Competition
betweenshapeand
shell
inin
CuCu
clarifiedbythe
thenovelnovel
magnetic moment measurement

Y. Ichikawa,∗1 H. Nishibata,∗1,∗2 A. Takamine,∗1 K. Imamura,∗1,∗3 T. Fujita,∗1,∗2 T. Sato,∗1,∗4 S. Momiyama,∗5Y. Shimizu,∗1 D. S. Ahn,∗1 K. Asahi,∗1,∗4 H. Baba,∗1 D. L. Balabanski,∗1,∗6 F. Boulay,∗1,∗7,∗8 J. M. Daugas,∗1,∗8T. Egami,∗9 N. Fukuda,∗1 C. Funayama,∗4 T. Furukawa,∗10 G. Georgiev,∗11 A. Gladkov,∗1,∗12 N. Inabe,∗1Y. Ishibashi,∗1,∗13 T. Kawaguchi,∗9 T. Kawamura,∗2 Y. Kobayashi,∗1,∗14 S. Kojima,∗4 A. Kusoglu,∗6,∗11,∗15I. Mukul,∗16 M. Niikura,∗5 T. Nishizaka,∗9 A. Odahara,∗2 Y. Ohtomo,∗1,∗4 T. Otsuka,∗5 D. Ralet,∗11G. S. Simpson,∗17 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 L. C. Tao,∗1,∗18 Y. Togano,∗4 D. Tominaga,∗9Y. Tsunoda,∗19 H. Ueno,∗1 H. Yamazaki,∗1 and X. F. Yang∗200.6

The structure of a nucleus is a result of competitionbetween the shell evolution and the shape eﬀects, suchas surface vibration and deformation. In this study, wedemonstrate the precision analysis of the competition
by focusing on an isomeric state of a neutron-rich 75 Cu
nucleus1,2) , where an intriguing shell evolution along
the Cu isotopic chain has been reported3–6) , throughits nuclear magnetic moment.
The experiment of the magnetic moment measurement was conducted at the BigRIPS at RIBF, taking advantage of a spin-aligned RI beam obtained ina scheme of two-step projectile fragmentation with atechnique of momentum-dispersion matching, recently
established7) . The 75 Cu beam with spin alignment
reaching 30% was produced from a primary beam of238
U via an intermediate product 76 Zn. For the measurement of the magnetic moment, a method of timediﬀerential perturbed angular distribution (TDPAD)
was employed. Owing to the high spin alignment realized with the two-step scheme, the oscillation in theR(t) ratio which represents the change of anisotropy of
γ-ray emission synchronized with the Larmor precession was observed for 66.2-keV γ rays with signiﬁcancelarger than 5σ, as shown in Fig. 1. The spin-parity ofthe 66.2-keV level was ﬁrmly ﬁxed to be 3/2− . The
magnetic moment of the 66.2-keV isomer was determined for the ﬁrst time to be μ = 1.40(6)μN .
The magnetic moment thus obtained shows a consid-

0.4

R(t)

0.2
0-0.2-0.4
-0.6

0100

200

300

400

500

600

700

800

Time (ns)Fig. 1. R(t) ratio for the 66.2-keV γ ray observed in theTDPAD measurement. The solid line represents thetheoretical R(t) after ﬁtting to the experimental R(t).

erable deviation from the Schmidt value, μ = 3.05μN ,for the p3/2 orbital. The analysis of the magnetic moment with a help of state-of-the-art shell-model calculations8) reveals that this state contains a considerable
fraction of the mixed f5/2 conﬁguration in addition tothe primary p3/2 conﬁguration. The same holds true
for the 5/2− ground state, except that the roles playedby the two orbitals are interchanged. Through the decomposition of the total angular momentum into thespins and the orbital angular momenta of the protonand the neutron, the admixing conﬁguration is foundto be brought to this state by a neutron quadrupole
excitation in the g9/2 orbital which may also play anessential role in the emergence of exotic phenomena inthis extremely neutron-rich region.

∗1RIKEN Nishina Center
Department of Physics, Osaka University∗3 Department of Physics, Meiji University∗4 Department of Physics, Tokyo Institute of Technology∗5 Department of Physics, University of Tokyo∗6 ELI-NP, IFIN-HH∗7 GANIL, CEA/DSM-CNRS/IN2P3∗8 CEA, DAM, DIF∗9 Department of Advanced Sciences, Hosei University∗10 Department of Physics, Tokyo Metropolitan University∗11 CSNSM, CNRS/IN2P3, Université Pris-Sud∗12 Department of Physics, Kyungpook National University∗13 Department of Physics, University of Tsukuba∗14 Department of Informatics and Engineering, University ofElectro-Communications∗15 Department of Physics, Istanbul University∗16 Department of Particle Physics, Weizmann Institute∗17 LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3∗18 School of Physics, Peking University∗19 Center for Nuclear Study, University of Tokyo∗20 Intsituut voor Kern-en Srralingsfysica, K. U. Leuven∗2References1) J. M. Daugas et al.: Phys. Rev. C 81, 034304 (2010).
2) C. Petrone et al.: Phys. Rev. C 94, 024319 (2016).
3) S. Franchoo et al.: Phys. Rev. Lett. 81, 3100 (1998).
4) K. T. Flanagan et al.: Phys. Rev. Lett. 103, 142501(2009).
5) T. Otsuka et al.: Phys. Rev. Lett. 95, 232502 (2005).
6) M. Honma et al.: Phys. Rev. C 80, 064323 (2009).
7) Y. Ichikawa et al.: Nature Phys. 8, 918 (2012).
8) Y. Tsunoda et al.: Phys. Rev. C 89, 031301(R) (2014).

- 60 -