Interplay between nuclear shell evolution and shape deformation revealed by the magnetic moment of $^{75}$Cu

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 (1, 2) , J.M. Daugas (1) , T. Egami , N. Fukuda , C. Funayama , T. Furukawa , G. Georgiev (3) , N. Inabe , Y. Ishibashi , T. Kawaguchi , T. Kawamura , Y. Kobayashi , S. Kojima , A. Kusoglu (3) , I. Mukul , M. Niikura , T. Nishizaka , A. Odahara , Y. Ohtomo , T. Otsuka , D. Ralet (3) , G.S. Simpson (4) , T. Sumikama , H. Suzuki , H. Takeda , L.C. Tao , Y. Togano , D. Tominaga , H. Ueno , H. Yamazaki , X.F. Yang , A. Gladkov

1 DAM - Direction des Applications Militaires
2 GANIL - Grand Accélérateur National d'Ions Lourds
3 CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière
4 LPSC - Laboratoire de Physique Subatomique et de Cosmologie

Exotic nuclei are characterized by having a number of neutrons (or protons) in excess relative to stable nuclei. Their shell structure, which represents single-particle motion in a nucleus 1$^{,}$2 , may vary due to nuclear force and excess neutrons 3$^{–}$6 , in a phenomenon called shell evolution 7 . This effect could be counterbalanced by collective modes causing deformations of the nuclear surface 8 . Here, we study the interplay between shell evolution and shape deformation by focusing on the magnetic moment of an isomeric state of the neutron-rich nucleus$^{75}$Cu. We measure the magnetic moment using highly spin-controlled rare-isotope beams and achieve large spin alignment via a two-step reaction scheme 9 that incorporates an angular-momentum-selecting nucleon removal. By combining our experiments with numerical simulations of many-fermion correlations, we find that the low-lying states in$^{75}$Cu are, to a large extent, of single-particle nature on top of a correlated$^{74}$Ni core. We elucidate the crucial role of shell evolution even in the presence of the collective mode, and within the same framework we consider whether and how the double magicity of the$^{78}$Ni nucleus is restored, which is also of keen interest from the perspective of nucleosynthesis in explosive stellar processes.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

Y. Ichikawa, H. Nishibata, Y. Tsunoda, A. Takamine, K. Imamura, et al.. Interplay between nuclear shell evolution and shape deformation revealed by the magnetic moment of $^{75}$Cu. Nature Physics, 2019, 15 (4), pp.321-325. ⟨10.1038/s41567-018-0410-7⟩. ⟨hal-01909269⟩