Shape Coexistence at Zero Spin in ^{64}Ni Driven by the Monopole Tensor Interaction.

N Mărginean,S Toma,D Seweryniak,C Costache,A Oprea,Y Tsunoda,Krishichayan Krishichayan,P Chowdhury,C Petrone,L Stan,U Köster,K Auranen,T Lauritsen,P Mutti,A Mitu,B Fornal,M Ciemała,S Ziliani,S Călinescu,D Rhodes,J Li,C Michelagnoli,S Zhu,C Porzio,D Filipescu,M Krzysiek,J Dudouet,R Mărginean,S Pascu,A Ionescu,C Mihai,J Henderson,F Kandzia,A Bracco,D Schumann,S Ujeniuc,C Sotty,M Barani,I Gheorghe,S Fracassetti,J Wu,S Leoni,C Clisu,S Bottoni,M Jentschel,M Boromiza,A Gade,D Cline,G Korschinek,P C Bender ,A D Ayangeakaa ,Irina Dinescu ,Takaharu Otsuka ,F G Kondev ,I M Harca ,R V F Janssens ,Chuanbin Wu ,Y H Kim ,R Lică ,Michele Sferrazza ,A B Hayes ,H L Crawford ,Rareş Şuvăilă ,E A Maugeri ,A M Forney ,W B Walters ,F C L Crespi ,David Little ,A Negreţ ,A Turturică ,Cristina Niță ,Sanna Stolze ,M P Carpenter ,R Mihai ,Christopher M Campbell ,Nicoleta Mihaela Florea ,N Cieplicka-Oryńczak ,Ł W Iskra ,Adina Olacel

doi:10.1103/physrevlett.125.102502

Abstract

The low-spin structure of the semimagic ^{64}Ni nucleus has been considerably expanded: combining four experiments, several 0^{+} and 2^{+} excited states were identified below 4.5MeV, and their properties established. The MonteCarlo shell model accounts for the results and unveils an unexpectedly complex landscape of coexisting shapes: a prolate 0^{+} excitation is located at a surprisingly high energy (3463keV), with a collective 2^{+} state 286keV above it, the first such observation in Ni isotopes. The evolution in excitation energy of the prolate minimum across the neutron N=40 subshell gap highlights the impact of the monopole interaction and its variation in strength with N.

Highlights

The low-spin structure of the semimagic 64Ni nucleus has been considerably expanded: combining four experiments, several 0þ and 2þ excited states were identified below 4.5 MeV, and their properties established
The Monte Carlo shell model accounts for the results and unveils an unexpectedly complex landscape of coexisting shapes: a prolate 0þ excitation is located at a surprisingly high energy (3463 keV), with a collective 2þ state 286 keV above it, the first such observation in Ni isotopes
The appearance of ellipsoidal deformation is a realization of this effect with specific superpositions of spherical singleparticle states (e.g., Nilsson model [2]) induced by deformed mean potentials [3,4], or by quadrupole correlations [5,6], highlighting the interplay between single-particle states and collective modes

Summary

Introduction

The low-spin structure of the semimagic 64Ni nucleus has been considerably expanded: combining four experiments, several 0þ and 2þ excited states were identified below 4.5 MeV, and their properties established. Neutron-rich even 28Ni isotopes are a noteworthy example of shape coexistence: 68Ni exhibits a spherical ground state, while the 1605-keV, 0þ2 and 2511-keV, 0þ3 levels are understood as oblate and prolate excitations [11,16,17,18,19,20,21].

Results

Conclusion