Shape Coexistence at Zero Spin in 64Ni Driven by the Monopole Tensor Interaction

TL;DR

This study explores the complex coexistence of different nuclear shapes in 64Ni at zero spin, revealing the significant role of the monopole tensor interaction in shape evolution and energy landscape.

Contribution

It provides the first observation of a prolate 2+ state above a 0+ excitation in Ni isotopes and demonstrates the impact of the monopole interaction on shape coexistence.

Findings

Identification of multiple 0+ and 2+ states below 4.5 MeV in 64Ni.

Observation of a high-energy prolate 0+ excitation at 3463 keV.

Monte Carlo shell model explains the complex shape coexistence and the influence of the monopole interaction.

Abstract

The low-spin structure of the semimagic 64Ni nucleus has been considerably expanded: combining four experiments, several 0+ and 2+ 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 0+ excitation is located at a surprisingly high energy (3463 keV), with a collective 2+ state 286 keV 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.