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

Area of Science:

• Nuclear Physics
• Atomic and Molecular Physics

Background:

• The low-spin structure of the semimagic ^{64}Ni nucleus is crucial for understanding nuclear shell evolution.
• Previous studies have provided limited information on the excited states below 4.5 MeV.

Purpose of the Study:

• To experimentally identify and characterize new low-spin excited states in ^{64}Ni.
• To investigate the coexistence of nuclear shapes and the influence of shell effects.

Main Methods:

• Combining data from four distinct experiments.
• Spectroscopic analysis to establish properties of excited states.
• Application of the Monte Carlo shell model for theoretical interpretation.

Main Results:

• Several new 0^{+} and 2^{+} excited states were identified below 4.5 MeV.
• A prolate 0^{+} excited state was observed at 3463 keV, with a collective 2^{+} state 286 keV above it.
• The Monte Carlo shell model successfully reproduced the experimental findings, revealing complex coexisting shapes.

Conclusions:

• The ^{64}Ni nucleus exhibits a surprisingly complex landscape of coexisting shapes.
• The evolution of the prolate minimum across the N=40 subshell gap is significantly influenced by monopole interactions.
• This study provides the first observation of a collective 2^{+} state associated with a prolate minimum in Ni isotopes.