Shape coexistence revealed in the $N=Z$ isotope $^{72}$Kr through inelastic scattering

TL;DR

This study investigates shape coexistence in the $^{72}$Kr nucleus through inelastic scattering, revealing new excited states and providing evidence for oblate-prolate shape coexistence supported by experimental data and theoretical calculations.

Contribution

The paper reports the first observation of non-yrast $2^+$ and $4^+$ states and a new octupole $3^-$ candidate in $^{72}$Kr, and demonstrates shape coexistence using experimental and theoretical methods.

Findings

Observation of new non-yrast $2^+$ and $4^+$ states.

First determination of $B(E2)$ value for the second $2^+$ state.

Evidence for oblate-prolate shape coexistence in $^{72}$Kr.

Abstract

The $N=Z=36$ nucleus $^{72}$Kr has been studied by inelastic scattering at intermediate energies. Two targets, $^{9}$Be and $^{197}$Au, were used to extract the nuclear deformation length, $\delta_\text{N}$, and the reduced $E2$ transition probability, $B(E2)$. The previously unknown non-yrast $2^+$ and $4^+$ states as well as a new candidate for the octupole $3^-$ state have been observed in the scattering on the Be target and placed in the level scheme based on $\gamma-\gamma$ coincidences. The second $2^+$ state was also observed in the scattering on the Au target and the $B(E2;\;2^+_2 \rightarrow 0^+_1)$ value could be determined for the first time. Analyzing the results in terms of a two-band mixing model shows clear evidence for a oblate-prolate shape coexistence and can be explained by a shape change from an oblate ground state to prolate deformed yrast band from the first $2^+$ state. This interpretation is corroborated by beyond mean field calculations using the Gogny D1S interaction.