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

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, $\hat{I}{´}_{\text{N}}$, 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 ${\hat{I}}^3-{\hat{I}}^3$ coincidences. The second $2^{+}$ state was also observed in the scattering on the Au target and the $B(E2;2_2^{+}\to 0_1^{+})$ 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.

12 pages, 11 figures, accepted European Physical Journal A