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

12 pags., 11 figs., 2 tabs.
The N= Z= 36 nucleus Kr has been studied by inelastic scattering at intermediate energies. Two targets, Be and Au, were used to extract the nuclear deformation length, δ, 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 γ- γ coincidences. The second 2 state was also observed in the scattering on the Au target and the B(E2;22+→01+) 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.
We would like to thank the RIKEN accelerator and BigRIPS teams for providing the high intensity beams. We thank T. Furumoto for providing us with the optical potentials and A. Moro for giving access to an unpublished version of the FRESCO code. This work has been supported by UK STFC under Grant numbers ST/L005727/1 and ST/P003885/1, the Spanish Ministerio de Economía y Competitividad under Grants FPA2011-24553, FPA2014-52823-C2- 1-P, and PGC2018-094583-B-I00, the Program Severo Ochoa (SEV2014-0398), the European Research Council through the ERC Grant No. MINOS-258567, NKFIH (NN128072), and by the ÚNKP-19-4- DE-65 New National Excellence Program of the Ministry of Human Capacities of Hungary. G. K. acknowledges support from the János Bolyai research fellowship of the Hungarian Academy of Sciences. K. W. acknowledges the support from the Spanish Ministerio de Economía y Competitividad RYC-2017-22007.