γ-ray spectroscopy of low-lying yrast and non-yrast states in neutron- rich 94,95,96Kr

We report on γ -ray spectroscopy of low-lying excited states in the neutron-rich 94, 95, 96Kr isotopes measured as part of the “Shell Evolution And Search for Two-plus energies At RIBF” (SEASTAR) campaign at the RIKEN Radioactive Isotope Beam Factory. Excited yrast and non-yrast states were observed, and half-lives extracted via GEANT4 simulations. In 94, 96Kr candidates for the 3− 1 state were identified. For 95Kr, the prompt SEASTAR data were combined with delayed spectroscopic data measured with the EURICA array to observe transitions on top of the known (7/2)+ isomer at a level energy of 195.5(3) keV. The comparison of the new experimental results with five-dimensional collective Hamiltonian (5DCH) and mapped interacting boson model (IBM) calculations, both using the Gogny D1M interaction, could suggest oblate-prolate shape coexistence already in 96Kr.