The role of triaxiality for the coexistence and evolution of shapes in light krypton isotopes

The structure of low-lying states in the light krypton isotopes 72Kr, 74Kr, and 76Kr has been studied with the finite-range Gogny D1S effective interaction via Hartree-Fock-Bogolyubov based calculations within a configuration-mixing formalism treating axial and triaxial quadrupole deformations. The good overall agreement with the experimental low-lying excitation spectra and matrix elements supports the shape coexistence scenario and a transition of the ground-state shape from oblate in 72Kr to prolate in 76Kr. The triaxial degree of freedom is shown to be crucial to reproduce the experimental data in general and the inversion of the oblate and prolate configurations in particular.