Description of the shape coexistence in neutron-deficient 74,76Kr with IBM2

The shape deformation and shape coexistence in 74,76Kr isotopes are investigated within the framework of the proton-neutron interacting boson model (IBM2). By considering the relative energy of the d proton boson to be different from that of the neutron boson, the low-lying energy spectrum is in good agreement with experimental results both qualitatively and quantitatively. In particular, the low-lying 02+ states associated with the shape-coexistence phenomenon are reproduced quite well. The calculated key sensitive quantities of B(E2) transition branch ratios are fairly consistent with the experimental data except for R4. The predicated deformation parameter is very similar for the ground states in 74Kr and 76Kr, showing good agreement with the experimental result, and the calculated deformation parameter for the second 0+ state in 74Kr is close to the experimental data. The calculated results of the triaxiality parameter indicated an almost purely prolate shape for the ground state of 76Kr and a mostly prolate shape with a little triaxiality for the ground state of 74Kr. The calculations also show an oblate triaxial shape for the second 0+ state in 76Kr and maximum triaxiality for the second 0+ state in 74Kr. These results confirm the importance of the triaxial deformation for the description of such shape coexistence.