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

The shape deformation and shape coexistence in Kr-74,Kr-76 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 0(2)(+) 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 R-4. The predicated deformation parameter is very similar for the ground states in Kr-74 and Kr-76, showing good agreement with the experimental result, and the calculated deformation parameter for the second 0(+) state in Kr-74 is close to the experimental data. The calculated results of the triaxiality parameter indicated an almost purely prolate shape for the ground state of Kr-76 and a mostly prolate shape with a little triaxiality for the ground state of Kr-74. The calculations also show an oblate triaxial shape for the second 0(+) state in Kr-76 and maximum triaxiality for the second 0(+) state in Kr-74. These results confirm the importance of the triaxial deformation for the description of such shape coexistence.