Coexistence of Prolate and Oblate Shapes in ^98Sr Nuclei Using IBM2

The properties of the low-lying states and the shape coexistence in ^98Sr 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, it is found that the calculated energy levels and the B(E2) transition strengths agree with the experimental data perfectly. Particularly, the second 0^+ state, which is associated with the shape coexistence phenomenon and has the lowest energy E(0^+_2) among all known even–even nuclei, is reproduced very well. The behavior of the calculated quadrupole shape invariants is consistent with the experimental results.