Shape coexistence in ⁷⁶Se within the neutron–proton interacting boson model

Abstract

We have investigated the low-lying energy spectrum and electromagnetic transition strengths in even-even $^{76}$Se using the proton-neutron interacting boson model (IBM-2). The theoretical calculation for the energy levels and $E2$ and $M1$ transition strengths is in good agreement with the experimental data. Especially, the excitation energy and $E2$ transition of $0^+_2$ state, which is intimately associated with shape coexistence, can be well reproduced. The analysis on low-lying states and some key structure indicators indicates that there is a coexistence between spherical shape and $\gamma$-soft shape in $^{76}$Se.

Shapes and structure for the lowest states of the 42,44Ca isotopes

“…Recently, a proxy-SU(3) model [11][12][13] has been used for a better localization of these regions, conventionally called islands of shape coexistence [14,15]. Algebraic approaches, as the Interacting Boson Model (IBM) [16][17][18][19] and the Partial Dynamical Symmetry (PDS) [20], proved to be also appropriate tools in addressing this behavior in nuclei [21][22][23][24][25], especially in heavy mass region where the dimension of the SM configuration space is prohibitive. However, taking into account that mainly the discussion is about shapes of the lowest collective states of the same nucleus, perhaps the natural choice in the description of the shape coexistence and mixing phenomena would be the Bohr-Mottelson Model (BMM) [26], where the nucleus is considered as a liquid drop which vibrates and oscillates around spherical and deformed shapes.…”