Re-examination of nuclear structure properties and shape co-existence of nuclei around A ∼ 70

Abstract

We re-examine the nuclear structure properties of waiting point nuclei around A ∼ 70 using the interacting boson model-1 (IBM-1) and the relativistic mean field (RMF) model. Effective density-dependent meson-exchange functional (DD-ME2) and density-dependent point-coupling functional (DD-PC1) were used for the RMF calculations. We calculated the energy levels, the geometric shapes, binding and separation energies of nucleons and quadrupole deformation parameters (${\beta }_2$). The shape co-existence phenomena in A ∼ 70 nuclei (⁶⁸Se, ⁷⁰Se, ⁷⁰Br, ⁷⁰Kr, ⁷²Kr, ⁷⁴Kr, ⁷⁴Rb and ⁷⁴Sr) was later investigated. Spherical and deformed shapes of the selected waiting point nuclei were computed using the IBM-1 and RMF models, respectively. The proton-neutron quasiparticle random phase approximation (pn-QRPA) model was used to calculate β-decay properties (Gamow-Teller strength distributions, β-decay half-lives and branching ratios) of selected nuclei as a function of ${\beta }_2$. The results revealed a significant variation in calculated half-lives and Gamow-Teller strength distributions as the shape parameter was changed. The ${\beta }_2$ computed via DD-ME2 functional resulted in half-lives in best agreement with the measured data.