Sensitivity analysis of ${\hat{I}}^2$-decay half-life predictions for Ge, As, Zr and Mo nuclei within the mapped interacting boson model

Abstract

We analyze parameter sensitivities of the mapped interacting boson model (IBM) and boson-fermion-fermion model (IBFFM) in the description of ${\hat{I}}^2$-decay properties of the even-mass neutron-deficient Ge and As, and neutron-rich Zr and Mo isotopes. Based on the self-consistent mean-field calculations with a given energy density functional and a pairing interaction, the IBM Hamiltonian for even-even nuclei, single-particle energies, and occupation probabilities for unpaired nucleons, which are necessary building blocks of the IBFFM Hamiltonian and Gamow-Teller and Fermi transition operators, are completely determined. A few coupling constants of the boson-fermion and residual neutron-proton interactions are only phenomenological parameters fitted to reproduce low-energy spectra of odd-mass and odd-odd nuclei. It is found that the calculated $\log {}_{10}ft$ values for the $β^+$ decays ${}^{68}$As${\to }^{68}$Ge are particularly sensitive to the quadrupole-quadrupole boson interaction strength used for the parent (${}^{68}$As) nucleus. We further incorporate higher-order terms in the one-nucleon transfer operators in the boson system, and find that, while their effects are non-negligible, they do not significantly alter qualitative features of ${\hat{I}}^2$-decay properties. We report a novel application of the mapped IBM framework to compute ${\hat{I}}^2$-decay half-lives, and show that the observed trend along isotopic chains are reasonably reproduced.

18 pages, 13 figures, 2 tables