β -decay half-lives of the r -process waiting-point isotones of N=81 and 82 nuclei

Abstract

In this paper we perform systematic calculations of $\ensuremath{\beta}$-decay half-lives for the $r$-process waiting-point isotones of $N=81$ and 82, in the framework of nucleon-pair approximation. A phenomenological form of the Hamiltonian, which includes single-particle energies, pairing plus quadrupole interactions, and Gamow-Teller interactions is assumed, and the theoretical $\ensuremath{\beta}$-decay energies are taken based on the Bayesian machine learning. A good agreement with experimental values of half-lives is achieved by using the nucleon-pair truncated model space in which the $S$-pair condensation dominates. Our calculated half-lives are found to be very sensitive to $\ensuremath{\beta}$-decay energies on the one hand, and are quite robust with respect to extension of the model space and variation of interaction parameters on the other hand.