Microscopic study of β-decay and stellar weak rates in neutron-rich scandium isotopes

Abstract

Abstract

This study provides a critical investigation of the β-decay characteristics of neutron-rich scandium isotopes (53-65Sc) using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The theoretical framework allows for a microscopic understanding of spin-isospin excitation modes that are essential for examining weak interaction phenomena. Charge-changing Gamow-Teller (GT) strength distributions were calculated and found to agree well with existing experimental results, thereby confirming the model's capacity to accurately represent the nuclear configuration of these isotopes. The computed β-decay half-lives and corresponding log ft values exhibit good agreement with experimental data, further validating the GT strength distributions and reinforcing the consistency of the chosen model in this mass region. In particular, the predicted half-lives within factor of two agreement with the measured values of 90% of the selected nuclei. For the first time, we report calculated predictions of the half-lives of 64Sc and 65Sc which are 1.74×10-3s and 1.42×10-3s, respectively. Overall, it was observed that the general trend is a decrease in half-lives with increasing neutron number. The evaluated log ft values exhibit acceptable consensus with the measured data, within a factor of two. The model incorporates a notable methodological advancement by computing weak interaction rates without relying on the Brink-Axel hypothesis, which has traditionally been used to approximate GT transitions from nuclear excited states. At a lower density of ρYe=106 g/cm3, the total β--decay and positron capture rates vary by up to two orders of magnitude with increasing temperature, whereas at a higher density of ρYe=1010 g/cm3, the same temperature increase yields a variation of around seven orders of magnitude. Our study explores the fractional contribution of β--decay and positron capture processes under predetermined stellar conditions.