Stellar Weak Rates and Mass Fractions of 20 Most Important fp-shell Nuclei with A < 65

Abstract

This work presents stellar weak rates and mass fractions of 20 most important electron capture (ec) and beta-decay (bd) nuclei with A < 65, according to a recent study, during the presupernova evolution of massive stars. The mass fractions of these nuclei were calculated using the Saha’s equation, which assumes nuclear statistical equilibrium for a set of initial conditions ($T_9$, $\rho$ and $Y_e$) that represents the trajectory which a massive star’s central region takes after its silicon core burns. Our computed mass fractions were found in decent comparison in most cases, and up to a factor 4 difference was noted when compared with the Independent Particle Model results. The weak interaction (ec and bd) rates were calculated in a totally microscopic fashion using the proton-neutron quasiparticle random phase approximation model and without assuming the Brink-Axel hypothesis. The rates were computed for a wide range of density ($10 -10^{11}$) $g/cm^3$ and temperature ($0.01 - 30$) GK. In comparison with large-scale shell-model, our computed rates were found bigger at high values of core temperature. The current study may contribute in a more realistic simulation of stellar evolution processes and modeling of core-collapse supernovae.