Stellar weak-interaction rates for $rp$-process waiting-point nuclei from projected shell model

TL;DR

This paper introduces a projected shell model to calculate stellar weak-interaction rates for key rp-process waiting-point nuclei, revealing the influence of higher-order quasiparticle configurations on decay rates under stellar conditions.

Contribution

The study presents the first application of the projected shell model to compute stellar weak-interaction rates for eight rp-process waiting-point nuclei, incorporating extended configurations up to six-quasiparticles.

Findings

Higher-order quasiparticle configurations significantly affect Gamow-Teller strength distributions.

Thermal population of excited states decreases beta-plus decay rates at high temperatures.

Electron capture contributions increase with temperature and density, reducing effective half-lives.

Abstract

We propose a projected shell model (PSM) for description of stellar weak-interaction rates between even-even and odd-odd nuclei with extended configuration space where up to six-quasiparticle (qp) configurations are included, and the stellar weak-interaction rates for eight $rp$-process waiting-point (WP) nuclei, $^{64}$Ge, $^{68}$Se, $^{72}$Kr, $^{76}$Sr, $^{80}$Zr, $^{84}$Mo, $^{88}$Ru and $^{92}$Pd, are calculated and analyzed for the first time within the model. Higher-order qp configurations are found to affect the underlying Gamow-Teller strength distributions and the corresponding stellar weak-interaction rates. Under $rp$-process environments with high temperatures and densities, on one hand, thermal population of excited states of parent nuclei tends to decrease the stellar $\beta^+$ decay rates. On the other hand, the possibility of electron capture (EC) tends to provide increasing contribution to the rates with temperature and density. The effective half-lives of WP nuclei under the $rp$-process peak condition are predicted to be reduced as compared with the terrestrial case, especially for $^{64}$Ge and $^{68}$Se.