Beyond-mean-field calculations of allowed and first-forbidden $\beta^-$ decays of $r$-process waiting-point nuclei

Abstract

$\beta$-decay rates of neutron-rich nuclei, in particular those located at neutron shell closures, play a central role in simulations of the heavy-element nucleosynthesis and resulting abundance distributions. We present $\beta$-decay half-lives of even-even $N=82$ and $N=126$ $r$-process waiting-point nuclei calculated in the approach based on relativistic quasiparticle random phase approximation with quasiparticle-vibration coupling. The calculations include both allowed and first-forbidden transitions. In the $N=82$ chain, the quasiparticle-vibration coupling has an important impact close to stability, as it increases the contribution of Gamow-Teller modes and improves the agreement with the available data. In the $N=126$ chain, we find the decay to proceed dominantly via first-forbidden transitions, even when the coupling to vibrations is included.