Astromers in the radioactive decay of r-process nuclei

TL;DR

This paper investigates the role of nuclear isomers, or astromers, in r-process nucleosynthesis, highlighting their impact on nuclear decay pathways and radioactive heating in astrophysical environments.

Contribution

It introduces a method to compute transition rates and beta-decay feeding factors for isomers, and assesses their influence on nucleosynthesis and heating in r-process scenarios.

Findings

Isomers are significantly populated in r-process nucleosynthesis.

Certain isomers can alter decay pathways and energy release.

Population of isomers affects radioactive heating in astrophysical sites.

Abstract

We study the impact of astrophysically relevant nuclear isomers (astromers) in the context of the rapid neutron capture process (r-process) nucleosynthesis. We compute thermally mediated transition rates between long-lived isomers and the corresponding ground states in neutron-rich nuclei. We calculate the temperature-dependent beta-decay feeding factors which represent the fraction of material going to each of the isomer and ground state daughter species from the beta-decay parent species. We simulate nucleosynthesis by including as separate species nuclear excited states with measured terrestrial half-lives greater than 100 microseconds. We find a variety of isomers throughout the chart of nuclides are populated, and we identify those most likely to be influential. We comment on the capacity of isomer production to alter radioactive heating in an r-process environment.