Sensitivity of Neutron-Rich Nuclear Isomer Behavior to Uncertainties in Direct Transitions

TL;DR

This paper investigates how uncertainties in direct nuclear transition rates affect the behavior of neutron-rich nuclear isomers during the r-process nucleosynthesis, providing a categorization and data table for these isomers.

Contribution

It introduces a sensitivity study on unknown transition effects, categorizes astromers based on their environmental impact, and compiles a comprehensive table of neutron-rich isomers with key properties.

Findings

Identification of key transition rates affecting astromer behavior

Categorization of astromers by thermalization potential

Provision of a detailed isomer data table

Abstract

Nuclear isomers are populated in the rapid neutron capture process (r process) of nucleosynthesis. The r process may cover a wide range of temperatures, potentially starting from several tens of GK (several MeV) and then cooling as material is ejected from the event. As the r-process environment cools, isomers can freeze out of thermal equilibrium or be directly populated as astrophysical isomers (astromers). Two key behaviors of astromers -- ground state<->isomer transition rates and thermalization temperatures -- are determined by direct transition rates between pairs of nuclear states. We perform a sensitivity study to constrain the effects of unknown transitions on astromer behavior. We also introduce a categorization of astromers that describes their potential effects in hot environments. We provide a table of neutron-rich isomers that includes the astromer type, thermalization temperature, and key unmeasured transition rates.