Using Steady State Behavior to Assess Treatments of Nuclear Isomers in Astrophysical Environments

TL;DR

This paper introduces a formalism to accurately compute steady state nuclear level occupations in astrophysical environments, improving nucleosynthesis models by accounting for non-thermal equilibrium effects in nuclei with isomers.

Contribution

It develops a new method to evaluate steady state occupations of nuclear levels, aiding in the assessment of when thermal equilibrium assumptions are valid in nucleosynthesis calculations.

Findings

The formalism effectively models level occupations for 26Al, 34Cl, and 85Kr.

It helps determine the temperature thresholds for thermal equilibrium validity.

The approach reduces inaccuracies in reaction rate calculations involving nuclear isomers.

Abstract

Differing reaction rates of long-lived nuclear states can force the level occupations out of thermal equilibrium, causing calculations of overall rates which rely on thermal equilibrium to be inaccurate. Therefore, nucleosynthesis calculations which include nuclei with isomers must use techniques that do not assume thermal equilibrium, and it is imperative that such techniques appropriately account for transitions between the ground and isomeric states via higher-lying levels. We develop a formalism to compute the steady state occupations of nuclear levels and apply it to the examples 26Al, 34Cl, and 85Kr. We show that this approach is useful both for assessing the required number of nuclear levels and for determining the temperature above which thermal equilibrium rates are appropriate.