Effective Stellar $\beta$-Decay Rates of Nuclei with Long-lived Isomers: $^{26}$Al and $^{34}$Cl

TL;DR

This paper investigates the temperature-dependent beta-decay rates of isotopes with long-lived isomers, focusing on $^{26}$Al and $^{34}$Cl, and emphasizes the importance of treating ground and isomeric states separately in non-equilibrium conditions.

Contribution

It clarifies the calculation of effective beta-decay rates for isotopes with long-lived isomers, correcting recent misconceptions and emphasizing the need for separate treatment of states.

Findings

Confirmed previous beta-decay rate calculations for $^{26}$Al.

Ruled out recent reports of significantly different effective decay rates.

Highlighted the importance of defining separate rates for ground and isomeric states at low temperatures.

Abstract

Isotopes with low-lying long-lived isomers can behave very differently from other isotopes in astrophysical environments. In particular, the assumption of thermal equilibrium in computing the temperature-dependent $\beta$-decay rates of such isotopes can fail below certain temperatures. We focus on the $\beta$-decay of $^{26}$Al since it is one of the most important isotopes in observational astrophysics and has a low-lying isomeric state; we compare and contrast these results with $^{34}$Cl. We rule out recently reported $^{26}$Al effective $\beta$-decay rates that showed large differences from previous calculations, finding that we agree with the earlier results. We conclude that in general, effective $\beta$-decay rates should be defined separately for the ground and isomeric states at temperatures where thermal equilibrium cannot be achieved.