Effective Stellar ${\hat{I}}^2$-Decay Rates of Nuclei with Long-lived Isomers: ${}^{26}$Al and ${}^{34}$Cl

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 ${\hat{I}}^2$-decay rates of such isotopes can fail below certain temperatures. We focus on the ${\hat{I}}^2$-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 ${\hat{I}}^2$-decay rates that showed large differences from previous calculations, finding that we agree with the earlier results. We conclude that in general, effective ${\hat{I}}^2$-decay rates should be defined separately for the ground and isomeric states at temperatures where thermal equilibrium cannot be achieved.

9 pages, 7 figures