We develop a method to compute thermally mediated transition rates between the ground state and long-lived isomers in nuclei. We also establish criteria delimiting a thermalization temperature above which a nucleus may be considered a single species and below which it must be treated as two separate species: a ground-state species and an astrophysical isomer (“astromer”) species. Below the thermalization temperature, the destruction rates dominate the internal transition rates between the ground state and the isomer. If the destruction rates also differ greatly from one another, the nuclear levels fall out of or fail to reach thermal equilibrium. Without thermal equilibrium, there may not be a safe assumption about the distribution of occupation probability among the nuclear levels when computing nuclear reaction rates. In these conditions, the isomer has astrophysical consequences and should be treated as a separate astromer species which evolves separately from the ground state in a nucleosynthesis network. We apply our transition-rate methods and perform sensitivity studies on a few well-known astromers. We also study transitions in several other isomers of likely astrophysical interest.

我们开发了一种方法来计算基态与原子核中长寿命异构体之间的热介导的跃迁速率。我们还建立了界定热化温度的标准，在该温度之上，核可以视为单个物种，在其以下必须将其视为两个独立的物种：基态物种和天体异构体（“天体”）物种。在热化温度以下，破坏速率主导基态和异构体之间的内部转变速率。如果销毁率彼此之间也相差很大，则核能级将跌落或无法达到热平衡。如果没有热平衡，则在计算核反应速率时，可能无法安全地假设占领概率在核能级之间的分布。在这些情况下 该异构体具有天体物理学的后果，应被视为一个单独的astromer物种，它在核合成网络中与基态分开演化。我们应用过渡速率方法，并对一些著名的星际星进行敏感性研究。我们还研究了可能具有天体物理学意义的其他几种异构体的转变。