  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.
