Nuclear partition functions at high temperature

A Fermi-gas calculation of nuclear partition functions suitable for use in a Saha equation is presented. The model naturally includes both bound and continuum nuclear states constructed from an independent particle model. General formulas for the nuclear partition function and excitation energy are given in terms of Fermi integrals. The continuum is found to have the effect of reducing the partition function, as was suggested by Fowler et al. (1978), but not to the extreme of the truncated state-density integral. Results obtained for Ni-56 indicate that the partition function and mean excitation energy remain large even for temperatures as high as 100 billion K and that methods that truncate a state-density integral to calculate the nuclear partition function are incorrect.