Nuclear level densities at high excitations.

Abstract

We calculate level densities for {sup 20}Ne, {sup 40}Ca, and {sup 100}Ru nuclei using unrestricted uniform, single particle levels (Fermi gas) and for realistic levels restricted to those bound by centripetal and Coulomb forces. For the latter we use single particle levels due to Seeger, and results for a Woods-Saxon model. We show that the Fermi gas formulas become completely inadequate at temperatures well within the range of those relevant to heavy-ion reaction studies. We discuss likely consequences of these discrepancies with respect to the likelihood of forming equilibrated nuclei at these temperatures, and discuss possible pitfalls of interpreting reactions at high excitations using unrestricted Fermi gas formulas.