Energy dependence of the nuclear level density at energies above 100 MeV

Abstract

Level densities are calculated for the nucleus $^{40}\mathrm{Ca}$ using an exact iterative method for noninteracting fermions. Various single-particle energies are tested. It is found that the conventional Fermi-gas energy dependence provides a good representation of the actual level density only up to energies about 100 MeV. Above this point, the deviations rapidly grow, reaching many orders of magnitude at energies above 200 MeV. One calculation has also been made for $^{90}\mathrm{Zr}$. These results are similar, with the point of breakdown of the Fermi-gas form raised to about 200 MeV. The present results should have significant consequences for heavy-ion reaction studies of equilibration and for astrophysics.