Realistic microscopic level densities for spherical nuclei

Nuclear level densities play an important role in nuclear reactions such as the formation of the compound nucleus. A microscopic calculation of the level density is developed based on a combinatorial evaluation from a realistic single-particle level scheme. This calculation makes use of a fast Monte Carlo algorithm allowing to consider large shell model spaces which could not be treated previously in combinatorial approaches. Since our model relies on a microscopic basis, it can be applied to exotic nuclei with more confidence than the commonly used semi-phenomenological formulae. An exhaustive comparison of our predicted neutron s-wave resonance spacings with experimental data for a wide range of nuclei is presented. (author). 39 refs., 11 figs., 1 tab