Direct local parametrization of nuclear state densities using the back-shifted Bethe formula

Abstract

Level densities are often parametrized using the back-shifted Bethe formula (BBF) for nuclei that have experimental data for s-wave neutron resonance average spacings and a complete discrete level sequence at low excitation energies. However, these parametrizations require additional modeling of the dependence of the spin-cutoff parameter on excitation energy. Here we avoid the need to model the spin distribution of level densities by using the experimental data to parametrize directly the state densities, for which the BBF does not depend on the spin-cutoff parameter. This approach allows for a local parameterization of state densities that is independent of the spin-cutoff parameter. We provide these parameters in a tabulated form for applications in nuclear reaction calculations and for testing microscopic approaches to state densities.