Effects of Differing Energy Dependences in Three Level-Density Models on Calculated Cross Sections

Three level-density formalisms commonly used for cross-section calculations are examined. Residual nuclides in neutron interaction with 58Ni are chosen to quantify the well-known differences in the energy dependences of the three formalisms. Level-density parameters for the Gilbert and Cameron model are determined from experimental information. Parameters for the back-shifted Fermi-gas and generalized superfluid models are obtained by fitting their level densities at two selected energies for each nuclide to those of the Gilbert and Cameron model, forcing the level densities of the three models to be as close as physically allowed. The remaining differences are in their energy dependences that, it is shown, can change the calculated cross sections and particle emission spectra significantly, in some cases or energy ranges by a factor of 2.