An improved model for fission neutron spectrum calculation

An attempt was made to improve the Madland-Nix model for the calculation of the fission neutron spectrum. In the original Madland-Nix model, statistical equilibrium was assumed between the two fission fragments at the scission point. This was the ground for using a single value of the maximum nuclear temperature for both fragments. However, this assumption seems questionable, since the deformation energies of the fragments at the scission point, which are generally different for the nascent fragments, eventually converts into the internal excitation energy. The author tried to take into account the difference in the nuclear temperature of the light and heavy fragments in a empirical manner. This non-equitemperature model was applied to analyze the fission neutron spectra for neutron-induced fission of U-235 and Pu-239 and spontaneous fission of Cf-252. It was found that (i) consideration of the temperature difference had greater effects on the spectral shape than the previous attempts, and (ii) this modification of the model gave better account of the experimental spectra for these nuclides. (author)