Systematic behaviour of the average parameters required for the Los Alamos model of prompt neutron emission

Abstract

A large number of fissioning systems have been studied in the frame of the Los Alamos model which showed interesting regular behaviours of the average model parameters (the energy release in fission 〈 E r 〉, the total kinetic energy of the fission fragments 〈 TKE〉, the average neutron separation energy 〈 S n 〉 from the fission fragments, the prompt gamma-ray energy 〈 E γ 〉 and the level density parameter 〈 a〉 parameterized as 〈 C〉 = A/〈 a〉, where A is the mass number of the fissioning nucleus)) as well as of other quantities in connection with the prompt fission neutron emission (such as the total average prompt neutron multiplicity at thermal incident energy, the total average fission fragment excitation energy leading to prompt neutron emission, the total average prompt fission energy deposition, the average excitation energy given to the fragments, and the average center-of-mass energy of prompt neutrons and so on) and to elaborate systematics of model parameters. These systematic behaviours include two parts, the first one refers to the systematic behaviour of the average model parameters at thermal incident neutron energy and the second part contains the systematics concerning the average model parameter variation with the incident energy (or the same with the excitation energy of the fissioning nucleus). The relations expressing the systematic behaviour of the average model parameters can be a useful tool for prompt fission neutron data evaluation, their utility being relevant especially for fissioning nuclei that are far from the known and studied systems; these nuclei act as secondary fission chances of the main compound nucleus chain as well as of the secondary compound nucleus chains formed by charged particle emission at high incident energies. In cases with no experimental data and integral benchmarks, the regular behaviour of the nuclear quantities used to calculate prompt fission neutron emission can make possible an indirect validation of evaluation results.