Prompt Fission Neutron Spectra of 240Pu(n, F), 239Pu(n, F), and 238U(n, F)

Abstract

Pre-fission neutron spectra are indicators of the distribution of fission reaction energy between the kinetic energy of fragments and prompt fission neutrons. Using the ²⁴⁰Pu(n, F), ²³⁹Pu(n, F), and ²³⁸U(n, F) reactions as an example, it is shown how the shape of the observed prompt fission neutron spectra (PFNS) depends on the fissility (fission probability) of compound and residual nuclei. A correlation of this effect with the contributions of the (n, xnf) emission fission to the observed fission cross section and the competition of the (n, nγ) and (n, xn)^1,...x reactions is established. The exclusive spectra of the (n, xnf)^1,...x neutrons correspond to the consistent description of the observed cross sections for the ²⁴⁰Pu(n, F), ²³⁹Pu(n, F), ²³⁸Pu(n, F), ²³⁷Pu(n, F), and ²³⁶Pu(n, F) fission reactions, as well as ²³⁹Pu(n, xn) neutron emission spectra for neutrons with energies up to 20 MeV. The initial values of the model parameters for describing the ²⁴⁰Pu(n, F) PFNS are fixed when describing the prompt neutron spectra of ²⁴⁰Pu(sf) spontaneous fission. Taking into account the influence of the exclusive spectra of ²⁴⁰Pu (n, xnf)^1,...x prefission neutrons, the prompt fission neutron spectra, the total kinetic energy (TKE) of fragments and fission products, and the average number of ²⁴⁰Pu(n, F) prompt fission neutrons are predicted.