Multiplicities and Spectra of Prompt‐Fission Neutrons up to 200 MeV

Statistical model calculations were performed to interpret the prompt‐fission neutron spectra (PFNS) from 238U(n,f) and 232Th(n,f) reactions for the incident neutron energies En ∼ 6–18 MeV. Spectra of the pre‐fission (pre‐saddle) (n,xnf) reaction neutrons, were calculated with the Hauser‐Feshbach statistical model, fission and (n,xn) reaction cross‐section data being described consistently. The dependence of these contributions on the target nuclide fissility and incident neutron energy is shown to be pronounced in the PFNS shapes. A model is proposed to calculate the average number of prompt‐fission neutrons up to 200 MeV; contributions of pre‐ and post‐fission neutrons are estimated.