Mean energies of prompt fission neutrons in the neutron-induced fission of 235U at primary energies in the range En < 20 MeV

The spectra of neutrons accompanying the induced fission of 235U target nuclei are described theoretically. It is confirmed that a third neutron source must be introduced in order to reproduce the shape of experimental distributions at high energies of primary neutrons (previously, a third source was used in describing the spectra of neutrons emitted in 232Th and 238U fission). On the basis of experimental results and their analysis, the mean energy of fission neutrons is estimated as a function of the bombarding-neutron energy up to En = 20 MeV