Prompt fission neutron multiplicity and spectrum evaluation for 235U(n, f) in the frame of the multi-modal fission model Original Research Article

The multi-modal fission approach, in the frame of an improved version of the Los Alamos model, is used for the evaluation of the prompt fission neutron multiplicity and spectra for the neutron-induced fission of 235U. The three most dominant fission modes (standard I, standard II and superlong) are taken into account. The multi-modal parameters entering the multiplicity and spectrum model are determined on the basis of experimental data measured at IRMM. The total prompt fission neutron multiplicity and spectra, both obtained as superposition of the modal contributions are in good agreement with the experimental data. Also, the average prompt gamma-ray energy for each fission mode is obtained and the total prompt gamma-ray energy is in good agreement with the existing experimental data, too. The agreement of the prompt neutron spectrum with the experimental data is improved especially in the lower fission neutron energy region of the spectrum when the neutron emission anisotropy effect is taken into account.