This work is aim at studying the dependence of fission yields on incident neutron energy, so as to produce evaluated yield sets of the energy dependence. Experimental data at different neutron energies for gas fission products 85m,87,88Kr and 138Xe resulting from the 238U(n, f) reaction are processed using codes AVERAGE for weighed average and ZOTT for simultaneous evaluation. Energy dependence of the cumulative fission product yields on the incident neutron is presented. The evaluated curve of product yield is compared with the results calculated by the TALYS-0.64 code. The present evaluation is consistent with other main libraries in error permission. The fit curve of 87,88Kr can be recommended to predict the unmeasured fission yields. Comparisons of the evaluated energy dependence curves with theoretical calculated results show that the predictions using purely theoretical model for the fission process are not sufficiently accurate and reliable for the calculations of the cumulative fission yields for the 238U(n,f).
Low energy neutron induced fission of 235U is studied in the framework of the multi-modal fission model. The fission fragment properties, such as the yields, the average total kinetic energy distribution and the average neutron separation energy, are investigated for incident neutron energies from thermal to 6.0 MeV. The multi-modal fission approach is also used to evaluate the prompt fission neutron multiplicity and spectra for the neutron-induced fission of 235U with an improved version of the Los Alamos model for incident neutrons below the （n, nf） threshold. The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental data. The calculated results are in good agreement with the experimental data.
