Prompt fission neutron spectra of U-235 above emissive fission threshold

摘要

Statistical model calculations of prompt fission neutron spectra (PFNS) from U-235(n, F) reaction were performed for incident neutron energies up to E-n similar to 20 MeV. Exclusive spectra of the pre-fission (pre-saddle) (n, xnf) reaction neutrons, were calculated with Hauser-Feshbach statistical model, fission and (n, xn) reaction cross section data being described consistently. Spectra of neutrons, evaporated from the fission fragments, were approximated as a sum of two Watt distributions. The reduced neutron velocity in the center-of-mass system due to the neutron emission during fragment acceleration was assumed. PFNS component due to pre-saddle neutrons is evidenced in the shape of the measured PFNS data. We show it to be strongly correlated with the emissive fission contributions to the observed fission cross sections. (c) 2005 Elsevier B.V. All rights reserved.