Prompt Fission Neutron Spectra of 233U(n,F)

TL;DR

This study analyzes prompt fission neutron spectra of 233U up to 20 MeV, comparing measured and calculated data to improve understanding of neutron emissions and energy partitioning in fission reactions.

Contribution

It provides the first comprehensive prediction of 233U(n,xnf) neutron spectra and examines the influence of fissility and reaction channels on PFNS shape and energy.

Findings

PFNS of 233U(n, F) are harder than 235U(n, F) but softer than 239Pu(n, F)

Predicted 233U(n,xnf) spectra up to 20 MeV

Difference in average energies between 233U and 235U PFNS is 1-3%

Abstract

Prompt fission neutron spectra produced up to 20 MeV. Simultaneous analysis of measured and calculated data for 233U(n, F), 235U(n, F) and 239Pu(n, F) maintains stronger justification for the predicted PFNS of 233U(n, F). For the latter the reliable measured PFNS data are available at Eth only. Pre-fission neutron spectra influence the partitioning of fission energy between excitation energy and total kinetic energy of fission fragments. For the reactions 233U (n, F) and 235U (n, F) we have shown that the shape of PFNS depends on the fissility of composite and residual nuclei. The correlation of these peculiarities with contributions of (n, xnf) to the (n, F) and competition of (n, ng) and (n, xn) is established. Exclusive neutron spectra (n, xnf) are consistent with cross sections of 235U(n, F), 234U(n, F), 233U(n, F) and 232U(n,F) reactions, as well as neutron emissive spectra of 235U(n,xn) at 14 MeV. Initial model parameters for 233U (n,F) PFNS are fixed by description of prompt fission neutron spectra of 233U (nth, F). We predict the 233U(n,xnf) exclusive pre-fission neutron spectra of 233U(n,xn) reactions, total kinetic energy TKE of fission fragments and products, partials of average PFNS and observed PFNS of 233U(n,F). PFNS of 233U (n, F) are harder than those of 235U(n, F) PFNS, but softer than those of 239Pu(n, F). Difference of average energies of PFNS of 233U (n, F) and 235U(n, F) amounts to 1-3 %. At incident energies higher than (n, 2nf) reaction threshold the observed PFNS may seem similar, though the partial contributions of 233U(n,xnf) and 235U(n,xnf) are quite different. PFNS of 233U(n,xnf) are obtained in the energy range up to 20 MeV.