Experimental Prompt Fission Neutron Spectra Comparisons for the ^235,238U(n, f) and ²³⁹Pu(n, f) Reactions

¹ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
² Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

^* e-mail: devlin@lanl.gov

Published online: 26 May 2023

Abstract

The Chi-Nu project to measure prompt fission neutron energy spectra for the major actinides has now completed two measurements, for neutron-induced fission of ²³⁹Pu and ²³⁵U for incident neutron energies from 1 to 20 MeV, and has almost completed the prompt fission neutron spectrum measurement for ²³⁸U. In addition, similar data have been taken for spontaneous fission in some other isotopes, and a measurement of fission neutron spectra from ²⁴⁰Pu(n, f ) is in progress. These measurements are done at the same facility, with the same equipment and analyzed in a similar way. A useful way to look at such data is to examine ratios of the prompt fission neutron spectra among actinides, as some of the experimental uncertainties involved in these data are the same from isotope to isotope, making the ratios of fission neutron spectra less dependent on the experimental and analysis details. We discuss here the ratios of prompt fission neutron spectra between ²³⁹Pu(n, f ) and ²³⁵U(n, f ) , as well as the evolution of the mean fission neutron energy for ²³⁹Pu(n, f ) and ^235,238U(n, f ) with increasing incident neutron energy.