Measurement of the U238(n,f) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons with 1.5–20 MeV energy

With the recent emergence of fast nuclear reactors, there has been a corresponding increasing interest in $^{238}\mathrm{U}$-related nuclear data. However, while existing literature data span much of the energy ranges of interest for the prompt fission neutron spectrum (PFNS) for neutron-induced fission of $^{238}\mathrm{U}$, most literature data sets are highly correlated, and thus new, independent measurements of this quantity are needed. In this work, we report the results of a new measurement of the $^{238}\mathrm{U}$ PFNS at the Los Alamos Neutron Science Center for incident neutron energies from 1.5--20.0 MeV, and outgoing neutron energies of 0.01--10.0 MeV. With some notable exceptions, the present results generally agree with existing literature data, especially with regard to features relating to multichance fission and pre-equilibrium features in the PFNS, thus adding confidence to existing nuclear data evaluations and filling in gaps of knowledge at previously unmeasured incident neutron energies. This result is the third in a series of PFNS measurements by the Chi-Nu collaboration now spanning all three major actinides, $^{239}\mathrm{Pu}$, $^{235}\mathrm{U}$, and $^{238}\mathrm{U}$. Thus, for the first time, we report reliable experimental PFNS ratios and average PFNS energy comparisons for measurements of all three of these isotopes including accurate correlations between the different, but correlated experiments.