Measurement of the prompt fission neutron spectrum from 800 keV to 10 MeV for ²⁴⁰Pu(sf) and for the ²⁴⁰Pu($n,f$) reaction induced by neutrons of energy from 1–20 MeV

Here, the presence of ²⁴⁰Pu in nuclear fuels for reactors has resulted in high uncertainties in the results of reactor and nuclear transmutation calculations because of deficiencies in ²⁴⁰Pu-related nuclear data. Specifically for the prompt fission neutron spectrum (PFNS) of ²⁴⁰Pu, there is only one neutron-induced, (n,f), measurement at 0.85 MeV incident neutron energy and only one complete spontaneous fission, (sf), measurement. This limited availability of data does not sufficiently guide nuclear data evaluations of these quantities. Here we report on a measurement of both the ²⁴⁰Pu(sf) and the ²⁴⁰Pu(n,f) PFNS, both over the emitted neutron energy range of 0.79–10.0 MeV, and from incident neutron energies of 1.0–20.0 MeV for the (n,f) reaction. Measurements were made with a hemispherical array of liquid scintillators at the high-energy Los Alamos Neutron Science Center white neutron source at the Weapons Neutron Research facility as part of the joint LANL-LLNL Chi-Nu experimental campaign to measure actinide fission neutron spectra. These measurements are the first of their kind, and provide clear experimental evidence for second-chance fission, third chance fission, and pre-equilibrium neutron emission processes in neutron-induced fission of ²⁴⁰Pu, and are the first ever measurements above 1 MeV incident neutron energy.. Authors: Kelly, K. J. [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000228459644); Devlin, M. [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000269482154); O'Donnell, J. M. [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)]; Neudecker, D. [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)]; Wu, C. Y. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000157727196). DOE Contract: 89233218CNA000001; AC52-07NA27344. Subjects: 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; Nuclear Criticality Safety Program (NCSP); fission; neutron physics; nuclear reactors; nucleon induced nuclear reactions; transmutation & power generation with accelerators