Quasi differential neutron induced neutron emission measurements of U235 and Pu239

Abstract

235U and 239Pu are important isotopes with significant impact on the nuclear community,and the nuclear data which describes their behavior when subjected to incident neutrons directly supports calculations for nuclear reactor design and operation, criticality safety, and nonproliferation efforts. A neutron scattering measurement methodology developed at RPI was adapted and implemented to perform experimental measurements of the quasi-differential neutron induced neutron emission spectrum of 235U and 239Pu in the range of 1 to 20 MeV at the Los Alamos Neutron Science Center in response to increasing demand for investigations of these isotopes. The 800 MeV proton beam was directed at a Tungsten target, creating a neutron source through spallation. The time of flight technique was used to perform active neutron interrogation of a carbon reference sample, a 49.5g 93% 235U sample, and a 24.61g 93.9% Pu-Ga alloy sample. The experiment was simulated using the Monte-Carlo code MCNP6.2 and the emission spectrum of the carbon sample was used to quantify the systematic uncertainty associated with the replication of the experiment. Simulations of each sample were performed using ENDF/B-VIII.0 (USA), JEFF-3.3 (EU), and JENDL-4.0 (JP) nuclear data libraries in order to identify discrepancies between the simulation and the experiment, as well as discrepancies between the nuclear data libraries themselves. The results identified nuclear data problems in Carbon, 235U, and 239Pu, and provide some insight on the nature of the discrepancies such as angular distributions and the contributions of isolated reactions in the simulated emission spectrum.