Cross-Section Measurement of Plutonium-236 Formation in Plutonium-238 by ²³⁷Np(n, 2n)Reactions

High-energy neutron cross sections for ²³⁷Np are needed to calculate unwanted ²³⁶Pu contaminant in ²³⁸Pu product made for heat source applications in space and medical projects. Recent improved determination of ²³⁶Pu formation by ²³⁷Np(n, 2n) reactions completes the information needed to calculate ²³⁶Pu/²³⁸Pu ratios over a wide range of ²³⁷Np irradiation environments, from D_2O reflectors to pressurized-water-reactor fuel. The ²³⁷Np(n, 2n) ²³⁶&Np cross section is 63 ± 6 mb, averaged over the ²³⁵U fission spectrum >6.8 MeV; this result is consistent with the cross section calculated by Pearlstein.