Calculation and evaluation of n + 237Np cross sections

Knowledge of the production of 236Pu is important in the fabrication of fuel for fast reactors because of the hard (2.6 MeV) gamma rays emitted by its daughter product, 208Tl. The principal process for 236Pu production is via 237Np(n, 2n)236Np(βπ)236Pu for which data are sparse and the existing ENDF/B evaluation may be discrepant by almost a factor or two. A method that could aid in the solution of such problems is calculation of the 737Np(n, 2n) cross sections using the GNASH preequilibrium-statistical model code in a manner similar to our calculations for 239Pu(n, 2n). The GNASH code employs a realistic fission description so that the major competition from (n,xf) reactions can be modeled correctly. Also the code allows one to produce reasonable calculations of isomer ratios to enable meaningful comparisons to available data to be made. To prepare for such an effort we have made preliminary calculations of n + 237Np reactions with particular emphasis on inelastic scattering. We have included the results of the calculations in a revision to the current ENDF/B-V 237Np evaluation that covers the incident energy range up to 5 MeV. Additionally we have taken this opportunity to incorporate improvements to other data, particularly those for (n,γ), (n,f), vector nu, and prompt fission neutron spectra