Nuclear cross-section measurements at the Manuel Lujan Jr. Neutron Scattering Center

The Los Alamos Neutron Science Center (LANSCE) is a versatile user facility built around a proton linear accelerator. The 800-MeV proton beam is used to generate spallation neutrons in the Weapons Neutron Research (WNR) facility and the Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) optimized for nuclear physics and materials science research, respectively. Even though the Lujan Center facility is used extensively for material research, two out of 16 neutron flight paths (FP-5, FP-14) are devoted to nuclear physics experiments. The nuclear physics experiments (fission, neutron capture) carried out at these flight paths provide vital contributions to the nuclear data evaluation efforts. Better understanding of the systematic uncertainties of the experiments provides higher-quality data sets to the evaluators and allows for generation of reliable covariance matrices to be included in next releases of nuclear data libraries. The Lujan Center's target is a rather complex system consisting of many different materials, requiring a very detailed geometry description in our calculation model. In this report, we discuss our extensive Monte Carlo study carried out for the nuclear physics flight paths of the Lujan Center facility. We present the influence of the time distribution of the primary beam on the final response function of the Lujan Center's target system. We then compare our results to the experimental data showing a direction of actual implementation in the real data analysis. (author)