The measurement and analysis of neutron spectra in depleted uranium in the 10 EV to 2 MEV region

Abstract

Serious disagreement occurs between the experimental and calculated spectra, through and below the unresolved energy region, with all of the data sets, with the calculation underpredicting the flux, especially as one progresses outward from the neutron source. Sensitivity studies of the differential cross sections, calculations including the (n, ɣn') reaction, and the effects of the 0.2% U235 in the system are clearly in order to resolve the low energy discrepancies.

New measurements of the energy, space and angular dependent neutron spectra have been made for depleted uranium. The measurements have extended down to the 10 eV energy level from 2 MeV.

The resulting spectra have been analyzed and compared to calculations using ENDF/B-II, III, and IV data and the DTF-IV - SUPERTOG computer codes. The Version IV data is found to give the best overall fit to the experimental data in the region above 10 keV. This can be attributed to reductions in the inelastic scattering cross sections.

In the low energy, resolved resonance region, calculations were made using various weighting functions to produce the self-shielded group cross sections. Spectra calculations with the various group constants show considerable variation with changes in the weight. The best results were obtained with a weight of l/E(σT + σb) which also appears to most closely represent the actual physical situation.