Comparison of some Monte Carlo models for bound hydrogen scattering

Three approximate models for incoherent inelastic scattering of epithermal neutrons from 1H bound in water are examined. The theoretical relationships between them are outlined, and the effects of using one versus another in Monte Carlo calculations are determined. A scattering law model based on the use of the short collision time approximation for down scattering, which simultaneously preserves detailed balance, gives the best results for the distribution of post-collision energies. For some criticality benchmark models, the differences in keff between the models can be as much as 50 pcm. (authors)