Sensitivity of Photoneutron Production to Perturbations in Cross-Section Data?

Abstract

The most recent release of photonuclear interaction data for Monte Carlo applications is the ENDF/B-VII library. While this current version offers several improvements over its predecessors, it does not address the observed, sometimes quite significant variance in the measured data. For instance, for 238U, the cross-section data in the ENDF/B-VII library is consistently larger than all measurements except for those by Caldwell, et al., occasionally by as much as 20%. The objective of the work performed here was to investigate the sensitivity of photoneutron production to perturbations in photonuclear cross-section data. The effect of these perturbations on common experimental observables was assessed using the MCNPX/MCNP-PoliMi code system. Since the standard MCNPX perturbation routines are not available for photonuclear reactions, we developed and implemented a new methodology to evaluate the sensitivity of commonly-measured parameters to perturbations in photonuclear cross-section data. The results of the analysis show that the maximum variance applied to the cross section (20%) results in an integral detector response change that in general varies between 4% and 8%.