Study of self-shielding and multiple-scattering effects to reduce the uncertainties in the Am-243 neutron capture cross section measurement using the PHITS code

Leong, L.; Sato, Tatsuhiko   ; Kimura, Atsushi   ; Iwamoto, Osamu  ; Harada, Hideo   

Minor Actinides (MAs) are produced abundantly in the nuclear reactor. Most of them are considered as high radioactive waste. Transmutation technology is an issue to convert these radioactive MAs to stable state and it require the very accurate nuclear data of the MAs. Am-243 (n,g) capture cross section was recently measured at ANNRI. In order to achieve the accurate cross section measurement, we need to estimate the background due to the self-shielding and the multiple-scattering effects. In this work, we studied specifically the impacts of these effects for the purpose of estimating the background, using Monte Carlo simulation PHITS. In fact, due to the high neutron absorption, these two effects in the Am-243 capture cross section measurement in resonance region are large and lead a high uncertainty on the data. As these backgrounds are difficult to be estimated by experiment, therefore we corrected these two effects and eventually conciliated the percent uncertainties in resonance region.