Evaluation of N50 neutron slab monitor detection efficiency with TRIPOLI-4.3 Monte Carlo code

Monte Carlo code TRIPOLI-4.3 has been used to evaluate the N50 neutron slab monitor detection efficiency benchmark organised by the non-destructive assay (NDA) working group of European Safeguards Research and Development Association (ESARDA). The lattice geometry of TRIPOLI-4.3 was applied to simplify the modelling of the N50 monitor, which consists of four 3He tubes embedded in a high-density polyethylene (HDPE) moderator. Using additional HDPE slabs and/or Cd sheets, 10 geometry configurations with different states of moderation were considered in this study. Two cross section libraries from ENDF/B-VI.4 and JEF2.2 and three representations of the 252Cf fission spectrum were investigated and the calculation experiment (C/E) ratios were discussed. The perturbation option was used in order to study the sensitivity to the HDPE density. The S(alpha,beta) thermal scattering in HDPE was also tested to quantify its impact on the N50 detection efficiency calculations.