Studies on optimization of moderator thickness for BF₃ detectors used for monitoring of fissile material

Abstract

811-813Monitoring of fissile material content in waste drums requires an energy independent neutron response due to the inherent moderation of neutrons in the waste matrix. For this purpose, a detector assembly consisting of three BF3 detectors each 100 cm long and covered with 3.7 cm thick HDPE moderators arranged in a linear geometry has been set-up. The response of the assembly as measured using different neutron sources was observed to be appropriate within acceptable limits. Response of the detector assembly to a 252Cf source which has a fission neutron spectrum similar to that of fissile materials was measured and compared with the FLUKA based simulations. The sensitivity of the system as evaluated using FLUKA simulations for a 252Cf neutron source was found to be in good agreement with the experimental values. This study indicates that the optimum range of moderator thickness for effective monitoring of fissile material using BF3 neutron detector assembly is 6-7 cm