Monitoring 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 HOPE 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 IOOnitoring of fissile material using BF₃ neutron detector assembly is 6-7 cm.