Moderator-free neutron detection

Recent investigations have indicated that moderator-free thermal neutron detection may hold advantages for applications such as long-range neutron source detection and remote-handled TRU waste characterization. Moderator-free neutron detection involves the use of a directionally shielded thermal neutron detector to record only those thermal neutrons incident from a particular direction. Minimization of the amount of moderating material at the location of the detector avoids the detection of fast neutrons, which constitute a substantial fraction of background neutrons. Experimental results reported in this paper were generated using a square meter instrument constructed at Pacific Northwest National Laboratory (PNNL). Such an approach to neutron detection should allow the reasonably rapid detection of modest neutron sources from distances greater than 50 meters and the partial characterization of waste with contact dose rates as high as 10,000 R/hr.