Methods and Instruments for Fast Neutron Detection

Pacific Northwest National Laboratory evaluated the performance of a large-area (~0.7 m2) plastic scintillator time-of-flight (TOF) sensor for direct detection of fast neutrons. This type of sensor is a readily area-scalable technology that provides broad-area geometrical coverage at a reasonably low cost. It can yield intrinsic detection efficiencies that compare favorably with moderator-based detection methods. The timing resolution achievable should permit substantially more precise time windowing of return neutron flux than would otherwise be possible with moderated detectors. The energy-deposition threshold imposed on each scintillator contributing to the event-definition trigger in a TOF system can be set to blind the sensor to direct emission from the neutron generator. The primary technical challenge addressed in the project was to understand the capabilities of a neutron TOF sensor in the limit of large scintillator area and small scintillator separation, a size regime in which the neutral particle’s flight path between the two scintillators is not tightly constrained