Recent progress in the commercialization of the Li Foil multi-wire proportional counter neutron detectors

Abstract

The scarcity and rising cost of 3He gas has introduced a push in alternative neutron detector technologies. The Li foil multi-wire proportional counter (Li Foil MWPC) neutron detectors have shown promise as a 3He replacement technology. Large, gas-filled proportional counters with five layers of 75 µm thick 6Li foils have been built and characterized, yielding over 55% thermal neutron detection efficiency, with the possibility of increasing the efficiency above 70% with ten 96% enriched 6Li foil layers. Most recently, a backpack radiation detector (BRD) was fabricated, equipped with four Li Foil MWPC devices. The neutron sensitivity-to-weight ratio of the Li Foil MWPC devices was first optimized using MCNP6 by simulating the angular response to an ANSI-moderated-252Cf source positioned 1.5 m away from the devices. The simulated neutron sensitivity results were compared and benchmarked to that of the commercially-available Thermo-Fisher PackEye v. 1.0 that contains two 14 in. long, 2 in. diameter, 2.5 atm 3He tubes. The experimental efforts studied the performance of the Li Foil MWPCs in the backpack instrument configuration. Fabrication advancements were implemented to the Li Foil MWPC devices to increase the device manufacturability and improve the commercialization capabilities. These advancements included weight reduction, new hermetic sealing techniques, optimizing active area, and anode wire cost reduction. The Li Foil MWPC BRD was evaluated as a part of a PNNL test campaign for neutron sensitivity where 0.36 cps/ng of 252Cf at 1.5 m was measured. The gamma-ray rejection ratio (GRR) of the BRD was also evaluated, yielding a measured value of 3.1 × 10−8 for a 137Cs exposure rate of 50 mR/Hr. Further evaluations were performed under the PNNL test campaign including detector response to neutron sources of 252Cf, AmBe, AmLi and WGPu, detector angular response, and the gamma absolute rejection ratio in the presence of neutrons (GARRn).