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Three different sizes of Li foil multi-wire proportional counter (MWPC) neutron detectors were constructed with effective areas ranging between 30-1250 cm 2 . These Li foil MWPC neutron detectors contain five 75 µm thick suspended Li foils. Each foil is less than the summed range (156 µm) of the triton and alpha particle reaction products from the 6 3 H reaction. Suspending Li foils offers several advantages over conventional coated gas-filled devices, such as increased detection efficiency and gamma-ray rejection capabilities. Improvements are a direct result of the reaction products simultaneously escaping both sides of suspended Li foils. The three categories of detectors constructed (large-area, mid-sized, handheld) were tested against 3 He neutron detectors. Two large-area detectors (1250 cm 2 effective area) were position back-to-back in HDPE housing. Various tests were completed with this large-area unit including: 1/R 2 , transient, field-of-view, and angular response. A mid-sized detector (550 cm 2 ) was delivered to a backpack test campaign where the device outperformed two commercially available 3 He tube backpack detectors. Both the large-area and mid-sized Li foil MWPCs had measured intrinsic thermal neutron detection efficiencies of 54% and a gamma-ray rejection ratio (GRR) of 3.0 x 10 -9 or better. Lastly, several handheld sized devices were constructed and compared to a 4 atm 3 th = 81.5%). A smaller version of the five layer devices was constructed (effective area: 30 cm 2 ). This five layer device and another device, referred to as thecomparable count rates to the 3 He detector.

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