Large-Area, Low-Cost, High-Efficiency Neutron Detector for Vehicle-Mounted Operation

Abstract

We have developed a large-area, low-cost, high-efficiency neutron detector for vehicle-mounted operation. The detector, which has overall dimensions 12.7 cm $\times 91.4$ cm $\times 102$ cm (5” $\times 36$ ” $\times 40$ ”), a sensitive area equal to $0.85~\text {m}^{{\mathbf {2}}}$ (1320 in2), and weight of 110 kg (242 lbs), employs an array of 90 boron-coated straw (BCS) detectors. PTI has also developed electronics to minimize cost and space while providing low-noise signal conditioning for both neutron and gamma detection channels, as well as low energy Bluetooth communication with handheld devices. Extremely low power consumption allows continuous use for 225 hours (~10 days) using three AAA lithium-ion rechargeable batteries. We present radiological, mechanical, and environmental tests, collected from four full-scale prototypes. Outdoor neutron-counting tests with a moderated 252Cf source 2 m away from the center of the detector face showed an average detection rate of 5.5 cps/ng with a standard deviation of 0.09 cps/ng over the four individual detector measurements. Measurements showed a gamma rejection ratio of $1.0\times 10^{{\mathbf {-8}}}$ , and gamma absolute rejection ratio (GARRn) of 0.93. The prototypes were also operated successfully onboard a moving vehicle for high-speed tests and a long-range 1433-mile, two-day road trip from Houston, TX, USA, to Laurel, MD, USA. Using auxiliary DARPA SIGMA equipment, the GPS, timestamp, gamma and neutron data were transmitted over the cellular network with 10 Hz resolution to a server and real-time tracking website. Mechanical impact and electrostatic discharge testing produced no spurious counts in either the neutron or gamma channels. Ambient environmental temperature testing showed less than ± 1% response variation over the range from −30°C to +55°C.