Wearable Detector Device with Wireless Modular Neutron Detectors and Modular Gamma-Ray Detectors

Sixteen Modular Neutron Detectors (MNDs) and two Modular Gamma-Ray Detectors (MGDs) were integrated into a Wearable Detector Device (WDD) for covert or overt operations regarding nuclear non-proliferation search and localization of Special Nuclear Material (SNM). Each MND contains an array of 24, 1-cm
²
active-area Microstructured Semiconductor Neutron Detectors (MSNDs) with intrinsic thermal-neutron detection efficiencies of approximately 30%. All necessary signal processing, communications, and power conditioning electronics are also housed within the MND, which measures 1.2 cm × 6.1 cm × 1.7 cm (4.4 in. × 2.4 in. × 0.65 in.). The battery within the MND allows for approximately three weeks of continuous operation on a single charge. The MGD comprises seven LND model 713 Geiger-Müller detectors, an on-board battery, and all necessary signal processing, communications, and power conditioning electronics. Each detector module interfaces with a handheld Android device through Bluetooth Low Energy communications. When the number of counts reported by the MNDs is greater than the background neutron environment, the Android device will alarm to alert the operator to the possible presence of neutron-emitting SNM. The reported count rate from the MGDs can then be used as secondary confirmation of SNM, because SNMs that emit neutrons also emit gamma rays. The neutron response of the WDD for bare
²⁵²
Cf with fluxes of 0.1, 1, and 10 n cm
^-2
s
^-1
measured at Pacific Northwest National Laboratory (PNNL) was 1.34 ± 0.02, 9.93 ± 0.01, and 99.65 ± 0.01 cps, respectively. The corresponding neutron background count rate was 0.36 ± 0.02 cps, significantly lower than any of the foreground count rates. When the
²⁵²
Cf source was placed in 4-cm thick, spherical HDPE moderator cask, the recorded count rate increased to 200.2 ± 0.5 cps for 10 n cm
^-2
s
^-1
flux. The Gamma Absolute Rejection Ratio for neutrons (GARRn) for the WDD was measured at PNNL and was determined to be 1.02 for a neutron flux of 10 n cm
^-2
s
^-1
and
⁶⁰
Co gamma-ray exposure field of 10 mR/h indicating excellent gamma-ray rejection for the neutron detector modules. The PNNL measurement results compared well to measurements repeated at Kansas State University.