Compton imager for detection of special nuclear material

A Compton imager design for the detection of Special Nuclear Material (SNM), with specific focus on shielded Highly Enriched Uranium (HEU) is presented. It is based on a large field-of-view Compton gamma-ray imager that uses 24 layers of 2 mm thick, position-sensitive (1.4 mm strips) silicon detectors, designed for room-temperature operation, as a scatterer and a position-sensitive NaI scintillator array as the absorber. Each layer of silicon detectors consists of double-sided silicon strip detectors daisy chained in a 3×3 array with a total active area of 729 cm2. The NaI detectors are 2.9×2.9 cm2 and 7.6 cm thick and will cover the bottom and sides of the instrument. Simulations of an ASIC-based readout system show that an energy resolution of 4.5 keV full-width at half-maximum (FWHM) at room temperature is attainable on each daisy-chained silicon strip assuming 35 pF of capacitance and 20 nA of leakage current. Full simulations of the current instrument design are shown and are demonstrated that it can detect 8 kg of shielded HEU at 2.5 m in 1 min in a realistic gamma-ray background environment.