Transparent Ceramic Garnet Gamma-Ray Spectrometer With Directionality

We have developed a handheld y-ray spectrometer based on 1024 pixels, 2.8 mm × 2.8 mm × 6 mm in size, of gadolinium-yttrium-gallium-aluminum garnet (GYGAG) ((Gd,Y,Ce)
₃
(Ga,Al)
₅
O
₁₂
) ceramic scintillator (total of 48-cm
³
detector volume) coupled to silicon photodiode (SiPD) arrays. The SiPD arrays and readout ASIC, originally developed for medical imaging applications, have been adapted for portability in a lightweight box with heatsink and thermoelectric cooling. Custom readout firmware for y-ray spectroscopy has been implemented, and a system user interface was developed that runs on an Android tablet. We have optimized the processing of the GYGAG(Ce), the pixel optical coupling, and electronics readout parameters to obtain single pixel energy resolution as good as R(662 keV) = 3.1% full-width at half-maximum and full device resolution with singles events from all pixels summed of 4.5%. When Compton-summed events are included, full-energy peak efficiency increases by ~2×, and R(662 keV) = 4.7% is obtained for the full device. The pixelated architecture is leveraged to locate point sources of radiological materials using Compton imaging and active masking techniques. Directional detection of a 1 mCi Cs-137 source at 10 m can be made to ±10° in ~2 s.