Performance Characterization of a Silicon Drift Detector for Gamma Ray Imaging

This study examined the intrinsic performance of silicon drift detector (SDD)-based gamma detectors under a variety of conditions. The prototype detector consisted of an array of seven hexagon-shaped SDDs optically coupled to a single slab of a scintillator. The active area of the SDD sensor was 15.2 mm in diameter, as measured from one vertex to another. The detector unit (SDD array, scintillator and preamplifier circuits) was operated in a cooling chamber with a typical operating temperature of -20°C. Nitrogen gas was supplied to the detector unit to prevent condensation. The drift time was measured using a LED pulse generation device and the longest drift time was measured to be 4.6 μsec from the edge of the sensor. The intrinsic energy resolution with a BBFe source for direct X-ray conversion was 3% at the 5.9 keV peak. For indirect conversion, i.e. photon detection, the energy resolution for CsI(Tl) and Nal(Tl) was 7.9% and 8.2% with a 13 μsec and 2.71 μsec shaping time, respectively. For this indirect conversion measurement, the temperature was set to -20°C and a 1 × 1 × 1 cm³ cube scintillator was coupled directly to the sensor. For the intrinsic spatial resolution measurement with a hole-phantom (3 × 2 mm diameter holes), the x and y directional profiles at a center hole were 2.2 and 2.1 mm in FWHM, respectively. Overall, the intrinsic performance of the SDD prototype is quite promising and advantages of this technology makes it highly feasible for use as a gamma ray detector.