Wilhelm Metzger

Impact of Photon Transport Properties on the Detection Efficiency of Scintillator Arrays

For spatially resolved X- and gamma ray detection pixelated scintillator arrays are used. In this study we simulate the quantum gain process of a scintillator array and its impact on the detective quantum efficiency of the detector system. The simulation tool comprises a full physical Monte-Carlo model of the X-ray interactions as well as the transport processes of the scintillation photons within the detector system. As an example, we analyze an Gd2O2S:Pr scintillator array with typical 1 mm pixel pitch and TiO2 based reflective material. The results indicate that for integrating systems fluorescence escape effects play a major role in the noise performance of scintillating pixel detectors. Additionally, the light generation and transport processes can have an impact on the signal-to-noise ratio.

Optimal Optical Conditions and Positioning Scheme for an Ultrahigh-Resolution Silicon Drift Detector-Based Gamma Camera

In this study, we optimized the optical conditions and associated positioning scheme for an ultrahighspatial-resolution, solid-state gamma detector. The detector module consisted of an array of seven hexagonal silicon drift detectors (SDDs) packed hexagonally and coupled to a single slab of crystal via a light guide glass. Because the optical behavior and requirements of the detector module and noise characteristics of the SDD sensor are different from those of conventional photomultiplier tube (PMT)-based detectors, the following parameters were studied to determine the optimum condition: scintillator selection, the effect of cooling on signal-to-noise ratio (SNR), the depth dependence of the scintillation light distribution, and optimum shaping time. To that end, a modified, Anger-style positioning algorithm with a denoise scheme was also developed to address the estimation bias (pincushion distortion) caused by the excessively confined light distribution and the leakage current induced by the SDD sensor. The results of this study proved that the positioning algorithm, together with the optimized optical configuration of the detector module, improves the positioning accuracy of the prototype detector. Our results confirmed the ability of the prototype to achieve a spatial resolution of about 0.7mm in full width at half maximum (FWHM) for 122 keV gamma rays under the equivalent noise count (ENC) of 100 (e- rms) per SDD channel. The results also confirmed NaI(Tl) to be a more desirable scintillator for our prototype with an energy resolution performance of about 8%.

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.

Preliminary evaluation of a silicon drift diode based gamma detector

Investigation has been conducted to characterize the intrinsic performance of a SDD (silicon drift diode) based gamma detector under various conditions.