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We present our results from testing 15\times 15\times 10~\mm^3 CdZnTe pixelated detectors using a readout system based on the H3D ASIC. Data obtained with an uncollimated ^137Cs source helped reveal details of the operational principle of such devices, and how the pulse-processing electronics may influence their performance. The responses of individual pixels were compared by using two different pulse processing approaches based on the analog shaping (H3D ASIC) and fitting of the waveforms as read out from hybrid preamplifiers. [ABSTRACT FROM PUBLISHER]

Abstract: CdZnTe (CZT) is a wide band-gap II–VI semiconductor and can be used as detector for hard X-rays in astronomical instrumentation and for medical applications. Angular and energy resolutions, as well as detection efficiencies are crucial parameters to characterize the performance of CZT detectors. We studied the detector performance as a function of the geometrical layout of the anode pixel matrix for two CZT detectors with thicknesses of 2mm and 5mm, respectively. We varied the pixel sizes as well as their relative distances and quantified the energy resolutions and detection efficiencies. We also studied how a steering grid located between pixels affects the energy resolution and detection rate. The results of the study are presented and suggest that a steering grid substantially improves the high-energy performance of thin detectors—whereas thick detectors mainly benefit from larger pixel widths. [Copyright &y& Elsevier]

We evaluated the X-Y position resolution achievable in 3D pixelated detectors by processing the signal waveforms readout from neighboring pixels. In these measurements we used a focused light beam, down to 10 μ m, generated by a ∼1 mW pulsed laser (650 nm) to carry out raster scans over selected 3 × 3 pixel areas, while recording the charge signals from the 9 pixels and the cathode using two synchronized digital oscilloscopes. [ABSTRACT FROM AUTHOR]

Following our successful demonstration of the position-sensitive virtual Frisch-grid detectors, we investigated the feasibility of using high-granularity position sensing to correct response non-uniformities caused by the crystal defects in CdZnTe (CZT) pixelated detectors. The development of high-granularity detectors able to correct response non-uniformities on a scale comparable to the size of electron clouds opens the opportunity of using unselected off-the-shelf CZT material, whilst still assuring high spectral resolution for the majority of the detectors fabricated from an ingot. Here, we present the results from testing 3D position-sensitive 15×15×10 mm 3 pixelated detectors, fabricated with conventional pixel patterns with progressively smaller pixel sizes: 1.4, 0.8, and 0.5 mm. We employed the readout system based on the H3D front-end multi-channel ASIC developed by BNL's Instrumentation Division in collaboration with the University of Michigan. We use the sharing of electron clouds among several adjacent pixels to measure locations of interaction points with sub-pixel resolution. By using the detectors with small-pixel sizes and a high probability of the charge-sharing events, we were able to improve their spectral resolutions in comparison to the baseline levels, measured for the 1.4-mm pixel size detectors with small fractions of charge-sharing events. These results demonstrate that further enhancement of the performance of CZT pixelated detectors and reduction of costs are possible by using high spatial-resolution position information of interaction points to correct the small-scale response non-uniformities caused by crystal defects present in most devices. [ABSTRACT FROM AUTHOR]

Intraocular cancer is a serious threat to the lives of those that suffer from it. Dosimetry for eye brachytherapy presents a significant challenge due to the inherently steep dose gradients that are needed to treat such small tumours in close proximity to sensitive normal structures. This issue is addressed by providing much needed quality assurance to eye brachytherapy, a novel volumetric dosimetry system, called Panoptes was developed. This study focuses on the preliminary characterisation and calibration of the system. Using ion beam facilities, the custom, pixelated silicon detector of Panoptes was shown to have good charge collection uniformity and a well defined sensitive volume. Flat-field calibration was conducted on the device using a 250 kVp orthovoltage beam. Finally, the detector and phantom were simulated with Monte Carlo in Geant4, to create water equivalent dose correction factors for each pixel across a range of angles. [ABSTRACT FROM AUTHOR]