3D position sensing on UltraPeRL CdZnTe detectors
Experimental results of depth and lateral position sensing on UltraPeRL pixellated CdZnTe detectors using signal ratios are presented. Each detector employs one CdZnTe crystal of 20 mm times 20 mm times 5 mm with 8 times 8 pixel electrodes fabricated on the anode surface. The anode pixel pitch is 2.4 mm. The signal ratios are calculated using the signals induced on the collecting pixel and the eight neighboring pixels. The signal on each collecting pixel is then corrected for depth of interaction using the signal ratios. We obtained 7.6%, 4.2% and 2.5% FWHM energy resolution at 122 keV, 356 keV and 662 keV, respectively.
Three-dimensional signal correction on U1traPeRL CZT detectors
Three-dimensional signal correction on pixellated CdZnTe (CZT) detectors for the UltraPeRL project has been studied using Monte Carlo simulations. Each 2 cm x 2 cm x 0.5 cm CZT detector has 8 x 8 pixellated anodes with a pitch of 2.4 mm. A depth and lateral correction algorithm has been developed in order to estimate both the depth of interaction (DOI) and the lateral position underneath the collecting pixel and therefore correct the signal amplitude. Using only the simple depth correction technique, the energy resolution can reach about 1.2% FWHM at 662 keV for single-pixel gamma-ray interactions. The relative detector-thickness photopeak efficiency is close to 79%. After lateral correction, the relative detector- thickness photopeak efficiency increased to about 88%, while the energy resolution changed little.
Multipixel characterization of imaging CZT detectors for hard x-ray imaging and spectroscopy
We report our in-depth study of Cd-Zn-Te (CZT) crystals to determine an optimum pixel and guard band configuration for Hard X-ray imaging and spectroscopy. We tested 20x20x5mm crystals with 8x8 pixels on a 2.46mm pitch. We have studied different types of cathode / anode contacts and different pixel pad sizes. We present the measurements of leakage current as well as spectral response for each pixel. Our I-V measurement setup is custom designed to allow automated measurements of the I-V curves sequentially for all 64 pixels, whereas the radiation properties measurement setup allows for interchangeable crystals with the same XAIM3.2 ASIC readout from IDEAS. We have tested multiple crystals of each type, and each crystal in different positions to measure the variation between individual crystals and variation among the ASIC channels. We also compare the same crystals with and without a grounded guard band deposited on the crystal side walls vs. a floating guard band and compare results to simulations. This study was carried out to find the optimum CZT crystal configuration for prototype detectors for the proposed Black-Hole Finder mission, EXIST.