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.
Detector and telescope development for ProtoEXIST and fine beam measurements of spectral response of CZT detectors
We outline our plan to develop ProtoEXIST, a balloon-borne prototype experiment for the Energetic X-ray Imaging Survey Telescope (EXIST) for the Black Hole Finder Probe. EXIST will consist of multiple wide-field hard X-ray coded-aperture telescopes. The current design of the EXIST mission employs two types of telescope systems: high energy telescopes (HETs) using CZT detectors, and low energy telescopes (LETs) using Si detectors. With ProtoEXIST, we will develop and demonstrate the technologies required for the EXIST HETs. As part of our development efforts, we also present recent laboratory measurements of the spectral response and efficiency variation of imaging CZT detectors on a fine scale (~0.5 mm). The preliminary results confirm the need for multi-pixel readouts and small inter-pixel gaps to achieve uniform spectral response and high detection efficiency across detectors.