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.
Event classification in 3D position sensitive semiconductor detectors
A set of analytical methods for pixelated 3D position sensitive semiconductor detectors has been developed to make better measurements of gamma-rays in the 30 keV to 3 MeV energy range. The ability to classify pixel charge sharing, x-ray escape, pair production, and Compton scattering allows for more accurate and efficient energy reconstruction and Compton imaging routines. The techniques are based on the analysis of digitized preamplifier waveforms from the electrodes that sense charge following an interaction. Accurate identification of an event is based on the comparison of an expected detector response with precise measurements of an interaction’s resulting signal amplitude, shape, and timing characteristics. A tungsten collimator is used to demonstrate the accuracy of the classification methods. Experimental results taken with large volume CZT and HgI2 detectors are compared with system simulations.
Anode readout for pixellated CZT detectors
Determination of the photon interaction depth offers numerous advantages for an astronomical hard X-ray telescope. The interaction depth is typically derived from two signals: anode and cathode, or collecting and non-collecting electrodes. We present some preliminary results from our depth sensing detectors using only the anode pixel signals. By examining several anode pixel signals simultaneously, we find that we can estimate the interaction depth, and get sub-pixel 2-D position resolution. We discuss our findings and the requirements for future ASIC development.