Spectroscopy for Compton interaction in pixelated CdZnTe detectors

Excellent spectroscopy for gamma rays can be obtained with pixelated CdZnTe detectors. Correction to the depth dependence of the pixel electrode signal can be made by simultaneously also measuring the common electrode signal. For high-energy gammas, thick detectors are required for increased detection efficiency. For increased efficiency, it is desirable to reconstruct Compton events, 2-pixel events that include the Compton scatter and re-interaction. The ambiguity in depth information for two pixel events in the same detector, with only one common signal, can be overcome taking advantage of sharp correlation with the relative difference of these two pixels. We present measurements made with a 1cm × 1cm × 1cm CdZnTe detector with the anode segmented to a 4 × 4 array of pad electrodes. For each gamma interaction, signals for all the 16 pad electrodes and for the common cathode electrode were digitized to enable further correction for the depth of gamma interaction, and for the reconstruction of Compton scatter interactions. We focus on the 1.115 MeV line of ⁶⁵ Zn source. For single pixel events, the summed corrected pad spectra yields an energy resolution of better than 1.0 % FWHM. Reconstruction of Compton events were made with signals from all combinations of 2 nearest neighbor pad electrodes, with corrections relying on the common electrode signal and also on the relative difference between the two pixel signals. A summed spectrum was for the Compton events was obtained with a energy resolution of 1.1 % FWHM for the 1.115 MeV line.