Performance of five-or-more-pixel event sequence reconstruction for 3-D semiconductor gamma-ray-imaging spectrometers

The performance of sequence-order reconstruction for five- and six-interaction events is investigated for a single 20 mm × 20 mm × 15 mm CdZnTe (CZT) detector as well as a 3 × 3 × 2 array of these detectors. Simulations are performed for both systems and experimental results are presented for a single 3-D-position-sensitive CZT detector. Two sequence reconstruction methods are evaluated. A deterministic method is based on the probability of each interaction to occur for a given event. A minimum squared difference (MSD) technique compares the scatter angles calculated from geometry and from deposited energies. These two methods are evaluated based on the percentage of reconstructed events that produce a correct Compton cone for image reconstruction. Since the scatteringangle uncertainty decreases in the array system due to the larger average separation between interactions, sequence reconstruction for the MSD method performs better for the array system than the single detector.