Performance of 3-D position sensitive CdZnTe detectors for gamma-ray energies above 1 MeV

A 3-dimensional position-sensitive CdZnTe gamma-ray detector employs a pixellated anode (11 × 11 pixels) and a planar cathode on a 15 × 15 × 10 mm³ or 20 × 20 × 15 mm³ CdZnTe single crystal. The signals from the 121 pixels and the cathode read out by Application Specific Integrated Circuits (ASIC) are used to reconstruct the energy depositions and 3-D coordinates of multiple gamma-ray interactions inside the detector. The best energy resolution of a given detector can be achieved by using the 3-D position sensitivity to correct the signal variations due to charge trapping and material non-uniformity. We have demonstrated excellent energy resolution of better than 1% FWHM at 662 keV in a dozen CdZnTe detectors ranging from 2.25 cm³ to 6 cm³ in size. In this study, the energy resolution of four 6 cm³ 3-D position sensitive CdZnTe detectors at gamma-ray energies higher than 1 MeV (up to 2.6 MeV of ²²⁸Th) are reported. Various challenges in events calibration/reconstruction at high gamma-ray energies and possible solutions are discussed.