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

Abstract

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 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> or 20 × 20 × 15 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> 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 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in size. In this study, the energy resolution of four 6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> 3-D position sensitive CdZnTe detectors at gamma-ray energies higher than 1 MeV (up to 2.6 MeV of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">228</sup> Th) are reported. Various challenges in events calibration/reconstruction at high gamma-ray energies and possible solutions are discussed.