Analysis of Cadmium Zinc Telluride Detector Performance and Characteristics for Applications in Gamma-Ray Imaging Spectrometers.

Abstract

Cadmium Zinc Telluride (CdZnTe) is a promising material for gamma-ray measurement applications. It operates at room temperature with high-quality energy resolution. Pixellated anode read-out, the small pixel effect and the theory behind weighting potential can be used to determine the 3-D position of each interaction in the device. If an incident gamma ray interacts via Compton scattering, the physics of the interaction can be used to predict the incident direction of the gamma ray, allowing for gamma-ray imaging to also be performed using CdZnTe detectors. The combination of gamma ray imaging and high-quality spectroscopic performance makes CdZnTe one of the most promising materials for gamma-ray measurement applications. This work will focus on analysis of the spectroscopic performance of these detectors. Two 18-detector CdZnTe array systems have been built and operated over the past several years. Each system operates at room temperature and is capable of high-quality spectroscopy and gamma-ray imaging. The first system achieved 1.44% FWHM at 662 keV for all events. The second system achieved 1.21% FWHM at 662 keV. A large number of 20x20x15 mm3 CdZnTe detectors were studied to determine the factors that are correlated to better spectroscopic performance. The electron transport properties of the detectors were found to be correlated to the uncalibrated spectroscopic performance, but uncorrelated to the calibrated spectroscopic performance. Further analysis of the performance of CdZnTe detectors was performed through coincidence interactions with an HPGe detector. From measurements of coincident full-energy interactions from a Cs-137 source, the energy resolution and energy non-linearity were studied as a function of deposited energy in the CdZnTe detector. Analysis of the energy non-linearity showed that most of the measured offset in energy at low energies is related to the ASIC's non-linearity. Finally, the efficiency of CdZnTe detectors was studied. Calibration data from the second 18-detector array system showed that there are not any complete trapping defects, which cause degraded efficiency. Comparisons between simulation and measurement of a Co-60 source showed that the intrinsic efficiency of the CdZnTe system is lower than expected due to energy losses to small trapping defects and unreconstructed events.