Three-dimensional position sensitive cadmium zinc telluride gamma ray spectrometers

To date, CdZnTe is the most promising material in the development of large volume room temperature gamma ray detectors. Although the performance of large volume CdZnTe detectors has been greatly improved in recent years, it still suffers from the problem of material non-uniformity. To further improve the performance, 3-D position sensitive CdZnTe spectrometers were introduced and investigated in this research.; Monte Carlo simulation was performed for 3-D CdZnTe detectors having 11 x 11 pixellated anodes. The simulation showed that single-pixel events only account for ∼30% of the 662 keV full energy deposition events. This indicated the necessity to reconstruct the energy spectrum from the multiple-pixel events. Two interaction depth sensing techniques were modeled. The modeling showed that for 662 keV single-pixel full energy deposition events, depth resolutions (FWHM) of ∼2–3% and ∼5% of the detector thickness can be achieved using the C/A ratio (the ratio of the signals from the cathode and anode pixel) method and the drift time method, respectively.; Two generations of 3-D CdZnTe gamma ray spectrometers were developed. The first generation 3-D detector was built using a 1 cubic centimeter CdZnTe crystal. During operation, 3-D pulse height correction was applied to the single-pixel events using depth sensing by C/A ratio. The second generation 3-D detector was developed using a 1.5 x 1.5 x 1 cm3 CdZnTe crystal. During operation, 3-D pulse height correction was applied to both single-pixel and multiple-pixel events using depth sensing by C/A ratio and by electron drift time.; In the experiments testing interaction depth sensing, it was demonstrated that the depth resolution of both the C/A ratio method and the drift time method was better than 0.5 mm FWHM for 662 keV single-pixel full energy deposition events. The application of 3-D pulse height correction to the single-pixel events showed excellent energy resolution (∼1.2–1.5% at 662 keV) from the normal pixels. This clearly demonstrated the potential of the 3-D CdZnTe spectrometers. However, degradation of energy resolution due to material non-uniformity was also observed, which indicated that the overall performance of a 3-D CdZnTe spectrometer still depends on the quality of the CdZnTe material. Reconstruction of the energy spectrum from the two-pixel events was investigated, and the results are discussed.