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Excellent spectroscopy for higher energy gamma-rays is obtained with thick pixelated CdZnTe detectors, despite the large hole trapping inherent in the CdZnTe material. Our detector design was assisted by means of a theoretical Monte-Carlo code for optimizing the pixelated detector geometry for obtaining pad signals with minimum dependence on the depth of gamma interaction. We present spectra obtained for the 662-keV line of [sup.137]Cs taken with a 1 cm x 1 cm x 1 cm CdZnTe detector with the anode segmented to a 4 x 4 array of pad electrodes. For each gamma interaction, signals for all 16 pad of the electrodes and for the common cathode electrode were digitized to enable further correction for the depth of gamma interaction and for the reconstruction of Compton scatter interactions. For single pixel events, the summed pad spectrum yields an energy resolution of 1.0% FWHM. For the reconstruction of Compton events with signals in two pad electrodes, we obtain a summed peak with an energy resolution of 1.4% FWHM. Index Terms--CdZnTe detectors, gamma spectroscopy.

This review paper presents the current state of the art imaging systems using room-temperature CdTe and CdZnTe X-ray and gamma-ray detectors. Imaging systems composed of both single elements and monolithic segmented CdTe and CdZnTe arrays are used in medical diagnostics, astronomy, research and industry. This paper is divided into two sections: The first section describes different types and configurations of CdTe or CdZnTe detectors used in imaging systems, with the emphasis on single charge carrier collection detectors and front-end read-out electronics in the form of application specific integrated circuits associated with these detectors. It also discusses the advantages, disadvantages and limitations with respect to the efficiency and area of the imaging systems using CdTe and CdZnTe detectors compared to other types of X and gamma ray detectors. The second section describes several examples of imaging systems utilizing CdZnTe detectors: 1) a large area imaging telescope for the detection of gamma ray bursts using a coded aperture collimator; 2) a large area medical nuclear camera for cardiology and scintimammography using a parallel hole collimator; 3) a large field of view gamma camera based on a rotating slat collimator; and 4) a prototype of an electronically collimated Compton camera.

We present results for 1 cm x 1 cm x 1 cm pixelated CdZnTe gamma detectors with coarse segmentation. Large pixelated CdZnTe detectors are important for spectroscopic and imaging applications requiring sensitivity for higher gamma energies. For each gamma interaction, we process signals from all pixels and from the common electrode, and employ correction techniques developed at Soreq NRC for improving the energy resolution and the photopeak efficiency. For irradiation with an uncollimated [sup.133]]Ba source, we obtain a combined pad spectrum with energy resolution of ~5% full width half maximum (FWHM) for the 81-keV peak and ~1.5% FWHM for the 356-keV peak. We show spectra for two selected detectors, one with [([micro][tau]).sub.e] = 7.3 x [10.sup.-3] [cm.sup.2]/v, and one with [([micro][tau]).sub.e] = 2.9 x [10.sup.-3] [cm.sup.2]/v. We discuss the importance of detector material with high electron [([micro][tau]).sub.e] for thick pixelated detectors. The experimental results are compared to theoretical simulations. These simulations contribute to our understanding of large pixelated detectors and provide a tool for designing new pixelated detector configurations. Index Terms--CdZnTe, room temperature, solid-state gamma detectors.

Edge effects in pixelated CdZnTe detectors occur due to the high dielectric constant of the CdZnTe detector material, and the tendency of the field lines emanating from the "hole" charge carriers to remain within the detector volume. As a result, spectra, for edge and corner pixels tend to exhibit a longer low energy tail at the expense of the number of events in the photo-peak. We focus on a thick pixelated CdZnTe detector, where, the detector thickness is comparable to the lateral size. We develop a theoretical Monte-Carlo simulation that well describes the experimentally observed edge effects. We show that when the same detector is embedded in an array of similar detector at the same HV, the edge effects disappear, and the spectral properties the edge and corner pixels improve markedly. [ABSTRACT FROM AUTHOR]

Excellent spectroscopy for gamma rays can be obtained with pixelated CdZnTe detectors. Correction to the depth dependence of the pixel electrode signal can be made by simultaneously also measuring the common electrode signal. For high-energy gammas, thick detectors are required for increased detection efficiency. For increased efficiency, it is desirable to reconstruct Compton events, 2-pixel events that include the Compton scatter and re-interaction. The ambiguity in depth information for two pixel events in the same detector, with only one common signal, can be overcome taking advantage of sharp correlation with the relative difference of these two pixels. We present measurements made with a 1cm × 1cm × 1cm CdZnTe detector with the anode segmented to a 4 × 4 array of pad electrodes. For each gamma interaction, signals for all the 16 pad electrodes and for the common cathode electrode were digitized to enable further correction for the depth of gamma interaction, and for the reconstruction of Compton scatter interactions. We focus on the 1.115 MeV line of 65Zn source. For single pixel events, the summed corrected pad spectra yields an energy resolution of better than 1.0 % FWHM. Reconstruction of Compton events were made with signals from all combinations of 2 nearest neighbor pad electrodes, with corrections relying on the common electrode signal and also on the relative difference between the two pixel signals. A summed spectrum was for the Compton events was obtained with a energy resolution of 1.1 % FWHM for the 1.115 MeV line. [ABSTRACT FROM AUTHOR]