부산대학교 도서관

This work examines the properties of CdZnTe pixellated detectors, in terms of coincidence-timing performances. Through this review it can be see that one of the strongest effects over the CdZnTe timing is the amount of charge collected, or in other words, the influence of the 'small pixel effect.' A figure is presented which gives a simple illustration of this mechanism. This effect is highly noticed when measuring coincidence signals from a single pixel, positioned either at the center of the CdZnTe-detector edge. The CZT coincidence jitter time with the NaI(Tl)+PMT FWHM value varies from a minimum of 4 ns up to 84 ns. Variations in FWHM, as mentioned, are due to the number of CdZnTe pixels connected and their position. The more pixels added to the pixels sum, the more dark current was added to the total signal. The dark current (system noise) increases the jitter time resolution. A trade off between the 'small pixel effect' and the dark current noise was found at a nine (3x3) pixel sum. Signal from the pixels at the crystal edge have more noise deriving from surface currents. The current source is mainly from the broken crystallographic structure. The edge current increases the system noise increasing in time jitter resolution.