* Corresponding author. Tel.: #972-8-9434191; fax: #972- 8-9434676. E-mail addresses: shor@ndc.soreq.gov.il (A. Shor), yosef@ndc. soreq.gov.il (Y. Eisen), mardor@ndc.soreq.gov.il (I. Mardor). Nuclear Instruments and Methods in Physics Research A 458 (2001) 47}54 Spectroscopy with pixelated CdZnTe gamma detectors } experiment versus theory A. Shor*, Y. Eisen, I. Mardor Applied Radiation Technologies Division, Soreq NRC, Yavne 81800, Israel Abstract Methods for obtaining excellent spectroscopy with pixelated CdZnTe gamma detectors are explored experimentally and theoretically. For a monolithic CdZnTe detector with pad segmentation, the dependence of the induced charge on the depth of interaction is found to be much weaker than for a planar detector, even for coarse pad segmentation and despite the large hole trapping. Two methods are described for removing the dependence on depth of gamma interaction for pixelated detectors. One method is by introducing a mild amount of electron trapping to compensate for the almost complete hole trapping found in most CdZnTe detectors. Proper tuning of the electron trapping by adjusting the detector applied voltage can remove the dependence on depth of interaction over most of the detector volume. At the optimum voltage, we obtain an energy resolution of 1.7% full width at half maximum (FWHM) for the 356 keV line of Ba. Excellent quantitative agreement with theoretical calculations provides a basis for detector design based on these calculations. A second method for obtaining excellent spectroscopy is achieved by simultaneously measuring the pad signal and the signal from the common electrode. Individual gamma lines are observed as sharp bands in the correlation pro"le between these two signals. A correction is performed to linearize these bands so that they will project onto the photopeak. Using this procedure, we obtain for the 356 keV gamma line of Ba an energy resolution of 1.0}1.5% FWHM with a peak-to-valley ratio approaching 100/1.  2001 Elsevier Science B.V. All rights reserved. Keywords: Pixel CdZnTe gamma detectors; Theoretical model; Experimental veri"cation; E!ect of various parameters; Bias; Energy 1. Introduction CdZnTe semi-insulating material has generated much interest as room-temperature solid-state X- and gamma ray detectors [1] partly because of the high resistivity of 10}10  cm. Despite the large degree of hole trapping typically found in CdZnTe, electrode structures have been developed to pro- vide true single-charge carrier detection which rely on the excellent charge transport properties of the electron charge carriers only [2}4]. Many applica- tions for room-temperature X- or gamma-ray de- tection require spectroscopy, spatial imaging, or both [5,6]. Pixelated CdZnTe detectors, i.e., mono- lithic detectors with the anode segmented to pad electrodes, are becoming very popular. We show that excellent spectroscopy can be obtained with pixelated CdZnTe detectors, even with only coarse pad segmentation and despite the large hole 0168-9002/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 8 5 0 - 0 SESSION II.