Analysis of detector response using 3-D position sensitive CZT gamma-ray spectrometers

Two 2.25 cm/sup 3/ CdZnTe gamma-ray spectrometers with 3-D position sensitivity were constructed and tested. By using 11 by 11 pixellated anodes and depth sensing technique, individual spectral data for each of over 2000 voxels were collected throughout the detector volume. Energy resolution of 1.11% FWHM, 1.57% FWHM and 2.13% FWHM at 662 keV were obtained for one, two and three-pixel events respectively from the 120 working pixels of one detector. Spatial variation of electron mobility and lift time product, energy resolution, photopeak efficiency and total efficiency have been observed and analyzed. This analysis provides a direct observation on the uniformity of detector response (due to material and electric field distribution) in 3-dimension. The impact of the spatial variation of detector response on a CZT gamma-ray spectrometer will be discussed.