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This paper reports experimental results obtained from an 8×8 pixellated CZT detector provided by Imarad Imaging Systems. Three arbitrarily selected pixels were independently tested using γ rays of different energies. The signals from an anode pixel and the cathode were read out simultaneously. From the observations of the pulse waveforms from both the anode pixel and the cathode, the electron-injection effect leading to electron–hole combination was not observed. The best energy resolution at 122 keV from the three pixels was 7.8, 6.6 and 9.4 keV, respectively, while resolution at 662 keV was 29.3, 11.8 and 26.5 keV, respectively. The electronic noise from the three pixels was similar (5 keV), so the variation in the best energy resolution indicates material nonuniformity in the detector. For the material underneath the three selected pixels, the mobility-lifetime product for electrons was measured to be 3.4, 2.4 and 1.8 ( ×10 −3 cm 2 / V ), respectively, and the resistivity was measured to be 8, 10 and 8.3 ( ×10 9 Ω cm ), respectively. The variation in these results also shows the material nonuniformity across the detector. In the test with 662 keV γ rays, the pulse-height ratio of the signals from the cathode and pixel can be used to infer the interaction depth of single-pixel events. Results and analyses are presented in this paper. |
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