Evaluation of Cdte as an Integral Gamma-Ray Counter

The integral gamma-ray counting efficiency was measured for six CdTe detectors using gammas from 57Co, 85Kr, 137Cs, and 60Co. Changes in efficiency were measured as a function of temperature (−50 to 66°C), detector bias (50 to 100 V), pulse clipping time (0.25 to 1.6 μsec), and energy threshold setting (25, 50, 75, and 100 keV). The change is mainly due to trapping and detrapping of charge carriers. For a clipping time of 1 μsec, changes in efficiency as high as 300% were observed over the temperature range −50 to 66°C. This change in efficiency was reduced to <10% by using only the fast component of the pulses generated. Total gamma-ray efficiency approaching the theoretical limit was measured at 23°C. Presently, CdTe detectors are not intended for use as spectrometers, but are intended to be used as gamma-ray counters over a wide temperature range.