Gamma-radiation dosimetry with semiconductor CdTe and CdZnTe detectors

Problems related to the dosimetry of γ-radiation, in particular of high intensity, are investigated together with operational performances of detectors, their temperature stability, reproducibility and reliability of detector measurements. A comprehensive study was carried out of CdTe detectors, obtained by the Bridgman growth method, and CdZnTe detectors, crystallized by the Bridgman method at high pressure of inert gas. All the investigated ingots were of p-type conductivity. The current–voltage characteristics and dynamic resistance of detectors from CdTe and CdZnTe were measured over a wide range of operational temperatures (−30 to +70°C) and bias voltages (−300…+300 V). The dosimetry performance of CdTe and CdZnTe γ-radiation detectors was tested with standard calibration dosimetry rigs of different intensity. The relation between the detector count rate (count mode of operation) or detector anode current (integrated, or current mode of operation) and the exposure dose rate (EDR) of the γ-radiation was established. The count rate of the radiation registered from different sources (241Am, 137Cs, 60Co) in the count mode depends linearly on EDR in the EDR range from ∼10 μR/h up to ∼1 R/h. In high-intensity radiation fields a measurement of the current induced by the γ-radiation, i.e. with the detector operating in “current mode”, is preferable. In this case, our researches have shown that the EDR dependence of the output voltage of the current–voltage converter is linear in the range from ∼20 R/h up to 5000 R/h. Several designs of “detector-absorbing filter” sets were proposed for the correction of the energy dependence of the CdTe and CdZnTe detector absorption efficiency. An experimental detector unit equipped with an optimized “detector-filter” set had a discrete sensitivity of ∼350 counts/R (±20%) in the energy range 0.06…1.2 MeV.