Gamma radiation detectors on the base CdTe for environmental monitoring

Full text: The purpose of the given work is development of small - sized dosimeters of gamma - radiation on basis CdTe for definition of a radiations level in an environment and for the control over the illegal moving of radioactive substances. It is supposed, that these dosimeters will replace devices in which as Geiger counters are used. Cadmium telluride (CdTe) is the first material to have been developed as a room-temperature semiconductor detector. Its Egap of 1,45 eV gives a high enough resistively for room temperature operation, and Z of 48 and 52 gives a higher gamma radiation detection efficiency that either Si (Egap=1,12 and Z=14) or Ge (Egap=0,66 and Z=32). Gamma rays and charged particles interact with a solid by converting most of their energy into electron-hole pairs. In scintillators like NaI (Tl) the intensity of the fluorescence arising from these charge carriers is observed with a photomultiplier tube and is proportional to the radiation energy. Semiconductor detectors instead use an electric field to collect the charge carriers and the resulting current pulse is amplified and is proportional to the radiation energy. Polarization effects, which are temporary decrease in either the depleted thickness or the charge collection properties. The primary limitation on increasing E for CdTe detectors is the requirement to avoid excessive noise due to a high leakage current. Low resistively n-type CdTe has resistively between 10 :104 cm, which limits both E and depleted thickness. High resistively CdTe has between 106 : 1010 cm. CdTe detectors with between 106 : 107 cm have been operated at 0 degrees Celcium which reduces the leakage current and allows E to be increased. However, a major disadvantage is the lack of room-temperature operation. High-Z room-temperature detectors have a number of different applications as spectrometers, radiation counters. CdTe provides improved energy-resolution compared to NaI without the need for bulky cooling systems. Work on CdTe probes has reached the clinical stage in both tracer studies (diagnostics) and dosimetry (therapy). The advantages of these probes are: 1) high sensitivity which allows small sized probes; 2) body temperature operation; 3) good energy resolution. As the number of applications expands, the decrease in detector cost will in turn increase the number of applications. Such potential low-cost detector applications include use in a photoconductivity mode for computer tomography scanners, as high speed counters in positron camera, and as gamma-ray imaging systems. So, due to specific features of CdTe, the detectors created on its basis, are considered as the most perspective among a wide spectrum of detectors developed at present gamma-radiations. Simplicity, compactness, sensitivity, work room temperature cause advantages of use of CdTe-detectors in portable dosimetric devices