Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy detector of the IBIS telescope on–board the INTEGRAL satellite. PICsIT operates in the gamma–ray energy range between 175 keV and 10 MeV, with a typical energy resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a ~100 square degree field of view, with the possibility to locate intense point sources in the MeV region at the few arcmin level. PICsIT is based upon a modular array of 4096 independent CsI(Tl) pixels, ~0.70 cm2 in cross–section and 3 cm thick. In this work, the PICsIT on–board data handling and science operative modes are described. This work presents the in–flight performances in terms of background count spectra, sensitivity limit, and imaging capabilities.

The volume extinction coefficient produced by aerosol particles at wavelength λ is generally proportional to λ−α as found by Ånström. On the other hand, particle size spectra frequently give a particle number density approximately proportional to the inverse of the radius power with exponent ν, as found by Junge. On the basis of computations made using a very accurate Mie extinction algorithm, a study of the relationship curve between exponents α and ν is made for aerosol particle polydispersions of different radius intervals and for different refractive index values. Moreover, a set of relationship curves is obtained for realistic particulate extinction models based on different size distribution curves and refractive index models. The results show that the linear relationship α = ν − 2 is not valid in most cases. In particular, exponent α assumes appreciably lower values than ν − 2 in the range ν > 3 for all the particulate extinction models. Abstract The volume extinction coefficient produced by aerosol particles at wavelength λ is generally proportional to λ−α as found by Ånström. On the other hand, particle size spectra frequently give a particle number density approximately proportional to the inverse of the radius power with exponent ν, as found by Junge. On the basis of computations made using a very accurate Mie extinction algorithm, a study of the relationship curve between exponents α and ν is made for aerosol particle polydispersions of different radius intervals and for different refractive index values. Moreover, a set of relationship curves is obtained for realistic particulate extinction models based on different size distribution curves and refractive index models. The results show that the linear relationship α = ν − 2 is not valid in most cases. In particular, exponent α assumes appreciably lower values than ν − 2 in the range ν > 3 for all the particulate extinction models.

CdZnTe crystals were grown by the vertical Bridgman method in closed quartz ampoules. The crystalline quality and the impurity content of these crystals were studied. Several X-ray detectors were cut out of these crystals. The resistivity, emission spectra, μτ product, and spectroscopic characteristics of these detectors were extensively measured and compared with the characteristics of detectors obtained from CdZnTe crystals grown by the boron oxide encapsulated vertical Bridgman technique. The detectors prepared from crystals grown without boron oxide show good μτ value, spectroscopic resolution, and higher reproducibility. The influence of growth method on impurity content and on detector response was discussed.