CdZnTe crystals for the realization of x-ray and gamma ray detectors

CdZnTe is a particularly suited material for the realization of room temperature x-ray and gamma ray detector. The properties that make CdZnTe (CZT) so promising are the high resistivity of the material (ρ≥1010 Ω∙cm), combined with a relatively small band gap (~1.6 eV at RT). Moreover the high atomic number (Z) of the material determines the application on a large range of energies. In this work the authors report on the crystal growth of several crystals of high resistivity Cd1-xZnxTe (x=0.1) by two vertical Bridgman technique: with and without the boron oxide encapsulation[1]. The ingots obtained have been extensively studied on both the crystal qualities and the detector performances. Using the PL mapping technique the interface shape was studied on many ingots, together with an accurate analysis of the Zn segregation along the growth axis [2]. The resistance of the devices was studied using the current-voltage characteristic in the low voltage range. The spectroscopic result of the CZT detector is satisfactory for both the growth techniques. Several x-ray sources have been used to characterize the ingots, ranging from 10 KeV up to 300 KeV. The μτ product, a good indicator of the device transport properties, was measured with an alpha particle source, giving good results for the electronic μτ, while holes μτ still need to be improved

Study of the spectral response of CZT multiple-electrode detectors

Cadmium zinc telluride (CZT) is a promising material for room temperature X-ray and gamma-ray detectors. The high atomic number and the wide band-gap give high quantum efficiency and good room temperature performances. Due to hole trapping, particular electrode structures have been developed to provide single-charge carrier collection (electrons), exploiting the excellent charge transport properties of the electrons. In this work, the spectroscopic performances of two CZT detectors (CZT1: 5 mm times 5 mm times 0.90 mm; CZT2: 4.8 mm times 5 mm times 0.55 mm) with five electrodes (cathode, anode and three steering electrodes) were studied. The anode-collecting electrode, surrounded by three steering electrodes (biased for optimum charge collection), is mostly sensitive to electron carriers, overcoming the effects of hole trapping in the measured spectra (hole tailing). We investigated on the spectroscopic response (241Am source; 59.5 keV) of the detectors at different bias voltages of the electrodes. The detectors exhibit excellent energy resolution (CZT1: 2.0% FWHM at 59.5 keV; CZT2: 1.7% FWHM at 59.5 keV; working temperature -10degC) and low tailing (CZT1: FW.1M to FWHM ratio of 1.93 at 59.5 keV; CZT2: 2.35 at 59.5 keV). This study stresses on the excellent spectroscopic properties of the CZT detectors equipped with a custom anode layout, making them very attractive candidates as x-ray spectrometers mainly for medical applications

Radiation Protection Legislation and Sustainable Development of a Rural Green Tuff Village of Ischia Island

Radiological risk affects the quality of the environment in buildings since population and workers can be potentially exposed to high levels of radiation. Radon gas emanating from both subsoil and building materials represents the most important source of radiation exposure for people. This study investigates the sustainability concept of a small rural village of Ischia Island, named Ciglio, in relation to radiation protection legislation concerning the radiological risk for workers. Radon activity concentration was measured in typical green-tuff dwellings and in water samples collected from a local waterfall E-Perm devices. Moreover, for green tuff as building material, the radon emanation coefficient was calculated by gamma spectroscopy. The results highlight the importance of performing environmental radon monitoring and investigating the radon content of building materials, especially in geographical areas characterized by traditional use of typical stones for constructions. In conclusion, the sustainable development of rural buildings is possible if the radiological risk for inhabitants and workers is assessed in line with the national radiation protection legislation

Development of carbon nanotube based radiation detectors

Multi Wall Carbon NanoTubes (MWCNT) are one-dimensional structures with diameters ranging between 5 and 30 nm and lengths up to hundreds of micrometers. They show a metallic-like behaviour and enhanced field emission capability; their sensitivity to the radiation is very peculiar, depending on their diameter and chirality. The wide range of their bandgaps (from 0.4 to ≈ 6 eV) makes these devices very suitable for fabrication of sensors of electromagnetic radiation, from UV to IR. This opens the possibility to build wide sensitive range radiation detectors for space researches and environmental controls. Preliminary tests have been performed by exposing a prototype detector made up of a MWCNT carpet grown by the CVD technique between two gold electrodes on a 500 micrometer thick silicon substrate to pulsed UV, visible and IR radiation. First results on the charge generated by pulsed laser are reported