Search

The semiconductor nuclear detector structure is usually a superposition of several different layers: the metallic electrode, the interface, the depleted zone, the nondepleted one, and finally the second electrode. All inactive layers, and particularly the 'dead layer' region below the metallic electrodes, give rise to absorption for photons (X, [beta]) and to energy loss for charged particles. As a consequence, the detectors measure lower count rates for photons, particularly at low energies, and lower energies for charged particles. The amount of this effect can be only partially attributed to the inactive metallic electrode; the main part has to be attributed to the highly defected zone below the electrode in the interfacial region. This is a structural drawback which needs to be studied to reduce this effect, e.g., by developing new polishing and deposition techniques, or to perform the appropriate corrections. We have measured the thickness of this dead layer for various solution dilution electroless depositions of Pt electrodes on CdTe devices. These measurements were carried out by using collimated (X, [lambda]) rays beams impinging at different angles, especially the grazing ones, and comparing the count rates registered at two selected angles, and by measuring Rutherford backscattering spectra and energy loss of [sup.4] He ions. Index Terms--CdTe detectors, dead layer, energy loss, Rutherford backscattering spectrometry (RBS) measurements, various irradiation angles, X-ray measurements.

In the classic irradiation configuration of solid-state X- and Gamma-ray detectors, where the photons impinge normally to the cathode, the electrode and detector dead layer thickness affect the detection efficiency and the spectroscopic performance of the device, mainly at the lowest incident photon energies. The concentration of defects in the near-electrode regions greatly depends on the mechanical and chemical treatments used for the surface preparation (polishing and etching), before electrode deposition, as well as on metallic diffusion in the crystal, which result in differently thick dead layers. In this paper, we evaluate, in an easy, experimental way, the dead layer thickness, irradiating a detector by a narrow photon beam, at various incident angles. The areas relevant to the 14-keV ([sup.57]Co) and to 22-keV ([sup.109]Cd) photopeaks, at different angles of incidence, are independently used to solve a linear equation depending on the photons absorption in the electrodes (Pt) and the dead layer (CdTe) material. As an example, data obtained with a CdTe detector 2-mm-thick and 3 X 10 [mm.sup.2] electrode area are presented and discussed.

The spectroscopic response of CdTe detectors has been investigated with an unusual irradiation geometry, i.e., with the beam impinging at various angles through the cathode surface. In fact, the classical planar parallel field (PPF) irradiation geometry, i.e., with photons impinging perpendicularly to the cathode, limits the spectroscopic performance at high energies (E > 60 keV), if thick detectors are used, owing to the large spread in the paths of the charge carriers. These paths for the holes can be greatly reduced by using larger impinging angles, thus improving the energy resolution without losses in detection efficiency. Several sets of measurements have been carried out with a narrow photon beam, coming from collimated [sup.57]Co, [sup.109]Cd and [sup.241]Am sources; measurement angles ranged from 0[degrees] (orthogonal to the cathode) to 87[degrees] (beam grazing the cathode). The spectroscopic responses of the detectors for 14, 22, 60 and 122 keV photon energies have been analyzed. Detectors equipped with both full anodes and microstrip anodes were used. In this last case the rectangular collimated spot of the beam was used with the long side both parallel and orthogonal to the strip direction. The experimental results show that an actual improvement in the spectroscopic performance is obtained, mostly for the high-energy X-rays, by this tilting procedure. Further, this technique allows the evaluation of the detector dead layer thickness. The obtained performance and possible medical and space applications are discussed. Index Terms--CdTe detectors, CCE, spectroscopy, various irradiation angles.

Indoor radon exposure is the second most important risk factor for lung cancer incidence on human. The purpose of this study was to assess the status of the knowledge of radon gas in the general population and high school students, in the metropolitan area of Naples. A survey was planned in order to obtain data on both public knowledge of radon gas and its health effects. The results on 6705 collected questionnaires showed that a similar percentage of respondents asserted to know radon gas, 31% and 38% in general and student population, respectively. This study demonstrate that actual educational programs have to be enhanced in order to provide the spread of the radon knowledge and the awareness of the exposure risk. [ABSTRACT FROM AUTHOR]

Rutherford Backscattering Spectrometry (RBS) using 6 MeV alpha particles and X-Ray Fluorescence (XRF) with a Pd-anode X-Ray generator were performed to characterize Au and Pt contacts deposited by electroless technique and thermal evaporation on differently treated surfaces of CdZnTe and CdTe crystals. The aim of this study is to understand and improve the structure of the material-electrode interface. The thickness, the stoichiometry and the concentration profiles of platinum, gold, cadmium, zinc, tellurium and oxygen present at the surface layers were determined. The distribution of Cd deficiency at the interface layers was profiled using simulations and showed complex profiles in the samples, which can greatly affect the electrical quality of the detectors. [ABSTRACT FROM AUTHOR]

The spectroscopic response of CdTe detectors has been investigated with an unusual irradiation geometry, i.e., with the beam impinging at various angles through the cathode surface. In fact, the classical planar parallel field (PPF) irradiation geometry, i.e., with photons impinging perpendicularly to the cathode, limits the spectroscopic performance at high energies (E > 60 keV), if thick detectors are used, owing to the large spread in the paths of the charge carriers. These paths for the holes can be greatly reduced by using larger impinging angles, thus improving the energy resolution without losses in detection efficiency. Several sets of measurements have been carried out with a narrow photon beam, coming from collimated 57Co, 109Cd and 241Am sources; measurement angles ranged from 0° (orthogonal to the cathode) to 87° (beam grazing the cathode). The spectroscopic responses of the detectors for 14, 22, 60 and 122 keV photon energies have been analyzed. Detectors equipped with both full anodes and microstrip anodes were used. In this last case the rectangular collimated spot of the beam was used with the long side both parallel and orthogonal to the strip direction. The experimental results show that an actual improvement in the spectroscopic performance is obtained, mostly for the high-energy X-rays, by this tilting procedure. Further, this technique allows the evaluation of the detector dead layer thickness. The obtained performance and possible medical and space applications are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]