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Introduction to fifth international workshop on mercuric iodide nuclear radiation detectors

Description: Mercuric iodide is a wide bandgap semiconductor, with Eg approx. = 2.14 eV at room temperature. Therefore, HgI/sub 2/ is totally different from the well-studied, narrower gap, elemental semiconductors such as Si and Ge, and also different in its physical and chemical properties from the known semiconductor binary zinc-blend compounds such as GaAs or InP. The purpose of studies in the last decade was to further our understanding of HgI/sub 2/; recent progress is reported. (WHK)
Date: January 1, 1982
Creator: Schieber, M.
Partner: UNT Libraries Government Documents Department

Crystal growth and applications of mercuric iodide. Report S-242-TP

Description: A brief summary is given of a paper which discusses the crystal growth of mercuric iodide, a high-Z wide bandgap semiconductor suitable as a low noise, room temperature x-ray and gamma-ray detector. The paper summarized also reviews the state-of-the-art of the synthesis and purification of the starting material, mechanical properties and dislocation structure of HgI/sub 2/, and recent success in the development of thick HgI/sub 2/ spectrometers. (LEW)
Date: January 1, 1983
Creator: Schieber, M.; Roth, M. & Schnepple, W.F.
Partner: UNT Libraries Government Documents Department

Search for improved surface treatment procedures in fabrication of HgI/sub 2/ x-ray spectrometers

Description: The influence of various fabrication parameters on the surface quality of HgI/sub 2/ x-ray spectrometers was studied in detail. Exposure of etched HgI/sub 2/ to ambient atmosphere for approx. 24 hours may reduce the electron surface recombination velocity by almost an order of magnitude. Reduction of the etching solution temperature (KI in water) to about 0/sup 0/C and an increase of the KI concentration to approx. 20 wt % are also important.
Date: January 1, 1980
Creator: Levi, A.; Burger, A.; Nissenbaum, J.; Schieber, M. & Burshtein, Z.
Partner: UNT Libraries Government Documents Department

Preliminary studies of charge carrier transport in mercuric iodide radiation detectors

Description: Mercuric iodide single crystals have been grown by static and dynamic sublimation methods. Characteristics of contacts and detector capacitance have been studied by photon excitation methods. Gamma and x-ray spectrometry has been carried out with completed detectors showing resolutions comparable to the best results published to date. A measurement of hole trapping length has been made from the spectral shapes observed and has been found to be approximately 0.3 mm. Transient waveform analysis with alpha-particle excitation shows hole mobilities of approximately 3 cm/sup 2//V-sec for a highly purified crystal and 0.05 for an expected less pure crystal. Electron mobilities of 120 cm/sup 2// Vsec are observed. An attempt is made to explain the observed tansient waveforms in terms of a single dominant trap model, With only partial success. Due to the strongly excitonic character of the material, it is proposed that the unfamiliar observations made regarding transport properties with the HgI/sub 2/ detectors studied may be due to exciton dissociation under high electric fields, to long exciton lifetimes and to interactions between excitons and trapping centers in the material. (auth)
Date: January 1, 1973
Creator: Llacer, J.; Watt, M.K.; Schieber, M.; Carlston, R. & Schnepple, W.
Partner: UNT Libraries Government Documents Department

Improved fabrication of HgI/sub 2/ nuclear radiation detectors by machine-cleaving

Description: The perfection of machine-cleaved sections from HgI/sub 2/ bulk crystals was examined. The perfection of the machine-cleaved sections as established by gamma diffraction rocking curves was found to be much better than the perfection of hand-cleaved sections or as grown thin platelets, reaching a perfection similar to that of the wire-sawn sections of HgI/sub 2/. A correlation between the perfection and the thickness of the machine-cleaved section was also found, i.e., the thicker the cleaved-section the more perfect it is. The reproducibility of the fabrication was significantly improved by using machine cleaving in the process of fabrication. Large single crystals of HgI/sub 2/ weighing 20 to 200 g, can be grown from the vapor phase using the TOM Technique. In order to fabricate nuclear radiation detectors from these single crystals, thin sections of about 0.4 to 0.8 mm thickness have to be prepared. Up till now, the state-of-the-art of fabricating HgI/sub 2/ nuclear radiation detectors involved two methods to get thin sections from the large single crystals: (1) hand-cleaving using a razor-blade and (2) solution wire sawing. The chemical wire sawing method involves a loss of about 50% of the crystal volume and is usually followed by a chemical polishing process which involves a significant loss of volume of the original volume. This procedure is complicated and wasteful. The traditional fabrication method, i.e., hand-cleaving followed by rapid nonselective chemical etching, is simpler and less wasteful.
Date: January 1, 1982
Creator: Levi, A.; Burger, A.; Schieber, M.; Vandenberg, L.; Yellon, W.B. & Alkire, R.W.
Partner: UNT Libraries Government Documents Department

Fabrication of HgI/sub 2/ nuclear radiation detectors by machine cleaving

Description: A new device has been designed to facilitate the cleaving of thin sections from bulk crystals of mercuric iodide. Crystallographic perfection of the machine-cleaved sections was established by gamma-ray diffraction rocking curves and was found to be higher than the perfection of hand-cleaved sections or of as-grown thin platelets, approaching the perfection of string-sawn sections of HgI/sub 2/. A correlation was found between the perfection and thickness of the machine-cleaved sections, i.e., the thicker the section the more perfect it is. Reproducibility of the fabrication was significantly improved by using machine cleaving in the fabrication process.
Date: January 1, 1982
Creator: Levi, A.; Burger, A.; Schieber, M.; van den Berg, L.; Yelon, W.B. & Alkire, R.W.
Partner: UNT Libraries Government Documents Department

Correlation between nuclear response and defects in CZT

Description: Vertical high pressure Bridgman (VHPB) was considered until now to be the most successful crystal growth method to produce Cd{sub 1{minus}x}Zn{sub x}Te (CZT), (0.04 < x < 0.24), for X- and gamma-ray detector crystals. Recently Horizontal Bridgman (HB) Cd{sub 1{minus}x}Zn{sub x}Te crystals produced by IMARAD Co. have also been successfully fabricated into nuclear spectroscopic radiation detectors. In view of the database of many years' study of the electrical properties of VHPB CZT grown and obtained from various sources, the authors also studied the HB CZT crystals in order to compare the defects present in both different kinds of crystals grown by different methods. The VHB-grown samples were examined using thermoelectric emission spectroscopy (TEES), X- and gamma ray spectroscopy and laser induced transient charge technique (TCT). The surface and the bulk crystalline homogeneity were mapped using triaxial double crystal x-ray diffraction (TADXRD) and infrared transmission spectroscopy (IR). They have found a correlation between crystallinity, IR transmission microstructure and trapping times. Spectrometer grade VHPB CZT crystals exhibit trapping times of 20 {micro}s for electrons and 7 {micro}s for holes, however, regions, which were opaque to IR transmission, had trapping times shorter by one order of magnitude. The trapping times of HB CZT for electrons, were 10--15 {micro}s. A similar trend has been observed on VHPB CZT crystals with poor crystallinity. The HB CZT crystals that they measured in this study had a crystallinity that was inferior to that of the best spectroscopic grade VHPB crystals.
Date: July 19, 1999
Creator: Hermon, H.; Schieber, M.; James, R. B.; Lee, E.; Cross, E.; Goorsky, M. et al.
Partner: UNT Libraries Government Documents Department

Analysis of CZT crystals and detectors grown in Russia and the Ukraine by high-pressure Bridgman methods

Description: Sandia National Laboratories (SNL) is leading an effort to evaluate vertical high pressure Bridgman (VHPB) Cd{sub 1-x}Zn{sub x}Te (CZT) crystals grown in the former Soviet Union (FSU) (Ukraine and Russia), in order to study the parameters limiting the crystal quality and the radiation detector performance. The stoichiometry of the CZT crystals, with 0.04 < x < 0.25, has been determined by methods such as proton-induced X-ray emission (PIXE), X-ray diffraction (XRD), microprobe analysis and laser ablation ICP mass spectroscopy (LA-ICP/MS). Other methods such as triaxial double crystal x-ray diffraction (TADXRD), infrared transmission spectroscopy (IR), atomic force microscopy (AFM), thermoelectric emission spectroscopy (TEES) and laser induced transient charge technique (TCT) were also used to evaluate the material properties. The authors have measured the zinc distribution in a CZT ingot along the axial direction and also its homogeneity. The (Cd+Zn)/Te average ratio measured on the Ukraine crystals was 1.2, compared to the ratio of 0.9-1.06 on the Russian ingots. The IR transmission showed highly decorated grain boundaries with precipitates and hollow bubbles. Microprobe elemental analysis and LA-ICP/MS showed carbon precipitates in the CZT bulk and carbon deposits along grain boundaries. The higher concentration of impurities and the imperfect crystallinity lead to shorter electron and hole lifetimes in the range of 0.5--2 {micro}s and 0.1 {micro}s respectively, compared to 3--20 {micro}s and 1--7 {micro}s measured on US spectrometer grade CZT detectors. These results are consistent with the lower resistivity and worse crystalline perfection of these crystals, compared to US grown CZT. However, recently grown CZT from FSU exhibited better detector performance and good response to alpha particles.
Date: January 10, 2000
Creator: Hermon, H.; Schieber, M.; James, R. B.; Lee, E. Y.; Yang, N.; Antolak, A. J. et al.
Partner: UNT Libraries Government Documents Department

Evaluation of CZT crystals from the former Soviet Union

Description: Vertical high pressure Bridgman (VHPB) Cd{sub 1{minus}x}Zn{sub x}Te (0.04 < x < 0.24) detector crystals grown in the Ukraine and Russia have been evaluated and compared to US-grown materials. Various analytical techniques were used to study the materials for trace impurities, precipitates, crystallinity, and electrical transport properties. Relatively high concentrations of carbon and trace impurities such as Se, Nd and Si have been detected in the crystals. In most cases, the crystals showed lower resistivity than US-grown CZT. However, recent crystals grown in Russia exhibited better detector performance than those grown in prior years, and good response to an {sup 241}Am radioactive source was found. Electron lifetimes below 1 {micro}s were measured in crystals having significant numbers of micro-defects, compared to lifetimes of 5--15 {micro}s found in spectrometer grade materials produced in the US. Furthermore, the zinc composition along the growth axis showed better homogeneity in comparison with the US material.
Date: January 26, 1998
Creator: Hermon, H.; Schieber, M.; James, R. B.; Antolak, A. J.; Morse, D. H.; Brunett, B. et al.
Partner: UNT Libraries Government Documents Department