The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. The performance of these detectors is limited by the degree of uniformity in both electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alpha-particle response characterization of CdZnTe crystals fabricated into simple planar detectors is an effective tool to accurately study electron generation and transport. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. A clear correlation has been observed between the distribution of precipitates near the entrance contact on some crystals and their alpha-response maps. Further studies are ongoing to determine the mechanism for the observed response variations and the reason for the correlation. This paper presents the results of these studies and their relationship to coplanar-grid gamma-ray detector performance.

Detector grade, charge compensated Cd_1-xZn_xTe (CZT) crystals were treated by mechanical polishing, chemical solution etching, and radio-frequency gold sputtering. The crystals and detectors were next studied using direct current (DC) photoconductivity and low-temperature photoluminescence (PL). The DC photocurrent was analyzed with a steady state continuity equation and the results were correlated with PL and gamma-ray detector performance tests. The dependence of the electron lifetime on the light intensity of the CZT detector was consistent with a Shockley-Read one-center model. It was found that the surface recombination velocities, the effective mobility-lifetime products, and gamma-ray performances of CZT crystals are modified dramatically by the choice of chemical etchant.

Surface processing plays a major role in manufacturing CdZnTe semiconductor devices used for radiation detection. We are conducting a thorough, systematic study of surfaces and contacts and their effect on charge transport and signal formation in CdZnTe devices. We are investigating wet chemical processing techniques as well as treatment of surfaces with energetic neutral atoms. Our goal is to develop and implement improved surface treatment methods and device manufacturing techniques for large-volume CdZnTe detectors. In addition, we will determine how surfaces and electrical contacts affect the performance of CdZnTe devices used for radiation detection. In this paper, we will show how surface electronic properties influence carrier transport and signal formation in devices designed to simulate coplanar grid detectors. By altering the surface using a wet chemical process, we will show that charge collection is significantly effected by the conductivity of the surface.

We present results of experiments to characterize two large- volume, multi-element CdZnTe detectors for gamma-ray spectroscopy at high energy. The first detector consisted of four 1.5cm x 1.5cm x 0.75cm coplanar grid detectors. The measurements for the four-element design were performed with various configurations. The second detector consisted of eight 1 cm x 1 cm x 0.5 cm coplanar grid detectors arranged in a 2x2x3 array. The high-energy gamma-ray sources included ⁶⁰Co(1332), ²²⁸Th(2614), ²⁴⁴Cm/¹³C(6129), and Fe(n,(gamma) )(7645). The front end-electronics consisted of eight spectroscopy-grade preamplifiers/shapes/pulse stretchers, built on circuit boards close to the arrays. For the four-element measurements the shapers/pulse stretchers were replaced with commercial amplifiers. An eight-channel data acquisition system with list mode output was used to record gamma-ray events for each detector element in each array. The list mode data were analyzed to produce coincidence and single spectra and efficiencies for the various sources. The Compton continuum and the escape peaks are suppressed in the coincidence spectra relative to the singles spectra. We compare these spectra and efficiencies at high energy to results at lower energies and to Monte Carlo predictions.

We present preliminary results of X-ray measurements on three small format compound semiconductor arrays. The devices, a 4x4 pixel GaAs array fabricated on 325 micrometers epitaxial material, a 4x4 pixel CdZnTe array fabricated on a 4X4X1 mm³ mono crystal and a 3x3 TlBr array fabricated on a 2.7 x 2.7 x 1.0 mm³ mono crystal. The pixel size for all arrays is 350x350micrometers ². Results are presented of ⁵⁵Fe and ²⁴¹Am measurements at 5.9 keV and 59.54 keV. For detector temperatures <+5 degree(s)C typical FWHM energy resolutions of 410 eV, and 600 eV at 5.9 keV and 640 eV and 1.4 keV at 59.54 keV were recorded for the GaAs, and CdZnTe arrays, respectively. Unlike the GaAs and CdZnTe arrays, the TlBr array showed a much wider variation in pixel performance and was difficult to operate with all pixels at a common bias. For example, biasing the detector so that all pixels worked within the operating envelope of the preamplifiers resulted in average energy resolutions of 20 keV at 59.54 keV. However, optimizing the operating conditions of individual pixels resulted in a marked improvement to ~2keV.

A new class of hand-held, portable spectrometers based on large area (1cm²) CdTe detectors of thickness up to 3mm has been demonstrated to produce energy resolution of between 0.3 and 0.5% FWHM at 662 keV. The system uses a charge loss correction circuit for improved efficiency, and detector temperature stabilization to ensure consistent operation of the detector during field measurements over a wide range of ambient temperature. The system can operate continuously for up to 8hrs on rechargeable batteries. The signal output from the charge loss corrector is compatible with most analog and digital spectroscopy amplifiers and multi channel analyzers. Using a detector measuring 11.2 by 9.1 by 2.13 mm³, we have recently been able to obtain the first wide-range plutonium gamma-ray isotopic analysis with other than a cryogenically cooled germanium spectrometer. The CdTe spectrometer is capable of measuring small plutonium reference samples in about one hour, covering the range from low to high burnup. The isotopic analysis software used to obtain these results was FRAM Version 4 from LANL. The new spectrometer is expected to be useful for low-grade assay, as well as for some in-situ plutonium gamma-ray isotopics in lieu of cryogenically cooled Ge.

Semi-insulating Cd_1-xZn_xTe (x = 0.1) with improved structural perfection has been grown using a gradient freeze technique and active control of the Cd partial pressure in the ampoule, both during crystal growth and cool-down of the ingots. The crystal growth was performed in low temperature gradients to minimize thermal stress and achieve material with low dislocation density. Low growth rates were also used to avoid constitutional super-cooling effects. The gradient-freeze technique allowed the growth of large single crystals extending across the entire cross-section of the ingots. The control of the Cd partial pressure allowed the solidification and cool-down of the ingots close to the stoichiometric composition. As a result, the formation and incorporation of large size (>= 1 micrometers diameter) Te inclusions was avoided during crystallization and ingots with high structural perfection were achieved. The improved structural perfection of the material was found to be associated with large spatial variation in the compensation conditions in the ingots and a resulting spatial variation of the bulk electrical resistivity of the material, ranging from 10⁵ (Omega) cm to 10¹⁰ (Omega) cm. Samples cut from the high-resistivity sections of the ingots yield detectors exhibiting good spectral performance and an electron mobility-lifetime product of micrometers (tau) _e=1.2x10^-3 cm²/V.

Most single grains in cadmium zinc telluride (CdZnTe) grown by the high-pressure Bridgman (HPB) technique contain multiple twin boundaries. As a consequence, twin boundaries are one of the most common macroscopic material defects found in large area (400 to 700 mm²) CdZnTe specimens obtained from HPB ingots. Due to the prevalence of twin boundaries, understanding their effect on detector performance is key to the material selection process. Twin boundaries in several 2 mm thick large area specimens were first documented using infrared transmission imaging. These specimens were then fabricated into either 2mm pixel or planar detectors in order to examine the effect of the twin boundaries on detector performance. Preliminary results show that twin boundaries, which are decorated with tellurium inclusions, produce a reduction in detector efficiency and a degradation in resolution. The extent of the degradation appears to be a function of the density of tellurium inclusions.

The spectroscopic performance of cadmium zinc telluride (CZT) room temperature radiation detectors is currently limited by both bulk and surface imperfections introduced during the growth, harvesting and fabrication of these devices. Bulk imperfections including impurities, vacancies, interstitials, grain boundaries and dislocations have been relatively well studied and are known to trap charge and reduce detector performance. However, the effect of specific traps on the electronic decay process has been difficult to quantify. Surface imperfections including mechanical damage or adsorbed chemical species are also known to trap charge or increase leakage current, but it has proven difficult to characterize the electronic properties of CZT surfaces prior to electrode deposition. Here it is shown that the pulsed laser microwave cavity perturbation method can provide important information on the electronic decay process both in the bulk and at the surface of high pressure Bridgman CZT crystals. Electronic decay process both in the bulk and at the surface of high pressure Bridgman CZT crystals. Electronic decay time was measured as a function of temperature and surface conditions. It is shown that the electronic decay process in bulk CZT is consistent witha single deep hole trap at an energy between 600meV and 700meV. The effect of surface quality was resolved by analyzing distinct features in the photoconductivity decay curves. Atomic force microscopy was used to characterize the surface roughness. Rough or damaged surfaces exhibited persistent photoconductivity, which could be eliminated by etching with a bromine methanol solution.

Lead Iodide purified by zone refining, sublimation and evaporation and without purification was used as starting material for growing platelets by the vapor transport method. Growth was performed at vacuum and at 500 mmHg of Ar, during times from 10 to 25 days. Platelets grew at 200 -250 degree(s)C less than the source temperature, in the zone of maximum temperature gradient and perpendicular to the ampoule wall. Growth was performed several times and results were reproducible. Crystals have rectangular or hexagonal (0 0 1) faces, sizes up to 4x6 mm² and thickness from 50 to 250 micrometers , an exceptional good optical clarity and reflecting surfaces. Purity and stoichiometry of starting materials were determined by Inductively Coupled Plasma and wet techniques. Platelets were characterized by optical microscopy. Radiation detectors were fabricated with them and detector current density and apparent resistivity were determined by I-V curves, giving results 300 pA/cm² (30V) and 10¹³ (Omega) .cm. X-ray spectra were performed determining detector's energy resolution for different emissions, giving a resolution of 1 keV in the range of 10 - 20 keV radiations. According to electrical and spectrometric performance, optical microscopy and production yields, it was not necessary to use high purity starting material for obtaining excellent platelets. Correlation between optical and electrical properties of the crystals grown from this method and others previously grown from the melt are also discussed. Comparison between the growth of lead iodide platelets and mercuric iodide ones is included.

Polycrystalline films were grown by physical vapor deposition using lead iodide purified by evaporation as starting material. Purity and stoichiometry of starting material were determined by Inductively Coupled Plasma and wet procedures. Palladium film was thermal deposited as rear contact onto glass and alumina substrates 5x5 cm² in size. Onto it, lead iodide films were grown by evaporation with source temperatures from 430 to 450 degree(s)C in a 500 mmHg Argon atmosphere. Substrate temperature were from 200 to 250 degree(s)C and deposition times from 2 to 10 days. Film thickness was measured by 59.5 keV (²⁴¹Am) emission absorption, resulting values up to 50micrometers . The films were characterized by optical and atomic force microscopy, giving an average grain size up to 2micrometers . Film's low temperature photoluminescence confirmed the purity of the starting material. X-ray diffraction measurements of film's reflections show an intensity relation [(Sigma) I(0 0 l)] / [(Sigma) I(h k l)] from 0.2 to 0.9 that correlates to the film deposition temperature. For determining electrical and spectrometric properties, front palladium thermal deposition contacts and acrylic encapsulation were done onto the lead iodide films. Apparent resistivities from 10¹² to 10¹⁵ (Omega) .cm and current densities in the order of 6 pA/cm² (50 V) were determined. X-ray film response and uniformity was checked by irradiating with an X-ray medical equipment. Film properties and performance were correlated with starting material and substrate temperature, with previous results for lead iodide films grew by other methods and with similar results for mercuric iodide films.

An evaluation of the spectral performance of eight planar mercuric iodide (HgI₂) gamma-ray detectors under continuous bias voltage for a duration of up to 2000 hours has demonstrated the high degree of long-term stability of mercuric iodide as a radiation detector material. Spectral parameters determined in this evaluation include the %FWHM, the peak-to-valley and peak-to-background ratios, the gain stability of the full energy peak, and the preamplifier offset voltages. Isotopes with three distinct energies were used for these measurements: ¹³⁷Cs (662 keV), ⁵⁷Co (122 keV) and ²⁴¹Am (59 keV). The spectra were analyzed and spectral parameters were generated using Robwin, a spectral analysis program developed by Constellation Technology. Robwin performs simultaneous non-linear fitting of several key elements of the spectrum, emphasizing the continuum for the entire spectrum, the photopeak response function of all lines in the spectrum, the relative intrinsic efficiency of the detector and the photopeak resolution width. These findings provide further support for the widespread use of mercuric iodide as a room temperature semiconductor radiation detector material for energy spectrometry.

A new gamma camera with intrinsically high-resolution is described. A scintillating crystal is imaged onto a photon-counting 2D imaging detector. Most of the light is directed to PMTs for energy determination in this patented detector. Detection time and position can be recorded. Time resolution is as fine as the scintillation pulse allows. Sub-millimeter resolution has been achieved and 2048 linear pixels are possible. We are fabricating a transportable detector with 25 cm sensitive diameter and 1024x1024 pixels. Results taken with a prototype detector are presented.

This paper presents a novel technique for the presentation and display of x-ray images. This technique offers in a single image the ease of interpretation of the backscatter image with the penetration information from the transmission image. The Transmission Enhanced Backscatter Image (patent pending) also combines the features from a pair of transmission and backscatter images. The combination algorithm is discussed in terms of standard image processing operations. Sample images are included as well as potential applications of the Transmission Enhanced Backscatter Images to the security inspection industry.

A germanium-detector based, gamma-ray imaging system has been designed, fabricated, and tested. The detector, cryostat, electronics, readout, and imaging software are discussed. An 11 millimeter thick, 2 millimeter pitch 19x19 orthogonal strip planar germanium detector is used in front of a coaxial detector to provide broad energy coverage. The planar detector was fabricated using amorphous germanium contacts. Each channel is read out with a compact, low noise external FET preamplifier specially designed for this detector. A bank of shaping amplifiers, fast amplifiers, and fast leading edge discriminators were designed and fabricated to process the signals from preamplifiers. The readout system coordinates time coincident x-y strip addresses with an x-strip spectroscopy signal and a spectroscopy signal from the coaxial detector. This information is sent to a computer where an image is formed. Preliminary shadow and pinhole images demonstrate the viability of a germanium based imaging system. The excellent energy resolution of the germanium detector system provides isotopic imaging.

This study is concerned with the simulation and design of low-noise front-end electronics monolithically integrated on the same high-resistivity substrate as multielectrode silicon detectors, in a process made available by the Istituto per la Ricerca Scientifica e Tecnologica (ITC-IRST) of Trento, Italy. The integrated front-end solutions described in this paper use N-channel JFETs as basic elements. The first one is based upon an all-NJFET charge preamplifier designed to match detector capacitances of a few picofarads and available in both a resistive and a non resistive feedback configuration. In the second solution, a single NJFET in the source-follower configuration is connected to the detector, while its source is wired to an external readout channel through an integrated capacitor.

We report X-ray measurements on a prototype 1.1 cm², 32x32 GaAs pixel array produced to assess the technological feasibility of making large area, near Fano-limited arrays which operate near room temperature. Measurements were carried out on four widely separated pixels bot in our laboratories and using monochromatic X-ray pencil beams at the HASYLAB synchrotron research facility in Hamburg, Germany. The pixels were found to be very uniform both in their energy and spatial responses. For example, typical energy resolutions of 300 eV at 10.5 keV, rising to ~560 eV at 60 keV were achieved. The corresponding resolutions measured under full-area illumination were found to be the same within statistics, indicating uniform crystallinity and stoichiometry. Likewise, by raster scanning at 15 keV, 15x15 micrometers 2 beam across each of the pixels, the gain uniformity across the pixels (and by implication the entire array) was determined to be statistically flat.

Galactic cosmic rays (GCR) constantly impinge all planetary bodies and produce characteristic gamma-ray lines and leakage neutrons as reaction products. Together with gamma-ray lines produced by radioactive decay, these nuclear emissions provide a powerful tool for remotely measuring the chemical composition of planetary surfaces having little or no atmospheres. While lunar gamma-ray spectroscopy was first demonstrated with Apollo Gamma-Ray measurements, the full value of combined gamma-ray and neutron spectroscopy was shown for the first time with the Lunar Prospector Gamma-Ray (LP-GRS) and Neutron Spectrometers (LP-NS). Any new planetary mission will likely have the requirement that instrument mass and power be kept to a minimum. To satisfy such requirements, we have been designing a GR/NS instrument which combines all the functionality of the LP-GRS and LP-NS for a fraction of the mass and power. Specifically, our design uses a BGO scintillator crystal to measure gamma-rays from 0.5 - 10 MeV. A borated plastic scintillator and a lithium glass scintillator are used to separately measure thermal, epithermal, and fast neutrons as well as serve as an anticoincidence shield for the BGO. All three scintillators are packaged together in a compact phoswich design. Modifications to this design could include a CdZnTe gamma-ray detector for enhanced energy resolution at low energies (0.5 - 3 MeV). While care needs to be taken to ensure that an adequate count rate and background suppression is achieved for specific mission designs, previous mission successes demonstrate that a combined GR/NS provides essential information about planetary surfaces.

The n-type conduction of CdTe and Cd_0.96Zn_0.04Te crystals grown from melts with excess tellurium indicates that the origin of the donors with an energy level at 0.01 eV below the conduction band are most likely singly ionized tellurium antisites instead of cadmium interstitials. Based on this model, the deep level at 0.75 eV below the conduction band is therefore doubly ionized tellurium antisites. After increasing the zinc content over 7%, CdZnTe turns to p-type. The conduction type variation of CdZnTe crystals as a function of zinc contents is explained by the compensation between the donors of Te-antisites and the acceptors of Cd vacancies. High resitivity Cd_0.9Zn_0.1Te crystals are produced by compensating the p-type crystals with indium at a low doping level of 1- 5x10¹⁵ cm^-3. At room temperature, the high yield CdZnTe radiation detectors can resolve the six low energy peaks from the Am²⁴¹ source, a performance comparable to the best reported CdZnTe detectors.

Room-temperature semiconductor detectors are used in the field of nuclear safeguards. Gamma spectra obtained with hemispherical CdZnTe detectors present distortions due to incomplete charge collection. The full-energy peaks are asymmetric and they are characterized by a long low energy tailing. In the present work, the full-energy peak of 14 detectors CZT/500 (RITEC) and 8 CZT/60 (RITEC) was described with a set of four functions. The fit parameters were determined as a function of the energy for each detector and were applied to the calculation of the efficiency. The results show that, the fit parameter values are highly variable over the individual detectors of each type. It is not possible to associate a unique set of parameters to describe the full energy peak of a group of detectors. However, the use of individual parameter sets leads to a more precise evaluation of gamma spectra of fission products in nuclear spent fuel.

A review of growth methods used to produce Cd_1-xZn_xTe (0.0<x<0.20) crystals for radiation detector applications is presented. Most of the results emphasize the high-pressure Bridgman (HPB) method. For selected melt- grown HPB ingots, the liquid/solid segregation coefficients of some impurities were measured. The correlation of the impurity content and nuclear detector performance will be discussed. Extended defects and surface and bulk crystallinity were measured using triple and double axis x- ray diffraction techniques (TAD and DAD XRD), X-ray topography, and infrared microscopy. X-ray diffraction maps and IR images were generated and compared to gamma-ray detector tests to correlate macroscopic defects with the nuclear detector responses. Defects states of CZT were also investigated using low-temperature photoluminescence spectroscopy. Comparisons between the material and detector properties for different CZT growth methods will be discussed.

Basic operation principles of phonon-mediated low-temperature detectors of radiation are briefly reviewed. Physical properties required for the energy absorbers and for the phonon sensors of the detectors are introduced and discussed. Semiconductor thermistors, superconductive tunnel junctions and transition edge films as phonon sensors are presented and critically compared. State-of-art of single quantum detection with these devices is reported. Particular emphasis is given to the detection of X-rays and Gamma-rays. In this field, low temperature devices can provide higher efficiency and energy resolution than conventional technology. The main point is that phonon-mediated low temperature detectors are characterized by a large flexibility in the choice of the material for the active part of the device. High Z materials with the proper thermal properties can therefore be selected, providing at the same time high efficiency and high signal-to-noise ratio. The unique features of low temperature detectors allow their use in many fields, ranging from fundamental physics (neutrino properties, dark matter search, astronomy) to industrial applications (X-ray fluorescence analysis).

High-Z low-temperature calorimeters are developed by an Italian collaboration (Milano-Como-Gran Sasso Underground Laboratories) in order to search for rare nuclear events and Dark Matter massive candidates. They exhibit an excellent energy resolution, close to that of Ge-diodes, but a much higher efficiency. Different high-Z materials were initially employed . A many-years optimisation work on tellurium oxide (TeO2) lead to impressive results: devices with total masses around 750 g present FWHM energy resolutions on gamma-ray peaks ranging from 1 KeV (close to the 5 KeV energy threshold) to 2.6 KeV at 2615 KeV (208Tl gamma line). A 3.2 KeV FWHM energy resolution was obtained at 5.4 MeV (210Po alpha line), which is by far the best one ever achieved with any alpha detector. These devices, operated at about 10 mK, consist of a TeO2 single crystal thermally coupled to a 50 mg Neutron Transmutation Doped (NTD) Ge crystal working as a temperature sensor. Special care was devoted to methods for response linearization and temporal stabilisation. Devices based on the same principle and specifically optimised could find applications in several fields like gamma-ray astrophysics, nuclear physics searches, environmental monitoring and radiation metrology.

The description of the High Pressure Xenon Gamma-Ray Detector (HPXeD) and its main characteristics are considered in the context of the search for hidden fissile materials. The results of HPXeD measurements of gamma-radiation from radioactive sources, which are covered by lead, iron and aluminium shields, are analyzed and discussed. The use of special software for processing data is shown to improve the potential of radioactive material detection, including the identification and estimation of the main protective shield parameters.

PELAN (Pulsed ELemental Analysis with Neutrons) is a portable system for the detection of explosives, weighing less than 45 kg. It is based on the principle that explosives and other contraband contain various chemical elements such as H, C, N, O, etc. in quantities and ratios that differentiate them from other innocuous substances. Neutrons are produced with a pulsed 14 MeV (d-T) neutron generator. Separate gamma-ray spectra from fast neutron, thermal neutron and activation reactions are accumulated and analyzed to determine elemental content. Data analysis is performed in an automatic manner and a final result of whether a threat is present is returned to the operator. Recently, a number of modifications were performed to improve PELAN. Since the bismuth germanate detector's light output changes with temperature, an automatic gain stabilization system has been designed. Also, the signal-to-noise ratio has been increased by the innovative use of a veto shield placed around the bismuth germanate detector. This shield reduces Compton-continuum as well as the background gamma rays. Results from tests of the gain stabilization and the veto shield will be shown.

A DT neutron generator has been integrated into the Canadian Improved Landmine Detection Program's Thermal Neutron Activation sensor. The generator has been redesigned from a commercial version, and the moderator structure around the generator has been completely redesigned. These developments allow the DT generator and its moderator structure to be placed interchangeably into the location currently occupied by a ²⁵²Cf source and its moderator structure. Experimental and calculational studies have helped to define the optimal operating parameters for the neutron generator in this application. Performance comparisons between the old californium-based system and the new DT-generator-based system have demonstrated that the new system out-performs the old in all tested scenarios, particularly when the mine is deeply buried or when the source is not directly over the explosive. This is in excellent agreement with calculations performed in the design phase of this system. Combined with the myriad other benefits associated with DT generators over isotopic sources, these results demonstrate the desirability of using a DT generator in a TNA land mine detection system.

A multi-channel, fast, hard x-ray diode spectrometer is being developed at the Nevada Terawatt facility. This spectrometer helps facilitate the study of the time evolution of hard x-ray emissions from hot, dense plasma. Each channel in the array can be adjusted individually with shielded view areas, allowing small areas of an x-ray source to be isolated and studied by region. This spatial resolution capability will permit a better understanding of the mechanisms present in hot, dense plasma. Results will be presented of experimental tests, and their interpretation, pertaining to the hard x-ray emissions generated from an x-pinch source in a pulse-power type device.

A new five-channel spectrometer is designed for registration of x-ray spectral line emissions from plasmas with temporal resolution. All channels are independent from each other and include wide variety of dispersing elements (crystals and/or multiplayer mirrors) and detectors (Si-diodes or PCD). Sixth channel is used for device alignments with minimum adjustments can be used as channel for transmission diffraction grating spectrometer or channel for another time resolved detector. The device was used in experiments with different plasma sources in different configurations and showed its reliability and flexibility.

Ramo's theorem provides a convenient way of simulating the currents induced on the electrodes of a radiation detector by the movement of charge carriers. The concept of weighting potential or of weighting field is the key ingredient in the calculation of the induced currents. The effect of the space charge present in the detector on the weighting potentials is discussed. Three types of space charge are considered and are shown to have different effects on the induced currents. These are 1) the polarization space charge, 2) a fixed volume space charge and 3) the charge stored in the depletion layer of a semiconductor detector. A new definition of the weighting potential is proposed that is valid for all situations.

In this paper we present results of our investigations on the technology improvement for high-grade CdTe<Cl> and CdZnTe single-crystals growth as well as results of the obtained materials testing by photoluminescence method. Perspectives for the materials utilization in detectors and devices of radiation control are discussed. Design features and characteristics of the developed personal (gamma) - and X-radiation dosimeters on the base of CdTe<Cl> detectors and (gamma) -radiation spectrometers on the base of CdZnTe detectors are presented and discussed as well.

Experimental conditions for a growth of near stoichiometric high resistive CdTe single crystals with a minimized concentration of point defects have to be defined. The position of the stoichiometric line in the pressure-temperature (P-T) phase diagram was evaluated from high-temperature in situ galvanomagntic measurements. Calculations based on a model of two major native defects (Cd vacancy and Cd interstitial) show, that a very small variation of Cd pressure P_{Cd} results in a strong generation of uncompensated native defects. Modelling of room temperature carrier density in dependence of the deep defect density N_DD, P_Cd, and annealing temperature T shows, that the range of optimal P_Cd, at which the high resistivity can be reached, broadens with increasing N_DD or decreasing T. It is shown, that at low T<450 degree(s)C the deep defect density <10¹⁵cm^-3 is sufficient to grow the high resistive CdTe. CdTe doped with Vanadium is used as a model example.

Thermoelectric Effect Spectroscopy and Thermally Stimulated Current measurements were used to investigate trapping levels in a semi-insulating CdTe and Cd_1-xZn_xTe crystals from multiple ingots grown by vertical Bridgman with over pressure control and high-pressure Bridgman methods. The crystals from different growth methods have different dislocation densities as well as Zn concentrations. The thermal ionization energies of these levels were extracted using both the variable heating rate and initial rise methods; the trapping cross sections were then calculated using the temperature maximum method. We report here that the shallow levels observed at E₁=0.11+/- 0.02 and E₂=0.17+/- 0.02 eV are intrinsic and the latter level is most likely related to the dislocation density.