Cadmium Zinc Telluride (CZT) achieves excellent spatial resolution and good energy resolution over the broad energy range from several keV into the MeV energy range. In this paper we present the results of a systematic study of the performance of CZT detectors manufacturered by Orbotech (before IMARAD) depending on surface preparation, contact materials and contact deposition. The standard Orbotech detectors have the dimension of 2.0×2.0×0.5 cm. They have a pixellated In anode with 8×8 pixels and a monolithic In cathode. Using the same CZT substrates several times, we have made a direct comparison of the performance of different contact materials by replacing the cathode and/or the anode contacts with several high- workfunction metals. We present the performance of the detectors and conclude with an overview over our ongoing detector optimization.

A high-intensity X-ray beam collimated down to a 10-micrometer spot size, available at Brookhaven's National Synchrotron Light Source (NSLS), was employed to perform X-ray mapping to measure the correlation between microscopic defects (precipitates) and variations in the collected charges in long-drift CdZnTe (CZT) detectors. First, we use X-ray diffraction topography (XDT) measurements at the high-energy beamline and IR microscopy to identify the defects distribution and strains in the bulk of CZT crystals. Then, we perform X-ray raster scans of the CZT detectors to measure their responses with 10-micrometer spatial resolution. The brightness of the source allows for good statistics in very short times. Precipitates that were singled out with X-ray scans are locally investigated by applying pulse-shape analysis. The presentation discusses how precipitates affect the device performance.

The limitations of energy resolution of scintillation detectors are discussed with a special emphasis on non-proportionality response of scintillators to gamma rays and electrons, which is of crucial importance to an intrinsic energy resolution of the crystals. Examples of the study carried out with different crystals and particularly those of tests of undoped NaI and CsI at liquid nitrogen temperature with the light readout by avalanche photodiodes are presented suggesting strongly that the non-proportionality of the crystals are not only their intrinsic property and may be improved due to selective co-doping.

In this paper, we report on the growth of a relatively new scintillator from the crystal K₂LaX₅ family (X=Cl, Br, I), K₂LaBr₅:Ce³⁺, and its scintillation properties for γ-ray spectroscopy. The material was synthesized by reacting stoichiometric amounts of LaBr₃ and KBr. Prior to synthesis, the material was heated under dynamic vacuum to remove water molecule from the starting material. The synthesized material was then mixed with 10 mol % CeBr₃, subsequently sealed in an evacuated quartz ampule. The crystals were grown by vertical Bridgman growth technique. An energy resolution of ~ 5% (FWHM) for the 662 KeV gamma ray was obtained with an encapsulated K₂LaBr₅:Ce³⁺ scintillator. The light yield non-proportionality achieved versus the energy range of 31 KeV to 1333 KeV was about 3%.

Solid scintillators are gaining interest due to their increased applications in radiation detection. A series of sol-gel monoliths were prepared from polystyrene and 4,4'-bis(triethoxysilyl)biphenyl through a room-temperature sol-gel method based on π-π interactions. The hybrid organic-inorganic scintillating dye is serving not only as a scintillator but also as a silica precursor, which has the advantage of eliminating leaching of the fluorescent sensitizer from the matrix as well as enhancing the loading of the dye without causing phase separation. The photoluminescence studies of the gel samples show emission in the blue region. The efficiencies of these plastic scintillators were measured through detection of alpha particles.

An X-ray color scanner that can distinguish between different photon energies has been developed using X-ray line sensors. This scanner consists of a 64-channel cadmium telluride (CdTe) radiation detection array, a 64-channel application specific integrated circuit (ASIC), and a signal processing circuit that controls both the ASIC and data communication. An X-ray or gamma ray photon absorbed by the CdTe detector is converted into an electric charge proportional to the energy of the incident photon and amplified to an electric pulse with an amplitude proportional to the photon's energy. The pulse's height is then analyzed by the ASIC using 5 different threshold voltages. The X-ray color scanner has the ability to count up to approximately 2 million photons per CdTe element per second. When used as a photon counting system, the X-ray color sensor has a very high signal to noise ratio, since it removes electric noise in the low energy spectrum during the analysis process. When appropriately selected energy thresholds are used, X-ray color scanners, used for X-ray imaging or X-ray CT, were shown to remove the effects of beam-scattering noise and beam-hardening.

Polycrystalline PbI₂ films were deposited by Physical Vapor Deposition on ITO and gold coated glass substrates. The structural characterization of the samples was studied by using X-ray diffraction and Scanning Electron Microscopy. Two different preferred orientations - [00l] and [110] directions were found as a function of substrate temperatures, and type of substrate (ITO or Gold). The [110] direction is perpendicular to the c-axis in the hexagonal system. Four types of crystalline preferred orientations were found and named as A, B, C, and D type. The different samples were also annealed at different temperatures to improve their densities. The nuclear spectroscopic data for single crystal and polycrystalline samples were taken with 5.64 MeV Alpha particles emitted from ²⁴¹Am source. The samples were also measured for their response to a blue light LED irradiation. Both polarities were studied for all samples. In most measurements it was confirmed that holes are the major carriers. The correlation between microstructure and electrical properties as affected by annealing and crystalline orientation is discussed.

The stability of high-pressure xenon gamma-ray specrometers has been measured at Mirmar Sensor. Stability was measured by tracking the ¹³⁷Cs peak of the entire spectroscopy system including detector, preamplifier, amplifier, and multichannle analyzer over 6 days in a laboratory setting. Overall system gain drift is about 0.016%. Resolution drifts are about 0.15%. The overall energy resolution is between 1.7 and 1.8% at 662 keV.

We report progress in the study of a thick CZT strip detector module designed to perform gamma-ray spectroscopy and 3-D imaging. We report preliminary performance measurements of 7.5 mm thick single-sided charge-sharing strip detector prototype devices. This design features both row and column contacts on the anode surface. This electron-only approach addresses problems associated with poor hole transport in CZT that limit the thickness and energy range of double-sided strip detectors. This work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA Black Hole Finder Probe (BHFP)and Advanced Compton Telescope (ACT). This new design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125 μm anode contacts on 225 μm pitch. Our results demonstrate the principle of operation but suggest that even finer anode contact feature sizes will be necessary to achieve the desired performance.

The procedures of fabrication of electrical contacts and modification of their properties in high-resistivity CdTe:Cl crystals have been investigated to obtain diodes for nuclear radiation detectors. Excimer laser annealing was utilized to attain heavy In doping of the CdTe surface region. Using various preliminary treatments of the CdTe crystal surface and studying electrode vacuum deposition procedures and laser processing of CdTe crystals pre-coated with an In dopant film, the optimal conditions of fabrication of In/CdTe/Au diode structures were elaborated. It was considered that a Schottky barrier at the Au-CdTe contact was formed and a shallow built-in p-n junction at the In-CdTe interface arose as a result of both thermal In diffusion and effect of laser-induced shock waves under irradiation of the samples from the In-contact side. The In/CdTe/Au diodes had sharp I-V characteristics. Laser irradiation remarkably decreased the leakage current and increased the forward current. Moreover, the electrical properties of laser-formed p-n junctions were being improved after storage of the samples. The detectors showed a low leakage current (1-8 nA/cm² at 100 V and 300 K), optimal electrical barrier (0.72 eV) and high energy resolution (3.1 keV FWHM at 122 keV at γ-ray peak of Co-57). Variations in leakage currents and radiation detection properties of fabricated CdTe wafers and pixels diced from the wafers were associated with laser stimulated defect formation in the bulk of CdTe and generation of extended defects during the pixels performance. The regimes of injection and recombination in fabricated CdTe diodes have been analyzed.

We have been developed Si/CdTe semiconductor Compton telescope to explore the universe in the energy band from several 10 keV to a few MeV. In our Si/CdTe Compton telescope, a stacked thin CdTe pixel detector is a key component to achieve higher detection effciency for MeV gamma-rays maintaining high energy resolution. In this paper, results from a prototype stacked CdTe pixel detector are reported, which consists of three layers of CdTe pixel detectors and one CdTe pixel detector at their side. With this prototype detector, we succeeded in Compton reconstruction of images and spectra in the energy band from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively.

Pulse shape analysis is proved to be a powerful tool to characterize the performance of CdZnTe devices and understand their operating principles. It allows one to investigate the device configurations, electron transport properties, effects governing charge collection, electric-field distributions, signal charge formation, etc. This work describes an application of different techniques based on the pulse shape measurements to characterize pixel, coplanar-grid, and virtual Frisch-grid devices and understand the electronic properties of CZT material provided by different vendors. We report new results that may explain the performance limits of these devices.

New results from studies of coplanar-grid CdZnTe (CZT) detectors are presented. The coplanar-grid detectors were investigated by using a highly collimated X-ray beam available at Brookhaven's National Synchrotron Light Source and by applying a pulse-shape analysis. The coplanar-grid detector operates as a single-carrier device. Despite the fact that its operational principle is well known and has been investigated by many groups in the past, we found some new details that may explain the performance limits of these types of devices. The experimental results have been confirmed by extensive computer modeling.

A new approach to hard X-ray imaging is proposed, based on staring optics consisting of a lobster-eye lens. This new Staring Imaging Lobster-Eye X-Ray approach is especially suited to X-ray lobster-eye imaging of non-astronomical objects at finite distances, because the staring optics replacing the standard scanning optics, result in an extremely efficient power budget, making possible not only the use of low-efficiency Compton backscattering but also operation with low-flux X-ray beams, increasing operator safety. The lobster-eye optics, consisting of square-cross-section microchannels, transmit an X-ray beam by total external reflection. This mode of operation has already been verified for viewing astronomical objects. Its major challenge is minimizing image defocusing by apodization. For this purpose, a new lens imaging equation is derived, and a new local optical axis concept is defined. Applications include medical imaging, cargo inspection, non-destructive testing, industrial and security safeguards, and surveillance.

The transport properties of electrons and holes in mercuric iodide determine the performance of detectors. The relatively low levels of these properties limit the volume of detectors with high spectral resolution that can be fabricated and leads to long pulse collection times. These transport parameters can be increased by optimizing the material processing, the crystal growth, and the detector fabrication. This paper will present our own results obtained by analysis of individual pulse shapes. The values for the mobilities generally measured are between 60-90 cm²/Vsec for electrons and 2-4 cm²/Vsec for holes. These results will be compared with the values published by other investigators. Possible reasons for the differences in the reported values will be discussed and explanations will be suggested.

Results obtained from development, construction, testing, and evaluation of GaAs:Cr ionizing radiation detectors and X-ray digital imaging systems based on such detectors are presented. The technology devised is shown to make possible the development of detectors with the following parameters: electron mobility - electron lifetime product of 10^-4cm²/V, hole mobility - hole lifetime product of 10^-6cm²/V, gamma-radiation resistance of ≥ 51Mrad, active layer thickness as great as 800μm, and detector chip dimensions of 51×51mm². The detectors under consideration exhibit high speed of response (≤10ns) and high X- and charged-particle radiation sensitivity. The detector output signal is linearly dependent on the X-ray irradiation dose rate up to 120mR/s and X-ray quantum energy up to 3MeV. Scanning detection units to be used in mammographs and fluorographs and in nondestructive testing devices were constructed and tested. The spatial resolution of the detection systems is 5lp/mm.

The performance of semiconductor radiation detectors is a function of electronic properties which are in turn related to crystallographic quality. In this paper we used devices from <100> and <110> growth regions of several different HgI₂ crystals grown by the PVD method. We measured I/V characteristics of HgI₂ devices over the range of +/-1000V. Voltages were ramped at different rates and at a range of temperatures (-70^oC to +20^oC) and the dark current decreased with temperature. Several devices exhibited negative differential resistance indicating field enhanced trapping and/or the formation of high-field domains. These devices exhibited NDR at both positive and negative voltages and it was observed that the current peak reduced with repeated cycling of positive bias indicating the reduction of carriers with time. After applying a negative bias, the current peak on the positive bias increased dramatically indicating that the traps were repopulated. These experimental results were modeled with several analytical expressions of conduction processes, considering both semiconductor and insulator models, e.g., Frenkel-Poole, Schottky, and space-charge-limited emission, toward lending insight to mechanisms resulting in HgI₂ detector conditioning.

Diamond has the highest radiation-damage level among radiation-detector semiconductor materials. Besides, low carbon nucleus charge, Z=6, provides tissue equivalence of diamond detectors. This made it possible to create unique natural diamond ionizing-radiation detectors possessing properties unachievable, for present time, for other materials. Perfection and new developments of diamond-based detectors encounter a number of obstacles, the main of which is related to empirical approach to the development in consequence of the lack of detailed understanding in physical mechanisms of such detector operation. This paper is an attempt to approach such understanding with the use of computer modeling of diamond detector operation and the comparison of this model with experimental results obtained for natural- and synthetic-diamond detectors. The model developed first makes it possible to explain main experimentally observed peculiarities of characteristics of natural diamond detectors exposed to hard X- and gamma rays, neutrons, alpha particles, and UV radiation. It is shown that for this purpose the model must be based on the charge carrier recombination process that ensures the variation of carrier lifetimes depending on the space charge value, in the whole detector volume. All calculations are conducted for two-level model of recombination which fits this requirement and, in particular, ensures experimentally observed lifetimes of charge carriers on the order of 10^-8 s with the concentration of impurities of 10¹⁷ cm^-3 real for natural diamond.

512-pixel CdTe super-liner imaging scanner was developed. This device was consist with 512 chips of M-π-n CdTe diode detector fabricated by excimer laser doping process, 8 chips of photon-counting mode 64ch ASIC with FPGA circuit, USB2.0 interface with 1-CPU. It has 5 discriminated levels and over 2Mcps count rate for X-ray penetration imaging. This imaging scanner has 512 discrete CdTe chips for detector arrays with the length of 2.0mm, width of 0.8mm and thickness of 0.5mm. These chips were mounted in four plover array rows for high-resolution imaging with 0.5mm-pitch, therefore the pixel pitch was over the pixel width. When images were taken with scanning system with this arrays, we could obtain over-resolution than pixel width. In this paper, this "over-resolution" imaging will be called "super resolution imaging". In high-resolution imaging device, the pixel devices on one substrate were formed by integrated process, or many discrete detector chips were installed on circuit board, usually. In the latter case, it is easer to make each detector chips than former case, and it are no need to consider charge sharing phenomena compare with one-chip pixel devices. However, a decrease in pixel pitch makes the mount to the detector chip to the ASIC board difficult because the handling will also be difficult The super-resolution technique in this scanner by pixel-shift method for X-ray imaging is shown in this paper

We report on a new photon-counting detector possessing unprecedented spatial resolution, moderate spectral resolution and high background-rejection capability for 0.1-100 keV X-rays. It consists of an X-ray charge-coupled device (CCD) and scintillator. The scintillator is directly deposited on the back surface of the X-ray CCD. Low-energy X-rays below 10 keV can be directly detected in the CCD. The majority of hard X-rays above 10 keV pass through the CCD but can be detected in the scintillator, generating visible light photons there. Since CCDs have a moderate detection effciency for visible light photons, they can be absorbed by the CCD. We evaluated the spectroscopic performance for hard X-rays at the synchrotron facility, SPring-8, and found a good linear relationship between the incident X-ray energy and the pulse height up to 80 keV. The on-axis image of the hard X-ray telescope, supermirror, was measured by our device at 40 keV. A sharp core and the wing structure can be clearly imaged and high imaging capability of the SD-CCD can be demonstrated.

Wide-gap II-VI semiconductor crystalline materials are conventionally used in laser optics, light emitting devices, and nuclear detectors. The advances made in the studies of nanocrystals and in the associated technologies have created great interest in the design of semiconductor devices based on these new materials. The objectives of this work are to study the microstructure and the properties of the new material produced through CdTe nanopowder compression and to consider the prospects of its use in the design of ionizing-radiation detectors and in laser optics. Highly dense material produced of 7-10 nm CdTe particles under pressure of 20-600 MPa at temperatures from 20 to 200°C was analyzed using x-ray diffractometry, texture analysis, light and scanning electron microscopy, and optical spectrophotometry. The mechanical and electrical properties of the compacted material were measured and compared with similar characteristics of the conventionally grown single crystals. Phase transformation from metastable to stable crystal structure caused by deformation was observed in the material. Sharp crystallographic texture {001} that apparently affects specific mechanical, electrical and optical characteristics of compacted CdTe was observed. The specific resistivity calculated from the linear current-voltage characteristics was about 10¹⁰ Ohm×cm, which is aapromisingly high value regarding the possibility of using this material in the design of semiconductor radiation detectors. The optical spectra show that the transmittance in the infrared region is sufficient to consider the prospects of possible applications of CdTe ceramics in laser optics.

Preliminary studies on ZnO single crystals implanted with In (donor), As (acceptor) and ¹¹¹Ag (acceptor) are presented. Each dopants electronic structure was investigated by means of positron annihilation lifetime (PALS) and photoluminescence (PL) measurements. For some of the crystals, the lifetime spectra revealed the presence of effective positron traps. Moreover, for all samples the luminescence spectra consist of a near-band-edge (NBE) and a deep-level (DL) emission. The observed trends will be discussed in terms of the origin, nature and charge state of the induced defects involved.

Photon-counting mode CdTe two-dimension X-ray imaging device with energy distinction function was investigated. Two-dimension M-π-n CdTe detectors were fabricated on 0.5mm-thick single CdTe wafer by the excimer laser pattern doping technique. It is important that the imaging detector shows uniform performance in all pixels, so we measured energy spectra of the two-dimensional detector fabricated by the excimer laser pattern doping technique. The energy spectra about 4 keV of FWHM of 122 keV peak of Co-57 were obtained, and it was found that uniformity was high in all pixels. For investigating charge share problem, 2 x 2 structured patterned-dope detector with and without separation ditches were prepared and compared. Both sample showed almost same crosstalk carrier, about 3% calculated from Co-57 radioisotope energy spectrum above 50 keV regions. Only 0.05 % crosstalk counts was obtained from both samples by using narrow 6 KeV energy windows at 122 keV for estimation in energy distinction imaging with energy window. These results show that patterned n-type doping by metal mask and excimer laser technique is effective for pixel separation CdTe x-ray imaging device.

M-π -n detector and Schottky detector which were different barriers were evaluated by measuring spectrum as imaging detectors. These spectrum performances showed that the effect of polarization in these detectors was similarly occurred. The current-time characteristics and capacitance-time characteristics were measured for the detectors and it was found that these characteristics were due to the effect of polarization.

We used detector arrays of types "scintillator-photodiode" (S-PD) and scintillator-photoreceiving device (PRD). In non-destructive testing systems using S-PD arrays it is possible to use scintillators of different atomic number and density, which allows functioning in the energy range from 20 keV to 10 MeV, i.e., steel equivalent thickness I from 100μm to 300mm. For different objects and different purposes, different types of detector arrays and methods of control can be recommended. Results of experimental studies of detector arrays S-PD and S-PRD used for X-ray digital radiography have shown that there exist further possibilities to increase spatial resolution of this system for up to 2-3 line pairs per mm. It was investigated experimental results with used two array detectors for low-energy and high - energy detections (HED and LED). It is show in principle to distinguish not only organic from inorganic materials, but so as safety organic from explosive. Our aim was to show (theoretically and experimentally) that is could be possible to substantially increase the accuracy of separation of substances in the inspected object by their atomic number, as well as to increase the sensitivity of the method as a whole by using a multi-energy approach and detectors that have substantially different sensibility in the low-and high-energy range of the X-ray emitter spectrum. It was show the possibility to distinct materials with effective atomic number difference about 10-15%. It can be used in inspection systems, including anti-terrorist activities, in technical diagnostics, medicine.

The proposed pulse height analysis technique is based on the constant and linear relationship between pulse width and pulse height generated from front-end electronics of nuclear spectroscopic and imaging systems. The present technique has successfully implemented into the sump water radiation monitoring system in a nuclear power plant. The radiation monitoring system uses a NaI(Tl) scintillator to detect radioactive nuclides of Radon daughters brought down by rain. The technique is also used for a nuclear medical imaging system. The system uses a position sensitive photomultiplier tube coupled with a scintillator. The proposed techniques has greatly simplified the electronic design and made the system a feasible one for potable applications.