The effects of Te precipitates on the performances of CdZnTe nuclear radiation detectors were investigated with wide X-ray or alpha-particle beams. In these measurements, the degradations in the device performances were correlated with the areas of high concentrations of Te precipitates aggregated around the crystalline defects or with large-size (>100 μm) individual precipitates. The critical role of the small-size, 1-20 μm in diameter, precipitates was not clearly established, because of the large size of the particle beams used in prior studies (300-400-μm diameter). Our recent measurements conducted with a highly collimated, <10 μm, x-ray beam and thin, ~1 mm, CZT crystals proved that even a single small-size precipitate affects the local charge transport properties in CdZnTe detectors. The next step is to determine the extent of the potential cumulative effect of randomly distributed Te precipitates on the properties of CZT detectors. In this work, we report on the modeling of the effects of Te precipitates on measurable characteristics such as energy resolution, detection efficiency, electron mobility-lifetime product, and others and compare with the experimental results.

CZT material quality improvement has been achieved by optimizing the crystal growth process. N-type conductivity has been measured on as-grown, undoped Cd_0.9Zn_0.1Te. Cd _0.85 Zn _0.15Te crystals have been grown for producing high resistivity CZT radiation detectors. The best FWHM of ⁵⁷Co 122KeV spectrum was measured to be 3.7% and (µτ)_e was 3x10^-3 cm²V^-1. The microscopic gamma ray response using a beam size of 10µm has been used to map the entire 4 mm x 4 mm detector. Several black spots indicating no signal responses were observed while all other areas showed an average of 65-70% collection efficiency. The black spots suggest that at those locations, the Te precipitates are larger than 10μm. Detailed microscopic infrared transmission measurement on the sample found that most Te precipitates have sizes of 4-6μm. Theoretical analysis of the results suggests that singly and doubly ionized TeCdVCd² might be the shallow and deep donors previously assigned to Te_Cd by us.

Te-rich secondary phases existing in CdZnTe (CZT) single crystals degrade the spectroscopic performance of these detectors. An unpredictable number of charges are trapped, corresponding to the abundance of these microscopic defects, thereby leading to fluctuations in the total collected charge and strongly affecting the uniformity of charge-collection efficiency. These effects, observed in thin planar detectors, also were found to be the dominant cause of the low performance of thick detectors, wherein the fluctuations accumulate along the charge's drift path. Reducing the size of Te inclusions from a virtual diameter of 10-20 μm down to less than 5 μm already allowed us to produce Frisch-ring detectors with a resolution as good as ~0.8% FWHM at 662 keV. Understanding and modeling the mechanisms involving Te-rich secondary phases and charge loss requires systematic studies on a spatial scale never before realized. Here, we describe a dedicated beam-line recently established at BNL's National Synchrotron Light Source for characterizing semiconductor detectors along with a IR system with counting capability that permits us to correlate the concentration of defects with the devices' performances.

Previous measurements of the scintillation properties of members of the single-alkali, rare-earth double-phosphate family have demonstrated high light output and fast decay times when exposed to ionizing radiation. Cerium-doped K₃Lu(PO₄)₂ and Rb₃Lu(PO₄)₂ scintillators have exhibited light outputs of 32,500 and 28,200 photons/MeV respectively and decay times of 37 and 34 nanoseconds respectively. Because of the ease with which the alkali constituents (Li, Na, K, Rb, Cs) of the crystal matrix may be interchanged (e.g. K₂CsLu(PO₄)₂ and CsLi₂Lu(PO₄)₂), the rare-earth double-phosphate family of scintillators provides an ideal system for the study of matrix effects on scintillation efficiency and kinetics. In order to better understand and to ultimately optimize the scintillation properties of these scintillators, new members of the rare-earth double-phosphate family have been synthesized by high temperature flux growth. These new samples, represented by the general formula (A,B)₃Lu(PO₄)₂:Ce where A and B are alkali elements, incorporate mixed alkali rather than single alkali components and varying levels of Ce doping. Light output, scintillation decay times, and photoluminescence measurements for the most promising of the samples to date are reported. In this paper, we identify promising samples and results that clearly demonstrate outstanding light output, up to 270% of BGO, fast decay times, 29-39 nanoseconds, and peak emission wavelengths of ~ 400 nm for many of the samples.

We report on the material selection, testing and fabrication technology development of high performance CdZnTe quasihemispherical CAPture^TM Plus radiation detectors. Quasi-hemispherical CdZnTe detectors offer a cost effective alternative to other single-polarity (electron-only) detector configurations such as co-planar grid, pixilated or Frisch ring CdZnTe detectors with comparable energy resolution both in the high (>500 keV) and low energy range (<500 keV). The performance of the quasi-hemispherical detectors is controlled by charge transport properties of the CdZnTe crystals, quality of device fabrication and device integration. Similarly to other single-polarity CdZnTe device configurations the charge transport uniformity of the CdZnTe crystals is critical for achieving high energy resolution. We realized this by carefully selecting high electron transport CdZnTe crystals (μτ_e greater than or equal to 6.0×10^-3 cm²/V) with uniform distribution of structural defects. Infra-red microscopy was employed for structural defect mapping of the crystals. Low sub-surface damage state-of-the art multi- and single-wire saw technologies were used to slice and dice the single crystal detector elements out of the CdZnTe ingots. Dimensional control of the crystals was preserved throughout chemical etching and chemo-mechanical polishing by minimizing material removal. Device fabrication employing state-of-the art photolithography, electrode deposition and surface passivation enabled the application of bias voltages as high as 5000 V/cm on the devices. With carefully selected high uniformity CdZnTe crystals and low-noise preamplifier energy resolution better than 4.8% FWHM at 81 keV, 3.0% FWHM at 122 keV and 1.5% FWHM at 662 keV was achieved on 10×10×5 mm³ quasi-hemispherical detectors.

We report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform spectroscopy and 3-D imaging of gamma-rays. We report laboratory measurements including spectroscopy, efficiency and 3-D imaging capability of prototype detectors (15 × 15 × 7.5mm³) with 11×11 unit cells. We also report on Monte Carlo simulations (GEANT4 v7.1) to investigate the effect of multihits on detector performance in both spectroscopy and imaging. We compare simulation results with data obtained from laboratory measurements and discuss the implications for future strip detector designs.

In this paper we report on the simulation, design, and testing of high performance CdZnTe quasi-hemispherical CAPture^TM Plus radiation detectors. Quasi-hemispherical CdZnTe detectors offer a cost effective alternative to other single-polarity (electron-only) detector configurations such as co-planar grid, pixilated or Frish ring CdZnTe detectors with comparable energy resolution both in the high (>500 keV) and low energy range (<500 keV). We have used the device simulation package eVDSIM to design optimal electrode geometry together with the necessary material selection criteria for charge transport properties of the CdZnTe crystals. A test set of 10x10x5mm³ CAPture^TM Plus detectors has been built using state-of-the art fabrication technology. The measured spectral and efficiency performance of these detectors is compared to the theoretical predictions of simulation. Our results demonstrate that with careful selection of uniform material and high-quality fabrication, this design of CAPture^TM Plus detectors is capable of regularly achieving FWHM @ 81keV of 5%, FWHM @ 122keV of <3%, and FWHM @ 662keV of <2%.

We explored the dependence of electron mobility-lifetime product (μτ) and surface recombination velocity ( S/μ) on surface processing and temperature for Cd_1-xZn_xTe (CZT) radiation detectors. The surfaces of the CZT crystals were mechanically polished and then chemically etched with 2% bromine-in-methanol. Different regions at the Au contacts were illuminated with light at a wavelength of 650-, 800-, 900-, and 940-nm. The position-dependent and temperature- dependent values of the electron mobility-lifetime product and surface recombination velocity were measured using a direct current (DC) photoconductivity technique. The study revealed that this technique is a valuable and practical method to measure the spatial- and temperature-variations of the surface recombination velocity and bulk lifetime for CZT detectors. We discuss the correlation between the DC photoconductivity and measurements of the detector performance.

One of the key aspects of a detector material for space-borne hard X-ray and gamma-ray telescopes is the rate of prompt and delayed background events generated inside the material by charged and neutral particles striking the detector. These particles are Cosmic Rays, particles trapped in Earth's magnetic field, and secondaries from Cosmic Ray interacting with the atmosphere and the spacecraft. Here, we present a preliminary study of Cadmium Zinc Telluride (CZT) and its behaviour in space environments. We have used the simulation package MGGPOD to estimate the background of the CZT detectors in the proposed Energetic X-ray Imaging Survey Telescope (EXIST) for possible orbital parameters. The EXIST mission will make use of ~6 m² of >0.5 cm thick CZT detectors to record cosmic X-rays in the energy range from 10 keV to 600 keV. The detectors will be shielded by a fully or partly active shield. For the specific detector and shielding geometry considered here and an orbit with a low (7°) inclination, the background rate is dominated by diffuse extragalactic photons below ~200 keV. Prompt and delayed hadronic backgrounds grow increasingly important above this energy, becoming the main contributors to the total background above ~1 MeV. A fully active shield performs slightly better than a half active/half passive shield.

Although the physics describing the interactions of neutrons with matter is quite different from that appropriate for hard x-rays and gamma rays, there are a number of similarities that allow analogous instruments to be developed for both types of ionizing radiation. A pinhole camera, for example, requires that the radiation obeys some form of geometrical optics, that a material can be found to absorb some of the radiation, and that a suitable position-sensitive detector can be built to record the spatial distribution of the incident radiation. Such conditions are met for photons and neutrons, even though the materials used are quite different. Neutron analogues of the coded-aperture gamma camera and the Compton camera have been demonstrated. Even though the Compton effect applies only to photons, neutrons undergo proton-recoil scattering that can provide similar directional information. There is also an analogy in the existence of an energy spectrum for the radiation used to produce the images, and which may allow different types of sources to be distinguished from each other and from background.

Detecting and identifying organic and metallic targets at distances from 50 m to 100 m is difficult for hard X-ray detection devices, especially when targets (such as improvised explosive devices (IEDs)) are concealed behind metal (steel) and non-metal (plastic, wood, rocks, soil, etc.) walls. At least two problems are inherent to detection at such long distances: (1) the air attenuation of X-rays, which can be significant for standoff distances of x = 50 m (100 m total for 2x); and (2) a scattering factor proportional to x⁴ that comes from the divergence of X-rays propagating from a source to a target and X-rays backscattering from a target (usually, Compton backscattering in low Z-number materials). The compensation of these factors by novel lobster-eye hard X-ray optics is analyzed in this paper. The analysis and the optimization of the hard X-ray lobster eye lens for realistic parameters are also discussed.

A 40-fold segmented coaxial HPGe detector was operated in a low background counting facility for 1 year to experimentally evaluate background rejection efficiencies of proposed segmentation and pulse shape discrimination techniques for the proposed Majorana double-beta decay experiment. Significantly diminished resolution for multisegment events was encountered due to inter-segment cross-talk. A cross-talk correlation matrix has been constructed allowing the restoration of acceptable energy resolution for multi-segment events. Efforts to determine the optimum segmentation pattern for multi-site interaction events are ongoing.

We are developing a detector system for locating environmental radiation sources. The design emphasizes compact size (ideally hand-held), wide field of view and high detection efficiency, and uses cadmium-zinc-telluride (CZT) detectors and electronic collimation via Compton-scatter detection. The detector design is a 6-sided box with a primary scatter detector on one end. GEANT4 simulations, allowing variations of detector parameters and source energies/locations, provided performance estimates. A partial prototype, using 16x16-pixel 38x38x5-mm³ CZT detectors, was developed and tested. Two methods to calculate source direction in real-time from the Compton scatter data were evaluated: (1) filtered backprojection of cones onto a sphere; (2) intersection with the sphere of bounding boxes circumscribed around the cones. Simulation results of the 6-sided box with the current CZT modules indicated 1-5% of incident gamma rays produce valid direction angles, with an angular resolution of ~15°. The directional algorithms allowed a FOV (directional error <10°) of approximately ±60°. The direction algorithms converge on a source direction estimate in as few as 100 detected events. With improvements in detector energy and spatial resolution, reasonable performance seems achievable for a range of radioisotopes, e.g., from Am-241 through Co-60.

Wired array studies are being conducted at the SNL Z accelerator to maximize the x-ray generation for inertial confinement fusion targets and high energy density physics experiments. An integral component of these studies is the characterization of the time-resolved spectral content of the x-rays. Due to potential spatial anisotropy in the emitted radiation, it is also critical to diagnose the time-evolved spectral content in a space-resolved manner. To accomplish these two measurement goals, we developed an x-ray spectrometer using a set of high-speed detectors (silicon PIN diodes) with a collimated field-of-view that converged on a 1-cm-diameter spot at the pinch axis. Spectral discrimination is achieved by placing high Z absorbers in front of these detectors. We built two spectrometers to permit simultaneous different angular views of the emitted radiation. Spectral data have been acquired from recent Z shots for the radial and axial (polar) views. UNSPEC1 has been adapted to analyze and unfold the measured data to reconstruct the x-ray spectrum. The unfold operator code, UFO², is being adapted for a more comprehensive spectral unfolding treatment.

A microfocus x-ray tube is useful in order to perform magnification digital radiography including phase-contrast effect. The 100-µm-focus x-ray generator consists of a main controller for regulating the tube voltage and current and a tube unit, with a high-voltage circuit and a fixed anode x-ray tube. The maximum tube voltage, current, and electric power were 105 kV, 0.5 mA, and 50 W, respectively. Using a 3.0-mm-thick aluminum filter, the x-ray intensity was 26.0 µGy/s at 1.0 m from the source with a tube voltage of 60 kV and a current of 0.50 mA. Because the peak photon energy was approximately 35 keV using the filter with a tube voltage of 60 kV, the bremsstrahlung x-rays were absorbed effectively by iodine-based contrast media with an iodine K-edge of 33.2 keV. Real-time magnification radiography was performed by twofold magnification imaging with an image intensifier camera, and angiography was achieved with iodine-based microspheres 15 µm in diameter. In angiography of non-living animals, we observed fine blood vessels of approximately 100 µm with high contrasts.

Two dimension real-time radiation imaging device for the hard ray with photon-counting type CdTe radiation detector was researched and developed. It is a device with the 35×35 arranged 1225 pixels including a virtual pixel in pixel pitch 1/10-inch pitch. All pixels are independently connected by original ASIC, and it has the energy distinction ability with five energy thresholds. The desecrated CdTe diodes were adopted in the photoelectric conversion elements by using eight ASIC of original development with maximum count rate 2Mcps / pixel and 5 energy distinction thresholds in this prototype. This prototype is a portable type device that can be the room temperature operation, it is possible to connect it with the laptop computer as a camera device of two dimension type to be able to take move of a real-time scene (an actual frame rate depends on signal conditioning PC) via USB2.0. The imaging area is about 3.5-inch corner. This time, it has been understood to be able to detect slight information that has tended to be overlooked up to now because it is possible to take picture of Am241, Co57, and Cs137 simultaneously, to try the animation taking picture that distinguishes three isotopes, and to set the best range of each at the same time as being able to distinguish these three kinds by the energy distinction clearly. It characterizes in corresponding to an incidence rate at the X-ray tube level, and it corresponds to taking picture of the animation of the penetration image that uses X rays.

The samarium-target x-ray tube is useful in order to perform cone-beam K-edge angiography because K-series characteristic x-rays from the samarium target are absorbed effectively by iodine-based contrast media. This generator consists of the following components: a constant high-voltage power supply, a filament power supply, a turbomolecular pump, and an x-ray tube. The x-ray tube is a demountable diode which is connected to the turbomolecular pump and consists of the following major devices: a samarium target, a tungsten hairpin cathode (filament), a focusing (Wehnelt) electrode, a polyethylene terephthalate x-ray window 0.25 mm in thickness, and a stainless-steel tube body. In the x-ray tube, the positive high voltage is applied to the anode (target) electrode, and the cathode is connected to the tube body (ground potential). In this experiment, the tube voltage applied was from 50 to 70 kV, and the tube current was regulated to within 0.10 mA by the filament temperature. The exposure time is controlled in order to obtain optimum x-ray intensity. The electron beams from the cathode are converged to the target by the focusing electrode, and bremsstrahlung x-rays were absorbed using a 50-µm-thick tungsten filter. The x-ray intensity was 1.04 μGy/s at 1.0 m from the x-ray source with a tube voltage of 60 kV and a tube current of 0.10 mA, and angiography was performed using a computed radiography system and iodine-based microspheres 15 µm in diameter. In angiography of non-living animals, we observed fine blood vessels of approximately 100 µm with high contrasts.

The Cardius^TM-3 (C-3) camera is a triple-head small field-of-view camera dedicated to cardiac SPECT imaging. It is built on Digirad's solid-state detector technology with 6mm x 6mm CsI:Tl crystals. The system demonstrates upright imaging with the patient rotating in a SPECTour^TM chair while the gantry keeps stationary during data acquisition. A region of interest (ROI) tool on the persistence scope (p-scope) is used to position the heart at the center of rotation to avoid cardiac-truncation. The tool also provides the count rate in the ROI so the users can determine the acquisition time for different patients to meet the American Society of Nuclear Cardiology (ASNC) guidelines. The intrinsic energy resolution, reconstructed spatial resolution with scatter and NEMA extrinsic planar sensitivity of the solid-state detector were measured and results are reported. C-3 can acquire high dose tomographic studies in 7 minutes at 20 seconds/projection (based on actual patient study). This short acquisition time (compared with conventional Anger style dual and single head systems) not only improves the patient comfort but also reduces patient motion, which in turn improves the image quality. Anthropomorphic phantom and patient studies performed in this work showed that C-3 image quality and diagnostic outcome were equivalent to those from a dual head camera, but the acquisition time could be reduced by 38%. The reduced acquisition time (compared with conventional Anger style dual and single head systems) not only improves the patient comfort but also reduces patient motion, which in turn can improve the image quality.

We have developed and characterized large volume amorphous (a-) selenium (Se) stabilized alloys for room temperature medical imaging devices and high-energy physics detectors. The synthesis and preparation of well-defined and high quality a-Se (B, As, Cl) alloy materials have been conducted using a specially designed alloying reactor at EIC and installed in an argon atmosphere glove box. The alloy composition has been precisely controlled and optimized to ensure good device performance. The synthesis of large volume boron (B) doped (natural and isotopic ¹⁰B) a-Se (As, Cl) alloys has been carried out by thoroughly mixing vacuum distilled and zone-refined (ZR) Se with previously synthesized Se-As master alloys, Se-Cl master alloys and B. The synthesized a-Se (B, As, Cl) alloys have been characterized by x-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infra-red spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectroscopy (ICP-MS), and detector testing. The a- Se alloys have shown high promise for x-ray detectors with its high dark resistivity (10¹⁰-10¹³ Ωcm), good charge transport properties, and cost-effective large area scalability. Details of various steps about detector fabrication and testing of these imaging devices are also presented.

We proposed a new addressing method that used a field emitter type electronic source for the radiation imaging detector. We enabled this device to operate room temperature by using Cadmium Telluride (CdTe) diode. In this addressing method, the energy of the electron from electronic source in each pixel was much uniformed and the electron beams can be focused within a micro meter diameter. Therefore, because this proposed device was lead out by field emitter, it was expected to achieve the super-high resolution X-ray imager. In this paper, we used the carbon nanoneedle field emitter, and the proposed device operation was confirmed by verifying principle about one pixel.

We have developed high energy and high spatial resolution 1D and 2D solid state imaging detectors and their custom integrated circuits (ICs). Readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors, especially for Si and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 1D or 2D structure. The 1D structure types are mostly used for scanning purposes with some staring type imaging while 2D pixel detectors can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state detectors and their ICs that have been developed within this effort are presented.

This generator consists of the following components: a constant high-voltage power supply, a filament power supply, a turbomolecular pump, and an x-ray tube. The x-ray tube is a demountable diode which is connected to the turbomolecular pump and consists of the following major devices: a tungsten hairpin cathode (filament), a focusing (Wehnelt) electrode, a polyethylene terephthalate x-ray window 0.25 mm in thickness, a stainless-steel tube body, a pipe target, and a rod target. The pipe and rod targets are useful for forming linear and cone beams, respectively. In the x-ray tube, the positive high voltage is applied to the anode (target) electrode, and the cathode is connected to the tube body (ground potential). In this experiment, the tube voltage applied was from12 to 20 kV, and the tube current was regulated to within 0.10 mA by the filament temperature. The exposure time is controlled in order to obtain optimum x-ray intensity. The electron beams from the cathode are converged to the target by the focusing electrode, and clean K-series characteristic x-rays are produced through the focusing electrode without using a filter. The x-ray intensities of the pipe and rod targets were 1.29 and 4.28 μGy/s at 1.0 m from the x-ray source with a tube voltage of 15 kV and a tube current of 0.10 mA, and quasi-monochromatic radiography was performed using a computed radiography system.

We describe the detector development for a balloon-borne wide-field hard X-ray (20-600 keV) telescope, ProtoEXIST. ProtoEXIST is a pathfinder for both technology and science of the proposed implementation of the Black Hole Finder Probe, Energetic X-ray Imaging Survey telescope (EXIST). The principal technology challenge is the development of large area, close-tiled modules of imaging CZT detectors (1000 cm² for ProtoEXIST1). We review the updates of the detector design and package concept for ProtoEXIST1 and report the current development status of the CZT detectors, using calibration results of our basic detector unit - 2 x 2 x 0.5 cm CZT crystals with 2.5 mm pixels (8 x 8 array). The current prototype (Rev1) of our detector crystal unit (DCU) shows ~4.5 keV electronics noise (FWHM), and the radiation measurements show the energy resolution (FWHM) of the units is 4.7 keV (7.9%) at 59.5 keV, 5.6 keV (4.6%) at 122 keV, and 7.6 keV (2.1%) at 356 keV. The new (Rev2) DCU with revised design is expected to improve the resolution by ~30%.

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 diamondbased ionizing-radiation detectors possessing properties unachievable, for present time, for other materials. These detectors have found the applications in a number of areas including thermonuclear plasma diagnostics at world leading tokamaks and medical dosimetry. Perfection and new developments of diamond-based detectors, including those on natural and synthetic crystals as well as on CVD films, 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 further development, theoretical and experimental, of our earlier proposed model of the operation of a radiation detector based on high-resistivity semiconductor which first made it possible to explain main experimentally observed peculiarities of characteristics of natural diamond detectors exposed to various kinds of radiation. The model is 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. It is shown that a weak generation of free charge carriers from impurity levels in addition to the main band-to-band generation can significantly increase the operation voltages of the detector. A decrease of detector temperature is shown to widen the circle of the materials on which the detectors operating in accordance with the model can be developed. Results of modeling of operation of the detector on detector samples based on silicon, as the most perfect technologically developed material, are presented. The experimental studies were performed at a temperature of 14 K to ensure sufficiently low concentration of trapping impurity centers in this material. A technique is proposed for evaluation of the concentration of trapping levels in high-resistivity semiconductors.

The hard X-ray detector (HXD-II) is one of the scientific payloads onboard Suzaku, the 5th Japanese cosmic X-ray satellite. After the launch in July 2005, all the HXD-II components, including the sensors and analog/digital electronics, have been working normally. In order to archive the maximum performance of the HXD-II, especially the GSO/BGO well-type phoswich counters, extensive in-orbit qualification and calibration have been carried out utilizing the data acquired in early operations. Major items of these efforts include; to estimate the circuit dead time, calibrate energy scale, optimize the event selection criteria for background reduction, study the background, and examine the detector response. As a result of these in-orbit calibrations, the HXD-II background in the 10-600 keV range has been successfully lowered to (0.5-5.0) x 10^-4 cs^-1 keV^-1 cm^-2 This the lowest among the background ever achieved in orbit by cosmic hard x-ray detectors.

The angular distribution of the inelastic scattering of photons at low energies (≤80 KeV) has been measured in organic material, soil, rocks, wood, steel sheet, and water. The measurements have been performed under air inside an X-ray shield cabinet using X-rays tube as a photon source and a thermoelectrically cooled CdTe detector. Measurements have been taken for both single and combined materials. The contributions of inelastic scattering of photons for the lower Z material in a given configuration have been extracted. The measured signal is primarily Compton scattering. The measured inelastic scattering contributions were compared with the calculated inelastic scattering cross sections according to the Klein-Nishina theory, updated to include a practical energy distribution of an X-ray tube beam. Relatively good agreement was found for all targets under investigation. The slight discrepancy is attributed to photoelectric effect and sample configuration. Present results may act as a guide for optimization of X-ray imaging sensors and in particular of those based on lobster eye X-ray optics suitable for cargo inspection, improvised explosives detection, non-destructive evaluation, and medical imaging.

In comparison with traditional sensors, semiconductor dosimeters have certain advantages because of their high sensitivity, small sizes and weights and simple readout. However in case of the MOS type Gamma radiation sensors, stored dosage data was easily volatile at high temperature. A typical Si-Oxide-Nitride-Oxide-Si (SONOS) device processed by semiconductor technology can be a candidate for nonvolatile Gamma Radiation sensors. The Gamma ray radiation induces a significant decrease of threshold voltage for SONOS. The change of threshold voltage after Gamma ray expose can be correlated to the dose of Gamma ray exposure as well. This SONOS type of Gamma radiation sensor, has the following characteristics :(1) the stored dose recorded in this SONOS device is always nonvolatile during data read and write, even at high temperature. (2) Data in the SONOS can be erased to original null state by charges injection, but it can't be annealed by high temperature. (3) Data can be accumulatively stored in the SONOS.

Large volume single crystals of CdTe and Cd_0.9Zn_0.1Te (CZT) have been grown by a controlled vertical Bridgman technique using in-house zone refined precursors and characterized through structural, electrical, optical, and spectroscopic methods. The grown crystals (diameter greater than or equal to 2.5 cm and length >10 cm) have shown promising characteristics for high-resolution room temperature solid-state radiation detectors due to their high resistivity (~1010 Ω-cm for CdTe, and >1011 Ω-cm for CZT) and good charge transport properties [μτ_e ~ (2-5)x10-3 cm²/V]. The fabricated detectors in planar single element and Frisch collar configurations have shown very low leakage currents and high count rates for various sources, including Am-241, and Cs-137. The grown crystals have been further characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), and transmission two-modulator generalized ellipsometry (2-MGE). Details of the CdTe and CZT characterization results, detector fabrication steps, and testing with radiation sources are presented. The CdTe and CZT crystals have shown high prospects for low power rating solid-state nuclear spectrometers and medical imaging devices.

We present new results from our studies of defects in current single-crystal CdZnTe material. Our previous measurements, carried out on thin (~1 mm) and long (>12 mm) CZT detectors, indicated that small (1-20 μm) Te inclusions can significantly degrade the device's energy resolution and detection efficiency. We are conducting detailed studies of the effects of Te inclusions by employing different characterization techniques with better spatial resolution, such as quantitative fluorescence mapping, X-ray micro-diffraction, and TEM. Also, IR microscopy and gamma-mapping with pulse-shape analysis with higher spatial resolution generated more accurate results in the areas surrounding the micro-defects (Te inclusions). Our results reveal how the performance of CdZnTe detectors is influenced by Te inclusions, such as their spatial distribution, concentration, and size. We also discuss a model of charge transport through areas populated with Te inclusions.

We report here on the optimization of 0.5 cm thick pixelated Orbotech CZT detectors with regards to the best contacting materials and the use of steering grids. We evaluated the performance of different contacting materials. Our study differs from earlier ones in that we investigated the performance of different anode and cathode materials separately. We obtain the best performance with Au cathodes. For different anode materials Ti and In give the best energy resolutions. The detector (2.0×2.0×0.5 cm³, 8×8 pixels) shows excellent 59 keV, 122 keV and 662 keV energy resolutions of 1.4 keV, 1.9 keV, and 7.4 keV, respectively. Furthermore, we report on using steering grids to improve on the performance of the pixelated detectors. Previously, the benefit of steering grids had been limited by additional electronic noise associated with currents between the negatively biased steering grids and the anode pixels. We are currently exploring the possibility to isolate the steering grid from the CZT substrates by a thin layer of Al₂O₃. We performed a series of measurements to determine by how much the isolation layer reduces the grid-pixel currents. Comparing the currents between two Au contacts before and after isolating one of the two contacts from the CZT with a 700 nm thick layer of Al₂O₃, we measure that the isolation layer reduces the currents by a factor of about 10 at 500 V. We present some results from a detector before and after deposition of an isolated steering grid. The grid indeed improves on the detectors energy resolution and detection efficiency. We show that simulations can be used to model the anode to cathode charge correlation in excellent agreement with the experimental results.

When bias is applied to a mercuric iodide detector with planar contacts, placed in a light-tight enclosure, the leakage current initially increases with increasing bias, as can be expected for a semiconductor detector. At some value of the bias however, the current starts to decrease sharply, and reaches very low values when the bias is further increased. This phenomenon of negative differential conductivity has been observed previously in high-bandgap semiconductors with deep electron and hole traps. This combination of traps can provide an effective recombination channel which reduces the number of free electrons and holes at high electric fields. It is suggested in this paper that mercuric iodide contains a set of traps with the required properties in the form of doubly ionized mercury interstitials and iodine vacancies. These traps are incorporated in the single crystals by the processing methods used to obtain the pure material and by the presence of mercurous iodide in the synthesized material. The main advantage of this behavior is the apparent low leakage current of the detectors at high fields (1000 V/mm) at ambient temperatures. The disadvantage is that carriers generated by ionizing radiation will also be subject to this recombination process, so that complete charge collection may be impaired. Additional details of this hypothesis will be presented for discussion.

Crystals of the compound semiconductor Cd_0.55Mn_0.45Te were grown by modified Bridgeman technique. The resulting crystals were transparent, with a deep red color. There were no precipitates visible up to the 1.5μm resolution of the optical transmission microscopy system used. The electrical resistivity was measured to be 1x10⁵Ωcm. The ability to grow large precipitate free crystals makes this system a good candidate for radiation detector elements. Electrical properties must be improved through better control of the concentration of electronically active impurities.

In order to check possible novel neutron detectors based on composite semiconductor detectors containing nuclides with large cross sections for neutron, we tested their response to alpha particles. In the present paper we describe results obtained with composite samples made of hexagonal Boron Nitride particles bound with Polystyrene or Nylon-6. The samples were tested under 5.5 MeV alpha particle radiation emitted from ²⁴¹Am source and 4.8MeV alpha particle of ²²⁶Ra source. Some of the responses of these composite detectors to thermal neutrons were already reported and here we shall show some newer results obtained with thermal neutrons, from a low intensity ²⁴¹Am - ⁹Be and also from a medium intensity ²⁵²Cf source, which were thermalized using 10 cm thick paraffin. The Alpha detection experiments show that all the tested samples, regardless of the binder, show a well-defined peak around the 270 energy channel. There was very little polarization of the alpha radiation, since the amplitude of the alpha peak is reduced after ~ 2min from start of the irradiation, from 100% to 95% and it stayed stable at this level for another 10 minutes. The alpha spectrum detected from a PbI₂ single crystal is also shown for comparison. The neutron spectrum obtained by the composite BN samples showed an apparent peak around the 150 energy channel. The Signal to noise ratio for neutron detection from radionuclide shown here is about 2 only, whereas recent results to be published later, obtained with our composite BN detectors from a neutron beam of about 10⁷ sec^-1cm^-2 is ~2 5. The 1.4 and 1.7 MeV alpha peaks resulting from the nuclear reaction of thermal neutrons with ¹⁰B of the boron nitride detector are not buried in the noise range. The capacitance noise requires small contact areas, therefore for large area detectors it is necessary to produce an electronic read-out device which can add up a multitude of small (less than 10sq.mm) pixilated contacts.

In this paper different sol gel syntheses strategies are adopted in order to produce Ce-doped silica-glasses scintillators with improved properties. Variations on the synthesis procedure are adopted to reduce the hydroxyl content of the sol gel glass; to this purpose, a fluorine derivative of silicon alkoxide was added in the sol gel reaction. Since a drawback of Ce-doped sol gel glasses is the partial oxidation of Ce³⁺ to Ce⁴⁺ in the matrix probably occurring during the sintering procedure, both Ce-doped xerogel and fluorinated xerogel were treated under reducing atmosphere (H₂:Ar) instead of the usual oxidizing atmosphere. Glasses obtained in such ways are compared with commercial synthetic glasses and with previously produced sol gel samples by spectroscopic IR absorption measurements, and by radio-luminescence experiments.

Xenon-filled ionization detectors, due to their high atomic number fill gas (Z=54), moderate densities (~0.3 g/cm³-0.5 g/cm³) and good energy resolution (2%-4% at 662 keV), fill an important niche between more familiar technologies such as NaI(Tl) scintillators and Germanium detectors. Until recently, difficulties with obtaining sufficient Xenon purity, reducing microphonic sensitivity, and developing low-noise electronics compatible with small ionization signals have hampered the development of this nuclear detection field. Constellation Technology Corporation, whose experience with xenon detectors goes back to the mid 1990's, has made significant progress in these areas and has developed a commercial line of detectors with active volumes ranging from small (35 g Xe) to large (1400 g Xe). Here we will discuss our development of a mobile, large area, spectroscopic array.

A measurement data processing method, that will allow increasing detecting sensitivity of XeGRD to gammaradioactive sources, is considered. Description of a multifunctional portal monitor provided with a xenon gamma-ray detector (XeGRD) for detection and identification of radioactive and fissile materials is presented. Analysis of calibration and test results of the XeGRD included in the real portal monitor is presented. It is shown that the xenon gamma-ray spectrometer can be successfully used in portal monitors for detecting as well as for identification of various radio-nuclides.

The prototype TIGRE Tracking and Imaging Gamma-Ray Experiment is being prepared for a scientific balloon flight in fall, 2006. TIGRE is a Compton telescope for 0.5-10 MeV gamma rays and a pair telescope for 10-100 MeV gammas. It uses multiple layers of thin silicon strip detectors as both the Compton and pair converter and the charged particle tracker. The event coincidence requirement is completed with arrays of CsI(Tl)-photodiode detectors surrounding the converter/tracker and large Na(Tl)-PMT detectors below. The purpose of this flight is to demonstrate the background suppression capabilities of the TIGRE instrument with Compton recoil electron tracking and the improved angular resolution for pairs with silicon as the converter material. Details of the control and readout of the detectors will be described. Calibration results using laboratory radioisotopes will likewise be presented.

Multi-energy radiography is a new direction in non-destructive testing. Its specific feature is separate detection of penetrating radiation in several energy channels. Multi-energy radiography allows quantitative determination of the atomic composition of objects. This is its principal advantage over conventional radiography. In particular, dual-energy radiography allows determination of the effective atomic number of a material with an accuracy of up to 80-90%. Development of three-energy radiography and radiography of higher multiplicity makes it possible to further improve the reconstruction of an object's chemical composition. This presents the possibility, for example, of detection of explosives and other illegal objects in luggage with a reliability approaching 95-98%. These developments can find application not only in anti-terrorist activities, but also in industrial testing and nuclear medicine.

Due to disadvantages of scintillator ZnSe(Te) - poor transparence to own emission (10^-1 cm^-1), long decay time, low density and Z_eff-this material had no practical applications in the ranges of X-ray energies about 120-140 keV. After the development of dual energy X-ray inspection scanners, CT and digital radiography situation changed on the contrary at whole. Both theory and experiments show that now it is the best material for low energy array detectors. The pilot-industrial production of ZnSe(Te) crystals is organized, their usage in CT and inspection X-rays scanners being already started. It has become possible to get tomography imaging simultaneously with automatic recognition of dangerous objects and substances, which is due to the unique parameters of ZnSe(Te). Presently several leading western companies look for possibilities to use ZnSe(Te) for medical X-ray CT. Our aim was to unveil the nature of luminescence centers and the emission mechanism in crystals of ZnSe(Te) compounds with isovalent dopants from the results of our studies of optical, spectroscopic and kinetic characteriestics of these crystals. Basing on the obtained understanding of the emission centers, we aimed at creation of a reproducible production technology of scintillators for application in inspection and medical equipment. The research described in this publication was made possible in part by INTAS Project Ref. Nr. 05-104-7519.

The energy resolution and position sensing with two types of pixelated anode designs of high pressure xenon gamma-ray spectrometer were investigated. The first design is composed of a single planar cathode and four anode pixels embedded in the center of a "non-collecting" anode plate. The second design is composed of a cylindrical surface cathode and seven pixelated central cylinder anodes. These designs remove the Frisch grid which can suffer from excessive micro-phonics in real-world applications. The distribution of electron cloud created by interaction between gamma-rays and Xe was obtained with Monte Carlo (GEANT4) simulations and shows the dimension of electron clouds increasing from approximately 0.1 mm to ~100 mm for gamma-ray energy range from 50 keV to 10 MeV in Xe at ~50 atm pressure (~0.5g/cm³ density). The charge collecting efficiency and waveform of induced charge on each anode were obtained by tracking electron cloud drifting. The position sensing based on both position dependence of weighting potential and the distribution of induced charge among anode pixels were also probed.

In women with radiographically dense breasts, the sensitivity of mammography is less than 50%. With the increase in the percent of women with dense breasts, it is important to look at alternative screening techniques for this population. This article reviews the strengths and weaknesses of current imaging techniques and focuses on recent developments in semiconductor-based gamma camera systems that offer significant improvements in image quality over that achievable with single-crystal sodium iodide systems. We have developed a technique known as Molecular Breast Imaging (MBI) using small field of view Cadmium Zinc Telluride (CZT) gamma cameras that permits the breast to be imaged in a similar manner to mammography, using light pain-free compression. Computer simulations and experimental studies have shown that use of low-energy high sensitivity collimation coupled with the excellent energy resolution and intrinsic spatial resolution of CZT detectors provides optimum image quality for the detection of small breast lesions. Preliminary clinical studies with a prototype dual-detector system have demonstrated that Molecular Breast Imaging has a sensitivity of ~90% for the detection of breast tumors less than 10 mm in diameter. By comparison, conventional scintimammography only achieves a sensitivity of 50% in the detection of lesions < 10 mm. Because Molecular Breast Imaging is not affected by breast density, this technique may offer an important adjunct to mammography in the evaluation of women with dense breast parenchyma.

We are developing a probe for image-guided surgery of cancer to be used in conjunction with traditional beta emitting radiopharmaceuticals such as I¹³¹ and F¹⁸-FDG. This device is based on a combination of two novel technologies, a microcolumnar film scintillator, CsI(Tl) and low-noise high sensitivity Electron-Multiplying CCD (EMCCD). The former allows high spatial resolution nuclear imaging and the latter facilitates detection of signal with significantly higher SNR than conventional CCDs by the virtue of internal signal gain built into its readout register. CsI(Tl) is bonded to the EMCCD via a flexible coherent fiberopic cable for easy handling. Due to its high sensitivity the probe is capable of functioning in real time providing high spatial resolution nuclear images for precise detection, delineation and excision of tumors. The evaluation of the probe using standard clinical phantoms as well as the operational data obtained on swine models and in clinical surgery will be presented.

Direct detection of x-ray using the technology of selenium on Thin Film Transistor (TFT) has been used in a number of medical imaging and other products for almost 10 years. The spatial resolution of this Direct Conversion Technology with MTF approaches the theoretical Sinc Function remains unsurpassed. However, there are rooms for improvement in several areas that may further advance the performance. This paper is to examine some of these areas and to explore potential solutions.

In radiology diagnosis, film is being quickly replaced by computer monitors as the display medium for all imaging modalities. Increasingly, these monitors are color instead of monochrome. It is important to have instruments available to characterize the display devices in order to guarantee reproducible presentation of image material. We are developing an imaging colorimeter based on a commercially available color digital camera. The camera uses a sensor that has co-located pixels in all three primary colors.

Radiation detectors monitored trains at two international borders to evaluate the performance of NaI(Tl) and plastic (polyvinyltoluene: PVT) gamma-ray detectors to characterize rail cargo. The detectors included a prototype NaI(Tl) radiation-portal-monitor panel having four large detectors (10-cm × 10-cm × 41-cm) and a PVT panel with a 41 cm × 173 cm × 3.8-cm detector. Spectral data from the NaI(Tl) and PVT detectors were recorded. Of particular emphasis was the identification of naturally occurring radioactive material (NORM) and the resultant frequency of nuisance alarms. For rail monitoring, the difficulty in stopping trains to perform secondary inspection on alarming cars creates a need for reliable identification of NORM during initial screening. Approximately 30 trains were monitored, and the commodities in individual railcars were ascertained from manifest information. At one test site, the trains carried inter-modal containers that had been unloaded from ships, and at the other site, the trains contained bulk cargo in tanker cars and hopper cars or individual items in boxcars or flatbeds. NORM encountered included potash, liquefied petroleum gas, fireworks, televisions, and clay-based products (e.g., pottery). Analysis of the spectral data included the use of the template-fitting portion of the program GADRAS developed at Sandia National Laboratories. For most of the NORM, the NaI(Tl) data produced a correct identification of the radionuclides present in the railcars. The same analysis was also used for PVT data in which the spectral information (no peaks but only gradual spectral changes including Compton edges) was limited. However, the PVT analysis provided correct identification of ⁴⁰K and ²²⁶Ra in many cases.

X-ray diffraction (XRD) profiles are conventionally used to determine lattice spacings via Bragg's law in order to characterize crystalline materials. It does not appear to be widely known that they also permit compositional information, such as effective atomic number and a density descriptor, to be determined from materials having little or no crystal structure. A ratio method is introduced that relates x-ray scatter intensities in two adjacent momentum transfer bands of the diffraction profile corresponding to the "tip" region of the primary x-ray spectrum. It is shown that this ratio depends on the effective atomic number, Z, of the scattering sample. Conversely, Z may be derived from measurement of the ratio. Error sources in this ratio method are briefly analyzed. Once Z is known, the IAM (independent atom model) cross section can be extrapolated from the high momentum transfer region to lower values, where molecular interference effects manifest themselves in the XRD profile. This procedure enables the molecular interference function, s(x), to be determined. On the assumption that the structure of liquids and amorphous materials can be represented by the hard sphere (HS) model, the packing fraction, η, of atoms in the scattering sample can be ascertained from the second moment of s(x). The effective atomic number, Z and the density descriptor, η, usefully complement information provided by more traditional material analysis techniques based on XRD profiles.

Micro-Pocket Fission Detectors (MPFD) have been developed as real-time in-core neutron flux monitors. Tests have demonstrated linear operation with neutron flux varying through six orders of magnitude while surviving neutron fluences greater than 10¹⁶ n^.cm^-2. Their design is naturally background insensitive with high signal to noise pulses. Built from alumina ceramics, these devices are relatively simple to build and are inexpensive. They have been designed for fabrication into large arrays to facilitate 3-D mapping of a reactor core.