Recent results have shown that capacitive Frisch grid structures significantly improve spectroscopic performance of planar CZT detectors especially at higher energies. This paper presents results obtained with larger detectors than those previously reported on. Devices with various aspect ratios and grid length-to-device thickness ratios were fabricated and evaluated. A FWHM energy resolution of approximately 2% at 662 keV was obtained for a device with dimensions of 5 mm x 5 mm x 9.2 mm.

We have developed large format CdZnTe pixel detectors optimized for astrophysical applications. The detectors, designed for the High Energy Focusing Telescope (HEFT) balloon experiment, each consists of an array of 24x44 pixels, on a 498 μm pitch. Each of the anode segments on a CdZnTe sensor is bonded to a custom, low-noise application-specific integrated circuit (ASIC)optimized to achieve low threshold and good energy resolution. We have studied detectors fabricated by two different bonding methods and corresponding anode plane designs---the first detector has a steering electrode grid, and is bonded to the ASIC with indium bumps; the second detector has no grid but a narrower gap between anode contacts, and is bonded to the ASIC with conductive epoxy bumps and gold stud bumps in series. In this paper, we present results from detailed X-ray testing of the HEFT pixel detectors. This includes measurements of the energy resolution for both single-pixel and split-pixel events, and characterization of the effects of charge trapping, electrode biases and temperature on the spectral performance. Detectors from the two bonding methods are contrasted.

We have begun a program to develop CZT-based detectors optimized for Synchrotron Radiation (SR) applications. SR provides high brightness beams of hard x-rays, typically in the range 5-100keV. Below 10keV, Peltier-cooled silicon detector arrays can provide high throughput with good spectroscopic resolution. At higher energies, only cryo-cooled germanium detectors or scintillation counters are available. Neither are easily available in large arrays, and scintillation counters lack energy resolution. CZT offers a solution to both these problems. Our development has focused on surface preparation and contact definition technologies which minimize device leakage currents while allowing high-definition contact patterns suitable for SR applications. We have used SR also for diagnostic purposes in these developments, both for detector testing and material characterization. X-ray diffraction, Infrared microscopy and photoemission are all relevant SR-based tools which we are using in our work. As an example, we have observed that bromine remains attached to the CZT surface after chemical etching, and is remarkably persistent in the face of surface cleaning and argon ion sputtering, as revealed by photoemission spectroscopy and x-ray absorption spectroscopy.

This paper describes a gamma detector employing an array of eight cadmium-zinc-telluride (CZT) crystals configured as a high resolution gamma ray spectrometer. This detector is part of a more complex instrument that identifies the isotope, displays this information, and records the gamma spectrum. Various alarms and other operator features are incorporated in this battery operated rugged instrument. The CZT detector is the key component of this instrument and will be described in detail in this paper. We have made extensive spectral measurements of the usual laboratory gamma sources, common medical isotopes, and various Special Nuclear Materials (SNM) with this detector. Some of these data will be presented as spectra. We will also present energy resolution and detection efficiency for the basic 8-crystal array. Additional data will also be presented for a 32-crystal array. The basic 8-crystal array development was completed two years ago, and the system electronic design has been improved recently. This has resulted in significantly improved noise performance. We expect to have a much smaller detector package, using 8 crystals, in a few months. This package will use flip-chip packaging to reduce the electronics physical size by a factor of 5.

The effect of the location of the high resistivity region within the crystal boule is investigated for 10% zinc with 1.5% excess Te. By varying the indium doping concentration in several CdZnTe boules, the region of high resistivity is changed along the vertical length of the crystal. The variation of the zinc concentration within the crystal boule is compared with the location of the high resistivity region along the length of the crystals. The concentration of zinc is extracted from FTIR measurements, and the segregation coefficient is calculated using data obtained from the CdZnTe crystals. The zinc distribution is plotted in terms of the location along the crystal length in order to correlate the concentration with detector performance. Radiation spectra obtained from these boules reveal a strong dependence between detector performance, and the relative location of the high resistivity region within the crystal. Initial results suggest that there are three semi-distinct regions along the length of the boule that give very different characteristics, where it can be said that the best detector performance is in the middle region. It is determined that this middle region has a zinc concentration of ~9-11%, which varies slightly from the original concentration of 10%. The differences in the performance characteristics is discussed, and defect distribution within the crystal as the main source of the variation is suggested. Also, based on the results, it is believed that the role of indium is essentially to compensate the vacancies in the crystal, and therefore, secondary to the crystalline properties and impurities within the boule.

Recent progress has been made in the development of the Modified Vertical Bridgman (MVB) technique for the growths of 3-inch diameter CZT crystals for fabrication of x-ray and gamma-ray detectors to operate at room temperature. 40% and 80% of the ingots have the single crystal volumes over 300cm³ and 100 cm³ per ingot respectively. Defects (such as Cd-vacancies, Indium dopants and purity) in CZT have been systematically studied. Detectors fabricated from these CZT ingots showed sharp energy resolution and good uniformity.

CdTe and (Cd,Zn)Te high resistivity crystals were grown by the Vertical Bridgman method with diameters from 25 mm up to 75 mm. Different dopants had been applied to obtain resistivities of 5 x 10⁸ Ωcm up to 2 x 10¹⁰ Ωcm and 3 x 10^-3 cm²/V for the mobility-lifetime product for electrons for the indium doped material.

It is well known that the attenuation length of radiation in any dense material increases with radiation energy. We propose a novel method of measuring x-ray and gamma spectra based on this principle. The multispectral x-ray and gamma spectrometer concept employs a scintillating material and optical camera system coupled via optical fibers. The optical fibers are placed sequentially at increasing depth with respect to the radiation path along the length of the scintillating material. Light generated by the interaction of radiation with the scintillating material is transported to the camera for recording and subsequent analysis. The proposed system will be used to determine the spectrum of incident radiation by deconvolving the radiation spectrum from the optical intensity (as a function of depth) of the recorded signals.

A brief survey of plastic scintillators for various radiation measurement applications is presented here. The utility of plastic scintillators for practical applications such as gamma radiation monitoring, real-time radioisotope detection and screening is evaluated in laboratory and field measurements. This study also reports results of Monte Carlo-type predictive responses of common plastic scintillators in gamma and neutron radiation fields. Small-size plastic detectors are evaluated for static and dynamic gamma-ray detection sensitivity of selected radiation sources.

Simultaneous detection of gamma rays and neutrons emanating from an unknown source has been of special significance and importance to consequence management and first responders since the earliest days of the program. Bechtel Nevada scientists have worked with ⁶LiI(Eu) crystals and ⁶Li glass to develop field-operable dual sensors that detect gamma rays and neutrons simultaneously. The prototype ⁶LiI(Eu) counter, which has been built and tested, is designed to collect data for periods of one second to more than eight hours. The collection time is controlled by thumbwheel switches. A fourpole, high pass filter at 90 KHz reduces microphonic noise from shock or vibration. ⁶LiI(Eu) crystals generate completely separable gamma-ray and thermal neutron responses. The ⁶LiI(Eu) rate meter consists of a single crystal 3.8 x 3.8 cm (1.5 x 1.5 in) with a 2.54-cm-(1-in-) thick, annular, high-density, polyethylene ring around the cylinder. Special features are (1) thermal and epithermal neutron detection (0.025eV to 250keV) and (2) typical gamma resolution of 8% at 661.6 keV. Monte Carlo N-Particle calculations for characteristics of gamma spectral behavior, neutron attenuation length, relative neutron and gamma detection efficiency are reported.

This paper explores the use of mixed oxide materials such as In₂O₃ and SiO with various compositions in the form of thermally deposited thin films for gamma radiation dosimetry application. 137Cs radiation source with an activity of 370 kBq was used for exposing the samples to γ-radiation. The absorption spectra for as-deposited and γ-irradiated films were recorded using CARY 1E UV-Visible Spectrophotometer. The values of the optical band gap E_opt were obtained in the view of the Mott and Davis’ theory. It was found that the optical properties of thin films were highly affected by composition and manufacturing conditions. For comparison, E_opt of as-deposited thin film with composition 75 wt.% of In2O3 and 25 wt.% of SiO was found to be 0.9 eV, whereas films with 50 wt.% of In2O3 and 50 wt.% of SiO have E_opt=1.15 eV, in all cases assuming indirect allowed transition. It was noted that E_opt decreased with the increase in radiation dose, i.e. the overall disorder of the system has increased. Thin films of In₂O₃ and SiO mixtures might be regarded as a cost-effective alternative to the existing commercially available radiation detectors.

Milano collaboration has been developing for many years large mass bolometers for particle detection, and in particular for the study of neutrinoless double beta decay of ¹³⁰Te. The active components of the detectors are large mass (340 g and 790 g) TeO₂ crystals, while Neutron Transmutation Doped Ge thermistors are used as phonon sensors. These devices work at low temperatures, about 5-10 mK. The mechanical and thermal connections of the detector to the thermal bath are made with PTFE pieces that hold the crystal on copper frames. Gold wires are used as electric connections. We have developed a complete thermal model for the bolometers and "ad hoc" measurements of the thermal parameters involved were performed in the Florence cryogenic laboratory. These studies have permitted to simulate the static and dynamic behaviours of the detectors. A satisfactory agreement between simulated and the experimental response has been obtained as far as the static behaviour is concerned, while the dynamic behaviour is not yet fully understood. These preliminary results however will enable us to design new detector structures in order to improve the signal-to-noise ratio and the reproducibility. Given the good performances of these devices (excellent energy resolutions were obtained, of the order of 2 keV at 911 keV and of 5 keV at 2615 keV), this technique is particularly suitable to detectors for gamma ray spectroscopy. Encouraged by this results, the Milano-Como group has joined a large international collaboration for the realization of CUORE (Cryogenic Underground Observatory for Rare Events), seraching for Dark Matter and neutrinoless Double Beta Decay, a crucial phenomenon for neutrino physics. The Cuoricino detector, a small scale test of CUORE detector, is an array of 62 large mass bolometers like those already described, and it is now in operation in the Gran Sasso undergrand laboratory (Italy). It is the largest array of bolometric detectors ever constructed.

Vortex^TM, a high performance Silicon Multi-Cathode Detector (SMCD), has been developed and extensively tested for potential X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) applications. As a type of Silicon Drift Detector (SEE), it utilizes our patented structure design and has achieved very low capacitance and very low leakage current with a relatively large active area (~50 mm²). Results will be presented to demonstrate its superior performance over the conventional cryogenic Si(Li) detectors, especially in the resolution and throughput at short peaking times. The detector operates at near room temperature and is thus very compact in size. These features make it idea for XRD and XRF applications.

Radiation hardness is one of the most important aspect of a charge coupled device (CCD) working in the space environment. A notch structure is employed so that a charge packet is confined in a notch region within a pixel. We report here the effect of the ’notch structure’ inside the CCD that is designed to be radiation hard. Using a proton beam, we confirmed that the notch structure improved the charge transfer inefficiency (CTI) by a factor of 3. We applied a mesh technique in the proton beam experiment on a CCD. The CCD employed has 1024×1024 pixels with a notch structure. The mesh technique enables us to confine the proton beam of about 600 keV to a circular region of 2 μm diameter within a 24μm pixel. The total proton fluence is 2 × 10⁹ protons/cm² before the mesh that corresponds to 100 protons for each hole. Some pixels are damaged in the notch region while others in the out-of-notch region. After the proton irradiation, we measured the CTI for each pixel using X-rays from ⁵⁵Fe. We found that the CTI of pixels damaged in the notch region is larger by a factor of 3 than that of pixels damaged in the out-of-notch region. We experimentally showed how the notch structure improved the CTI of the CCD.

A new high efficiency, low-bandgap phosphor, ZnSe:Cu,Ce,Cl is described which exhibits a significantly higher quantum gain than conventional x-ray phosphors and more closely matches the spectral sensitivity of silicon sensors. For many imaging applications this phosphor thus promises significantly superior performance compared to conventional phosphors.

High-current pulsed bremsstrahlung X-ray sources with endpoint energies in the 100 keV to 1 MeV regime are commonly used to radiograph dynamic events. Knowledge of the output spectra can assist in both improving these sources and in analyzing the imagery. Consequently, we have begun developing a spectrometer for this regime, which we refer to as the Collimated Step-wedge Spectrometer (CSS). It is based on a set of severl input channels, each comprising a collimator, X-ray filter, and scintillator. The scintillation light from all channels is recorded in a single from of a high-S/N CCD camera. Knowledge of the filters' attentuation and the scintillator's spectral response should allow unfolding an X-ray spectrum. An Initial test was performed with a bremstrahlung source of 300 keV endpoint energy, but with a non-optimal filter set.

Photoconductive polycrystalline mercuric iodide deposited on flat panel thin film transistor (TFT) arrays is one of the best candidates for direct digital X-ray detectors for radiographic and fluoroscopic medical imaging. The mercuric iodide is vacuum deposited by Physical Vapor Deposition (PVD). This deposition technology has been scaled up to the 20cmX25cm size required in common medical imaging applications. A TFT array with a pixel pitch of 127 microns is used for these imagers. In addition to successful imager scale up, non-TFT based detectors were developed in order to improve analysis methods of the mercuric iodide photoconductor itself. These substrates consist of an array of palladium or ITO stripes on a glass substrate. Following deposit of the photoconductor, striped bias electrodes are deposited on top of the photoconductor at a 90 degree orientation to the bottom electrodes. These substrates provide more information than was previously available on the dark current and signal uniformity of the mercuric iodide photoconductor without the use of expensive TFT arrays. Mercuric iodide photoconductor thicknesses between 110 microns and 300 microns were tested with beam energy between 40 kVp and 120 kVp utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluoroscopic images at up to 15 pulses per second were demonstrated. Resolution tests on resolution target phantoms were performed and performance close to the theoretical sinc function up to the Nyquist frequency of ~3.9 lp/mm is shown (127 micron pixel pitch).

The effects of elevated temperatures on the spectral performance of a planar mercuric iodide (HgI₂) gamma ray detector were evaluated at 25°C, 35°C, 45°C and 55°C using two test isotopes. ¹³⁷Cs at 662 keV and ²⁴¹Am at 59 keV. Spectral analysis was used to determine the spectral parameters (i.e. %FWHM of the full energy peak, the peak channel position and the peak to background ratio). Spectral performance degraded slightly with increasing test temperatures, but recovered on returning to ambient conditions. The results demonstrate that temperature excursions up to 55°C minimally degrade the spectral performance of mercuric iodide detectors.

We describe the mode of operation of a detector for direct photon-electron conversion at room temperature, made of epitaxially grown GaAs. Contrary to bulk grown materials, epitaxial layers are free of defects, i.e. exhibit long lifetimes and high carrier mobilities, and have uniform electronic properties. However, the depleted zone is of limited extension, consequence of the level of the residual doping impurities, which are not compensated by defects. These detectors are adapted to X-ray imaging, in particular for low energy medical applications such as mammography, because of the availability of large areas (up to 4 inches in diameter), standard technological processes for making pixellated detectors and cost. However, charges in the neutral region can be collected by diffusion and we shall present data allowing to illustrate and evaluate this effect. Finally photocurrent measurements obtained under medical conditions demonstrate that, for the detector used, only a small fraction of the photocurrent originates from diffusing charges. They also show how a 120 μm thick GaAs epitaxial detector competes with a 0.5 mm thick CdZnTe detector.

Various modifications of xenon detectors and their parameters in comparison with gamma-detectors of other types are considered. Prospects of xenon detectors' applications in gamma-spectroscopy based on experimental results are discussed including detection and control of radioactive and fissile materials displacement, definition of uranium enrichment rate, and measurements of nuclear reactor radioactive gas waste concentration. Possibilities for xenon detector use for environmental control and measurement of cosmic gamma radiation on orbital stations are considered.

Phosphor-coupled CCDs are established as one of the most successful technologies for x-ray diffraction. This application demands that the CCD simultaneously achieve both the highest possible sensitivity and high readout speeds. Recently, wafer-scale, back illuminated devices have become available which offer significantly higher quantum efficiency than conventional devices (the Fairchild Imaging CCD 486 BI). However, since back thinning significantly changes the electrical properties of the CCD the high speed operation of wafer-scale, back-illuminated devices is not well understood. Here we describe the operating characteristics (including noise, linearity, full well capacity and CTE) of the back-illuminated CCD 486 at readout speeds up to 4 MHz.

We have demonstrated a new amplifier topology for coplanar-grid detectors that provides true differential readout with a single, fully-differential, charge-sensitive preamplifier. A prototype, multi-detector system with adjustable gain for each detector has been demonstrated using this fully differential approach. In its initial implementation using general-purpose amplifier chips, this system produces comparable noise performance to the traditional two-amplifier readout with specialized, charge-sensitive preamplifiers. In lieu of a differential gain to correct for electron trapping, the circuit uses a differential sampling scheme. This method enables a symmetrical photopeak to be obtained, but introduces some undesired filtering that limits energy resolution.

We demonstrated the wide-range isotopic analysis of plutonium with a portable Peltier cooled CdTe detector in late 2000. These were the first results of this kind for a non-cryogenic detector. The energies used in those early analyses were in the range 125-414 keV. We have since extended the analysis into the X-ray region where the gamma rays are many times more intense than in the higher energy region. We describe the plutonium and uranium analysis of CdTe spectra in the X-ray region.

The properties of large diameter (140 mm) semi-insulating Cd_1-xZn_xTe (x = 0.1) ingots grown by the vertical High-Pressure Electro-Dynamic Gradient (HP EDG) technique are discussed. The HP EDG crystal growth technology recently developed and introduced at eV PRODUCTS significantly improves the downstream CdZnTe detector fabrication yield compared to earlier versions of the HP crystal growth technology. These yield improvements stem from the improved structural and charge transport properties of the HP EDG CdZnTe ingots. Improvements were achieved in three areas: a) reduced thermal stress in the ingots, b) improved single crystal yield, and c) improved electron transport properties. The new state-of-the-art HP EDG crystal growth systems offer exceptional flexibility, thermal and mechanical stability and allow the growth of high purity CdZnTe materials. The flexibility of the multi-zone heater system allows the dynamic control of heat flow to optimize the growth-interface shape during crystallization. This flexibility combined with an advanced control system, improved system diagnostics and realistic thermal modeling provides an excellent platform for further process development. Results on the initial HP EDG CdZnTe ingots grown with low temperature gradient show the complete elimination of ingot cracking. The increased single crystal yield combined with the improved electron transport properties allows the fabrication of large volume electron-only devices at higher yield. The CdZnTe ingots regularly contain sections with electron mobility-lifetime product μτ_e≥5.0x10^-3 cm²/V and occasionally yield material with μτ_e≥8.0x10^-3 cm²/V.

The current-voltage characteristics are investigated in single crystals of CdTe doped with Cl. Measured samples were ntype conductivity with resistivity ρ=(0.5-2.0)×10⁸ Ohm×cm, electron concentration n=(0.5÷2.0)×108 cm^-3 and electron mobility μ=280÷300 cm²/Vxs. Experimental data are explained in the framework of theory of highly doped and highly compensated (HDHC) semiconductors. The mobility-lifetime product measured at room temperature is found to be of the order of (1÷5)x 10^-4 cm²xV^-1. It means that this material can be used for manufacture of X-ray detectors.

The properties of 32k CdZnTe detectors have been studied in the pre-flight calibration of Burst Alert Telescope (BAT) on-board the Swift Gamma-ray Burst Explorer (scheduled for launch in January 2004). After corrections of the linearity and the gain, the energy resolution of summed spectrum is 7.0 keV (FWHM) at 122~keV. In order to construct response matrices for the BAT instrument, we extracted mobility-lifetime (μτ) products for electrons and holes in the CdZnTe. Based on a new method applied to ⁵⁷Co spectra taken at different bias voltages, μτ for electrons ranges from 5.0x10^-4 to 1.0x10^-2cm²V^-1, while μτ for holes ranges from 1.0x10^-5 to 1.7x10^-4cm²V^-1. We show that the distortion of the spectrum and the peak efficiency of the BAT instrument are well reproduced by the μτ database constructed in the calibration.

Fast neutrons can be detected with relatively high efficiency, >15%, using two planes of hydrogenous scintillator detectors where a scatter in the first plane creates a start pulse and scatter in the second plane is separated by time-offlight. Indeed, the neutron spectrum of the source can be determined as the sum of energy deposited by pulse height in the first added to the energy of the second found by time-of-flight to the second detector. Gamma rays can also create a double scatter by Compton interaction in the first with detection in the second, but these events occur in a single time window because the scattered photons all travel at the speed of light. Thus, gamma ray events can be separated from neutrons by the time-of-flight differences. We have studied this detection system with a Cf-252 source using Bicron 501A organic scintillators and report on the ability to efficiently detect fast neutrons with high neutron/gamma detection ratios. We have further studied cosmic-ray neutron background detection response that is the dominant background in long range detection. We have found that most of the neutrons are excluded from the time-of-flight window because they are either too high in energy, >10MeV, or too low, < 10 keV. Moreover, if the detection planes are position-sensitive, the angular direction of the source can be determined by the ratio of the energy of scattered protons in the first detector relative to the position and energy of the scattered neutron detected in the second. This ability to locate the source in theta is useful, but more importantly increases the signal to noise relative to cosmic-ray produced neutrons that are relatively isotropic. This technique may be used in large arrays to detect neutrons at ranges up to 0.5 kilometer.

The Burst Alert Telescope (BAT) aboard the Swift Gamma-ray Burst Explorer (scheduled for launch in January 2004) is a coded aperture telescope that includes an array of 32,768 CZT planar detectors, each 4 mm x 4 mm x 2 mm thick. The mobility-lifetime products for holes and electrons are used to characterize the charge transport properties of each detector and were measured during pre-flight calibration tests in early 2003. These values were found to vary over an order of magnitude from detector to detector. In addition to the charge transport models, other more empirical models are used to characterize the remaining components of the response of the BAT array to 15 - 150 keV gamma radiation from any direction in BAT's field-of-view (FOV). The full angular and spectral response of the array as a whole can be parameterized and the spectral response of the instrument over the range of angles and energies can thus be generated in an overall instrument response model. Here we present a preliminary instrument response model and discuss the general characteristics of the detector array. The software to generate the response matrix for BAT is currently under development.

Miniaturized Micro-Pocket Fission Detectors (MPFD) are under investigation as real-time neutron flux monitors. The devices are capable of performing near-core and in-core reactor power measurements. The basic design utilizes neutron reactive material confined within a miniaturized gas pocket, similar to that of a fission chamber. Device size ranges from 500 microns to a few millimeters thick, thereby allowing them to be inserted directly between fuel elements of a reactor core. Fabricated from inexpensive ceramic materials, the detectors can be fashioned into a linear array to facilitate 3-D mapping of a reactor core neutron flux profile in "real-time". Initial tests have shown these devices to be extremely radiation hard and potentially capable of operating in a neutron fluence exceeding 10¹⁶ n cm^-2 without noticeable degradation.

Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographic screening technique that combines high radiation penetration with very good sensitivity and specificity to nitrogenous explosives. The method is particularly well-suited to inspection of large, massive objects (since the resonant γ-ray probe is at 9.17 MeV) such as aviation and marine containers, heavy vehicles and railroad cars. Two kinds of γ-ray detectors have been employed to date in GRA systems: 1) Resonant-response nitrogen-rich liquid scintillators and 2) BGO detectors. This paper analyses and compares the response of these detector-types to the resonant radiation, in terms of single-pixel figures of merit. The latter are sensitive not only to detector response, but also to accelerator-beam quality, via the properties of the nuclear reaction that produces the resonant-γ-rays. Generally, resonant detectors give rise to much higher nitrogen-contrast sensitivity in the radiographic image than their non-resonant detector counterparts and furthermore, do not require proton beams of high energy-resolution. By comparison, the non-resonant detectors have higher γ-detection efficiency, but their contrast sensitivity is very sensitive to the quality of the accelerator beam. Implications of these detector/accelerator characteristics for eventual GRA field systems are discussed.

For multi-energy digital radiography, a sandwich structure is proposed, comprising "scintillator-photodiode" (S-PD) type detectors. This will allow obtaining information on an object simultaneously for two or three energies in the 20-400 keV X-ray range. Criteria have been formulated and a procedure proposed that determine requirements to detector characteristics for distinction of specified substances. Under this procedure, the following characteristics have been determined for two- and three-energy detecting systems. For a two-energy detector system used for organic substances (Z_eff=6-8) and iron/steel (Z_eff=26), the X-ray tube anode voltage VA=140 kV, sensitivity range of the low-energy detector (LED) and the high-energy detector (HED) 40-60 keV and 100-140 keV, respectively. The average detector sensitivity of LED should be closer to 40 keV, and that of HED - to 140 keV. There is a limitation that is imposed upon the detector sensitivity by sensitivity of the radiographic system. For such variant, LED are made on the basis of a photodiode and a ZnSe(Te) scintillator, ensuring good sensitivity in this range and transparence in the HED range. HED can be made on the S-PD base using CsI(Tl), CdWO₄ or Cd₂O₂S. In a three-energy system, where elements with Z_eff=6,7 and 8 should also be determined detector sensitivity ranges should be as follows: LED - 10-35 keV, medium-range energy detector (MED) - 40-80 keV, HED - 100-140 keV. Such subdivision into ranges is ensured by the use of a semiconductor sensor (e.g., silicon) as LED, S-PD with ZnSe(Te) as MED, and CsI(Tl), CdWO₄ or Cd₂O₂S - as HED.

The development prospects of a scintillator-photodiode type detector with an improved energy resolution attaining few per cent, about 1.5 to 2.5%, are considered. The main resolution components have been analyzed theoretically, their theoretical and physical limits have been established. Empirical data on the properties of novel scintillators have been considered confirming the possibility of the energy resolution improvement. Ways have been proposed to optimize the detector statistical fluctuations and the scintillator intrinsic resolution. A specific importance of the intrinsic resolution is shown as a limiting threshold factor at the ionizing radiation energy values from 662 keV to 10 MeV and over.

This paper discusses a safety inspection system that applies x-ray technology to check passengers on some important sites, such as airports. In the actual inspection, passengers are required to take off their shoes to be checked at the airports. This system will realize instant inspecting function, utilizing the x-ray’s penetrating property, while people pass with shoes on. X-ray generating module, inspecting module, information receiving and converting module as well as the processing module constitute all of the system. The X-ray generating module brings out x-ray of appropriate and safe dose. The inspecting module introduces infrared detection method to realize automatic checking flow. A LLL system is developed as the third module in which information is collected and digitized to deal with later. Then the processing module is to achieve, process information and show the results by means of information pick-up, image processing, remote conveying and controlling, building bank of information etc. The system improves inspecting speed and accuracy. At the same time, it extends the detection sorts largely so that not only metal but also other organic substances can be perceived. Finally we give a resolution expression of this kind of system and discuss the influence factors. Then some approaches to improve the system’s performance have been presented, which have great significance in improving and developing this kind of system.

For monitoring of intense radiation fields, such as around nuclear reactors, high energy accelerators, it is requested to develop a reliable radiation sensing method with high radiation resistance. As one of the promising methods, we propose a novel radiation remote-sensing method based on high sensitive cavity ring-down (CRD) laser spectroscopic measurement of radiation induced radicals. To verify the detection principle, we have made basic experiments on the CRD spectroscopic measurement of the radiation induced ozone concentration in the air irradiated by ⁶⁰Co gamma-rays, while we have also developed the calculation model to estimate the yields of radiation induced radicals by solving simultaneous rate equations numerically. Through comparison between the experiments and the calculations, we have confirmed the detection principle and the validity of the calculation model, where the results show that the detectable range for the absorbed dose rate is from 4.8x10^-2 to 3.2 Gy/s with time resolution of 35 sec by controlling the flow rate of the irradiated air.

The Schottky barrier formation are investigated in Au/p-CdTe contacts. The contacts were manufactured by electroless deposition of Au at the surfaces prepared by wet chemical etching. The influence of the surface treatment on the Schottky barrier height are studied. The potential barrier height is determined from the photoemission current spectra measurements. The secondary ion-mass spectroscopy (SIMS) profiling is carried out to study the compositional structure in as-deposited contacts as well as stored under normal laboratory conditions during one-year period. The effect of thermal annealing on electrical and photoelectrical properties of the contacts is studied. For comparison, the contacts Cu/p-CdTe prepared by the same method are studied too.

New Ce³⁺ - doped high-grade silica glasses are synthesized by a modified sol-gel method, to be used as scintillators for the detection of X-rays and low energy particles. These glasses have efficiency a factor of 2 higher than state-of-the-art Bi₄Ge₃O₁₂ crystals, high radiation hardness and high compatibility with the silica-based photonic technology. Powder-in-tube and rod-in-tube techniques are used to fabricate low-loss optical fibres with 135, 220 and 660 microns diameter. Device prototypes are obtained by fusion-splicing these fibres to commercial high numerical aperture optical fibres.

This study investigates the effectiveness of chemical etchants to remove surface damage caused by mechanical polishing during the fabrication of Cd_0.9Zn_0.1Te (CZT) nuclear radiation detectors. We evaluate different planar CZT devices fabricated from the same CZT crystals. All detectors used electroless Au for the metal contacts. Different polishing particle sizes ranging from 22.1-μm SiC to 0.05-μm alumina were used, which caused different degrees of surface roughness. Current-voltage measurements and detector testing were used to characterize the effects of surface roughness and etching on the material and detector properties.

We have fabricated a new experimental pixel array using 2mm-thick CdZnTe. The trial arrays have been bump-bonded to the Rockwell PICNIC readout IC which provides low noise read out of pixel signals. First measurements are presented from the detector characterisation, which in particular, demonstrate that a very high bond yield (>99%) was achieved. It is envisaged that these detectors will be suitable for future X-ray astronomy and planetary missions as well as ground based applications such as non-destructive testing, threat detection and baggage scanning.

High power pulsed x-ray sources (XRS) are common place for many radiographic and plasma physics applications. Developing such XRS’s for particular applications require accurate end-point voltage and dose measurements to adequately characterize and model these devices. A simple mathematical relationship, which yields end-point energy results as function of measured peak voltage and time response, has been extracted from the data sheets and specifications of a proprietary manufactured Silicon x-ray detector (XRD). The model takes into account the fractional energy absorbed, response time, linear absorption coefficients (including both photo-electric and Compton incoherent interactions), physical geometry, and transfer function of the biasing circuit.

The response of a transverse biased photoconductive detector (PCD) may be modeled as a continuously variable parallel resistor through the depth of the detector. Since the bias is perpendicular to the dose gradient the electric field is constant and the mean conductivity is proportional to the mean dose rate. The response of a parallel biased PCD can be modeled as a continuously variable series resistor through the depth of the detector with the bias electric field dependent on the resistivity at the given depth in the detector. Hence, even though the front region the PCD becomes highly conductive, the PCD will not respond unless free carriers are generated through the entire depth of the PCD between the bias electrodes. Experimental measurements on parallel biased gallium arsenide, GaAs, PCDs using the MBS (Modular Bremsstrahlung Source) pulse x-ray source at AEDC (Arnold Engineering Development Center) are given that substantiate the response model. Agreement in the response between PCDs of varying x-ray filtration were observed with the effective dose model given in the paper as opposed to a 40% discrepancy when the mean dose is used.

In radiometers for X-range, the use of scintillators based on gadolinium orthosilicate (GSO) has many advantages over alkali halide scintillators, e.g., NaI(Tl). The shape of spectra obtained with GSO and cadmiug tangstate (CWO) scintillators has certain features that substantially increase the sensitivity of radiometers which use the windows method algorithm and are designed for simultaneous detection of low-energy gamma-radiation of ²⁴¹Am (59.6 keV) and ¹³⁷Cs (~33 keV). These features of oxide scintillators have allowed a substantial increase in sensitivity of the radiometer RK-AG-02M, which is designed for detection of ²⁴¹Am on the background of ¹³⁷Cs. The results obtained in this work show that the use of GSO and (in several cases) CWO scintillators in the instruments involving X-ray range of radiation (e.g., meters of thickness, radiometers) is very promising field of their application. We consider also the effects of different factors related to thermal treatment upon dopant-activated complex oxide crystal to improve its optic-luminescent, scintillation and other functional characteristics. In the selective radiometer RK-AG-02M are using a scintillation block based on GSO scintillator. To increase the measurement accuracy in the bulk density range of 0.6-2.5 g/cm³ correcting function has been obtained for the radiometer sensitivity.