The use of conventional glass scintillators for x-ray imaging has been limited by the need of a severe trade-off between the detection efficiency of glasses, that is low if the incoming energy exceeds about one hundred keV for conventional glasses, and the achievable spatial resolution, that is greatly affected if the thickness of the glass is increased above 2 mm. Scintillating fiber optic detectors solve this problem thanks to their light guidance properties. A set of different scintillating fiber optic plates (SFOP) has been produced to optimally detect both low (up to 50 kVp) and high (up to some hundreds kVp) energy x-rays. These detectors are coupled to a fiber optic taper which drives the light to a CCD camera through a MCP image intensifier. Alternatively, a focusing lens is employed. The detectors have been used for image acquisitions for digital radiography in the medical field (particularly at the lower energies) and for nondestructive testings, with a particular interest for the preservation of the cultural heritage.

The measurements of light yield of PbWO₄ crystals with normal methods may have relatively large errors because the crystals have a low light yield. The measurements of light yield of PbWO₄ crystals by single photoelectron method with normal radioactive sources are described. The results of the measurements for several PbWO₄ samples produced by Beijing Glass Research Institute are reported. Also, scintillation decay times and relative light intensities of the samples are presented.

We report on studies of a small field of view scintimammography camera based on a position sensitive PMT and a crystal scintillator array. A 5 inch R3292 Hamamatsu PMT was coupled to a variety of scintillators, including pixelized NaI(Tl), CsI(Na) and YAP. Laboratory and phantom studies were performed to compare performances of the above scintillator sensors with special emphasis on spatial resolution and scatter rejection. The results of Monte Carlo simulations for different pixel sizes are also presented.

The TRIUMF PET detector group is developing a public domain platform to simulate the position and energy responses of scintillation counters for hard x-ray and gamma-ray imaging applications. The simulation allows us to treat the tracking of gamma-ray interactions in the active volume of the detector, the non-proportionality of the scintillation response, the propagation and detection of individual scintillation photons through complex multicrystal geometries as well as the noise associated with signal amplification in the readout units. This is achieved by interfacing gamma-ray interaction tracking to the program DETECT, which simulates the transport of scintillation photons. The interface takes the form of a high level language which allows easy specifications of the detector geometry and readout units. The approach has been put to a validation test with a model of a BGO multicrystal detector manufactured by Siemens-CTI for high resolution positron emission tomography. Here, we present an updated discussion of the main components of this modeling platform as well as of the functionalities it offers in assisting the design of photon imaging detectors based on scintillators. Areas of future improvements are also discussed.

The microstructure and chemical inhomogeneities of commercially available Cd_1-xZn_xTe (CZT) have been evaluated using electron microscopy and microanalytical techniques. Since imperfections, such as inclusions, cracks and extended crystallographic defects are known to affect the performance of CZT gamma-ray spectrometers, understanding the nature and origins of such imperfections is vital to the improvement of device performance. CZT that is grown using a high-pressure Bridgeman method has a polycrystalline microstructure containing numerous grain boundaries, twins and inclusions. In this study, scanning electron microscopy and x- ray energy-dispersive spectroscopy were used to analyze inclusions and cracks inside CZT material. Such analysis found regions of material rich in C, O, Si, Zn, and Te. Transmission electron microscopy revealed small subgrains and thin platelets of a second phase material located inside the large- grain CZT matrix. Details of these microstructural features and their possible origins are discussed.

Performance and yield of CdZnTe (CZT) nuclear radiation detector arrays are sensitive to bulk defects introduced at all stages of material processing. Ingots of CZT grown by the high pressure Bridgman process contain several kinds of bulk material defects (BMDs) which can affect nuclear detector performance. In this study infrared transmission imaging was used to locate and identify certain BMDs in four-inch CZT wafers produced by Digirad. The correlation of performance of subsequently processed pixel arrays with IR image features demonstrates the predictive value of this method.

Cadmium zinc telluride (CZT) gamma-ray detectors show great potential in medical and nuclear material imaging applications. These imagers rely on pixellated arrays of CZT for their operation. Systematic and random material variation among the pixels can introduce noise into the system and makes data analysis more complicated. Photo induced transient current spectroscopy (PICTS), and low temperature photoluminescence have been employed to analyze 4 by 4 pixellated arrays and to determine material variation among the pixels. Particular pixels that have proven to perform well or poorly have been studied in detail to try and identify the origin of this performance variation. This paper reports preliminary results and comments on future analysis.

Polarized transmission optical profiles were used to characterize the CdZnTe (CZT) room-temperature radiation detectors. The internal electric field distributions of the CZT detectors under bias were probed by a 952 nm illumination between two crossed Glan-Taylor polarizers. A 16-bit digital charge coupled device (CCD) was employed as an image sensor. The 2-dimensional (2D) images reflecting the internal electrical field intensity changes were obtained utilizing the Pockels electro-optic effect. CZT detectors of crystal sizes of 5 by 5 by 5 mm were investigated under different bias voltages. Uniform and nonuniform internal electric field distributions throughout the detector volumes, under different light illumination conditions, were observed and analyzed. A theoretical model of the semiconductor energy band structure under the bias was established and used to understand the measurement results.

High resistivity CdZnTe has attracted extensive interests for its use as x-ray and gamma-ray detector operated at room and elevated temperature due to its superior electro-optical and structural properties compared to other materials. The post- growth surface annealing under constituent over pressure, passivation, oxidation and chemical etching in terms of restoring stoichiometry, reducing surface damage and charge carrier trapping centers have been investigated by low temperature photoluminescence, x-ray photoelectron spectroscopy and atomic force microcopy. The choice of contacting metal and deposition method also plays an important role in lowering surface leakage current and increasing the ohmic behavior between contact and detector, and subsequently directly affects the detector performance. The data revealed by spectroscopic and microscopic measurements were correlated with current-voltage and x-ray spectrum results to give an improved detector fabrication process based on CdZnTe detector. These results are presented and discussed.

CdTe and CdZnTe detectors provide unique opportunities to solve difficult measurement tasks in international safeguards and related applications. Their development has been supported by the IAEA since more than a decade. Significant progress can be reported in the fields of development of high resolution pin type CdTe detectors (HRCD) and in the development of large volume hemispheric CdZnTe detectors.

A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. Two dimensional orthogonal strip detectors with 100 micrometer pitch have been fabricated and tested for a large area array (approximately 60 cm² with 36 detectors). Details for the fabrication and evaluation of the detectors are presented. Critical issues to be addressed include fabricating metal contacts with low leakage current and with excellent wire bonding yield, achieving high yield for good strips, and surface cleaning and passivation.

Researchers at Digirad Corporation have developed an innovative method for eliminating the effects of hole trapping in radiation detectors made from compound semiconductors such as CdTe or CdZnTe. The technique involves no additional electronics. Working devices have been manufactured in a variety of configurations including imaging arrays. This paper presents results from some simple structures.

The review of experimental research on transmission of soft x- ray radiation (approximately 1.5 keV) through capillary structures for synchrotron radiation beam of the S-60 accelerator is presented. The main synchrotron parameters and characteristics of synchrotron radiation beam in addition to a description of layout, studied capillary structures, procedure of objects' adjustment and detection of radiation behind capillary systems are given. A comparative analysis of experimental and theoretical data is argued. Some discussions about a requirement to experimental setup and a use of similar structures for x-ray beams of synchrotron radiation sources are described.

It has been suggested that low-energy-x-ray fluorescence (LEXRF) could be a surface analysis technique used for measuring elemental composition and thickness of thin films on a Si substrate. Conventional XRF, due to constraints on primary beam flux, requires close coupling of the sample to the source and illumination of a large area, making measurements inconvenient with limited spatial information. Polycapillary optics capture a large solid angle of x rays from a source and efficiently focus them to a submillimeter spot on the wafer with significant flux gains. Polycapillary optics do not suffer from the 1/r² losses in going to longer source to sample distances. A prototype focusing optic has been constructed and characterized at Cu L (0.93 keV) and Al K (1.49 keV). The optic collects 0.043 sr of x rays from a point source and focuses the beam to a point 0.46 mm and 0.42 mm in diameter (FWHM) for the Cu L and Al K source, respectively. The optic is 76 mm in length and has an input and output focal length of 64 mm. Compared to the direct beam 100 mm away from the source, the average flux gains within the output focal spot (FWHM) are 94 and 168 times greater for Cu L and Al K, respectively. It is estimated that coupling this optic with a 18 W (1.8 kV 10 mA) Cu source would allow a 4 nm SiO₂ layer on a Si wafer to be measured within 1 minute with a statistical accuracy of (sigma) equals 2%.

The spatial resolution of the modern x-ray and neutron detectors is limited by the range of secondary particles. It was shown theoretically that polycapillary Kumakhov optics can avoid this limit. Such systems can provide resolution less than 1 micrometer for energy 17 keV even using ordinary x-rays sources and detectors. The results of experimental investigations of polycapillary cone for imaging of objects with micron level resolution are present. This work is an extension of our last report at SPIE-96. New technology allows us to decrease the entrance capillary diameter to 0.5 micron. On this base we received resolution on the level 1.5 - 2 microns.

The data of investigation of the total sensibility of the element analysis method using Kumakhov lenses are given. The possibilities of the effective use of that method in medicine are shown.

The method of investigating polycapillaries quality is presented. This method is based on a special experimental arrangement which excludes the influence of exterior geometrical factors (source size, source-capillary distance, etc.) and allows us to obtain essential transmissional properties of polycapillaries in the x-ray range. The energy dependence of the radiation transmission coefficient contains important information concerning quality of reflecting surfaces, presence of polycapillary small bents, glass composition, etc. Experimental results are compared with the ray tracing calculations. This comparison allows us to estimate the values of roughness and waviness which characterize the polycapillary under investigation.

Hard x-rays radiation (100 keV and above) is widely used at present in medicine and industry. However modern collimators don't always provide necessary resolution of an object's details. For the first time the image transfer by polycapillary systems as collimators for hard x-ray region is investigated. The properties (resolution, sensitivity) of different types of polycapillary systems are presented.

The use of polarized x-ray beams provides drastic reduction of background connected with Compton scattering from the sample under investigation. In conventional x-ray tubes with isotropic distribution of x rays, the intensity of polarized beam after polarizer is very small. We have carried out the experiment with Kumakhov lens and Barcla polarizer to receive intense x-ray polarized beams. X-ray fluorescent spectra are observed by exciting a sample with both: polarized and unpolarized beams. A significant reduction in magnitude of the scattering radiation was observed with Kumakhov lens and Barcla polarizer.

Some new possibilities for filtration and monochromatization of x-ray radiation providing by Kumkhov optics are discussed. Concrete experiments at the Institute for Roentgen Optics and their results are considered.

In the paper an analysis of x-ray passage through a single monocapillary under the regime of a one reflection is presented. It is shown that a ray approximation does not explain the results obtained experimentally. A qualitative estimation of the phenomenon observed and computer simulation by a wave theory are given.

The scientific objectives, status, and future instrumental requirements of high energy X-ray astronomy (20 to 200 keV) are discussed. Two particularly compelling requirements are: (1) an improvement in sensitivity to a level of about 5 microCrab and (2) a survey of the sky at a sensitivity of about 0.1 milliCrab, which will discover and characterize about 10,000 new sources. The first requirement can be fulfilled by imaging telescopes that use large-area focusing X-ray mirrors, which are effective over 5-30 arcminute fields, and the second requirement can be met by arrays of large area coded mask imagers with wide fields, about 50 deg. Multilayer mirror and CdZnTe detector technology now in development offers the potential to meet these objectives. Position-sensitive CdZnTe detectors are well-suited to both of these imaging techniques, and instrument concepts that use these detectors are described. Detectors with pixel readout are better suited for focusing telescopes, and those with crossed-strip readout are better suited for coded mask imagers. Technical aspects of these detectors are discussed. Recent work at UCSD and WU on CdZnTe strip detectors is described in detail. Studies with small, 40 micron, X-ray beams have mapped a crossed-strip detector's spatial response with fine spatial resolution.

Measurements have been performed on a prototype CdZnTe linear array designed for direct digital mammography. Direct detection of x-ray photons without conversion to visible light avoids the trade-off between resolution and efficiency with phosphor thickness inherent in the conversion process. Polycapillary x-ray optics can be used to shape the x-ray image in a manner similar to the use of fused fiber optic tapers with visible light. The polycapillary optics also provide significant scatter rejection and resultant contrast enhancement. The theoretical detector quantum efficiency of CdZnTe at mammographic energies (20 keV) is quite high. Measurements were performed of DQE values and uniformity from 13 - 256 keV in large single pixel detectors. Uniformity and imaging measurements were also performed on a prototype 1 cm long linear detector array with 50 micrometer pixels attached to read-out electronics using indium bump bonding technology.

Polycrystalline mercuric iodide nuclear radiation detectors have been prepared using different ceramic fabrication methods, such as hot pressing, hot wall vapor phase deposition and screen printing. Areas varying between 0.01 to 100 cm² and thicknesses varying between 30 to 600 microns, have been fabricated. Gold or carbon electrodes were deposited having the shape of single continuous, linear strip or square pixel contacts and tested for their response to lower and higher gamma energy and beta particles. The (mu) (tau) value is of the order of 10^-7 cm²/V for both holes and electrons and therefore can act as particle counter without energy resolution. THe low production cost for potential large detector area make these compounds interesting for certain imaging applications.

We discuss the physical and electrical properties of semiconducting crystals necessary for use in orthogonal strip detectors. We also compute what constraints the properties of existing CdZnTe crystals place on the design of orthogonal strip detectors. First we consider the constraints imposed by uniform material that has limited charge carrier transport properties and resistivity. Next, we consider what effects spatially varying electrical properties (non-uniformities) have on the performance of detectors. Finally, we discuss the properties of CZT crystals available today that we have measured in our laboratory, and what ramifications these measured properties have on the design and construction of orthogonal strip detectors.

We have designed and constructed an orthogonal strip imaging system for use with room temperature semiconductor strip detectors. The system has been tested with both HgI₂ and Cd_1-xZn_xTe (CZT) detector elements. Our first system consists of complete readout electronics and software for spectroscopy and imaging with 8 by 8 orthogonal strip detectors. The readout electronics consist of 16 channels of hybrid charge sensitive preamplifiers, and 16 channels of parallel discriminators, shaping amplifiers, and a 16 channel ADC implemented in CAMAC and NIM. The software used to readout the instrument is capable of performing intensity measurements as well as spectroscopy on all 64 pixels of the device. In this paper we describe measurements to determine the factors limiting the performance of this system.

The coplanar-grid technique provides substantial spectral performance improvement over that of conventional detector designs and electronics when applied to gamma-ray detectors based on compound semiconductors. The technique realizes this improvement by measuring the difference between the induced charge signals from two interdigitated coplanar-grid electrodes. By adjusting the relative gain between the two grid signals prior to subtraction, the difference signal can be made less sensitive to the poor carrier transport properties of the detector material and thus improve the spectral response of the detector. In this paper, we discuss a variation of the coplanar-grid method in which the signal from only one grid electrode is read out. The signal response is optimized by changing the relative areas of the two grid electrodes and the bias applied across the detector. In this scheme, only one preamplifier is needed and signal subtraction is not necessary. This eliminates the electronic noise contribution from the additional preamplifier used in the normal coplanar-grid implementation, and conventional single- amplifier detector electronics can be used. Experimental results using CdZnTe detectors are presented.

We report new performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector under study as a prototype imaging spectrometer for astronomical x-ray and gamma-ray observations. The prototype is 1.5 mm thick with 375 micron strip pitch in both the x and y dimensions. Previously reported work included demonstrations of half-pitch spatial resolution (approximately 190 microns) and good energy resolution and spectral uniformity. Strip detector efficiency measurements have also been presented. A model that includes the photon interaction, carrier transport and the electronics was developed that qualitatively reproduced the measurements. The new studies include measurements of the CdZnTe transport properties for this prototype in an effort to resolve quantitative discrepancies between the measurements and the simulations. Measurements of charge signals produced by laser pulses and (alpha) -rays are used to determine these transport properties. These are then used in the model to predict gamma-ray efficiencies that are compared with the data. The imaging performance of the detector is studied by scanned laser and gamma beam spot measurements. The results support the model's prediction of nearly linear sharing of the charge for interactions occurring in the region between electrodes. The potential for strip detectors with spatial resolution much finer than the strip pitch is demonstrated. A new design scheme for strip detectors is shortly discussed.

Breast cancer is the most common cancer of American women and is the leading cause of cancer-related death among women aged 15 - 54; however recent years have shown that early detection using x-ray mammography can lead to a high probability of cure. However, because of mammography's low positive predictive value, surgical or core biopsy is typically required for diagnosis. In addition, the low radiographic contrast of many nonpalpable breast masses, particularly among women with radiographically dense breasts, results in an overall rate of 10% to 25% for missed tumors. Nuclear imaging of the breast using single gamma emitters (scintimammography) such as ^99mTc, or positron emitters such as F-18- fluorodeoxyglucose (FDG) for positron emission tomography (PET), can provide information on functional or metabolic tumor activity that is complementary to the structural information of x-ray mammography, thereby potentially reducing the number of unnecessary biopsies and missed cancers. This paper summarizes recent data on the efficacy of scintimammography using conventional gamma cameras, and describes the development of dedicated detectors for gamma emission breast imaging. The detectors use new, high density crystal scintillators and large area position sensitive photomultiplier tubes (PSPMTs). Detector design, imaging requirements, and preliminary measured imaging performance are discussed.

We have developed the analog electronics of the ASTRO-E hard x-ray detector (HXD). The ASTRO-E is the fifth Japanese x-ray astronomy satellite scheduled for launch in 2000. Three experiments will be on board the satellite, one of which being the HXD. The detector consists of 16 units of well-type phoswich counters with silicon PIN diodes embedded therein, and covers the energy range of 10 approximately 600 keV with photon collecting area of about 350 cm². The readout circuit for the HXD handles many signal channels (96 channels in total) under the limitation of power consumption and size set by the satellite. To meet the limitations, we have developed two types of bipolar semicustom LSIs. One is the pulse-shape discriminator (PSD-LSI) for phoswich counters and the other is for silicon PIN diodes (PIN-LSI). The PSD-LSI selects clean GSO hits and reduces the off-aperture x rays and internal background of the detector down to 10^-5 c/s/cm²keV. One PIN-LSI handles signals from two PIN diodes, each consisting of an amplifier, a peak-hold circuit, and a comparator to trigger the readout system. Test pieces of these LSIs meet the specifications such as power consumptions and linearities. Using PIN-LSI, we could successfully obtain x-ray spectrum from ²⁴¹Am with a PIN diode.

ASTRO-E is the next Japanese x-ray satellite to be launched in the year 2000. It carries three high-energy astrophysical experiments, including the hard x-ray detector (HXD) which is unique in covering the wide energy band from 10 keV to 700 keV with an extremely low background. The HXD is a compound-eye detector, employing 16 GSO/BGO well-type phoswich scintillation counters together with 64 silicon PIN detectors. The scintillation counters cover an energy range of 40 - 700 keV, while the PIN diodes fill the intermediate energy range from 10 keV to 70 keV with an energy resolution about 3 keV. In this paper, we report on the developments of the large area, thick silicon PIN diodes. In order to achieve a high quantum efficiency up to 70 keV with a high energy resolution, we utilize a double stack of silicon PIN diodes, each 20 by 20 mm² in size and 2 mm thick. Signals from the two diodes are summed into a single output. Four of these stacks (or eight diodes) are placed inside the deep BGO active-shield well of a phoswich counter, to achieve an extremely low background environment. Thus, the HXD utilizes 64 stacked silicon PIN detectors, achieving a total geometrical collecting area of 256 cm². We have developed the 2 mm thick silicon PIN diodes which have low leakage current, a low capacitance, and a high breakdown voltage to meet the requirements of our goal. Through various trials in fabricating PIN diodes with different structures, we have found optimal design parameters, such as mask design of the surface p⁺ layer and the implantation process.

We report on the development of a high resolution radiation imaging system which is capable of detecting and imaging the coincident gamma and x-ray emissions of the radioisotope iodine 125 (¹²⁵I). Iodine 125 is commonly available as a label to molecular biology probes. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27 - 32 keV x rays. A coincidence condition can be set to detect the ¹²⁵I decays thus reducing background radiation contribution to the image. We are testing the use of arrays of CsI(Na) crystal scintillators coupled to position sensitive photomultiplier tubes for this application. Laboratory studies have thus far been done on mice using a prototype of our detector which is intended to be used to image gene expression in live mice to advance research in neurobiology.

The paper describes some results concerning technology and behavior of x and gamma-ray N⁺PP⁺ silicon detectors used in physics research, industrial and medical radiography and non-destructive testing. These detectors work at the room-temperature and can be used individually to detect x- and soft gamma-rays, or coupled with scintillators for higher incoming energies. Electrical characteristics of these photodiodes, their modification after exposure to radiation and results of spectroscopic x- and gamma-ray measurements are discussed. Devices manufactured under this technology proved to be stable after an exposure in high intensity gamma field with the dose range of 10 krad - 5 Mrad. Nuclear radiation resistance was studied by irradiation with ⁶⁰Co gamma source (1.17, 1.33 MeV) at dose rates of 59 krad/hour and 570 krad/hour. Results indicate that proposed structures enable the development of reliable silicon detectors to be used in high gamma-radiation environments encountered in a lot of applications.

Thermoelectrically cooled semiconductor detectors, such as Si- PIN, Si-strip and HgI₂, coupled to miniaturized low-power x-ray tubes, are well suited for constructing portable systems for energy-dispersive x-ray fluorescence analysis (EDXRF) of samples of archaeological interest. The Si-PIN detector is characterized by a thickness of about 300 micrometer, an area of about 2 by 3 mm², an energy resolution of about 250 - 300 eV at 5.9 keV and an entrance window of 75 micrometers. The Si-strip detector has approximate the same area and thickness, but an energy resolution of 145 eV at 5.9 keV. The efficiency of these detectors is around 100% from 4 to 10 keV, and then decreases versus energy, reaching 10% at 30 keV. Coupled to a miniaturized 10 kV, 0.1 mA, Ca-anode or to a miniaturized 30 kV, 0.1 mA, W-anode x-ray tubes, completely portable systems can be constructed, which are able to analyze K-lines of elements up to about silver, and L-lines of heavy elements. The HgI₂ detector has an efficiency of about 100% in the whole range of x rays, and an energy resolution of about 200 eV at 5.9 keV. Coupled to a small 50 kV, 1 mA, W- anode x-ray tube, a portable system can be constructed, for analysis of practically all elements. These equipments were applied to analysis in the field of archaeometry and in all applications for which portable systems are needed or at least useful (for example x-ray transmission measurements, x-ray microtomography and so on). More specifically, concerning EDXRF analysis, ancient gold samples were analyzed in Rome, in Mexico City and in Milan, nuragic bronzes in Sassari, ceramics of various origin in Merida, La Habana and Sassari, and sulfur (due to pollution) in an old Roman fresco in S. Stefano Rotondo (Rome). Concerning transmission measurements, ancient copper coins and wood samples were analyzed, and microtomographic measurements are in progress to improve the quality of the image.

In the early history of the liquid noble gas spectrometers it was expected that their energy resolution would be similar to the resolution of semiconductor spectrometers. Then it became clear that the energy resolution was explained by the fluctuations of delta electrons. Apparently it is true in the low field region and for high LET particles. But now it is evident that for low LET particles and gammas and in the range of electric field where the best resolution can be obtained the energy resolution is not determined by known factors. In 1992 on the International Conference on Liquid Radiation Detectors the author presented the paper where the energy resolution of liquid rare gas gamma- and beta-spectrometers in the MeV region was analyzed. Five years have gone. It's high time now two analyze the situation.

Spectrometric properties, such as light output, energy resolution BGO crystals before and after ⁶⁰Co gamma-ray (dose 10⁴ - 10⁶ R) and neutron irradiation (fluence 10¹⁴ cm^-2) are investigated. Condition for degradation of spectrometric properties and their recovering after irradiation are studied. The energy spectrum of the photons emitted from BGO crystals irradiated with neutron fluence contains the long living background peak which is caused by self-irradiation with radioactive isotopes produced in the crystals. The defect production was studied in crystals under the high dose gamma-irradiation with ⁶⁰Co isotope. It was found that after doses above 10⁸ R the color center at 365 nm and doses higher than 10⁹ R a wide absorption band in the region of 300 - 350 nm occur. Comparison of these results with those of reactor irradiation has shown that under the high dose gamma-irradiation the structure defect production takes place.

For high sensitivity hard x-ray detector applications there is a solid-state alternative using high purity silicon as starting material. The paper presents some original results concerning a radiation hardened technology to be used for obtaining x-ray silicon detectors and the behavior of the special designed devices in a specific radiation environment. Original processing sequences were experimentally tested and results concerning the most performant technology suited for this specific application are presented. Specially designed gettering steps were applied by backside ion implantation and annealing for enhancing the minority carriers lifetime in the substrate material and for reducing leakage currents at orders less than 10 nA. After a complete presentation of the specific characteristics of the as obtained detectors, they were exposed and completely characterized in x-ray ambient up to dose levels of 10⁸ rad (E greater than 50 keV). Solutions for increasing the detector sensitivity and stability in radiation environments are proposed.

More recent Russian grown single crystals of Cd_0.8Zn_0.2Te (CZT) were evaluated using proton induced x ray emission (PIXE), x ray diffraction (XRD), photoluminescence (PL), infra red (IR) transmission microscopy, leakage current measurements and response to nuclear radiation. Whereas in the past the Russian grown samples were not acceptable for gamma ray detectors application, the present samples had a somewhat better crystallinity and a higher resistivity, and did even show distinct photopeaks for an ²⁴¹Am spectrum. Differences in the material properties between various Russian (n- and p-type) and U.S. (n-type) CZT are described.

The goal of polycapillaries and Kumakhov lens study is to bring out possible and liable ameliorations in terms of spatial resolution, brightness and spectral discrimination to a flash radiography chain used to image moving objects. Different kinds of polycapillaries have been tested with an x ray tube and a synchrotron beamline (DCI/LURE), in order to determine the performances of each type and highlight principal parameters which influence transmission and divergence. This report presents theoretical and experimental methods used to characterize polycapillaries and Kumakhov lens. The energy range studied is 10 to 50 keV. Tested polycapillaries are 5 to 20 cm in length. The number of capillaries inside the polycapillaries is: 550, 1250, and 2700. Various profiles have been checked: linear, circular arc curvatures, double circular arc curvatures and cubic curvatures. The transmission measurement is carried out either with a germanium diode or through fluorescence on a metallic foil. The divergence is analyzed either by photosensitive plate or by an x ray camera. Kumakhov lenses are tested in the same way. The knowledge of polycapillaries characteristics allows us to design future collection of polycapillaries (lens) to satisfy restraint, dimensions, positioning in radiography experiment.

This paper provides a comparison of imaging parameters of two portal imaging systems at 6 MV: a flat panel detector and a CCD-camera based portal imaging system. Measurements were made of the signal and noise and consequently of signal-to-noise per pixel as a function of the exposure. Both systems have a linear response with respect to exposure, and the noise is proportional to the square-root of the exposure, indicating photon-noise limitation. The flat-panel detector has a signal- to-noise ratio, which is higher than that observed wit the CCD-camera based portal imaging system. This is expected because most portal imaging systems using optical coupling with a lens exhibit severe quantum-sinks. The paper also presents data on the screen's photon gain (the number of light-photons per interacting x-ray photon), as well as on the magnitude of the Swank-noise, (which describes fluctuation in the screen's photon gain). Images of a Las Vegas-type aluminum contrast detail phantom, located at the ISO-Center, were generated at an exposure of 1 MU. The CCD-camera based system permits detection of aluminum-holes of 0.01194 cm diameter and 0.228 mm depth while the flat-panel detector permits detection of aluminum holes of 0.01194 cm diameter and 0.1626 mm depth, indicating a better signal-to-noise ratio. Rank order filtering was applied to the raw images from the CCD-based system in order to remove the direct hits. These are camera responses to scattered x-ray photons which interact directly with the CCD of the CCD-camera and generate 'salt and pepper type noise,' which interferes severely with attempts to determine accurate estimates of the image noise.