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Single phase polycrystalline hexagonal boron nitride (BN) or mixed with boron carbide (BxC) embedded in an insulating polymeric matrix acting as a binder and forming a composite material as well as pure submicron size polycrystalline BN has been tested as a thermal neutron converter in a multilayer thermal neutron detector design. Metal sheet electrodes were covered with 20–50 μm thick layers of composite materials and assembled in a multi-layer sandwich configuration. High voltage was applied to the metal electrodes to create an interspacing electric field. The spacing volume could be filled with air, nitrogen or argon. Thermal neutrons were captured in converter layers due to the presence of the 10B isotope. The resulting nuclear reaction produced α-particles and 7Li ions which ionized the gas in the spacing volume. Electron-ion pairs were collected by the field to create an electrical signal proportional to the intensity of the neutron source. The detection efficiency of the multilayer neutron detectors is found to increase with the number of active converter layers. Pixel structures of such neutron detectors necessary for imaging applications and incorporation of internal moderator materials for field measurements of fast neutron flux intensities are discussed as well.

Mercuric iodide (HgI2) and lead iodide (PbI2) materials have been investigated for several years as direct converter layers for digital x-ray imaging applications. A difficult challenge of both lead iodide and mercuric iodide is the higher than desired leakage currents. These currents are influenced by different factors such as applied electrical field, layer thickness, layer density, electrode structure, material purity and by the deposition parameters. Minimizing the leakage current must also be achieved without adversely affecting charge transport, which plays a large role in gain and is influenced by these parameters. Other challenges relate to increasing film thickness without degrading electrical properties. This paper compares some imagers as the result of optimization process. We deposited the above materials on flat panel thin film transistor (TFT) arrays with 127 um pixel pitch. The imagers were evaluated for both radiographic and fluoroscopic imaging. Modulation Transfer Function (MTF) was measured as a function of the spatial frequency. The MTF data were compared to values published in the literature for indirect detector (CsI). Image lag characteristics of mercuric iodide appear adequate for fluoroscopic rates. The structure and x-ray diffraction data of the two materials were compared to explain the difference in image lag between them

Polycrystalline films of HgI2, which are used as nuclear radiation detectors, are fabricated by two different methods, either by Physical Vapor Deposition (PVD) or glued with a polymeric binder called also "Particle in Binder" (PIB). Both types of PVD or PIB Detectors are deposited directly on Thin Film Transistor TFT technology imagers and can be used for X-ray imaging. The present review is concentrated on PVD- Polycrystalline-HgI2. However, the main review body is a summary of the work performed by RTR, HU, and Varian. Works by other groups are mentioned briefly. The PVD process is explained by reviewing X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) data. The charge transport properties of the PVD-Polycrystalline HgI2 detectors as they improved with R&D efforts are shown. The response of these PVD detectors to 241Am and 57Co gamma rays and their X-ray imaging properties such as dark currents, sensitivity, imaging resolution and Detector Quantum Efficiency (DQE) are reviewed

Polycrystalline films of HgI/sub 2/ Prepared by Physical Vapor Deposition (PVD) exhibited electrical charge transport properties similar to those of single crystals. Transient charge transport (TCT) measurements were used to evaluate their electrical properties. The mobility /spl mu/, trapping time /spl tau/, and surface recombination velocity s of electrons or holes were determined by analyses of transient voltages developed across the sample in response to a drift of the corresponding charge carriers created by alpha particle absorption near one of the electrodes. Typical electron-, and hole mobilities were /spl mu//sub n/ = 88 cm/sup 2//V/spl middot/s and /spl mu//sub p/ = 4.1 cm/sup 2//V/spl middot/s, respectively; Trapping times were /spl tau//sub n/ >/spl tilde/16 /spl mu/s and /spl tau//sub p/

Polycrystalline HgI 2 thick film detectors are among the leading semiconductor materials to be used as direct converters in X-ray digital radiography. Their properties along with a survey of the properties of alternative materials, such as PbI 2 or A-Se, will be given. The preparation of HgI 2 detector plates, both by direct evaporation (Physical vapor deposition, (PVD)) and by binding the individual crystallites with polymeric glue, forming screen-printed (SP) detector plates, will be described. The microstructure of the PVD thick films showing a columnar morphology, as determined by SEM measurements, will be shown. The X-ray response to radiological X-ray generator of 85 kVp using the current integration mode will be reported for both PVD and SP films. Finally, some X-ray images taken at Xerox-Parc using HgI 2 polycrystalline detectors will be shown.

Characterizations of Cd1−xZnxTe (0.04

This paper reviews some of the progress obtained in the understanding of defects in detector grade cadmium zinc telluride material (CZT). Several techniques have been utilized to elucidate some of the issues related to compositional uniformity, effects of precipitates, grain boundaries, and surface defects related to mechanical and chemical treatments. In few cases, special mapping capabilities had to be developed to allow correlations with detector performance.

The ability of HgI2 powders, used as precursors in mercuric iodide crystal growth, to produce high-quality detectors may be predicted by non-destructive methods like photoluminescence. In fact, it is possible to correlate the presence and the intensity ratio of specific bands in the photoluminescence spectrum of a HgI2 crystal to its impurity content and stoichiometry. These quantities determine the detector grade that may be achieved using that starting material. Nine different HgI2 precursors, obtained by different purification methods, have been characterized. The lowest impurity content is achieved via poly-ethylene treatment, which gives also a powder of relatively good stoichiometric quality.

Potentially low cost and large area polycrystalline mercuric iodide room-temperature radiation detectors, with thickness of 100–600 μm have been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors are fabricated by depositing HgI 2 directly on an insulating substrate having electrodes in the form of microstrips and pixels with an upper continuous electrode. The deposition is made either by direct evaporation or by screen printing HgI 2 mixed with glue such as Poly-Vinyl-Butiral. The properties of these first-generation detectors are quite uniform from one detector to another. Also for each single detector the response is quite uniform and no charge loss in the inter-electrode space have been detected. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology equipment, which is an attractive feature where low cost and large area applications are needed. The detectors which act as radiation counters have been tested with a beta source as well as in a high-energy beam of 100 GeV muons at CERN, connected to VLSI, low noise electronics. Charge collection efficiency and uniformity have been studied. The charge is efficiently collected even in the space between strips indicating that fill factors of 100% could be reached in imaging applications with direct detection of radiation. Single photon counting capability is reached with VLSI electronics. These results show the potential of this material for applications demanding position sensitive, radiation resistant, room-temperature operating radiation detectors, where position resolution is essential, as it can be found in some applications in high-energy physics, nuclear medicine and astrophysics.

The material showing the greatest promise today for production of large-volume gamma-ray spectrometers operable at room temperature is cadmium zinc telluride (CZT). Unfortunately, because of deficiencies in the quality of the present material, high-resolution CZT spectrometers have thus far been limited to relatively small dimensions, which makes them inefficient at detecting high photon energies and ineffective for weak radiation signals except in near proximity. To exploit CZT fully, it will be necessary to make substantial improvements in the material quality. Improving the material involves advances in the crystallinity, purity, carrier lifetimes, and control of the electrical compensation mechanism. A more detailed understanding of the underlying material problems limiting the performance of CZT gamma-ray detectors is required; otherwise, problems with supply, delivery times, and unit cost of large-volume (>5 cm3 active volume) CZT spectrometers are expected to continue. A variety of analytical and numerical techniques have been employed to quantify crystallinity, strain, impurities, compositional and stoichiometric variations, bulk and surface defect states, carrier mobilities and lifetimes, electric field distributions, and surface passivation. Data from these measurements were correlated with spatial maps of the gamma-ray and alpha particle spectroscopic response, and feedback on the effectiveness of crystal growth and detector fabrication procedures has been generated. The results of several of these analytical techniques will be presented in this paper.

CVD diamond radiation sensors are being developed for possible use in trackers in the LHC experiments. The diamond promises to be radiation hard well beyond particle fluences that can be tolerated by Si sensors. Recent results from the RD 42 collaboration on charge collection distance and on radiation hardness of CVD diamond samples will be reported. Measurements with diamond tracking devices, both strip detectors and pixel detectors, will be discussed. Results from beam tests using a diamond strip detector which was read out with fast, 25 ns shaping time, radiation-hard pipeline electronics will be presented.

Mercuric iodide ceramic radiation detectors, which can act as nuclear particle counters, have been fabricated with single continuos electrical contacts and with linear strip contacts. They have been tested with different kinds of γ and β sources as well as in a high energy beam at CERN. The detectors were also successfully tested for radiation hardness with irradiation of 5*10 14 neutrons/cm 2 . The ratio of detected photons over the number of absorbed photons has been measured with T sources of different energies, and it ranges from 20% at 44 keV up to about 30% at 660 keV. An absolute efficiency of 70% has been measured for a 350 gm thick detector for β particles emitted by a 90 Sr source. Charge collection efficiency, defined as the amount of charge induced on the electrodes by a Minimum Ionizing Particle (MIP) traversing the detector, has been measured in two samples. The average collected charge fits well with a linear curve with slope of 35 electrons/(kV/cm) per 100 pro. This result is well described by a dynamic device simulation, where the free carrier mean lifetime is used as a free parameter, adjusted to a value of 1.5 ns, i.e. about 1/100 of the corresponding lifetime in single crystal HgI2 detectors. The response to MIP has also been studied with a high energy (100 GeV) muon beam in CERN. A preliminary beam profile is presented while a more detailed analysis is still in progress and will be presented elsewhere. These results together with the low cost of the material make ceramic HgI 2 detectors excellent candidates for large area particle tracking and imaging applications, even in a radiation harsh environment.

Polycrystalline mercuric iodide nuclear radiation detectors have been produced in a novel technology. Unlike the normal single-crystal technology, there is no intrinsic limit to the surface on which these detectors can be produced. Detectors with areas up to about 1.5 cm/sup 2/, thicknesses from 30 to 600 /spl mu/m, and with single electrodes as well as microstrip and pixel contacts have been fabricated and successfully tested with photons in the range of 40-660 keV, /spl beta/ particle's emitted from a Sr-Y source, and high energy (100 GeV) muons. Results on both charge collection and counting efficiency are reported as well as some very preliminary imaging results. The experimental results on charge collection have been compared with simulation, and a combined /spl mu//spl tau/ product 10/sup -7/ cm/sup 2//V for electrons has been estimated.

The crystalline perfection of solid state radiation detectors was examined using triple axis x-ray diffraction. Triple axis techniques provide a means to analyze the origin of diffraction peak broadening: the effects of strain (due to deviations in alloy composition or stoichiometry) and lattice tilts (mosaic structure) can be separated. Cd1 − xZnxTe (x ≈ 0.1), HgI2, and GaAs detector materials were studied. In the cases of Cd1 − xZnxTe and HgI2 the crystalline properties of detectors with different spectral responses to γ-radiation were determined. Increased mosaicity was universally found to be related to deteriorated detector properties. For Cd1 − xZnxTe, detectors with poor performance possessed greater levels of diffuse scatter due to lattice tilts than did high quality detectors. For GaAs, low angle grain boundaries were attributed to impaired detector performance. Additionally, in large HgI2 detectors, deviations from stoichiometry were also related to reduced performance. Interestingly, HgI2 detectors which possessed a sharp spectral response to γ-radiation but also showed polarization were of comparable crystallinity to those detectors which did not exhibit polarization effects. This initial analysis suggests that polarization is related to native point defects or chemical impurities which do not significantly alter the crystallinity of the material. Overall, within a given class of materials, improved detector performance (better spectral response) always correlated with better material quality.

GaAs is a wide band gap (1.42 eV) semiconductor that has shown promise as a room temperature operated γ-ray detector. A practical γ-ray detector would be large in volume, hence the resistivity of the material must be high to ensure large depletion volumes and low leakage currents. Commercially available semi-insulating (SI) bulk GaAs is compensated by a balance between native defect deep donors (EL2) and residual dopant impurities. The high concentrations of electrically active deep and shallow levels are believed to contribute to electric field distortions observed in γ-ray detectors fabricated from SI bulk GaAs. Hence, the controlled reduction of native defects and contaminant impurities may yield improved bulk GaAs for γ-ray detectors. Custom grown vertical zone melt (VZM) bulk GaAs is presently under investigation as an alternative material for room temperature operated γ-ray detectors. The VZM technique allows for zone refinement (ZR) and zone leveling (ZL) of the GaAs ingots. Custom growth of the material allows for controlled changes in the bulk crystal, including deliberate reductions in EL2 and impurity concentrations. Comparisons are made to commercial vertical gradient freeze (VGF) and liquid encapsulated Czochralski (LEC) bulk GaAs.

The primary problems with mercuric iodide for use in room-temperature radiation detectors are the low yield of high quality devices and the problems with detector stability. It is believed that one of the prime causes of these failures is the presence of certain detrimental impurities. Previous experiments have demonstrated that these impurities can be introduced during processing and that they can strongly affect detector performance. Significant effort has been expended to develop and utilize various mercuric iodide purification schemes. While these techniques are effective to some degree, the level of impurities in detector materials is still higher than that found in more established semiconductors. In this work we developed and investigated a new purification scheme that is based on the mobility of many of the impurities in mercuric iodide under an applied electric field. In this “electrodrift” process undesirable metallic impurities are removed from a portion of a bulk mercuric iodide charge to produce higher purity material for detector crystal growth. The lower level of impurities results in fewer charge-trapping centers and therefore there is the potential for significant improvements in the carrier lifetimes and detector stability. This paper reports on some preliminary results of the effectiveness of this method.

Red mercuric iodide (α-HgI 2 ) has been studied extensively for use as a room-temperature radiation-detector material. Although it has several properties which make it an extremely attractive material for such applications, it has not seen large-scale deployment, particularly in the commercial market, because of several continuing problems. These problems arise, in part, from some of the intrinsic properties of the material. However, the primary limiting factors at this point are related to the phenomena of incomplete charge collection and device polarization. This paper examines one purported cause for both the carrier trapping and the device instability. In particular, silver is an elemental impurity that is known to exist in typical HgI 2 . Leakage-current experiments demonstrate how this electrically active impurity is mobile in bulk HgI 2 . Detector characterization shows how the presence of the silver degrades the performance and affects the spectral properties of the device over time. These results are combined with related work on impurities in HgI 2 to develop a picture of the effects of silver on detectors and the processing requirements for detector fabrication.

Vertical zone melt (VZM) bulk GaAs boules have been zone refined (ZR) and zone leveled (ZL) to reduce EL2 deep donor levels and impurity concentrations with the intent of improving properties for gamma ray detectors. ZR and ZL GaAs boules had background impurity levels and deep donor EL2 concentrations near or below detectable limits. The crystal mosaic of the material at locations near the seed end was slightly superior to commercial liquid encapsulated Czochralski (LEC) material, and nearly equivalent to commercial vertical gradient freeze (VGF) material. The crystal mosaic in ZL material degraded towards the tail end. The homogeneity of the electrical properties for the ZL and ZR VZM material was inferior compared to commercially available bulk GaAs material. Post growth annealing may help to homogenize some electrical properties of the material. The charge collection efficiency of the ZR GaAs detectors was only 30% maximum, and only 25% maximum for the ZL GaAs detectors. Resulting gamma ray spectra was poor from detectors fabricated with the ZL or ZR VZM material. Detectors fabricated from material that was both ZR and ZL did not demonstrate gamma ray resolution, and operated mainly as counters. The poor spectroscopic performance is presently attributed to the inhomogeneity of the electrical properties of the ZR and ZL GaAs materials. Comparisons are made with detectors fabricated from VGF SI bulk GaAs.

Wir berichten von einem 42-jahrigen Patienten mit Diagnose einer kontralateralen inguinalen Metastase eines klassischen Seminoms. Anamnestisch waren bei dem Patienten zuvor beidseitige, offene Leistenherniotomien und eine skrotale Vasoresektion beidseits durchgefuhrt worden. Im CT-Staging fanden sich keine weiteren Lymphome oder Organmetastasen. Nach Kontaktaufnahme mit einem Zweitmeinungszentrum und Diskussion der moglichen adjuvanten Therapiemoglichkeiten erhielt der Patient eine Therapie mit 3 Zyklen Cisplatin, Etoposid und Ifosfamid. Die Entstehung der kontralateralen inguinalen Metastasierung ist am wahrscheinlichsten als Folge der Voroperationen zu bewerten, wobei ein primar atypischer, retrograder Metastasierungsweg nicht endgultig auszuschliesen ist. Eine klinische Untersuchung der inguinalen Lymphknoten sollte bei Hodentumorpatienten mit inguinalen und skrotalen Voroperationen unbedingt erfolgen.

Composite, polycrystalline, semiconductor, hexagonal BN alone or mixed with B4C or BMg2 and cubic LiF were embedded in an insulating matrix which acts as a binder and tested as alpha particle and neutron detectors. The boron containing semiconductors have the natural abundance of 10B which is ~20%. In the case of LiF is the natural content of 6Li only 7.4%. The matrix binder further reduces the contents of 10B and 6Li to about one half. For alpha particles from a 241Am alpha source of ~105 cm-2s-1, 5.5 MeV gives the detector a wide peak in the spectrum. In the case of the thermal neutron detection, if the sources are very weak of only ~100 cm-2sec-1, the neutron counting is possible by subtracting the total signal from the noise. The resulting a signal to noise (S/N) ratio is of only ~2 and one needs a larger collection time of hours for a larger number of pulses to be collected. With a source of a higher neutron flux such as a nuclear reactor, which can offer flux of 107 cm-2s-1, is the S/N ratio of ~33. LiF composites with only 3.7% of 6Li could also detect very weak neutron sources, but the very low amount of 6Li produced a S/N ratio of ~1.4. Compared with widely used 3He detectors is the thermal neutron detection efficiency of the BN and LiF based detectors significantly higher for the same sizes of detectors. Even at a pressure of 3 atmospheres of an inch in diameter 3He detector is the detection efficiency 64% compared with ~72% of a 1 mm thick composite BN detector. Results of enriched 6LiF and mixed BN composite detector measurements with stronger neutron sources will be also reported.

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 241 Am source and 4.8MeV alpha particle of 226 Ra source. Some of the responses of th ese composite detectors to thermal neutrons were already reported and here we shall show some newer results obtained w ith thermal neutrons, from a low intensity 241 Am - 9 Be and also from a medium intensity 252 Cf source, which were thermalized using 10 cm thick pa raffin. 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 PbI

Polycrystalline PbI 2 films were deposited by Physical Vapor Deposition on ITO and gold coated glass substrates. The structural characterization of the samples was studied by using X-ray diffraction and Scanning Electron Microscopy. Two different preferred orientations - [00l] and [110] directions were found as a function of substrate temperatures, and type of substrate (ITO or Gold). The [110] direction is perpendicular to the c-axis in the hexagonal system. Four types of crystalline preferred orientations were found and named as A, B, C, and D type. The different samples were also annealed at different temperatures to improve their densities. The nuclear spectroscopic data for single crystal and polycrystalline samples were taken with 5.64 MeV Alpha particles emitted from 241 Am source. The samples were also measured for their response to a blue light LED irradiation. Both polarities were studied for all samples. In most measurements it was confirmed that holes are the major carriers. The correlation between microstructure and electrical properties as affected by annealing and crystalline orientation is discussed.

Mercuric iodide (HgI/sub 2/) and lead iodide (PbI/sub 2/) have been under development for several years as direct converter layers for digital X-ray imaging. We deposited these materials on flat panel thin film transistor (TFT) arrays and found that they are good candidates for X-ray imaging applications in medical imaging, security applications, and non destructive testing (NDT). This paper present basic imaging parameters and compares both lead iodide and mercuric iodide imagers. A difficult challenge of both lead iodide and mercuric iodide is the higher than desired leakage currents. These currents are influenced by factors such as applied electrical field, layer thickness, layer density, electrode structure and material purity. Minimizing the leakage current must also be achieved without adversely affecting charge transport, which plays a large role in gain and is influenced by these parameters. New deposition and annealing technologies (M. Schieber, et al., 2003) have been developed through which the leakage current has now decreased by more than an order of magnitude while showing no negative affects on gain. Other challenges relate to increasing film thickness without degrading electrical properties. Both lead iodide and mercuric iodide were vacuum deposited by physical vapor deposition (PVD) on a-Si TFT arrays with 127 /spl mu/m pixel pitch. This coating technology is scalable to sizes required in common X-ray imaging applications, as proven by the present 4"/spl times/4" and 8"/spl times/10" imager results (G. Zentai, et al., 2003). The imagers were evaluated for both radiographic and fluoroscopic imaging. Modulation transfer function (MTF) was measured as a function of the spatial frequency. The MTF data were compared to values published in the literature for indirect detectors (CsI). Resolution tests on resolution target phantoms showed that resolution is limited by the TFT array Nyquist frequency (/spl sim/3.9 Ip/mm). The ability to operate at moderate voltages (/spl sim/0.5-1.0 V//spl mu/m) provides acceptable dark current for most applications and permits low voltage electronics design. Image lag characteristics of mercuric iodide appear adequate for fluoroscopic rates. The structure and X-ray diffraction data of the two materials were compared to explain the difference in image lag between them.

Use of physical vapor deposition (PVD) of polycrystalline HgI/sub 2/ films on Si-TFT arrays brought about a breakthrough in the use of HgI/sub 2/ for large area pixellated X-ray imaging. Latest advances in the deposition process led to full-texture high-density films, with highly orientated crystallites, as evidenced for example by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The good structural data also yielded excellent electrical charge transport properties, which approached those of single crystals. Transient charge transport (TCT) with alpha-particle near-surface absorption was used to measure carrier mobility, trapping time, and surface recombination velocity for each sample. Typical electron and hole mobility of high quality polycrystalline HgI/sub 2/ films were /spl mu//sub n/ = 88 cm/sup 2//V /spl middot/ s and /spl mu//sub p/ = 4.1 cm/sup 2//V /spl middot/ s, respectively. Trapping times were /spl tau//sub n/ /spl cong/ 18 /spl mu/s and /spl tau//sub p/ /spl cong/ 3.5 /spl mu/s, and surface recombination velocities s/sub n/ /spl cong/ 1.4 /spl times/ 10/sup 5/ cm/s and s/sub p/ /spl cong/ 3.7 /spl times/ 10/sup 3/ cm/s. The performance of these detectors as spectrometers in a standard nuclear spectroscopy system was evaluated. We used a gamma source of /sup 241/Am with the characteristic 59.6 keV gamma photo-peak. The full width at half maximum (FWHM) of the detector photo peak depended on its charge transport properties. High quality polycrystalline HgI/sub 2/ film detectors yield a peak of approximately 38 keV FWHM, while lower quality ones yield a much broader peak of FWHM > 70 keV. Such widths are still inferior to those of a single crystal (typically /spl sim/5 keV), yet the results suggest that further improvement through optimization of manufacturing conditions is possible. The talk reviews our past efforts, recent new results, and plans for the future.

Mercuric iodide (HgI2) and lead iodide (PbI2) materials as direct converter layers for digital x-ray imaging have been studied for several years. This paper present results of basic imaging parameters by comparing dark current, sensitivity and image lag properties of these materials. A difficult challenge of both lead iodide and mercuric iodide photon detectors is higher than desired leakage currents. These currents are influenced by factors such as applied electrical field, layer thickness, layer density, electrode structure and material purity. Minimizing the leakage current must also be achieved without adversely affecting charge transport, which plays a large role in gain and is also influenced by these parameters. New deposition technologies have been developed through which the leakage current has now decreased by more than an order of magnitude while showing no negative affects on gain. Other challenges relate to increasing film thickness without degrading electrical properties. The image lag of the polycrystalline PbI2 is much larger than that of the polycrystalline HgI2 material, however, no significant image lag is observed for single crystal PbI2. Optical microscopy and SEM studies showed that the polycrystalline PbI2 has a low density, randomly oriented morphology with small crystallites while the best HgI2 has a much better oriented (single crystal-like) structure. We believe that the long image lag can be attributed to the large number of deep defect states generated on the surface of the small PbI2 crystallites. The imagers were evaluated for both radiographic and fluoroscopic imaging modes. MTF was measured as a function of the spatial frequency. The MTF data were compared to values published in the literature for indirect detectors (CsI) and direct detectors (a-Se). Resolution tests on resolution target phantoms showed that for both materials resolution is mostly limited by the TFT array Nyquist frequency.

Photoconductive polycrystalline mercuric iodide deposited on flat panel thin film transistor (TFT) arrays is being developed for direct digital X-ray detectors that can perform both radiographic and fluoroscopic medical imaging. The mercuric iodide is either vacuum deposited by Physical Vapor Deposition (PVD) or coated onto the array by a wet Particle-In-Binder (PIB) process. The PVD deposition technology has been scaled up to the 20 cm x 25 cm size required in common medical imaging applications. A TFT array with a pixel pitch of 127 microns is used for these imagers. Arrays of 10 cm x 10 cm size have been used to evaluate performance of mercuric iodide imagers. Radiographic and fluoroscopic images of diagnostic quality at up to 15 pulses per second were demonstrated. As we previously reported, the resolution is limited to the TFT array Nyquist frequency of ~3.9 lp/mm (127 micron pixel pitch). Detective Quantum Efficiency (DQE) has been measured as a function of spatial frequency for these imagers. The DQE is lower than the theoretically calculated value due to some additional noise sources of the electronics and the array. We will retest the DQE after eliminating these noise sources. Reliability and stress testing was also began for polycrystalline mercuric iodide PVD and PIB detectors. These are simplified detectors based upon a stripe electrode or circular electrode structure. The detectors were stressed under various voltage bias, temperature and time conditions. The effects of the stress tests on the detector dark current and sensitivity were determined.

We previously reported on 2"x 2" and 4" x 4" size imagers, direct digital radiography X-ray detectors, based on photoconductive polycrystalline mercuric iodide deposited on a flat panel thin film transistor (TFT) array, as having great potential for use in medical imaging, NDE, and security applications. Recently we successfully upgraded our mercuric iodide deposition technique to 20 cm x 25 cm size, the size required in common NDE and security imaging applications. A TFT array with a pixel pitch of 127 microns was used for this imager. The mercuric iodide direct conversion layers were vacuum deposited onto TFT array by Physical Vapor Deposition (PVD). In addition to successful imager scale up, more sophisticated, non-TFT based detectors were developed in order to improve analysis methods of the mercuric iodide photoconductor. Measurements on mercuric iodide photoconductor were performed using a 36 x 6 electrode array on a 10cm x 10cm substrate (total of 216 measurement points). The array is formed by 36 palladium stripes on the glass substrate, upon which the mercuric iodide is deposited, and 6 palladium stripes that are deposited on top of the mercuric iodide layer. These two sets of electrodes are oriented at 90 degrees to each other to create the measurement matrix. These detectors were evaluated in radiographic mode, continuous fluoroscopic mode and pulsed fluoroscopic mode. Mercuric iodide coatings with thickness ranging between 140 microns and 300 microns were tested using beams with energies between 40 kVp and 100 kVp utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluroscopic images at up to 15 pulses per second were demonstrated. We evaluated the dark current, sensitivity and MTF characteristics. The MTF is determined primarily by the aperture and pitch of the TFT array with Nyquist frequency of ~3.93 mm -1 (127 micron pixel pitch). The MTF curve of a good quality HgI2 imager is very close to the theoretical sinc function. Image lag characteristics of mercuric iodide appear adequate for fluoroscopic rates.

Mercuric iodide (HgI2) and lead iodide (PbI2) have been under development for several years as direct converter layers in digital x-ray imaging. Previous reports have covered the basic electrical and physical characteristics of these and several other materials. We earlier reported on 5cm x 5cm and 10cm x 10cm size imagers, direct digital radiography X-ray detectors, based on photoconductive polycrystalline mercuric iodide deposited on a flat panel thin film transistor (TFT) array, as having great potential for use in medical imaging, NDT, and security applications. This paper, presents results and comparison of both lead iodide and mercuric iodide imagers scaled up to 20cm x 25cm sizes. Both the mercuric iodide and lead iodide direct conversion layers are vacuum deposited onto TFT array by Physical Vapor Deposition (PVD). This process has been successfully scaled up to 20cm x 25cm -- the size required in common medical imaging applications. A TFT array with a pixel pitch of 127 microns was used for this imager. In addition to increasing detector size, more sophisticated, non-TFT based small area detectors were developed in order to improve analysis methods of the mercuric and lead iodide photoconductors. These small area detectors were evaluated in radiographic mode, continuous fluoroscopic mode and pulsed fluoroscopic mode. Mercuric iodide coating thickness ranging between 140 microns and 300 microns and lead iodide coating thickness ranging between 100 microns and 180 microns were tested using beams with energies between 40 kVp and 100 kVp, utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluoroscopic images have been generated at up to 15 frames per second. Mercuric iodide image lag appears adequate for fluoroscopic imaging. The longer image lag characteristics of lead iodide make it only suitable for radiographic imaging. For both material the MTF is determined primarily by the aperture and pitch of the TFT array (Nyquist frequency of ~3.93 mm-1 (127 micron pixel pitch).

Recently developed semiconducting HgI 2 polymeric composite x-ray detectors are very promising for digitalradiography and non-destructive testing. We present a new model that explains well the variation of the detector'ssensitivity with applied bias and crystallite shape and size, based on charge transport between grain boundaries throughthe polymeric layer gaps. A previously published model 1 , which was developed for a different polymer/semiconductorcomposite failed to account for many details of our experimental results. The new polymeric binder presented in thepresent paper showed non-linear dark current versus voltage dependence, and a higher sensitivity. At the low voltagerange, it showed a higher sensitivity for a reduced grain size. The new model addresses the grain geometry as animportant factor, and accounts well to most sensitivity characteristics of our detectors. The model excludes itself from adebate in the literature concerning specifics of charge transport mechanisms in composites containing electricallyconducting particles. However, certain charge transport between neighbor crystallites is necessary in order to explainthe experimental results.

Mapping of single crystals of Cd/sub (1-x/)Zn/sub x/Te (x=0.2) grown in Russia by the high pressure vertical Bridgman method, (HPVBM) under argon pressure of 2 to 10 MPa was performed using X-ray fluorescence (XRF), X-ray diffraction (XRD), photoluminescence (PL) and leakage current uniformity. The crystals were more uniform in Zn composition than US produced material but had a poorer crystallinity and in the best case could only count nuclear radiation. Differences in the material properties between Russian and US material will be described.

Radiation detectors have been fabricated from very thick films (100-600 /spl mu/m) of mercuric iodide (HgI/sub 2/). These devices, which function as nuclear particle counters and not as spectrometers, have been prepared with single continuous electrical contacts, linear microstrips and square pixel contacts. The word ceramic is used to distinguish the detectors from single crystals which are usually studied for this application. The detectors have been tested with different kinds of gamma and beta sources as well as in a high energy beam of 100 GeV muons at CERN. The presented results show the potential of this material for applications demanding position sensitive, radiation resistant, room-temperature operating radiation detectors, where position rather than spectroscopic resolution is essential, as it can be found in some specific applications in high energy physics, nuclear medicine and astrophysics. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology shaping equipment, which is an attractive feature where low cost and large area applications are needed.

Polycrystalline Mercuric Iodide coated TFT arrays are now the best candidates for direct digital radiographic detectors for both static and dynamic (fluoroscopic) applications. Their high X-ray sensitivity, high resolution, low dark current, low voltage operation, and good lag characteristics meet the required imaging performance parameters. Small area (2'x2') mercuric iodide x-ray detectors were already reported to have good resolution and high x-ray sensitivity. The present paper reports results obtained with good quality large active area (4'x4') HgI2 imagers deposited on an a-Si TFT matrix containing 768 x 768 pixels with pitch dimensions of 139 micrometers . Coating thickness of the HgI2 is between 150 micrometers and 250 micrometers and the imagers were tested in the 25 kVp-100 kVp x-ray energy range utilizing exposures typical for both fluoroscopic and radiographic imaging. The resolution of the imagers is practically limited only by the pixel size (139micrometers ). The imager works at 15 Hz fluoro rate and the image lag is very small. The imager can use exceptionally low dose-rate x-ray illumination because of the very high x-ray sensitivity, which exceeds any other known X-ray imager materials. The paper also discusses potential application fields of this new unique imager.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New results for polycrystalline Hg12 detectors are reported here. Due to its decent electrical properties and high stopping powerfor X-rays and gamma rays, Hg12 is a good candidate for many medical imaging applications. Hg12 were deposited by a hot wallPhysical Vapor Deposition (PVD) method, and the electrical properties of the films, including X-ray response and dark currentdata are reported. Results of imaging capabilities and spatial resolution obtained by polycrystalline Hg12 deposited onto a 2"x2"TFT imaging array on an amorphous silicon substrate are also given. These tests were carried out at Xerox-PARC ResearchCenter.Keywords: imaging, x-ray, polycrystalline, mercuric iodide1. IntroductionThere is intense interest in digital radiography, which offers convenience, faster results, ease of processing and ease of storagethan traditional photographic techniques. Applications include medical diagnostics, port security and non-destructive testing.There are two ways to obtain images: (i) indirect detection whereby a phosphor coating is combined with a photodiode lightsensor material, and (ii) direct detection using a thick X-ray sensitive photoconductor. Both these detection methods utilize pixelarrays. The pixel size limits the spatial resolution that is achievable, and is one of the fundamental design parameters of adetector.

Polycrystalline mercuric iodide (HgI2) photoconductor material was directly deposited on flat panel amorphous silicon (a-Si) thin film transistor (TFT) pixel arrays in order to test their application as direct x-ray conversion detectors. The 4' x 4' and 2' x 2' detector plates were fabricated either by Physical Vapor Deposition (PVD) or the Screen-Print (SP) method. Although developed for medical radiological imaging, they can also be used for nondestructive test imaging. The present HgI2 arrays have 100 μm x 100 μm pixels on the 2' x 2' detector and 139μm x 139μm on the 4' x 4' imager. The initial results are very promising and show high x-ray sensitivity and low leakage current. The advantage of these detectors is that they can be directly deposited on the pixellated arrays containing the TFTs and other electronic read out circuits and can be fabricated in large sizes. These polycrystalline PVD-HgI 2 thick film detectors have now been fabricated up to 1,800μm thick, which makes them also useful for higher-energy X-ray applications. Imaging results obtained by both PVD- and SP-HgI 2 will be shown. The effect of the crystallite size on the imaging properties will be demonstrated and the difference in sensitivity applying positive or negative bias on the top electrode will be discussed. Comparison of x-ray sensitivity to other photoconductor materials such a-Se and PbI 2 will also be presented.

We report x-ray imaging results on polycrystalline HgI2 detector used for direct x-ray imaging. Due to its good electrical properties and high stopping power for x-rays and gamma rays, the material is a good candidate for many applications in medical imaging. The deposition of the HgI2 thick films is made by hot wall physical vapor deposition, (PVD) method and some of the structural features are described here. The x-ray response and some dark current data measured on some recently prepared detectors are reported. Some results obtained with poly-HgI2 thin film deposited on an amorphous-Si TFT's imaging array 4' X 4' performed at the Ginzton Technology Center is reported for the first time. Also phantom images received with a similar deposited poly-HgI2 thin film deposited on an amorphous- Si TFT's imaging array 2' X 2' performed at Xerox-PARC Research Center is also given here. The status of HgI2 technology will be discussed.

Measurements of polycrystalline HgI2 films on active matrix direct detection image sensors are described, for possible application to high sensitivity room temperature x- ray detection. The arrays exhibit low leakage current and very high sensitivity - roughly an order of magnitude better than has been demonstrated with other designs. The uniformity of the response varies randomly from pixel to pixel, for reasons that are not yet understood, but are probably related to the large grain size.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

For the first time polycrystalline HgI2 photoconductor material directly evaporated on a-Si array for direct conversion of x-rays for imaging purposes, were successfully imaged at Xerox-Palo Alto Research Center. The initial results are very promising and show a high x-ray sensitivity and low leakage current. Since Ti-W alloys are used as pixel electrodes, an intermediate passivation layer must be used to prevent a chemical reaction with the detector plate. The thickness that these Polycrystalline HgI2 thick film detectors have been fabricated until now is up to 1,800 micrometers , which makes them useful also for high energy applications. The characterization of the Polycrystalline HgI2 thick films deposited with or without the passivation layers by measuring their dark currents, sensitivity to 65 and 85 kVp x-rays and residual signals after 1 minute of biasing, will be shown for several detectors. Some preliminary results will be shown for some novel screen-printed HgI2 detectors.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Various types of Cd1-xZnxTe (0.04 < X < 0.24) detector crystals grown by vertical high pressure Bridgman (VHPB), low pressure Bridgman (LPB) i.e. vertical ambient pressure Bridgman (VB), horizontal ambient pressure Bridgman (HB) and vapor grown crystals have been evaluated and compared. We have used the following methods in order to evaluate the CZT: (1) Triaxial crystal x-ray diffraction (TAD) for determination of the surface crystalline homogeneity, (2) Nuclear spectroscopic response of detectors and (3) Sensitivity to radiation from high flux x-rays for investigations of the suitability for x-ray digital imaging. Finally a comparison between the various methods of CZT crystal growth will be given.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on a-Si direct detection x-ray image sensors with polycrystalline PbI2, and more recently with HgI2. The arrays have 100 micron pixel size and, we study those aspects of the detectors that mainly determine the DQE, such as sensitivity, effective fill factor, dark current noise, noise power spectrum, and x-ray absorption. Line spread function data show that in the PbI2 arrays, most of the signal in the gap between pixels is collected, which is important for high,DQE. The leakage current noise agrees with the expected shot noise value with only a small enhancement at high bias voltages. The noise power spectrum under x-ray exposure is reported and compared to the spatial resolution information. The MTF is close to the ideal sinc function, but is reduced by the contribution of K-fluorescence in the PbI2 film for which we provide new experimental evidence. The role of noise power aliasing in the DQE and the effect of slight image spreading are discussed. Initial studies of HgI2 as the photoconductor material show very promising results with high x-ray sensitivity and low leakage current.

A first image of some tiny screws were obtained for the first time with polycrystalline HgI2 acting as the photoconductor material deposited on a-Si direct conversion X- ray image sensors, produced by Xerox -- Palo Alto Research Center. The initial results are very promising and show a high X-ray sensitivity and low leakage current. The response of these detectors to a radiological X-ray generator of 65 kVp has been studied using the current integration mode. Already its sensitivity expressed in (mu) C/R*cm2, is very high, values of 20 (mu) C/R*cm2 have been measured for films of 100 - 250 microns thickness and bias of 50 - 200 volts respectively, which is superior to the published data for competing materials such as polycrystalline PbI2 and a-Se detectors. The fabrication and characterization measurements of the Polycrystalline HgI2 thick film detectors will be given. The characterization data which will be reported here consists of: (a) sensitivity, (b) dark currents, (c) stability of sensitivity dependence on the number of exposure, (d) X-ray response dependence on dose energy and (e) signal decay dependence on the number of exposures.

Thin films of YBa2Cu3O7-x (YBCO) were deposited by laser ablation on substrates of sapphire and MgO coated with buffer layers of YSZ(Y2O3 stabilized ZrO2) and SrTiO3 deposited by both OMCVD, organometallic chemical vapor deposition, and laser ablation. The Tc(R=O) of YBCO on YSZ was 91 K and on SrTiO3 was 93 K. The Jc at 77 K were 5*103 and 5*106 A/cm2 for YSZ and SrTiO3 buffer layers respectively.

Our objective was to evaluate long-term outcome of children born after inadvertent administration of a gonadotrophin-releasing hormone agonist (GnRHa) in early pregnancy, compared to a control group of children born to matched women undergoing in-vitro fertilization and children born after spontaneous pregnancies. Six children from six pregnancies, exposed to a long-acting gonadotrophin agonist, comprised the study group and 20 children were included in the control groups. Pre-, peri- and postnatal data were collected and the children were followed and examined at a mean age of 7.8 +/- 2.0 years. All children underwent physical and neurological examination, and psychological tests. In the study group, one child was born with a major congenital malformation (cleft palate), and four children subsequently demonstrated neurodevelopmental abnormalities, including epileptic disorder (n = 1), attention deficit hyperactivity disorder (n = 3), motor difficulties (n = 3) and speech difficulties (n = 1). In the control groups, one child had attention deficit hyperactivity disorder. This observation of neurodevelopmental abnormalities in four of six children in the study group justifies the need for long-term follow-up of more children previously exposed to gonadotrophin-releasing hormone agonist.

A theological model is presented which analyses the sensitivity of composite detectors to a flux of x-rays emerging form a radiological x-ray generator. The model describes the many factor which influenced the x-ray response, for the case where the detector is composed of several layers of crystallites separated by a polymeric glue as is the case of composite HgI 2 detectors fabricated by the screen print method. The model also describes the variation of the sensitivity with grain size and dielectric constant, taking into account the dielectric constant of the binder showing also the experimental result. Finally, the experimental result of the sensitivity vs. the voltage is shown for single crystal and composite HgI 2 detectors and these results are compared with polycrystalline PbI 2 and a-Se, which are the main material candidates for medical digital radiology.

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 between0.01 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 fortheir response to lower and higher gamma energy and beta particles. The rr value is of the order of iO cm2/V forboth holes and electrons and therefore can act as particle counter without energy resolution. The low production costfor potential large detector area make these compounds interesting for certain imaging applications.Keywords: imaging, x-ray, polycrystalline, mercuric iodide 1. INTRODUCTION The best known radiation detectors which operate at room temperature are Si, Hg12, CdTe, Cd1 ZnTe, GaAs andlately also polycrystalline diamond. The energy per electron-hole pair formation, W, is 3.6, 4.2, 4.4, 4.5, 4.7 and14 eV respectively. Thus polycrystalline Hg12 which has a high atomic number Z, wide band gap and low Wcompetes favorably with the other semiconductors for radiation particle counting and imaging where spectralresolution is not needed. The basic properties of Hg12 nuclear radiation detectors are summarized in recent book'and the technology of single crystal Hg12 detectors is described in the first chapter of this book2 .

The direct deposition of polycrystalline semiconductor HgI 2 detectors on pre-deposited specially designed pixel electrodes is described, using two methods, the hot wall vapor deposition, HWVD, and thick film screen print (SP) methods. Some characterization results of the HgI 2 material used to facilitate the detectors are described. The pre-deposited substrate is made by standard hybrid technology. The electrode pattern is a 16*16 pixel square pattern each with a size of 1.48 mm and with 0.1 mm spacing; the total area covered by the pixels is (25.28 mm) 2 equals 639.078 mm 2 . In order to fan out the pixels to read-out electronics, holes were made through the ceramic thickness and connecting lines were drawn on the opposite side of the ceramic alumina substrate, where complicated patterns can be produced. The pixel detector is tested with beta particles, and data showing the leakage current vs. bias, are given showing a resistivity of about 2*10 12 ohm cm. The current and the average charge signal are reported for three different HgI 2 pixel detectors. The signal for one of the detectors is about 1100 electrons at 800 V bias voltage and for the second detector, the resistivity is in the same order of magnitude and the charge collection is somewhat better, reaching 1600 electrons at 700 V. One of the detectors was connected to a second hybrid designed for mounting of 8 castor 1.0 chips. CASTOR 1.0 is a VLSI circuit designed for imaging and the results are being evaluated.

More recent Russian grown single crystals of Cd0.8Zn0.2Te (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.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Preparation of polycrystalline mercuric iodide very thin (1 μm) films using laser ablation and thick films (100–600μm), using hot pressing, hot wall vapor deposition and screen printing methods, fabricated as radiation detector plates are briefly described. X-ray diffraction, photoluminescence and optical microscopic measurements as well as response to nuclear radiation will be given. Finally, recent results obtained with a large area imaging pixel detector will be shown.

Diamond, as the hardest material known, has an extremely high binding energy suggesting that it will be a radiation hard material. Given that it is also a semiconductor, one is led to believe that diamond might perform well as a high resolution semiconductor tracking detector in very hostile radiation environments in which more conventional detectors would fail. In this paper we, the RD42 Diamond Detector Collaboration, review the progress that we have made in the development of chemical vapor deposition (CVD) diamond as a detector material, its radiation hardness, and the performance we have achieved with diamond tracking detectors.

Most of the efforts on Cd 1- x Zn x Te (CZT) gamma ray spectrometers have been motivated by the benefits and commercial success of cadmium-tellurium (CdTe) devices and the possibility of manufacturing relatively large homogeneous CZT crystals at an acceptable cost. CdTe detectors have been shown to operate at room temperature, have good stopping power for energetic photons, produce reliable spectra, and be rugged in field applications. CdTe devices and instruments are sold today for environmental monitoring, waste remediation, industrial gauging, monitoring nuclear materials, and medical instrumentation. This chapter focuses on CZT detector technology. It discusses CdTe and growth of CZT crystals. The chapter reviews the properties of the material, particularly those properties that pertain to detector performance. A review of the performance of CZT gamma and x-ray spectrometers and imaging arrays are also presented. The chapter concludes with a brief discussion of future work needed to advance the technology.