By separating the Wiener spectra of screen mottle of a medical screen/film system for various tube voltages into those of quantum mottle and structure mottle, we experimentally determined the tube voltage dependence of the detective quantum efficiencies (DQEs) of the front of back screens. For the purpose, using the DQE, the equation of the Wiener spectrum of the quantum mottle has been expressed, and using the equation, our method for separating the Wiener spectra of the screen mottle was modified. Both the DQEs of the front and back screens decreased with tube voltage. The DQE of the front screen at each tube voltage was greater than that of the back screen. We explained the tube voltage dependence of the DQEs using the dependence of the first and second moments of absorbed x-ray energy distribution in the screen obtained using our data of incident x-ray spectra for various tube voltages and Swank's noise-equivalent absorption spectra.

There is a need in the x-ray imaging community for phosphors with short persistence (I/I₀ < 0.1-0.01% in less than 0.5 ms). Persistence limits a detector's performance by defining the minimum x-ray exposure discernable for a given time after a previous exposure, by ghosting of previous images, and by limiting the dynamic range. The description of the luminescence decay time for any particular phosphor is tedious since the decay time is usually a complicated function of the excitation intensity, the exposure time, the phosphor temperature, and the impurity concentration, as well as the manufacturing procedure. We have characterized commercially available and specially synthesized gadolinium oxysulfide (Gd₂O₂S) phosphors with a variety of activators in terms of persistence, and relative light output, and discussed their possible usefulness for particular x-ray imaging experiments. We have found that the level of long-term persistence for Gd₂O₂S x-ray phosphors can differ by more than an order of magnitude solely due to changes in the exposure time. The persistence of these phosphors is characterized as a function of x-ray intensity, exposure time, and, when possible, imppurity concentrations.

Some measurements have been performed in order to fully characterize metachrome as down- converter fluorescent layer in the far and vacuum ultraviolet, from 46 up to 254 nm. In particular, a couple of samples having different thickness provided by Photometrics Inc. have been tested and their performances have been compared with the ones obtained by tetraphenyl butadiene (TPB), another scintillator widely used in this spectral region. The emission angular distribution, the fluorescent spectrum and the absolute conversion efficiencies have been measured for all the phosphors. The results show that TPB offers higher efficiency than metachrome, but also that the latter is well efficient in all the investigated spectral region. This is interesting in the case of using this phosphor as down-converter with silicon detectors, so permitting for example to have CCD sensitive also in the extreme ultraviolet region.

Focused x-ray images are reported for 21 X 21mm² microchannel plate (MCP) optics having an eleven micron square-channel geometry. These are the smallest channel size square-pore MCPs yet evaluated. Because the limiting focal spot size in such optics is twice the channel width, their construction represents a significant advance towards focusing elements capable of very high intensification. The MCPs were fabricated with channel length- to-diameter ratios of 40 to 1 and 75 to 1; with an open area fraction of 85%. X-ray images were first obtained at 0.28keV and 1.74keV using a planar MCP geometry with a zero degree bias angle. These images indicate that subtle deviations from an ideal square channel geometry (i.e. vertex 'radiusing') can strongly influence the focal spot structure. Finally, one of the MCPs was spherically 'slumped' to a 1m radius and remeasured in x-rays, demonstrating for the first time the operation of a slumped square-channel MCP.

A new X-ray tube unit with a super smooth-surface anode and a built-in waveguide collimator is proposed. The unit makes it possible to obtain narrow-collimated beams of X-ray radiation with a line microfocus. Calculation procedure and experimental results for the glancing angle X—ray fluorescence are presented. Keywords: X—ray tubes, X—ray waveguides, X—ray fluorescence

We report for the first time, fabrication of photoconducting UV detectors made from GaN films grown by molecular beam epitaxy. Semi-insulating GaN films were grown by the method of electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy. Photoconductive devices with interdigitated electrodes were fabricated and their photoconducting properties were investigated. In this paper we report on the performance of the detectors in terms of UV responsivity, gain-quantum efficiency product, spectral response, and response time. We have measured responsivity of 125A/W and gain-quantum efficiency product of 600 at 254nm and 25V. The response time was measured to be on the order of 20ns for our detectors, corresponding to a bandwidth of 25Mhz. The spectral response showed a sharp long-wavelength cutoff at 265nm, and remained constant in the 200nm to 365nm range. The response of the detectors to low-energy x-rays was measured and found to be linear for x- rays with energies ranging from 60kVp to 90kVp.

Photoconductor array devices were fabricated using molecular beam epitaxially (MBE) grown CdTe. The detectors are stable in the presence of hard x-rays, and they have been tested at room temperature for over a year without any noticeable degradation. The performance of the photoconductor was greatly improved when the detector was cooled using the Peltier effect. The uniformity of the 64 element linear array device was measured at various temperatures. We observed an exponential decrease of the photoconductor dark current with temperatures down to 200 degrees K. The dark current and noise of the array detector decreased by more than 3 orders of magnitude from 300 degrees K to 200 degrees K. As a result, the minimum sensitivity to x-ray photons was increased by nearly 3 orders of magnitude. Finally an x-ray transmission image was obtained using a single element MBE CdTe photoconductor at 230 degrees K.

In the vacuum ultraviolet and soft x-ray spectral ranges the radiometry laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY offers two different methods for the calibration of radiation detectors. The electron storage ring BESSY, in combination with suitable monochromators, reproducible produces monochromatic radiation of tunable photon energy, high spectral purity, and high radiant power which can be reduced by twelve orders of magnitude. With this source of monochromatic radiation a cryogenic electrical substitution radiometer (ESR) is operated as a primary detector standard in the photon energy range from 3 eV to 1500 eV. The ESR is optimized for synchrotron radiation, capable of measuring radiant power in the order of some (mu) W with an uncertainty below 0.2%. Radiation detectors can be calibrated against the ESR with uncertainties well below 1%. Recent progress in this field will be demonstrated for the calibration of photodiodes. The electron storage ring BESSY is also used as a primary source standard, in the photon energy range from the infrared to the soft x-ray range. The spectral and spatial distribution of the broadband radiation, emitted in the range from 1 eV to 15 keV, is calculable from the known storage ring parameters with uncertainties from 0.04% to 0.35%, respectively. This allows the detection efficiency of energy-dispersive detectors such as solid-state detectors, charge- coupled devices, and others to be determined, provided the detector response function to monochromatic radiation is measured as well.

The first in-situ x-ray monitoring was applied for superthin (20-250 A) diamond-like carbon (DLC) films investigation. The film thickness, density, roughness, and growth rate were calculated from reflectivity measurements during deposition and etching processes. The objects of in-situ investigations were DLC films obtained by RF-method in C₆H₁₂+Ar and C₆H₁₂+N₂ mixtures on silicon substrates. The results of an investigation reveal that the roughness and the density of DLC films were varied at early stages. It was shown that obtained results can be explained by island mechanism of DLC films growth. It was shown that in-situ x-ray monitoring system permits us to examine the ultra thin layers and also to carry out the diagnostic of transient processes as the deposition conditions changes.

The electrical properties of semi-insulating CdTe crystals were characterized considering the application of the material as a room temperature radiation detector. Requirement for the detector application is a high resistivity material which is achieved by the compensation of shallow levels by deep donors in the middle of the band gap. These deep donors are obtained by doping the CdTe crystals with titanium or vanadium or by the influence of chlorine and intrinsic defects like the antisite defect. The energies of the deep levels are within the range of 0.31 eV and 0.95 eV determined by photoinduced current spectroscopy and admittance measurements. To calculate the compensation effects we applied a model originally developed for semi-insulating GaAs. To form detectors with a high local resolution, homogeneous material is needed. Homogeneity was tested by time dependent charge measurements. While CdTe:Cl showed variations of about 20% other high resistivity materials could vary up to one order of magnitude across one wafer. The variation of resistivity in CdTe crystals could be attributed to the crystal growth by a combined segregation-compensation model.

This paper reports on the charge-coupled device (CCD) x-ray detector development for imaging and diffraction applications at CHESS, the Cornell High Energy Sychrotron Source. The detector currently under test is based on the Kodak KAF-0400 chip, featuring 512 X 768 pixels at 9 micrometers square pixel size. The final version of the device will use the KAF- 1600, which has four times the active area at the same pixel size. Different x-ray detection schemes are planes to adapt the detector most efficiently to the application. For imaging at high spatial resolution the x-rays are converted to visible light by phosphors, i.e. Gd₂O₃S:Tb screens or CdWO₄ single-crystals. An optical lens system focuses the phosphor image onto the CCD. Typical magnification factors for the optics are 3 to 1 to 1 to 1. This detector has been designed for radiography in materials science and biology. First tests on the performance of the device showed a good spatial resolution at a dynamic range of approximately 10 bits. To comply with the needs in diffraction experiments, e.g. microbeam and surface diffraction experiments, a second type of detector will be built. The front end of this device will consist of a scintillator coupled to a fiberoptic taper. The output of the demagnifying taper is focused onto the CCD. This concept allows a very compact design, necessary for a detector to be used routinely by users of the CHESS facility.

This paper describes the progress of a multi-modality (three detector type) system for x-rays and gamma-rays developed for the waste inspection tomography (WIT) program. WIT provides mobile semi-trailer mounted nondestructive examination (NDE) and assay (NDA) for nuclear waste drum characterization. WIT uses various computed tomography (CT) methods for both NDE and NDA of nuclear waste drums. Without opening waste drums, WIT inspects and characterizes radioactive waste, including low level (LLW), transuranic (TRU), and mixed waste. With externally transmitted x-ray NDE techniques, WIT has the ability to identify high density waste materials like heavy metals, define drum contents in 2D and 3D space, quantify free liquid volumes through density and x-ray attenuation coefficient discrimination, and measure drum wall thickness. With waste emitting gamma-ray NDA techniques, WIT can locate gamma emitting radioactive sources in 2D and 3D space, identify gamma emitting isotopic species, identify gamma emitting isotopic species, identify the extermal activity approximations, and provide the data needed for waste classification as LLW or TRU.

A CCD camera is going to be realized as detector applied to the ALOISA experimental chamber at the ELETTRA synchrotron ring in Trieste, Italy. In this chamber, a high energy monochromatic beam is focused at grazing incidence on a sample to study its surface analyzing the photoelectron diffraction, the scattered and reflected x-ray photons. The aim of this camera is to collect these x-ray photons to determine the position, intensity, and distribution of the diffraction pattern. Moreover, moving the sample, the camera will be able to detect the intensity of the incident beam arriving on the sample from the monochromator. The x-ray photons hit on a P45 phosphor coated faceplate which interfaces the ultra-high vacuum chamber with the detector placed in air. The faceplate is coupled to a taper and then a 512 X 512 pixels CCD collects the visible photons through a fiber optics window. In this paper we describe the design of this detector and report the theoretical evaluation of its performances.

A digital x-ray detector applying hybrid detector technology based on indium metal bump- bonding techniques was evaluated at x-ray energies of about 19.5 keV. Silicon of about 1 mm thickness forms the actual detector, converting x-rays directly into electrons (rather than generating light and converting light to photo-electrons). Time-delay-integration increases the sensitivity. Linearity, modulation transfer function, and noise power spectrum were evaluated. The results demonstrate that the system is useful as scanning x-ray detector for digital mammography and can meet and even exceed the performance of the conventional film/screen system.

The possibility of Kumakhov lenses usage as a spectrometer with high resolution was demonstrated. The experimental results on CuK$_(alpha) 1)- and CuK_(alpha 2)-lines resolution are presented.

Possibility of using the capillary reflecting structures (cones, lenses, pillars) for creating a new type of antiscatter grid was investigated. The use of capillary structures allows us to suppress a scattered radiation and improve the contrast during an image transfer.

The experimental results on spatial redistribution of radiation density for quasiparallel beams after Kumakhov lens are presented. The possibility of using these results in the diffractometry and x-ray lithography are discussed.

Recently, an instrument capable of measuring x-rays between 8 and 90 keV was conceived to help understand conditions pertaining to pulsed-power research. This resulted in the development of a versatile device that would incrementally detect x-rays emitted at predetermined energy bands over this range. To accomplish this, an array of well characterized filter-fluorescer combinations were produced which would allow fluoresced x- rays to be observed by time resolved electro-optical devices. As many as 16 channels could be utilized with each channel having a corresponding background channel. Upon completion of the device, a three week series of experiments was then successfully carried out.

Medical imaging was one of the earliest applications of x radiation and remains one of the most common and most important. Despite the advent of ultrasound and magnetic resonance imaging, x-ray imaging is still the most widely used medical imaging modality. Its low cost and ease of use are critical for mass screening, for example in cancer detection. The recent invention of Kumakhov polycapillary x-ray optics allows for a new mechanism of control of broadband x-ray radiation for imaging. Polycapillary x-ray optics provide nearly complete scatter rejection, and can be used to magnify or demagnify the x-ray image without conversion to visible photons. Measurements have been made of the performance of prototype magnifying antiscatter optics. Significant contrast enhancement and resolution improvement have been measured. The potential application of polycapillary optics to focused beam therapy is also discussed.

A multifiber collimating lens designed to collect divergent Cu-K(alpha) x-rays over an 8.6 degree angle has been tested in a standard diffraction geometry. The lens was first characterized with a small (0.30 mm diameter) spot source and found to have transmission efficiency of 27%, output divergence of 0.22 degrees, and input focal spot size in the transverse and axial directions of 0.71 mm and 14.7 mm (FWHM), respectively. The lens was then tested with a standard rotating anode diffraction system for a variety of thin film structure and stress analyses. The measured data are compared to thoses obtained from a fixed tube parafocusing Bragg-Brentano geometry system. The effect of the lens on measurement efficiency was found to depend on the specific application, ranging from no benefit for small area (1.5 cm diameter) films to as much as 8.4 X computed gain in efficiency for highly textured films with finite-size broadened reflections. Typical efficiency gains for the same power and angular resolution were about 3.2 X. In general, the parallel beam geometry provided by the lens was more convenient then the Bragg-Brentano geometry because of reduced sample displacement and general defocusing errors. Since the lens was simply incorporated into systems optimized for non-lens measurements, it is felt that further diameter exceeded that of the soller slit, monochromator crystal, and detector. The geometric gain of the lens with respect to a pinhole with the same resolution is 74 for a line source in the point focus geometry and 159 for a point source. Incorporating straight capillary bundles as soller slits could provide a better match than traditional soller slits to diffraction system using a capillary lens and they may also be beneficial in reducing x-ray diffraction background. Optimization and other aspects of the use of the capillary lens in 'real world' analysis applications will be discussed.

Several applications of Kumakhov polycapillary optics require extended exposure to intense x- ray radiation. No degradation of performance has been observed when using polycapillary x- ray optics with laboratory sources. As part of an ongoing study to develop an understanding of damage mechanisms and performance limitations, borosilicate glass polycapillaries have been exposed to white beam bending magnet synchrotron radiation with peak energies of 5 and 11 keV, and focused broad band energy centered at 1.4 keV synchrotron radiation. In situ and ex situ measurements of degradation of x-ray transport efficiency have been performed at doses up to 1.8 MJ/cm² at ambient and elevated temperatures. No decrease in transmission was observed for in situ measurement of fibers exposed to 1.4 keV photons at doses up to 1.4 MJ/cm². Ambient temperature exposure to higher photon energies causes degradation that can be recovered by low temperature annealing. Exposure at elevated temperatures prevented any measurable damage to rigid fibers, at doses up to 800 kj/cm².

The properties of polycapillary x-ray fibers at medium energies for applications such as crystal diffraction and mammography have been extensively measured and reported. However, many medical and industrial applications for x-rays, such as chest radiography, x-ray orthovoltage therapy, and nondestructive testing, require higher x-ray energies, up to or exceeding 100 keV. In order to investigate the feasibility of using Kumakhov capillary x-ray optics on these applications, measurements have been performed on the behavior of capillary optics at higher energies. Transmission efficiency of straight polycapillary fibers of different types have been measured as a function of source location and x-ray energy from 10 to 80 keV. The measurements are compared to geometrical optics simulations, which have also been extended to these energies. Despite the lower critical angle for total external reflection at high energies, capillary x-ray optics appear promising for many applications.

We are developing a large area structured CsI(Tl) imaging sensor for macro-molecular x-ray crystallography for use with both intense synchrotron sources and rotating-anode laboratory x- ray sources. The CsI(Tl) scintillator is grown on a specially designed optical substrate. Our work has produced x-ray sensors with up to 70% more light output, orders of magnitude faster decay time response, and greater spatial resolution (15% MTF at 20 lp/mm) than Gd₂O₂S screens currently used in CCD-based detectors for biological structure determination. These advances in performance will address some of the limitations of existing area detector technology. Performance measurements for a prototype CsI(Tl) scintillator are presented. With these new sensors the development of larger area x-ray crystallography detectors with millisecond data acquisition capabilities and high spatial resolution, suitable for synchrotron applications will be possible.

We studied the UV and x-ray double-resonance absorption process in the case of 1 micrometers tryptohan. By adopting a three-state model for ultra-violet (UV) absorption we could calculate the excited molecular density. We also calculated the x-ray transmittance dependence on the UV-laser photon flux using x-ray absorption cross section obtained by a calculation based on the atomic Hartree-Slater method. We found that strong x-ray absorption occurs in the UV region with a photon flux of approximately 10²⁵ photons/cm²/sec. Furthermore, we considered the feasibility of x-ray microscopy using double-resonance absorption. It is expected that only the images of selected molecules can be obtained with a good S/N.