Journal of X-Ray Science and Technology - Volume 7, issue 2
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Journal of X-Ray Science and Technology is an international journal designed for the diverse community (biomedical, industrial and academic) of users and developers of novel x-ray imaging techniques. The purpose of the journal is to provide clear and full coverage of new developments and applications in the field.
Areas such as x-ray microlithography, x-ray astronomy and medical x-ray imaging as well as new technologies arising from fields traditionally considered unrelated to x rays (semiconductor processing, accelerator technology, ionizing and non-ionizing medical diagnostic and therapeutic modalities, etc.) present opportunities for research that can meet new challenges as they arise.
Abstract: An anecdotal description of the trials and tribulations encountered by the first investigators in the field of x-ray optics starting in the late 1940s and how they managed to overcome them is provided. Some of the players, in addition to the author, included Paul Kirkpatrick, Hussein El Sum, and Howard Pattee of Stanford. At the University of Redlands we became interested in producing an x-ray microscope based on the concepts of holography which Dennis Gabor had demonstrated. This led to correspondence with Gabor and the opportunity to meet him and many other investigators at the first International Conference on X-Ray…Microscopy and Microradiography held in Cambridge, England, in 1956. With the help of V.E. Cosslett and William Nixon, a point-focus x-ray tube was obtained by the University of Redlands for its experiments in x-ray holography in the1950s.
Abstract: Advances in x-ray laser plasma sources and zone plate optics since the early 1980s are reviewed. The improvements are projected into the early years of the 21st century and it is demonstrated that applications such as x-ray microscopy will become increasingly amenable to small scale laboratory systems.
Abstract: The silicon drift detector (SDD) is a semiconductor device based on high resistivity silicon fully depleted through junctions implanted on both sides of the semiconductor wafer. The electrons generated by the ionizing radiation are driven by means of a suitable electric field from the point of interaction toward a collecting anode of small capacitance, independent of the active area of the detector. A suitably designed front-end JFET has been directly integrated on the detector chip close to the anode region, in order to obtain a nearly ideal capacitive matching between detector and transistor and to minimize the stray capacitances of…the connections. This feature allows it to reach high energy resolution also at high count rates and near room temperature. The present work describes the structure and the performance of SDDs specially designed for high resolution spectroscopy with soft x rays at high detection rate. Experimental results of SDDs used in spectroscopy applications are also reported.
Abstract: In this article, we review current progress in the development of several techniques for extreme ultraviolet, soft x-ray, and x-ray optical instrumentation. Applications of these concepts include diagnostics of hot plasmas, spectroscopic studies of the interaction of multicharged ion beams with matter (atoms, ions, molecules, microstructures, surfaces, solids), and biomedical x-ray microscopy. Novel applications of components include the use of glass capillary converters (GCCs) and multilayer mirrors (MLMs) or crystals. GCC devices provide guiding, focusing, and polarization analysis of short wavelength radiation over a wide bandwidth. The MLM or crystal optical elements can be used for dispersing, focusing, and polarization-sensitive…studies of radiation within a narrow bandwidth. In this report we focus on the development and testing of optical diagnostic devices for the short wavelength spectral region 0.1 nm < λ < 100 nm.
Abstract: We report the preparation and structural characterization of lithium hydride and lithium fluoride thin films. These materials, due to their low absorption in the soft x-ray range, may have a role as spacer layers in multilayer mirrors. Theoretical reflection calculations suggest that an epitaxial crystalline multilayer stack of a nitride and a lithium compound spacer layer could produce respectable reflectance for short soft x-ray wavelengths (λ < 10 nm). Lithium targets were magnetron sputtered in the presence of hydrogen or ammonia to prepare the LiH films and nitrogen trifluoride to prepare the LiF films. The films were deposited on room…temperature Si (100) or MgO (100) substrates. A near IR-Visible-UV spectrometer indicated a drop in reflectance at ~250 nm for a 100-nm-thick LiH film. This corresponds to a 5-eV band gap (characteristic of LiH). UV fluorescence indicated characteristic LiH defect bands at 2.5, 3.5, and 4.4 eV. The UV fluorescence characterization also indicated a possible lithium oxide (Li2 O) contamination peak at 3.1 eV in some of our thin films. Film surface morphology, examined by scanning electron microscopy, appeared extremely rough. The roughness size varied with reactive gas pressure and the type of substrate surface. A LiH/MoN multilayer was constructed, but no significant d spacing peak was seen in a low angle CuKα XRD scan. It is believed that the roughness of the LiH film prevented smooth, uniform planar growth of the multilayer stack. Possible reasons of rough growth are briefly discussed.
Abstract: The focusing properties of very large (≈33 × 33 cm2 ) spherically and toroidally curved crystals with a radius of curvature of ≈10 m were determined numerically with an x-ray tracing code and are compared to those of cylindrically bent crystals. Large spherically and toroidally curved crystals are of interest for the diagnostic of future large tokamak fusion experiments and possibly for other extended x-ray sources. Compared with cylindrically bent crystals—which are now widely used for the plasma diagnostic in tokamak experiments, in particular, for Doppler-broadening measurements to determine the central ion temperature—2D-curved crystal spectrometers can provide a significant enhancement…of the intensity due to the additional focusing of the sagittal rays.
Abstract: A novel x-ray imaging system based on a microchannel-plate combined with a multi-pinhole camera has been employed to study x-ray emission from laser-produced plasmas in the 0.5–3 keV photon energy range. In particular, the interaction of intense laser radiation with such plasmas, under conditions relevant to inertial confinement fusion, was monitored by recording a sequence of consecutive x-ray images with a temporal resolution of 140 ps and a spatial resolution of 10 μm. These images provide valuable information on the main physical mechanisms involved in the interaction process, including collisional absorption of the incident laser energy and electron thermal conduction.
Abstract: In this study, the electric field dependence on the charge collection process of CdZnTe detectors, at different x-ray tube settings, within the x-ray diagnostic energy range, is investigated. In addition, the detector contrast at different applied bias voltages and x-ray tube settings have been experimentally determined. The experimental results suggest that an efficient charge collection process is obtained by increasing the applied bias voltage. Once the applied bias voltage is sufficiently high, charge collection becomes complete and the detector operates in the saturation region. This is a prerequisite for high contrast and spatial resolution. As a result, the detector contrast…is enhanced significantly. Therefore, CdZnTe detectors appear to be potential candidates for digital radiographic applications.