Browsing by Author "Shevchuk, Alex"
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Item Open Access Combined X-ray diffraction and absorption tomography using a conical shell beam(2019-07-15) Shevchuk, Alex; Evans, J. Paul O.; Dicken, A. J.; Elarnaut, D.; Downes, D.; Godber, S. X.; Rogers, Keith D.We combine diffraction and absorption tomography by raster scanning samples through a hollow cone of pseudo monochromatic X-rays with a mean energy of 58.4 keV. A single image intensifier takes 90x90 (x,y) snapshots during the scan. We demonstrate a proof-of-principle of our technique using a heterogeneous three-dimensional (x,y,z) phantom (90x90x170 mm3) comprised of different material phases, i.e., copper and sodium chlorate. Each snapshot enables the simultaneous measurement of absorption contrast and diffracted flux. The axial resolution was ~1 mm along the (x,y) orthogonal scan directions and ~7 mm along the z-axis. The tomosynthesis of diffracted flux measurements enable the calculation of d-spacing values with ~0.1 Å full width at half maximum (FWHM) at ~2 Å. Thus the identified materials may be color-coded in the absorption optical sections. Characterization of specific material phases is of particular interest in security screening for the identification of narcotics and a wide range of homemade explosives concealed within complex “everyday objects.” Other potential application areas include process control and biological imaging.Item Open Access Confocal energy-dispersive X-ray diffraction tomography employing a conical shell beam(Optical Society of America, 2019-07-01) Dicken, Anthony; Evans, J. Paul O.; Rogers, Keith; Prokopiou, Danae; Godber, Simon; Elarnaut, F.; Shevchuk, Alex; Downes, D.; Wilson, M.We introduce a new high-energy X-ray diffraction tomography technique for volumetric materials characterization. In this method, a conical shell beam is raster scanned through the samples. A central aperture optically couples the diffracted flux from the samples onto a pixelated energy-resolving detector. Snapshot measurements taken during the scan enable the construction of depth-resolved dark-field section images. The calculation of dspacing values enables the mapping of material phase in a volumetric image. We demonstrate our technique using five ~15 mm thick, axially separated samples placed within a polymer tray of the type used routinely in airport security stations. Our method has broad analytical utility due to scalability in both scan size and X-ray energy. Additional application areas include medical diagnostics, materials science, and process controlItem Open Access High energy transmission annular beam X-ray diffraction(Optical Society of America, 2015-02-02) Dicken, Anthony; Shevchuk, Alex; Rogers, Keith; Godber, Simon; Evans, PaulWe demonstrate material phase retrieval by linearly translating extended polycrystalline samples along the symmetry axis of an annular beam of high-energy X-rays. A series of pseudo-monochromatic diffraction images are recorded from the dark region encompassed by the beam. We measure Bragg maxima from different annular gauge volumes in the form of bright spots in the X-ray diffraction intensity. We present the experiment data from three materials with different crystallographic structural properties i.e. near ideal, large grain size and preferred orientation. This technique shows great promise for analytical inspection tasks requiring highly penetrating radiation such as security screening, medicine and nondestructive testing.