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The discretized representation of a continuum of Debye rings forming external and internal termini together with a Poisson spot analog at the imager. The internal terminus at converges or collapses, with increasing imager to sample separation, to form a diffraction spot at ; a further increase in separation produces a diverging or expanding circular terminus described by the pattern at .
Experiment apparatus. (a) X-ray port, (b) annular slit collimator, (c) sample, (d) camera, and (e) translation stages.
Schematic depicting the experiment setup employing a tubular cone of x-rays incident upon a planar polycrystalline sample to enable a camera to capture diffraction images along the symmetry axis.
An image sequence demonstrating the formation of four Poisson spot analogs extracted from a master sequence of 820 images, obtained at 0.1 mm increments, along the symmetry axis. Image 1 corresponds to a 21.8 mm separation from the aluminum oxide sample, with the remainder of the example sequence made up of every fifth image (or 0.5 mm step) to complete a set of 36 images. The crystallographic planes responsible for the diffraction spots apparent in images 3, 8, 22, and 35 are identified by their Miller indices (116), (024), (113), and (110), respectively.
A transmission mode diffractogram obtained by sampling a central, 80 pixel, area throughout the 820 image sequence to provide an angular range in 2-theta space from approximately 10° to 34°. The profile in blue color is produced by the Poisson technique and the profile in green color is produced by a pencil beam approach. For demonstration purposes the synchronization of the plotting of a limited set of 38 data points, including one for each of the 36 images presented in Fig. 4, over a 2-theta range from approximately 17° to 27°, is highlighted by a moving dot in red color. This movie sequence demonstrates the agreement between the Poisson spot images and the expected Bragg maxima for an aluminum oxide sample (enhanced online). [URL: http://dx.doi.org/10.1063/1.3514235.1]10.1063/1.3514235.1
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