A Television System for the Direct Analysis of X-Ray Diffraction Patterns

Abstract
Further progress has been made with a direct recording system of X-ray diffraction patterns from single crystals. In this system the pattern is formed on a phosphor screen and viewed by a T.V. camera tube whose video output is digitised and presented to a computer. Earlier work had shown that with a sufficiently high degree of light amplification between the phosphor and and the T.V. camera, individual 8keV quantum scintillations could be detected and moderately weak patterns could be displayed on a T.V. monitor. However, for quantitative work on weak patterns the limit is set by the quantum noise due to the low X-ray flux; consequently, in the present system the camera tube, which is now an Image Isocon, is operated in an integrating mode. After each 'exposure', during which the reading beam is switched off, the integrated charge pattern on the target of the Isocon is read out in a strobing fashion: the target is scanned at normal speeds but the beam is switched on only at those points where diffraction spots are known to be situated. The charge image of a diffraction spot is neutralised when the spot has been scanned, i.e. the read-out from the camera is destructive. It has been found that, owing to slight crystal misorientation and to aberrations in the light-and electron-optical systems, the positions of the diffraction spots can only be predicted approximately from the lattice spacings and initial orientation of the crystal: a computer-controlled search for the spots is, therefore, necessary.

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