![]() ![]() Plane indices less than 8 have been identified in cubic, tetragonal and orthorhombic crystals. If the uncertainty of the measurements is high or if n is too low, this method gives the possible orientations for the crystal. Since the pair of reflecting planes related to spots 1 and 2 belongs to (E), each computed pair of planes is tried, in order to determine the orientation of the crystal and to check whether the coordinates of the (n-2) other spots can be matched to dense planes of indices less than 8. The set (E) of all the pairs of planes (h 1 k 1 l 1) and (h 2 k 2l 2) making an angle α close to αsup(m) is then computed. In each, the film is flat and placed perpendicular to the incident beam. Their indices are assumed to be less than 5. Laue method back-reflection There are two variations of the Laue method, depending on the relative positions of source, crystal, and film (Fig. Two spots 1 and 2 separated by a wide angular distance αsup(m) are carefully chosen. en A computation method is presented which allows a rapid indexing of any unknown spot pattern obtained by back-reflection or transmission Laue methods. ![]() ![]() 17.18) is similar to a stereographic projection of the crystal planes (Fig. Laue’s method is used to determine the cell orientation of a single crystal of known structure. It is used because a special preparation of the sample is not required and there is no thickness restriction, while the transmission method needs thin samples with. In the Laue method, the crystal has a fixed (not rotated) orientation with respect to a polychromatic X-ray beam. The Cartesian coordinates of n spots are measured in an orthonormal frame referred to the photographic film. This method consists in analyzing a group of diffraction points (called spots) produced on the film, since the positions of these points are determined by the crystal orientation. A computation method is presented which allows a rapid indexing of any unknown spot pattern obtained by back-reflection or transmission Laue methods. ![]()
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