OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 In [33] symmetric (Fig. 15 a) and asymmetric (Fig. 15 b, c) reflection of X-rays are distinguished when analyzing optical schemes in Bragg and Laue geometry. a b Fig. 14. The channel-cut monochromator with three diffracting faces [32]. View of the crystal from two different sides a b c Fig. 15. Variants of orientation of atomic planes in monochromator crystals The schemes with symmetric and asymmetric reflection differ in the length of the ray path in the crystals. In the case of symmetric reflection, shown in Fig. 15 a, the atomic planes are parallel to the crystal surface. In the case of asymmetric reflection, the crystal planes are oriented at an angle to the atomic planes, which is usually 5–10° [34, p. 283]. The variants of crystals providing asymmetric reflection are shown in Fig. 15 b, c. When using the asymmetric reflection scheme, the optical path length of the beam incident on the crystal differs from the path length of the reflected beam [35]. Using such a scheme makes it possible to form a denser monochromatic radiation compared to the scheme with symmetric reflection. The distance between the SR beam entering the monochromator and the beam leaving it is called beam offset. In Fig. 16, this parameter is denoted by the symbol h. Depending on the mounting scheme of the a b c Fig. 16. Constant displacement of the beam when changing the angle of incidence θ (fixed beam exit from the monochromator: h1 = h2 = h3)
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