OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 acting on the material. Multilayer monochromators are characterized by the manifestation of mutual atoms diffusion in heterogeneous materials and the possibility of forming new phases at the layer boundaries. In English-language literature, double mirror monochromators are referred to as DMM (Double Multilayer Monochromator). Configurations and geometry of optical elements The principle of diffraction providing monochromatization of X-ray radiation can be realized using two schemes. One of them, the Bragg scheme (Fig. 10 a), assumes reflection of rays by the surface layers of the crystal. The first monochromators based on this scheme were proposed in 1921 by Davis and Stempel [17]. In contrast to the Bragg scheme, the Laue scheme presented in [18] is based on the passage of radiation through the crystal (Fig. 10 b). In both cases, the Wolf – Bragg condition is realized. Dependingon the choiceof geometryandorientationof themonochromator crystals, the radiation received from the monochromator is characterized by a different degree of monochromaticity (Fig. 11). Two crystals (corresponding to the variant shown in Fig. 11 a) have the same spatial lattice. Its crystallographic surfaces are oriented in the same way in space. In such a “non-dispersive” configuration, the beammonochromaticity when reflected from the second crystal is not improved. The role of the second crystal when realizing this scheme is to restore the original direction of the beam path. In English-language literature, such two-crystal monochromators are referred to by the abbreviation DCM (double crystal monochromator). a b Fig. 10. Diffraction of radiation on crystals of a monochromator: a – diffraction according to the Bragg scheme (reflection of X-rays); b – diffraction according to the Laue scheme (passage of X-rays through the crystal) a b c d Fig. 11. Configuration of non-dispersive (a) and dispersive (b–d) crystals When improving the degree of monochromaticity is necessary, one of the three solutions schematically presented in Fig. 11 b–d can be used. The second crystal, unlike the first one, has a different crystallographic orientation (Fig. 11 b, d), or is made from a different material (Fig. 11 c) with other orientation of the surfaces. Dispersion schemes provide an increased monochromaticity of radiation due to additional diffraction on the second crystal, contributing to the isolation of a narrower band of wavelengths. The number of photons transmitted in the required direction is reduced. In [19] the analyzed schemes are described in more
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