Figure 2.3.5.6

Parrish, W.; Langford, J. I.

doi:10.1107/97809553602060000578

International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

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International Tables for Crystallography (2006). Vol. C. ch. 2.3, p. 77

Figure 2.3.5.6

W. Parrish^a ^‡ and J. I. Langford^b

^a IBM Almaden Research Center, San Jose, CA, USA, and ^bSchool of Physics & Astronomy, University of Birmingham, Birmingham B15 2TT, England

Figure 2.3.5.6

Crystal monochromators most frequently used in powder diffraction. (a)–(c) Non-focusing parallel beam, (d)–(f) focusing bent crystals. All may be cut parallel to the reflecting lattice plane (symmetric cut) or inclined (asymmetric cut). The latter are used to expand or condense beam depending on the direction of inclination, and to change focal lengths. (a) Flat symmetric plate. (b) Flat asymmetric plate in orientation to expand beam and increase intensity (Fankuchen, 1937). (c) Channel monochromator cut from highly perfect ingot (Bonse & Hart, 1965). (d) Focusing crystal bent to radius 2R (Johann, 1931). (e) Crystal bent to 2R and surface ground to R (DuMond & Kirkpatrick, 1930; Johannson, 1933). (f) Crystal bent to section of logarithmic spiral (Barraud, 1949; de Wolff, 1968b).