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

International Tables for Crystallography (2006). Vol. C, ch. 2.2, pp. 34-35

Section Recording of upper layers

J. R. Helliwella

aDepartment of Chemistry, University of Manchester, Manchester M13 9PL, England Recording of upper layers

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Upper-layer photographs are usually recorded in equi-incli­nation geometry [i.e. μ = −ν in equations ([link] and ([link]]. The X-ray-beam direction is made coincident with the generator of the cone of the diffracted beam for the layer concerned, so that the incident and diffracted beams make equal angles (μ) with the equatorial plane, where [\mu=\sin^{-1}\zeta_n/2.\eqno (]The screen has to be moved by an amount [s\tan\mu,\eqno (]where s is the screen radius. If the cassette is held in the same position as the zero-layer photograph, then reflections produced by the same orientation of the crystal will be displaced [D\tan\mu\eqno (]relative to the zero-layer photograph. This effect can be eliminated by initial translation of the cassette by [D \tan \mu].

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