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

© International Union of Crystallography 2006
International Tables for Crystallography (2006). Vol. C. ch. 2.2, pp. 35-36

Section 2.2.5.4. Recording of upper-layer photographs

J. R. Helliwella

a Department of Chemistry, University of Manchester, Manchester M13 9PL, England

2.2.5.4. Recording of upper-layer photographs

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The recording of upper-layer photographs involves isolating the net of relp's at a distance from the zero layer of ζn = nλ/b, where b is the case of the b axis antiparallel to the X-ray beam. In order to determine ζn, it is generally necessary to record a cone-axis photograph. If the cell parameters are known, then the camera settings for the upper-level photograph can be calculated directly without the need for a cone-axis photograph.

In the upper-layer precession photograph, the film is advanced towards the crystal by a distance [D\zeta_n\eqno (2.2.5.4)]and the screen is placed at a distance [s_n=r_s\cot\bar\nu_n=r_s\cot\cos^{-1}(\cos\bar\mu-\zeta_n).\eqno (2.2.5.5)]The resulting upper-layer photograph has outer radius [D(\sin\bar\nu_n+\sin\bar\mu)\eqno (2.2.5.6)]and an inner blind region of radius [D(\sin\bar\nu_n-\sin\bar\mu).\eqno (2.2.5.7)]








































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