Open AccessDivergent-beam X-ray photography of crystals
Author(s) -
Kathleen Lonsdale
Publication year - 1947
Publication title -
philosophical transactions of the royal society of london. series a, mathematical and physical sciences
Language(s) - English
Resource type - Journals
eISSN - 2054-0272
pISSN - 0080-4614
DOI - 10.1098/rsta.1947.0002
Subject(s) - misorientation , optics , beam (structure) , bragg's law , photographic plate , crystal (programming language) , texture (cosmology) , perfect crystal , wavelength , materials science , crystallography , physics , chemistry , diffraction , microstructure , programming language , artificial intelligence , computer science , grain boundary , image (mathematics) , vacancy defect
Divergent-beam X-ray photography of single crystals by transmission can be used to study the ‘extinction’, that is, the diminution of thetransmitted radiation that takes place at the Bragg reflexion angles. The intensity and geometry of the absorption lines observed give useful information about the texture of the crystal. Divergent beam photographs have shown that many crystals of organic compounds are unexpectedly perfect, and that sudden cooling to liquid-air temperatures will increase the mosaic character of their structure by an important factor and make them more suitable for structural analysis by the usual methods. Type I diamonds, and natural ice even near to its melting-point, are also found to possess a high degree of perfection, which cannot be removed by liquid-air treatment. The divergent beam method may be used for the determination of orientation, but it is important that the wave-length of X-rays employed should be correctly related to the size and nature of the crystal. In certain favourable cases it is possible to make precision measurements of lattice constant or of wave-length from divergent beam photographs, without the use of any kind of precision apparatus. By such means it has been shown that the C—C distance in individual diamonds varies from 1541.53(± 0-02) to 1541.27X, (1.54465-1-54440A), a difference presumably due to varying impurity content. Using diamond and a brass anticathode, the Zn Ka1 wave-length, relative to Cu K Ka1 as 1537.40X, is found to be 1432.21 ( ± 0-04) X. Temperature control would improve the accuracy of this measurement, which is, however, in good agreement with the latest value obtained by orthodox precision methods.