An X-ray goniometer using beams of large aperture for photographically recording crystal-powder reflections

The factors which determine the various aberrations of X-ray reflections from microcrystalline powders are considered in relation to the design of a goniometer using beams of large aperture. Expressions are derived for the aberrations from a flat layer and from a toroidal powder surface in relation to the angular setting. An instrument using wide beams is described in detail and indications are given regarding its operation. According to the procedure adopted such aberrations as lead to asymmetrical diffusion effects are reduced, and in this way sharp lines with correctly located peaks are obtained. Powder layers with spherical and toroidal surfaces are discussed in detail and data are given for their use; as compared with flat layers they make it possible to employ considerably wider beams with correspondingly shorter exposures, particularly in the range of medium and large angles.