My invention relates to an x-ray powder diffractometer and in particular to a diffractometer for determining the structure and texture of a powder sample mounted for rotation in the path of a beam of monochromatic X-rays and a photon detector.
The standard powder X-ray diffractomer, described by W. Parrish, E. W. Hamacher and K. Lowitzsch, Philips Technical Review, 16, pp 123-133 (Oct. 1954) employs the Bragg-Brentano symmetric parafocussing geometry, maintains a flat specimen equi-distant from the X-ray focal source and the photon-counting detector. Diffraction spectra are measured with the diffraction vector virtually collinear with the surface normal. High quality intensity data are measureable in this arrangement only if the sample comprises a large number of randomly oriented small crystalline particles.
Two specimen related effects contribute to the degradation of the accuracy of the measured intensity as characteristic of the diffracting material. The first, or "particle statistics" (number of particles in the diffracting position) effect is manifest when the size distribution of the crystallites is such that the diffracting volume varies intractably with 2.theta.. The second effect is manifest when the crystallites are not randomly oriented, but are instead distributed in some "preferred orientation". Both effects can be avoided in such cases where some control can be exercised over the sample preparation.
A symmetrical focussing reflection method described by L. G. Schulze in Journal of Applied Physics, 20, p. 1030-1033, (November 1949) involves a departure from the foregoing method involving employing narrow horizontal slits to collimate the incident beam into a flat wedge, i.e. to collimate the incident beam into parallelism in the vertical direction but still diverging in the horizontal plane. The sample was also mounted for rotation about an axis normal to its surface and rotation of the sample holder about an axis collinear with the X-ray focal source to detector displacement. This method permitted determining pole figures of flat samples with a Geiger or scintillation counter spectrometer.