The development of the X-ray divergent-beam (Kossel) technique over the last 50 years is traced. The fundamentals of this technique and ways to implement it experimentally are considered, and its potential for studying the real structure of crystals is analyzed in detail.

X-ray divergent-beam (Kossel) technique: A review

Lattice constant determination from Kossel patterns observed by CCD camera

Most of the common X-ray diffraction methods, e. g. the sin2Y - method [l], for obtaining residual stresses from crystalline materials only provide integrated information about several square millimeters of the surface. Local deviations from the measured mean value of the stress component, especially within a single grain, cannot be identified (excepting extremely coarsegrained materials). It is well-known that the really acting local residual stresses are associated with local inhomogeneities (dislocations, inclusions / dispersoids, lattice vacancies, etc.) and with further material defects (extrusions, intrusions, microcracks, etc.). Hence, the knowledge of such local stresses additionally to other features of the real structure is supposed to be of great interest. In the present paper a new method to measure and determine the residual stresses in micron regions will be discussed in detail. Referring to a physical effect discovered by W. KOSSEL in 1934 [2] the high lateral resolution had been achieved. A fine focused electron beam incident on a crystal causes fluorescent radiation (characteristic X-rays) which may be diffracted in the target crystal itself. Both conductive and nonconductive materials can be investigated when the fluorescent radiation is excited by an external X-ray source. However, this interesting kind of the excitation of KOSSEL interferences, discovered by BORRMANN [3], has not been of great practical importance over many years. But nowadays the situation is completely different. When using synchrotron radiation for the excitation of KOSSEL diffraction lines, as shown by H.-J. ULLRICH and co-workers in 1992 for the first time [4], a further scaling down of the analyzed specimen area (in the range of pm2) is not in conflict with an acceptable exposure time (a few seconds or minutes). More detailed information about the synchrotron excited KOSSEL technique and its application fields (overview) is presented by BAUCH et al. in the proceedings of the 47fh Annual Denver X-ray Conference in 1998 (also see [5], [6], [7]).

Measurements of residual stresses in micron regions by using synchrotron excited kossel diffraction

The XRT technique is a further special X-ray microdiffraction method where local X-ray interferences are produced by directing an X-ray or synchrotron beam from an external source with default monochromatic radiation of high intensity and a small diameter (e.g. application of capillary optics) on a crystalline region of a sample. Thereby for each diffracting net plane set a cone can be indicated with the half-opening angle equal to (90°Θhkl) for which the Bragg equation (1) is satisfied.

X‐ray Rotation‐Tilt‐Method — First Results of a new X‐ray Diffraction Technique

Advances in X-ray excitation of Kossel patterns by a focusing polycapillary lens

Starting from the origin and the informational content of Kossel interferences excited by electron and synchrotron radiation beams selected examples of microstructural applications, such as the precision determination of lattice constants, the precision determination of crystallographic orientation of single grains, the determination of local stresses/strains and the determination of tetragonal distortions of cubic lattices including the description of a variety of methods for analysis are presented.

H. Lin

Papers

Innovative Analysis of X‐ray Microdiffraction Images on Selected Applications of the Kossel Technique