Kossel-lines

Striking confirmation of the cubic structures of BP I and BP II was obtained by Onusseit and Stegemeyer and others, who succeeded in growing beautiful single crystals of up to a few hundred microns in size (fig. 4.8.2(a)). Optical Kossel diagrams, analogous to the Kossel lines observed in X-ray diffraction from crystals, have confirmed their symmetry (fig. 4.8.2(f))). 

In a single crystal, the excited X rays are Bragg diffracted at the lattice plane, and their isotropic angular characteristics show defect and excess Kossel lines of apex angle 90°-0b. which can be used for accurate measurement of lattice parameters and strains when the Kossel pattern is recorded on a photographic emulsion. 

Figure 7.10. Interference patterns for Kossel lines intersecting at right angles. Left experiment. Right theory (from Miller et al. [69]).

The authors in 1920 compared the frequencies of certain L emission lines with the differences in frequency between corresponding L and M absorption limits.1 Kossel first pointed out that these quantities should be equal on Bohr s theory. At that time we found each L emission frequency to be equal to a corresponding difference in absorption frequencies within the limits of experimental error. Coster2,8 has recently extended... 

G.44 Shuji Taira, ed. X-Ray Studies on Mechanical Behavior of Materials (Kyoto Society of Materials Science, Japan, 1974). A collaborative account by twenty-seven Japanese investigators of x-ray studies of phenomena affecting the strength of materials. X-ray stress measurements are described, as well as texture determination, line-broadening studies, microbeam methods, pseudo-Kossel patterns, small angle scattering, and x-ray topography. 

The interpretation of X-ray spectra was given by Kossel (1917). In the atom the electrons are arranged in shells, there being a K shell, an L shell, c. The electrons are most firmly bound in the K shell, less firmly in the L shell, still less firmly in the M shell, and so on. The. energy levels >v-indicated by horizontal lines in fig. 15 //-correspond to the electrons in the individual shells. The excitation of a JT-line,... 

Fig. 15.—Term scheme of X-ray levels (after Kossel), with the transitions corresponding to the X-ray lines.

According to Kossel the emission lines are caused by an electron falling in from a higher quantum orbit to replace the ejected electron, whereby the energy of the atom decreases. Further, an electron from a still higher quantum orbit can fall into the vacated place until finally the last gap will be filled by a free electron. 

In the b) variant the convergence angle is increased by using a very large limiting aperture or none. Thus, the individual round diffraction spots produce large overlap and superimposed black and white lines are obtained, similar to the Kossel or the Kikuchi lines formed from electrons diffusely scattered in thick crystals. The separation of these line pairs can be used as a measure of crystal curvature. 

Fig. 3. Model of the Kossel-Mollestedt fringes showing the useful lines for the thickness determination...

Figure 2.21 (c). Kossel diagram of the Blue Phase II seen along the twofold axis [110]. Let us note that the (100), (010), and (110) lines have common intersection points. 

Borrmann was already quite familiar with the Dahlem research institutes. He worked under Laue at the KWI for Physics in 1935 while a student of Walther Kos-sel, and he moved to Hechingen in 1943 along with the rest of the institute. There he remained true to the line of research he had begun under Kossel in Danzig, the most important result of which was the identification of the Borrmann effect demonstrated in 1941. The Bormann effect refers to the anomalously low absorption of X-rays by ideal crystals when the X-rays strike the ciystals at angles that... 

---