Danger diffraction

There are many variants of this system which can be envisaged as means by which the current possibilities for automation in data collection can be applied for specific purposes. There are considerable dangers in this approach in that it may be all too easy to build in restrictions which predetermine the results. These dangers, however, are not likely to be worse than those normally encountered in electron microscopy or single crystal diffraction where the one particularly "good-looking picture is taken as being "typical" of a sample. 

Along this line, the limitations of the technique used must be recognized. Some measure predominantly bulk properties, e.g., X-ray diffraction and magnetic susceptibility whereas, others are sensitive to surface composition, e.g., adsorption and ESCA. For example, in one reported study only cobalt in tetrahedral coordination was found on a catalyst by diffuse reflection spectroscopy, but magnetic measurements revealed that octahedral cobalt must also be present (10). Thus, it is dangerous to rely on any one method to characterize these catalysts. 

In order to experience continued attention, any physical technique must satisfy a pressing need. The development of XDI has been stimulated by a so-called killer application , that of detecting and identifying explosives (and drugs) whose illegal use represents a grave danger to society. Physical parameters provided by XDI diffraction profiles that are useful in explosives detection are detailed in Section 3. 

Kaye, B.H. Dangers of curve fitting in the deduction of size distribution from diffraction data. Proceedings of the Powder and Bulk Solids Conference, May, 6, 1991. 

Fiber x-ray diffraction can be expected to provide at least some evidence relative to all the above questions. With the available ratio of data to parameters, however, some questions may well remain unanswered. Samples of far higher crystallinity would be needed to accomplish a complete determination, and there Is some danger that such samples would not completely correspond to samples of more general interest. 

All modern X-ray diffraction equipment features built-in safeguards that minimize the operator s risk of exposure to radiation under normal working conditions. However, the use of this equipment can be dangerous because of both the nature of the radiation itself and the high voltage used by the equipment to generate the X-rays. X-radiation can kill even very brief exposure to the direct X-ray beam can cause permanent skin damage. Because the effect of exposure to shortwave radiation of any form is cumulative, extreme care must be taken to avoid all exposure. 

Fig. 18. SAXSAVAXS experiment on the isothermal crystallization of iPP. The saxs invariant and the crystallinity derived from the integrated intensity of the crystalline waxs peaks are coplotted with an arbitrary vertical axis. In this data set, the rise of the invariant precedes the rise of the crystallinity, which can indicate a spinodal-like crystallization mechanism. To base theories regarding crystallization solely on the outcome of such an experiment is dangerous since the results could be influenced by both instrumentation shortcomings and the physics behind the diffraction phenomena. —A— saxs invariant — — waxs crystallinity.

FIGURE 3.2 A Fraunhofer diffraction pattern under two different contrast levels. The circle drawn around the right hand pattern has a radius 1.5 times that of the geometrical shadow of the object. The area between the shadow and the circle represents the area from which the light to form the pattern is obtained. (The patterns were calculated using the Fresnel Diffraction Explorer, which may be obtained from Danger Research http //daugerresearch.com/)... 

Generally it is difficult and dangerous to prophesy, and in science it is still more so. Unknown factors always have to be anticipated. However, electron diffractionists at least seem to believe in the future of their method for the study of gas molecules. Unless an entirely new method is developed that can take over great parts of what electron diffraction is doing today, one must expect that electron diffraction studies are going to extend and improve lists of bond distances and valency angles, that electron... 

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