When a series of back reflection x-ray powder pictures of a freshly crushed coarse crystalline powder is taken, successive pictures exhibit a progressive change. Individual spots sharpen, diffuse portions of powder rings disappear, and the number of spots increases markedly with time. The increase in spots is not caused by breaking up of the particles. An account of the technique used for observing the effect is given. Experiments are described which indicate that the changes are definitely associated with the surface. The time rate of change increases with the hardness of the material and appears to be related to the degree of valance binding in the structure. A tentative explanation of the phenomenon is proposed which can account for all the observed effects.
© 1945 Optical Society of AmericaFull Article | PDF Article
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