Effet d'un gradient thermique sur l'intensité des rayons X diffractés par un cristal de sulfate de glycocolle (T.G.S.)

Abstract

Anisotropic strains in anisotropic crystals (i.e.T.G.S. crystals) due to a uniform thermal gradient are calculated. The X-ray reflecting power of the sample is related to the strain gradient. Experimental measurements of the reflecting-power oscillations under an oscillating thermal gradient are compared with the results of calculations of the anisotropic strain-gradient oscillations and are in good agreement. Random fluctuations of the room temperature in normal operating conditions distort the sample sufficiently for the Pendell~Ssung fringes on X-ray section topographs to be completely blurred.

Elimination of extinction by a temperature gradient

“…They disappear when the crystal is at thermal equilibrium. Analogous observations were made by Izrael & Petroff (1973), who noted that random fluctuations in room temperature are enough to blur the Pendell~sung fringes on X-ray topographs of triglycine sulphate. In both cases, small elastic disturbances of the crystal perfection must be involved.…”

“…Quantitative planes caused by thermal gradients have been made by Penning & Polder (1961) and by Izrael & Petroff (1973). The influence of such lattice deformation on the integrated intensity has been discussed by Katagawa & Kato (1974).…”