Determination of the sign of the burgers vector for nearly screw dislocations a direct application of x-ray dynamical theory

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Abstract
Nearly screw dislocations perpendicular to the crystal surfaces of KDP have been studied by the Lang X-ray topography technique in the case of reflections where the bulk strain tensor gives no contrast. Stress-relaxation deformations at the intersections with the crystal surfaces give images which have been studied in both reflected and refracted beams on section topography. The interpretation of the contrast is based on dynamical theory for slightly distorted crystals and leads to the determination of the sign of the Burgers vector. The formulation adopted here (after Malgrange 1975) leads to a convenient interpretation (both qualitative and semi-quantitative) of the contrast. In particular, the interpretation of the shape and size of the stress-relaxation-deformation images is a good example of what can be done on the basis of results of dynamical theory and without any computer calculation.