Application of contrast conditions to dynamical images of immobile dislocations

Abstract
In X-ray topography, the Burgers vector of a dislocation is usually determined by finding those diffracting planes for which the image of the dislocation becomes invisible. The conditions H – b = 0 and H – b × n = 0 would then be applied to determine the Burgers vector. In this paper, these conditions of invisibility have been applied to a particular pattern of straight line images observed by Borrmann disruption in thick crystals (μL>15) using many diffracting planes. It is found that the condition H – b = 0 alone is sufficient to determine that the images are caused by Lomer sessile edge dislocations. Furthermore, it is found that the condition H – b × n = 0 was not necessary to predict the invisibility of these images. This fact is attributed to the complexities of image formation by dynamical diffraction in imperfect crystals.