X-ray diffraction from a crystal containing isolated imperfections

The X-ray scattering amplitude of a crystal containing isolated imperfections is expressed in terms of the Fourier transform of the atomic displacement vectors. The amplitude contains only the local properties of the imperfections which are `seen' by the incident beam of a finite size. Disruption of the Borrmann transmitted (or diffracted) beam, narrowing of the dynamical diffraction range and `diffuse' scattering caused by dynamically diffracted X-rays are some of the results obtained from the calculated amplitude. Black, white and black-white images in topographs are explained by the present theory. Image contrast is also discussed in terms of the thickness of the crystal.