Abstract

The second part of an investigation of the conditions of X-ray propagation in a crystal for a three beam case is described. In the first part, the crystal was supposed to be built of non-absorbing point-atoms. In this part, these are replaced by absorbing atoms of finite size described by complex atomic scattering factors. The dynamical equations are studied without any restrictions as far as possible: at the beginning no limit is put either to the number n of strong rays or to the strength of absorption. The theory is then further specialized to the cases of two strong rays and of three non-coplanar strong rays under the hypothesis of small absorption. It is then possible to show that, also including absorption, a relation holds between the closest approach of the surface of dispersion to the Laue point and the extent to which absorption is reduced (Borrmann effect). Finally, the theory is applied to two special cases relating to germanium crystals in which the double Borrmann effect has been observed, the simultaneous reflections (111/11) and (111/1). For the first of these, the six sheets of the surface of dispersion are illustrated as they develop for varying wavelengths. Curves for the six corresponding absorption coefficients are drawn.