ABSORPTION IN THE MODEL OF SELF-CONSISTENT X-RAY SCATTERING. W. A. Keller, D. S. de Vasconcelos, Instituto de Física, Universidade Federal da Bahia, Salvador, Brazil

Absorption is approached as a local and statistical event in contrast with a background of the global and strictly determined pattern of x- ray crystal scattering. While particular and detailed physical mechanism of the absorption phenomenon is here considered irrelevant, the main concern is given to the overall effects of absorption on the earlier developed self-consistent model of x-ray scattering. The above model substitutes a single dipole, used originally in Ewald's papers as the scattering unit, by the plane of dipoles, but at the same time taking advantage of the self-consistency principle as determining the scattering mode. The following points, diverging with the previous work, are: i) Absorption takes place exclusively at the electron sites arranged in a set of dipole planes. ii) The flux of photons incident in each dipole plane is divided into two branches. The first one, as suffering unknown a priori frequency changes, is considered redundant for the model. The second branch is that of the unchanged wavelength. It is scattered under exact satisfaction of the Ewald self-consistency principle and gives rise to the overall scattering pattern of a crystal. This principle, for a non-absorbing case, can guarantee that energy is conserved for each dipole plane separately and for the model as a whole. iii) Absorption is considered as a localized occurrence, with probability factor which can be proportional to the first or higher powers of intensity of the resulting stationary and local field. iv) The latter is calculated separately for both polarization states, which for an non-absorbing crystal are quite independent of each other. The absorption is thus a unique link which interlaces these two states in the absorption effect. v) Absorption and refraction in this model of scattering are two distinct phenomena, which means that there is no necessity to introduce a complex index of refraction for absorbing crystals. The calculated absorption profiles reproduce the experimental results without the necessity of the corrections usually made by means of additional and arbitrary parameters.