Basic concepts of dynamic X-ray diffraction are applied in distinguishing between the propagation along the atomic planes characterized by the linear absorption coefficient and the perpendicular propagation on the atomic planes. Propagation is responsible for the generation of the standing waves through the anomalous absorption coefficient on dispersion branches of diffraction.
TopIntuitively, it is expected that, for a direction of energetic “flow” the absorption to depend only on the direction of propagation, but not also by the way of selection of this direction, i.e. by the external parameters of the angle of incidence and by the tilt of the physical surface of the crystal.
We have seen in Chapter 12 of the dynamic theory, that the absorption is determined by the imaginary component of the wave vector transmitted by the crystal according to the self-consistency at propagation. But, as the imaginary components correspond to the planes of equal absorption and are, therefore, correlated with the depth in the crystal, the corresponding absorption coefficient means a normal factor of absorption (Zachariasen 1946; Batterman & Cole 1964; Laue 1960; Renninger 1967):
(14.1) this time the linear coefficient having the generic meaning of average of absorption factor by the whole crystal, to which will be expressed the normal coefficient and then an arbitrary one.