Nonsymmetrical X-ray diffraction in a perfect rectangular txl crystal. Extinction and absorption

A theoretical investigation of diffraction in a rectangular t x I crystal f or nonsymmetrical coplanar scattering has been undertaken. The asymmetry in the scattering geometry, measured by an angle gamma, causes different weig hts for the mixed Laue-Bragg contributions to the integrated power. Primary extinction and ordinary absorption are only moderately affected when the v alue of the geometrical parameter zeta = (t/l) tan theta(oh) < 1, theta(oh) being the Bragg angle. For increasing values of zeta and gamma the surface integration set-up for the Laue and Bragg regions is extensively changed, leading to pronounced effects. Analytical results for the normal absorption factor are presented.