SYMMETRICAL X-RAY-DIFFRACTION IN A PERFECT RECTANGULAR TXL CRYSTAL - EXTINCTION AND ABSORPTION

The boundary-value Green function technique has been used with the Tak agi-Taupin equations to explore analytically the diffraction in a perf ect rectangular t x iota crystal for a symmetrical coplanar scattering mode. The important contribution is the development of the integratio n structure over the entrance and exit surfaces of the crystal. A sing le parameter, zeta = (t/iota) tan theta(oh), maps the different crysta ls and the scattering geometries. In the limits zeta --> 0 and zeta -- > infinity, the well known functions for the primary extinction factor s for perfect semi-infinite crystals in the case of Laue and Bragg sca ttering are retrieved. Numerical integrations extend the range of appl icability of the method. Both ordinary absorption and generalized exti nction, i.e. the joint effect on the kinematical integrated power due to multiple scattering and resonant scattering, are addressed. Germani um is used as a model system for some of the calculations.