On the integrated reflectivity of perfect crystals in extremely asymmetric Bragg cases of X-ray diffraction

In the case of grazing incidence, the integrated reflectivity calculated according to the theory appropriate for extreme asymmetry is smaller than that calculated according to the conventional theory. In the case of grazing emergence the results calculated according to each theory exhibit smaller differences than for the first case within a great range of extreme asymmetry. In the conventional theory the integrated reflectivity tends to zero for α - θ_B tending to zero, whereas the theory for extremely asymmetric cases provides a non-zero value for the reflectivity for α- θ_B tending to zero.