Mixing Symmetric and Oblique Bragg Reflections in Rigid Channel-Cut Crystals

Because the Bragg angle and Darwin range of total reflection in symmetric and oblique Bragg reflections vary with the angle between the Bragg planes and the crystal surface, it is generally believed that the resulting mismatch causes a loss of intensity in monolithic channel-cut crystals that is unacceptable in practice. It has been discovered that in the unique case of the 220 Bragg reflection from germanium no mismatch occurs, so that oblique and symmetric reflections can be mixed in one rigid channel-cut crystal. The results are valid for both X-ray and neutron channel-cut monochromators.