A high-resolution multiple-crystal monochromator for X-ray diffraction studies

This work proposes a new four-crystal monochromator particularly indicated for applications in the field of high-resolution X-ray diffraction. The monochromator is made of two monolithic crystal elements. The first one is a channel-cut crystal consisting of two symmetrically cut components set in a parallel nondispersive geometry. The second monolithic crystal is composed of two crystal components in a parallel nondispersive geometry but the crystal surfaces are miscut with respect to the diffraction planes. The diffraction geometry for both components of the second monochromator crystal element is the glancing-incidence condition. The peculiar properties of this monochromator are investigated theoretically. An appropriate rotation of the second component of the second monolithic block with respect to the first components corrects the beam deviation caused by the refraction effect. This monochromator system may allow one to obtain highly monochromatized and collimated beams with high angular resolution (about 0.01 mrad) and wavelength dispersion of about 4 x 10(-5) The intensity reduction of the proposed crystal arrangement in comparison with other monochromators is discussed, including wavelength spread and beam size increase.