PROFILES IN ASYMMETRIC DIFFRACTION WITH PSEUDO-PARALLEL-BEAM GEOMETRY

Bragg reflection profiles in asymmetric diffraction using pseudo-parallel-beam geometry were examined and compared with the experimental data. For high collimation and strict monochromatization of the X-ray beam, an Si(111) channel-cut crystal was mounted on the incident-beam side while a receiving slit or a Ge(111) flat-crystal analyzer was used on the diffracted-beam side. Profile intensities for CeO2 powders, observed by symmetric theta-2 theta scanning and asymmetric 2 theta scanning at various fixed incident angles alpha (1-45 degrees), were analyzed using individual-profile-fitting techniques. The variations of observed peak width and integrated intensity with alpha and 2 theta were in good agreement with the theory. Practically no peak broadening occurred for alpha>10 degrees while the peak width increased gradually with decreasing cc below 10 degrees. With a Ge(111) flat-crystal analyzer, the peak broadening at alpha<10 degrees was suppressed below 0.05-0.07 degrees in full width at half-maximum.