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 θ–2θ scanning and asymmetric 2θ scanning at various fixed incident angles α (1–45°), were analyzed using individual-profile-fitting techniques. The variations of observed peak width and integrated intensity with α and 2θ were in good agreement with the theory. Practically no peak broadening occurred for α > 10° while the peak width increased gradually with decreasing αbelow 10°. With a Ge(111) flat-crystal analyzer, the peak broadening at α < 10° was suppressed below 0.05–0.07° in full width at half-maximum.