Standard reference materials for the measurement of instrument resolution functions: effect of transparency

Standard Reference Materials (SRMs) for determining instrumental line profiles should not exhibit measurable broadening from structural imperfections, but owing to the effects of sample transparency, the quality of potential standards for this purpose is not easy to assess with data from a conventional divergent-beam diffractometer. The problem of transparency can be avoided if a synchrotron source and a diffractorneter with a Soller-type receiving-slit assembly is used. Data from such a configuration were used to assess the quality of powder samples of KCl, BaF2, and LaB6, three SRMs currently employed in line-profile analysis with widely differing X-ray absorption coefficients. These data revealed some residual sample broadening in the BaF2, and, to a lesser extent, in the LaB6.