About Na2Ca3Al2F14 in the previous mail, some more data were added at : http://www.cristal.org/powdif/low_fwhm_and_rp.html#NAC showing results from a variable slits setting. The 1/sin(theta) correction is shown to be efficient, at least if applied to these data. Not a lot of Rietveld software can cope with such data (WinMProf to my knowledge). The best being to multiply the calculated pattern by sin(theta) rather than to divide the observed pattern by sin(theta). With such variable slits, the conventional X-ray pattern looks like a very good neutron pattern (i.e., less intensity decrease at large angle than with fixed slits, but better resolution than the best neutron data with minimum FWHM ~0.05� (2-theta) ;-) Best, Armel Le Bail - Universite du Maine, Laboratoire des Fluorures, CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France http://www.cristal.org/
