In response to Dana Griffen: SRM 1976 exhibits preferred orientation such
that a March-Dollase r of about 0.6 is obtained with GSAS. This isn't the
best SRM for use as a check of a Rietveld analysis of divergent beam x-ray
data. I use SRM 660 to obtain (starting) instrument parameters and to
check instrument performance and alignment with fitting of individual
profiles. I then use SRM 676 (non-orienting alumina powder) to check for
intensity response via decent atomic parameters and an LP factor.
Regards,
Jim
James P. Cline Cline@Credit.NIST.gov
Ceramics Division Voice (301) 975 5793
A256/223 FAX (301) 990 8729
National Institute of Standards and Technology
Gaithersburg, MD 20899 USA