Hi Kurt, If you plot the results in POWPLOT & do the "statistical analysis" what does the delt/sig vs 2-theta plot look like? If weights are right then the band of delt/sig ought to be roughly 2-3 sig wide. Is your data in cpm? Some instruments make that by default. That will mess up the R-factors. Bob
________________________________ From: Kurt Leinenweber [mailto:[EMAIL PROTECTED] Sent: Fri 2/15/2008 12:44 AM To: rietveld_l@ill.fr Subject: advice on new powder diffractometer Hi All, I am attempting to assist others to choose a new powder x-ray diffractometer. We are currently looking at a Panalytical X'Pert Pro in alpha-1 configuration, and I would like to know if anyone has any experience with this for Rietveld refinements? For other reasons we would like to keep the sample flat, but then we could not use the alpha-1 configuration, so instead we would consider a "hybrid" monochromator - I would like to ask if this monochromator makes it impossible to do Rietveld? Also, any other insights and suggestions for systems that are competitive with these would be welcome. We are at an early stage and have time to think about this, will be looking at other possibilities, and I would appreciate any suggestions. Incidentally, I received some data on quartz (supplied by me) from the alpha-1, and refined it using GSAS. The refined structural and thermal parameters are fine, but I get strange r-factors, with wRp of 25% and crystallographic R also near 25%, chi**2 of 0.5. Does anyone know why this might happen? With my old Siemens D5000 I easily get down to 10% or better in the r-factors right away, so something obvious must be wrong. Thank you, - Kurt Leinenweber
