Hi Blaise In Bragg-Brentano mode, sample spinning does nothin for PO. This is because the diffraction vector is normal to the sample surface, and sample spinning rotates along this vector.
Spinning does increase your particle statistics, which almost always helps. If you're looking at a capillary, spinning the capillary does help with PO, but just being in a capillary helps PO. As to spinning speeds, a good guide is one revolution per data point. Cheers Matthew ________________ Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] ________________________________ From: Mibeck, Blaise [mailto:[EMAIL PROTECTED] Sent: Wednesday, 29 October 2008 01:25 To: rietveld_l@ill.fr Subject: RE: Quantitative analysis I am learning QPA and am worried about PO. I wonder why sample spinning isn't discussed more. I am luckily able to barrow time on a newer diffractometer with a sample spinner. Does this reduce PO? Or completely eliminate it? There is a set up variable in GSAS for whether you are spinning the sample - are there guidelines for how many revolutions to spin the sample if you just want to reduce PO? Thanks to all for there help!!! Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy & Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]> -----Original Message----- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 9:09 AM To: Martin; [EMAIL PROTECTED]; rietveld_l@ill.fr Subject: RE: Quantitative analysis I agree that it's always best to avoid preferred orientation, but that is easier said than done on a routine basis. I have personally had good luck with the M-D PO correction on many known samples, as long as the PO was not severe. However, I imagine that Mario's problems are related to microabsorption in this case. Mario, if you can re-measure your data with a Co or Fe tube, it would be a good test of this. Dave Bish At 08:51 AM 10/28/2008 -0400, Martin wrote: Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin ------------------------------------------ M Vickers Dept of Chemistry UCL ________________________________ > Subject: Re: Quantitative analysis > Date: Tue, 28 Oct 2008 02:53:20 -0700 > From: [EMAIL PROTECTED] > To: Rietveld_l@ill.fr > > Dear Mario, > > One more possible problem of applying preferred orientation corrections in > QPA is that not all of them are normalized. For example, the March-Dollase > correction is normalized and can be applied safely, but the Rietveld-Toraya > correction is inapplicable to QPA as it does not preserve the scale > normalization. > > Best regards, > Leonid > > ******************************************************* > Leonid A. Solovyov > Institute of Chemistry and Chemical Technology > K. Marx av., 42 > 660049, Krasnoyarsk Russia > Phone: +7 3912 495663 > Fax: +7 3912 238658 > www.icct.ru/eng/content/persons/Sol_LA<http://www.icct.ru/eng/content/persons/Sol_LA> > ________________________________ For the best free wallpapers from MSN Click here!<http://wallpapers.msn.com/?ocid>
