In principle, the LP correction for a multi-bounce monochromator is similar to that for a single-crystal one with the same crystal type and reflection indexes (or diffraction angle). The exact LP value depends, as well, on the crystal perfection (mosaicity) and for supremely precise measurements one might consider refining the LP value as was mentioned by Kurt and Peter. Besides the angular range, the correlation with thermal parameters, and the instrument alignment, one more problem of the LP refinement is the correct choice of the atomic scattering curves in accordance with the oxidation states which might be not quite obvious in general.
Leonid ******************************************************* Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov ******************************************************* --- On Sun, 7/26/09, Peter Y. Zavalij <pzava...@umd.edu> wrote: > From: Peter Y. Zavalij <pzava...@umd.edu> > Subject: RE: LP factor in the Rietveld refinement > To: rietveld_l@ill.fr > Date: Sunday, July 26, 2009, 5:03 AM > That's right. LP refinement works > just fine within TOPAS but angular range > as wide as possible is needed. If it is up to 140-150 deg. > 2thteta LP does > not correlate much with thermal parameters. Refined LP is > not exact but very > close. > > Peter Zavalij > > X-ray Crystallographic Center > University of Maryland > College Park, MD > > Office: (301)405-1861 > Lab: (301)405-3230 > Fax: (301)314-9121 > > > > > -----Original Message----- > From: Kurt Leinenweber [mailto:ku...@asu.edu] > Sent: Saturday, July 25, 2009 8:53 PM > To: alor...@unex.es; > Leonid Solovyov > Cc: rietveld_l@ill.fr > Subject: RE: LP factor in the Rietveld refinement > > Hi all, > > I haven't actually DONE this, so maybe I shouldn't put my 2 > cents in, but > can't you refine the polarization factor by using a > standard such as Y2O3 > and fixing the structure and thermal parameters of the > standard while > refining the polarization angle? > > The angle so obtained should agree with what the theory > tells you for your > diffractometer configuration, but it seems more comforting > to verify it by a > measurement. > > - Kurt > > ________________________________ > > From: alor...@unex.es > [mailto:alor...@unex.es] > Sent: Sat 7/25/2009 1:29 PM > To: Leonid Solovyov > Cc: rietveld_l@ill.fr > Subject: Re: LP factor in the Rietveld refinement > > > > In this context: > > What about the LP for a Goebel mirror followed by a > 4-bounce or 2-bounce > primary monochromator? > > Best regards > > angel l. ortiz >
