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
> 



      

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