Dear James,

For me too, please, if it would not be much of a trouble.
Thank you in advance!

Eduard

On Mon, 2 May 2016 11:09:31 +0000, Cline, James Dr. (Fed) wrote
> Bob Cheary and I developed and presented a workshop several times in the 
> 1990's that included a discussion of this issue.  I can send you the notes 
> for it ifyou would like them.
>  
> Jim
>  
>  
> James P. Cline
> Materials Measurement Science Division                  
> National Institute of Standards and Technology
> 100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ]
> Gaithersburg, MD 20899-8523    USA
> jcl...@nist.gov
> (301) 975 5793
> FAX (301) 975 5334
>  
> From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr]On Behalf 
> Of Matthew Rowles
> Sent: Monday, May 02, 2016 1:53 AM
> To: RIETVELD_L Distribution List <rietveld_l@ill.fr>
> Subject: Parafocussing definition?
>  
> 
> Hi all
> 
>  
> 
> I've been trying to find a good explanation of what parafocussing (wrt 
> Bragg-Brentato geometry) actually is, but haven't been able to find one.
> 
>  
> 
> Klug and Alexander just reference Brentano's papers.
> 
>  
> 
> "The Basics of Crystallography and Diffraction" 2nd ed say that B-B geometry 
> is "semi-focussing" because the sample is flat, and not curved to follow the 
> focussing circle (this doesn't sound right to me)
> 
>  
> 
> Brentano, J Appl. Phys. 17, 420 (1946) says that a ray reflecting off the arc 
> defined by ACB where A is the source, C is the centre of the gonio, and B is 
> the detector (ie the focussing circle)  is automatically parafocussing, 
> because youonly can establish the location of the crystallites, not their 
> orientation, but then goes on to say that you can actually find the 
> orientation, as the lattice plane normal bisects the angle ACB.
> 
>  
> 
> I also haven't been able to find a use of the word "parafocus" outside of the 
> diffraction literature, so I can't see how the word is used elsewhere.
> 
>  
> 
> Any ideas?
> 
>  
> 
>  
> 
> Matthew

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