RE: U,V,W cagliotti peak width parameters

[Cline, James Dr. (Fed)]

As Alan states, the U, V, and W terms are often employed in situations where 
their physical meaning is minimal:

http://nvlpubs.nist.gov/nistpubs/jres/120/jres.120.013.pdf

Jim


James P. Cline
Materials Measurement Science Division
National Institute of Standards and Technology
100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ]
Gaithersburg, MD 20899-8523USA
jcl...@nist.gov<mailto: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 
Alan Hewat
Sent: Monday, August 29, 2016 7:49 AM
To: Yashwanth Padarthi 
Cc: rietveld_l@ill.fr
Subject: Re: U,V,W cagliotti peak width parameters

Cagliotti shows how U,V,W are related to the collimation alpha1, alpha2, alpha3 
and mosaic spread beta of the monochromator crystal for a classical neutron 
powder diffractometer; a further discussion is given 
here<http://hewat.net/science/papers/1975%20Design%20for%20a%20conventional%20high-resolution%20neutron%20powder%20diffractometer.pdf>.
 In general, a quadratic function of tan(theta) can be an approximate 
description of how the peak width varies with scattering angle, even if an 
ideal neutron diffractometer is not being used, but then U,V,W may not have 
much physical meaning.
Alan.

On 29 August 2016 at 10:36, Yashwanth Padarthi 
mailto:yashwanth.padarthi...@gmail.com>> wrote:
Dear sir,

Can i know what is the significance of U,V,W separately?what do they signify if 
i have a plot of two theta Vs intensity how can one show what U,V,W is 
separately? i have researched a lot but they are no particular significant 
meaning. i only know they depend on the instrument resolution function(IRF) 
which depends on diffractometer..

Do you have any idea how U,V,W are calculated or refined?

I know this formula by caglioti et al(1958)
FWHM = (U*tan^2 theta + V*tan theta + W)^0.5

but this doesn't help me knowing the real individual significance like in 
fullprof we can actually vary them individually and see the changes in the 
pattern accordingly by varying U,V,W separately

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__
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
mailto:alan.he...@neutronoptics.com>> 
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Re: U,V,W cagliotti peak width parameters

[Alan Hewat]

Cagliotti shows how U,V,W are related to the collimation alpha1, alpha2,
alpha3 and mosaic spread beta of the monochromator crystal for a classical
neutron powder diffractometer; a further discussion is given here
.
In general, a quadratic function of tan(theta) can be an approximate
description of how the peak width varies with scattering angle, even if an
ideal neutron diffractometer is not being used, but then U,V,W may not have
much physical meaning.
Alan.

On 29 August 2016 at 10:36, Yashwanth Padarthi <
yashwanth.padarthi...@gmail.com> wrote:

> Dear sir,
>
> Can i know what is the significance of U,V,W separately?what do they
> signify *if i have a plot of two theta Vs intensity how can one show what
> U,V,W is separately*? i have researched a lot but they are no particular
> significant meaning. i only know they depend on the instrument resolution
> function(IRF) which depends on diffractometer..
>
> Do you have any idea how U,V,W are calculated or refined?
>
> I know this formula by caglioti et al(1958)
> FWHM = (U*tan^2 theta + V*tan theta + W)^0.5
>
> but this doesn't help me knowing the real individual significance like i*n
> fullprof we can actually vary them individually *and see the changes in
> the pattern accordingly by varying U,V,W separately
>
> ++
> Please do NOT attach files to the whole list  >
> Send commands to  eg: HELP as the subject with no body
> text
> The Rietveld_L list archive is on http://www.mail-archive.com/
> rietveld_l@ill.fr/
> ++
>
>
>


-- 
__
*   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE *
 +33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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