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 20899-8523 USA 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 <yashwanth.padarthi...@gmail.com> 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 <yashwanth.padarthi...@gmail.com<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 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> Send commands to <lists...@ill.fr<mailto:lists...@ill.fr>> 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 <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> +33.476.98.41.68 http://www.NeutronOptics.com/hewat ______________________________________________
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> 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/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
