It's a VERY old can of worms - been there got the T-shirt which by now is very worn and full of holes. Give the standard approach a try. I never did the stand-alone primary parallel mirror but the twin mirrors gave me a LP factor equivalent to unpolarized (the focusing one didn't)
-----Original Message----- From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of Julian R Tolchard Sent: Monday, 07 April, 2014 4:48 PM Cc: rietveld_l@ill.fr Subject: RE: Re[4]: Polarization factor por Ge (111) monochromator I seem to have opened up a can of worms here. Sorry about that. So in summary: 1. Easiest option is to use a value of 0 and accept that thermal parameters will be a bit wrong 2. Second easiest option is to measure a well characterized standard and refine the polarization. 3. Harder option is to hire a clever physicist to model the system and calculate a value via ray-tracing? It strikes me as a little surprising that we are all buying these, but the associated corrections are not well documented... jools ________________________________________ From: Whitfield, Pamela S. [whitfiel...@ornl.gov] Sent: 07 April 2014 21:31 To: Artem Babaryk Cc: Julian R Tolchard; rietveld_l@ill.fr Subject: RE: Re[4]: Polarization factor por Ge (111) monochromator If you want some REALLY ancient history try this one... http://www.mail-archive.com/rietveld_l%40ill.fr/msg01654.html The email from Nicolae is perfectly correct and I don't think anyone would argue with it for monochromators. The formulae themselves should be just as applicable to mirrors and summing all the effects from differing diffracting angles of the mirror should give a decent average but there are some devils in the details. Consider a flat plate experiment with a parallel mirror. Different parts of the sample will be hit by X-rays that have been diffracted by different angles off the mirror due to the construction. If the diffracted beam isn't 'averaged'/collapsed by using a secondary optic/0D detector does it make a difference? Makes for an interesting puzzle? Pam -----Original Message----- From: Artem Babaryk [mailto:baba...@bigmir.net] Sent: Monday, 07 April, 2014 3:14 PM To: Whitfield, Pamela S. Cc: Julian R Tolchard; rietveld_l@ill.fr Subject: Re[4]: Polarization factor por Ge (111) monochromator Hi everybody, Nobody is trying to be prickly (at all)! The topic has been started with particular case for Panalytical machines, and, again, a 'minute quote' from archive: "This is obtain from the help of X'Pert HighScore Plus..." As the first instance question is so the same kind of answer is coming... And I would never made a feedback if I was not curious to the topic too. I remember following branch clearly: http://www.mail-archive.com/rietveld_l%40ill.fr/msg04948.html And to be really pricky and boring=), see http://www.mail-archive.com/rietveld_l%40ill.fr/msg04979.html That makes me think again that there is nothing new under the sun... Between, I like to send postcards=) Cheers, Artem 07.04.2014 19:00, "Whitfield, Pamela S." <whitfiel...@ornl.gov> >Now, now no need to be prickly > > To be fair to Julian he didn't ask what the polarization was - he > asked how it was calculated. Given that Goebel mirrors are graded > multilayers (i.e. not a fixed diffracting angle) it's a fair question > and one I asked myself in 2001. As the 'minute quote' demonstrates > with the lack of d-spacing, etc, the value of 0.999 seems to have been > picked from thin air > > The experimental (as opposed to theoretical) methodology for > determining polarization was posted on the CCP14 website many moons > ago by Bob Von Dreele > http://www.ccp14.ac.uk/solution/gsas/graphite_monochromator_and_gsas.h > tml > > I also used the same sort of methodology for a focusing mirror. That requires > a little bit of lateral thinking to cancel out the effect of capillary > absorption - answers on a postcard! > > Pam > > -----Original Message----- > From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On > Behalf Of Artem Babaryk > Sent: Sunday, 06 April, 2014 4:21 PM > To: Julian R Tolchard > Cc: rietveld_l@ill.fr > Subject: Re[2]: Polarization factor por Ge (111) monochromator > > Dear Julian, > > Here is a minute quote following the link to the excerpt from the Rielveld > Mailing list archive I've posted below: > > "Monochromator Wavelength [Å] Material Reflection /d/-spacing [Å] 2/θ/_m [°] > POL ... > All mirrors All wavelengths - - - - 0.999 " > Just be attentive... > > Cheers, > Artem > > 06.04.2014 23:00, Julian R Tolchard <julian.r.tolch...@ntnu.no> > >Whilst we are on the topic - is the polarization factor from a Göbel mirror > >calculated the same way as for a mono? > > > > > > ________________________________________ > > From: rietveld_l-requ...@ill.fr [rietveld_l-requ...@ill.fr] on > > behalf of Artem Babaryk [baba...@bigmir.net] > > Sent: 06 April 2014 20:56 > > To: Josu Friedrich > > Cc: rietveld_l@ill.fr > > Subject: Re: Polarization factor por Ge (111) monochromator > > > > Dear Josu, > > > > Somethimes browsing the Rietveld list archive I'm strengthening > > myself that there is nothing new under the sun... > > > > So, look there: > > > > http://www.mail-archive.com/rietveld_l%40ill.fr/msg05129.html > > > > Best, > > Artem > > > > 06.04.2014 20:11, Josu Friedrich <josue.friedr...@gmail.com> > > >Good afternoon, > > > > > > Does anyone know the polarization factor for an incident beam germanium > > > (111) monochromator used in a Panalytical XPert Pro diffractometer? > > > > > > Many thanks, > > > Josue
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