Jools,
To get the value more directly I think you can also measure the
scattering at two theta of 90 degrees in the horizontal versus vertical
plane. We did this last week at the synchrotron in the course of making
some detector correction files and there was a nice hole in the
diffraction patterns in the horizontal due to the polarisation. If you
set up the right experiment it should be very obvious what the
polarisation is and not at all mysterious.
Cheers,
Jon
On 07/04/2014 22:48, Julian R Tolchard wrote:
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 Tolchardjulian.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
