Re: [Ifeffit] Ifeffit Digest, Vol 155, Issue 16

[Christopher Thomas Chantler]

Dear Jason
Good topic

We have published a few papers discussing analysis with thickness distributions 
and roughness. Normally the XERT method will address this especially for small 
samples.

Particularly see J. L. Glover, C. T. Chantler, M. D. de Jonge, ‘Nano-roughness 
in gold revealed from X-ray signature,’ Physics Letters A373 (2009) 1177-1180. 
The general topic of thickness effects is of course wider, and partially 
addressed in a couple of other papers.

Hope this helps
Chris

Christopher Chantler, Professor, FAIP
Editor-in-Chief, Radiation Physics and Chemistry
Chair, International IUCr Commission on XAFS
President, International Radiation Physics Society
School of Physics, University of Melbourne
Parkville Victoria 3010 Australia
+61-3-83445437 FAX +61-3-93474783
chant...@unimelb.edu.au chant...@me.com
http://optics.ph.unimelb.edu.au/~chantler/xrayopt/xrayopt.html
http://optics.ph.unimelb.edu.au/~chantler/home.html



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Subject: Ifeffit Digest, Vol 155, Issue 16

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Today's Topics:

   1. Re: Effect of gradual thickness variation in beam (Jason Gaudet)


--

Message: 1
Date: Fri, 29 Jan 2016 14:32:43 -0500
From: Jason Gaudet 
To: XAFS Analysis using Ifeffit 
Subject: Re: [Ifeffit] Effect of gradual thickness variation in beam
Message-ID:

Content-Type: text/plain; charset="utf-8"

Hi Anatoly,

Sorry, I meant to write 1000 um inner diameter.

Energies will be V and Fe, 5465 & 7112 eV.  Samples are roughly 1
absorption length thick for the metal (V, Fe) and about 2-2.5 absorption
lengths for the entire sample.

Bruce,

I may just flip over the sample holder and have the sample tubes in plane
with the storage ring to take advantage of the greater horizontal spread,
rather than focusing on the vertical.  Cutting the vertical slits down to
100-300 um while keeping the horizontal around 500 um ought to get me the
most beam at the least variation in mu(E), especially if I go with 1500 um
ID tubes.  The samples are nice and concentrated so I can afford to give up
a lot of photon flux.  Bar-napkin calculations tell me with a 1500 um ID
tube and 200 um V 750 um H slits I'll lose an acceptable amount of photon
flux and have a <1% thickness variation.  I'm fairly confident I've made
pressed pellets with as much or more variation from one spot to another,
without noticeable mu(E) changes from spot to spot, in the vicinity of this
energy range.

I'll go ahead and take your advice, and amend my setup procedure with some
measurements of Io intensity and mu(E) reproducibility as a function of
slit width.  While a bit of a bother, it's still worth it to keep our
sample prep simple and inexpensive.

Thanks,

Jason


On Thu, Jan 28, 2016 at 9:12 AM, Bruce Ravel  wrote:

> On 01/27/2016 07:05 PM, Jason Gaudet wrote:
>
>> I'm planning on some transmission-mode XAS with smaller than usual
>> sample tubes.  I'm realizing I might be in danger of creating excessive
>> non-uniformity in my samples by having the beam size on the same order
>> of magnitude as the sample tube radius.
>>
>> For example, let's say I want to measure liquid in a sample tube with a
>> 1000 micron outer diameter, with a beam 500 microns wide and centered on
>> the sample tube. If the tube is orthogonal to the ring plane, the entire
>> vertical portion of the beam will pass through the same length of
>> liquid.  But in the horizontal plane, the center of the beam will pass
>> through 1000 microns of sample while the edges of the beam will pass
>> through 866 microns of sample, due to the curvature of the sample cell
>> across the horizontal plane.
>>
>> Most of what I know about the statistics of thickness effects are about
>> leakage and pinholes - nonlinearity caused by a few spots having very
>> low or negligible sample thickness.  But I don't know how significant a
>> "mild" thickness distribution might be.  If this sort of thickness
>> distribution is going to be an issue it would be 

[Ifeffit] pi/2deltak

[Ritimukta Sarangi]

Hello,

I was recently asked about the accuracy of this formulation for obtaining
EXAFS resolution and I did not have a good answer. Can someone point to a
reference or explain here?
Thank you for your time,
Best,
-Riti
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