Re: [Ifeffit] energy resolution

The reason I mentioned using transmission is that you could get to a true back-reflection condition that way, thus removing sensitivity to incidence angle. Another possibility for detecting the reflection is to look for a peak in I0, caused by the back-reflecting beam going back into the I0 chamber. mam On 5/5/2010 11:49 AM, Frenkel, Anatoly wrote:

This is a quote from Joseph Dvorak' report on energy resolution measurements at the NSLS beamlines:

The energy resolution was measured as follows. A Si 220 crystal was used as an analyzer crystal.

This was placed in the hutch in near back reflection condition (87 deg inc). The reflected x-rays were

detected with a Si photodiode. Oriented as such, the analyzer crystal reflects at its fundamental (3233 eV)

and all higher order reflections (440, 660, ...). The beamline monochromator was then scanned

successively through the various reflections of the analyzer crystal. Since the energy bandpass of the

analyzer crystal in back reflection is very narrow compared to the fundamental of the beamline

monochromator (true for all the higher order analyzer crystal reflections, and possibly true for the

fundamental depending on the monochromator crystal), a measurement of the width of the reflected beam

gives a direct measurement of the energy resolution. The second monochromator crystal was set to full

tune.

Anatoly

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From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Matthew Sent: Wed 5/5/2010 2:42 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] energy resolution

That method only works at one energy, and assumes something about the width of the V2O5 feature. Another possible method might be to measure, in back-reflection, a high-order Bragg reflection from a Si crystal. For instance, the 555 reflection would be at 9.9keV. If you put up a 111 Si crystal and did a transmission scan, maybe you could detect the reflection as a transmission dip. You would then play with the orientation of the crystal so that the energy at which this dip occurred was as low as possible, meaning that you were at back-reflection. This condition is useful because it gives the least sensitivity to beam divergence. You could then calculate the Darwin broadening of the 555 reflection to correct the observed value. By choosing different reflections, you could measure the resolution at different energies. Of course, I haven't tried this myself. mam ----- Original Message ----- From: "Bruce Ravel" To: ; "XAFS Analysis using Ifeffit" Sent: Wednesday, May 05, 2010 11:19 AM Subject: Re: [Ifeffit] energy resolution

...

On Wednesday 05 May 2010 02:12:38 pm M Ceolin wrote:

...

Hi all.

I would like to know if anyone knows an experimental method to determine the energy resolution in the XANES region of a XAS spectrum. I do not explored the previous entries in the list so I beg you pardon if it was already discussed. Thank you for the information. Hi Marcelo,

A few years back the folks at the APS used the method described about half-way down the page at:

http://xafs.org/APSXAFS/APS_XOR_Eval

One example evaluation is shown at

http://xafs.org/APSXAFS/APS_XOR_Eval/20BM/EResolution

HTH, B

--

Bruce Ravel ------------------------------------ bravel@bnl.gov

National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973

My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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