[Ifeffit] energy resolution

[Matthew Marcus]

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
> 
>  
> ________________________________
> 
> From: ifeffit-bounces at 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" <bravel at bnl.gov>
> To: <mrceolin at yahoo.com.ar>; "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
> 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 at 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 at millenia.cars.aps.anl.gov
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>>
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