[Ifeffit] Is good EXAFS data possible with 0.01 transmission coefficient

[Scott Calvin]

Oops--Matthew's interpretation is doubtless what you actually meant--i.e., that It < 0.01 I0. Therefore disregard my previous comment!

And I concur with Matthew's comments, now that I understand the circumstances.

--Scott Calvin
Sarah Lawrence College

On Jul 25, 2013, at 4:33 PM, Matthew Marcus <mamarcus at lbl.gov> wrote:

> Is most of the transmission loss due to the Mn  or the matrix (C, KOH, etc)?  Is that 0.01 above or below the edge?
> If most of the absorption is due to the matrix with the Mn providing an edge jump of <1, then I'd say that you have a shot.
> However, you become very sensitive to harmonics and glitches.  If the Mn provides an edge jump of much less than 1, them fluorescence
> would be the way to go, if possible.  With thick samples in transmission, you have an issue with hole effect.  For instance, it's
> possible that your 1% transmission comes entirely from 1% area of pinholes, with the actual material being almost completely
> opaque.  If that happens, you get a reduced edge jump and reduced EXAFS amplitude, with distortions resembling overabsorption.
> 
> If you're in the thick-matrix scenario, a possible workaround would be to make a sample which contains only matrix and is as nearly as
> possible exactly as thick as the real sample, and measure its transmission, and subtract.
> 	mam
> 
> On 7/25/2013 1:07 PM, Damon Turney wrote:
>> Hi IFEFFIT community,
>> 
>> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
>> sample is a powder mixture of carbon powder, MnO2 powder, and
>> potassium hydroxide liquid.  The transmission coefficient of 6.5keV
>> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
>> 0.01.  I am told that the ionization chamber detectors can easily
>> detect the x-ray beam after this ~0.01 transmission loss (by
>> increasing the gain on the detector), but I would like to ask the
>> IFEFFIT community if there will be other problems with the EXAFS
>> technique when the transmission coefficient is so low.  Does anybody
>> have comments?
>> 
>> Much thanks -- if you have any info I greatly appreciate it!
>> Damon Turney
>> City College of New York
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