[Ifeffit] S02 selection from reviewer

[Kelly, Shelly D.]

Hi Peng:

It might be helpful to understanding some of Matt's points regarding S02 transferability, Ei and energy resolution by looking at this paper. 

Comparison of EXAFS foil spectra from around the world 
DOI: 10.1088/1742-6596/190/1/012032 

Kind regards,
Shelly

-----Original Message-----
From: Ifeffit <ifeffit-bounces at millenia.cars.aps.anl.gov> On Behalf Of Matthew Marcus
Sent: Saturday, October 2, 2021 9:04 AM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: Re: [Ifeffit] S02 selection from reviewer

Since S02 is a parameter in the description of EXAFS and not of the experiment, it's independent of technique.  Overabsorption (misnamed
'self-absorption') can reduce the *measured* amplitude, an effect which can be fudged in analysis by reducing S02.  If the sample is truly homogeneous (on the scale of the absorption length), then you can calculate the amount of overabsorption to see if it's significant. 
However, many kinds of samples, such as concentrated powders mixed with a diluent such as BN, this condition is not met.  If the particles are large enough for each to have significant absorption edge jumps, then diluting them in BN doesn't fix the problem.
	mam

On 10/2/2021 12:49 AM, Peng Liu wrote:
> Dear IFEFFIT members,
> 
> I am sorry to bother you again. I asked about S02 selection for the 
> first major revision. I just received the second revision. The 
> reviewer is not satisfied with one S02 value for all our samples.
> "
> 
> 1. I am still not satisfied with selected SO2 value (it is set to 0.85). 
> SO2 is not transferable between different samples and detection methods. 
> It is not possible to use a value obtained from different compound 
> using transmission measurement mode to completely different other 
> compound measured using fluorescence mode. One method to fix SO2 value 
> is to measure diluted solution (to avoid self-absorption) of reference 
> material in fluorescence mode. Other is to use multiple spectra 
> fitting for all samples of interest (e.g. with Sb(V)) measured using 
> fluorescence mode where SO2 parameter is the same for all samples.
> 
> At the same time I am confident that CN values 5.6, 7.1 and 6.9 
> correspond to CN(Sb-O)=6. I suggest reconsidering the SO2 value for 
> measurements in fluorescence mode.
> 
> "
> 
> We do get the S02 from a similar reference material measured in 
> transmission mode, and our samples were all measured in fluorescence 
> mode. It is not possible to measure the diluted reference material in 
> fluorescence mode in one or two months. If you could give me some 
> suggestions, that would be great.
> 
> 
> --
> Best Regards,
> 
> Peng Liu
> 
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