[Ifeffit] Basic question in normalization and background removal

[Bajamundi Cyril]

Thank you Bruce. I'll take your suggestions into consideration.

Warm regards, 
Cyril


-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Bruce Ravel
Sent: Friday, February 08, 2013 3:45 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Basic question in normalization and background removal

On Friday, February 08, 2013 01:22:14 PM Bajamundi Cyril wrote:
> My first naïve approach to the approximation  of the normalization 
> range is to choose a range such that the post-edge line is parallel 
> with pre-edge line, this in my novice eyes this seems to be the case 
> between these line two lines, at least in the XANES range. This 
> observation came from playing with some spectra in the databases I 
> found online. May I know the pitfalls of this approach?

Pre- and post-edge lines are sometimes parallel, but not in general.
As I said, the details of the sample and the method of measurement have a lot to do with what the data look like.

I really cannot answer your question in general.  What you suggest may work for you, it may not.  At the end of the day, the defensibility of an analysis is the bottom line.  Can you convince your reader (or thesis advisor or potential boss in a job interview or whatever) that your intepretation of the analysis of your data is correct?

In the context of linear combination fitting, you have another tool at your disposal.  You can prepare defined mixtures of your standards and measure those the same way youmeasure your actual data.  If your normalization procedure and LCF analysis works on the defined mixtures and gives an answer that is consistent within its uncertainty with how you made the mixtures, that gives you confidence that you can correctly analyze the unknowns.

Of course that means spending an hour or two at the beamline measuring those defined mixtures.  That takes time away from measuring the real samples.  But if you end up in a better position to interpret the real data, that seems like a win to me.

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

 Homepage:    http://xafs.org/BruceRavel
 Software:    https://github.com/bruceravel

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