[Ifeffit] Is it legitimate to merge transmission data with fluorescence data?

Maurits van den Berg maurits.vandenberg at techem.rub.de
Tue Aug 11 02:44:27 CDT 2009

Dear All,

Just picking up on Bruce's point about self-absorption. If you are using 
Viper <http://www.cells.es/Beamlines/CLAESS/software/viper.html>, I know 
that there is a way of correcting the measured fluorescence data for 
self-absorption. This correction is based on work by Tro"ger 
<http://prola.aps.org/abstract/PRB/v46/i6/p3283_1> et al., and is quite 
easy to perform, using the "corrections" button in the "get chi" box of 
Viper. Of course the correction is based on an /estimation/ of the 
"real" self-absorption...

Best wishes,

Bruce Ravel wrote:
> On Monday 10 August 2009 06:13:32 pm jrkizews at ncsu.edu wrote:
>> Dear XAFS community members,
>> I have a question concerning data merge. We normally collect XAFS data in
>> both transmission mode and fluorescence mode. We normally have to merge a
>> few scans to enhance signal-to-noise ratio. For one particular sample, I
>> want to know if it is legitimate to merge its transmission scans with its
>> fluorescence scans to improve data quality?
> Hi Fiona,
> There is no a priori reason not to do so and certainly not a numerical
> reason.  From a numerical perspective, you can merge anything with
> anything! 
> My one concern is that the fluorescence and transmission data are
> really equivalent.  That is, if the fluo data are affected by
> significant self-absorption attenuation or if the transmission data
> suffer from significant pin-hole effects, then you run the risk of
> degrading the entire data set by doing the merge.  But if the data are
> merely noisy, then I think you are safe doing so.
> Think about it this way: when you use a multi-element detector, you
> are making several measurements which are presumed to be identical.
> We routinely merge the channels of an MED.  You situation is, from a
> measurement theory perspective, analogous.  Assuming your data do not
> suffer from the problems mentioned above, it seems all right to me.
> B

Dr. M.W.E. van den Berg
Ruhr Universitaet Bochum
Lehrstuhl fuer Technische Chemie
Gebaeude NBCF-Sued 04/686
Universitaetsstrasse 150
44780 Bochum
Tel.: +49-234-3226907
Fax:  +49-234-3214115
E-mail: Maurits.vandenberg at techem.rub.de

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