[Ifeffit] Normalization of XANES spectra

[Kelly, Shelly]

Hi Jens,

Here is my stab at pitching in.

The x-ray fluorescence signal is a sum of the signals from all the N
atoms in the sample that are in the x-ray beam. (Assume that the sample
is not too thick so that all the fluorescent x-rays can get out of the
sample.) The background slope of the spectra and the absolute signal
values (detector gain, detector absorption, ect) are removed by
normalizing the XANES signal. What this does is put your absorption
signal on a relative scale rather than an absolute scale. Since the
fluorescence signal is linear combination of the signals from each type
of atomic environment of your sample, we can normalize the spectra and
still get out the percentage of each phase based on its relative
contribution. We can then compare spectra from different beamlines, and
different detectors and come up with a relative percentage of each phase
in the sample(s). We can not get the absolute concentration of that
phase in the sample.

HTH
Shelly

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-
> bounces at millenia.cars.aps.anl.gov] On Behalf Of Jens Kruse
> Sent: Wednesday, October 29, 2008 1:31 PM
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: Re: [Ifeffit] Normalization of XANES spectra
> 
> Thanks for your replay and sorry for the confusing question. but I
think
> it not getting better.
> 
> Scott, you are right LCF would be helpful but even with lot of
standards
> it is hard to get a meaningful result from low concentrated samples at
the
> N k-edge.
> I think my problem is than I don`t understand the physical meaning of
a
> edge step normalized spectra. Is it the spectrum 1 x-ray photon would
> produce? Is it right that I loose the information of the absolute
> concentration after normalization so that I still can identify
relative
> proportions of different compounds with in a sample but I can`t
compare
> different spectra in an absolute way anymore? The extreme case would
be a
> comparison of pure and a diluted spectra.
> 
> jens
> 
> 
> 
> 
> 
> 
> 
> 
> ifeffit-request at millenia.cars.aps.anl.gov schrieb:
> > Send Ifeffit mailing list submissions to
> > 	ifeffit at millenia.cars.aps.anl.gov
> >
> > To subscribe or unsubscribe via the World Wide Web, visit
> > 	http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> > or, via email, send a message with subject or body 'help' to
> > 	ifeffit-request at millenia.cars.aps.anl.gov
> >
> > You can reach the person managing the list at
> > 	ifeffit-owner at millenia.cars.aps.anl.gov
> >
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Ifeffit digest..."
> >
> >
> > Today's Topics:
> >
> >    1. Normalization of XANES spectra (Jens Kruse)
> >    2. Re: Normalization of XANES spectra (Frenkel, Anatoly)
> >    3. Re: Normalization of XANES spectra (Scott Calvin)
> >
> >
> >
----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Wed, 29 Oct 2008 15:02:54 +0100
> > From: Jens Kruse <jens.kruse at uni-rostock.de>
> > Subject: [Ifeffit] Normalization of XANES spectra
> > To: ifeffit at millenia.cars.aps.anl.gov
> > Message-ID: <49086D0E.2000603 at uni-rostock.de>
> > Content-Type: text/plain; charset="ISO-8859-15"; format=flowed
> >
> > Hi everyone,
> >
> > I have a general question:
> > I know Normalizing is something we do so that we can compare samples
> > measured
> > under different experimental conditions (removes the effect of
different
> > gains ...) but I have problems in understanding and applying
> > normalization when also quantitative conclusions are needed when
> > comparing different spectra.
> >
> > If I have two XANES spectra (a) and (b) measure under the same
> > conditions but with different concentration of the absorbing atom
with
> > in different molecules.If both normalized spectra show a peak 1 ,
but
> > this peak is higher in intensity in spectrum (a) than in spectrum
(b),
> > does this mean that compound which produced peak 1 is also absolute
> > higher in concentration in sample/spectrum (a) or do I loose this
> > information after normalization?
> > Or can I just say: in the normalized spectrum (a) peak 1 is higher
than
> > peak 2 suggesting that the compound leading to peak 1 is more
abundant
> > (just relative proportions).But I can't say: The intensity of peak 1
in
> > the also normalized spectrum 2 is lower than in spectrum one,
Therefore,
> > the compound leading to peak 1 is less abundant in spectrum/sample
> 2. ????
> >
> >
> > I hope somebody can help me to understand this issue.
> >
> > Thanks a lot,
> >
> > jens
> >
> >
> 
> --
> Jens Kruse
> Institute for Land Use
> Faculty for Agricultural and Environmental Sciences
> Rostock University
> Justus-von-Liebig-Weg 6
> 18059 Rostock GERMANY
> Phone: +49(0)381-498 3190
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit