[Ifeffit] Fwd: Athena troubleshooting

[Bruce Ravel]

On Wednesday 07 October 2009 05:14:44 pm Bruce Ravel wrote:
> I have run 14 samples (each 4 times) on the beamline, and I'm looking for a
> shift in the oxidation state of Uranium (4+ to 6+).  I'm not sure and can't
> seem to find any literature on how significant the shift must be to prove
> anything. 

That surprises me.  The literature on XAFS studies of uranium valence
is enormous, much of it written by people who read this mailing list.
Hopefully one of those fine people will offer up a wealth of
suggestions for places to look.

> Of the 14  samples the uranium peaks for almost all are the
> samples are at 17160 eV, however a couple samples are at 17158 and another
> at 17159 eV.  The beamline was filtered for both Thorium and Strontium and
> a zirconium foil standard was implemented.  I have aligned all of the
> zirconium standards peaks, and still have this slight shift in the energy
> of uranium. Do you have any insight?

See my comment below on the value of attaching a small project file
which demonstrates the problem.

> Also, this is more of a software question.  I'm not sure why, but about
> half of the samples flip their orientation 180 degrees (from positive y to
> negative y) when "normalizing" them.  But when I'm trying to display
> several samples at once about half are showing positive peaks and half are
> negative peaks.  For instance, samples 10, 3 and 1 don't flip when
> normalized, however all of the other samples do. 

I don't really know what you are talking about, but I suspect that you
have poorly chosen values for the pre-edge or nromalization
parameters:

   http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/bkg/norm.html
   
This is a situation where preparing a small project file which
deomnstrates the problem and posting it along with your question to
the mailing list is the most productive course of action.  With a
project file, one of us has a chance to replicate your problem on our
own computer.

It is really important to remember that if the person of whom you are
asking your question cannot replicate the problem, it is highly
unlikely that person can actually answer your question.  One of the
points of the Athena project file is to allow exactly this sort of
communication.

> If this isn't a good enough explanation I could send files or we
> could trouble shoot over the phone.

I don't do telephone support for the software.  There are far too many
users for that sort of thing.  Don't call.  Use this mailing list.

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

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/