Andrew, I suspect that you are seeing what Grant refers to in his tutorials as "leakage". That is, your transmission data appears to my eye to be what happens when you have a wide spread in sample thickness under the beam, ranging from gaps to very thick particles. If you go to http://gbxafs.iit.edu/training/tutorials.html And follow the link to the "Sample preparation" presentation, the effect of leakage is shown on slide 16. On the following slide, Grant points out that this thickness effect always reduces amplitudes. That is the case above the edge for your data. And if you normalize data distorted in that way, you end up with an artificially enhanced pre-edge peak, again as in your data. My US$0.02, B On Wednesday 05 May 2010 09:55:16 am Andrew Campos wrote:

Hi everyone,

My lab mates are running in-situ H2 reduction of Cobalt/SiO2 catalysts using the Co K-edge and are obtaining differences between the fluorescence and transmission signals. The in-situ cell does have quite a bit of sample thickness (2-3 mm approx) and I was wondering if the fluorescence signal only has a penetration depth of a few micrometers. If this is the case that would explain it where the side that is further away from the heating element is more oxidized than the rest of the sample.

Has anyone run into this problem before? We're using the basic furnace/cryostat unit (in-situ cell manufactured by the exafsco) and a 13 element fluorescence detector (germanium diode).

I appreciate any insight into the issue, I have attached a fluorescence and transmission spectrum collected at the same time where the transmission and fluorescence are in the .prj file.

Thanks so much! Andrew

-- Bruce Ravel ------------------------------------ bravel@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/