Greetings all! I'm trying to explain self absorption for our group's guide to EXAFS and I need some help understanding some of the finer details of self absorption. In the realm of fluorescence EXAFS, am I correct in that at a given energy there is a certain penetration depth of the X-rays that is expected (in a thick, dilute sample), but in a thick, concentrated sample, the penetration depth is actually less than the expected depth in thick, dilute samples (causing the decrease in the amplitude of the oscillation peak in Bruce's "wiggle up" of the XAFS oscillation)? Then, in the "wiggle down" of the XAFS oscillation, the penetration depth is actually more than what would be expected so the depth of the oscillation valley decreases. As a result, for thick concentrated samples like a metal foil, in the "wiggle up," the fluorescence accounts for fewer than expected absorbing atoms and in the "wiggle down" the fluorescence accounts for more than expected absorbing atoms. Next, in our amorphous silicates (doped with Ti, V, Cr, W, or Sn), is the self absorption effect greater in the lower Z elements (like titanium) than in the higher Z elements (like tin)? Does the high background due to the silicon at the lower energies (4.9 keV) in relation to the higher energies (29.2 keV) have an effect or is it just an underlying, independent issue that is more pronounced with the lower Z elements when self absorption occurs? Thanks! -Richard -- Richard Mayes Graduate Research Assistant Barnes Group 450/452 Buehler Hall Department of Chemistry University of Tennessee Knoxville, TN 37996