X-Ray Absorption-Based Methods

FIGURE 7.12 X-ray powder diffraction patterns of a soil clay fraction untreated (top) and treated (bottom) with dithionite-citrate-bicarbonate attack, which removes all secondary Fe oxides Cn = a-AljOj (corundum) Gt = goethite Hm = hematite PS = phyllosilicates and Qz = quartz. Hematite identification is uncertain because of strong overlap with phyllosili-cate and goethite peaks, hence the question marks. Samples contained a-Al203 as an internal standard. (Reprinted from Schulze, D. G., Clays Clay Miner. 34, 6, 681-685, 1986. With permission from the Clay Minerals Society.) 

FIG U RE 7.13 Schematic representation of the main processes involved in the interaction of x-ray radiation with matter there are also other processes (i.e.. Auger electrons and electron-positron pair formation) that are usually minor and not represented here. 

FIGURE 7.14 X-ray absorption spectroscopy (XAS) spectrum of arsenate with the x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) regions indicated. (Reprinted from Luo, L., and S. Zhang, Sci. China Chem. 53, 12, 2529-2538, 2010. With permission from Science China Press.) 

Rehr and Ankudinov 2001). It is worth mentioning at this point that these techniques often require high-intensity x-ray beams, which can only be obtained from a synchrotron facility thus, its application is limited by the availability of such equipment. 

Sq is the passive electron reduction factor the number of neighbors of type i at a distance R f(E), the amplitude of the scattering wave from the neighbor of type i a factor describing static and dynamic disorders k(]C) the mean free path of the photoelectron, a phenomenological term accounting for inelastic losses and /fe) 

---