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Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637
The ability of high-energy synchrotrons to produce highly collimated, intense
x-ray radiation makes them ideal sources for x-ray microprobe analysis of earth
and environmental materials. Such synchrotron based x-ray microprobes allow for
trace element quantification (x-ray fluorescence), chemical speciation
determination (x-ray absorption spectroscopy), and phase identification (x-ray
diffraction). In the design of such instruments Kirkpatrick-Baez mirrors have
proved particularly useful for producing x-ray microbeams because of their
achromaticity, photon density gains in excess of 104, and long working
distances (centimeters). In the earth and environmental sciences, instrument
development and utilization has been driven by the need for the determination
of material compositions, structures, oxidation states, and bonding
characteristics with trace element sensitivity and micrometer spatial
resolution. A number of examples will be discussed that show flexibility of
this technique, but two particular examples will be highlighted. These include
the use of x-ray fluorescence analysis and x-ray absorption spectroscopy in
evaluating the contaminant history of Ni, U, and other metals within annual
rings of willows ( Salix nigraL.) from a former de facto radiological settling
basin (Punshon, et al., 2003). We'll also examine how x-ray microbeam
compositional imaging, absorption spectroscopy, and diffraction techniques have
been used to quantify the co-existence of As3+ and As5+ in oxidized rims of
roaster iron oxide grains in mine tailings from gold mining activities in the
Yellowknife area (Canada).
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