Extended X-ray absorption fine structure (EXAFS) analysis of zinc sorption on montmorillonite showed that different types of surface complexes or surface precipitates were formed depending on the reaction time. With an initial zinc concentration of 10(-3) M at neutral pH, zinc remained octahedrally coordinated with about six oxygen atoms at Zn-O bond distances of 2.02-2.07 A for up to six months. For samples aged up to 11 days, the Zn-Zn contribution in the second shell suggested formation of multinuclear surface complexes or surface precipitates. For samples aged 20 days and more, Zn-Zn and Zn-Si contributions in the second shell suggested formation of mixed metal coprecipitates such as a Zn phyllosilicate-like phase. Formation of these mixed metal solids probably accounts for the slow continuous sorption reaction at aging times exceeding 20 days. Sequestration of Zn in mixed metal precipitates and the stability of these phases can reduce the concentration, mobility, and toxicity of Zn in soils or sediments.

A highly strained, curved silicon crystal in the Laue geometry has been used as a large-area x-ray fluorescence analyzer for x-ray absorption spectroscopy. The analyzer is able to resolve the Lα fluorescence lines for neighboring actinide elements. A large gain in the signal to background ratio has been demonstrated for small quantities of Np in the presence of U, with the U fluorescence peak approaching 1000 times the magnitude of the off-peak background.

We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA-about 14 eV at the Cu Kα line-allows resolution of the Cu Kα 1 and CuKα 2 lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position-typically CuKα 1 line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu.

There is a growing interest in the biomedical community in obtaining information concerning the distribution and local chemical environment of metals in tissues and cells. Recently, biological X-ray fluorescence microscopy (XFM) has emerged as the tool of choice to address these questions. A fastscanning high-flux X-ray microprobe, built around a recently commissioned pair of 200 mm-long Rh-coated silicon Kirkpatrick-Baez mirrors, has been constructed at BioCAT beamline 18ID at the Advanced Photon Source. The new optical system delivers a flux of 1.3 Â 10 12 photons s À1 into a minimum focal spot size of $ 3-5 mm FWHM. A set of Si drift detectors and bent Laue crystal analyzers may be used in combination with standard ionization chambers for X-ray fluorescence measurements. BioCAT's scanning software allows fast continuous scans to be performed while acquiring and storing full multichannel analyzer spectra per pixel on-the-fly with minimal overhead time (< 20 ms per pixel). Together, the high-flux X-ray microbeam and the rapid-scanning capabilities of the BioCAT beamline allow the collection of XFM and micro X-ray absorption spectroscopy (microXAS) measurements from as many as 48 tissue sections per day. This paper reports the commissioning results of the new instrument with representative XFM and microXAS results from tissue samples.

The Biophysics Collaborative Access Team (BioCAT) undulator beam line at the Advanced Photon Source, Argonne, IL is a user facility devoted to the study of partially ordered and disordered biological materials by X-ray scattering, diffraction and absorption spectroscopy. Two sagital focussing, double-crystal (Si(111) and Si(400)) monochromators and a 1 m mirror provide monochromatic, horizontally and vertically focussed X-ray beams in the range of 4-35 keV. The small focal spots produced by this optics are well matched to novel XAFS detectors developed by BioCAT: a multilayer analyzer array and Bent Laue crystal based analyzers. Fast on-the-fly scans (∼5 s/scan) have been implemented to take full advantage of the high X-ray flux at the Advanced Photon Source. Such fast scans not only allow high throughput but also reduces radiation damage to labile biological samples. A closed-cycle displex cryostat is routinelly used for low temperature XAS measurements. For continuous flow and time resolved XAS experiments, a dual syringe stopped-flow system has been implemented.