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Biological XAFS at the BioCAT undulator beamline 18ID at the APS

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 routinely used for low temperature XAS measurements. For continuous flow and time resolved XAS experiments, a dual syringe stopped-flow system has been implemented.