BEAMLINE OPTICAL COMPONENTS & DETECTOR CHARACTERIZATION: SYNCHROTRON RADIATION

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In the first year since first light (year three of five for the project) we demonstrated that the BioCAT undulator line is a superb instrument for Biological fiber diffraction. The bulk of recent activities have aimed towards making it a similarly high performance instrument for X-ray absorption spectroscopy. We have made significant progress towards this goal. Technological developments that have occurred include removal of the APS commissioning window to obtain good flux at the low energy end of the spectrum. Another development essential for low energy operation was commissioning of the cryogenically cooled Si(111) first monochromator crystal with an energy range of 3.4 KeV to 14.6 KeV. The x-ray flus has been measured in the range of 1 to 3 x 1013 photons/sec/100 ma. The second monochromator was commissioned with water cooled Si 400 crystals to provide high energy resolution from 7.9 to 33.8 keV. We will be upgrading this to cryo-crystals in the next few months. Obtaining good XAS data from dilute specimens has been a struggle. Much of our effort over the past year has been focussed on improving the stability of the monochromator and linearity of response of the X-ray detectors. Recently, we recorded XAS form 0.5 mM Cu-Carbonate using a Lytle fluorescence X-ray detector with a filter and soller slits. We were able to obtain good statistics from this system in a single scan at 1 s/point. The Multilayer analyzer detector (designed to obtain data from dilute specimens at full flux of the APS) requires the X-ray beam to be focused to 100 micrometers or less and to be stable to ~10 micrometers. We are close to achieving this goal. Another recent development is slew-scanning whereby the monochromator energy is scanned continuously with an encoded DC-servo motor and data recorded on the fly to prevent deterioration of specimens in the beam. The current approach allows us to record a 1000 eV XAS scans in 80 seconds with approximately 2 eV resolution.