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An analyzer for detection of fluorescence radiation has been developed for XAFS of dilute samples in the 15–25keV range. The analyzer is a thin bent Laue crystal of logarithmic spiral shape held in a machined frame. A large solid angle of k fluorescence lines can be collected with moderate reflectivity using the asymmetric [111] reflection of a silicon crystal 200 microns thick. The crystal (35mm by 120mm active area) covers a solid angle of 0.1 sr of the sample fluorescence. A set of Soller slits to match the virtual x-ray source and reject scatter were designed and fabricated. Experiments were performed at the APS BioCAT and MRCAT ID beamlines using silver fluorescence x-rays. Measurements of the performance of this device and plans for a detection system are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A ‘beam cleaner’ for selection of a harmonic from the beamline monochromator and rejection of other harmonics has been developed using a bent Laue crystal post-monochromator. This is a set of cylindrically bent Si (111) crystals that are aligned to diffract the 2nd harmonic (3× fundamental) from the beamline Si (111) monochromator. This device will reject the fundamental and other harmonics up to the Si (999) reflection from the monochromator. It has particular advantages over a flat crystal device since the reflectivity width is approximately 0.2 milliradian. This makes it insensitive to vibration and alignment errors. Over a narrow energy range it does not require adjustment. The diffraction efficiency of each crystal at 25 keV is ∼80% with an overall efficiency of the crystal pair ∼60%. The device is intended to be used for EXAFS at higher x-ray energies using the beamline monochromator harmonic. An additional benefit is that the crystal set can be passively adjusted to nearly eliminate (to the micron level) the vertical beam motion of a channel-cut mode beamline monochromator. Measurements and plans are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]