A bent Laue analyzer for fluorescence EXAFS detection

An analyzer for detection of fluorescence radiation was developed for fluorescence XAFS of dilute samples at energies above 13 keV. The analyzer is a bent Laue crystal of logarithmic spiral shape. The K fluorescence lines can be collected with a large solid angle and moderate reflectivity using the asymmetric [111] reflection of silicon crystals of 200 micron thick. Tuning of the analyzer diffraction energies for different samples can be made with one adjustment. Experiment was performed at the APS BioCAT ID beamline using a silicon crystal bent to an average radius of 200 mm to diffract silver fluorescence x-rays. The crystal (35 mm by 120 mm active area) covers a solid angle of 0.1 SR of the sample fluorescence. The measured reflectivity was 10%.