MULTILAYER ANALYSER FOR XAFS: X RAY FLUORESCENCE DETECTOR

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The objective of the project is to develop energy-resolving x-ray fluorescence detectors using synthetic multilayers. A 20-element multilayer array detector using graded multilayers was fully tested at the BioCAT beamline. The elements were aligned relative to each other using the fine adjustment mechanism. The detector calibration curve was obtained by rotating all the elements in the diffraction plane with a fixed beam entrance slits. The throughput of the detector is approximately 26%. Similar throughput of the detector was obtained when calibrated at other fluorescence energies, such as Mn, Co, Cu and Zn, with essentially the same throughput. The detector was tested on dilute biological systems. The signal to background ratio is approximately 5 to 1, while the signal to background ratio without the analyzer is 1 to 3. Thus the total rejection rate is approximately 15 times. To improve the throughput of the analyzer detector, we have carefully chosen the factors relative to multilayer deposition, in particular the factors affecting the reflectivity. A 24-element analyzer array detector has been design and are being fabricated. Similar to the 20-element unit, the total detection solid angle is 0.21 at Mn Ka and 0.14 at Zn Ka fluorescence energies. Tests on the unit with 7-elements installed show that the throughput is 35%, much better than the 20-element unit. This new unit will be completed and tested for operation within half year.