An Energy-Resolving X-ray Fluorescence Detection System

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An energy-resolving x-ray fluorescence detector system has been proposed. The detector system uses the concept of selecting x-ray fluorescence from an elastically scattered background by the diffraction from a synthetic multilayer. The multilayer will be linearly graded as to satisfy the diffraction condition everywhere on the multilayer. Preliminary evaluation shows that such a detector can be made with a good energy resolution (sufficient background rejection), large solid angle, and fast time response. The project will be carried out in two phases. The first phase of the project is to simulate the performance of such a detector and to fabricate a prototype detector with 3-4 multilayer elements. Based on the results of Phase I, a multilayer analyzer array detector containing 40 multilayer elements will be developed in Phase II. The detector will be tested and used by research groups on various metalloproteins. Since the use of graded synthetic multilayers for fluorescence energy selection, to our knowledge, is an original idea, we try to come up with more detailed designs and procedures. The evaluation of the performance of the proposed detector shows that it is more efficient than the currently operating detectors, such as the 13-element Ge detector and ionization chamber, when collecting data on a bending magnet beamline using a few mM sample. The advantages of the array detector become more evident under the conditions of increased photon flux and/or decreased sample concentration. The detector will provide tremendous opportunities for conducting XAFS experiments either on time-resolved transient states or on very dilute systems at third generation synchrotron sources, such as the APS. The detector will greatly benefit the research projects of the P.I. in the same fashion by largely improved efficiency and data quality. However, due to the page limitation and the nature of this proposal, the scientific aspects of these projects are not discussed. The cost for co nstructing the detector is comparable to the cost for purchasing a 13-element Ge detector, and is well justified in view of the efficient increase and the cost for building new beamlines. In addition, long term operation and maintenance are planned (see Section I. Special Information) to insure the access of a wide circle of potential users to the detector through its useful life.