It has become a general consensus that the development of better XAS detector systems is urgently needed to solve the problem of detectors are lagging behind synchrotron sources. The multilayer analyzer array detector (MAAD) using linearly graded multilayers has been successfully developed to handle the large photon flux from the third generation sources. However, this type of detector has limited detection solid angle restricted by its vertical and horizontal acceptance. The detectors will suffer large loss of throughput as well as degraded energy resolution if horizontal acceptance angle is increased from the current 0.4 radian level. The detection situation, with count rate limitation at 1 hand and the detection solid angle at the other, not only limits the effective use of the powerful third generation and beyond synchrotron sources, but also puts excess radiation burden on biological samples. We now propose to substantially increase the horizontal acceptance angle by using """"""""radial gradient multilayers"""""""" (instead of linearly gradient multilayers) in the multilayer array detector design. This will give a 2.5 times of solid angle increase over the linearly graded MAAD without too much complication in the detector design. Furthermore, the radial gradient multilayer detector will have a substantial improvement in throughput, and a large reduction in energy resolution. Defining the Figure of Merit of the fluorescence detector as the product of solid angle and throughput divided by the energy resolution, the Improvement of the Figure of Merit of the new design is 5 to 10 times. The detector is very desirable in the soft x-ray region due to its superb energy resolution and large solid angle. In Phase I, we will fabricate a prototype detector consists of 2 radial gradient multilayers, and will evaluate its performance in 2-8 KeV energy range. The Phase II project will develop the array detectors to cover a 5-10% of total solid angle and to operate in a large energy region. Combining narrow bandwidth multilayers with dual multilayer analyzer technique, the system can be made with very high background rejection capability.
