It has been repeatedly emphasized in the BioSync Report that the development of better XAS detector systems is critical in solving the problem of detectors lagging behind synchrotron sources. The detector bottleneck encountered is in two areas: one is detector count rate limitation, and the other is its limited rejection rate of background in order to examine very dilute systems. By the development of the multilayer analyzer array detector (MAAD), we effectively increased the count rate, and therefore the efficiency of fluorescence detection. Now, we are proposing to largely increase the rejection rate by developing muitilayer analyzer pair array detectors (MAPAD). Our Phase I project has shown that such a detector can be made with a high rejection rate and a reasonable throughput. With two-stage rejection of primary and secondary multilayers, the rejection rate will exceed 200 times with a 15 to 20% throughput. With 28 double multilayer pairs, the detector will collect close to 2% total solid angle at 6 KeV. The anticipated gain on the effective photon counts will be as high as 40 times on very dilute systems. The detector can be made tunable in a large energy region, and easy to operate. With a flexible design, the detector can perform the pair rejection as well as the single multilayer rejection, just like a MAAD. Thus the detector can cover a large sample dilution range from a few mM down to 20 microM or a few ppm. For trace metal detection, the approachable concentration can go even lower. This kind of sensitivity should enable us to approach new systems, such as the examination of biological relevant metals in vivo as well as very dilute systems in environmental, material, physical and chemical research. The detector has a very good market potential benefiting efficient use of high flux beamlines. By expanding the XAS technique to new systems, the detector can potentially enter into new markets.
