DEVELOPMENT OF HGI2 ARRAYS FOR SYNCHROTRON RADIATION

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This program's long term objective is to develop new technologies for creating large arrays of advanced, energy dispersive x-ray detectors for biomedical research at Synchrotron Radiation (SR) research facilities. With single HgI-2 array elements attaining energy resolutions of 250-300 eV at 6 keV, at rates exceeding 50,000 cps/element, a completed 100 element array would count at over 5xl0-6 cps, yet cost about $1000 per element. The projected increases in count rate capability and solid angle collection efficiency will allow research at ultra-low dilutions (or as a function of time, temperature, or concentration) that would otherwise be infeasible or impossible. Used with wigglers and undulators on both existing and next generation SR sources, these arrays will enhance our ability to obtain the direct structural, bonding and compositional information which has been found to be so important in unravelling the mechanisms of protein and enzyme function at the molecular level. While this project uses HgI-2 detector elements because of its near room temperature operation and ease of passivation, the low-cost, hybridized signal processing electronics work equally well with Si or Ge energy dispersive detectors. This detector development program has four specific goals. First, (Year 1) complete construction of the 100 element hard x-ray detector system currently in progress. Its HgI-2 pixel array and all developmental and production engineering are complete. What remains is to fabricate 100 channels of hybridized electronics and install the system for general user community XAS measurements at the Stanford Synchrotron Radiation Laboratory (SSRL). Second, (Years 2-3) devise improved detector design and electronic processing techniques to extend array detector benefits to the soft x-ray range between 500 and 3000 eV. Meeting this goal will require re-engineering the major system components to reduce electronic noise to 125 eV or better from the current value of 250 eV. This will be achieved by: improving the HgI-2 crystal quality; refining the front end detector module design; reducing preamplifier noise by developing new FET structures and implementing a new, small signal, prompt reset scheme; developing a new, time variant amplifier to accommodate the new reset scheme; re-examining the principles of pileup rejection; and replacing the SCAs with hybridized MCAs to record entire spectra. Also a high speed deconvolution procedure will be developed to cope with spectral peak overlaps, which will still occur even with 125 eV resolution. Third (Year 4) construct a 100 element soft x-ray detector array using these technologies and deploy it in support of existing NIH biotechnology research programs at SSRL or elsewhere. Fourth, formulate an upgrade path, and seek additional funding, for the hard x-ray detector amy, focusing particularly on improving its throughput.