SILICON DETECTOR SYSTEM FOR HIGH-RATE EXAFS APPLICATIONS

A multichannel silicon pad detector for EXAFS (Extended X-ray Absorpti on Fine Structure) applications has been designed and built. The X-ray spectroscopic measurements demonstrate that an adequate energy resolu tion of 230 eV FWHM (corresponding to 27 rms electrons in silicon) can be achieved reliably at -35 degrees C. A resolution of 190 eV FWHM (c orresponding to 22 rms electrons) has been obtained from individual pa ds at -35 degrees C. At room temperature (25 degrees C) an average ene rgy resolution of 380 eV FWHM is achieved and a resolution of 350 eV F WHM (41 rms electrons) is the best performance. A simple cooling syste m constituted of Pettier cells is sufficient to reduce the reverse cur rents of the pads and their related shot noise contribution, in order to achieve resolutions better than 300 eV FWHM which is adequate for t he EXAFS applications.