A detector for low-energy (few hundred eV-20 keV) X-rays in the presence of a high background of high-energy X-rays

The Vanderbilt University FEL Center project for the production of monochro matic X-rays uses Compton backscattering of the infrared light from the FEL by the 40 MeV electron LINAC to produce nearly monochromatic pulses of X-r ays in the 10-20 keV range. Detecting these requires the ability to disting uish the small flux of 15 keV X-rays produced by the backscattering from th e large flux of X-rays from low energy to many MeV resulting from scattered electrons from the beam. We have constructed a detector using two thin sil icon surface-barrier detectors as calorimeters, separated by an aluminum ab sorber, so that the front detector sees both high- and low-energy X-rays, a nd the back one sees only high-energy X-rays. Using a carefully balanced di fferential amplifier chain, we can detect a soft X-ray flux which is only a bout 5% of the broadband flux observed by our detector. (C) 1999 Elsevier S cience B.V. All rights reserved.