Fast X-Ray Spectroscopy Using Si-Drift Detectors

Fast counting applications with energy discrimination like X-ray absorption spectroscopy require an energy resolution of some hundred eV even at highest count rates and ask for small form factors. The development, fabrication and test of a small number of 7-cell Si-drift detectors have been successfully finished at DESY fitting these claims with a good cost-versus-performance tradeoff. The monolithic 7-cell sensor chip and a corresponding readout chip are the key components of the sensor head. The module's length and wrench size amounts to 21.2 and 1.6 cm, respectively. Its active area is similar to 7 x 7 mm(2) and main energy range is 2.5 to 18 keV. Between similar to 5 and 20 keV the nonlinearity in a six-modules setup is well within +/- 2% and +/- 0.5% when uncompensated and compensated, respectively. The Cu - K(alpha) line width is (271 +/- 46) eV when operated at 10 degrees C. With the best SDD chip we achieved (223 +/- 7) eV at 10 degrees C and (294 +/- 10) eV at 24 degrees C. By selection of the three best devices the spectral resolution reaches 400 and 600 eV at 10 degrees C and a sum-count rate of 3.3.10(6) s(-1) and 6.7.10(6) s(-1), respectively. XAFS measurements have shown that the peak shift and line-width variations remain below 5 eV and 17 eV, respectively.