Fast X-ray spectroscopy using Si-Drift Detectors

Fast counting applications with energy discrimination like X-ray absorption spectroscopy or X-ray standing waves 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 ∼7 × 7 mm² and main energy range is 2.5 to 18 keV. Between ∼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-Kα FWHM-line width is (271 ± 46) eV when operated at 10°C. With the best SDD chip we achieved (223 ± 7) eV at 10°C and (294 ± 10) eV at 24°C. By selection of the three best devices the spectral resolution reaches 400 and 600 eV at a sum-count rate of 3.3 Mcts/s and 6.7 Mcts/s, respectively. XAFS measurements have shown that the peak shift and line-width variations remain below 5 eV and 17 eV, respectively.