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 ~ 7 times 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 plusmn 2% and plusmn 0.5% when uncompensated and compensated, respectively. The Cu-K_alpha line width is (271 plusmn 46) eV when operated at 10degC. With the best SDD chip we achieved (223 plusmn 7) eV at 10degC and (294 plusmn 10) eV at 24degC . By selection of the three best devices the spectral resolution reaches 400 and 600 eV at 10degC and a sum-count rate of 3.3middot10⁶ s^-1 and 6.7middot10⁶ s^-1, respectively. XAFS measurements have shown that the peak shift and line-width variations remain below 5 eV and 17 eV, respectively.