A microstrip germanium detector for position-sensitive X-ray spectroscopy

For the current X-ray spectroscopy program at the ESR storage ring (GSI-Darmstadt), a position-sensitive germanium detector system was completed. The position-sensitive structure of the detector was realized on an area of 47 x 23.4 mm by an array of 200 strips (200 mum wide and 23.4 mm long) separated by 35-mum-wide grooves etched through boron implanted contact. The thickness of the detector, including a 0.6-mm-thick Li-diffused rear contact, amounts to 4.1 mm. Each strip has been joined to a preamplifier placed outside the cryostat with printed leads inside the flexible Kapton-foil. The energy resolution of the strips was about 1.8 keV [FWHM] for 60-keV photons. Coincidences between neighboring strips were measured showing that a time resolution of 70 ns [FWHM] was obtained. First preliminary results obtained with the detector mounted at the transmission X-ray spectrometer FOCAL demonstrated that an energy resolution better than 100 eV is achievable together with a high detection efficiency. Along with a new kind of X-ray spectrometer, this detector may play a key role for the next step of high-precision X-ray experiments: aiming for a precise test of quantum electrodynamics in the heaviest one-electron systems, such as hydrogen-like uranium.