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

For the current X-ray spectroscopy program at the ESR storage ring (GSI-Dar mstadt), 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) separat ed by 35-mum-wide grooves etched through boron implanted contact. The thick ness of the detector, including a 0.6-mm-thick Li-diffused rear contact, am ounts to 4.1 mm. Each strip has been joined to a preamplifier placed outsid e the cryostat with printed leads inside the flexible Kapton-foil. The ener gy resolution of the strips was about 1.8 keV [FWHM] for 60-keV photons. Co incidences between neighboring strips were measured showing that a time res olution of 70 ns [FWHM] was obtained. First preliminary results obtained wi th the detector mounted at the transmission X-ray spectrometer FOCAL demons trated that an energy resolution better than 100 eV is achievable together with a high detection efficiency. Along with a new kind of X-ray spectromet er, 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 t he heaviest one-electron systems, such as hydrogen-like uranium.