A micro-strip 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 has been completed. The position sensitive structure of the detector has been realized on an area of 47×23.4 mm² by an array of 200 strips (200 μm wide and 23.4 mm long) separated by 35 μm wide grooves etched through a boron implanted contact. The thickness of the detector inclusive of 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 has been about 1.8 keV [FWHM] for 60 keV photons. Coincidences between neighbouring strips were measured whereby 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 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 a hydrogenlike uranium