Preparing Herschel's commissioning phase: Ge:Ga detector tuning

The Photodetector Array Camera and Spectrometer (PACs) instrument aboard the HERSCHEL space observatory contains an integral field spectrometer with two camera channels which consist of 25 linear arrays of 16 stressed Gallium doped Germanium crystals (Ge:Ga) each. The space radiation environment induces changes in the detector performance. Therefore, testing the Ge:Ga detectors under space radiation environment during the commissioning phase (CP) is important for optimization of later detector operation in orbit. The test program for Ge:Ga detector tuning during this phase has been designed according to findings obtained in laboratory experiments: Protons as well as a Cs-137-gamma-source have been used to simulate the space radiation environment arid to induce the radiation impacts on the photoconductor arrays. From comparison of the performance of the detectors during CP versus laboratory tests the best strategy for operating the detectors during scientific observations will be derived. This includes annealing, proposals for on-board data reduction algorithms and the best estimated strategy for well-calibrated scientific measurements.