  The silicon detectors used in the H1-PLUG calorimeter have shown increasing
aging effects during the '94 run period of the electron proton storage ring
HERA. These effects were particularly manifest as degradation of the signal to
noise level and the calibration stability. The reasons for this behaviour have
been found to be correlated with radiation damage to the silicon oxide
passivation edges of the detectors in strong and fluctuating increases of the
leakage currents and in severe changes of the flat band voltages. Depletion
voltages however are found to be stable and therefore bulk damage of the
silicon can be excluded. A comparison with measurements made by
thermoluminescence dosimeters as well as related laboratory experiments suggest
that the aging is due to very low energetic electrons and photons.
