A SOLID IONIZATION-CHAMBER OPERATED AT 20 MK

We have built a germanium ''solid ionization chamber'' with aluminium evaporated electrodes. We obtained very low leakage current complete c harge collection at 23 mK. However, we found that the spectra evolved as a function of time. To investigate this effect, the detector has be en irradiated with the 43, 87, 105, and 662 keV photons of Eu-155 and Cs-137 and we analyzed this time evolution taking into account the dif ferent penetration depths of the photons. We also studied the influenc e of the ''history'' of the detector (the previous polarization voltag es). We found that the electric field due to the built-in space charge (presumably induced by carriers trapping) plays an important role, an d that the time evolution cannot be explained solely by the trapping o f the carriers generated by each photon.