High Resolution Gamma-Ray Spectroscopy on the P78-1 Satellite

On February 24, 1979, two cooled germanium spectrometers operating in the range 0.05 to 2.5 MeV were successfully launched into polar orbit on the P78-1 satellite. Each independent spectrometer system consists of a single large (85 cm3) IGe detector which is shielded by a NaI, polyscin, anticoincidence scintillator and cooled by either one or both of two mechanical Stirling cycle refrigerators. The instrument design and performance during the first 6 months in orbit are presented. After approximately 70 days in orbit, radiation damage effects became evident by the gradual degradation of the resolution from 3.0 - 3.5 keV at 0.511 MeV to greater than 20 keV after about 125 days. An important aspect of these results is the apparent capability of stabilizing the radiation effects by partially restoring the performance of these detectors to resolutions of 15 - 20 keV at 511 keV by annealing at ambient (~280 K) temperatures for a few days.