Behaviour of γ-ray detectors from high purity germanium at low temperature

γ-ray spectrometers prepared from high purity germanium have been studied at low temperature down to 5° K. If sufficient bias voltage was applied the same energy resolution at 5°K than at 77°K was found. At lower bias voltage, below 10°K, the resolution deteriorated rapidly due to the appearance of a slow rising component (up to several microseconds) in the pulses. This behaviour seems to be related to the effect on the signal of the resistance and capacitance of the undepleted region -the resistivity becoming significant at low temperature due to carrier freeze-out on the primary shallow donors-rather than to the effectγ of carrier trapping by shallow level impurities.