High-Energy Proton Radiation Damage of High-Purity Germanium Detectors

Motivated by their applicability to gamma-ray spectroscopy experiments in space, quantitative studies of radiation damage effects in high-purity germanium detectors due to high-energy charged particles have been initiated with the irradiation by 6 GeV/c protons of two 1.0 cm thick planar detectors maintained at 88°K. The threshold for resolution degradation and the annealing characteristics differ markedly from those previously observed for detectors irradiated by fast neutrons. Under proton bombardment, degradation in the energy resolution was found to begin below 7 × 107 protons/cm2, and increased proportionately in both detectors until the experiment was terminated at a total flux of 5.7 × 108 protons/cm2, equivalent to about a six year exposure to cosmic-ray protons in space. At the end of the irradiation, the FWHM resolution measured at 1332 keV stood at 8.5 and 13.6 keV, with both detectors of only marginal utility as a spectrometer due to the severe tailing caused by charge trapping. The two detectors displayed a significant difference in proton damage sensitivity, which is consistent with fast neutron damage effects. To ensure that detector variability did not influence the comparision of proton-and neutron-induced damage effects, one of the detectors had been used previously in a neutron damage experiment. The threshold for high-energy proton damage was found to be markedly lower, roughly 5 × 107 protons/cm2, compared to 3 × 109 neutrons/cm2 for fast neutrons. Annealing these detectors after proton damage was found to be much easier than after neutron damage.