Solar proton damage in high-purity germanium detectors

High-purity germanium (HPGe) detectors used in space for gamma-ray spectroscopy in astrophysics and planetary exploration are known to be damaged by energetic particles. For interplanetary missions close to the Sun such as Messenger or BepiColombo to explore planet Mercury, solar protons represent an important source of damage. In this work, irradiation tests were performed on two large-volume coaxial n-type HPGe detectors with mono-energetic beams of 50-60 MeV protons. One of the detectors, designed for spatial applications, was incrementally exposed to a proton fluence up to 7.5 x 1010 p/cm2 and the other to a unique fluence of 10(10) p/cm(2.) The results showed that the degradation of the energy resolution appeared for fluences higher than 5 x 108 p/cm(2). Moreover, a loss in detection efficiency was observed for fluences above 1010 p/cm(2). Annealings above 80 degrees C allowed the recovery of the initial resolution but not the initial efficiency. By extrapolating the results beyond the experimental conditions, this study also establishes the limits for the use of spaceborne HPGc detectors in harsh low-energy proton environment. (c) 2006 Elsevier B.V. All rights reserved