Radiation damage of germanium detectors

In the course of a continuing study of the proton damage of germanium detectors, a reverse electrode configuration coaxial detector that had been fabricated at Lawrence Berkeley Laboratory (LBL) five years ago and a 1 cm thick planar detector made from the same crystal were irradiated with 5.1 GeV protons in a recent experiment. These detectors were irradiated simultaneously--there were actually a total of five detectors in line. The coaxial detector was considerably less sensitive to the high-energy proton damage than was the planar detector. These data indicate a factor of approx. 3. This would imply a factor of approx. 60 when comparing coaxial detectors having the opposite electrode configuration. Although additional experiments must be done, the evidence is now quite strong that coaxial germanium detectors having the n+ contact on the coaxial periphery should not be used in any situation subject to significant radiation damage such as on an extended mission in space