Radiation damage effects of silicon PIN photodiodes were studied by using evaporation neutrons from nuclear spallation reactions of a copper target with 12 GeV protons. Photodiode samples were placed in the backward direction from the copper target and neutron flux was determined by the foil activation method. The average neutron energy was estimated to be about 6 MeV. The damage effects were observed in terms of the increase of leakage current with reverse voltage which is expected to be approximately proportional to radiation dose of neutrons. The present result of the leakage current constant is of the order of 3 to 4 times those measured by using identical photodiodes exposed to reactor neutrons with the average energy of about 2 MeV. The observed energy dependence of the leakage current constant can be qualitatively explained by the NRT model.
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