Comparison between fast neutron and gamma irradiation of optical fibers

A variety of undoped multimode step-index fibers and Ge-doped single mode and graded index fibers is irradiated by 14 MeV neutrons and 60Co gamma rays up to the same total dose. Radiation-induced loss and breaking stress are measured. The loss induced during gamma irradiation of Ge-doped fibers is about 2.5 times higher than during neutron irradiation with the same dose rate, up to a fluence of about 3 x 1012 cm-2 (14 MeV). This loss ratio decreases to ≤2.0 after about 1013 cm-2 (14 MeV). Monte Carlo calculations of the dose enhancement as caused by fast recoil protons out of the H-containing acrylate coating are confirmed experimentally. 14 MeV neutron irradiation up to ≤1013 cm-2 seems to decrease fiber breaking stress by 3--4%, whereas 60Co gamma irradiation up to the same total dose has no effect