Comparison between fast neutron and gamma irradiation of optical fibres

A variety of undoped multimode step-index fibres and Ge-doped single mode and graded index fibres is irradiated by 14 MeV neutrons and /sup 60/Co 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 fibres is about 2.5 times higher than during neutron irradiation with the same dose rate, up to a fluence of about 3/spl times/10/sup 12/ cm/sup -2/ (14 MeV). This loss ratio decreases to /spl les/2.0 after about 10/sup 13/ cm/sup -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 /spl les/10/sup 13/ cm/sup -2/ seems to decrease fibre breaking stress by 3-4%, whereas /sup 60/Co gamma irradiation up to the same total dose has no effect.