COMPARISON BETWEEN FAST-NEUTRON AND GAMMA-IRRADIATION OF OPTICAL FIBERS

A variety of undoped multimode step-index fibres and Ge-doped single m ode and graded index fibres is irradiated by 14 MeV neutrons and Co-60 gamma rays up to the same total dose. Radiation-induced loss and brea king stress are measured. The loss induced during gamma irradiation of Ge-doped fibres is about 2.5 times higher than during neutron irradia tion with the same dose rate, up to a fluence of about 3x10(12) cm(-2) (14 MeV). This loss ratio decreases to less than or equal to 2.0 afte r about 10(13) cm(-2) (14 MeV). Monte Carlo calculations of the dose e nhancement as caused by fast recoil protons out of the H-containing ac rylate coating are confirmed experimentally. 14 MeV neutron irradiatio n up to less than or similar to 10(13) cm(-2) seems to decrease fibre breaking stress by 3 - 4 %, whereas Co-60 gamma irradiation up to the same total dose has no effect.