Origin of the radiation-induced OH vibration band in polymer-coated optical fibers irradiated in a nuclear fission reactor

We measured in situ the radiation-induced absorption of pure silica core fibers exposed to a fission nuclear radiation. We observed the growth of the 1.38-μm OH vibration band in polymer coated fiber. Two contributions, a gamma-induced hydrogen diffusion and the recoil protons, are compared. The major contribution to the OH content growth is identified to originate from the gamma-induced hydrogen diffusion. The identification of the parameters governing the mechanism has important implications on the design of a fast-neutron fiber optic monitor.