Characteristics of optical fibers to radiation

Recently, various reports have been issued on the radiation resistivity of optical fibers. Many of them treated the examination on the increase of transmission loss and the recovery characteristics after stopping irradiation when γ- or X-ray, neutron or electron beam was irradiated to optical fibers. Lately, however, the theoretical studies which were focused to the optical bleaching effect and the change of glass structure were also presented. In this report, the radiation characteristics of the optical fibers employed for communication and control cables and the various phenomena which have been the problems in image guides and light guides are described. The optical fibers used for the experiment were the graded index fibers of Ge- and P-doped core, and the SI type fibers of OH-doped silica glass core and highly pure silica glass core. The increase of transmission loss was measured on these fibers of 15 to 100 m length. For communication and control optical fibers, the loss was determined by the amount of dose, and did not depend on dose rate in GI type, but the loss depended on both dose and dose rate in SI type. For the optical fibers employed for image and light guides, in addition to the increase of loss by irradiation, it is generally said that the generation of fluorescence from optical fibers should also be carefully investigated. When X-ray was irradiated to the fibers of silica glass core, the generation of fluorescence increased with the increase of dose. This suggests that the problems such as the increase of background due to fluorescence may occur when light guides and the like are used in radiation fields. (Wakatsuki, Y.)