Radiation-induced absorption and luminescence in specially hardened large-core silica optical fibers

Radiation-induced absorption and luminescence are measured in the visible spectral region in H-2-loaded and as-drawn fibers with KU and KS-4V silicas in the core in the process of gamma-irradiation (Co-60-source). The induced absorption in H-2-loaded fibers is shown to be much lower than in as-drawn fibers, at least up to 1.2 MGy. A 'blue' band prevails in the luminescence spectra of all the fibers. Its intensity is greater in a KS-4V fiber than in a KU fiber. It is also somewhat greater in H-2-loaded fibers than in unloaded ones. The luminescence lifetime in a KU fiber has been measured under excitation with a pulsed reactor to be 100 mu s at lambda=488 nm and 60 mu s at lambda=633 nm. It is concluded that the 'blue' radioluminescence cannot be attributed either to relaxation of the oxygen-deficient center or to Cerenkov emission. A fabrication technology of radiation-hardened H-2-containing fibers with a hermetic aluminum coating is reported. Such fibers appear to be the best candidates for various applications in radiation environments.