Influence of neutron and gamma-ray irradiations on rad-hard optical fiber

We investigated point defects induced in rad-hard Fluorine-doped optical fibers using both a mixed source of neutrons (fluences from 10¹⁵ to 10¹⁷ n/cm²) and γ-rays (doses from 0.02 to 2 MGy) and by a γ-ray source (dose up to 10 MGy). By combining several complementary spectroscopic techniques such as radiation-induced attenuation, confocal micro-luminescence, time-resolved photo-luminescence and electron paramagnetic resonance, we evidenced intrinsic and hydrogen-related defects. The comparison between the two irradiation sources highlights close similarities among the spectroscopic properties of the induced defects and the linear correlation of their concentration up to 10¹⁶ n/cm². These results are interpreted on the basis of the generation processes of defects from precursors sites, that are common to both γ-rays and neutrons. In contrast, the highest neutron fluence (10¹⁷ n/cm²) causes peculiar effects, such as the growth of a photoluminescence and variations of the spectral and decay properties of the emission related with nonbridging oxygen hole centers, that are likely due to silica network modification.