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 10 super(15) to 10 super(17) n/cm super(2)) and gamma -rays (doses from 0.02 to 2 MGy) and by a gamma -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 10 super(16) n/cm super(2). These results are interpreted on the basis of the generation processes of defects from precursors sites, that are common to both gamma -rays and neutrons. In contrast, the highest neutron fluence (10 super(17) n/cm super(2)) 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.