Radiation-induced attenuation in SiO/sub 2//F-SiO/sub 2/ fibres under low neutron flux

In order to check for the impact of a low fission neutron flux on the ionising radiation sensitivity of silica fibres, and in view of applications in the periphery of reactor cores, an irradiation experiment was carried out on optical fibres involving thermal and fast neutrons in a high gamma background. After this neutron test, the fibres were further irradiated in a pure gamma field. This gamma test was also performed on another set of identical fibres but preirradiated with gamma rays only, approximately up to the same total equivalent dose. The specific neutron induced degradation has been checked by comparing the gamma sensitivity of these two sets of fibres. The sensitivities of neutron preirradiated samples were found to be higher than the sensitivities of gamma preirradiated ones for the three fibres under test, possibly revealing a specific neutron degradation. These preliminary results show that 1) the gamma sensitivity of fibre samples preirradiated separately with gamma rays and low fission neutron flux can change; 2) this change leads to a higher sensitivity of neutron preirradiated samples compared to gamma preirradiated ones; 3) this change depends on the fibre core material and its fabrication process.