Models for the radiation induced attenuation in pure silica optical fibres: Spectral dependencies and absorption band kinetics

Over the past years, various attempts have been made to accurately model the radiation response of the optical attenuation in optical fibres for nuclear environments. In this paper we present the results of a study on pure silica fibres where both the spectral and kinetic behaviour are explored during and after irradiation in spent fuel gamma facilities. Basic first- and second-order kinetic models are considered, as they provide insight into fundamental dependencies on temperature and dose-rate. Other popular models, like the power-law and stretched exponential forms of the basic kinetic paradigms, are investigated with emphasis on the spectral dependence of the constituting parameters. Since the radiation induced attenuation is in general the sum of contributions from different absorption bands, related to underlying radiation induced defects, the spectral dependencies are also tackled by Gaussian resolution. With this method, the recorded absorption spectra in the range from 450 to 1600 nm are decomposed into individual absorption bands, with fixed positions and widths in the photon-energy domain for the course of the experiments. The resulting amplitudes from the non-linear estimation process are then evaluated with respect to the same models used as for the radiation induced attenuation at single wavelengths.