Modeling of Absorption Induced by Space Radiation on Glass: A Two-Variable Function Depending on Radiation Dose and Post-Irradiation Time

NBK7 and FK51 glass from SCHOTT commonly employed on space optical instrumentation design have been gamma irradiated in order to relate the color centers generated by effect of the radiation to the changes in their optical properties. The effects of gamma radiation on the glass optical properties have been analyzed from transmission measurements and ellipsometric characterization. The absorption bands induced on glass by gamma-radiation were included in the optical model by Gaussian absorption peaks. The variations obtained of the real part of the refractive index and surface roughness were negligible. An exponential function is proposed to describe the absorption increase when the total dose rises. Additionally, a study of the amplitude decrease of these absorption bands with the time is carried out in order to determine relaxation functions. Finally, a two variable function-absorption peak amplitude versus total dose and relaxation time-is proposed in order to link the exponential growth of the absorption peak amplitude with the relaxation function of the absorption bands. The model proposed provides a description of the possible changes produced in the glass optical properties by effect of gamma radiation and predicts the glass behavior with the time