Coupled temperature and γ-radiation effect on silica-based optical fiber strain sensors based on Rayleigh and Brillouin scatterings.

Coupled temperature and γ-ray influence on Brillouin (PPP-BOTDA) and Rayleigh (TW-COTDR) scatterings are quantified. Aging tests of these distributed strain measuring systems are performed on-line, up to 1 MGy, at room temperature, 80  ∘C, 100  ∘C and 120  ∘C. Brillouin and Rayleigh frequency shifts remain identical regardless of the temperature: 3 MHz (2 MHz) and 7 GHz (3 GHz) for Ge-doped (respectively F-doped) fiber at 1 MGy. Meanwhile, radiation-induced attenuation is diminished because of the higher temperature; hence, the maximal distance range is less deteriorated. These tests help to explain the origin of the Brillouin frequency shift under γ-rays, with an acoustic velocity variation of about 1 m/s in 1 MGy irradiated samples.