The combined effects of temperature (from −80 °C to +80 °C) and 100 kV X-ray exposure (up to 108 kGy(SiO₂)) on the physical properties of Brillouin scattering and losses in three differently doped silica-based optical fibers, with varying dopant type and concentration (4 wt%(Ge), 10 wt%(Ge) and 1 wt%(F)), are experimentally studied in this work. The dependencies of Brillouin Frequency Shifts (BFS), Radiation-Induced Attenuation (RIA) levels, Brillouin gain attenuation, Brillouin frequency temperature (C_T) and strain (C_ε) sensitivity coefficients are studied under X-rays in a wide temperature range [−80 °C; +80 °C]. Brillouin sensing capabilities are investigated using a Brillouin Optical Time Domain Analyzer (BOTDA), and several properties are reported: (i) similar behavior of the Brillouin gain amplitude decrease with the increase in the RIA; (ii) the F-doped and heavily Ge-doped fibers do not exhibit a temperature dependence under radiation for their responses in Brillouin gain losses. Increasing Ge dopant concentration also reduces the irradiation temperature effect on RIA. In addition, Radiation-Induced Brillouin Frequency Shift (RI-BFS) manifests a slightly different behavior for lower temperatures than RIA, presenting an opportunity for a comprehensive understanding of RI-BFS origins. Related temperature and strain sensors are designed for harsh environments over an extended irradiation temperature range, which is useful for a wide range of applications.

This work provides the analysis of two thermal treatments for the annealing regeneration process of RPL dosimeters used in high-level dose measurements. After regeneration, dosimeter sensitivity was assessed through several irradiation campaigns, with doses reaching up to 500 kGy using 60Co gamma radiation and X-rays with an energy spectrum up to 100 keV. The regenerated dosimeters exhibited good agreement, with deviations less than 10% up to 10 kGy. Fading effects were also monitored, and the proposed thermal treatments had no significant impact on the decay rate of the optical centers. Both annealed and pristine dosimeters have shown negligible fading effects over 300 days, confirming the stability of the optical centers.

We demonstrate a real-time high-spatial-resolution (3 cm) ionizing dose 2-D mapping sensor achieved by analyzing a phosphorus-doped silica-based optical fiber with a Rayleigh-Optical Frequency Domain Reflectometry (R-OFDR) interrogator. The dose is monitored through the radiation induced attenuation (RIA) around 1550 nm measured on the OFDR traces. This study aims at studying the sensor performances and to assess its dose mapping capabilities. The RIA spectrum from the P-doped fiber is first characterized and the fiber radiation sensitivity is calibrated by evaluating the dose-rate. Then, the dose-rate dependence (from 10 mGy/s up to 4 Gy/s) of the RIA levels and kinetics has been investigated up to a cumulated dose of 2 kGy(SiO ₂ ). The achievable spatial RIA resolution with the R-OFDR is equal to 3 cm for precise distributed measurements. Finally, a 2-D square mapping of our X-ray beam has been performed during irradiation with a 10 s acquisition period. These results highlight the significance of distributed and active R-OFDR dosimetry for doses up to 2 kGy, as well as beam shape sensing with high spatial resolution.

We investigate the radiation and temperature effects on the performance of carbon and aluminum-coated silica-based optical fibers that are designed to prevent the diffusion of hydrogen into their cores. We first present the behavior of fiber samples in hydrogen-rich environments, highlighting the impact of the gas presence on their Rayleigh scattering signatures and their silica matrix, as well as quantifying and comparing the H₂ gas penetration into the fiber cores for different coating types. Then, we examine the temperature dependence of the gas loading kinetics and explore how the combination of radiation type (X-rays, γ-rays, and mixed-field neutrons and γ-rays) and temperature (from 30 °C to 80 °C) affects their gas-blocking capabilities. This work reveals a strong impact of environmental temperature and a significant impact of irradiation on both carbon and aluminum coating layer efficiency as a barrier to hydrogen diffusion towards the optical fiber core. Experimental data presented in this work encompass a broad spectrum of potential optical fiber-based monitoring applications in harsh environments including hydrogen and/or high radiation fields, such as in nuclear waste repositories. This work also highlights the need for future in-depth studies to better understand the alteration mechanism of the different coating types.