Opto-Mechanical Fiber Sensing of Gamma Radiation

The monitoring of ionizing radiation is critical for the safe operation of nuclear and other high-power plants. Fiber-optic sensing of radiation has been pursued for over 45 years. Most protocols rely on radiation effects on the optical properties of the fiber. Here we propose a new concept, in which the opto-mechanics of standard fibers coated by thin layers of fluoroacrylate polymer are observed instead. The time-of-flight of radial acoustic waves through the coating is evaluated by forward stimulated Brillouin scattering measurements. The time-of-flight is seen to decrease monotonically with the overall dosage of gamma radiation from a cobalt source. Variations reach 15% of the initial value for 180 Mrad dose and remain stable for at least several weeks following exposure. The faster times-of-flight are consistent with a radiation-induced increase in the coating stiffness, observed in offline analysis. The effects on the coating are independent of possible changes in the optical parameters of the fiber. The combination of opto-mechanical analysis together with established fiber sensing protocols may help disambiguate the evaluation of multiple radiation metrics and reduce environmental cross-sensitivities. The technique is suitable for online monitoring and may be extended to spatially distributed measurements.