Evaluation of Distributed OFDR-Based Sensing Performance in Mixed Neutron/Gamma Radiation Environments

Abstract

We report the study of a radiation resistant single mode optical fiber doped with fluorine exposed to mixed neutron and $\gamma $ -radiation up to $10^{17}$ n/cm2 fluence and >2 MGy dose to evaluate its performances when used as the sensing element of a distributed Optical Frequency Domain Reflectometry (OFDR). The use of complementary spectroscopic techniques highlights some differences between the responses of solely $\gamma $ -radiation (10 MGy) or mixed neutron and $\gamma $ ( $10^{17}$ n/cm $^{2}+>2$ MGy) irradiated samples. Those differences are linked to the defect generation rather than to structural changes of the ${a}$ -SiO2 host matrix. We show that a modification of the refractive index of $\sim 10^{\mathrm {-5}}$ is induced at the highest investigated neutron fluence. However, the feasibility of distributed temperature measurements along the irradiated fiber is demonstrated with an accuracy of 0.1 °C over a sensing length up to ~ 130 m with the tested OBR4600 interrogator. These results are very promising for the integration of OFDR sensors in mixed neutron and gamma radiation environments.