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

We report the study of a radiation resistant single mode optical fiber doped with fluorine exposed to mixed neutron and γ-radiation up to 10¹⁷ 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 γ-radiation (10 MGy) or mixed neutron and γ (10¹⁷ n/cm²⁺ 2 MGy) irradiated samples. Those differences are linked to the defect generation rather than to structural changes of the α-SiO₂ host matrix. We show that a modification of the refractive index of ∼10^-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 degrees 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 γ radiation environments. (authors)