14-MeV and Atmospheric Neutron Monitoring Through Optical Fiber Dosimeters

Radiation-induced attenuation (RIA)-based dosimetry exploiting phosphosilicate optical fiber (OF) has been established as a reliable and precise dosimetry technique, to monitor the total ionizing dose (TID) in a variety of harsh environments. We evaluate here the potential of this technology to monitor 14-MeV and atmospheric neutrons. Experiments performed at the TRIUMF Neutron Facility (TNF) from TRIUMF and Frascati neutron generator (FNG) from ENEA demonstrate that after calibration, the fiber dosimeter can serve as an efficient fluence monitor, with the RIA being linearly dependent on the neutron fluence. Using Geant4 simulations, we show that the radiation sensitivity of the fiber, around 3.5 dB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> km<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{-1}~\cdot $ </tex-math></inline-formula> Gy−1 for 14-MeV neutrons, agrees with the ones found in previous studies for photons and protons. For atmospheric neutrons, the calibration differs by a factor of up to 2.5 with respect to the usual factor. Extensive simulations are performed showing that in these neutron environments, the consideration of the real 3-D structure of the fiber coil is mandatory for a fine calibration of the dosimeter. Perspectives for fiber dosimetry of neutron-rich environments are then discussed.