X-Rays, $\gamma$ -Rays, and Proton Beam Monitoring With Multimode Nitrogen-Doped Optical Fiber

We investigated the potential of a multimode (50- $\mu \text{m}$ core diameter) nitrogen doped silica-based optical fiber for X-rays, protons, and $\gamma $ -rays radiation detection and dosimetry. X-rays results confirm that this N-doped fiber presents a strong radioluminescence (RL) around 550 nm when exposed to radiation. The RL observed from a few centimeter long samples linearly depend on the dose rate at least in the 1-mGy/s–50-Gy/s range. Low dose rate $\gamma $ -ray t ests demonstrate the radiation detection at dose rate as low as $40~\mu $ Gy/s with a 2-m-long fiber sample. This fiber is also associated with an optically stimulated luminescence (OSL) when exposed to a 1064-nm laser light postirradiation. This OSL signature provides shortly after the irradiation a precise estimation of the accumulated dose at least in the 1-Gy–10-kGy range. Under proton exposure, we benchmarked the performances of the N-doped fiber with the ones of a conventional Markus chamber used by the TRIUMF proton-therapy team. This comparison highlights the potential of the small-size N-doped fiber to partially overcome the known limitations of commercial fiber-based dosimeters for medical applications. The obtained results are very promising for the future design of more complex spatially resolved beam monitoring systems.