Investigation of the Dosimetry Properties of Radioluminescent Nitrogen-Doped Tapered Optical Fibers

We investigated the feasibility to develop miniaturized fiber radioluminescent dosimeters by drawing tapered nitrogen-doped silica-based optical fibers. We show that these tapered fibers can efficiently monitor in real-time 100-kV X-ray flux at dose rates ranging from ~0.02 to 6 Gy(SiO2)/s. The material radiation sensitivity is shown to increase due to the fiber tapering process, to the extent that we could monitor the X-ray flux with an N-doped fiber with a core of less than 1 ~\mu \text{m} in diameter. Monte Carlo simulations with the Geant4 toolkit confirm that this sensitivity increase cannot only be explained by the change in the dose deposition caused by different sensor geometries. These tapered optical fibers appear as promising devices for in situ microscale embedded dosimetry of small-size beams, e.g., for radiation therapy treatments. In this context, these sensors could overcome the challenge of providing the highest possible spatial resolution in order to have increasingly precise treatments with microbeams. The obtained results can also be exploited to predict the potentialities and limits on the use of these tapered sensors in other environments involving higher energy particles.