We report here the response of a commercial ultra-low loss (ULL) single-mode (SM) pure silica core (PSC) fiber, the Vascade EX1000 fiber from Corning, associated with 0.16 dB/km losses at 1.55 µm to 40 keV X-rays at room temperature. Today, among all fiber types, the PSC or F-doped ones have been demonstrated to be the most tolerant to the radiation induced attenuation (RIA) phenomenon and are usually used to design radiation-hardened data links or fiber-based point or distributed sensors. The here investigated ULL-PSC showed, instead, surprisingly high RIA levels of ~3000 dB/km at 1310 nm and ~2000 dB/km at 1550 nm at a limited dose of 2 kGy(SiO₂), exceeding the RIA measured in the P-doped SM fibers used for dosimetry for doses of ~500 Gy. Moreover, its RIA increased as a function of the dose with a saturation tendency at larger doses and quickly recovered after irradiation. Our study on the silica structure suggests that the very specific manufacturing process of the ULL-PSC fibers applied to reduce their intrinsic attenuation makes them highly vulnerable to radiations even at low doses. From the application point of view, this fiber cannot be used for data transfer or sensing in harsh environments, except as a very efficient radiation detector or beam monitor.

The potential of fiber-based sensors to monitor the fluence of atmospheric neutrons is evaluated through accelerated tests at the TRIUMF Neutron Facility (TNF) (BC, Canada), offering a flux approximatively 10⁹ higher than the reference spectrum observed under standard conditions in New York City, USA. The radiation-induced attenuation (RIA) at 1625 nm of a phosphorus-doped radiation sensitive optical fiber is shown to linearly increase with neutron fluence, allowing an in situ and easy monitoring of the neutron flux and fluence at this facility. Furthermore, our experiments show that the fiber response remains sensitive to the ionization processes, at least up to a fluence of 7.1 × 10¹¹ n cm⁻², as its radiation sensitivity coefficient (~3.36 dB km⁻¹ Gy⁻¹) under neutron exposure remains very similar to the one measured under X-rays (~3.8 dB km⁻¹ Gy⁻¹) at the same wavelength. The presented results open the way to the development of a point-like or even a distributed dosimeter for natural or man-made neutron-rich environments. The feasibility to measure the dose caused by the neutron exposure during stratospheric balloon experiments, or during outer space missions, is presented as a case study of a potential future application.

We exploited the potential of radiation-induced emissions (RIEs) in the visible domain of a nitrogen-doped, silica-based, multimode optical fiber to monitor the very high dose rates associated with experiments at different pulsed X-ray facilities. We also tested this sensor at lower dose rates associated with steady-state X-ray irradiation machines (up to 100 keV photon energy, mean energy of 40 keV). For transient exposures, dedicated experimental campaigns were performed at ELSA (Electron et Laser, Source X et Applications) and ASTERIX facilities from CEA (Commissariat à l’Energie Atomique—France) to characterize the RIE of this fiber when exposed to X-ray pulses with durations of a few µs or ns. These facilities provide very large dose rates: in the order of MGy(SiO₂)/s for the ELSA facility (up to 19 MeV photon energy) and GGy(SiO₂)/s for the ASTERIX facility (up to 1 MeV). In both cases, the RIE intensities, mostly explained by the fiber radioluminescence (RIL) around 550 nm, with a contribution from Cerenkov at higher fluxes, linearly depend on the dose rates normalized to the pulse duration delivered by the facilities. By comparing these high dose rate results and those acquired under low-dose rate steady-state X-rays (only RIL was present), we showed that the RIE of this multimode optical fiber linearly depends on the dose rate over an ultra-wide dose rate range from 10⁻² Gy(SiO₂)/s to a few 10⁹ Gy(SiO₂)/s and photons with energy in the range from 40 keV to 19 MeV. These results demonstrate the high potential of this class of radiation monitors for beam monitoring at very high dose rates in a very large variety of facilities as future FLASH therapy facilities.

We investigated in this work the radioluminescence properties of a Ce-doped multimode silica-based optical fiber (core diameter of 50 µm) manufactured by the sol–gel technique when exposed to the high-energy X-rays (~600 keV) of the ORIATRON facility of CEA. We demonstrated its potential to monitor in real-time the beam characteristics of this facility that can either operate in a pulsed regime (pulse duration of 4.8 µs, maximum repetition rate of 250 Hz) or in a quasi-continuous mode. The radiation-induced emission (radioluminescence and a minor Cerenkov contribution) linearly grew with the dose rate in the 15–130 mGy(SiO₂)/s range, and the afterglow measured after each pulse was sufficiently limited to allow a clear measurement of pulse trains. A sensor with ~11 cm of sensitive Ce-doped fiber spliced to rad-hard fluorine-doped optical fiber, for the emitted light transport to the photomultiplier tube, exhibited interesting beam monitoring performance, even if the Cerenkov emission in the transport fiber was also considered (~5% of the signal). The beam monitoring potential of this class of optical fiber was demonstrated for such facilities and the possibilities of extending the dose rate range are discussed based on possible architecture choices such as fiber type, length or size.

We present a simulation-assisted methodology for the design of point or distributed fiber dosimeters exploiting the linear dependence of the infrared radiation-induced attenuation of a single-mode phosphosilicate optical fiber. We demonstrate by comparing Monte Carlo simulations and experiments at different irradiation facilities (X-rays, γ-rays, protons and atmospheric neutrons) that the sensitivity coefficient of this fiber is independent on the nature of particles and on dose rate, at least up to total ionizing doses in the order of 500 Gy. Our simulations allow us to simulate the dose deposited in the fiber core (and then the Radiation Induced Attenuation (RIA) levels) for the different classes of particles (photons, electrons, neutrons, protons and heavy ions) and for different energy ranges. From this data, and knowing the environments of targeted applications for the fiber optic dosimeters, we can discuss the different designs and achievable performance using this fiber. Examples are discussed with space applications, atmospheric balloon experiments and fusion-devoted facilities.