We report the results of several complementary radiation tests to qualify and calibrate a highly radiation sensitive Single-Mode (SM) Optical Fiber (OF) for distributed dosimetry application at CERN. The Radiation Induced Attenuation (RIA) is the physical phenomenon used to evaluate the Total Ionizing Dose (TID) received by the OF sensor. The radiation response tests comprise online RIA in the Near InfraRed (NIR) domain under $\rm {}^{60}Co \gamma -rays$ , X-rays and proton irradiations, as well as post mortem Optical Attenuation (OA) measurement to evaluate long term fading effects of the RIA. In this work, we focus on the effect of successive irradiations, dose rate dependence and effects related to the change of the irradiation temperature up to 45 °C. On the basis of our investigation, we conclude that the studied OF is a suitable TID sensor and that it is well adapted for distributed OF radiation dose sensing. It is fully compatible with commercially available SM Optical Time Domain Reflectometers (OTDR), with some noticeable advantages with respect to previously developed systems based on Multimode OFs. Finally, the OF we investigated has been selected for the distributed monitoring of low radiation dose levels at CERN in the injector chain (Proton Synchrotron Booster, Proton Synchrotron, Super Proton Synchrotron) and parts of the Large Hadron Collider (LHC).

In this paper, we report on the development and first deployment of a distributed optical fiber radiation sensor (DOFRS) for the online monitoring of radiation levels in the high-energy accelerator facilities of CERN. The DOFRS is composed of two basic parts: a set of suitably chosen radiation sensitive optical fibers (OFs), to be installed in the machine tunnel, and an optical time domain reflectometer (OTDR), to be installed in a radiation-free area. We carried out a calibration of the radiation response of a P-doped multimode OF under ⁶⁰ Co $\gamma $ -rays and in the mixed-field radiation environment of the CHARM facility at CERN. By performing OTDR measurements, we are able to probe the radiation-induced attenuation in the OF along its length and calculate the deposited radiation dose with a spatial resolution of 1 m. In this paper, we describe the main features associated with DOFRS implementation in the proton synchrotron booster (PSB) at CERN. We also report the first results obtained from the monitoring of PSB radiation levels since its recommissioning in April 2017. The performances and advantages of the DOFRS system are discussed.

Distributed optical fiber radiation sensing is a technique recently adopted at CERN for the monitoring of radiation dose levels in the Proton Synchrotron Booster (PSB) and in the Proton Synchrotron (PS). In this paper, we present the progress made on our previous work by benchmarking the rich information contained in the spatially distributed Optical Fiber (OF) dose measurement with the radiation levels simulated with the FLUKA Monte Carlo code. We begin by discussing the experimental results for the qualification/calibration of a new radiation sensitive single-mode OF, currently being deployed in the accelerator tunnels. We performed this calibration tests online under 60Co γ-rays source. We then move on to report the results of the online irradiation tests that we carried out in the CERN High energy AcceleRator Mixed field facility (CHARM). Finally, we compare the OF radiation maps with the dose levels calculated along the OF cable with FLUKA for two very different configurations of the facility. This study is a first, promising example of combining 3-D Monte Carlo simulations of complex mixed field environment with the 1-D spatially distributed dose measurements provided by the OF-based dosimetry.

Point or distributed optical fiber (OF)-based dosimeters can exploit the observed linear dependence of the radiation-induced attenuation (RIA) at 1550 nm in phosphosilicate OFs to monitor the total ionizing dose (TID). The temperature dependence of the radiation sensitivity coefficients at 1550 nm (expressed in dB km ^-1 Gy ^-1 ) of three phosphorus-doped single-mode OFs has been investigated between -80 °C and 300 °C for TID ranging from 1 Gy to 1 kGy(SiO ₂ ). Our measurements reveal the same temperature dependence of the calibration factor for the three fibers at the higher temperatures (>120 °C) where the P1 defects, at the origin of the IR-RIA, are metastable. However, the uncertainties on the TID measurements through the fiber-based dosimeter remain within the 15% for temperatures ranging from -80 °C to 120 °C for the three tested fibers. The independence of the RIA and then of the dose measurements from the dose rate is also maintained in this temperature range.

We investigated the online radiation-induced attenuation of two single-mode optical fibers (OFs) that were X-rays irradiated with doses up to 100 kGy(SiO₂) at room temperature at 10.7 Gy/s. One of the two samples was doped only with phosphorous, whereas the other was codoped with phosphorous and cerium. Both OF types are very radiation sensitive in the near-infrared (NIR) domain and of interest for applications involving radiation detection. The addition of Ce to the P-doped core lowers the radiation sensitivity of the OF and introduces a spontaneous postirradiation recovery process at room temperature, which is negligible in the purely P-doped OF. We show that the diffusion of molecular hydrogen into the OFs allows the full recovery of the NIR losses caused by radiation-induced P-related point defects. However, the radiation response of the H₂-regenarated samples is substantially different from that of the pristine ones. We conclude that the H₂-loading procedure cannot be at the moment considered as a valid technique for the regeneration of a depleted P-doped OF radiation sensor.