We investigated the potential of an optical material (Ce-doped silica rod of ~0.5 mm in diameter and ~1 cm in length) developed by a sol-gel process to perform in situ proton beam profile measurement ...through the monitoring of its visible radioluminescence (RIL) features peaking around 480 nm. Various test configurations (collimator sizes and varying distances from the collimators) have been performed to assess the sensor performances at the TRIUMF facility in Vancouver offering a 63-MeV proton beam. The obtained results are promising, showing their potential to characterize the flux and beam profile at this facility offering radiation testing capabilities or medical treatments. The reported performances could be improved by pre-irradiating the probe sample to reduce the observed slight bright burn effect on the quality of the profile measurements. These results open the way to most advanced sensors' architecture such as ribbons of optical fibers drawn from this sol-gel rod, to acquire in one step the complete beam profile.
We investigated the combined effects of temperature and 40 keV mean energy fluence X-ray photons on Fluorine-doped, Ge-doped and P-doped optical fibers to doses up to 155 kGy(SiO 2 ) and in the -50 ...°C to 50 °C temperature range. We studied the effects of different constant temperatures or thermal cycles during the irradiation on the 1550 nm radiation-induced attenuation (RIA) levels to evaluate the various fiber performances as part of radiation tolerant optical system or as sensitive dosimeters. Thermal cycles reveal the complex RIA responses of our optical fibers with temperature. The temperature strongly affects the generation and bleaching mechanisms of radiation induced point defects, also slightly impacts the fiber light guidance properties. Our results show that typical space thermal cycles can limit the impact of the observed RIA increase at lower temperatures.
Rare-earth-doped silica glasses are promising materials for ionizing radiation dosimetry. In this paper, a bulk glassy silica doped with Ce ions, was prepared via the sol-gel technique and drawn at ...about 2000 °C into a cylindrical capillary rod. Under X-rays, this sample presents a radioluminescence (RL) signal that can be exploited for dose rate real-time monitoring with remarkable linear response spanning 6 decimal orders of magnitude. In order to elucidate RL signal dynamics associated with free carriers trapping-detrapping and recombination during and after X-ray irradiation, we studied the obtained RL signals using a kinetic model involving one or several trapping states and one recombination center. With this model and using appropriate sets of trapping parameters, extracted from the thermoluminescence data, the RL signal was numerically simulated, along with the populations of the relevant traps and centers. Several experimentally observed characteristics of the RL signals were explained using the model.
Combined temperature and photobleaching (PB) effects on the 1550 nm radiation-induced attenuation (RIA) levels and kinetics of a commercial Ge-doped single-mode optical fiber have been investigated. ...The main goal of this study was to evaluate if synergetic effects could impact the performances of free space optical communication links in space. For this, we performed accelerated (0.5 Gy(SiO 2 )/s) irradiation runs with 100 kV X rays up to the total ionizing dose of 150 kGy(SiO 2 ), varying the irradiation temperature between -80 °C and 80 °C. First, we evaluate the irradiation temperature effects: infrared RIA largely increases at negative temperatures. Second, the effects of injecting different optical powers at the different temperatures have been characterized: if at temperatures exceeding room temperature (RT), PB effects are almost negligible, a PB effect is clearly observable at lower temperatures where the germanosilicate optical fiber present large RIA levels due to the contribution of metastable defects absorbing at 1550 nm. Increasing the injected powers allows reducing the concentration of these radiation-induced unstable defects, but not as much as thermal treatment consecutive to the irradiation. These results highlight the complex physics of radiation induced defects absorbing at 1550 nm in Ge-doped optical fiber, but also the vulnerability of this class of fiber for space telecommunication links. Regarding the unstable nature of point defects causing the RIA at lower temperature, it seems possible to mitigate the loss excess by thermal cycles at RT or higher temperatures. We also could expect that our accelerated tests represent a worst-case scenario in terms of RIA levels at the maximum dose.
Vulnerability of Optical Frequency Domain Reflectometry (OFDR) based sensors to high γ-ray doses (up to 10 MGy) is evaluated with a specific issue of a radiation-hardened temperature and strain ...monitoring system for nuclear industry. For this, we characterize the main radiation effects that are expected to degrade the sensor performances in such applicative domain: the radiation-induced attenuation (RIA), the possible evolution with the dose of the Rayleigh scattering phenomenon as well as its dependence on temperature and strain. This preliminary investigation is done after the irradiation and for five different optical fiber types covering the range from radiation-hardened fibers to highly radiation sensitive ones. Our results show that at these high dose levels the scattering mechanism at the basis of the used technique for the monitoring is unaffected (changes below 5%), authorizing acceptable precision on the temperature or strain measurements. RIA has to be considered as it limits the sensing range. From our vulnerability study, the OFDR sensors appear as promising candidates for nuclear industry even at doses as high as 10 MGy.
We analyzed the simultaneous response to radiation and temperature exposure of radiation-sensitive optical fibers doped with aluminum, phosphorus and/or Germanium in the framework of the CERTYF ...(Combined Effects of Radiations, Temperature and hYdrogen on silica-based optical Fibers) project, whose aim is to build a predictive model based on intrinsic and extrinsic optical parameters.
We investigate the radiation effects on a Brillouin-based optical fiber sensor (OFS). This OFS exploits a single-mode optical fiber (SMF) having a Brillouin signature presenting multiple peaks. This ...specificity allows performing distributed and discriminated measurements of the temperature and strain time evolutions along the fiber. The particular structure (composition and refractive-index profile) of the investigated SMF was first conceived and optimized, thanks to a home-made simulation tool to assess its capability to discriminate between the two environmental parameters. At the same time, it should also present a good radiation tolerance in order that the sensor could operate in radiation-rich environments (up to MGy levels). The modeled germanosilicate SMF has then been manufactured by the modified chemical vapor deposition process by iXblue and its sensing performances have been experimentally demonstrated. Samples of the SMF have been irradiated under steady-state X-rays at a dose rate of 2.3 Gy(SiO 2 )/s up to 180 kGy at room temperature. The radiation tests showed that the Brillouin sensor can be implemented in such severe environments. At these dose levels, radiation-induced errors are limited to \sim 3 °C and <inline-formula> <tex-math notation="LaTeX">\sim 0.15~\mu \varepsilon </tex-math></inline-formula> in the worst conditions. Finally, we discuss perspectives about possible new fiber structures to target even more challenging applications in terms of radiations and sensing requirements.
Germano-silicate fibers, mostly employed for telecom applications, are also implemented in radiation environments for data links or sensing. In this field, the understanding of radiation-induced ...mechanisms leading to the degradation of the performances of silica optical fibers has an essential role. Particularly, the estimation of the activation energies of the density of trapped states (DOTSs) governing the radiation-induced attenuation (RIA) is of primary importance. To investigate these mechanisms, the thermoluminescence (TL) is a powerful technique, by which the extrapolation of DOTSs has been previously largely achieved for pure and Al-, P-, Er-, and Yb-doped silica. Despite the key applications related to Ge-doped silica, one cannot do the same for this kind of fiber, due to an "anomalous" increase of their TL response along with the heating rate. The objective of this work is primarily to elucidate the specific radiation-induced mechanisms associated with the presence of Ge in silica that notably induce the anomalous TL response. We show from the experimental study of the RIA thermal annealing during the TL readout, and its correlation with the TL glow curve, that oxygen-deficient centers (ODCs) centers, trapping electrons during irradiation, form deep states which act as recombination center (RC) in the TL process. Finally, and most important, we propose a model that explains the TL anomalous features and how they are arisen from two specific properties of the annealing processes of Ge-related radiation-induced centers.
Abstract
Optical fibers hold promise for accurate dosimetry in small field proton therapy due to their superior spatial resolution and the lack of significant Cerenkov contamination in proton beams. ...One known drawback for most scintillation detectors is signal quenching in areas of high linear energy transfer, as is the case in the Bragg peak region of a proton beam. In this study, we investigated the potential of innovative optical fiber bulk materials using the sol-gel technique for dosimetry in proton therapy. This type of glass is made of amorphous silica (SiO
$_{2}$$
2
) and is doped with Gd
$^{3+}$$
3
+
ions and possesses very interesting light emission properties with a luminescence band around 314 nm when exposed to protons. The fibers were manufactured at the University of Lille and tested at the TRIUMF Proton Therapy facility with 8.2–62.9 MeV protons and 2–6 nA of extracted beam current. Dose-rate dependence and quenching were measured and compared to other silica-based fibers also made by sol-gel techniques and doped with Ce
$^{3+}$$
3
+
and Cu
$^{+}$$
+
. The three fibers present strong luminescence in the UV (Gd) or visible (Cu,Ce) under irradiation, with the emission intensities related directly to the proton flux. In addition, the 0.5 mm diameter Gd
$^{3+}$$
3
+
-doped fiber shows superior resolution of the Bragg peak, indicating significantly reduced quenching in comparison to the Ce
$^{3+}$$
3
+
and Cu
$^{+}$$
+
fibers with a Birks’ constant, k
$_{B}$$
B
, of (0.0162
$$\pm $$
±
0.0003) cm/MeV in comparison to (0.0333
$$\pm $$
±
0.0006) cm/MeV and (0.0352
$$\pm $$
±
0.0003) cm/MeV, respectively. To our knowledge, this is the first report of such an interesting k
$_{B}$$
B
for a silica-based optical fiber material, showing clearly that this fiber presents lower quenching than common plastic scintillators. This result demonstrates the high potential of this inorganic fiber material for proton therapy dosimetry.
The radiation-resistance of different types of gratings, such as types I-UV, II-IR, and III, was investigated at −120 °C up to the accumulated dose of 100 kGy(SiO 2 ). The grating temperature ...sensitivity was evaluated from room temperature down to −120 °C, before and after irradiation. We demonstrated no radiation effect on the temperature sensitivity at the accumulated dose of 100 kGy. This article is a preliminary one to explore the best candidate among the grating types for their integration in low-temperature applications and shows that the performances of both type II-IR and type III FBGs written in the F-doped fiber are not influenced by X-rays at −120 °C up to a dose of 100 kGy.
PDF
