Optical fibers dedicated to the detection of ionizing radiation : towards extreme dosimetry

Depuis quelques dizaines d’années, la surveillance des rayonnements ionisants est particulièrement importante dans des endroits difficiles d’accès, voire dangereux, surtout en environnement sévère. La fibre optique constitue une solution de choix lorsqu’une mesure à distance est obligatoire. De plus, les fibres optiques assurent la séparation spatiale de la sonde, sensible aux rayonnements, et du système de traitement électronique, ce qui permet des mesures à distance dans des géométries complexes. Lors de ce travail, des verres à base de silice élaborée par voie sol-gel et codopée par des ions actifs Ce/Tb ou Ce/Cu ont été soudés à une ou deux fibres de transport pour réaliser des mesures de débits de dose et de dose à distance. De plus, la présence au sein de la matrice de deux types de centres luminescents émettant à des longueurs d’ondes différentes permet d’étendre la gamme spectrale de luminescence. Ces échantillons ont été caractérisés, avant et après irradiations 1MGy, par plusieurs techniques spectroscopiques. Dans le cas des verres dopés Cu ou Tb seul, des défauts (NBOHC, HC1...) ont été créés après irradiation. Grace à la présence des ions cérium dans la silice codopé Ce/Cu ou Ce/Tb qui a joué un rôle très important où il a protégé la matrice et atténue la création de certains défauts sous irradiation. Des mesures dosimétriques réalisées sous rayons X ont permis d’évaluer la linéarité du signal RL et OSL pour les verres de silice codopés Ce/Tb et Ce/Cu. Concernant les verres codopés Ce/Cu, le signal de RL présente une réponse linéaire dans la gamme 0,0011 - 34 Gy/s à Saint-Etienne et entre 13,3 µGy/s et 7,3 Gy(SiO2)/s à Nice et la linéarité d’OSL a été démontrée jusqu’à 50 Gy à Saint-Etienne et 33 Gy à Nice. Les verres codopés Ce/Tb ont montré une sensibilité en RL dans la gamme de débits de dose comprise entre 13,3 µGy/s et 7,3 Gy/s avec une excellente reproductibilité des mesures. Il a été démontré que ce matériau a une réponse OSL qui reste proportionnelle à la dose jusqu’à 66 Gy(SiO2). Grâce à ces résultats, on en déduit que ces échantillons codopés constituent une solution pour les mesures dosimétries à distance en environnement sévère.For several decades now, monitoring ionizing radiation has been particularly important in places that are difficult to access or even dangerous, especially in harsh environments. Optical fiber is the solution of choice when remote measurement is mandatory. In addition, the optical fibers ensure the spatial separation of the probe, sensitive to radiation, and the electronic processing system, which allows remote measurements in complex geometries. During this work, silica-based glasses developed by the sol-gel route and codoped with active Ce / Tb or Ce / Cu ions were welded to one or two transport fibers to make measurements of dose rates and remote dose. In addition, the presence within the matrix of two types of luminescent centers emitting at different wavelengths makes it possible to extend the spectral range of luminescence. These samples were characterized, before and after 1MGy irradiation, by several spectroscopic techniques. In the case of Cu or Tb doped glasses alone, defects (NBOHC, HC1 ...) have been created after irradiation. Thanks to the presence of the cerium ions in the codoped silica Ce / Cu or Ce / Tb which played a very important role where it protected the matrix and attenuates the creation of certain defects under irradiation. Dosimetric measurements carried out under X-rays made it possible to evaluate the linearity of the RL and OSL signal for the codoped silica glasses Ce / Tb and Ce / Cu. For Ce / Cu codoped glasses, the RL signal has a linear response in the range 0.0011 - 34 Gy / s in Saint-Etienne and between 13.3 µGy / s and 7.3 Gy (SiO2) at Nice and the linearity of OSL has been demonstrated up to 50 Gy in Saint-Etienne and 33 Gy in Nice. Co-coded Ce / Tb glasses showed sensitivity in RL in the dose rate range of between 13.3 µGy / s and 7.3 Gy / s with excellent reproducibility of the measurements. This material has been shown to have an OSL response which remains dose proportional up to 66 Gy (SiO2). Thanks to these results, we deduce that these codoped samples constitute a solution for remote dosimetry measurements in severe environment

Mesure fibrée de la Radioluminescence et de l’OSL d’un verre de Silice Sol-gel Codopé Cu+/Ce3+ sous Irradiation X

International audienc

Investigation of TSL properties of potential fibered-OSL dosimeter materials

International audienc

Remote Measurements of X-rays Dose Rate using a Cerium-doped Air-clad Optical Fiber

PosterInternational audienc

Cu/Ce-co-Doped Silica Glass as Radioluminescent Material for Ionizing Radiation Dosimetry

International audienceOptically activated glasses are essential to the development of new radiation detection systems. In this study, a bulk glassy rod co-doped with Cu and Ce ions, was prepared via the sol-gel technique and was drawn at about 2000 °C into a cylindrical capillary rod to evaluate its optical and radioluminescence properties. The sample showed optical absorption and photoluminescence (PL) bands attributed to Cu + and Ce 3+ ions. The presence of these two ions inside the host silica glass matrix was also confirmed using PL kinetics measurements. The X-ray dose rate was remotely monitored via the radioluminescence (RL) signal emitted by the Cu/Ce scintillating sensor. In order to transport the optical signal from the irradiation zone to the detection located in the instrumentation zone, an optical transport fiber was spliced to the sample under test. This RL signal exhibited a linear behavior regarding the dose rate in the range at least between 1.1 mGy(SiO2)/s and 34 Gy(SiO2)/s. In addition, a spectroscopic analysis of this RL signal at different dose rates revealed that the same energy levels attributed to Cu + and Ce 3+ ions are involved in both the RL mechanism and the PL phenomenon. Moreover, integrated intensities of the RL sub-bands related to both Cu + and Ce 3+ ions depend linearly on the dose rate at least in the investigated range from 102 mGy(SiO2)/s up to 4725 mGy(SiO2)/s. The presence of Ce 3+ ions also reduces the formation of HC1 color centers after X-ray irradiation

Doped sol–gel silica glasses for radiation dosimetry in harsh environment

InvitéInternational audienc

Sol–gel silica glasses for radiation dosimetry

PosterInternational audienceIn the field of new techniques for radiotherapy, also in harsh environment such as in nuclear facilities or in space industry, ionizing radiation dosimetry requires monitoring over long distances and/or with high space resolution of the measurement. For these applications, fibered solutions seem particularly adapted, but in this domain, new sensitive materials, able to be drawn into fibers, are needed. Indeed, scintillating fibers already exist, generally made of tissue-equivalent organic materials, which are particularly interesting to remotely measure real-time X-ray doses in radiotherapy applications. However, these plastic optical fibers exhibit rather poor guiding properties and could suffer from radiation in hostile environment. Thereby, increased attenuation losses and degradation of the scintillating dopant may occur in those devices when exposed to high dose rates, which is a problem in nuclear industry where radiation hardening of the safety or radioprotection devices is a crucial point. Inorganic radio-sensitive optical elements, like doped silicate glasses, can overcome these drawbacks. Moreover, compared to their crystalline counterpart, the glassy scintillators show higher mechanical and thermal stabilities, facilitating their shaping as optical fibers. Hence, this presentation will focus on the potentialities of doped sol-gel silica glasses for in-vivo / in-situ or high dose rate remote measurements.This work deals with the spectroscopic and optical properties of a bulk cerium-doped sol–gel vitreous glass, obtained by densification either in air or in helium atmosphere. In comparison with the glass densified under air atmosphere, the one obtained after sintering the xerogel under helium gas presents improved optical properties, with an enhancement of the photoluminescence quantum yield up to 33 %, which is attributed to a higher Ce3+ ions concentration. The second kind of samples are sol-gel silica glasses activated with various concentrations of Cu+ ions. Here again, we show that the densification atmosphere has a decisive impact on the visible luminescence performance of the glass. The exposition of these Cu-doped samples to high doses of X-ray or -radiation induces point defects, a visible darkening and a strong reduction of their photoluminescence quantum yield. However, the materials remain optically active and can be used in a dosimetry setup.Such glassy cylindrical samples have been drawn at high temperature into thin canes, pieces of which have been used as active materials in fibered remote X-ray radiation dosimeters. The samples exhibited a reversible linear radioluminescence intensity response versus the dose rate up to 50 Gy s−1. The optically stimulated luminescence properties of these doped silica rods have also been investigated using the same fibered setup. These results confirm the potentialities of such materials for in- vivo / in-situ or high dose rate remote dosimetry measurements

Projet SURFIN : nouveaux matériaux pour la SURveillance par Fibre optique des Installations Nucléaires

International audienc