Thesis of Jessica Bahout

Amphithéâtre Pierre Glorieux (CERLA) Thesis defense of Jessica Bahout - laboratory Phlam Optical fibers dedicated to the detectionof ionizing radiation : towards extreme dosimetry Abstract For several decades now, monitoring of ionizing radiation has been particularly important in places that are difficult to access or even dangerous, especially in harsh environments. Optical fiber dosimetry is the choice solution when a high space resolution is sought, like in radiotherapy, or when remote measurements in complex geometries are mandatory, like in the nuclear domain. The materials constituting optical fibers or the probes at their tip are of crucial importance since they have to provide the radiosensitivity of the devices together with their radiation resistance at high dose level. During this work on silica glasses prepared by sol-gel route, a codoping strategy with active ions (couple Ce³⁺/Tb³⁺ or Ce³⁺/Cu⁺) has been adopted. Indeed, the presence of cerium ions allows protecting the matrix by lowering point defects creation under X irradiation. Moreover, codoping the silica matrix with two types of luminescent centers, emitting at different wavelengths, makes it possible to extend the luminescence spectral range. These glasses have been firstly characterized by various spectroscopic techniques (Raman, absorption, photoluminescence, thermoluminescence) before and after irradiation under 1 MGy. Then, capillary vitreous rods have been drawn and spliced to one or two transport fibers, in order to perform remote radioluminescence (RL) and optically stimulated luminescence (OSL) measurements under X-rays.  Concerning the Ce/Cu codoped glassy rods, the RL signal had a linear response against the dose rate in the range 13 µGy/s - 34 Gy/s, namely on 6 decades, which is still unseen in dosimetry. The linearity of OSL versus dose has been demonstrated up to 33 Gy. The Ce/Tb codoped glasses showed sensitivity similar to the Cu/Ce-doped rods, in RL as well as in OSL. Finally, our first RL measurements with Ce- or Cu/Ce-doped sol-gel core optical fibers have paved the way to their use in remote dosimetry systems in harsh environment. Mots clés : Optically stimulated luminescence (OSL), Radioluminescence (RL), Optical fiber, Codoping, Dosimetry, Sol-gel silica glass