Thesis of Ismail Zghari

Defense of thseisi Ismail Zghari - laboratory PhLAM

Abstract :

Radiotherapy has seen several advancements in recent years concerning the size and intensity of X-ray beams. This has led to the emergence of new techniques (intensity-modulated conformal radiotherapy, flash therapy, proton therapy). These techniques require in vivo and real-time measurements of the absorbed dose with high spatial and temporal precision. In this context, which is the framework of the ANR FIDELIO project (Fiber-based In-vivo realtime Dosimetry for Pulsed Radiotherapy), we propose the study of scintillating fiber dosimeters based on the radioluminescence (RL) of doped silica glasses. We are thus interested in the temporal dynamics of the radioluminescence (RL) signal of silica glass doped with rare earth ions and the effects of measurement temperature on this signal. Dosimetric measurements were carried out at different temperatures using rods and fibers of silica doped with Ce3+, Gd3+, or Ce/Gd ions, with the rods being welded to a radiation-hardened transport fiber. For all measurement temperatures, the behavior of the RL is linear with respect to the dose rate. Furthermore, the RL response increases with the irradiation temperature. To explain this increase, a theoretical model reproducing the RL response at different temperatures has been developed for glasses doped with Ce3+, Gd3+, and co-doped Ce3+/Gd3+ ions. This model has highlighted the mechanisms and dynamics involved in these radiation-sensitive materials. This approach, based on the confrontation of theoretical and experimental data, opens up broad perspectives for the development of optical fiber dosimeters suitable for environments with radiation or temperature fluctuations. By combining simultaneous measurements of multiple luminescence processes (radioluminescence, thermoluminescence, and even optically stimulated luminescence), these dosimeters offer temperature independence and allow real-time assessment of the cumulative dose. This advancement represents a significant step forward in the field of optical dosimetry.

Keywords : Optical fiber,Dosimetry,Silica glass,Spectroscopy,Radiation,Point defects