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Quantitative methods to evaluate the radioprotection and shielding activation impacts of industrial and medical applications using particle accelerators

par Tesse, Robin
Président du jury Sparenberg, Jean-Marc
Promoteur Pauly, Nicolas
Co-Promoteur De Lentdecker, Gilles
Publication Non publié, 2018-11-15

Thèse de doctorat

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Résumé :

Proton therapy facilities, as other industrial applications using ionizing radiations, are confronted to radioprotection problems and seek to mitigate the undesirable effects. The aim of this thesis is to study the IBA compact proton therapy center, the Proteus®One in this radioprotection context. The compactness of this system implies important radioprotection issues, mainly the concrete shielding activation where a model allowing to predict and characterize the impact of secondary radiations on the system is required. Numerical simulations using Monte Carlo methods are used and in particular, a benchmark between different existing software has been carried out to validate the use of the Geant4 software in this work. The first part of this thesis focuses on the design of the structural shielding taking into account neutron sources in the model. In particular, the concept of neutron-equivalent source is introduced. In this framework, the quantity and the localization of the generated nuclear waste in concrete are determined. The second part of the work investigates the beam properties and its interactions with matter along the transport beamline. After the analysis of the existing system, a new degrader, which is one of the critical elements for the emission of secondary radiations and for the performances of the device, is proposed. Comparisons between existing (aluminium, graphite, beryllium) and novel (boron carbide and diamond) degrader materials are provided and evaluated against semi-analytical models of multiple Coulomb scattering. The use of diamond with a geometry adaptation allows beam emittance reduction and beam transmission increase. The third part of this thesis considers a complete 3D model of the Proteus®One system. It contributes to acquire a detailed knowledge of the beam properties inside the beamline. This model is validated with experimental data and the assumption of neutron-equivalent source is verified. Finally, maps of proton and neutron interactions are generated to provide a complete mapping of the secondary radiations in the system. These maps can be used to determine dosimetric or radioprotection quantities.