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Ultimo aggiornamento 26 gen 2018
Autore
Chiara Magni
Sesso F
Esperimento BEAT_PRO
Tipo Laurea Magistrale
Destinazione dopo il cons. del titolo Altro
Università Universita' Di Pavia
Strutt.INFN/Ente
Pavia
Titolo Neutron activation and dosimetry studies for the design of an accelerator-based BNCT clinical facility at CNAO
Abstract The context of this thesis is the project of a Boron Neutron Capture Therapy (BNCT) clinical facility based on proton accelerator at CNAO. The work concerns the study of the issues related to the neutron activation of materials present in the Beam Shaping Assembly (BSA: the ensamble of materials to moderate and collimate the neutron beam produced at the target) and in the irradiation room. The first part of the study consists in the characterization of powders of AlF3, aluminium fluoride, the material chosen as the neutron moderator in the BSA. Powders of different purity have been tested, in particular a chemical grade powder ('pure') and an industrial one ('raw'). In order to verify the isotopic composition of the different types of aluminium fluoride and to evaluate the radioprotection aspects of its use, AlF3 samples have been irradiated in the TRIGA Mark II nuclear reactor in Pavia. The analysis of the activated samples by gamma spectroscopy allowed the identification of the isotopes present in the materials and information on their neutron activation. Dose measurements of the irradiated samples over a period of about 2 weeks gave indications about the possibility to use the available materials as the main component of the BSA, not to overcome the limits imposed by radiation protection. Monte Carlo simulations of AlF3 neutron activation have been performed by MCNP, validated by the measurement results and used to calculate the dose in the environment around the beam as a function of the time. The outcome of these analysis has led to a complete characterization of AlF3 in its isotopic composition and neutron activation aspects. Dose measurements have shown that for the described purposes the best choice for the BSA is the raw AlF3, since the dose decreases with time more rapidly if compared to pure material. This is due to the presence of antimonium with a half-life of about 60 days in pure alluminum fluoride. Further studies on sintered aluminium fluoride are foreseen, to prove that exposition to radiation does not change the mechanical properties of the solid material and to test if isotopic composition and dose characteristics are modified by the sintering process. Chosen the BSA material, the second part of the work focuses on some crucial aspects concerning the radiation protection for the design of the BNCT clinical facility at CNAO, in particular of the patient irradiation rooms. The effects of neutron irradiation in the environment have been studied by MCNP simulation, calculating the neutron flux and the induced activation in the components of the facility, in the patient and in the air of the treatment room. Particular attention has been devoted to the reaction 40Ar(n,gamma)41Ar. Simulations have assessed the impact of irradiation time and of different materials that can be used as constituents of the walls of the room. The results obtained allow the estimation of the biological dose in the room and in the patient organs not directly irradiated, leading to radioprotection evaluations and measures to be taken, according to regulation in matter of ionizing radiations.
Anno iscrizione 2015
Data conseguimento 28 set 2017
Luogo conseguimento Dipartimento di Fisica, Università di Pavia
Relatore/i
Silva Bortolussi   
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