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artículo con referato
"Optimization of a neutron production target and beam shaping assembly based on the 7Li(p,n)7Be reaction"
A.A. Burlón, A.J. Kreiner, A.A. Valda Ochoa, D.M. Minsky, H.R. Somacal, M.E. Debray and P. Stoliar
Nucl. Instrum. Meth. B 229(1) (2005) 144-156
In this work a thick LiF target was studied through the 7Li(p,n)7Be reaction as a neutron source for Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT) to provide a testing ground for numerical simulations aimed at producing an optimized neutron production target and beam shaping assembly design. Proton beams in the 1.88–2.0 MeV energy range were produced with the tandem accelerator TANDAR (TANDem ARgentino) at the Comision Nacional de Energía Atomica (CNEA) in Buenos Aires, Argentina. A cylindrical water-filled head-phantom, containing a boric acid sample, was irradiated to study the resulting neutron flux. The dose deposited in the boric acid sample was inferred through the Compton-suppressed detection of the gamma radiation produced from the 10B(n,αγ)7Li capture reaction. The thermal neutron flux was evaluated using bare and Cd-covered activation gold foils. In all cases, Monte Carlo simulations have been done showing good agreement with the experimental results. Extensive MCNP simulation trials have then been performed after the preliminary calculation tool validation in order to optimize a neutron beam shaping assembly. These simulations include a thick Li metal target (instead of LiF), a whole-body phantom, two different moderator-reflector assemblies (Al/AlF3/LiF, Fluental®, as moderator and lead as reflector and a combination of Al, PTFE (polytetrafluoroethylene) and LiF as moderator and lead as reflector) and the treatment room. The doses were evaluated for proton bombarding energies of 1.92 MeV (near to the threshold of the reaction), 2.0MeV, 2.3MeV (near the reaction resonance) and 2.5MeV, and for three Fluental® and Al/PTFE/LiF moderator thicknesses (18, 26, 28 and 34cm). In a later instance, the effect of the specific skin radiosensitivity (an RBE of 2.5 for the 10B(n,α)7Li reaction) and a 10B uptake 50% greater than the healthy tissue one, was considered for the scalp. To evaluate the doses in the phantom, a comparison of the different assemblies and beam energies was done using a Tumor Control Probability (TCP) model. The simulations show the advantage of irradiating with nearresonance-energy protons (2.3MeV) because of the relatively high neutron yield at this energy, which at the same time keeps the fast neutron healthy tissue dose limited and leads to the shortest treatment times. A moderator of 34cm length (either Fluental or Al/PTFE/LiF) has shown the best performance among the studied cases.
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