Development of irradiation field for neutron capture therapy using direct neutrons from compact proton accelerator

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We examined the characteristics of the target assembly for the direct usage of near threshold^7L i(p,n)^7Be neutrons for BNCT. We were able to clarify the following :1) We performed a parametric survey, via simulation, of the dependence of the characteristics of the BNCT irradiation field on the thickness of the lithium target. Neutron and gamma ray fluxes were determined in order to verify the usability of the irradiation fields for BNCT. We also investigated the influence of incident proton energy on the irradiation field by considering energies between 1.89MeV to 1.92MeV. The evaluation indices applied were the treatable protocol depth (TPD) and boron-dose enhancer (BDE) thickness.2) Regarding gamma ray production in the target assembly, our experiment at the HIRRAC in Hiroshima University showed that tungsten and molybdenum were better than copper and aluminum as backing materials at the proton energy of 1.9MeV. During the same experiment, solid Li with thickness of 10μm deposited … More on a W plate had exfoliated after several hours of irradiation at 150μA. It was therefore judged that solid Li is not suitable for practical use from the viewpoint of target life-time. Based on this result, we performed fundamental experiments on the potential use of thin film liquid Li target simulated by water flow formation. We confirmed that practical liquid film will be possible for a thickness of 1mm at 50mm in width and 50mm in length and a flow rate of 30m/s generated from a linear array of nozzles and flowing against a guide plate.3) The liquid Li-metal flow experiment (2005) in the IFMIF project and the remarkable achievement of the group of ANL suggested that liquid Li thin film formation is technically possible and the prospect of its practical implementation is high.As to the neutrons from the near threshold^7Li (p,n) ^7Be reaction, we are going to continue to develop a BNCT irradiation field, and will push for the future implementation of accelerator BNCT irradiation system. Less