Design of filtered epithermal neutron beams for BNC

The design principles of filters (installed in nuclear reactors) to provide epithermal neutron beams suitable for use in 10B Neutron Capture Therapy (BNCT) are reviewed. The goal of such filters is to provide epithermal neutron beams within an energy range of 1 keV to 30 keV with fluxes in excess of 5 x 108 neutrons/cm2.s, and having acceptably low contaminant fast neutron (> 30 keV) and gamma components. Filters considered for this application include 238U, Sc, Fe/Al and Al/S. It is shown that in order to achieve a goal epithermal neutron flux of > 5 x 108 neutrons/cm2.s, such filters must be located in radial beam channels which view essentially the complete reactor core. Based on considerations of estimated epithermal fluxes, cost and availability of materials, and transmitted neutron energy spectrum, it is suggested that a filter consisting of elements of Al, S, Ti and V might prove to be an optimum design for BNCT applications. 13 references, 3 figures, 8 tables