Modeling an epithermal neutron beam for a DIDO type reactor using MCNP - A Monte Carlo code

Epithermal neutron beams are currently being developed for use in BNCT. They have the advantage over thermal beams in that they can achieve better penetration and can therefore treat deeper tumors. It has been shown that the optimum energy range for epithermal neutrons is approximately from 0.5 eV to 10 keV; energies above this range give significant damage due to proton recoil. The original aim of this project was to design an epithermal neutron beam for Harwell's DIDO reactor 10H beam tube, but the reactor was closed down in March, 1990. DIDO was a 25MW(th) research reactor, cooled and moderated by D2O. To model the reactor the Monte Carlo code MCNP was used. Initially, calculations were made to model an experimental setup that was used in 1987 to carry out cell irradiations with an Al/S/Ar filtered beam. Using this experience a study was begun to design an optimum epithermal beam for the 10H beam tube, a 10 inch diameter horizontal tube which penetrates the shield and radial reflector to within 9 cm of the core