The effects to dose distributions of different shield materials used for tunnel design in proton accelerators

Fast neutrons are generated when high - energy particles interact with matter. Neutrons are electrically neutral particles therefore they cannot be affected or stopped by electric force. Neutrons ionize matter only indirectly, which makes neutrons highly penetrating type of radiation. To protect personnel and the environment from the effects of radiation, shielding is necessary. Radiation shielding involves at placing a shielding material between the ionizing radiations source and object to be protected in order to reduce the radiation rate in protecting area. Neutron shielding is very difficult because of the much lower absorption cross sections at higher energies. Thus, fast neutrons are slowed down when they undergo elastic or inelastic scattering and then slow neutrons are absorbed. For neutrons, shield materials are used such as concrete, iron. Because of its not effective for lower neutron energies, an additional absorber material is usually needed. In this study, two different type of ferroboron structure; FeB and Fe2B were investigated as shield material in shield design of tunnel for high - energy protons. FeB and Fe2B are alloys of boron which is effective in absorbing slow (thermal) neutrons and iron effective in slowing down fast neutrons. Minimum shield thicknesses of tunnel were determined in the form of a single material and added to concrete in a form of particle alloy. The formations and energies of neutrons depend on the energies of protons. Therefore, proton energies of 50-1000 and 1000 in MeV were taken in the form of a single material and added to concrete alloy, respectively. FLUKA Monte Carlo simulation code was used for dose distributions of neutron and shield design of tunnel. According to the simulation results, FeB and Fe2B were found to be effective shield materials for neutrons. The shield thicknesses vary with intensity at high energies, while they vary with amount of absorbing material at low energies. It is seen that FeB having more boron content is better shield material than Fe2B at lower energies.