Shielding data for 100 250 MeV proton accelerators: Double differential neutron distributions and attenuation in concrete

Double differential distributions of neutrons produced by 100, 150, 200 and 250 MeV protons stopped in a thick iron target were simulated with the FLUKA Monte Carlo code at four emission angles: forward, 45°, transverse and 135° backwards. The attenuation in ordinary concrete of the dose equivalent due to secondary neutrons, protons, photons and electrons was calculated. Some of the resulting attenuation curves are best fitted by a double-exponential function rather than a single-exponential. The effect of various approximations introduced in the simulations is thoroughly discussed. The contribution to the total ambient dose equivalent from photons and protons is usually limited to a few percent, except in the backward direction where photons contribute more than 10% and up to 35% to the total dose for a shield thickness of 1–2 m. Source terms and attenuation lengths are given as a function of energy and emission angle, along with fit to the Monte Carlo data. An extensive comparison is made of values obtained in the present work with published experimental and computational data.