Simulations for bulk shielding design around rare isotope accelerator targets

The planned Rare Isotope Accelerator (RIA) facility in the US would become the most powerful radioactive beam facility in the world. Beam energies of up to 1 GeV for protons and up to 500 MeV per nucleon for heavy ions are foreseen with beam powers up to 400 kW. The magnitude of the prompt radiation generated at the target stations and characterization of radiation doses and their spatial distribution outside of the bulk shielding will be a significant element of the overall hazard analysis of the facility. To determine the distribution of neutron and photon doses, Monte Carlo radiation transport calculations were carried out for p, d, and ³He beams using MCNPX, and for p, d, ³He, ²²Ne, ⁴⁸Ca, ¹³⁶Xe, and ²³⁸U using PHITS. Results were compared where possible. Simulations using PHITS were also compared to experiment and agreed well. Simulations were also compared with a Moyer semi-empirical approach as a check on results. The simulation results for the dose rate outside of concrete shielding and cast iron shielding agreed reasonably well with the Moyer semi-empirical approach. Results obtained using PHITS and MCNPX agree reasonably well for light ions (p, d, ³He) with and without shielding.