Space explorers’ exposure to intense Solar Particle Events beyond LEO: RBE-weighted organ doses and effective doses behind different shielding materials

Space exploration beyond Low Earth Orbit presents significant challenges, also due to the crew members’ exposure to Galactic Cosmic Rays and Solar Particle Events. The main purpose of this work therefore consists of quantifying the effectiveness of shielding materials other than aluminum (hydrogen-rich materials such as polyethylene, water and different hydrides, as well as Carbon Fiber Reinforced Plastic) in case of exposure to an intense Solar Particle Event. An interface between the FLUKA radiation transport code and the BIANCA biophysical model, which provides values of Relative Biological Effectiveness depending on particle type, energy, and total dose, was exploited. RBE-weighted organ doses were calculated for a male and a female human voxel phantom exposed to the August 1972 and the October 2003 events, and were compared with the 30-day NASA limits for non-cancer effects. Effective doses were also calculated, and the results were compared with the NASA career limits. All considered materials were found to out-perform aluminum in reducing doses and thus in lowering the risk associated with intense events; these materials can therefore be considered as a valid alternative for shielding optimization in future space missions. In particular, composite materials such as Carbon Fiber Reinforced Plastic represent a very interesting option because they offer a good compromise between shielding efficiency and volume constraints thanks to their high mechanical strength, which makes them suitable to be used as structural materials.