Impacts of Galactic Cosmic Rays on human brains in deep space and on the surface of Mars

Space radiation is an important factor for astronaut safety as they venture on long-duration missions to outer space such as Moon or Mars. Such a mission will expose astronauts to unavoidable cosmic radiation in deep space and on the Martian or lunar surface. Thus, a better understanding of the radiation environment for such a mission and the consequent biological impacts on humans, in particular the human brains, is critical. To investigate the impact of cosmic radiation on human brains and the potential influence on the brain functions, we model and study the cosmic particle-induced radiation dose in a realistic head structure using 134 slices of computed tomography (CT) images of an actual human head as a 3D phantom in Geant4 (GEometry ANd Tracking).

As a first step, we calculate the Brain Response Functions(BRFs) of dose distribution in different parts of the brain, for the most important particle types encountered during a deep space mission inside a spacecraft or habitat such as protons, helium ions, neutrons and some major heavier ions like carbon, nitrogen, and iron. We considered two different scenarios, a human head without shielding protection and a human head with an aluminum shielding of varying thicknesses.

We use these BRFs to calculate the dose rates in the different lobes of the human brain by folding them with various input spectra for galactic cosmic rays (GCRs). These calculations are performed for GCR input spectra in deep space as well as on the surface of Mars. We repeat them for different GCR input spectra to cover the full range of solar modulation and compare our calculations with measurements on the surface of Mars with MSL's Radiation Assessment Detector(RAD).