Regolith-Based Lunar Habitat for Astronaut Radiation Protection and Organ Dose Assessment.

Protecting astronauts from radiation is a critical challenge for extended missions on the lunar surface. To mitigate the risks from Galactic Cosmic Rays (GCR) and solar flares, future habitats must be designed with robust shielding against these hazards. Utilizing lunar regolith presents a promising solution, offering effective radiation protection to avoid transporting heavy, prefabricated materials. In this work, we simulated a two-layer lunar dome made of a thin aluminum-based alloy as an inner layer and an outer layer made of lunar regolith. Combined with an advanced mesh-type computerized human phantom, these simulations give a detailed insight into the radiation exposure of astronauts in such habitats. Using the ICRU (International Commission on Radiation Units) sphere as a simplified human phantom we computed the dose equivalent (DE) as a function of the thickness of the outer layer using the BON2020 GCR model. The simulation was repeated at different thicknesses using the ICRP 145 computerized female human phantom to characterize the impact on individual organs. Our study introduces a novel model giving the DE and effective dose equivalent (EDE) exposure experienced by astronauts within a regolith-made lunar dome under GCR during solar minimum conditions, contingent upon the dome's wall thickness. Our comprehensive analysis reveals a decrease in EDE when stacking regolith until 45 g·cm^-2. Until 105 g·cm-2, the production of secondary particles would potentially induce more dose than it would protect. We observe rapid attenuation of heavy ions within 45 g·cm^-2 of regolith thickness, while the presence of secondary neutrons produced by the interaction of primary protons and alphas with the regolith increases the impact on radiation exposure. Notably, the EDE behind a shield comprised of only 1.136 g·cm^-2 of aluminum measures 291 mSv·y^-1 with a body-averaged mean quality factor of 3.3, whereas adding 45 g·cm^-2 of regolith reduces this exposure to 213 mSv·y^-1 and the quality factor to 2.2. Our investigation identifies the skin, breasts, brain, and surface bones as the organs most affected by radiation exposure, with comparable magnitudes of impact across all organs. These findings also underscore the importance of considering organ-specific effects when assessing radiation hazards in space environments.