Synthetic Mars Analog Soils are Efficient Photon Shielding Materials

The primary objective of this study was to evaluate the effectiveness of Mars synthetic soils with varying chemical compositions in shielding photons of different energies. Analysis of the contribution of the partial radiation attenuation effects to the total mass attenuation coefficient showed that for the lowest photon energy (0.015 MeV), photoelectric absorption was the primary photon absorption mechanism (96 to 97%). For intermediate photon energies (0.1 to 1 MeV), incoherent scattering (70 to 99%) is the most significant mechanism. At the highest photon energy (100 MeV), pair production was the primary mechanism of photon absorption, accounting for 90% of the attenuation. The mass attenuation coefficient was strongly influenced by the chemical composition of the Mars soil simulant samples, especially at lower energies. The sample with a higher content of heavier elements, such as Ca, Fe, and S, based on the composition of their respective oxide contents (CaO, Fe₂O₃, SO₃), showed the highest attenuation. At higher energies, the variations were minor. The mean free path, half-value layer, and tenth-value layer parameters showed dependence on chemical composition and density. Denser soils and samples composed of heavier elements, such as Ca, Fe, and S, showed greater shielding capacity. The effective atomic number was also strongly influenced by the chemical composition of the samples, which were composed of heavier elements, showing higher values. Our results indicate that regoliths with distinct chemical compositions exhibit differences in radiation shielding capacity. Consequently, depending on the material, different shielding strategies may be necessary. For high-energy photons (100 MeV), a regolith thickness of 50 to 65 cm is adequate to shield 90% of these photons.