FLUKA Simulation of the Radiation Environment on the Surface of Mars

Uncertainties persist regarding the assessment of the carcinogenic risk associated with galactic cosmic ray (GCR) exposure. The GCR spectrum peaks in the range of 300 MeV/n to 700 MeV/n and is comprised of elemental ions from H to Ni. While Fe ions represent only 0.03% of the GCR spectrum in terms of particle abundance, they are responsible for nearly 30% of the dose equivalent in free space. Because of this, radiation biology studies focusing on understanding the biological effects of GCR exposure generally use Fe ions. Acting as a thin shield, the Martian atmosphere alters the GCR spectrum in a manner that significantly reduces the importance of Fe ions. Additionally, albedo particles emanating from the regolith complicate the radiation environment.

The present study uses the Monte Carlo code FLUKA to simulate the response of a tissue-equivalent proportional counter on the surface of Mars to produce dosimetry quantities and microdosimetry distributions. The dose equivalent rate on the surface of Mars was found to be 0.18 Sv/y with an average quality factor of 2.9 and a dose mean lineal energy of 18.4 keV/?m. Albedo neutrons accounted for 25% of the dose equivalent. Additionally, differential energy spectra were generated in order to determine the fractional contribution to frequency, dose, and dose equivalent for each elemental ion from H to Ni on the surface of Mars. Fe ions were found to account for just 1.3% of the dose equivalent while H and He ions were found to account for 32% and 17%, respectively. It is anticipated that these data will provide relevant benchmarks for use in future risk assessment and mission planning studies.