Radiation Exposure and Shielding Effects on the Lunar Surface

Abstract

The Moon will be a primary target for human space exploration in the near future. A limiting factor for a crewed mission to the Moon is the radiation dose during their stay on the lunar surface. While the total dose is expected to be dominated by the galactic cosmic radiation (GCR), the potential occurrence of large solar energetic particle events may lead to severe short-term effects and endanger the success of the mission. This work investigated the expected dose rates for maximum GCR intensity and the total dose from several historical solar energetic particle events, including the NASA reference event, through the application of numerical simulations with the Geant4 Monte-Carlo framework. An evaluation of the shielding effect of lunar regolith was carried out. For the solar particle events a shielding of more than 4 g/cm2 of regolith would reduce the expected dose to below the current 30-day limits and a shielding of more than 10 g/cm² would result in a safety margin factor of two. For GCR adding additional mass shielding did not reduce the absorbed dose significantly. The estimated total dose equivalent received utilizing around 180 g/cm² of regolith amounted to 200 mSv/year, which is only about 25% below the corresponding estimates for an unshielded environment. The comparison to model and experimental data from literature showed reasonable agreement to measurements but the analysis of various earlier model results revealed, that substantial differences between the models exist, despite all improvements that have been achieved in recent years.