Radiation Exposure in the Vicinity of a Simple Crater on the Moon

The Moon has a harsh radiation environment that poses significant challenges to future science and exploration activities. Exposure hazards from space radiation are primarily due to galactic cosmic rays (GCRs) and solar energetic particles (SEPs) that are incident at the lunar surface from all directions. The level of exposure at a given location on the Moon is dependent on the amount of space radiation incident from above the local horizon. This means that, radiation dosage depends on the surrounding terrain for any location on the surface, so it can vary substantially from point to point. Here we consider the radiation exposure around simple lunar craters that are representative of the types of landforms that will be encountered by future landed missions. Of particular concern will be radiation exposure to biological targets, such as astronauts, and to critical electronic systems. Therefore, we use Geant4 Monte Carlo simulations to compute the dose response for spherical targets composed of water and silicon, as proxies for biological and electronic systems respectively. These targets are surrounded by shells of aluminum of varying thickness to approximate the influence of localized shielding from space suits, rovers, and habitats. To determine the dose rates from primary space radiation (e.g., in rads per year), we convolve the Geant4-computed dose responses with representative GCR and SEP spectra. In comparison with dose received on a planar surface, we find that radiation dosage can be reduced by almost 50 percent for regions inside craters, while for areas outside the crater rim it can be reduced by as much as 10 percent. These are important considerations when selecting sites for permanent habitats, as well as for choosing routes and for contingency planning during surface operations.