Modelling of the dose-rate variations with depth in the Martian regolith using GEANT4

The environmental radiation field at the Martian surface consists mainly of Galactic Cosmic Rays (GCR) and charged particles ejected during the Solar Particle Events (SPE). Interactions between these radiation fluxes and the regolith result in a complex radiation field that varies both as a function of depth and time and can only be quantified using radiation transport models. We first describe here the main issues and constraints in deriving Martian dose rates. Preliminary results, obtained using the GEANT4 Monte Carlo simulation tool kit, suggest the surface dose rate is ∼63 mGy a−1 during quiet periods in solar activity. The accuracy of the model predictions has been tested by comparison with published observations of cosmic ray dose-rate variation in the Earthʹs atmosphere.