| Summary: | Permafrost on Mars is considered a primary target for the search for life. On a microscopic scale permafrost is highly non-uniform and the effective radiation dose absorbed by a microbe, and thus its survival probability, depends strongly on its microscopic location and its environment. The goal of this work was to determine how long microbes will survive in a dormant state under the influence of radiation from radionuclides in the Martian regolith, and how fast radiation will destroy the remnants of dead microbes. Our approach was to model the radiation environment that microbes are exposed to in the Martian subsurface using the Geant4 Monte Carlo programs DosiSed and DosiVox. This dissertation describes the methodologies and results of this study. The reliability and precision of DosiVox and DosiSed simulations were rigorously tested on dose distributions measured with Al2O3:C dosimeters buried in terrestrial samples and by reproducing published data. The optimum simulation parameters were determined for the infinite dimensional models for the Martian subsurface and dose rate distributions were determined. Finally, the results and limitations of our calculated survival probabilities and probabilities of preservation of biomarkers in the Martian subsurface are presented and discussed. Our result shows that microbes can survive for as long 50 billion years depending on their location and whether they are exposed to the full spectrum of the radiation or only gamma radiation. For microbes that are exposed to only gamma radiation, the most radio-resistant of them can survive up to 350 billion years while those that are exposed to the full spectrum will not survive for more than 500 million years.
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