Proton irradiation of Antarctic cryptoendolithic communities for the CRYPTOMARS project

An irradiation campaign for astrobiology research was carried out at ENEA Frascati Research Center within the CRYPTOMARS project. The aim of the campaign was to characterize the responses of microbial communities colonizing Antarctic sandstone to ionizing radiation, at a dose level informed by the Martian surface environment. Proton irradiation is one of several stress factors applied separately within the project. The experiment was carried out at the TOP-IMPLART proton accelerator, a technology demonstrator of a fully linear protontherapy machine with 71 MeV maximum beam energy. Challenges of this experiment lie mainly in the realization of a tailored accelerator set-up, allowing a reproducible and controlled delivery of very low doses (down to 50 mGy with irradiation times of at least half an hour) to 70 Antarctic rock samples. This was achieved thanks to the capabilities of the accelerator to be operated at currents down to 1 µA and perform dose-driven irradiations. To further reduce the dose-rate, the samples were irradiated in a specifically designed support in order to be exposed to the beam halo only. Doses down to 65 μGy per pulse were achieved with this set-up. We report the experimental set-up design, the dosimetric characterization and the beam monitoring of the campaign; the biological analyses are ongoing and will be reported separately.