Theoretical studies of physical and chemical aspects of primary processes in fundamental radiobiology

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If, nowadays, a panorama of the phenomena that underly the radiation chemistry of aqueous systems has reasonably been obtained in a number of cases, it appears that certain key aspects of this radiolysis are not yet fully resolved. This is especially true for the fundamental processes that link chemistry with the early physical interactions initiated by radiation. For example, recent fascinating observations have suggested the existence of new mechanisms in liquid-water radiolysis at very short times that now have to be identified and quantified. Bridging the gap in our understanding of this physicochemical interface is of obvious relevance to radiobiology and related science (e.g., free-radical biology) as liquid water is by far the most abundant constituent of biological cells. Knowledge of this "physicochemical" stage of radiolysis is central to a reliable description of the chemical nature and spatial distribution of the reactive species produced initially and precursors of radiobiological damage. This is also true for the radiolysis due to high linear energy transfer (LET) radiations, where it is critical to understand the complex nature of heavy-ion tracks (i.e., the "track structure") and their chemical effects (such as multiple ionization, Coulomb explosion, and thermal spike) for a number of practical reasons (e.g., hadrontherapy, space radiation effects). This is true as well when we want to account for the pivotal role played in the early stages of radiation chemistry by the numerous low-energy secondary electrons generated in the slowing of primary ionizing radiations, or for the fact that the aqueous medium itself is not continuous on a molecular scale. Using state-of-the-art stochastic Monte-Carlo methods and molecular dynamics calculations in combination with the knowledge gained from current experimental efforts, the proposed research program is aimed at designing experiment-and-theory based models to help advance our understanding of those challenging areas of the radiolysis of aqueous systems for which, we feel, a molecular-level characterization of the underlying chemistry is essential to produce a complete, accurate picture of this radiolysis. It is, without doubt, part of a major challenge in fundamental radiobiology.