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

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Understanding radiation-induced processes in water is of crucial importance to many areas of basic/applied radiobiological physics and chemistry, medicine, and a variety of technological/industrial applications, including the nuclear industry. Despite decades of efforts to better understand the basic phenomena underlying the radiation chemistry of water, certain quantitative aspects of this radiolysis remain unresolved. This is especially true for ultrafast processes that link chemistry and physics following the initial energy deposition. Since water is by far the most abundant component of biological cells, understanding the interface between radiation physics and radiation chemistry of water is of obvious relevance to fundamental radiobiology. In fact, a detailed knowledge of the early physical and chemical stages of radiation action (e.g., "breaking the picosecond barrier") is of utmost importance for a reliable description of the chemical nature and the highly nonhomogeneous spatial distribution of all reactive species that are created on the (sub-) picosecond timescale and are involved as precursors to radiobiological damage     Theoretical in nature, this project, therefore, focuses primarily on the characterization of the "physicochemical stage" of radiation action. There are, in particular, three open questions that we wish to investigate over the next five years under an NSERC Discovery Grant: (i) the physical behavior of the numerous low-energy (<30 eV) electrons, generated as the radiation passes through, and their pivotal role as precursors of hydrated electrons on the transient subsequent chemistry in the radiation track development; (ii) high-dose-rate effects in the face of the considerable challenges in finding the mechanisms of the "FLASH effect", a new revolutionary modality in radiotherapy; and (iii) the fact that the aqueous medium itself is not continuous at the molecular level (all track physics programs have so far viewed water as a continuum). For this, we will attempt to generate a track in a way that recognizes the molecular nature of the target medium.     Taken together, the proposed research program will use state-of-the-art Monte Carlo methods and molecular dynamics calculations in combination with the findings from current experimental efforts to design experiment-and-theory based models to advance our knowledge of the radiolysis of (dilute and concentrated) aqueous systems. We strongly believe that early-time characterization of the underlying chemistry at the molecular level is crucial to get a complete and accurate picture of this radiolysis. It is, without a doubt, part of a major challenge in fundamental radiobiology with the long-term goal of gaining a global understanding of the effects of radiation in biological systems and using this knowledge to increase the therapeutic and diagnostic efficiency of radiation.