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

了解水中的辐射诱导过程对基础/应用放射生物物理和化学、医学以及包括核工业在内的各种技术/工业应用的许多领域至关重要。尽管几十年来人们一直在努力更好地理解水的辐射化学背后的基本现象，但这种辐射分解的某些定量方面仍未得到解决。对于在初始能量沉积之后连接化学和物理的超快过程尤其如此。由于水是迄今为止生物细胞中最丰富的成分，因此了解水的辐射物理和辐射化学之间的界面与基础放射生物学具有明显的相关性。事实上，对辐射作用的早期物理和化学阶段的详细了解（例如，“打破皮秒屏障”）对于可靠地描述化学性质和在（亚）皮秒时间尺度上产生的所有反应性物种的高度非均匀空间分布至关重要，这些反应性物种是辐射生物学损伤的前兆。主要集中在辐射作用的“物理化学阶段”的特征。特别是，在NSERC发现资助下，我们希望在未来五年内研究三个开放性问题：(i)辐射通过时产生的大量低能（<30 eV）电子的物理行为，以及它们在辐射轨迹发展中作为水合电子前体在瞬态后续化学反应中的关键作用；（ii）面对寻找“闪速效应”机制的巨大挑战，高剂量率效应，这是一种新的革命性放射治疗方式；（三）水介质本身在分子水平上不是连续的（迄今为止所有的轨道物理程序都将水视为连续体）。为此，我们将尝试以一种识别目标介质分子性质的方式生成轨道。总的来说，拟议的研究计划将使用最先进的蒙特卡罗方法和分子动力学计算，结合当前实验成果，设计基于实验和理论的模型，以提高我们对（稀和浓）水系统辐射分解的认识。我们坚信，在分子水平上对潜在化学的早期表征对于获得完整和准确的辐射分解图像至关重要。毫无疑问，这是基础放射生物学的一个重大挑战，其长期目标是全面了解辐射对生物系统的影响，并利用这些知识提高辐射的治疗和诊断效率。

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.