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

水系统中辐射诱导过程的理解是至关重要的基础和应用放射生物物理学和化学，医学，以及在各种技术和工业应用的许多领域。如果说，如今，在许多情况下已经对水和水溶液的辐射化学现象有了一般性的了解，那么这种辐解的某些定量方面似乎还没有完全解决。这对于在能量沉积后的最初几皮秒内将化学和物理联系起来的超快过程尤其如此。理解辐射物理学和辐射化学之间的这种界面（即，“打破皮秒屏障”）与基础放射生物学和相关科学具有明显的相关性，因为液态水是生物细胞和组织中最丰富的成分（活细胞含有约70-85%重量的水）。最重要的是，它是一个可靠的描述的化学性质和高度不均匀的空间分布的所有反应性物种（分）皮秒的时间尺度上创建的，并参与作为前体的放射性生物损伤。这种理解对于创建可靠的预测模型也至关重要。本项目属于理论性质，将侧重于辐射作用的物理化学阶段（<1 ps）的表征。特别是，我们希望在未来五年内在NSERC发现资助下解决的一个难题是在初级电离辐射减慢过程中产生的大量低能（<30 eV）二次电子的物理行为，以及它们作为水合电子的前体在辐射径迹发展中的瞬态随后化学中的关键作用。我们希望研究的另一个非常重要的领域是，水介质本身在分子尺度上不是连续的（迄今为止，所有轨道物理程序都认为水是连续的）。我们将尝试以识别目标介质的分子性质的方式生成轨迹。使用国家的最先进的随机蒙特卡罗方法和分子动力学计算结合从目前的实验工作中获得的知识，拟议的研究计划的目的是设计实验和理论为基础的模型，以提高我们的知识的辐解（稀释和浓缩）含水系统，我们觉得，早期，基本化学的分子水平表征对于产生这种辐解的完整、准确的图像是必要的。毫无疑问，这是基础放射生物学面临的一项重大挑战的一部分，我们的长期目标是全面了解辐射对生物系统的影响，并将这一知识应用于提高辐射的治疗和诊断效率。

An understanding of radiation-induced processes in aqueous systems is vital to many areas of basic and applied radiobiological physics and chemistry, medicine, and in a variety of technological and industrial applications. If, nowadays, a general understanding of the phenomena that underline the radiation chemistry of water and aqueous solutions has been obtained in many cases, it appears that certain quantitative aspects of this radiolysis are not yet fully resolved. This is especially true forultrafast processes that link chemistry and physics in the first few picoseconds following energy deposition. Understanding this interface between radiation physics and radiation chemistry (i.e., "breaking the picosecond barrier") is of obvious relevance to fundamental radiobiology and related science as liquid water is by far the most abundant constituent of biological cells and tissue (living cells contain ~70-85% water by weight). Most importantly, it is central to a reliable description of the chemical nature and highly nonhomogeneous spatial distribution of all reactive species created on the (sub) picosecond time scale and involved as precursors of radiobiological damage. This understanding is also critical to creating reliable predictive models. Of a theoretical nature, the present project will focus on the characterization of the physicochemical stage of radiation action (<1 ps). In particular, one difficult problem that we wish to address in the next five years under an NSERC Discovery Grant is the physical behavior of the numerous low-energy (<30 eV) secondary electrons generated in the slowing of primary ionizing radiations and the pivotal role they can have, as precursors of hydrated electrons, on the transient ensuing chemistry in the radiation track development. Another aera of great importance that we wish to examine is the fact that the aqueous medium itself is not continuous on a molecular scale (all track physics programs have hitherto considered water as a continuum). We will attempt to generate a track in a manner that recognizes the molecular nature of the target medium. 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 aims to design experiment-and-theory based models to advance our knowledge of the radiolysis of (dilute and concentrated) aqueous systems for which, we feel, an early-time, 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 where our long-term goal is to achieve a global comprehension of the effects of radiation in biological systems and to apply this knowledge to enhance the therapeutic and diagnostic efficiency of radiation.