Ballarini F, Biaggi M, Merzagora M, Ottolenghi A, Dingfelder M, Friedland W, Jacob P, Paretzke H G
Dipartimento di Fisica, Università di Milano, Italy.
Radiat Environ Biophys. 2000 Sep;39(3):179-88. doi: 10.1007/s004110000060.
A new physical module for the biophysical simulation code PARTRAC has recently been developed, based on newly derived electron inelastic-scattering cross-sections in liquid water. In the present work, two modules of PARTRAC describing the production, diffusion and interaction of chemical species were developed with the specific purpose of quantifying the role of the uncertainties in the parameters controlling the early stages of liquid water radiolysis. A set of values for such parameters was identified, and time-dependent yields and frequency distributions of chemical species produced by electrons of different energies were calculated. The calculated yields were in good agreement with available data and simulations, thus confirming the reliability of the code. As the primary-electron energy decreases down to 1 keV, the *OH decay kinetics were found to get faster, reflecting variations in the spatial distribution of the initial energy depositions. In agreement with analogous works, an opposite trend was found for energies of a few hundred eV, due to the very small number of species involved. The spreading effects shown at long times by *OH frequency distributions following 1 keV irradiation were found to be essentially due to stochastic aspects of the chemical stage, whereas for 1 MeV tracks the physical and pre-chemical stages also were found to play a significant role. Relevant differences in the calculated e(aq) -yields were found by coupling the physics of PARTRAC with descriptions of the pre-chemical and chemical stages adopted in different models. This indicates a strict interrelation of the various stages, and thus a strong dependence of the parameter values on the assumptions made for the preceding and subsequent stages of the process. Although equally acceptable results can be obtained starting from different assumptions, it is necessary to keep control of such uncertainties, since they can significantly influence the modeling of radical attack on DNA and, more generally, radiobiological damage estimation. This study confirms the need for new, independently derived data on specific steps of water radiolysis, to be included in comprehensive biophysical simulation codes.
最近基于新推导的液态水中电子非弹性散射截面，为生物物理模拟代码PARTRAC开发了一个新的物理模块。在本工作中，开发了PARTRAC的两个模块，用于描述化学物种的产生、扩散和相互作用，其特定目的是量化控制液态水辐射分解早期阶段参数不确定性的作用。确定了一组此类参数的值，并计算了不同能量电子产生的化学物种的时间相关产率和频率分布。计算得到的产率与现有数据和模拟结果吻合良好，从而证实了该代码的可靠性。随着初级电子能量降至1 keV，发现OH衰变动力学变快，这反映了初始能量沉积空间分布的变化。与类似工作一致，由于涉及的物种数量极少，在几百电子伏特能量下发现了相反的趋势。发现1 keV辐照后OH频率分布在长时间显示的扩散效应主要归因于化学阶段的随机方面，而对于1 MeV径迹，物理和化学前阶段也被发现起重要作用。通过将PARTRAC的物理过程与不同模型中采用的化学前和化学阶段描述相结合发现，计算得到的e(aq) -产率存在相关差异。这表明各个阶段存在严格的相互关系，因此参数值强烈依赖于对该过程前后阶段所做的假设。尽管从不同假设出发可以得到同样可接受的结果，但有必要控制此类不确定性，因为它们会显著影响自由基对DNA攻击的建模，更普遍地说，会影响放射生物学损伤估计。本研究证实需要有关于水辐射分解特定步骤的新的、独立推导的数据，以便纳入综合生物物理模拟代码中。
