Meesungnoen Jintana, Jay-Gerin Jean-Paul
Département de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, 3001, 12 Avenue Nord, Sherbrooke (Québec) J1H 5N4, Canada.
J Phys Chem A. 2005 Jul 28;109(29):6406-19. doi: 10.1021/jp058037z.
Monte Carlo simulations are used to investigate the effects of multiple ionization of water molecules on the yields of formation of free radical and molecular species, including molecular oxygen, in the radiolysis of pure, deaerated liquid water by using different types of radiation (1H+, 4He2+, 12C6+, and 20Ne9+ ions) up to approximately 900 keV/microm, at neutral pH and 25 degrees C. Taking into account the double, triple, and quadruple ionizations of water, the primary (or "escape") yields (at 10(-6) s) of the various radiolytic species (G(e(aq)-), G(H*), G(H2), G(OH), G(HO2/O2*-), and G(H2O2) are calculated as a function of the linear energy transfer (LET) of the radiation. Our results quantitatively reproduce the large increase observed in G(HO2*/O2*-) at high LET. Under the conditions of this study, the mechanisms of triple and quadruple ionizations contribute only weakly to the production of HO2*/O2*-. With the exception of protons, our calculations also simultaneously predict a maximum in G(H2O2) corresponding to the LET of approximately 4.5-MeV helium ions (approximately 100 keV/microm) and approximately 110-MeV carbon ions (approximately 180 keV/microm). This maximum occurs where G(HO2*/O2*-) begins to rise sharply, suggesting, in agreement with previous experimental data, that the yields of HO2*/O2*- and H2O2 are closely linked. Moreover, our results show a steep increase in the initial and primary yields of molecular oxygen with increasing LET, giving support to the "oxygen in heavy-ion tracks" hypothesis. By contrast, it is found that, in the whole LET range considered, the incorporation of multiple ionization in the simulations has only little effect on the variation of our computed G(e(aq)-), G(H*), G(H2), and G(*OH) values as a function of LET. As expected, G(e(aq)-) and G(OH) decrease continuously with increasing LET. G(H) at first increases and then decreases at high LET. Finally, G(H2) monotonically rises with increasing LET. Our calculated yield values compare generally very well with experiment.
蒙特卡罗模拟用于研究在中性pH值和25摄氏度条件下，使用不同类型的辐射（1H⁺、4He²⁺、12C⁶⁺和20Ne⁹⁺离子），能量高达约900 keV/μm，对纯的、脱气的液态水进行辐射分解时，水分子的多次电离对自由基和分子物种（包括分子氧）形成产率的影响。考虑到水的双电离、三电离和四电离，计算了各种辐射分解物种（G(e(aq)⁻)、G(H*)、G(H₂)、G(OH)、G(HO₂/O₂*⁻)和G(H₂O₂)）在10⁻⁶ s时的初始（或“逸出”）产率与辐射线能量转移（LET）的函数关系。我们的结果定量地再现了在高LET下G(HO₂*/O₂*⁻)中观察到的大幅增加。在本研究条件下，三电离和四电离机制对HO₂*/O₂*⁻的产生贡献较弱。除了质子外，我们的计算还同时预测了G(H₂O₂)的最大值，对应于约4.5 MeV氦离子（约100 keV/μm）和约110 MeV碳离子（约180 keV/μm）的LET。这个最大值出现在G(HO₂*/O₂*⁻)开始急剧上升的地方，这与先前的实验数据一致，表明HO₂*/O₂*⁻和H₂O₂的产率密切相关。此外，我们的结果表明，随着LET的增加，分子氧的初始和初级产率急剧增加，支持了“重离子径迹中的氧”假说。相比之下，发现在所考虑的整个LET范围内，在模拟中纳入多次电离对我们计算的G(e(aq)⁻)、G(H*)、G(H₂)和G(*OH)值随LET变化的影响很小。正如预期的那样，G(e(aq)⁻)和G(OH)随着LET的增加而持续下降。G(H)在高LET时先增加后下降。最后，G(H₂)随着LET的增加而单调上升。我们计算的产率值与实验结果总体上比较吻合。
