Self-radiolysis of tritiated water. 3. The •OH scavenging effect of bromide ions on the yield of H2O2 in the radiolysis of water by 60Co γ-rays and tritium β-particles at room temperature
Self-radiolysis of tritiated water. 3. The •OH scavenging effect of bromide ions on the yield of H2O2 in the radiolysis of water by 60Co γ-rays and tritium β-particles at room temperature
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DOI：
10.1039/c4ra06707j
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发表时间：
2014-01-01
期刊：
影响因子：
3.9
通讯作者：
Jay-Gerin, Jean-Paul
中科院分区：
文献类型：
--
作者：
Mustaree, Shayla;Meesungnoen, Jintana;Jay-Gerin, Jean-Paul
蒙特卡罗轨迹化学模拟用于确定过氧化氢在中性水和稀溴化物水溶液中通过25℃的低线性能量转移（LET类似于0.3 keV μ m(-1)）辐射（例如，Co-60的伽马射线，快速电子或高能质子）和氚β粒子（平均LET类似于6 keV μ m(-1)）辐射分解的产率（或g值）。作为H2O2前体(OH)- o中心点自由基的选择性清除剂，对G（H2O2）对这两种类型辐射的抑制作用。在广泛的Br-浓度范围（5 × 10（-7）至0.2 M）下研究该体系，并使用在有或没有空气的情况下公认的辐射分解机制，我们检查了300 MeV辐照质子（在本工作中用于重现Co-60 γ /快速电子辐射分解的效果）和氚β电子辐射分解产生的H2O2清除能力的化学变化。我们发现这些变化可能与辐射分解物质初始空间分布的差异有关（即，电子轨道的结构，氚的低能β电子几乎完全以圆柱形“短轨道”的形式沉积其能量，而γ -辐射分解产生的高能康普顿电子主要形成球形“杂散”），与先前的实验和理论工作完全一致。模拟表明，与Co-60伽马射线相比，在水和溴化水溶液中，高LET氚β电子的短径几何形状有利于G（H2O2）的明显增加。此外，氧的存在可以在类似于10(-7)s的时间尺度上清除水合电子(e（aq)(-)）和h中心点原子，从而保护H2O2在辐射分解的均匀阶段不与这些物质发生进一步的反应。因此，这种对e(aq)（-）和h中心点原子的保护导致了长时间H2O2产率的增加，正如实验所见。最后，对于除氧溶液和曝气溶液，氚β -放射性溶解的H2O2产率比钴γ -放射性溶解更容易被抑制，并通过马刺和短径之间的定量化学差异来解释。这些差异的H2O2前体通过300 MeV辐照质子到氚β -电子辐照的清除能力与实验数据很好地吻合，从而有力地支持了氚β -辐射溶解在高局域LET短径方面的观点。
Monte Carlo track chemistry simulations were used to determine the yields (or G-values) of hydrogen peroxide in the radiolysis of neutral water and dilute aqueous bromide solutions by low linear energy transfer (LET similar to 0.3 keV mu m(-1)) radiation (e.g., gamma-rays from Co-60, fast electrons or high-energy protons) and tritium beta-particles (mean LET similar to 6 keV mu m(-1)) at 25 degrees C. We investigated the influence of Br- ions, as selective scavengers of (OH)-O-center dot radical precursors of H2O2, on the inhibition of G(H2O2) for these two types of radiation. Studying this system under a wide range of Br- concentrations (5 x 10(-7) to 0.2 M) and using a well-accepted mechanism for radiolysis in the presence or absence of air, we examined the chemical changes in the scavengeability of H2O2 produced by 300 MeV irradiating protons (used in this work to reproduce the effects of Co-60 gamma/fast electron radiolysis) and tritium beta-electron radiolysis. We found that these changes could be related to differences in the initial spatial distributions of radiolytic species (i.e., the structure of the electron tracks, the low-energy beta-electrons of tritium depositing their energy almost entirely as cylindrical "short tracks" and the energetic Compton electrons produced by gamma-radiolysis forming mainly spherical "spurs"), in full agreement with previous experimental and theoretical work. Simulations showed that the short track geometry of higher LET tritium beta-electrons in both water and aqueous bromide solutions favored a clear increase in G(H2O2) compared to Co-60 gamma-rays. Moreover, the presence of oxygen was seen to scavenge hydrated electrons (e(aq)(-)) and H-center dot atoms on the similar to 10(-7) s time scale, thereby protecting H2O2 from further reactions with these species in the homogeneous stage of radiolysis. This protection against e(aq)(-) and H-center dot atoms therefore led to an increase in the long time H2O2 yields, as seen experimentally. Finally, for both deaerated and aerated solutions, the H2O2 yield in tritium beta-radiolysis was found to be more easily suppressed than in the case of cobalt gamma-radiolysis, and interpreted by the quantitatively different chemistry between spurs and short tracks. These differences in the scavengeability of H2O2 precursors in passing from 300 MeV irradiating protons to tritium beta-electron irradiation were in good agreement with experimental data, thereby lending strong support to the picture of tritium beta-radiolysis in terms of short tracks of high local LET.