Sanguanmith Sunuchakan, Meesungnoen Jintana, Stuart Craig R, Causey Patrick, Jay-Gerin Jean-Paul
Département de médecine nucléaire et de radiobiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke 3001, 12e Avenue Nord Sherbrooke Québec J1H 5N4 Canada
Reactor Chemistry and Corrosion Branch, Canadian Nuclear Laboratories Chalk River Ontario K0J 1J0 Canada.
RSC Adv. 2018 Jan 12;8(5):2449-2458. doi: 10.1039/c7ra12397c. eCollection 2018 Jan 9.
The effect of the azide ion N on the yield of molecular hydrogen in water irradiated with Co γ-rays (∼1 MeV Compton electrons) and tritium β-electrons (mean electron energy of ∼7.8 keV) at 25 °C is investigated using Monte Carlo track chemistry simulations in conjunction with available experimental data. N is shown to interfere with the formation of H through its high reactivity towards hydrogen atoms and, but to a lesser extent, hydrated electrons, the two major radiolytic precursors of the H yield in the diffusing radiation tracks. Chemical changes are observed in the H scavengeability depending on the particular type of radiation considered. These changes can readily be explained on the basis of differences in the initial spatial distribution of primary radiolytic species (, the structure of the electron tracks). In the "short-track" geometry of the higher "linear energy transfer" (LET) tritium β-electrons (mean LET ∼5.9 eV nm), radicals are formed locally in much higher initial concentration than in the isolated "spurs" of the energetic Compton electrons (LET ∼0.3 eV nm) generated by the cobalt-60 γ-rays. As a result, the short-track geometry favors radical-radical reactions involving hydrated electrons and hydrogen atoms, leading to a clear increase in the yield of H for tritium β-electrons compared to Co γ-rays. These changes in the scavengeability of H in passing from tritium β-radiolysis to γ-radiolysis are in good agreement with experimental data, lending strong support to the picture of tritium β-radiolysis mainly driven by the chemical action of short tracks of high local LET. At high N concentrations (>1 M), our H yield results for Co γ-radiolysis are also consistent with previous Monte Carlo simulations that suggested the necessity of including the capture of the precursors to the hydrated electrons (, the short-lived "dry" electrons prior to hydration) by N . These processes tend to reduce significantly the yields of H, as is observed experimentally. However, this dry electron scavenging at high azide concentrations is not seen in the higher-LET H β-radiolysis, leading us to conclude that the increased amount of intra-track chemistry intervening at early time under these conditions favors the recombination of these electrons with their parent water cations at the expense of their scavenging by N .
利用蒙特卡罗径迹化学模拟并结合现有实验数据，研究了叠氮离子N 在25℃下对钴γ射线（1 MeV康普顿电子）和氚β电子（平均电子能量7.8 keV）辐照水时分子氢产率的影响。研究表明，N 因其对氢原子具有高反应活性而干扰H 的形成，并且对水合电子（扩散辐射径迹中H 产率的两种主要辐射分解前体）的反应活性较低。根据所考虑的特定辐射类型，观察到H 的清除能力发生了化学变化。这些变化很容易基于初级辐射分解物种的初始空间分布差异（即电子径迹的结构）来解释。在较高“线能量转移”（LET）的氚β电子（平均LET5.9 eV nm）的“短径迹”几何结构中，自由基在局部形成的初始浓度比由钴-60γ射线产生的高能康普顿电子（LET0.3 eV nm）的孤立“刺”中高得多。因此，短径迹几何结构有利于涉及水合电子和氢原子的自由基-自由基反应，导致与钴γ射线相比，氚β电子的H 产率明显增加。从氚β辐射分解到γ辐射分解过程中H 清除能力的这些变化与实验数据高度一致，有力地支持了氚β辐射分解主要由高局部LET的短径迹化学作用驱动的观点。在高N 浓度（>1 M）下，我们关于钴γ辐射分解的H 产率结果也与先前的蒙特卡罗模拟一致，该模拟表明有必要考虑N 对水合电子前体（即水合前的短寿命“干”电子）的捕获。这些过程往往会显著降低H 的产率，正如实验所观察到的那样。然而，在较高LET的氚β辐射分解中未观察到高叠氮浓度下的这种干电子清除现象，这使我们得出结论，在这些条件下早期介入的径迹内化学作用增加，有利于这些电子与其母体水阳离子的重组，而不是被N 清除。
