Evaluation of water decomposition by irradiation of heavy ion beam and development of the visualization of the ion track in matter

重离子束照射水分解的评价以及物质中离子轨迹可视化的发展

• 批准号: 16310036
• 负责人: KATSUMURA Yosuke
• 金额: $ 7.81万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2004
• 资助国家: 日本
• 起止时间: 2004 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16310036/
• 关键词: water radiolysis; ion beam; intra-track reaction; scavenger; Monte Carlo calculation; spur diffusion model; LET; RBE; ビーム可視化

Water radiolysis has been investigated with heavy ions having energies up to 28GeV produced from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIR). Beams of ^4He^<2+>, ^<12>C^<6+>, ^<20>Ne^<10+>, ^<28>Si^<14+>, ^<40>M^<18+> and ^<56>Fe^<26+> with respective energies of 150, 400, 300, 490, 500 and 500MeV/u corresponding LET values of 2.2, 13, 30, 54, 92 and 183eV/nm, respectively, were taken for the irradiation. The LET changes in sample solutions can be neglected due to their high energies for the irradiation of 1 cm cells. Primary g values have been determined for three important products, hydrated electron (e^-_<aq>), hydroxyl radical (●OH) and hydrogen peroxide (H2O2) as track segment yields (Differential yields) under the condition of neutral pH.With increasing LET, the g values of e^-_<aq> and ●OH decrease from 2.4 and 2.6 in ^4He^<2+> radiolysis to 0.9 and 1.1 numbers/100 eV in ^<56>Fe^<26+> radiolysis, respectively. It wa … More s also found that the primary g value of _<e-aq> is smaller than that of ●OH for any type of ion beam. For the ^<12>C^<6+> beam, other energies such as 290, 220, 135MeV/u were taken for the irradiation to investigate the effects of type or atomic number of ions on the measurement yields. Furthermore, effects of dissolved oxygen on enhancement of H_2O_2 production have also been investigated with aerated NaNO_3 solutions. The presence of dissolved oxygen caused 15-35% enhancement in H_2O_2 yields for all beams.As a second chemical system, we chose methyl viologen (MV^<2+>) solution in the presence of various concentration of formate and measured the yield of methyl viologen radical cation (MV^<●+>). The G(MV^<●+>) increases with increasing formate concentration. In ^4He^<2+> radiolysis, G(MV^<●+>) increases from 5.7 to 7.1 as the concentration of formate is increases from 10mM to 2M, while in ^<56>Fe^<26+> radiolysis, the MV^<●+> yield changes from 2.2 to 4.1. Other values lie between these ^4He^<2+> and ^<56>Fe^<26+> data. G(MV^<●+>) decreases with increasing LET. In the case of C^<6+> radiolysis, G(MV^<●+>) increases with increasing energy of the carbon ion from 135 to 400 MeV/u corresponding to the decrease of the LET of 21 to 11 eV/nm.In parallel to above measurement, Monte-Carlo simulations of the radiolysis of MV^<2+>/formate solutions have been performed. Ionic strength effects on reactions between charged species are taken into account. To reproduce the experimental results, unreported reactions such as MV^<・+> + ●OH and COO^<・-> + ●OH were introduced in the reaction scheme. After optimization, the rate constants of the reactions have been determined to be 3x10^<10> and 5x10^<10>M^<-1>s^<-1>, respectively. On the contrary, reaction between e^-_<aq> and MV^<・+> is too slow to affect G(MV^<・+>).Furthermore, reproducibility of the Monte Carlo and Spur diffusion calculations was compared. Less

国家放射科学研究所(NIR)千叶重离子医疗加速器(HIMAC)产生的能量高达28GeV的重离子对水进行了辐射分解。横梁^4He^&lt；2+>，^&lt；12&>；C^&lt；6+&>，^&lt；20&>；N^&lt；10+&>，^&lt；28&>；Si^&lt；14+&>，^&lt；40；M^&lt；18+&>和^&lt；56&>T；Fe^^&lt；26+&gt；当能量分别为150、400、300、490、500和500 MeV/u时，相应的Let值分别为2.2、13、30、54、92和183 eV/nm。样品溶液中的LET变化可以忽略不计，这是因为样品溶液中的LET对1 cm细胞的照射能量很高。在中性pH条件下，测定了水合电子(e^-lt；aq&gt；)、羟基自由基(OH)和过氧化氢(H_2O_2)三种重要产物的g值。随着LET的增加，在^4He^&lt；2+&gt；2+&gt；辐解中，e^-&lt；Aq&gt；和OH的g值分别从2.4和2.6下降到0.9和1.1个/100 eV。IT Wa…更多的S还发现，对于任何类型的离子束，_&lt；e-aq&gt；的初级g值都小于OH的g值。对于~-lt；12&gt；C^&lt；6+&gt；束流，分别用290、220、135 MeV/u的能量进行辐照，研究离子类型或原子序数对测量产额的影响。此外，还考察了溶氧对NaNO_3溶液中H_2O_2产量的影响。作为第二个化学体系，我们选择甲基紫精(MV^&lt；2+&gt；)溶液，在不同浓度的甲酸盐存在下，测量了甲基紫精自由基阳离子(MV^&lt；+&gt；)的产率。G(mv^&lt；+&gt；)随甲酸盐浓度的增加而增大。当甲酸盐浓度从10 mM增加到2M时，G(mV^&lt；+&gt；)从5.7增加到7.1；而在^&lt；56&gt；Fe^&lt；26+&gt；辐照中，mV^&lt；+&gt；产量从2.2增加到4.1。其他值位于这些^4He^&lt；2+&gt；和^&lt；56&gt；Fe^&lt；26+&>数据之间。G(mV^&lt；+&gt；)随LET增大而减小。在C^&lt；6+&gt；辐射分解的情况下，G(mv^&lt；+&gt；)随碳离子能量从135 MeV/u增加到400 MeV/u而增大，对应的LET从21 eV/nm减小到11 eV/nm。考虑了离子强度对带电物种间反应的影响。为了重现实验结果，在反应方案中引入了未见报道的MV^&lt；·+&gt；+OH和COO^&lt；·-&gt；+OH等反应。优化后的反应速率常数分别为3x10^-lt；10-gt；10-gt；M^&lt；-1&gt；S^-1&gt；反之，e^-&lt；Aq&gt；与mv^&lt；·+&gt；反应太慢，不影响G(mv^&lt；·+&gt；)。此外，还比较了蒙特卡罗方法和杂散扩散方法的重复性。较少