Effects Of Let On Oxygen-Dependent And-Independent Generation Of Hydrogen Peroxide In Water Irradiated By Carbon-Ion Beams

Linear energy transfer (LET) dependence of yields of O-2-dependent and O-2-independent hydrogen peroxide (H2O2) in water irradiated by ionizing radiation was investigated. The radiation-induced hydroxyl radical (center dot OH) generation in an aqueous solution was reported to occur in two different localization densities, the milli-molar (relatively sparse) and/or molar (markedly-dense) levels. In the milli-molar-level center dot OH generation atmosphere, center dot OH generated at a molecular distance of similar to 7 nm are likely unable to interact. However, in the molar-level center dot OH generation atmosphere, several center dot OH were generated with a molecular distance of 1 nm or less, and two center dot OH can react to directly make H2O2. An aliquot of ultra-pure water was irradiated by 290-MeV/nucleon carbon-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan). Irradiation experiments were performed under aerobic or hypoxic (<0.5% oxygen) conditions, and several LET conditions (13, 20, 40, 60, 80, or >100 keV/mu m). H2O2 generation in irradiated samples was estimated by three methods. The amount of H2O2 generated per dose was estimated and compared. O-2-independent H2O2 generation, i.e. H2O2 generation under hypoxic conditions, increased with increasing LET. On the other hand, the O-2-dependent H2O2 generation, i.e. subtraction of H2O2 generation under hypoxic conditions from H2O2 generation under aerobic conditions, decreased with increasing LET. This suggests that the markedly-dense center dot OH generation is positively correlated with LET. High-LET beams generate H2O2 in an oxygen-independent manner.