@misc{oai:repo.qst.go.jp:00078937,
 author = {Ken-ichiro, Matsumoto and Ueno, Megumi and Nyui, Minako and Shoji, Yoshimi and Nakanishi, Ikuo and Matsumoto, Kenichiro and Ueno, Megumi and Nyui, Minako and Shoji, Yoshimi and Nakanishi, Ikuo},
 month = {Feb},
 note = {Radiation-induced generations of reactive oxygen species (ROS) were quantified and then possibilities of the sequential reactions were discussed based on its initial localized density at the generated site.
Two different localized densities of hydroxyl radical (•OH) generations were determined, the relatively sparse (milli-molar level) and extremely dense (molar level) generations. The intermolecular distances of the sparse •OH was estimated as 4.3‒6.6 nm,  and that of the extremely dense •OH was 1 nm or shorter. In the dense •OH cluster two •OH molecules are able to react and generate hydrogen peroxide (H2O2), and then one more •OH can react with H2O2 to generate hydroperoxy radical (HO2•). If the •OH source was abundant enough, two HO2• may react to generate H2O2 again. Therefore, in the dense •OH clusters the H2O2 could be generated independent of oxygen. Total •OH generation was identical with the same dose of X-ray and carbon-ion beam irradiation. The percentage of the dense •OH generation, however; increased with increasing linear energy transfer (LET).
Low LET radiations, such as X-ray or gamma-ray, make sparse •OH mainly. The sparse •OH, i.e. •OH generated milli-molar level, may not be a major biological attacker. Hydrogen radical (•H), which is generated simultaneously with the •OH through water radiolysis is the important factor. The •H and oxygen react and generates hydroperoxyl radical (HO2•). Therefore, low LET radiations generate H2O2 dependent of oxygen, and then the oxygen effect is more problematic on low LET radiations
There are two ways to generate H2O2 in water irradiated by ionizing radiation. Those are oxygen-dependent and oxygen-independent ways. The amount of oxygen-dependent H2O2 generation decreased while LET increased. In contrast, the oxygen-independent H2O2 generation increased while LET increased. The oxygen, however, could not affect the total amount of •OH generation or the total amount of ionization caused in water irradiated by ionizing radiation.
The possibility of the reaction between a hydroxyl radical and another molecule may be dependent on the molecular distance between them. The differences in ROS generation and distribution could make a difference in the quality of radiation therapy., Oxygen Radicals, Gordon Research Conference},
 title = {Free Radical Generations and Reactions in an Aqueous Sample Irradiated by X-ray or 290 MeV Carbon-Ion Beam},
 year = {2020}
}