Mitsumasa Taguchi

Yield of OH radicals in water under high-density energy deposition by heavy-ion irradiation

Abstract Taguchi, M. and Kojima, T. Yield of OH Radicals in Water under High-Density Energy Deposition by Heavy-Ion Irradiation. Radiat. Res. 163, 455–461 (2005). The purpose of the present study was to evaluate the dependence of the OH radical yield on the atomic number and the energy of the heavy ions to understand chemical reactions of aqueous solutions. The total yields of oxidized products from phenol in water increased superlinearly as the incident energy increased from 5 MeV/nucleon to 18 MeV/nucleon for carbon and neon ions. The radiolytic yields of OH radicals produced by the ions were determined by analyzing the relationships of the oxidation yields of phenol to the incident energies up to 18 MeV/nucleon for ions in the range of LET from 110 eV/nm to 550 eV/nm and from 320 eV/nm to 1100 eV/nm for carbon and neon ions, respectively. The yields of the OH radicals increased with the specific energy for the same kind of ion and decreased with the atomic number for different ions used at the same specific energy.

Irradiation of single mammalian cells with a precise number of energetic heavy ions-Applications of microbeams for studying cellular radiation response

Abstract A single cell irradiation system has been developed for targeting cells individually with a precise number of high-LET heavy ions to elucidate radiobiological effects of single heavy ions and to investigate the interaction of damages produced by separate events. The system has been installed at a high-energy collimated heavy-ion microbeam apparatus under a vertical beam line of the JAERI-Takasaki AVF-cyclotron. Using the heavy ion microbeam apparatus, mammalian cells are irradiated in the atmosphere with a single or precise number of heavy ions, 13.0 MeV/u 20 Ne or 11.5 MeV/u 40 Ar. Positional data of the individual cells are obtained at an off-line microscope before irradiation, then the cells are targeted and irradiated semi-automatically using the on-line microscope of the microbeam apparatus according to the obtained data. The number of ions penetrating the cells attached on the ion track detector CR-39 were counted with a plastic scintillator-photomultiplier tube assembly and a constant fraction discriminator. Immediately after the irradiation, the position and the number of ion tracks traversed the cell was detected with etching of CR-39 from the opposite side of the cell with alkaline-ethanol solution at 37 °C. The growths of the cells were observed individually up to 60 h after irradiation. The continuous observation of the individual cell growth indicated that a single ion traversal of a cell nucleus resulted in complete growth inhibition of the irradiated cells.

Radical formation in the radiolysis of solid alanine by heavy ions

Abstract Radical formation in solid α-alanine irradiated with 175-MeV Ar8+ and 460-MeV Ar13+, 220-MeV C5+, and 350-MeV Ne8+ ions were studied by the ESR method. The radical yield (number of radicals per incident ion) is constant below the critical fluence of about 1010 ions cm−2 for the Ar ions, 1011 ions cm−2 for the C ion, and 5 × 1011ions cm−2 for the Ne ion. Above the critical fluence, the yield decreases with increasing ion fluence. G-value of the radical formation was obtained from the constant yield at the low fluences. The G-value is not a simple function of LET. This is ascribed to the difference in lateral dose distribution of ion tracks. Assuming a simple cylindrical shape of the ion tracks, the average dose in and the radius of the ion tracks were estimated from the G-values. The radius is 8–25 nm, which is larger than the radius of 2–5 nm for 0.5–3 MeV H+ and He+ ion-irradiations. The fluence-yield curves were simulated with the cylindrical tracks and with the dose-yield relationship for the radical formation in γ-irradiated alanine. The simulated curves agree well with the experimental ones. With the cylindrical model of ion tracks, the variation of the radical yield at the high fluences can be estimated for solid alanine irradiated with several hundreds of MeV heavy ions.

Hydrogen production in gamma radiolysis of the mixture of mordenite and seawater

Hydrogen production by γ-radiolysis of the mixture of mordenite, a zeolite mineral, and seawater was studied in order to provide basic points of view for the influences of zeolite minerals, of the salts in seawater, and of rise in temperature on the hydrogen production by the radiolysis of water. These influences are required to be considered in the evaluation of the hydrogen production from residual water in the waste zeolite adsorbents generated in Fukushima Dai-ichi Nuclear Power Station. As the influence of the mordenite, an additional production of hydrogen besides the hydrogen production by the radiolysis of water was observed. The additional hydrogen can be interpreted as the hydrogen production induced by the absorbed energy of the mordenite at the yield of 2.3×10−8 mol/J. The influence of the salts was observed as increase of the hydrogen production. The influence of the salts can be attributed to the reactions of bromide and chloride ions inhibiting the reaction of hydrogen with hydroxyl radical. The influence of the rise in temperature was not significantly observed up to 60°C in the mixture with seawater. The results show that the additional production of hydrogen due to the mordenite had little temperature dependence.

Yield of OH radicals in water under heavy ion irradiation.Dependence on mass,specific energy,and elapsed time

Abstract Dependence of yields of OH (hydroxyl) radicals on the mass and specific energy of heavy ions and elapsed time after irradiation was investigated, to understand chemical reactions of aqueous solutions. The yields of irradiation products of phenol, super-linearly increased with the incident energy of He, C, and Ne ions ranging from 2 to 18 MeV/u. The yields of the OH radicals were estimated by analyzing the yields of the irradiation products of phenol. The yields of the OH radicals increased with the specific energy for each ion, but decreased both with the mass of each ion at the same specific energy and elapsed time after irradiation.

Radial dose distribution around a heavy ion's path☆

Abstract Ionization currents produced in a small wall-less ionization chamber located at varying distance from the 200 MeV Ni 12+ ions path traversing Ar gas were measured and utilized to construct a track structure model. Using the LET value of 200 MeV Ni 12+ and G (Fe 3+ ) in Fricke solutions (= 15.4) for fast electrons, we estimate G (Fe 3+ ) for 200 MeV Ni 12+ to be 5.0.

Crosslinking of polymers in heavy ion tracks

Gelation of polydimethylsiloxane irradiated with 256 MeV Ar, 306 MeV Ne and 204 MeV C ions was examined. The insoluble residue of the irradiated polydimethylsiloxane was separated with membrane filters. The weight of the insoluble residue was proportional to the number of irradiated ions. This result indicates that gelation occurs in the high local dose region in the ion tracks. A gel string is generated in each ion track. The yield of the insoluble residue depends on the ion beams. The radius of the gel strings estimated using the G-value of crosslinking for low-LET radiation and with appropriate dose distributions in the ion tracks agrees with the experimental results.

Mechanism of radiation-induced reactions in aqueous solution of coumarin-3-carboxylic acid: Effects of concentration, gas and additive on fluorescent product yield

Abstract The radiation-induced reactions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated in aqueous solutions by pulse radiolysis with a 35 MeV electron beam, final product analysis following 60Co γ-irradiations and deterministic model simulations. Pulse radiolysis revealed that C3CA reacted with both hydroxyl radicals (•OH) and hydrated electrons (e− aq) with near diffusion-controlled rate constants of 6.8 × 109 and 2.1 × 1010 M−1 s−1, respectively. The reactivity of C3CA towards O2• − was not confirmed by pulse radiolysis. Production of the fluorescent molecule, 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), was confirmed by final product analysis with a fluorescence spectrometer coupled to a high performance liquid chromatography (HPLC) system. Production yields of 7OH-C3CA following 60Co γ-irradiations depended on the irradiation conditions and ranged from 0.025 to 0.18 (100 eV) −1. Yield varied with saturating gas, additive and C3CA concentration, implying the presence of at least two pathways capable of providing 7OH-C3CA as a stable product following the scavenging reaction of C3CA with •OH, including a peroxidation/elimination sequence and a disproportionation pathway. A reaction mechanism for the two pathways was proposed and incorporated into a deterministic simulation, showing that the mechanism can explain experimentally measured 7OH-C3CA yields with a constant conversion factor of 4.7% from •OH scavenging to 7OH-C3CA production, unless t-BuOH was added.

Estimation of Yields of Hydroxyl Radicals in Water under Various Energy Heavy Ions

Abstract Taguchi, M., Kimura, A., Watanabe, R. and Hirota, K. Estimation of Yields of Hydroxyl Radicals in Water under Various Energy Heavy Ions. Radiat. Res. 171, 254–263 (2009). This article reports the determination of yields of OH (hydroxyl) radicals in water irradiated with helium, carbon, neon and argon ions ranging from 2 to 18 MeV/nucleon. The yields of the OH radicals depend on the atomic number and energy of the incident ion and the reaction time just after the irradiation based on the track structure theory. The yields of the OH radicals estimated by analyzing the yields of the irradiation products from phenol were at almost 0 to 3.1 per 100 eV absorbed energy on a time scale from 0.75 to 300 ns and were lower than the corresponding ones after exposure to low-LET radiation. The yields of OH radicals decreased with decreasing specific energy for each ion, with increasing atomic number of each ion at a similar specific energy, and with the average reaction time after irradiation. In addition, Monte Carlo simulations were conducted and compared with the OH radical yields obtained experimentally.

An ion-track structure model based on experimental measurements and its application to calculate radiolysis yields

Abstract An ion track structure model proposed previously on the basis of classical binary collision theory and experimental measurements of ionization distribution around ion path using low-pressure gas has been applied to calculate the radiolysis yields for heavy ion bombarded Fricke solution and solid alanine dosimeter. The calculation results are compared satisfactorily with reported experimental G -values.