[en] Gelation of polydimethylsiloxane irradiated with 256 MeV Ar ion was examined. The insoluble residue of the irradiated polydimethylsiloxane was separated with membrane filters. The weight of the insoluble residue is proportional to the number of irradiated ions. This result indicates that gelation occurs in the high local dose region of the ion tracks. A gel string is generated in each ion track. The weight of a gel string increases in proportion to the initial molecular weight (M_n) of polydimethylsiloxane. It arises from an increase in the radius of the gel strings with increasing M_n. The gelation dose decreases with increasing M_n. The region with a dose higher than the gelation dose is found in the ion tracks. The radius of the gel strings estimated using the G-value of crosslinking for low-LET radiation and with an appropriate dose distribution in the ion tracks explains the experimental results well

[en] 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

[en] The G-values of the acridine C-radical in poly(vinyl alcohol) film produced by the irradiation with several hundred MeV heavy ions decreased with increasing linear energy transfer (LET) value for the same ion. The radical yield was dependent on the fluence of the ions and was analyzed using the 'chemical' track model. The estimated radius of the chemical track decreases with increasing incident velocity of the same ion. At the same incident velocity, the radius increases with increasing atomic number of the ion

[en] Effects of ion beam irradiation on α-alanine, adipic acid and polydimethylsiloxane were examined. Stable radicals were generated in the radiolysis of solids of α-alanine and adipic acid by γ-ray, 220 MeV C ions, 350 MeV Ne ions and 175 MeV Ar ions. The G-value decreases in this order. The G-value for adipic acid decreases more than that for α-alanine. The decreases in the G-value are ascribed to high local dose in the ion tracks. Effective G-value of the radicals for γ-irradiations decreases at high doses. The local dose in the ion tracks exceeds those doses, and the G-values for the ion irradiation are hence smaller than the G-value for γ-irradiations. The difference in the dependence of the G-values for α-alanine and adipic acid on the ion beams is due to difference in the dose-yield relationship for radical formation. The high local dose in the ion tracks exceeds the gelation dose of some of polymers. Formation of gel strings of polydimethylsiloxanes generated in heavy ion tracks was observed by atomic force microscopy

[en] 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 ²⁰Ne or 11.5 MeV/u ⁴⁰Ar. 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 deg. 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

[en] Effect of oxygen on radiation-induced reactions in zeolite-water mixture was studied, in order to obtain a fundamental understanding on radiolytic hydrogen production from the mixture. Understanding of the radiation effect will provide a basis for safe operations of water treatments using zeolites in nuclear accidents. In this study, the effect of oxygen was investigated because oxygen is an abundant molecule that potentially affects the radiation-induced reactions. The hydrogen production from the mixture of an X-type zeolite with aqueous solution was examined under argon-saturated, aerated, and oxygen-saturated conditions. The hydrogen production from the mixture was decreased by the presence of oxygen, although a considerable production of hydrogen from the zeolite was still observed under oxygen-saturated condition. Three effects of oxygen were proposed based on the observed dependence of hydrogen production on the solid-liquid ratio of the mixture under the different gas conditions. One effect is preventing dissolved aluminum from producing hydrogen. The presence of oxygen decreased the hydrogen production from aqueous solution containing small amounts of the zeolite. The solution contained dissolved aluminum, which produces hydrogen through a reaction with hydrated electron. The decrease in hydrogen production and the observation of aluminum elution indicate that oxygen reacts with hydrated electron in competition with dissolved aluminum. Another effect is inhibition of hydrogen produced from the irradiated zeolite. The inhibiting effect was observed in the irradiation of the zeolite with adsorbed water. Oxygen inhibited the hydrogen production from the hydrated zeolite. The other effect is indirect inhibition of hydrogen by promoting hydrogen peroxide generation. The hydrogen production under oxygen-saturated condition was further inhibited when the zeolite was submerged in water. The further inhibition was interpreted as showing that hydrogen peroxide from the interstitial water inhibited the hydrogen production. The radiolysis of water generates hydrogen peroxide. Oxygen promotes the hydrogen peroxide generation. This interpretation is supported by the observation that the concentration of hydrogen peroxide in the irradiated mixture decreased with increasing solid-liquid ratio. The decrease in the hydrogen peroxide concentration indicates that hydrogen peroxide was involved in the reactions induced by irradiation of the zeolite. (author)

[en] Radical formation in solid alanine irradiated with H⁺ and He⁺ ions of 0.5-3.0 MeV and with heavy ions of hundreds of MeV was examined by the ESR method. Radical yield is constant below a critical fluence, and the yield decreases above the fluence. The critical fluence for the H⁺ and He⁺ ions is about 10¹² ions cm^-2, while the critical fluence for the heavy ions is 10¹⁰-10¹¹ ions cm^-2. G-value of the radical formation (radicals per 100 eV absorbed dose) is obtained from the constant yield at the low fluences. The G-value depends on the radiation quality. This dependence is ascribed to the difference of local dose in the ion tracks. The fluence-yield curves were simulated with a model assuming cylindrical shape of ion tracks and dose-yield relationship for γ-irradiation. This model well explains the fluence-yield curves for the ion irradiations. (author)

[en] High energy heavy ions are utilized not only for atomic- and nuclear- physics but material development, biology, and treatment. It is very important for these applications that clarifying physical stage (dose deposition), physical-chemical stage (behavior of initial species) and chemical stage (radical yield) induced by the single ion. The researches on heavy ion induced chemical reactions in aqueous solutions are explained on the four-subjects: dose distribution, average reaction yield, differential reaction yield, and direct observation of transient species. New vistas of the future research are described. (author)

[en] The radiation-induced decomposition of a trace amount of 17 β-estradiol (E2) in water was studied as a function of the dose of 60Co γ-rays. Concentration of both E2 and E2 activity were estimated by LC-MS and ELISA, and decreased with an increase in the dose of γ-rays. E2 at 1.8-nM in water was degraded almost completely by irradiation at 10 Gy (=J/kg), but the E2 activity of the same sample still remained, and decreased by 30 Gy to be lower than the threshold level of contamination to induce some estrogenic effects on the environmental ecology. (author)

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