Yosuke Katsumura

Pulse radiolysis study of concentrated sulfuric acid solutions. Formation mechanism, yield and reactivity of sulfate radicals

In the pulse radiolysis of concentrated sulfuric acid solutions, the absorption spectrum and the molar absorption coefficient (1600 dm3 mol–1 cm–1) of the sulfate radical are unchanged up to 10 mol dm–3 H2SO4, suggesting that the sulfate radical exists in the dissociated form (SO–4). Two formation processes for the sulfate radical have been directly demonstrated in sulfuric acid and hydrogensulfate solutions: a fast one completed in the duration of the electron pulse, and a slow one occurring over a microsecond time range. For sulfate solutions only the fast formation process is observed. In sulfuric acid solutions the slow formation process is OH + HSO–4→ H2O + SO–4(4.7 × 105 dm3 mol–1 s–1) and OH + H2SO4→ HSO4+ H2O → SO–4+ H3O+(1.4 × 107 dm3 mol–1 s–1), and the fast formation process is the direct action of radiation on sulfuric acid with a G value of (2.7 ± 0.4)× 10–2 molecule eV–1. The yields of (OH + SO–4) and H can be quantified as: G(OH + SO–4)= 2.9fw+ 2.7fs and G(H)= 3.7fw+ 2.7fs. The yields of SO–4 have also been evaluated and the decay kinetics and reactions of the sulfate radical studied.

Hydrated electron in subcritical and supercritical water: a pulse radiolysis study

Temperature dependences of the eaq− spectrum and Gemax were investigated by the pulse radiolysis method over a temperature range of 25–400°C including the supercritical condition and the eaq− formation in supercritical water (D2O) was confirmed. With increasing temperature, the absorption peak (λmax) of eaq− shifts significantly to longer wavelength. The value of Gemax in supercritical water is considerably smaller than in liquid water at room temperature. The behavior of eaq− revealed here is helpful for an extensive understanding of water radiolysis and for the study of eaq− involving radical reactions in supercritical water.

The formation process of the excited state of cycloalkane liquid using picosecond pulse radiolysis

Abstract Fluorescence from excited cycloalkanes in neat liquid produced by electron irradiation was observed. Emission spectra, lifetimes and relative yields of the excited states were obtained. From the measurement with a high time resolution, it was clearly shown that the formation rate of the excited state is dependent on the kind of liquid. Based on above results, formation process of the excited cycloalkanes following geminate ion recombination process are discussed.

The ultra-fast process of picosecond time-resolved energy transfer in liquid cyclohexane by picosecond single-pulse radiolysis

Abstract Two formation processes of singlet states of solute molecules in irradiated liquid cyclohexane have been observed by using a single picosecond electron pulse-radiolysis technique. The slower process corresponds to the very fast formation process reported by Beck et al. The faster process is an ultra-fast process which finishes immediately after a picosecond electron pulse, and is hardly quenched by CCl 4 on triethylamine. The ratio of the faster component to the slower component in liquid cyclohexane is very different from that in liquid toluene.

γ-Radiolysis study of concentrated nitric acid solutions

The formation of nitrous acid has been studied in the 60Co-γ radiolysis of concentrated nitric acid solutions. The yields of nitrous acid are proportional to the electron fraction of nitric acid, on the basis of which, an additional reaction path, NO–3 [graphic omitted]→ O(3P)+ NO–2 with a primary yield of 0.16 µmol J–1, has been verified for the direct action of radiation on nitric acid.

Isotopic ratio and vertical distribution of radionuclides in soil affected by the accident of Fukushima Dai-ichi nuclear power plants

The results of γ analyses of soil samples obtained from 50 locations in Fukushima prefecture on April 20, 2011, revealed the presence of a spectrum of radionuclides resulted from the accident of the Fukushima Dai-ichi nuclear power plant (FDNPP). The sum γ radioactivity concentration ranged in more than 3 orders of magnitude, depending on the sampling locations. The contamination of soils in the northwest of the FDNPP was considerable. The (131)I/(137)Cs activity ratios of the soil samples plotted as a function of the distance from the F1 NPPs exhibited three distinctive patterns. Such patterns would reflect not only the different deposition behaviors of these radionuclides, but also on the conditions of associated release events such as temperature and compositions and physicochemical forms of released radionuclides. The (136)Cs/(137)Cs activity ratio, on the other hand, was considered to only reflect the difference in isotopic compositions of source materials. Two locations close to the NPP in the northwest direction were found to be depleted in short-lived (136)Cs. This likely suggested the presence of distinct sources with different (136)Cs/(137)Cs isotopic ratios, although their details were unknown at present. Vertical γ activity profiles of (131)I and (137)Cs were also investigated, using 20-30 cm soil cores in several locations. About 70% or more of the radionuclides were present in the uppermost 2-cm regions. It was found that the profiles of (131)I/(137)Cs activity ratios showed maxima in the 2-4 cm regions, suggesting slightly larger migration of the former nuclide.

High-LET Ion Radiolysis of Water: Visualization of the Formation and Evolution of Ion Tracks and Relevance to the Radiation-Induced Bystander Effect

Abstract Muroya, Y., Plante, I., Azzam, E. I., Meesungnoen, J., Katsumura, Y. and Jay-Gerin, J-P. High-LET Ion Radiolysis of Water: Visualization of the Formation and Evolution of Ion Tracks and Relevance to the Radiation-Induced Bystander Effect. Radiat. Res. 165, 485–491 (2006). Ionizing radiation-induced bystander effects, commonly observed in cell populations exposed to high-linear energy transfer (LET) radiations, are initiated by damage to a cellular molecule which then gives rise to a toxic signal exported to neighboring cells not directly hit by radiation. A major goal in studies of this phenomenon is the identification of this initial radiation-induced lesion. Liquid water being the main constituent of biological matter, reactive species produced by water radiolysis in the cellular environment are likely to be major contributors to the induction of this lesion. In this context, the radiation track structure is of crucial importance in specifying the precise location and identity of all the radiolytic species and their subsequent signaling or damaging effects. We report here Monte Carlo track structure simulations of the radiolysis of liquid water by four different impacting ions 1H+, 4He2+, 12C6+ and 20Ne10+, with the same LET (∼70 keV/ μm). The initial radial distribution profiles of the various water decomposition products (eaq−, ·OH, H·, H2 and H2O2) for the different ions considered are presented and discussed briefly in the context of track structure theory. As an example, the formation and temporal evolution of simulated 24 MeV 4He2+ ion tracks (LET ∼26 keV/μm) are reported for each radiolytic species from 1 ps to 10 μs. The calculations reveal that the ion track structure is completely lost by ∼1 μs.

Interaction of hydrated electron with dietary flavonoids and phenolic acids: rate constants and transient spectra studied by pulse radiolysis.

The reaction rate constants and transient spectra of 11 flavonoids and 4 phenolic acids reacting with e(aq)- at neutral pH were measured. Absorption bands of the transients of e(aq)- reacting with the above compounds all located at a wavelength shorter than 400 nm. The e(aq)- scavenging abilities were divided into three groups: (+)catechin ((1.2 +/-0.1) x 10(8) M(-1)s(-1)) < 4-chromanol ((4.4 +/- 0.4) x 10(8) M(-1)s(-1)) < genistein ((6.2+/-0.4) x 10(9) M (-1) s(-1) approximately genistin ((8 +/- 1) x 10(9) M(-1)s(-1)) approximately rutin ((7.6 +/- 0.4) x M(-1)s(-1) approximately caffeic acid ((8.3 +/- 0.5) x 10(9)M(-1)s(-1)) < transcinnamic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately p-coumaric acid ((1.1 +/- 0.1) x 10(10) M(-1)s(-1) approximately 2,4,6-trihydroxylbenzoic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately baicalein ((1.1 +/- 0.5) x 10(10) M(-1)s(-1)) approximately baicalin((1.3 + 0.1) X 10(10) M(-1)s(-1)) approximately naringenin ((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately naringin ((1.0 +/- 0.1) x 10(10) M(-1)s(-1)) approximately gossypin((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately quercetin((1.3 +/- 0.5) x 10(10) M(-1)s(-1)). These results suggested that C4 keto group is the active site for e(aq)- to attack on flavonoids and phenolic acids, whereas the o-dihydroxy structure in B ring, the C2,3 double bond, the C3-OH group, and glucosylation, which are key structures that influence the antioxidant activities of flavonoids and phenolic acids, have little effects on the e(aq)- scavenging activities.

High-energy-ion-irradiation effects on polymer materials: 3. The sensitivity of cellulose triacetate and poly(methyl methacrylate)

Abstract The changes in sensitivity of a cellulose triacetate (CTA) film dosimeter is reported as a function of linear energy transfer (LET). The change in molecular weight of poly(methyl methacrylate) (PMMA) is also reported. For both materials, little or no LET effect was observed up to a threshold LET, but the sensitivity or radiation yield decreased with increasing LET above this threshold level. The threshold LET level was similar for both polymers, occurring at around a few hundreds of MeV cm2g−1, with this level probably corresponding to the overlapping of spurs along the ions path.

Radiolysis of water at elevated temperatures—III. Simulation of radiolytic products at 25 and 250°C under the irradiation with γ-rays and fast neutrons

Abstract The G-values of water decomposition products under the irradiations with γ-rays and fast neutrons up to 250°C have been determined in previous studies. In order to clarify the characteristics of the determined G-values, computer simulations under the simplified conditions in nuclear reactors have been carried out. The recent G-values for γ-radiolysis reported by Elliot, Chenier and Quellete [(1990) Can. J. Chem. 68, 712; (1993) J. Chem. Soc. Faraday Trans. 89, 1193], Kent and Sims [(1992) Water Chemistry of Nuclear Reactor Systems 6, p. 153. BNES, London], and Sunaryo, Katsumura, Shirai, Hiroishi and Ishigure [(1994) Radiat. Phys. Chem. 44, 273] and Sunaryo, Katsumura, Hiroishi and Ishigure [(1995) Radiat. Phys. Chem. 45, 131] are almost equivalent from the point of simulations. On the contrary, G-values for fast neutron radiolysis give a significant influence to the result, which arises from the higher molecular yields and smaller radical yields of water decomposition in fast neutron radiolysis, and it has been revealed that the dose evaluation in the reactor is inevitably important. In addition, it was pointed out by the simulations that reverse reactions for H2+.OH→.H+H2O and eaq−+H+→.H, be neglected at room temperature, become important at higher temperatures.