Koji Matsuda

Effect of irradiation temperature on the radiolysis of methane

Abstract The G-values of most products increase with temperature in the radiolysis of methane in a flow-type experiment over the temperature range 50–280°C at atmospheric pressure. The apparent activation energies of most products are higher at higher temperature region above 150°C than those obtained below about 100°C. Irradiation at higher temperature favors the formation of olefins. The results are qualitatively understood on the basis of known nature and reactivity of free radicals.

Radiation effects on Fischer-Tropsch syntheses

Abstract Radiation effect on Fischer-Tropsch synthesis has been examined using high dose rate electron beams and Fe-Cu-diatomaceous earth catalyst. Yields of saturated hydrocarbons were found to increase by irradiation, but the yields of these compounds were decreased by raising reaction temperature without irradiation, suggesting the presence of radiation chemical process in catalytic reactions.

Studies on the radiation-induced coloration mechanism of the cellulose triacetate film dosimeter

Abstract The species responsible for the coloration of the cellulose triacetate (CTA) film dosimeter have been studied using ultraviolet, electron spin resonance, infrared and gas chromatographic techniques. The post-irradiation change in the optical density at 280 nm indicates that the coloration occurs not only during irradiation ( in situ coloration) but also after irradiation (post-irradiation coloration) and that in situ coloration is due to unstable and stable components. The species responsible for the unstable component of in situ coloration are ascribed to the radicals produced from CTA molecules and those for the stable component to the radiolysis products from CTA and triphenyl phosphate contained in the dosimeter. On the other hand, post-irradiation coloration is attributed to the formation of carbonyl groups in CTA molecules, which is induced by reaction with NO 2 produced by irradiation of air.

Nature of Oxygen Donors and Radiation Defects in Oxygen-Doped Germanium

The nature of oxygen donors and radiation defects in oxygen-doped germanium were studied through measurements of the infrared absorption spectrum, deep level transient spectroscopy spectrum and carrier concentration. It is revealed that a new donor is not formed in oxygen-doped germanium. An A-center (interstitial oxygen-vacancy pair) forms a complex with a thermal donor in its anneallng stage at 60°C-140°C. The introduction rate of defects by 1.5 MeV electron irradiation was enhanced in thermal-donor-doped samples.

Radiolysis of methane by electron beam irradiation over wide ranges of dose and dose rate

Abstract Radiolysis of methane has been carried out using electron beams in the dose range from 0.05 to 3 × 10 4 Mrad and dose rate range from 0.024 to 2.4 Mrad/s. The G -values of alkanes are almost independent of dose and dose rate except dose regions below 0.2 Mrad and above 5000 Mrad, while those of unsaturated hydrocarbons strongly depend on dose and dose rate.

Electron beam dosimetry for a multilayer absorber

Abstract Depth dose distributions were measured in a multilayer absorber of Ti-air-cellulose triacetate (CTA)-backing material (Pb, Sn, Fe, Al and CTA) irradiated with 300 and 800-keV electrons. The results are compared with the calculated value using computational code for multilayer absorbers (EDMULT) developed by Tabata et al. (1989, 1990). The absorbed dose in CTA exceeds the calculated value near the surface, while it is smaller than the calculated dose as the penetration depth becomes closer to the range of incident electrons. The measurements and computations show better agreement for the high-energy (800-keV) electrons than for the 300-keV electrons, probably because of the greater obiqueness of incidence at lower energies, which is not taken into account by the computation code.

Formation and quenching of NH fragments in excited states by high energy electron irradiation of helium-ammonia gas mixture

Abstract A gas mixture of helium and ammonia was irradiated with an electron beam from a Van de Graaff accelerator and emission intensities from excited NH fragments were measured as a function of pressure, concentration of ammonia, and the amounts of additives. The energy transfer process is discussed on the basis of the experimental results and kinetic analysis.

Thermal Donor Formation and the Effect of Copper Contamination in Oxygen-Doped Germanium

The structure of thermal donors in germanium was studied in oxygen-doped crystal (9×1016 oxygens/cm3). From the reduction of interstitial oxygen concentration after annealing, it was found that a single thermal donor contains three oxygen atoms on average. The diffusion of copper atoms from the surface in oxygen-doped germanium crystal was studied through electron irradiation effects. It was revealed that a copper atom migrates as an interstitial atom and it occupies a substitutional site at about 450°C.

Formation and quenching of CO and CO ion in excited states by high energy electron irradiation of heliumcarbon monoxide gas mixture

Abstract Gas mixture of helium and carbon monoxide was irradiated with electron beam from a Van de Graaff accelerator and emission intensities from excited CO and CO ion were measured as a function of pressure, concentration of carbon monoxide in wide ranges. The results are fitted with kinetic analytical formulae derived from simple competition reactions involving energy transfer process assuming steady state concentrations for intermediates, and reasonable agreements were obtained between the experimental results and those predicted in the range of reaction conditions studied in this work.

Photo-emission from excited CF2 radical by high energy electron irradiation of chlorofluorocarbons

Chlorofluorocarbons CCl2F2 (CFC-12) and CHClF2 (HCFC-22) in the gas phase were irradiated with high energy electron beam from a Van de Graaff accelerator and emission intensity of the excited CF2 (A1B1) radical was measured as a function of sample gas. The result shows that a formation path via a precursor exists besides of the direct formation by electron impact. Experiments were also made for mixtures of chlorofluorocarbons and helium or argon.