Radiation Physics and Chemistry (1977)最新文献

The radiation-chemical yields of ionic species formed upon irradiation of water by 3.5 MeV electrons have been determined directly using dc conductivity and optical measurements. Yields (expressed in μmol J^-1) at 10 and 110 ns after the end of a 10 ns pulse are: for H₃O⁺ = 0.371, 0.320; for OH^- = 0.082, 0.045, and for e^-_aq = 0.299 and 0.275, respectively.

The measurement of platelet adhesion to polyetherurethane films grafted (via the preswelling technique) with 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AAm), performed by means of the stagnation point flow experiment (SPFE-test) as well as with the aid of the bioluminescence assay, is described. Platelet adhesion is found to decrease if the interfacial free energy γ_sw of the polymer surfaces decreases. Adhesion to protein-coated, grafted polyetherurethane films (coated with albumin, γ-globulin, fibrinogen, fibronectin or a protein mixture) depends on the nature of the protein used: precoating of the films with albumin of γ-globulin leads to a decrease, precoating with fibrinogen or fibronectin to an increase in platelet adhesion.

Also we report about early experiences with HEMA-grafted polyetherurethane tubes in implantation experiments.

The decomposition of hydrogen peroxide in aqueous solution has been studied on silver-nickel oxide two-component catalysts containing various proportions of the components covering the entire region of 0–100% of one component. The catalytic activity of the system appears to be a non-monotonic function of its' composition. The activity of the samples containing 0–91 wt% NiO is determined by the catalytic efficiency of the silver component present in the catalyst and this efficiency seems to be connected with the surface concentration of Ag⁺ ions. The catalytic activity of samples containing more than 91 wt% NiO is determined by the activity of the nickel oxide. The γ irradiation (dose 10 kGy) of samples containing an excess of silver leads to a lower catalytic activity and irradiation of samples with a higher content of nickel oxide increases its' activity. Irradiation of catalysts with fast neutrons appreciably decreases their activity, irrespective of their composition, while irradiation with β radiation (dose 5.6 MGy) has no effect on their activity.

The radiation induced hydrogen abstraction from hydrogen-containing substrates, by CF₂Cl radical was studied in CF₂Cl₂ solution as a function of the RH concentration (where RH is cyclohexane, cyclohexene, and ethanol) and as a function of temperature in the range of -80 to +20°C. For the CF₂Cl₂-ethanol system it was found that the ratio between the concentration of the abstraction product CHF₂Cl and the square root of the concentration of the recombination product (CF₂Cl)₂ is linearly dependent on the ethanol concentration (as was expected). However, for the two other systems, no dependence was found between this ratio and the concentration of the hydrogen containing substrate. A new mechanism for explaining those results was suggested.

The isothermal luminescence of γ-irradiated frozen 3-methylpentane (3MP)-methylcyclohexane (MCH) mixtures (3MP mole fraction from 0 to 0.96) containing naphthalene (Nph) was investigated at 77K. At high Nph concentration (2.5 x 10⁻²mol dm^−>3) the luminescence is due to molecular ion recombination by tunnelling. In the soft glass (0.96 mole fraction 3MP) at low Nph concentration (10^-3 mol dm^-3) electron thermal detrapping seems to contribute to the emission. The experimental decay curves were interpreted based on the Bagdasar'yan relation as well as the continuous-time- random-walk formalism (assuming a first-order rate equation with a time dependent rate constant of the form k(t) = Bt^(α−1).

Gamma and electron-beam radiation induced graftcopolymerization of acrylic acid, methacrylic acid, trimethylolpropane trimethacrylate (TMPTMA) and tetraethyleneglycol dimethacrylate (TEGDMA) onto PVC-films has been investigated. Both swelling effect and oxygen retardation effect in air radiation phase were found to be nonsignificant below the dosages of 1.2 Mrad due to the protection of free radicals by the quick formed gel's network. The graft percentage was increased with the dose-rate and the total dosage, becoming slowly levelling over the doses of 2.4 Mrad. The grafting-rate is regarded to be proportional to the n-th power of the dose- rate, where the value of n being as 1.10

The formation of the grafted stratum on the PVC-film surfaces was found to induce the positive effects of big improvement in tensile-strength, excellent resistant toughness against the erasure of the prints on the grafted PVC-film surfaces and strong adhesive character with several adhesive chemicals.

The investigations of the Central Institute of Isotope and Radiation Research on the interaction between ionizing radiation and matter are devoted to the development of methods for analyzing chemical composition and structural parameters and to establishing the scientific basis of the development of irradiation technology. A brief survey on fundamental and applied research in these fields is given.

Neutralization reaction was investigated in negative ferric hydrous oxide sols. The adsorption isotherm of OH^- ions on the surface of colloidal particles was measured to provide the variation of their charge with pH. Impulse radiolysis generated the reacting ions in the sol. Using a fast DC conductivity setup for detection, a significant increase in the neutralization rate coefficient was found at low OH^- concentrations. The phenomenon was discussed in terms of the theory of diffusion controlled reactions for particles interacting with Coulomb and Yukawa potential.

The effect of gamma radiation on the corrosion of carbon St20 and stainless steel OX18H10T contacting high-temperature water have been studied. It was shown that irradiation does not seem to have a marked effect on the corrosion of stainless steel and accelerates the corrosion of carbon steel (3–4 times). The empirical equation of the corrosion rate dependence on the time of experimentation were found. The concentration of H₂O₂ in irradiated water contacting carbon steel changes by the fluctuation law with a period of 20–25 h and remains at the same level as for carbon steel.

The balance of ionizing radiation energy incident on an object being processed is discussed in terms of energy losses, influencing the amount really absorbed. To obtain the amount of heat produced, the absorbed energy is corrected for the change in internal energy of the system and for the heat effect of secondary reactions developing after the initiation. The temperature of a processed object results from the heat evolved and from the specific heat of the material comprising the object. The c_p of most materials is usually much lower than that of aqueous systems and therefore temperatures after irradiation are higher. The role of low specific heat in radiation processing at cryogenic conditions is stressed. Adiabatic conditions of accelerator irradiation are contrasted with the steady state thermal conditions prevailing in large gamma sources. Among specific questions discussed in the last part of the paper are: intermediate and final temperature of composite materials, measurement of real thermal effects in situ, neutralization of undesired warming experienced during radiation processing, processing at temperatures other than ambient and administration of very high doses of radiation.