Radiation Physics and Chemistry (1977)最新文献

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.

Solid agar-agar was irradiated with ⁶⁰Co gamma rays, and the effects of radiation on the electrolytic groups (sulfate group) of the agar-agar molecule were studied by colloid titrimetry. The after effects were also studied. Empirical equations for changes of colloid titration value were obtained.

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.

The thermal stability of radiation curable materials was determined via TGA measurements and related to functionality, chemical type, and cure conditions. The results indicate that Tri-, Tetra-, and Penta- functional acrylates are more thermally stable than lower functional acrylates and that acrylates have better thermal stability than methacrylates. A comparison of EB, UV, and thermal curing conditions for TMPTA showed that EB-cured material was more thermally stable than UV and that thermally cured TMPTA was the least stable. The thermal stability of acrylated epoxy oligomers is again in the order of increasing functionality The ¹³C carbonyl region and oxygen permeability measurements were used to determine the extent of cure and then related to thermal stability.

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.

A study of optical properties of H[AuCl₄]-containing polyvinyl alcohol (PVA) films allows the basis of a chain mechanism of their photolysis and radiolysis to be put forward. A suggestion is made, that in these chain reactions the Cl radical functions as an active particle, initiating the formation of two interacting chains in reactions of this radical with PVA and [AuCl₄]^- ions correspondingly.

G-values for crosslinking, G(X) and for chain scissions, G(S), have been determined for the electron beam irradiation at room temperature in vacuum of a polyetherimide called ULTEM by General Electric Co.. In addition, ESR studies of the free radicals produced in ULTEM by γ-irradiation in vacuum at 77K have also been carried out. In the electron beam irradiation experiments the very low G(X) and G(S) values, only 0.014 and 0.005 respectively, demonstrate the high radiation stability of this material. The decay at 70° and 160°C of the free radicals in the electron beam irradiated samples accurately followed the Waite equation. Also the solubility-dose data could be accurately interpreted in terms of the Charlesby-Pinner equation.

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.