Browsing by Author "Matthews, RW"

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    The radiation chemistry of aqueous sodium terephthalate solutions
    (Australian Atomic Energy Commission, 1980-04) Matthews, RW
    The radiation chemistry of cobalt-60 gamma-irradiated aqueous sodium terephthalate solutions has been studied. In aerated 4x10-4 M sodium hydroxide solutions, the main products are hydroterephthalate (HTA) (G = 0.99 + 0.01), carbonate (G = 1.31 + 0.08), and peroxides (G = 2.84 + 0.04). The HTA and carbonate species are both formed as a result of hydroxyl radical attack and account for approximately 90 per cent of hydroxyl radical reactions. Oxygen needs to be present for efficient conversion of the terephthalate-OH radical adduct to HTA and oxygenation increases G(HTA) above the aerated solution value. G(HTA) is unaffected by changes in terephthalate concentration between 1 x 10-4 M and 1 x 10-2 M in sodium hydroxide solutions at pH 10. Decreasing the solution pH does however affect G(HTA). In phosphate buffered solutions at pH 6.85, G(HTA) is 0.93 + 0.01 and lower values are obtained with further decrease in solution pH. The lowering of teh G(HTA) value is attributed to recombination reactions between the terephthalate-OH radical products and reducing radical products. Experimental evidence supporting the recombination postulate was obtained from the measurement of a parallel decrease in the peroxide yield and the observation of a dose rate effect on G(HTA). Competition kinetic studies with the added solutes carbonate and biocarbonate gave the rate ratios k(OH + TA=) : k(OH + CO3=) : k(OH + HCO3-) = 1 : 0.105 : 0.0036.
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    Reactions of the 'H atom' in gamma-irradiated ferrous sulphate solutions
    (Australian Atomic Energy Commission, 1977-10) Matthews, RW
    The effect of sulphuric acid, ferrous and ferric ion, and oxygen concentrations on G(Fe3+) values from cobalt-60 gamma-irradiated solutions has been studied. The ferrous sulphate concentrations ranged from (1.0 to 50.0)x10-3M and the oxygen concentrations from 0 to 1.25x10-3M in three solvents: 1.OM sulphuric acid, 0.4M sulphuric acid, and 0.04M sulphuric acid/0.1M sodium sulphate solutions. Kinetic expressions were derived for reaction models involving reactions of various forms of the H atom and additional reactions postulated to be of importance at high solute concentration. Three models were assumed invoking the additional reactions: (1) an independent yield of an excited water species; (2) increasing contributions from interspur reactions of well established species at increasing solute concentration; (3) inhibition of charge pair recombination by acid and scavenger species. The calculated G(Fe3+) values from the various models were compared by the least squares method with experimental G(Fe3+) values from over 600 irradiations. Models 1 and 2 provided good fits to the data when an equilibrium H4O+ £ H30+ + H was assumed. The kinetic salt relationship for the results from model 1 gave partial support for a reaction involving a positively charged H atom species; those from model 2 indicated no significant participation of positively charged H atom species. Model 3 provided the best fit to the data for the least number of adjustable parameters. No evidence for more than one form of H atom was found with this model. The G value for the charged pair was found to be 0.69 ± 0.05. The GH values at zero solute concentration calculated in model 3 ranged from 3.07 ± 0.05 to 3.18 ± 0.05 and were little affected by acid concentration.