Reactions of the 'H atom' in gamma-irradiated ferrous sulphate solutions

Abstract

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.