Direct and indirect radiolytic effects in highly concentrated aqueous solutions of bromide

Highly concentrated aqueous solutions of bromide were used to examine the total radical yield in the direct decomposition of water by γ-rays. Bromide concentrations were varied up to 6 M at which almost all OH• radicals, H• atoms, and hydrated electrons produced in the picosecond range oxidize bromide to ultimately form Br3−, a stable species that can easily be measured with a spectrometer. Considering only the decomposition of water in the presence of air and in acidic conditions, the apparent yield of oxidizing species is found to be around (10 ± 0.05) × 10−7 mol J−1. The absorption of irradiation dose by the solute at high concentration is discussed and quantitatively evaluated. At 6 M Br− solutions, 38% of the dose is absorbed by solutes and Br− is directly ionized. The optimal value for the initial yield of the radicals produced by direct radiolytic Br− ionization is found to be (9.6 ± 0.5) × 10−7 mol J−1.