On the Radiolytic Decomposition of Colloidal Silver Iodide in Aqueous Suspension

The decomposition of aqueous colloidal suspensions of AgI induced by ionizing radiation was investigated under various conditions using ¹⁸⁸Re as an in situ beta-radiation source. The suspensions were stabilized by an initial excess of either I^- or Ag⁺ ions. Although the results were somewhat scattered, the following trends were observed. With an initial excess of I^- and under strong oxidizing conditions (N₂O sparging) at pH 2, ~65% AgI was decomposed into nonvolatile and volatile iodine (ratio 2:1) for doses of ~20 kGy, and up to ~80% was decomposed (mostly nonvolatile iodine) at pH 5. Chloride ions greatly enhanced the volatile and lowered the nonvolatile fractions. Little decomposition (<10%) was obtained with air sparging at both pH 2 and pH 5. Chloride ions increased the maximum decompositions to ~60% (~47% volatile) and ~20% (mainly nonvolatile iodine), respectively. With an initial excess of Ag⁺ with N₂O sparging and at pH 2 and pH 5, very little volatile iodine was produced. The maximum decomposition was ~20% after ~20 kGy. Chloride ion addition at pH 2 had greatly enhanced the volatile iodine yield. The relevance of these results to the possible release of iodine to the environment following a nuclear reactor accident is discussed.