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