An experimental study of dilute aqueous radioiodine volatility

The partitioning of iodine between moist air and CsI solutions in the concentration range of 10-4 to 10-8 M, has been investigated experimentally using radiochemical methods. In this paper the observed dependencies of the partition coefficient on time, solution pH, iodide concentration, water quality, and gamma irradiation are discussed emphasizing their relevance to trace iodide oxidation. The partition coefficient decreased over time at a rate that appeared to be governed by the rate of iodide oxidation. After about one week a near constant value was reached that depended upon the pH and iodide concentration of the solution. For a 10-6 M CsI solution of pH ca. 5, prepared using high purity water, the partition coefficient was ca. 105; lower values were observed using solutions prepared using lower quality water. The rate of thermal iodide oxidation was found to be proportional to the square root of the hydrogen ion and iodide concentrations for solutions prepared in higher quality water. The thermal production of gaseous organic iodides was significant even at room temperature and organic iodides were eventually the predominant form of gaseous iodine. The gamma-photon irradiation of acidic 10-5 M iodide solutions caused the radiolytic oxidation of iodide 10-5 M iodide solutions caused the radiolytic oxidation of iodide resulting in the production of large amounts of volatile species of iodine and partition coefficients below 103. The final value of the partition coefficient following the irradiation of these solutions did not depend on the irradiation dose rate for dose rates ranging from 100 to 20 000 Gy/hr