A need for characterization of the iodine source term used in safety calculations for hypothesized light water reactor core disruptive accidents has motivated a study in iodine volatility. Previous experimental studies have been directed at evaluating volatility of iodine at a single time shortly (1 to 12 h) after introduction into the aqueous phase. The very important variables of time in solution and gamma radiation dose rate for a range of iodine concentrations (10-8 to 10-5 gI/ml) and pHs(5, 9, and 11) are explored. All experiments were performed at ∼25°C, first in the absence of a significant radiation field and later with a gamma radiation dose rate ranging from 0.003 to 0.06 Mrad/h. Iodine was introduced as either molecular I2 or Nal with 131I(8.04-day half-life) as a tracer. Results of experiments with nonirradiated systems indicated very little volatility with Nal-initiated studies. The I2-initiated systems at pH 5 were the most volatile whereas experiments at pH 9 and 11 showed decreasing iodine volatility with time. From the experiments at pH 9, it is inferred that the partition coefficient of HOI is ∼1000. A pronounced radiation-induced reduction in iodine volatility in pH 5 iodide solutions has been demonstrated as well as a dose rate dependence in the transient phase. As with nonirradiated systems, irradiated alkaline solutions exhibit low volatility. A computer-based model incorporating water radiolysis and iodine radiolytic chemical reactions has been formulated and tested. The model successfully predicts radiation-induced volatility changes in pH 5 iodide systems. The experimentally observed dose rate dependence is also verified. At pH 9, the agreement between experimental results and predicted results is not good.