Method for Improving the Collecting Performance of Iodine Samplers under High Relative Humidity

In airborne radioiodine monitoring, it is essential to establish an effective sampling technique that gives results independent of the form taken by the radioiodine and that works effectively under high humidity. Experiments were made to improve the performance of an iodine sampler embodying (a) cellulose asbestos filter paper (Toyo Roshi, Type HE-40) and activated charcoal filter paper (Toyo Roshi, Type CP-20) and (b) HE-40 filter paper and activated charcoal cartridge (Toyo Roshi, Type CHC-50). Based on the results, a new sampler was devised in which the air is heated to 70°∼90°C before reaching the filters. The dependence of the collecting efficiency on the chemical form taken by the airborne iodine and also on the duration of sampling period was studied.Severe conditions of environment, such as high humidity, were simulated in the experimental apparatus. The airborne radioiodine used was a mixture of inorganic and organic iodides, identified by radio-gaschromatography. It was found that the collecting efficiency of the sampler with activated charcoal cartridge and the activated charcoal filter paper, respectively, exceeded 99.5% and 85%, regardless of the form of airborne iodine even at 100% relative humidity throughout the whole range of sampling duration up to 16hr. Under conditions of high humidity, the collecting efficiencies were found superior to that of charcoal filter paper and charcoal cartridge impregnated with TEDA or SnI2 used without air heating.