Re-Emission of HTO into the Atmosphere After HT/HTO Conversion in the Soil

After HT is converted to HTO by the soil, the HTO is reemitted back into the atmosphere. Since HTO is more radiotoxic by a factor of 10⁴, this reemission is an important part of the radioecological pathway of HT¹. Laboratory studies show that the reemission rate from natural soil cores depends on the turnover in the gas space above the soil surface. Up to a wind velocity of about 4 m s⁻¹, the portion of HTO reemitted hourly increases to about 18 % of the initial amount of the reaction product. However, after the first hour, the observed reemission rate decreases quickly to about 3% h⁻¹. Varying the humidity of an air stream fed at a velocity of about 3 m s⁻¹ into the reaction chamber, had no influence on the reemission rate. For the Canadian release study, small soil samples were exposed to the plume and afterwards to the air. Then, at certain intervals following the release, the soil containers were sealed with gastight lids. The remnant HTO activity was then determined by azeotropic distillation. The reemission rate, determined by this procedure, was about 3% h⁻¹ during the day. During the night, no HTO loss was observed, possibly due to dew formation.