Field studies of HT behaviour in the environment

A release of 3.54 TBq of HT was conducted over an experimental field at Chalk River consisting of a 200 m diameter grassland and a further 200 m stretch of coarse sand having sparse vegetation. Tritiated hydrogen was released at a steady rate over a 30 minute period. Atmospheric sampling for HTO and HT was done using molecular sieve and Pd-loaded molecular sieve traps. HTO/HT ratios observed during the release ranged from 1.37 x 10/sup -5/ at 5 m to 7.0 x 10/sup -4/ at 400 m distance from the release point indicating an effective oxidation rate of about 1.5% h. Oxidation truly in the atmosphere must be much slower than this effective rate since HTO observed in the plume could be attributed primarily to evaporation of tritium oxidized in the surface coil of the field. The distribution of HT in the plume was similar in trend to that calculated from the Gaussian Plume Model but observed concentrations were about half of the calculated values