A kinetic discussion of the HT and HTO formation in the atmosphere indicates that the ratio of about 1 HT to 1000 HTO in nature and the very high T concentration of 4.10hyphen;15in atmospheric hydrogen compared with about 3.10hyphen;18in normal rain water can only be understood by means of a photochemical reaction. Since the tritium atoms are quickly removed by oxygen molecules in threehyphen;body collisions and form the TO2radical which in turn forms HTO, the TO2must be photochemically dissociated. The T atoms thus set free collide repeatedly with hydrogen atoms and undergo to a certain extent the exchange reaction H2+T=HT+H. On the other hand, the T atoms or TO2radicals may react with ozone to form a OT radical which combines with the hydrogen of the atmosphere into HTO. In low altitudes the reaction of TO2with air polluting bodies form HTO predominately. The ratio of these reactions is responsible for the ratio of HT and HTO in nature with the HTO brought down into the surface waters by rainfall.
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