Origin of High Tritium Content of Atmospheric Methane, Hydrogen and Stratospheric Water

Abstract

RECENT work (ref. 1 and Suess, H. E., private communication) has shown that atmospheric methane has a fractional tritium content orders of magnitude higher than that of rain water and approaching that of atmospheric hydrogen and stratospheric water. The rate of increase with time of this tritium in methane makes it appear likely that it originates in the testing of nuclear devices. (The finding by Bishop et al.¹ that the specific activity of atmospheric methane appears to be lower in the troposphere than in the stratosphere or at the surface is, however, not obviously explained on the basis of origin in thermonuclear explosion, or for that matter by origin from any single source.) However, no satisfactory mechanism by which such tritium can be incorporated in methane has been advanced. The high temperature and oxidizing conditions supposed to exist in the bomb fireball seemed to rule it out as a source of tritiated methane¹. Biological processes yielding methane of high specific activity are difficult to conceive; and indeed, sewage methane has little tritium content¹. High atmosphere, radiation-induced mechanisms for exchange of methane with high specific activity atmospheric hydrogen can be formulated, but these mechanisms suggest that the methane is likely to be oxidized under the conditions required (Libby, W. F., private communication).