Artificially produced radioactive noble gases in the atmosphere

Abstract

The present investigation was started in the spring of 1961, with the aim of looking for a possible summer maximum of Kr85 in tropospheric air. The maximum, similar to that of C14 [Broecker et al., 1963], was to be expected if Kr85 was supplied mainly from the stratosphere. However, the Kr85 activity as shown in Figure 1 does not show any resemblance to the C14 activity, as it should if it came from the same source, since both nuclides are long-lived with respect to radioactive decay as well as to other processes of removal from the atmosphere. This is obvious for the Kr, being a noble gas; it is equally true, however, for the C14 [Broecker et al., 1963]. Apart from considerable irregularities, the Kr85 activity shows a more or less steady increase, which could be described by a doubling time of 2 or 3 years. A summary of measurements done by several authors is given in Figure 2. Griesser and Sittkus [1961] suggested a year ago that Kr85 is not exclusively a bomb product but that it should be attributed to a large extent to the nuclear industry. They argued, using a plausible estimate of the average fission yield, that much more Kr85 is present in the atmosphere than could have been generated by the known amounts of fissionable material exploded thus far in the bomb test series. Their statement is strongly supported by the findings reported here.