Radioisotopes as biological tracers

Abstract

The presence of bomb carbon 14C in the atmosphere presents opportunities for the study of problems concerned with the metabolism of a tree. The Occurrence of Bomb Carbon Measurements of the 14CO2 concentration of the atmosphere of the Southern Hemisphere show that since 1954 the 14CO2 concentration has been increasing at an exponential rate, indicated in figure 1 G.T. Fergusson, Paper presented International Oceanographic Congress, New York, September 1959, T.A. Rafter and G.J. Fergusson, N.Z. J. Sci. Technol., 38B, 871 (1957). This increase is a result of the reactions of neutrons, released by nuclear explosions, with the nitrogen of the atmosphere to produce a significant amount of 14C, which is then carried up into the stratosphere by the movement of air caused by the heat associated with the explosions. Since 1954, when bomb tests were carried out, this 14C has been slowly diffusing into the atmosphere and increasing the 14CO2 concentration, until at this time the reported value is approximately 20% above that for 1954. It has also been shown T.A. Rafter and G.J. Fergusson, N.Z. J. Sci. Technol., 38B, 871 (1957) that the 14C specific activity of the contemporary portions of the biosphere has been increasing at the same rate. For example, the material in the annual rings of a tree formed after 1954 has an increasing proportion of 14C present. This increase can be readily detected by the apparatus used for 14C age dating (with a standard deviation of 1/2%).