Carbon-14 concentrations in environmental materials and their temporal fluctuations

Artificial 14C in the atmosphere is produced in nuclear reactions (14N(n, p) 14C) between nitrogen atoms in the air and neutrons liberated in the explosion of nuclear devices. Consequently 14C concentrations in the Earth's dynamic carbon reservoir have been substantially increased as a result of atmospheric testing during the past decade. Atmospheric carbon dioxide is the ultimate source of the carbon in all living organisms, so that fluctuations in the radiocarbon concentration of the former would be expected to produce parallel variations in the latter. This correlation between 14C concentrations of atmospheric and plant materials has been investigated. To measure the 14C activity of plant materials of recent but known age a number of spirit samples have been analysed. It was assumed that the 14C concentrations of samples would be indicative of the activity of the grain during the growth period. Fluctuations in atmospheric 14C concentrations during and after periods of nuclear-weapons testing have been followed by many workers. Individual data are available from several different latitudes, and results have been selected for comparison purposes. Data show that there is a general correlation between the 14C concentrations of spirits and atmospheric CO2 samples with the result that the year of manufacture of the spirits is predictable. The 'Suess effect' and the 'bomb effect' are considered in the light of this correlation. (author)