Low Level Liquid Scintillation Counting of Radioactivity in Food Products

The production rate is 7.5 kg isotope C-14 yearly. The C-14 concentration stays approximately constant due to rapid mixing of the atmosphere, although the cosmic intensity is higher at the poles due to the deflection of charged cosmic particles along the magnetic field lines of the earth (corresponding to neutron intensities in the ratio 5:1 at the poles and the equator, respectively). Consequently, C-14 atoms combine to form 'heavy' CO2, which, except in the radioactive decay (and isotopic fractionation effects), is indistinguishable from the ordinary carbon dioxide. The total amount of C-14 on earth in equilibrium is 62 tons, which is 10exp(-10) per cent of all carbon in biosphere, atmosphere and oceans.