Radio Carbon Dating

Radiocarbon

dating of historical wooden - derived objects is based on the knowledge that the cosmic ray intensity (responsible for ¹⁴C production) has been practically constant for thousands of years. ¹⁴C is formed in the upper atmosphere by the action of cosmic radiation on ¹⁴N.

The ¹⁴C so produced is eventually converted into CO₂, which in turn is incorporated into plants and trees by the process of photosynthesis and then finds way into animals, which eat plants. As there is a natural plant-animal cycle, an equilibrium is set up and all living matter contains the same small proportion of ¹⁴C as it occurs in the atmosphere. Once the plant or animal dies, the uptake of CO₂ by it ceases and the level of ¹⁴C in the dead begins to fall due to the decay, which ¹⁴C undergoes.

The half-life period of ¹⁴C is 5770 years. A comparison of the b^-1 activity of the dead matter with that of the carbon still in circulation enables measurement of the period of isolation of the material from the living cycle. The method, however, ceases to be accurate over periods longer than two or three half-life periods of ¹⁴C. The proportion of ¹⁴C to C¹² in living matter is 1:10¹².