Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.
One rare form has atoms that are 14 times as heavy as hydrogen atoms: carbon-14, or C ratio gets smaller.
A case of alpha radiation poisoning made international news a few years ago when Russian dissident Alexander Litvinenko was believed to have been poisoned with it by the Russian spy service.
When atoms decay, they emit three types of radiation, alpha, beta and gamma.
The alpha and beta radiation consist of actual matter that shoots off the atom, while gamma rays are electromagnetic waves.
This technique works well for materials up to around 50,000 years old.
Each radioactive isotope decays by a fixed amount, and this amount is called the half-life.