Nowadays, radiocarbon scientists had to perform calibration not only to convert their radiocarbon year results into calendar year but also to take into account the various factors that have major effects on the global levels of carbon 14, one of which is nuclear weapons testing.There are two human activities recognized to have irreparably changed the global radiocarbon levels—the burning of fossil fuel and nuclear weapons testing.
The phenomenon is often referred to as the bomb effect.The bomb effect refers to the phenomenon that produced “artificial” radiocarbon in the atmosphere due to nuclear bombs.Nuclear weapons testing brought about a reaction that simulated atmospheric production of carbon 14 in unnatural quantities.The radiocarbon dating method is based on certain assumptions on the global concentration of carbon 14 at any given time.One assumption is that the global levels of carbon 14 (also called radiocarbon) in the atmosphere has not changed over time.
The other assumption is the corollary of the first; the biosphere has the same overall concentration of radiocarbon as the atmosphere due to equilibrium.
Radiocarbon’s entry into the global carbon cycle starts in the atmosphere where it is formed by the interaction of neutrons produced by cosmic rays with nitrogen atoms.
The carbon 14 produced reacts with oxygen atoms in the atmosphere to form carbon dioxide.
This carbon dioxide is no different from those produced by carbon 12 and carbon 13; hence, carbon dioxide with carbon 14 has the same fate as those produced with the other carbon isotopes.
Mixing and exchanges happen between the atmosphere and the biosphere until such time that equilibrium is established.
Radiocarbon dating rests heavily on this assumption such that other sources of carbon 14 had, at first, not been considered nor accounted for.