Radiocarbon dating and the atomic bomb


11-Feb-2018 20:13

Plants which grow in the vicinity of active volcanic fumeroles will yield a radiocarbon age which is too old. (1980) measured the radioactivity of modern plants growing near hot springs heated by volcanic rocks in western Germany and demonstrated a deficiency in radiocarbon of up to 1500 years through comparison with modern atmospheric radiocarbon levels.Similarly, this effect has been noted for plants in the bay of Palaea Kameni near the prehistoric site of Akrotiri, which was buried by the eruption of the Thera volcano over 3500 years ago (see Weninger, 1989).In order to ascertain the ages of samples which were formed in equilibrium with different reservoirs to these materials, it is necessary to provide an age correction.Implicit in the Conventional Radiocarbon Age BP is the fact that it is not adjusted for this correction.Since about 1955, thermonuclear tests have added considerably to the C14 atmospheric reservoir.This C14 is 'artificial' or 'bomb' C14, produced because nuclear bombs produce a huge thermal neutron flux.In this page, we consider natural reservoir variations and variations brought about by human interaction].Radiocarbon samples which obtain their carbon from a different source (or reservoir) than atmospheric carbon may yield what is termed apparent ages.

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A CRA is derived using an age calculation based upon the decay corrected activity of the absolute radiocarbon standard (1890 AD wood) which is in equilibrium with atmospheric radiocarbon levels (as mentioned previously, 1890 wood is no longer used as the primary radiocarbon standard, instead Oxalic Acid standards I and II were correlated with the activity of the original standard).A shellfish alive today in a lake within a limestone catchment, for instance, will yield a radiocarbon date which is excessively old.The reason for this anomaly is that the limestone, which is weathered and dissolved into bicarbonate, has no radioactive carbon.This apparent age of oceanic water is caused both by the delay in exchange rates between atmospheric CO2 and ocean bicarbonate, and the dilution effect caused by the mixing of surface waters with upwelled deep waters which are very old (Mangerud 1972).