The fractionation technique dating
Fractionation during the geochemical transfer of carbon in nature produces variation in the equilibrium distribution of the isotopes of carbon (12C, 13C and 14C).Craig (1953) first identified that certain biochemical processes alter the equilibrium between the carbon isotopes.If it is the AMS δ13C, it cannot be used for dietary or metabolic pathway studies.Reported δ13C values from Beta are always the values measured in the IRMS.Some processes, such as photosynthesis for instance, favors one isotope over another, so after photosynthesis, the isotope C13 is depleted by 1.8% in comparison to its natural ratios in the atmosphere (Harkness, 1979).Conversely the inorganic carbon dissolved in the oceans is generally 0.7% enriched in 13C relative to atmospheric carbon dioxide.Fractionation also describes variations in the isotopic ratios of carbon brought about by non-natural causes.For example, samples may be fractionated in the laboratory through a variety of means; incomplete conversion of the sample from one stage to another or from one part of the laboratory to another.
PDB refers to the Cretaceous belemnite formation at Peedee in South Carolina, USA.
solid to gas, acetylene to benzene) then no laboratory-induced fractionation will occur.
A radiocarbon measurement, termed a conventional radiocarbon age (or CRA) is obtained using a set of parameters outlined by Stuiver and Polach (1977), in the journal Radiocarbon.
The Conventional Radiocarbon Age BP is calculated using the radiocarbon decay equationt=-8033 ln(Asn/Aon)Where -8033 represents the mean lifetime of 14C (Stuiver and Polach, 1977).
Aon is the activity in counts per minute of the modern standard, Asn is the equivalent cpm for the sample. A CRA embraces the following recommended conventions: About AMS Dating Accelerator Mass Spectrometry (AMS) dating involves accelerating ions to extraordinarily high kinetic energies followed by mass analysis.