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A time-independent level of C14 activity for the past is assumed in the measurement of a CRA.The activity of this hypothetical level of C14 activity is equal to the activity of the absolute international radiocarbon standard.Atoms of larger or smaller mass may be favored in such a situation.If, however, the entire sample is converted completely from one form to another (e.g.Isotopic fractionation of stable carbon isotopes Carbon-13 (13C) and Carbon-12 (12C) involves alterations in the ratios of isotopic species as a function of their atomic mass as a result of natural biochemical processes.Variations as such are unrelated to time and natural radioactive decay.
Reported δ13C values from Beta are always the values measured in the IRMS.
This nomenclature has recently been changed to VPDB (Coplen, 1994).
The δ13C value for a sample can yield important information regarding the environment from which the sample comes or the mixtures of materials used to produce it because the isotope value of the sample reflects the isotopic composition of the immediate environment.
This value is not reported but it is used to produce the correct “Conventional Radiocarbon Age”.
Important: Reporting conventions using “Conventional Radiocarbon Age” terminology indicate the result has been corrected for isotopic fractionation.– Beta also measures a second δ13C value in an isotope ratio mass spectrometer (IRMS δ13C).
solid to gas, acetylene to benzene) then no laboratory-induced fractionation will occur.