There are two situations that limit an age; the first is that the measured Fm is smaller than that of the corresponding process blank measured in the same suite of samples on the AMS.
If this is the case, then the reported age will be quoted as an age greater than the age of the process blank. The typical background age for organic combustions is 48,000 years and for inorganic carbon samples, 52,000 years.
The other method is “Relative Dating” which gives an order of events without giving an exact age (1): typically artefact typology or the study of the sequence of the evolution of fossils.
There are three carbon isotopes that occur as part of the Earth's natural processes; these are carbon-12, carbon-13 and carbon-14.
Fractionation must be corrected for in order to make use of radiocarbon measurements as a chronometric tool for all parts of the biosphere.
In order to remove the effects of isotopic fractionation, the Fraction Modern is then corrected to the value it would have if its original δC value to which all radiocarbon measurements are normalized.) The fractionation correction is done using the 13/12 ratio measured by the AMS system.
Using this measurement also corrects for any mass-dependent fractionation within the AMS system.
The Fraction Modern corrected for δC of a sample 10 separate times over the course of a run.It should be noted that the reported error is an estimate of the precision of our measurement of a single sample.Due to variability in sample homogeneity, sampling, and sample processing, the variability of multiple submissions of a sample are generally higher than the reported error for a single submission.Therefore a 1% error in fraction-modern leads to an 80 year error in the age.Ages are rounded according to the convention of Stuiver & Polach, shown below.The reproducibility of these measurements gives us a good estimate of the true experimental error.