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.Ages are calculated using 5568 years as the half-life of radiocarbon and are reported without reservoir corrections or calibration to calendar years.For freeware programs, we suggest that you look at the following web site for a list of programs that will calibrate radiocarbon results to calendar years (including making reservoir corrections).[ Radiocarbon-Related Information Sources] The error in the age is given by 8033 times the relative error in the Fm .Fractionation is the term used to describe the differential uptake of one isotope with respect to another.
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.
However, limiting ages or "backgrounds" are also determined by process blanks which correspond to the method used to extract the carbon from the sample.
» NOSAMS General Statement of C from contamination introduced during chemical preparation, collection or handling.
Organic materials, which require the most processing, are limited to younger ages by their corresponding process blank.
Due to counting and measurement errors for the blanks and samples, statistical errors are higher for very old samples.