In AMS, the filiamentous carbon or "graphite" derived from a sample is compressed into a small cavity in an aluminum "target" which acts as a cathode in the ion source.The surface of the graphite is sputtered with heated, ionized cesium and the ions produced are extracted and accelerated in the AMS system.
The final reported error is the larger of the internal or external errors.
Our measurements of secondary standards show that the deviation within a population of samples is generally 1-3 permil greater than the reported error for a single sample.
Radiocarbon age is calculated from Reporting of ages and/or activities follows the convention outlined by Stuiver and Polach (1977) and Stuiver (1980).
Although one can simply measure older samples for longer times, there are practical limits to the minimum sample activity that can be measured.
At the present time, for a 1 milligram sample of graphite, this limiting age is about ten half-lives, or 60,000 years, if set only by the sample size.
Thus, ages are limited by the age of the process blanks (more on that below) and by the statistical uncertainty of the C ratios of the blank, the sample and the modern reference, respectively.