Radiocarbon dating equation
One other situation that limits the age (if not already limited by the background age) is the error of the AMS result.
If twice the reported error of the Fraction Modern (let's call this 2sigma) is larger than the sample Fraction Modern, then a limiting age is reported.
After acceleration and removal of electrons, the emerging positive ions are magnetically separated by mass and the C counts per second are collected.
It is expected then, for a 5,570 year (1 half-life) or 11,140 year old (2 half-lives) sample that 125 or 63 counts per second would be obtained.
Due to counting and measurement errors for the blanks and samples, statistical errors are higher for very old samples.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.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.