) is only 5,730 years—that is, every 5,730 years, half of it decays away.After two half lives, a quarter is left; after three half lives, only an eighth; after 10 half lives, less than a thousandth is left.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.
However, when the organism dies, the amount of c14 declines such that the longer the time since death the lower the levels of c14 in organic tissue.
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.
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.