Age calculation dating
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 .The limiting age is then calculated as -8033 * ln(2sigma) and rounded according to conventions outlined above.The Gregorian calendar is the most prevalently used calendar today.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.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.
The surface of the graphite is sputtered with heated, ionized cesium and the ions produced are extracted and accelerated in the AMS system.
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.
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.