In AMS, the 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 cesium and the ions produced are extracted and accelerated in the AMS system. After acceleration and removal of electrons, the emerging positive ions are magnetically separated by mass and the From a contemporary sample, about 150 » NOSAMS General Statement of Process Blanks The process blanks contain small but measurable amounts of Fraction Modern The Fraction Modern (Fm) is computed from the expression: Where B, S and M represent the Fraction Modern is a measurement of the deviation of the δ ^{13}C CorrectionIn addition to loss through decay of radiocarbon,
Errors Atoms of Aside from the normal statistical errors intrinsic to the counting of This component of the Fm error is then added in quadrature as follows: Radiocarbon Age Radiocarbon age is calculated from the δ Age = -8033 ln (Fm) Reporting of ages and/or activities follows the convention outlined by Stuiver and Polach (1977) and Stuiver (1980). 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]
Rounding Convention
Limiting Ages 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. No age is reported greater than 60,000 years. The typical background age for organic combustions is 48,000 years and for inorganic carbon samples, 52,000 years. 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. The limiting age is then calculated as -8033 * ln(2sigma) and rounded according to conventions outlined above. Age > Modern Since Modern is defined as 95% of the Δ ^{14}C We also report the Δ Where lambda is 1/(true mean-life) of radiocarbon = 1/8267 = 0.00012097 References Karlen, I., Olsson, I.U., Kallburg, P. and Kilici, S., 1964. Absolute determination of the activity of two Olsson, I.U., 1970. The use of Oxalic acid as a Standard. In I.U. Olsson, ed., Radiocarbon Variations and Absolute Chronology, Stuiver, M. and Polach, H.A., 1977. Discussion: Reporting of Stuiver, M., 1980. Workshop on | ||||||||||||||||||||||||||||||||||||||

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