User:Jclerman/calib

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• Radiocarbon dating analyses are destructive. This means that the wood of treering samples is combusted to produce carbon compounds (carbon dioxide, benzene, etc) whose [specific raw (uncorrected, unnormalized) radio]activity can be detected by counting its disintegrations per minute.

• To attain the appropriate precision and accuracy, the determination of such raw activity requires grams of wood and weeks of counting its radioactive disintegrations.

• The computation of the net specific activity of each sample requires extra weeks analyzing background ("dead" radiocarbon) and modern ("AD1950") standard samples, then to be normalized to a standard C13 value.

• The raw radiocarbon ages are evaluated from the standardized specific net activities described above.

• The series of treerings to be dendrochronologically & radiocarbon dated to be used to calibrate the radiocarbon dating scale were the result of decades of explorations begun in the early 1960s. Remote sites were explored at diverse latitudes and elevations, searching for unique rare, living and dead millennary trees to obtain suitable samples. They were mostly from protected species.

• All the determinations of the radiocarbon activities described above have been cross-correlated and preserved as calibration curves (or tables). By definition a calibration curve has quantities of the same kind on both axis, namely calibrated dates (given as Calendar Years) on the horizontal axis and raw ages (given as Before Present years) on the vertical axis. See Example 1.

• Should a conversion curve be preferred, rather than a calibration curve, the ages on the vertical axis can be converted to the original radiocarbon activities by a simple mathematical operation.

• Any radiocarbon activity from a sample to be dated might match the radiocarbon activities of more than a single tree ring. In Example 1, the sample whose activity dated as 900BP old matches 5 different calendar dates which were obtained from 5 different dendrochronologically dated treerings.

• In practice, things are complicated by the statistical uncertainties (a) of the curve itself, which is really a band, (b) the uncertainty distribution of the sample's activity, and (c) the non-monotonic character of the calibration band. Graphical examples covering the statistical uncertainties and their propagation are given here [1] and here [2].