Godwin In places where the calibration curve is steep, and does not change direction, as in example t 1 in blue on the graph to the right, the resulting calendar year range is quite narrow. To determine this, a blank sample of old, or dead, carbon is measured, and a sample of known activity is measured. Contamination with modern carbon causes a sample to appear to be younger than it really is: The method of deriving a calendar year range described above depends solely on the position of the intercepts on the graph.
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A Guide to Radiocarbon Units and Calculationsp. Radiocarbon dating considerations. Inthe British Museum radiocarbon laboratory ran weekly measurements on the same sample for six months. These improved field methods were sometimes motivated by attempts to prove that a 14 C date was incorrect. With the development of AMS in the s it became possible to measure these isotopes precisely enough for them to be the basis of useful dating techniques, which have been primarily applied to dating rocks. The half-life of 14 C the time it takes for half of a given amount of 14 C to decay is about 5, years, so its concentration in the atmosphere might be expected to reduce over thousands of years, but 14 C is constantly being produced in the lower stratosphere and upper troposphereprimarily by galactic cosmic raysand to a lesser degree by solar cosmic rays. From Wikipedia, the free encyclopedia.