Half life and radiocarbon dating


Theoretically, if one could detect the amount of carbon-14 in an object, one could establish that object’s age using the half-life, or rate of decay, of the isotope.In 1946, Libby proposed this groundbreaking idea in the journal Physical Review.To test the technique, Libby’s group applied the anti-coincidence counter to samples whose ages were already known.Among the first objects tested were samples of redwood and fir trees, the age of which were known by counting their annual growth rings.Based on Korff’s estimation that just two neutrons were produced per second per square centimeter of earth’s surface, each forming a carbon-14 atom, Libby calculated a ratio of just one carbon-14 atom per every 10 carbon atoms on earth.Libby’s next task was to study the movement of carbon through the carbon cycle.At the time, no radiation-detecting instrument (such as a Geiger counter) was sensitive enough to detect the small amount of carbon-14 that Libby’s experiments required.

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(Fortunately for him, this was later proven to be generally true.) For the second factor, it would be necessary to estimate the overall amount carbon-14 and compare this against all other isotopes of carbon.Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms.The “radiocarbon revolution” made possible by Libby’s discovery greatly benefitted the fields of archaeology and geology by allowing practitioners to develop more precise historical chronologies across geography and cultures.Top of page You read statements in books that such and such a society or archeological site is 20,000 years old.