Founder of carbon dating
Libby received the Nobel Prize for his work in 1960.
The radiocarbon dating method is based on the fact that radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen.
In a liquid-scintillation counter, the beta-particle excites the emission of light from a complex organic molecule or "scintillant".
Because only about 13.5 decays per minute occur in one gram of modern carbon, it was necessary to use fairy large samples of several grams of carbon. 1977] were published simultaneously in , reporting on a development which added a particle accelerator into a mass spectrometer to produce an accelerator mass spectrometer (AMS).
C, using samples of several grams of carbon-black powder.
Unfortunately, in the 1950's, due to atmospheric nuclear testing, this method was subject to errors due to the absorption of nuclear contaminant.
Carbon-14 has a half-life of 5,730 ± 40 years— during the succeeding 5,730 years.
Because carbon-14 decays at this constant rate, an estimate of the date at which an organism died can be made by measuring the amount of its residual radiocarbon.
C, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.
Its existence had been suggested by Franz Kurie in 1934. The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide.
However, open-air nuclear testing between 1955–1980 contributed to this pool.
The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died.
The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.