Benefits of using radiocarbon dating
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View the full list Radiocarbon dating has transformed our understanding of the past 50,000 years.
Radiometric dating is also used to date archaeological materials, including ancient artifacts.
Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.
In common with other kinds of mass spectrometry, AMS is performed by converting the atoms in the sample into a beam of fast moving ions (charged atoms).
The mass of these ions is then measured by the application of magnetic and electric fields.
When an organism, eg a tree, dies it stops taking in carbon dioxide.
The amount of carbon-14 in the wood decreases with time as it decays into nitrogen with a half-life of about 5700 years.
The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
The sample is put into the ion source either as graphite or as carbon dioxide.
It is ionised by bombarding it with caesium ions and then focused into fast-moving beam (energy typically 25ke V).
Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons.
This means that although they are very similar chemically, they have different masses.