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Ams dating technique

So the most important things about AMS radiocarbon dating as opposed to conventional is that the sample size is much, much smaller.The measurement time is much more rapid – you don’t have to sit around and wait for the carbon-14s to decay – and also the precision is better.

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AMS is faster and needs a much smaller sample, but is more expensive.The measurement of radiocarbon by mass spectrometry is very difficult because its concentration is less than one atom in 1,000,000,000,000.The accelerator is used to help remove ions that might be confused with radiocarbon before the final detection.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.C atoms in the sample would greatly enhance the sensitivity, and some unsuccessful attempts were made in this direction using conventional mass spectrometry. This technique has allowed the measurement of radiocarbon in samples of much less than a milligram, or over a thousand times less material than is needed from the older counting methods.

Dr Christine Prior is Team Leader of the Rafter Radiocarbon Laboratory at GNS Science.

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.

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).

Before sampling, the surface layers are usually removed because these are most susceptible to contamination.