The carbon dioxide is collected in a glass ampoule or converted to graphite for radiocarbon measurement on the AMS system.
-counting method are the much greater sensitivity of the measurement.
Before sampling, the surface layers are usually removed because these are most susceptible to contamination.
They, however, do not have the sensitivity to distinguish atomic isobars (atoms of different elements that have the same atomic weight, such as in the case of carbon 14 and nitrogen 14—the most common isotope of nitrogen).
Thanks to nuclear physics, mass spectrometers have been fine-tuned to separate a rare isotope from an abundant neighboring mass, and accelerator mass spectrometry was born.
After chemical pre-treatment, the samples are burnt to produce carbon dioxide and nitrogen.
A small amount of this gas is bled into a mass spectrometer where the stable isotope ratios of carbon and nitrogen are measured.
A method has finally been developed to detect carbon 14 in a given sample and ignore the more abundant isotopes that swamp the carbon 14 signal.
There are essentially two parts in the process of radiocarbon dating through accelerator mass spectrometry.
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).
The chemical pre-treatment depends on the type of sample.