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).
AMS, on the other hand, can in principle detect a much higher proportion (typically about 1% of the total) allowing sample sizes to be smaller by a factor of about a thousand.
Probably the most important factor to consider when using radiocarbon dating is if external factors, whether through artificial contamination, animal disturbance, or human negligence, contributed to any errors in the determinations.
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.
-counting method) or by directly counting the radiocarbon atoms using a method called Accelerator Mass Spectrometry (AMS).
Measurement of the radioactivity of the sample works very well if the sample is large, but in 9 months less than 0.01% of the radiocarbon ions will decay, so in a reasonable measurement time (typically a few weeks) only a very small proportion of the radiocarbon atoms are detected by this method.