At the kinetic energies typically used in an AMS system it is possible to use well-established nuclear physics techniques to detect the individual C ions as they arrive at a suitable particle detector.This may be a solid-state detector or a device based on the gridded ionisation chamber.This requires sufficient atoms to be present to provide a large enough decay rate, as described above.
The original, and best known, application of AMS is radiocarbon dating, where you are trying to detect the rare isotope A nuclear particle accelerator consists essentially of two linear accelerators joined end-to-end, with the join section (called the terminal) charged to a very high positive potential (3 million volts or higher). Injecting negatively charged carbon ions from the material being analysed into a nuclear particle accelerator based on the electrostatic tandem accelerator principle. The negative ions are accelerated towards the positive potential.At the terminal they pass through either a very thin carbon film or a tube filled with gas at low pressure (the stripper), depending on the particular accelerator.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.The latter type of detector can measure both the total energy of the incoming ion, and also the rate at which it slows down as it passes through the gas-filled detector.
These two pieces of information are sufficient to completely identify the ion as C atoms at the rate at which they decay.
Collisions with carbon or gas atoms in the stripper remove several electrons from the carbon ions, changing their polarity from negative to positive. The positive ions are then accelerated through the second stage of the accelerator, reaching kinetic energies of the order of 10 to 30 million electron volts. This problem is solved in the tandem accelerator at the stripper –if three or more electrons are removed from the molecular ions the molecules dissociate into their component atoms. The kinetic energy that had accumulated up to now is distributed among the separate atoms, none of which has the same energy as a single C from the more intense "background" caused by the dissociated molecules on the basis of their kinetic energy.
Accelerating the ions to high energy has one more advantage.
-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.
After chemical pre-treatment, the samples are burnt to produce carbon dioxide and nitrogen.