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.Atoms of the same element that have different numbers of neutrons are called isotopes. Most carbon on Earth exists as the very stable isotope carbon-12, with a very small amount as carbon-13.Here’s an example using the simplest atom, hydrogen. Carbon-14 is an unstable isotope of carbon that will eventually decay at a known rate to become carbon-12.Radiocarbon dating is especially good for determining the age of sites occupied within the last 26,000 years or so (but has the potential for sites over 50,000), can be used on carbon-based materials (organic or inorganic), and can be accurate to within ±30-50 years.
Radiocarbon dating works by comparing the three different isotopes of carbon.
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.
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.
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.