Isotopes are atoms of the same element that have different atomic weights, due to varying numbers of neutrons (the neutrally-charged particles found in an atom's nucleus).
Mass spectrometers measure the range of possible masses of those isotopes. Depending on the isotopes that make up a particular sample, researchers glean clues about its origin and how it was formed.
The number of isotopes of a given element found in a material is known as the isotope’s relative abundance – relative, that is, to the other isotopes found in the sample.
