What Are Isotopes?

Isotopes are atoms of the same element that have different numbers of neutrons in the nucleus and therefore different atomic weights (shown as a superscript numeral in front of the element's symbol)

Isotopes may be stable or radioactive. Most elements have two or more isotopes. The isotopes most commonly used in geochemistry include: carbon (¹²C, ¹³C,¹⁴C), hydrogen (¹H, ²H, ³H), oxygen (¹⁶O,¹8O), sulfur (³²S, ³⁴S) and nitrogen (¹⁴N, ¹⁵N).

The elements listed above are important constituents in biological systems and are also involved in many geochemical reactions. Small differences in the concentration of isotopes exist in chemically identical compounds because of differences in the origin or certain processes that have occurred after the compounds was produced. These characteristics make isotope analyses very useful for determining the source of certain compounds in the environment and/or determining the geochemical reactions that have affected the concentration of the compounds or materials of interest. The radioactive isotopes are often used to determine the age of different types of materials.