Radiocarbon, or carbon 14, is a radioactive isotope of carbon. It is used to determine the age of fossils and other kinds of ancient objects. In addition, researchers use radiocarbon to study certain biological processes. Radiocarbon has a relative atomic mass of about 14 and is heavier than the most common isotope of carbon, which has a relative atomic mass of exactly 12. An isotope's relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of an atom of carbon 12.