Natural isotopes are either stable isotopes or radioactive isotopes that have a sufficiently long half-life to allow them to exist in substantial concentrations in the Earth (such as bismuth-209, with a half-life of 1.9 years,
potassium-40 with a half-life of 1.251(3) years), daughter products of those isotopes (such as
234Th, with a half-life of 24 days) or cosmogenic elements. The heaviest stable isotope is lead-208, but the heaviest 'natural' isotope is U-238.
Many elements have both natural and artificial isotopes. For example, hydrogen has three natural isotopes and another four known artificial isotopes.
A further distinction among stable natural isotopes is division into primordial (existed when the Solar System formed) and cosmogenic elements (created by cosmic ray bombardment or other similar processes).
What defines a natural isotope
Natural isotopes must be either stable, have a half-life exceeding about 7 years (there are 34 isotopes in this category, see
stable isotope for more details) or are generated in large amounts cosmogenically (such as
14C, which has a half life of only 6000 years but is made by cosmic rays colliding with
14N).
Naturally occurring radioisotopes
Some radioisotopes occur in nature with a half-life of less than 7{{e, 7 years (
carbon-14
Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
: 5,730 ± 40 years,
tritium: 12.32 years etc.). They are synthesised all the time by cosmic radiation. A practical use is
radiocarbon dating
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
The method was dev ...
with carbon-14.
See also
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Stable isotope
*
Environmental isotopes
Bibliography
Isotopes