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One of two or more forms of a chemical element having the same atomic number but different mass. Isotopes occur when atoms of an element have the same number of protons but different numbers of neutrons in their nuclei. Most elements have at least one isotopic form. The presence of isotopes was first demonstrated in 1912 by Sir Joseph Thomson. Now there are known to be about 280 naturally occurring stable isotopes of the 83 most abundant elements and over 800 radioactive isotopes. Nonradioactive isotopes are used to prepared heavy water. Radioactive isotopes are used as tracers in biochemical, metallurgical and medical research. They are also used for geochemical and archaeological dating techniques.

Synonyms and Related Terms


Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

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