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Two or more forms of an element that have the same atomic
number but different numbers of neutrons in the atomic nucleus and therefore a
different atomic weight. Most elements occur naturally as mixtures of isotopes.
The symbol for an isotope usually consist of the mass number placed as a leading
superscript before the elemental symbol. In atmospheric chemistry, long lived
isotopes such as carbon-14 (14C) are used to determine the age of
objects that contained living matter. Other isotopes are used to track the
routes of air parcels in the atmosphere.
[Science; v266; 1584-1586; 1994.]
[Dictionary of Science; R.K. Barnhart; page 337; 1986; Houghton Mifflin Company;
Boston.]
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