oxygen 18

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ox·y·gen 18 (18O),

A stable oxygen isotope making up 0.20% of natural oxygen; used in mass spectrometry and in NMR studies of tissue.
Synonym(s): heavy oxygen
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References in periodicals archive ?
Levels of oxygen 18 in ice core samples from the 1990s were more elevated than for any other time in the last 200 years, but were very similar to levels reached during some earlier decades.