Isotopes of fluorine
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Fluorine (9F) has 19 known isotopes ranging from 13
F to 31
F and two isomers (18m
F and 26m
F). Only fluorine-19 is stable and naturally occurring in more than trace quantities; therefore, fluorine is a monoisotopic and mononuclidic element.
The longest-lived radioisotope is 18
F; it has a half-life of 109.734(8) min. All other fluorine isotopes have half-lives of less than a minute, and most of those less than a second. The least stable known isotope is 14
F, whose half-life is 500(60) yoctoseconds, corresponding to a resonance width of 910(100) keV.