Fluorine (9F) has 19 known isotopes ranging from 13Fluorine to 31Fluorine and two isomers (18mFluorine and 26mFluorine). 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 [[Fluorine|18Fluorine]]; it has a half-life of 109.734 minutes. 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 14Fluorine, whose half-life is 500 yoctoseconds, corresponding to a resonance width of 910 keV.

List of isotopes

Fluorine-18

Of the unstable nuclides of fluorine, 18Fluorine has the longest half-life, 109.734 minutes. It decays to 18Oxygen via β+ decay. For this reason 18Fluorine is a commercially important source of positrons. Its major value is in the production of the radiopharmaceutical fludeoxyglucose, used in positron emission tomography in medicine. Fluorine-18 is the lightest unstable nuclide with equal odd numbers of protons and neutrons, having 9 of each. (See also the "magic numbers" discussion of nuclide stability.)

Fluorine-19

Fluorine-19 is the only stable isotope of fluorine. Its abundance is 100 %; no other isotopes of fluorine exist in significant quantities. Its binding energy is 147,801.365 keV. Fluorine-19 is NMR-active with a spin of 1/2+, so it is used in fluorine-19 NMR spectroscopy.

Fluorine-20

Fluorine-20 is an unstable isotope of fluorine. It has a half-life of 11.006 seconds and decays via beta decay to the stable nuclide 20Neon. Its specific radioactivity is 1.869 Bq/g and has a mean lifetime of 15.879 seconds.

Fluorine-21

Fluorine-21, as with fluorine-20, is also an unstable isotope of fluorine. It has a half-life of 4.158 seconds. It undergoes beta decay as well, decaying to 21Neon, which is a stable nuclide. Its specific activity is 4.781 Bq/g.

Isomers

Only two nuclear isomers (long-lived excited nuclear states), fluorine-18m and fluorine-26m, have been characterized. The half-life of 18mFluorine before it undergoes isomeric transition is 162 nanoseconds. This is less than the decay half-life of any of the fluorine radioisotope nuclear ground states except for mass numbers 14–16, 28, and 31. The half-life of 26mFluorine is 2.2 milliseconds; it decays mainly to its ground state of 26Fluorine or (rarely, via beta-minus decay) to one of high excited states of 26Neon with delayed neutron emission.

Sources