| 16 | rowspan=3| | rowspan=3| | β− () | | rowspan=3|(5/2+) | rowspan=3| | rowspan=3| |- | β−n () | |- | β−2n ? | ? |- | rowspan=3| | rowspan=3 style="text-align:right" | 9 | rowspan=3 style="text-align:right" | 17 | rowspan=3| | rowspan=3| | β− () | | rowspan=3|1+ | rowspan=3| | rowspan=3| |- | β−n () | |- | β−2n ? | ? |- | rowspan=3 style="text-indent:1em" | | rowspan=3 colspan="3" style="text-indent:2em" | | rowspan=3 | | IT () | | rowspan=3|(4+) | rowspan=3| | rowspan=3| |- | β−n () | |- | β− ? | ? |- | rowspan=3| | rowspan=3 style="text-align:right" | 9 | rowspan=3 style="text-align:right" | 18 | rowspan=3| | rowspan=3| | β−n () | | rowspan=3|5/2+# | rowspan=3| | rowspan=3| |- | β− () | |- | β−2n ? | ? |- | | style="text-align:right" | 9 | style="text-align:right" | 19 | | | n | | (4−) | | |- | rowspan=3| | rowspan=3 style="text-align:right" | 9 | rowspan=3 style="text-align:right" | 20 | rowspan=3| | rowspan=3| | β−n () | | rowspan=3|(5/2+) | rowspan=3| | rowspan=3| |- | β− () | |- | β−2n ? | ? |- | rowspan=3| | rowspan=3 style="text-align:right" | 9 | rowspan=3 style="text-align:right" | 22 | rowspan=3|# | rowspan=3|# [> ] | β− ? | ? | rowspan=3|5/2+# | rowspan=3| | rowspan=3| |- | β−n ? | ? |- | β−2n ? | ? |- Fluorine-18 Of the unstable nuclides of fluorine, has the longest half-life, . It decays to via β+ decay. For this reason 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 ; no other isotopes of fluorine exist in significant quantities. Its binding energy is . 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 and decays via beta decay to the stable nuclide . Its specific radioactivity is and has a mean lifetime of . Fluorine-21 Fluorine-21, as with fluorine-20, is also an unstable isotope of fluorine. It