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Fluorine (9F) has 17 known isotopes, with atomic masses ranging from 14F to 31F (with the exception of 30F), and two isomers (18mF and 26mF). Only fluorine-19 is stable and naturally occurring; therefore, fluorine is a monoisotopic element and only artificially produced fluorine isotopes have atomic masses other than 19.

Main isotopes of fluorine (9F)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
18F trace 109.739 min β+ (96.9%) 18O
ε (3.14%) 18O
19F 100% stable
Standard atomic weight Ar, standard(F)
  • 18.998403163(6)[1]

The longest-lived radioisotope is 18F; and it has a half-life of only 109.739 minutes. All other fluorine isotopes have half-lives of less than a minute, and most of those less than a second, so that fluorine is a mononuclidic element for practical purposes. The least stable known isotope is 14F, whose half-life is 500(60) × 10−24 seconds,[2] corresponding to a spectral linewidth of about 1 MeV.


List of isotopesEdit

Z(p) N(n)  
isotopic mass (u)[3]
half-life decay mode(s)[2] daughter
isotope(s)[n 1]
spin and
(mole fraction)
range of natural
(mole fraction)
excitation energy
14F 9 5 14.03432(4) 500(60)×10−24 s
[910 keV]
p 13O 2-
15F 9 6 15.017785(15) 1.1(0.3)×10−21 s
[1.0(2) MeV]
p 14O 1/2+
16F 9 7 16.011466(9) 11(6)×10−21 s
[40(20) keV]
p 15O 0−
17F 9 8 17.00209524(27) 64.370(27) s β+ 17O 5/2+
18F[n 2] 9 9 18.0009373(5) 109.739(9) min β+ (96.86%) 18O 1+
EC (3.14%)[4] 18O
18mF 1121.36(15) keV 162(7) ns IT 18F 5+
19F 9 10 18.9984031629(9) Stable 1/2+ 1.0000
20F 9 11 19.99998125(3) 11.163(8) s β 20Ne 2+
21F 9 12 20.9999489(19) 4.158(20) s β 21Ne 5/2+
22F 9 13 22.002999(13) 4.23(4) s β (89%) 22Ne (4+)
βn (11%) 21Ne
23F 9 14 23.00353(4) 2.23(14) s β (86%) 23Ne 5/2+
βn (14%) 22Ne
24F 9 15 24.00810(10) 384(16) ms β (94.1%) 24Ne 3+
βn (5.9%) 23Ne
25F 9 16 25.01217(10) 80(9) ms β (76.9%) 25Ne (5/2+)
βn (23.1%) 24Ne
26F 9 17 26.02002(12) 8.2(9) ms β (86.5%) 26Ne 1+
βn (13.5%) 25Ne
26mF 643.4(1) keV 2.2(1) ms IT (82%) 26F (4+)
βn (12%) 25Ne
βn (6%) 26Ne
27F 9 18 27.02732(42) 4.9(2) ms β, n (77%) 26Ne 5/2+#
β (23%) 27Ne
28F 9 19 28.03622(42) 46×10−21 s n 27F
29F 9 20 29.04310(56) 2.5(3) ms β, n (60%) 28Ne 5/2+#
β (40%) 29Ne
31F 9 22 31.06027(59)# 1# ms [>260 ns] β 31Ne 5/2+#
  1. ^ Bold for stable isotopes
  2. ^ Has medicinal uses
  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.


Of the unstable nuclides of fluorine, 18F has the longest half-life, 109.739 minutes. It has two decay modes, of which the main one is positron emission. For this reason 18F 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.

Like all positron-emitting radioisotopes, 18F also may decay by electron capture. In either case, 18F decays into 18O. The two decay modes do not happen equally frequently however; 96.86% of the decays are by beta plus (positron) emission and 3.14% by electron capture.[4]

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.)[5]


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 147801 keV. Fluorine-19 is NMR-active with spin of 1/2, so it is used in fluorine-19 NMR spectroscopy.


Fluorine-20 is one of the more unstable isotopes of fluorine. It has a half-life of 11.07 seconds and undergoes beta decay, transforming into its daughter nuclide 20Ne. Its specific radioactivity is 1.885 × 109 TBq/g and has a lifetime of 15.87 seconds.


Fluorine-21, as with fluorine-20, is also one of unstable isotopes of this element. It has a half-life of 4.158 seconds. It undergoes beta decay as well, which leaves behind a daughter nuclei of 21Ne. Its specific radioactivity is 4.78 × 109 TBq/g.


Only two nuclear isomers (long-lived excited nuclear states), fluorine-18m and fluorine-26m, have been characterized.[2] The half-life of 18mF before gamma ray emission is 162(7) nanoseconds.[2] 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.[2] The half-life of 26mF is 2.2(1) milliseconds; it decays mainly to the ground state of 26F or (rarely, via beta-minus decay) to one of high excited states of 26Ne with delayed neutron emission.[2]

External linksEdit


  • Isotope masses from:
    • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • Isotopic compositions and standard atomic masses from:
  • Half-life, spin, and isomer data selected from the following sources.
  1. ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  2. ^ a b c d e f Audi, Georges; Kondev, Filip G.; Wang, Meng; Huang, Wen Jia; Naimi, Sarah (2017), "The NUBASE2016 evaluation of nuclear properties" (PDF), Chinese Physics C, 41 (3): 030001–1—030001–138, Bibcode:2017ChPhC..41c0001A, doi:10.1088/1674-1137/41/3/030001
  3. ^ Wang, Meng; Audi, Georges; Kondev, Filip G.; Huang, Wen Jian; Naimi, Sarah; Xu, Xing (2017), "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF), Chinese Physics C, 41 (3): 030003–1—030003–442, doi:10.1088/1674-1137/41/3/030003
  4. ^ a b [1] F-18 branching ratio for positron emission vs. EC
  5. ^ National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.