Isotopes of fluorine

Fluorine (9F) has 17 known isotopes 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 and mononuclidic element, and only artificially produced fluorine isotopes have mass numbers 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; it has a half-life of 109.739 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 14F, whose half-life is 500(60) × 10−24 seconds,[2] corresponding to a spectral linewidth of about 1 MeV.

List of isotopes
Nuclide[3]
[n 1]		 Z N Isotopic mass (Da)[4]
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
[n 6]		 Spin and
parity
[n 7][n 4]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
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 8] 9 9 18.0009373(5) 109.739(9) min β+ (96.86%) 18O 1+ Trace
EC (3.14%)[5] 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+)
β−, n (11%) 21Ne
23F 9 14 23.00353(4) 2.23(14) s β− (86%) 23Ne 5/2+
β−, n (14%) 22Ne
24F 9 15 24.00810(10) 384(16) ms β− (94.1%) 24Ne 3+
β−, n (5.9%) 23Ne
25F 9 16 25.01217(10) 80(9) ms β− (76.9%) 25Ne (5/2+)
β−, n (23.1%) 24Ne
26F 9 17 26.02002(12) 8.2(9) ms β− (86.5%) 26Ne 1+
β−, n (13.5%) 25Ne
26mF 643.4(1) keV 2.2(1) ms IT (82%) 26F (4+)
β−, n (12%) 25Ne
β− (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. mF – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  6. Bold symbol as daughter – Daughter product is stable.
  7. ( ) spin value – Indicates spin with weak assignment arguments.
  8. Has medicinal uses

Fluorine-18
Main article: Fluorine-18

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.[5]

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.)[6]

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

Fluorine-20

Fluorine-20 is one of the more unstable isotopes of fluorine. It has a half-life of 11.13 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

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.

Isomers

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]

References
  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. Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  3. Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:
    Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  4. Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (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.
  5. F-18 branching ratio for positron emission vs. EC
  6. National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
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