Fluorine-18

Fluorine-18
Decay over 24 hours Full table
General
Name, symbol	Fluorine-18,^18F
Neutrons	9
Protons	9
Nuclide data
Natural abundance	Radioisotope
Half-life	109.771(20) min
Decay products	^18O
Isotope mass	18.0009380(6) u
Spin	1^+
Excess energy	873.431± 0.593 keV
Binding energy	137369.199± 0.593 keV
Decay mode	Decay energy
Positron emission (97%)	0.6335 MeV
Electron capture (3%)	1.6555 MeV

Fluorine-18 (¹⁸F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 97% of the time and electron capture 3% of the time. Both modes of decay yield stable oxygen-18.

Synthesis

In the radiopharmaceutical industry, F-18 is made using either a cyclotron or linear particle accelerator to bombard a target, usually of pure or enriched oxygen-18-water ^[1] with high energy protons (typically ~18 MeV protons). The fluorine produced is in the form of a water solution of F-18 fluoride, which is then used in a rapid chemical synthesis of the radiopharmaceutical. The organic O-18 pharmaceutical molecule is not made before the production of the radiopharmaceutical, as high energy protons destroy such molecules. Radiopharmaceuticals using fluorine must therefore be synthesized after the F-18 has been produced.

Chemistry

Fluorine-18 is often substituted for a hydroxyl group in a radiotracer parent molecule, due to similar steric and electrostatic properties. This may however be problematic in certain applications due to possible changes in the molecule polarity.

Applications

Fluorine-18 is an important isotope in the radiopharmaceutical industry, and is primarily synthesized into fluorodeoxyglucose (FDG) for use in positron emission tomography (PET scans). It is substituted for hydroxyl and used as a tracer in the scan. Its significance is due to both its short half-life and the emission of positrons when decaying.

References

1. Fowler J. S. and Wolf A. P. (1982) The synthesis of carbon-11, fluorine-18 and nitrogen-13 labeled radiotracers for biomedical applications. Nucl. Sci. Ser. Natl Acad. Sci. Natl Res. Council Monogr. 1982.