Fluorine-18

Properties and data of the isotope ¹⁸F.

Contents

General Data

Radioactive Decay

Isotones und Isobares

Literature

Fluorine-18 is a radioisotope of the chemical element fluorine, which, in addition to the element-specific 9 protons, has 9 neutrons in the atomic nucleus, resulting in the mass number 19. As a positron-emitting radionuclide, ¹⁸F is of practical importance in medical education (see below).

The radioactive isotope was first described in 1937: Fluorine-18 was observed during the irradiation of quartz and other solid oxides with protons (3.8 MeV) as a product of the nuclear reaction ¹⁸O (p,n)¹⁸F [1].

General data

Name of the isotope:Fluorine-18; F-18Symbol:¹⁸F or 189FMass number A:18 (= number of nucleons)Atomic number Z:9 (= number of protons)Neutrons N:9Isotopic mass:18.0009373(5) u (atomic weight of Fluorine-18)Nuclide mass:17.9960001 u (calculated nuclear mass without electrons)Mass excess:0.87309 MeVMass defect:0.147472232 u (per nucleus)Nuclear binding energy:137.36949927 MeV (per nucleus)
7.63163885 MeV (average binding energy per nucleon)Separation energy:S_N = 9.1499(5) MeV (first neutron)
S_P = 5.6071(5) MeV (first proton)Half-life:109.734(8) minDecay constant λ:0.00010527687871883 s^-1Specific activity α:3.522178849662 × 10⁺¹⁸ Bq g^-1
95194022.963857 Ci g^-1Spin and parity:
(nuclear angular momentum)1+Isobaric spin: 0Year of discovery:1937

Radioactive Decay

Half-life T_½ = 109.734(8) min (minutes) respectively 6.58404 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	Details	γ energy (intensity)
EC/β⁺	¹⁸O	100 %	1.6559(5) MeV	β⁺: 0.2498(3) MeV [96.73(4) %]	Annihilation: 0.5110 MeV [193.46(8) %]

Parent Nuclides

Direct parent isotope is: ¹⁸Ne.

Formation

Fluorine-18 can be produced artificially in nuclear reactors, but preferably in accelerators (cyclotrons and linear accelerators). Overall, there are a whole series of nuclear reactions that lead to ¹⁸F; these include:

- ¹⁸O(p,n)¹⁸F,

-¹⁶O(³He,p)¹⁸F,

- ¹⁶O(α,pn)¹⁸F,

- ²⁰Ne(d,α)¹⁸F,

- ²⁰Ne(p,2n)¹⁸F,

- ²⁰Ne(³He,n)¹⁸Ne, which then naturally leads to F decays,

- ⁶Li(n,α)³H/¹⁶O(³H,n)¹⁸F.

Fluorine-18 for medical and research purposes is produced by cyclotron irradiation of the respective target molecules (often Water-18O).

A detailed and comprehensive overview of fluorine-18 radiochemistry, ¹⁸F labeling strategies and the synthesis routes to ¹⁸F-labeled molecules has been published by Orit Jacobsen et al. in an open-access article [4].

Occurrence

Fluorine-18 only occurs in small traces in nature. The main sources here are the spallation by cosmic radiation of atmospheric argon and the reaction of protons with natural oxygen-18.

Fluorine-18 as a Radionuclide in Medicine

Fluorine-18 is an important source of positrons in medicine. Radiopharmaceuticals labelled with ¹⁸F are used in particular in positron emission tomography (¹⁸F-PET), an imaging technique that detects the positrons emitted by the radioactive decay of the isotope and processes them into an image that is used for diagnostic purposes.

(Chemical) data sheets are available here for the following radioactive ¹⁸F tracers:

- Flotufolastat F-18,

- Fludeoxyglucose F-18,

- Florbenazine (18F) (experimental),

- Florbenguane (experimental).

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^18mF	1121.36(15) keV	162(7) ns	5+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 9) and isobaric (same nucleon number A = 18) with Fluorine-18. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 9	Isobar A = 18
3	¹²Li
4	¹³Be
5	¹⁴B	¹⁸B
6	¹⁵C	¹⁸C
7	¹⁶N	¹⁸N
8	¹⁷O	¹⁸O
9	¹⁸F	¹⁸F
10	¹⁹Ne	¹⁸Ne
11	²⁰Na	¹⁸Na
12	²¹Mg	¹⁸Mg
13	²²Al
14	²³Si
15	²⁴P

External data and identifiers

CAS:13981-56-1SMILES:[18F]PubChem:ID 105162Adopted Levels, Gammas:NuDat 18F

Literature and References

[1] - L. A. DuBridge, S. W. Barnes, J. H. Buck:
Proton Induced Radioactivity in Oxygen.
In: Physical Review, 51, 995, (1937), DOI 10.1103/PhysRev.51.995.

[2] - Erin L. Cole et al.:
Radiosyntheses using Fluorine-18: The Art and Science of Late Stage Fluorination.
In: Current Topics in Medicinal Chemistry, 14, 7, (2014), DOI 10.2174/1568026614666140202205035.

[3] - Kaiqiang Zhang, Wanru Feng, Zhaobiao Mou, Jiayin Chen, Xiaoqun Tang, Prof. Dr. Zijing Li:
¹⁸F-Labeling Chemistry in Aqueous Media.
In: Chemistry - A European Journal, 29, 37, (2023), DOI 10.1002/chem.202300248.

[4] - Orit Jacobson, Dale O. Kiesewetter, Xiaoyuan Chen:
Fluorine-18 Radiochemistry, Labeling Strategies and Synthetic Routes.
In: Bioconjugate Chemistry, 26, 1, 1–18, (2014), DOI 10.1021/bc500475e.