Fluorine-21

Properties and data of the isotope ²¹F.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Fluorine-21 is a radioisotope of the chemical element fluorine, which has 12 neutrons in its atomic nucleus in addition to the element-specific 9 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 21. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²¹F is exclusively for academic purposes.

The discovery of the isotope was reported in 1955: The identification was achieved by irradiating fluoride-containing materials (calcium fluoride CaF₂ and lead difluoride PbF₂) with tritons (hydrogen-3 nuclei; 2.5 MeV) [1]:

¹⁹F(t,p)²¹F.

See also: List of individual Fluorine isotopes (and general data sources).

General data

Name of the isotope:Fluorine-21; F-21Symbol:²¹F or 219FMass number A:21 (= number of nucleons)Atomic number Z:9 (= number of protons)Neutrons N:12Isotopic mass:20.9999489(19) u (atomic weight of Fluorine-21)Nuclide mass:20.9950117 u (calculated nuclear mass without electrons)Mass excess:-0.0476 MeVMass defect:0.17445538 u (per nucleus)Nuclear binding energy:162.50413974 MeV (per nucleus)
7.73829237 MeV (average binding energy per nucleon)Separation energy:S_N = 8.1015(18) MeV (first neutron)
S_P = 11.1327(20) MeV (first proton)Half-life:4.158(20) sDecay constant λ:0.16670206362673 s^-1Specific activity α:5.019516544011 × 10⁺²¹ Bq g^-1
135662609297.61 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2+Magnetic dipole moment:μ(μ_N) = 3.9194(12)Quadrupole moment Q:0.110 barn (100 fm²)Nuclear g-factor:g_l = 1.56776Mirror nucleus:Magnesium-21Year of discovery:1955

Radioactive Decay

Half-life T_½ = 4.158(20) s.

Decay mode	Daughter	Probability	Decay energy	Details	γ energy (intensity)
β^-	²¹Ne	100 %	5.6842(18) MeV	β^-: 1.769(4) MeV [16.1(10) %] β^-: 2.452(4) MeV [74.1(22) %] β^-: 2.624(4) MeV [10(3) %]	1.395131(17) MeV [15.3(3) %]

Parent Nuclides

Direct parent isotopes are: ²¹O, ²²O.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 12) and isobaric (same nucleon number A = 21) with Fluorine-21. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 12	Isobar A = 21
4	¹⁶Be
5	¹⁷B	²¹B
6	¹⁸C	²¹C
7	¹⁹N	²¹N
8	²⁰O	²¹O
9	²¹F	²¹F
10	²²Ne	²¹Ne
11	²³Na	²¹Na
12	²⁴Mg	²¹Mg
13	²⁵Al	²¹Al
14	²⁶Si
15	²⁷P
16	²⁸S
17	²⁹Cl
18	³⁰Ar