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Properties and data of the isotope 3H.



Hydrogen-3 isotope

Hydrogen-3 - also known as tritium - is a radioactive isotope of hydrogen that occurs naturally in very small amounts in the atmosphere. It has a half-life of about 12.3 years and beta decays into helium-3. Tritium is used in the nuclear industry as a fuel in nuclear reactors and in the manufacture of nuclear weapons. It can also be used in special phosphors and as a tracer in medical investigations. However, being radioactive also poses certain risks, which limits its use.

The tritium atom consists of a proton - which is specific to H isotopes - and two protons.

See also: list of Hydrogen isotopes.


General data

Name of the isotope:Hydrogen-3; H-3Other names:TritiumSymbol:3H or 31HMass number A:3 (= number of nucleons)Atomic number Z:1 (= number of protons)Neutrons N:2Isotopic mass:3.01604928132(8) u (atomic weight of Hydrogen-3)Nuclide mass:3.0155007 u (calculated nuclear mass without electrons)Mass excess:14.94981 MeVMass defect:0.0091055826800002 u (per nucleus)Nuclear binding energy:8.48179563 MeV (per nucleus)
2.82726521 MeV (average binding energy per nucleon)
Half-life:12.32(2) aDecay constant λ:1.784052415191 × 10-9 s-1Specific activity α:3.581271648598 × 10+14 Bq g-1
9679.1125637792 Ci g-1
Spin and parity:
(nuclear angular momentum)
1/2+Magnetic dipole moment:μ(μN) = + 2.978962460(14)Charge radius:1.7591(363) femtometer fmMirror nucleus:Helium-3Year of discovery:1934


Radioactive Decay

The atomic nucleus of superheavy hydrogen decays into the stable isotope helium-3, releasing an electron e- and an antineutrino:

T → 3He + e- + ve.

The emitted electron receives an average kinetic energy of 0.0056817(12) MeV (log ft = 3.0524(8)) and the virtually intangible antineutrino 0.012906(3) MeV.

The unusually low energy released here makes the decay of the molecular tritium T2 (ditritium) interesting for experimental measurements of the absolute neutrino mass [1].

Half-life T½ = 12.32(2) a respectively 3.88524 × 108 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
β-3He100 %0.018592(0) MeV


Parent Nuclides

Direct parent isotopes are: 4H, 5H.



Tritium is produced, among other things, in nuclear reactors by neutron activation of lithium-6. The reaction takes place in so-called breeding ceramics, from which the gaseous tritium diffuses out.



Comparison of the natural Hydrogen isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):


Atomic Mass maQuantityHalf-lifeSpin
Isotopic mixture
1.008 u100 %
Isotope 3H3.01604928132(8) u
12.32(2) a1/2+
Isotope 1H1.0078250322(6) u99.99 %
[99.972 - 99.999 %]
Isotope 2H2.0141017781(8) u0.01 %
[0.001 - 0.028 %]


NMR data

Nuclear magnetic properties of the NMR active Nuclide 3H

Isotope:3H-NMRQuantity:SpurenSpin:1/2+Nuclearmagnetic moment
+ 2.978962460(14)Gyromagnetic ratio γ:28.535 · 107 rad T-1 s-1Nuclear g-factor:gl = 5.95792492Quadrupole moment Q:0 barn (100 fm2)Resonance frequency:v0 = 45.4148 at 1 TFrequency ratio:Ξ(3H) = 106.663974 %Relative Sensitivity:1.21354 (H0 = const.)
1.0667 (v0 = const.)
[related to 1H = 1.000]
Reference compound:
Tritiated tetramethylsilane (TMS-T1, < 1%) in Chloroform-d (CDCl3).

Tritium has the peculiarity that its atomic nucleus responds better to a magnetic field and therefore reacts more sensitively than the proton. Nevertheless, tritium NMR spectroscopy is a niche application: with an isotopic frequency - measured as the proportion of the 3H atom in natural hydrogen - of 10-15%, tritium is practically non-existent available. The availability of tritiated substance is poor; In addition, these chemicals are difficult to handle due to their radioactivity - and handling requires special safety precautions and technical aids. Nevertheless, there are some reports on the practical application of 3H NMR spectroscopy in the specialist literature, as the review article [2] shows.


Radiation Protection

The target organ (critical organ) of the radioactive tritium is the entire body. The biological half-life is 19 days.


Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 2) and isobaric (same nucleon number A = 3) with Hydrogen-3. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.


OZIsotone N = 2Isobar A = 3


External data and identifiers

CAS:10028-17-8PubChem:ID 24824Adopted Levels, Gammas:NuDat 3H


Literature and References

[1] - Y.-T. Lin, T. H. Burritt, C. Claessens et al.:
Beta Decay of Molecular Tritium.
In: Physical Review Letters, 124, 222502, (2020), DOI 10.1103/PhysRevLett.124.222502.

[2] - Leonid B. Krivdin:
Tritium NMR: A compilation of data and a practical guide.
In: MRC, 61(4), 195-247, (2023), DOI 10.1002/mrc.5329.


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Last update: 2023-11-28

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