Hydrogen-3

Properties and data of the isotope ³H.

Contents

General Data

Radioactive Decay

Isotones und Isobares

Literature

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.

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^-1Spin and parity:
(nuclear angular momentum)1/2+Magnetic dipole moment:μ(μ_N) = + 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^- + v_e.

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 T_½ = 12.32(2) a respectively 3.88524 × 10⁸ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	³He	100 %	0.018592(0) MeV

Parent Nuclides

Direct parent isotopes are: ⁴H, ⁵H.

Formation

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.

Occurrence

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

	Atomic Mass m_a	Quantity	Half-life	Spin
Hydrogen Isotopic mixture	1.008 u	100 %
Isotope ³H	3.01604928132(8) u	[trace]	12.32(2) a	1/2+
Isotope ¹H	1.0078250322(6) u	99.99 % [99.972 - 99.999 %]	stable	1/2+
Isotope ²H	2.0141017781(8) u	0.01 % [0.001 - 0.028 %]	stable	1+

NMR data

Nuclear magnetic properties of the NMR active Nuclide ³H

Isotope:³H-NMRQuantity:SpurenSpin:1/2+Nuclearmagnetic moment
μ/μ_N:+ 2.978962460(14)Gyromagnetic ratio γ:28.535 · 10⁷ rad T^-1 s^-1Nuclear g-factor:g_l = 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:
(conditions)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 Radiation Protection Ordinance (European Union), for example, specifies the following limit values for the isotope Hydrogen-3 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

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

Exemption level:10⁹ BqExemption level per gram:100 Bq/g
Unrestricted handling of solids and liquids.Activity HASS:2000 TBqSurface contamination:100 Bq/cm²Half-life:12.3 a

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.

Z	Isotone N = 2	Isobar A = 3
1	³H	³H
2	⁴He	³He
3	⁵Li	³Li
4	⁶Be
5	⁷B
6	⁸C
7	⁹N

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.