Eight isotopes are known for the lightest noble gas, helium, of which only two are stable: 3He and 4He occur in nature as an isotope mixture in a ratio of approx. 1:1,000,000 on. This results in a relative atomic mass for helium of 4.002602(2) u on average.
The isotopic composition in nature is subject to large fluctuations and is strongly dependent on the presence of 3H sources. Helium-3 occurs about 100 times more frequently in the interstellar medium than on Earth, and even terrestrial occurrences are subject to large fluctuations (factor 10).
3He and 4He show very different physical properties: because of the symmetry differences, helium-3 is one of the fermions, helium-4 one of the bosons.
Due to their different quantum properties, the two isotopes are immiscible in the liquid state (2 phases).
| Atomic Mass ma | Quantity | Half-life | Spin | |
| Helium Isotopic mixture | 4,002602 u | 100 % | ||
| Isotope 4He | 4,0026032541(4) u | 99,9998(2) % | stable | 0+ |
| Isotope 3He | 3,01602932(2) u | 0,0002(2) % | stable | 1/2+ |
Helium-4 occurrences on earth are mainly due to the alpha decay of radioactive elements.
At a pressure of 5036 Pa and a temperature < 2.1768 K (lambda point) helium-4 goes into the so-called superfluid state, which is called helium II. Above the lambda point and below a temperature of 4.21 K, helium forms a colorless liquid: Helium I.
* Diproton is a hypothetical helium isotope (helium-2, 2He) consisting of two protons and no neutrons in the nucleus.
* Halo nuclei: helium-6 (2-neutron halo); Helium-8 (4 neutron halo).
| Isotope Nuclide | E | N | Atomic Mass [Nuclear Mass] {Mass Excess} | Spin I (h/2π) | Parent |
|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 |
| Helium-3 | 32He | 1 | 3.01602932(2) u [3.0149322 u] {14.93122 MeV} | 1/2+ | 3H 4Li |
| Helium-4 | 42He | 2 | 4.0026032541(4) u [4.0015061 u] {2.42492 MeV} | 0+ | 5He 5Li 6Be |
| Helium-5 | 52He | 3 | 5.012057(21) u [5.0109598 u] {11.23102 MeV} | 3/2- | |
| Helium-6 | 62He | 4 | 6.01888589(6) u [6.0177887 u] {17.59209 MeV} | 0+ | 7He 11Li |
| Helium-7 | 72He | 5 | 7.027991(8) u [7.0268938 u] {26.07345 MeV} | (3/2)- | |
| Helium-8 | 82He | 6 | 8.03393439(10) u [8.0328372 u] {31.60968 MeV} | 0+ | 9He 10He |
| Helium-9 | 92He | 7 | 9.04395(5) u [9.0428528 u] {40.93916 MeV} | 1/2+ | |
| Helium-10 | 102He | 8 | 10.05282(10) u [10.0517228 u] {49.20151 MeV} | (0+) |
| Isotope | Radioactive Decay | Extern | |||
|---|---|---|---|---|---|
| Half-life | Decay Mode | Probability | Energy | ||
| 7 | 8 | 9 | 10 | 11 | 12 |
| He-3 | stable | AL | |||
| He-4 | stable | AL | |||
| He-5 | 7.61833 × 10-22 s | n ? → 4He | 0.290(71) MeV | AL | |
| He-6 | 806.7(15) ms | β- → 6Li | 3.50521(5) MeV | AL | |
| He-7 | 2.85688 zs | n → 6He | 11.166(8) MeV | AL | |
| He-8 | 119.1(12) ms | β- → 8Li β-, n → 7Li | 84 % 16 % | 10.66388(10) MeV 8.63126(9) MeV | AL |
| He-9 | 7.03231 zs | n → 8He | 100 % | 14.816(60) MeV | AL |
| He-10 | 2.68882 zs | n → 9He | 100 % | 15.759(71) MeV | AL |
Notes (related to the columns):
1 - name of the nuclide, isotope.
2 - E: isotope symbol with mass number (superscript; number of nucleons) and Atomic number (subscript; number of protons).
3 - N: number of neutrons.
4 - relative atomic mass of the Helium isotope (isotopic mass including electrons) and the mass of the atomic nucleus in square brackets (nuclear mass, nuclide mass without electrons), each related to 12C = 12.00000 [2]. In addition, the mass excess is given in MeV.
5 - nuclear spin I, unit: h/2π.
6 - source nuclides: Possible, assumed or actual source nuclides (mother nuclides, parent nuclides). If applicable, the corresponding decay modes can be found in the data for the respective starting nuclide.
7 - isotope notation in short form.
8 - decay: half-live of the Helium isotope (a = years; ; d = days; h = hours; min = minutes; s = seconds).
9 - decay mode: type of decay into the respective daughter nuclides with n = neutron emission; p = proton emission; α = alpha decay; β- = beta minus decay with electron emission; EC = electron capture; β+ = positron emission; ε = β+ and/or EC; Iso = isomeric transition; CD = cluster decay; SF = spontaneous decay.
10 - decay probability in percent (%).
11 - decay energy; Particle energy related to decay type.
12 - other information and notes: AL = Adopted Levels (link to external data [1]).
Miscellaneous:
()- Numbers in brackets: uncertainty to represent the spread of the reported value.
~ - Theoretical values or systematic trends.
- unlisted-: Nuclides that have already been mentioned in the literature but for some reason can no longer be found in the current nuclide tables because their discovery e.g. has not confirmed.
| Nuclide quantity 1) spin | Nuclear magnetic moment μ/μN | Gyromagnetic ratio {Quadrupole moment} | Resonant frequency v0 bei 1 T | Relative sensitivity H0 = const. v0 = const. 3) |
|---|---|---|---|---|
| 3He 0,0002(2) % 1/2+ | - 2,127625306(25) | -20,3801587 {} | 32,4380 | 0,44220 0,7619 |
1) Quantity Percentage of natural occurrence.
2) Gyromagnetic ratio: 107 rad T-1 s-1
Quadrupole moment: Q [barn] = [100 fm2]
3) Related to 1H = 1,000.
Properties of the Helium nucleides
[1] - NuDat: National Nuclear Data Center, Brookhaven National Laboratory, based on ENSDF and the Nuclear Wallet Cards.
[2] - G. Audi et. al.: The NUBASE evaluation of nuclear and decay properties. Nuclear Physics, (2003), DOI 10.1016/j.nuclphysa.2003.11.001.
[3] - Live Chart of Nuclides. Nuclear structure and decay data.
Helium: NMR properties - 3He-NMR
[4] - N. J. Stone: Table of nuclear magnetic dipole and electric quadrupole moments. Atomic Data and Nuclear Data Tables, (2005), DOI 10.1016/j.adt.2005.04.001.
[5] - Pekka Pyykkö: Year-2008 nuclear quadrupole moments. Molecular Physics, (2008), DOI 10.1080/00268970802018367.
[6] - Pekka Pyykkö: Year-2017 nuclear quadrupole moments. Molecular Physics, (2018), DOI 10.1080/00268976.2018.1426131.
[7] - N. J. Stone: Table of recommended nuclear magnetic dipole moments. IAEA, (2019).
More sources:
[8] - Isotopic abundances, atomic weights and isotopic masses: see respective keyword.
Last update: 2022-12-21
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