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Isotopes of Helium

List, data and properties of all known isotopes of Helium as well as radioactive decay products and intermediate products.


Helium isotopes

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.


Naturally Occurring Helium Isotopes

Atomic Mass maQuantityHalf-lifeSpin
Isotopic mixture
4,002602 u100 %
Isotope 3He3,01602932(2) u0,0002(2) %stable1/2+
Isotope 4He4,0026032541(4) u99,9998(2)stable0+


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 < sup>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).



Helium-4 occurrences on earth are mainly due to the alpha decay of radioactive elements.

At a pressure of 5036 Pa and a temperature < At 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.


Exotic isotopes

* 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 Table: Helium


Atomic Properties

ZANNameAtomic Mass
[Nuclear Mass]
{Mass Excess}
Spin I
3He231Helium-33.01602932(2) u
[3.0149322 u]
{14.93122 MeV}
1/2+- 2.12762531(3)3H
4He242Helium-44.0026032541(4) u
[4.0015061 u]
{2.42492 MeV}
5He253Helium-55.012057(21) u
[5.0109598 u]
{11.23102 MeV}
6He264Helium-66.01888589(6) u
[6.0177887 u]
{17.59209 MeV}
7He275Helium-77.027991(8) u
[7.0268938 u]
{26.07345 MeV}
8He286Helium-88.03393439(9) u
[8.0328372 u]
{31.60968 MeV}
9He297Helium-99.04395(5) u
[9.0428528 u]
{40.93916 MeV}
10He2108Helium-1010.05282(10) u
[10.0517228 u]
{49.20151 MeV}


Radioactive Decay Properties

IsotopeRadioactive DecayAEExtern
Half-lifeDecay ModeProbabilityEnergy
He-57.61833 × 10-22 sn ? → 4He0.290(71) MeVAL
He-6806.7(15) msβ-6Li3.50522(5) MeVAL
He-72.85688 × 10-21 sn → 6He11.166(8) MeVAL
He-8119.1(12) msβ-8Li
β-, n → 7Li
84 %
16 %
10.66388(10) MeV
8.63126(9) MeV
He-97.03231 × 10-21 sn → 8He100 %14.816(60) MeVAL
He-102.68882 × 10-21 sn → 9He100 %15.759(71) MeVAL


Notes (related to the columns):

1 - nuclide, isotope symbol.
2 - Z = number of protons (atomic number).
3 - Mass number A.
4 - N = number of neutrons.
5 - Identification of the Helium isotope.
6 - 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.
7 - Nuclear spin I, unit: h/2π.
8 - Nuclear magnetic moment μmag.
9 - 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.
10 - Decay: Half-live of the Helium isotope (a = years; ; d = days; h = hours; min = minutes; s = seconds).
11 - Decay: 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.
12 - Decay percentage in percent (%).
13 - Decay energy; Particle energy related to decay type.
14 - AE = Excitation energy for metastable nuclei.
15 - Other information and notes: AL = Adopted Levels (link to external data [1]).


()- 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.


NMR active Helium nuclides

quantity 1)
Nuclear magnetic
107 rad T-1 s-1
Q fm-2
v0 bei 1 T
H0 = const.
v0 = const. 2)
0,0002(2) %
- 2,12762531(3)- 20,3832,43800,44220

1) Quantity Percentage of natural occurrence.

2) Related to 1H = 1,000.


Literature Sources and References

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.


Category: Isotopes

Last update: 05.07.2020

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