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Properties and data of the isotope 3He.



Helium-3 isotope

Helium-3 is a stable isotope of the chemical element helium. The atomic nucleus of the nuclide consists of the element-specific 2 protons and a neutron, which results in the mass number 3. He-3 is - besides hydrogen-1 - the only stable isotope of an element with more protons than neutrons.

3He occurs naturally on Earth, but only in very small amounts (0.0002%); the other stable isotope is Helium-4 (with a fraction of 99.9998%).

See also: list of Helium isotopes.


General data

Name of the isotope:Helium-3; He-3Other names:HelionSymbol:3He or 32HeMass number A:3 (= number of nucleons)Atomic number Z:2 (= number of protons)Neutrons N:1Isotopic mass:3.01602932(2) u (atomic weight of Helium-3)Nuclide mass:3.0149322 u (calculated nuclear mass without electrons)Mass excess:14.93122 MeVMass defect:0.0082856599999999 u (per nucleus)Nuclear binding energy:7.71804258 MeV (per nucleus)
2.57268086 MeV (average binding energy per nucleon)
Separation energy:
SP = 5.493474497(22) MeV (first proton)
Cross section:σ(n.γ) = 5300 barn (thermal neutron capture cross-section)Half-life:stableSpin and parity:
(nuclear angular momentum)
1/2+Magnetic dipole moment:μ(μN) = - 2.127625306(25)Charge radius:1.9661(30) femtometer fmMirror nucleus:Hydrogen-3Year of discovery:1934


Parent Nuclides

Direct parent isotopes are: 3H, 4Li.



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


Atomic Mass maQuantityHalf-lifeSpin
Isotopic mixture
4.002602 u100 %
Isotope 4He4.0026032541(4) u99.9998(2) %stable0+
Isotope 3He3.01602932(2) u0.0002(2) %stable1/2+


NMR data

Nuclear magnetic properties of the NMR active Nuclide 3He

Isotope:3He-NMRQuantity:0.0002(2) %Spin:1/2+Nuclearmagnetic moment
- 2.127625306(25)Gyromagnetic ratio γ:-20.3801587 · 107 rad T-1 s-1Nuclear g-factor:gl = -4.255250612Resonance frequency:v0 = 32.4380 at 1 TFrequency ratio:Ξ(3He) = 76.179437 %Relative Sensitivity:0.44220 (H0 = const.)
0.7619 (v0 = const.)
[related to 1H = 1.000]
Reference compound:
Helium gas.

The gyromagnetic ratio of the doubly positively charged (electron-free) 3He2+ atom (helion) is a fundamental natural constant that has the following values:

Shielded Helionγ´h = 2.037894569(24) · 108 s-1 T -1
Shielded Helion in MHz/Tγ´h = 32.43409942(38) MHz T - 1

The relative standard uncertainty is 1.2 · 10-8.


Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 1) and isobaric (same nucleon number A = 3) with Helium-3. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.


OZIsotone N = 1Isobar A = 3


External data and identifiers

Adopted Levels, Gammas:NuDat 3He


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Last update: 2023-11-28

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