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Short description: Helium-3 isotope nucleus

A helion (symbol h) is a portmanteau for the naked nucleus of helium, a doubly positively charged helium ion. In practice, helion refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other stable isotope of helium, helium-4 isotope, which consists of two protons and two neutrons, is specifically called an alpha particle.

This particle is the daughter product in the beta-minus decay of tritium, an isotope of hydrogen:

31H →  32He1+  e  Electron Antineutrino

CODATA reports the mass of a helion particle as mh = 5.006412700(62)×10−27 kg3.01493224673(12) Da.[1]

Helions are intermediate products in the proton–proton chain reaction in stellar fusion.

An antihelion is the antiparticle of a helion, consisting of two antiprotons and an antineutron.


  1. See page 60 (Table 33) of Mohr, Peter J.; Newell, David B.; Taylor, Barry N. (2016). "CODATA recommended values of the fundamental physical constants: 2014". Rev. Mod. Phys. 88 (3): 1–73. doi:10.1103/RevModPhys.88.035009.