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.
- 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. http://physics.nist.gov/constants.