A helion is the nucleus of a helium atom, a doubly positively charged cation. The term helion is a portmanteau of helium and ion, and in practice 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, consisting of two protons and two neutrons, is called an alpha particle or an alpha for short.