A helion is a short name for the naked nucleus of helium, a doubly positively charged helium ion. In practice, helion refers to the stable helium-3 nucleus, in opposition to the other stable nucleus helium-4, which is usually referred to as an alpha particle. The (helium-3) helion consists of two protons and one neutron.
According to CODATA, the mass of a helion particle is 5.006 411 92(25) × 10−27 kg.