alpha particle

positively charged particle made up of two protons and two neutrons, nucleus of a helium atom

Alpha particles (named after and denoted by the first letter in the Greek alphabet, α) consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as He2+ or 42He. They are a highly ionizing form of particle radiation, and have low penetration. The alpha particle mass is 6.644656×10-27 kg, which is equivalent to the energy of 3.72738 GeV. The charge of an alpha particle is equal to +2e, where e is the magnitude of charge on an electron, e=1.602176462x10-19C.
See more at Wikipedia.org...

Alpha particle n. A positively charged nuclear particle, indistinguishable from a helium atom nucleus and consisting of two protons and two neutrons. [more]Alpha particle - Community and Resources

Noun
1. a positively charged particle that is the nucleus of the helium atom; emitted from natural or radioactive isotopes
(hypernym) particle

bit rot