1) Nuclear decay emission 2) Product of some decay 
(-ray) alpha radiation. A stream of alpha particles. Alpha rays rapidly dissipate their energy as they pass through materials, and are far less penetrating than beta particles and gamma rays.
Synonym for alpha particle ... <physics> A radioactive particle made up of two protons and two neutrons, these particles are created by the decay of a radioactive material or by nuclear bombardment, and they are the same as the nucleus of a helium-4 atom. ... (09 Oct 1997) ... 
Type: Term Synonyms: alpha particle
A positively charged particle emitted by certain radioactive materials.
a stream of alpha particles. Also called