A single alpha particle, ejected at high speed from a nucleus, can create up to 100,000 ions along its path before it gains two electrons to become a neutral helium atom. In air, an alpha particle travels about 4 cm before gaining the two electrons.
Alpha particles are released by high mass, proton rich unstable nuclei. The alpha particle is a helium nucleus; it consists of two protons and two neutrons. It contains no electrons to balance the two positively charged protons.