Alpha particle

An alpha particle is a helium-4 nucleus containing two protons and two neutrons, emitted in some radioactive decays. Its +2 electric charge and relatively large mass give it distinctive interactions with matter.

Alpha decay: A radioactive decay in which an unstable nucleus emits a helium-4 nucleus. This is the nuclear process that releases an alpha particle.
Helium-4: The stable helium isotope whose nucleus contains two protons and two neutrons. An alpha particle is precisely the nucleus of this isotope.
Americium-241: A radioactive isotope that emits alpha particles and is used in ionization smoke detectors. Its alpha emissions ionize air in a common smoke-detection design.
Beta particle: A high-speed electron or positron emitted in certain radioactive decays. Beta particles are much lighter and generally penetrate farther than alpha particles.
Nuclear binding energy: The energy required to separate a nucleus into its constituent protons and neutrons. The binding-energy difference makes alpha emission energetically possible in heavy nuclei.
Atomic nucleus: The dense central region of an atom, composed of protons and neutrons. Alpha particles are compact nuclei rather than complete atoms.
Radon: A naturally occurring radioactive noble gas whose isotopes decay by emitting alpha particles. Radon decay products deliver alpha radiation to lung tissue when inhaled.
Gamma ray: A high-energy photon emitted by atomic nuclei or other energetic processes. Gamma rays have no electric charge and penetrate matter far more deeply.
Geiger–Nuttall law: An empirical relation connecting an alpha emitter’s decay rate with the energy of its emitted alpha particles. It links alpha-particle energy to the striking range of radioactive half-lives.
Proton: A positively charged subatomic particle found in atomic nuclei. Two protons give an alpha particle its charge of +2.

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