Radioactivity

Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction.

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Proton

A stable, positively charged subatomic particle in the baryon family having a mass 1,836 times that of the electron.

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Radioactive Decay

Spontaneous disintegration of a radionuclide accompanied by the emission of ionizing radiation in the form of alpha or beta particles or gamma rays.

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Nucleus

The positively charged central region of an atom, composed of protons and neutrons and containing almost all of the mass of the atom.

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Neutron

An electrically neutral subatomic particle in the baryon family, having a mass 1,839 times that of the electron, stable when bound in an atomic nucleus, and having a mean lifetime of approximately 1.0 × 10³ seconds as a free particle. It and the proton form nearly the entire mass of atomic nuclei.

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Alpha Particle

A positively charged particle, indistinguishable from a helium atom nucleus and consisting of two protons and two neutrons.

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Beta Particle

A high-speed electron or positron, especially one emitted in radioactive decay.

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Gamma Ray

Electromagnetic radiation emitted by radioactive decay and having energies in a range from ten thousand (10⁴) to ten million (10⁷) electron volts.

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