Beta Decay Definition

An electron or positron is emitted in beta decay.
An electron or positron is emitted in beta decay. Getty Images

Beta Decay Definition: Beta decay refers to the spontaneous radioactive decay where a beta particle is produced.

There are two types of beta decay where the beta particle is either an electron or a positron.

β- decay occurs when an electron is the beta particle. An atom will β- decay when a neutron in the nucleus converts to a proton by the reaction

ZXAZYA+1 + e- + antineutrino

where X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, A is the atomic number of X.



β+ decay occurs when a positron is the beta particle. An atom will β+ decay when a proton in the nucleus converts into a neutron by the reaction

ZXAZYA-1 + e+ + neutrino

where X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, A is the atomic number of X.

In both cases, the atomic mass of the atom remains constant but the elements are transmuted by one atomic number.

Examples: Cesium-137 decays to Barium-137 by β- decay.
Sodium-22 decays to Neon-22 by β+ decay.

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Helmenstine, Anne Marie, Ph.D. "Beta Decay Definition." ThoughtCo, Feb. 7, 2017, thoughtco.com/beta-decay-definition-608733. Helmenstine, Anne Marie, Ph.D. (2017, February 7). Beta Decay Definition. Retrieved from https://www.thoughtco.com/beta-decay-definition-608733 Helmenstine, Anne Marie, Ph.D. "Beta Decay Definition." ThoughtCo. https://www.thoughtco.com/beta-decay-definition-608733 (accessed November 21, 2017).