Definition of Alpha Decay

This photo shows the alpha particles emitted by alpha decay from a particle of radium salt.
This photo shows the alpha particles emitted by alpha decay from a particle of radium salt. C. POWELL, P. FOWLER & D. PERKINS, Getty Images

Alpha Decay Definition

Alpha decay is the spontaneous radioactive decay where an alpha particle is produced. An alpha particle is essentially a helium nucleus or He2+ ion. Although alpha decay present a significant radiation risk if the radioactive source is inhaled or ingested, alpha particles are too large to penetrate very far through skin or other solids and require minimal radiation shielding.

A sheet of paper, for example, blocks alpha particles.

An atom that undergoes alpha decay will reduce its atomic mass by 4 and become the element two atomic numbers less. The general reaction for alpha decay is

ZXAZ-4YA-2 + 4He2

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.

Examples: 238U92 decays by alpha decay into 234Th90.

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Helmenstine, Anne Marie, Ph.D. "Definition of Alpha Decay." ThoughtCo, Dec. 13, 2015, thoughtco.com/definition-of-alpha-decay-604768. Helmenstine, Anne Marie, Ph.D. (2015, December 13). Definition of Alpha Decay. Retrieved from https://www.thoughtco.com/definition-of-alpha-decay-604768 Helmenstine, Anne Marie, Ph.D. "Definition of Alpha Decay." ThoughtCo. https://www.thoughtco.com/definition-of-alpha-decay-604768 (accessed January 19, 2018).