alpha particle

noun

Physics.

1. a positively charged particle consisting of two protons and two neutrons, emitted in radioactive decay or nuclear fission; the nucleus of a helium atom.

alpha particle

noun

1. a helium-4 nucleus, containing two neutrons and two protons, emitted during some radioactive transformations

alpha particle

1. A positively charged particle that consists of two protons and two neutrons bound together. It is emitted by an atomic nucleus undergoing radioactive decay and is identical to the nucleus of a helium atom. Because of their relatively large mass, alpha particles are the slowest and least penetrating forms of nuclear radiation. They can be stopped by a piece of paper.

2. See more at radioactive decay

Word History and Origins

Origin of alpha particle¹

First recorded in 1900–05