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

Example Sentences

Some particles — including protons, neutrons, alpha particles and beta particles — travel through space at high speeds.

From Science News For Students

Mercury 203 plus an alpha particle gives nice, stable Lead 207.

From Project Gutenberg

An alpha particle is the nucleus of a helium atom and is made up of two protons and two neutrons; it carries two positive charges.

From Project Gutenberg

There can thus be no doubt that the alpha particle becomes a helium atom when its positive charge is neutralized.

From Project Gutenberg

This stopping power of an atom for an alpha particle is approximately proportional to the square root of its atomic weight.

From Project Gutenberg

Ionium expels an alpha particle and becomes radium, which is a bivalent element resembling barium belonging to the second group.

From Project Gutenberg