alpha particle

WordReference Random House Unabridged Dictionary of American English © 2026

al′pha par′ticle, [Physics.]

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

• 1900–05

Collins Concise English Dictionary © HarperCollins Publishers::

alpha particle noun

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