alpha particle

American  

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.

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alpha particle British  

noun

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

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alpha particle Scientific  

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

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Etymology

Origin of alpha particle

First recorded in 1900–05

Example Sentences

Pluvicto carries a beta particle that travels for a longer range but is less lethal, while the new therapy uses an alpha particle that is more lethal but travels shorter distances, the analyst says.

From The Wall Street Journal • Jun. 2, 2026

It took 23 measurements with an instrument called an alpha particle X-ray spectrometer.

From BBC • Aug. 21, 2024

She'd already begun to establish her reputation as a physicist, working on alpha particle scattering.

From Scientific American • Sep. 7, 2023

An alpha particle is a nucleus of helium, a noble gas.

From Nature • Sep. 1, 2020

The deflections occurred only when the alpha particle happened to strike this kernel directly or come close enough to be deflected by its electric charge.

From "Big Science" by Michael Hiltzik