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

The Swiss drugmaker released data from an early-stage clinical trial for its 225Ac-PSMA-617 drug candidate that showed so-called alpha particle radioactive isotopes should work in fighting prostate cancer, 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

Added to this was the challenge of procuring radioactive curium-244, an alpha particle source that is central to APXS—and that Vadawale notes is “available only from Russia.”

From Scientific American • Jul. 13, 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