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.

---

alpha particle British  

noun

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

---

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

---

Etymology

Origin of alpha particle

First recorded in 1900–05

Example Sentences

Clearly, the alpha particle crosses a kind of energetic barrier that normally prohibited passage, but how?

From Scientific American • Aug. 18, 2021

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

From Nature • Sep. 1, 2020

Only later—when the scientists comb through the raw data and match every detected alpha particle to a specific element in the decay chain—can they reconstruct which element they initially created.

From Science Magazine • Jan. 30, 2019

Alpha decay is when an alpha particle, which consists of two protons and two neutrons, is emitted from the nucleus of an atom.

From Textbooks • Jan. 1, 2017

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