1. A high-speed electron or positron, especially one emitted in radioactive decay.
2. A small electrically charged particle thrown off by many radio-active materials.

It is identical to the electron and possesses the smallest negative electric charge found in nature.

Beta particles emerge from radioactive material at high speeds, sometimes close to the speed of light.

3. An electron emitted at high velocity from a radioactive atom that is undergoing spontaneous disintegration.

Beta particles do not exist in the nucleus but are created during disintegration, or beta decay, when a neutron converts to a proton to emit an electron.