A fast-moving electron that is given off from the nucleus during radioactive decay. These particles are also known as beta radiation or beta rays. Though this definition mentions electrons, a beta particle can also be a positron.
These particles have been around for a while, for they were discovered in the 1890s by scientist Ernest Rutherford. There are two types of beta decays that can makeup the beta particle. If it is an electron, the beta decay will be known as a beta minus. If it is a positron, the beta decay will be known as a beta plus.