A beta particle, sometimes called beta ray, denoted by the lower-case Greek letter beta (ß), is a high-energy, high-speed electron or positron emitted in the radioactive decay of an atomic nucleus, such as a potassium-40 nucleus, in the process of beta decay. Two forms of beta decay, ß^- and ß⁺, respectively produce electrons and positrons. Beta particles are a type of ionizing radiation.