Beta Particle

Beta Particle, one of three kinds of emission given off by radioactive substances (see Radioactivity). Beta particles were first isolated about 1900, when the British physicist Ernest Rutherford subjected radioactive emissions to an electric field. He found that two kinds of emissions, which were named alpha and beta, were deflected towards opposite electric poles. Alpha particles were subsequently identified as helium nuclei and beta particles as either electrons or their antimatter equivalent, positrons.