beta particle, one of the three types of radiation resulting from natural radioactivity . Beta radiation (or beta rays) was identified and named by E. Rutherford, who found that it consists of high-speed electrons . Unlike alpha and gamma particles, whose energy can be explained as the difference of the energies of the radioactive nucleus before and after emission, beta particles emerge with a variable energy. This apparent violation of the law of conservation of energy (see conservation laws ) led to the hypothesis that a second undetected particle, the neutrino , is emitted along with the electron and shares the total available energy. In some forms of induced, or artificial, radioactivity, the electron's antiparticle , the positron, is emitted from the excited nucleus; the positron in this case is also called a beta particle and denoted by β + (the ordinary beta particle is β −).
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