A radio-active transformation of an atomic number is increased or decreased by 1 by the simultaneous emission of a beta particle and a neutrino or antineutrino without change in the mass number; the decay of an unstable elementary particle in which an electron or positron is emitted.

【理】β 衰变(指原子核的放射性变换，发生时原子数因同时放射一粒 β 粒子及一微中子或反微中子而增加或减少了1，但质量不变；或指一不稳定的基本粒子的衰变，发生时放射出一粒电子或正电子)。