alpha particle
noun [ C ] physics specialized uk/ˈæl.fə ˌpɑː.tɪ.kəl/ us/ˈæl.fə ˌpɑːr.t̬ə.kəl/
α粒子（放射性原子分裂时所产生的带正电荷的微小粒子，通常在核反应时产生）
an extremely small piece of matter with a positive electrical charge, produced when a radioactive atom is broken down, usually in a nuclear reaction