An electron ejected from nucleus of a decaying atom. Although beta particles are stopped by a thin sheet of aluminum, they could penetrate the dead skin level, possibly causing burns off. They could present a significant direct or outside radiation hazard and certainly will be life-threatening with respect to the amount received. They even pose a critical internal radiation risk if beta-emitting atoms are ingested or inhaled.
a high-speed electron or positron emitted in decay of a radioactive isotope
Electron emitted from the nucleus when a neuton decays to a proton and an electron.