Definitions for "Alpha rays"
Rays of relatively low penetrating power emitted by radium and other radioactive substances, and shown to consist of positively charged alpha particles (helium nuclei) having enormous velocities but small masses. They are slightly deflected by a strong magnetic or electric field. Compare beta ray and gamma ray. Because the rays penetrate only a small distance in dense matter such as living tissue, small pellets of radioactive substances emitting alpha rays have been used to cause local destruction of tissue, as in cancer therapy.
Two protons and two neutrons, the nucleus of a Helium atom. Alpha particles have a positive charge. Alpha rays can be stopped by a sheet of paper.
radioactivity composed of doubly charged helium ions