Alpha Particles

Alpha particles ( α ) are nuclear decay particles and one form of ionizing radiation. Ernest Rutherford, discoverer of alpha particles, showed that these particles are simply composed of a helium atom nucleus (2 protons and 2 neutrons with a 2⁺ charge) ejected from radioactive elements.

Alpha particles are relatively large (mass = 6.65 x 10^-24 g/particle) compared to other forms of ionizing radiation. The alpha particles are expelled from a nucleus at a fairly slow speed, approximately one-tenth the speed of light. As a result of their large size and slow speed, alpha particles do not have much penetrating power. They can travel only a few inches in the air. An alpha particle can be stopped by a sheet of paper or clothing and are a minimal health risk upon direct exposure. However, alpha particles are extremely dangerous if ingested or inhaled into the body.

Some radioactive fission products spontaneously emit alpha radiation as they decay. Mostly alpha radiation comes from unused fission material like Uranium and Plutonium.