Beta radiation is the emission of an electron from the nucleus of a radioactive isotope. This electron comes from one of the neutrons in an unstable nucleus. The weak nuclear force is involved, and the neutron is converted into a proton when the beta particle is emitted. This produces an isotope of the next element in the periodic table, a process known as transmutation. The emitted beta particle travels through air at close to the speed of ligh t. However, it can be stopped by a sheet of aluminum foil greater than 0.12 in (3 mm) thick.

When French physicist Henri Becquerel (1852-1908) first discovered the property of radioactivity in 1896, he did not know that radiation consists of particles as well as energy. Beginning in 1898, Ernest Rutherford conducted experiments to determine the nature of this radiation. One experiment demonstrated that the radiation actu ally consisted of three different...