Alpha radiation is created by the radioactive decay of unstable atomic nuclei. The illustration to the left depicts schematically the decay of alpha radiation. Shown is a large nucleus consisting of protons (pink) and neutrons (light blue). An alpha particle of two neutrons and to protons is exiting this nucleus. The alpha particles are the heaviest particles in nuclear radiation. Based on its high mass and its strong capacity to react with matter, alpha radiation can easily be shielded (see illustration 1). When reaching the human organism, however, alpha radiation is very dangerous. Its range within air, on the other hand, spreads to only a few inches.
Beta radiation refers to radiating electrons which result from the beta decay of atomic nuclei. Electron radiation can also be generated artificially by an electron gun. Beta radiation, however, occurs only when it is caused by nuclear decay. Since beta radiation consists of light, charged electrons, it can easily be diverted in an electric field. As opposed to alpha radiation, theirs is less harmful for humans; beta radiation, however, is more difficult to shield (illustration 1). The range within air extends only to a few yards.
Gamma radiation consists of photons which are particles of light. This form of radiation contains much more energy than does visible light. Gamma radiation occurs when a nucleus passes from a state of high-energy to that of low-energy without changing the number of protons or neutrons in the nucleus. An atomic nucleus is in a state of high-energy when it rotates or when it is shaped most advantageously (often spherically). The range within air can extend to several miles. Gamma radiation can only be diminished by dense steel- or lead barriers.