Neutron radiation is a form of ionizing radiation most often found in nuclear reactors and nuclear bombs. It is composed of neutrons, neutral subatomic particles that make up the nucleus of atoms along with protons. Neutrons are found in all elemental nuclei except for hydrogen. Neutron radiation is a health risk and is considered the fourth major type of radiation after alpha particles, beta particles, and gamma rays.
Neutron radiation, and the neutron itself, were discovered in the early 1930s through experiments conducted by James Chadwick, Walter Bothe, Herbert Becker, and others. The radiation was released by bombarding the metal beryllium with alpha particles. Chadwick’s careful work in proving the existence of the neutron earned him the 1935 Nobel Prize in Physics.
The most famous role of neutron radiation in world history comes from 1942, when the world’s first nuclear reactor, Chicago Pile-1 was built underneath the University of Chicago's stadium. Scientists had theorized that energy would be released by bombarding the unstable uranium nuclei with neutrons. Furthermore, by breaking apart (fissioning) these uranium nuclei, a self-sustaining chain reaction could be initiated. The ultimate form of this is in a nuclear bomb, where an extremely quick sequence of nuclear reactions causes the release of a substantial amount of the nuclear energy in a core of enriched uranium, enough to blow away entire cities. Prior to the early 1940s, few scientists, not to mention the general public, could possibly have imagined such a powerful explosive or energy source.
Neutron radiation has the tendency to be absorbed by the nuclei of its target material, turning it radioactive. Most of the radioactive material produced during the explosion of a nuclear bomb is created in this fashion. When humans are exposed to too much neutron radiation, it can actually turn flesh radioactive, quickly killing the unfortunate person. This is the principle behind the neutron bomb, a weapon designed to release massive amounts of neutron radiation with comparatively little heat or light. The neutron bomb is a nuclear explosive that kills people and animals but leaves structures intact.