A neutron bomb, officially known as one type of Enhanced Radiation Weapon, is a low yield fission-fusion thermonuclear weapon (hydrogen bomb) in which the burst of neutrons generated by a fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components.
The weapon's radiation case, usually made from relatively thick uranium, lead or steel in a standard bomb, is, instead, made of as thin a material as possible, to facilitate the greatest escape of fusion produced neutrons. The "usual" nuclear weapon yield—expressed as kilotons of TNT equivalent—is not a measure of a neutron weapon's destructive power. It refers only to the energy released (mostly heat and blast), and does not express the lethal effect of neutron radiation on living organisms.
Compared to a pure fission bomb with an identical explosive yield, a neutron bomb would emit about ten times. the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of both gamma rays and neutrons is approximately 5% of the entire energy released; in the neutron bomb it would be closer to 40%. Furthermore, the neutrons emitted by a neutron bomb have a much higher average energy level (close to 14 MeV) than those released during a fission reaction (1–2 MeV). Technically speaking, all low yield nuclear weapons are radiation weapons, including non-enhanced variants. Up to about 10 kilotons in yield, all nuclear weapons have prompt neutron radiation as their most far reaching lethal component, after which point the lethal blast and thermal effects radius begins to out-range the lethal ionizing radiation radius. Enhanced radiation weapons also fall into this same yield range and simply enhance the intensity and range of the neutron dose for a given yield.