A nuclear weapon is a weapon deriving its energy from nuclear reactions. These weapons have enormous destructive potential and are possessed by only a handful of nations. They have been used only twice in combat, by the United States against the Japanese cities of Hiroshima and Nagasaki at the conclusion of World War II.
Types of Weapons
Fission bombs derive their power from nuclear fission, where heavy nuclei (uranium or plutonium) split into lighter elements, triggering a chain reaction. Fusion bombs (hydrogen bombs) are based on nuclear fusion where light nuclei combine, releasing large amounts of energy. Most modern weapons combine both: a fission device triggers fusion conditions.
Advanced Thermonuclear Designs
Modern weapons include a fissionable uranium outer shell. The cobalt bomb uses cobalt in the shell for long-term gamma radiation. The enhanced radiation weapon (neutron bomb) allows the burst of neutrons to escape, serving as the primary destructive mechanism.
Effects of a Nuclear Explosion
- Blast: 40–60% of total energy
- Thermal radiation: 30–50% of total energy
- Ionizing radiation: 5% of total energy
- Residual radiation (fallout): 5–10% of total energy
Blast Damage
Most buildings suffer moderate to severe damage from overpressures. The blast wind may exceed several hundred km/hr. Two phenomena are associated: static overpressure (sharp pressure increase) and dynamic pressures (drag from blast winds).
Thermal Radiation
Nuclear weapons emit large amounts of electromagnetic radiation. The chief hazards are burns and eye injuries, which can occur well beyond blast ranges. In Hiroshima, a tremendous fire storm developed within 20 minutes after detonation.