Characteristics of a Nuclear Explosion
A fireball, roughly spherical in shape, is created from the energy of the initial explosion. It can reach tens of millions of degrees.
A shockwave races away from the explosion and can cause great damage to structures and injuries to humans.
A mushroom cloud typically forms as everything inside of the fireball vaporizes and is carried upwards. Radioactive material from the nuclear device mixes with the vaporized material in the mushroom cloud.
Fallout results when the vaporized radioactive material in the mushroom cloud cools,condenses to form solid particles, and falls back to the earth. Fallout can be carried long distances on wind currents as a plume and contaminate surfaces miles from the explosion,including food and water supplies.
The ionization of the atmosphere around the blast can result in an electromagnetic pulse (EMP) that,for ground detonations,can drive an electric current through underground wires causing local damage. For high-altitude nuclear detonations, EMP can cause widespread disruption to electronic equipment and networks.
Unlike a "dirty bomb" which disperses radioactive material using conventional explosives,1 a nuclear attack is the use of a device that produces a nuclear explosion. A nuclear explosion is caused by an uncontrolled chain reaction that splits atomic nuclei (fission) to produce an intense wave of heat, light, air pressure, and radiation, followed by the production and release of radioactive particles. For ground blasts, these radioactive particles are drawn up into a "mushroom cloud" with dust and debris, producing fallout that can expose people at great distances to radiation.
Traditional cold-war concerns were focused on the possible use of military nuclear weapons. A nuclear terrorist attack might be carried out with an improvised nuclear device (IND), which is a crude nuclear device built from the components of a stolen weapon or from scratch using nuclear material (plutonium or highly enriched uranium).
Access and Use of Nuclear Materials or Weapons
The primary obstacle to a nuclear attack is limited access to weapon-grade nuclear materials. Highly enriched uranium, plutonium, and stockpiled weapons are carefully inventoried and guarded. Nuclear attack is also impeded because:
- Building nuclear weapons is difficult—general principles are available in open literature, but constructing a workable device requires advanced technical knowledge in areas such as nuclear physics and materials science.
- Crude nuclear weapons are typically very heavy, ranging from a few hundred pounds to several tons, and are difficult to transport, especially by air. Specially designed small nuclear weapons, including the so-called "suitcase nuclear weapons" are much lighter, but they are difficult to acquire and to construct.
1 The effects of RDDs (radiological dispersal devices, including "dirty bombs") are discussed in another brief in this series entitled, Radiological Attack: Dirty Bombs and Other Devices.