Radiological Dispersal Devices, RDDs; creating, deploying and detonating radiological bombs in Western European capitals

The term radiological bomb (dirty bomb) refers to a radiological weapon which combines radioactive material with conventional explosives. Though a radiological dispersal device (RDD) would be designed to disperse radioactive material over a large area, a bomb that uses conventional explosives would likely have more immediate lethal effect than the radioactive material. At levels created from most probable sources, not enough radiation would be present to cause severe illness or death. A test explosion and subsequent calculations done by the United States Department of Energy found that assuming nothing is done to clean up the affected area and everyone stays in the affected area for one year, the radiation exposure would be " fairly high", but not fatal. Recent analysis of the Chernobyl disaster fallout confirms this, showing that the effect on many people in the surrounding area, although not those in close proximity, was almost negligible.

Since a dirty bomb is unlikely to cause many deaths, many do not consider this to be a weapon of mass destruction. Its purpose would be to create psychological, not physical, harm through mass panic, and terror. For this reason dirty bombs are sometimes called " weapons of mass disruption". Additionally, containment and decontamination of thousands of victims, as well as decontamination of the affected area will require considerable time and expense, rendering areas partly unusable and causing devastating economic damage.

The term has also been used historically to refer to certain types of nuclear weapons. Due to the inefficiency of early nuclear weapons, only a small amount of the nuclear material would be consumed during the explosion. “Little Boy” had an efficiency of only 1.4%. “Fat Man”, which used a different design and a different fissile material, had an efficiency of 14%. Thus, they tended to disperse large amounts of unused fissile material, and the fission products, which are on average much more dangerous, in the form of nuclear fallout. During the 1950s, there was considerable debate over whether " clean" bombs could be produced and these were often contrasted with " dirty" bombs. " Clean" bombs were often a stated goal and scientists and administrators said that high-efficiency nuclear weapon design could create explosions which generated almost all of their energy in the form of nuclear fusion, which does not create harmful fission products.

But the Castle Bravo accident of 1954, in which a thermonuclear weapon produced a large amount of fallout which was dispersed among human populations, suggested that this was not what was actually being used in modern thermonuclear weapons, which derive around half of their yield from a final fission stage. While some proposed producing " clean" weapons, other theorists noted that one could make a nuclear weapon intentionally " dirty" by " salting" it with a material, which would generate large amounts of long-lasting fallout when irradiated by the weapon core. These are known as salted bombs; a specific subtype often noted is a “cobalt bomb”.