The term dirty bomb is most often used to refer to a Radiological Dispersal Device (RDD), a radiological weapon which combines radioactive material with conventional explosives. Though an RDD is designed to disperse radioactive material over a large area, the conventional explosive 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.
For this reason, a dirty bomb is not a weapon of mass destruction. Its purpose would presumably be to create psychological, not physical, harm through mass panic and terror. Additionally, decontamination of the affected area might require considerable time and expense, rendering affected areas unusable, and causing extensive economic damage.
The term first entered the public lexicon in this usage on June 10, 2002, when U.S. officials announced they had a month earlier captured an alleged al-Qaida terrorist named Josť Padilla in Chicago's O'Hare International Airport. Padilla was charged with assisting in the construction of such a device.
The term has also been used historically to refer to nuclear weapons. Due to the inefficiency of early nuclear weapons (such as "Fat Man" and "Little Boy"), 2% or less of the nuclear material would be consumed during the explosion. Thus, they tended to disperse large amounts of unused fissile material 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 in 1954, in which a thermonuclear weapon produced a large amount of fallout which was dispersed among many human populations, made it clear 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 note that one could make a nuclear weapon intentionally "dirty" by "salting" it with a material (most commonly a type of cobalt) which would generate large amounts of long-lasting fallout when radiated by the weapon core. In the post-Cold War age, this usage of the term has largely fallen out of use.
- U.S. Nuclear Regulatory Commission, Factsheet on Dirty Bombs
- Council on Foreign Relations, Terrorism Q&A: Dirty Bombs
- U.S. Dep't of Labor Occupational Safety & Health Administration, Radiological Dispersal Devices / Dirty Bombs
- American Institute of Physics, "Dirty Bombs" Much More Likely to Create Fear than Cause Cancer
- Federation of American Scientists, Dirty bomb threat analysis
- Health Physics Society, Factsheet
- Health Physics Society, January 2004 study, Dirty Bombs Could Cause Devastating Economic Damage
- CNN, Explosion, not radiation, "dirty bomb's" worst fallout