A dirty bomb or RDD (Radiological Dispersal Device) is usually a conventional bomb or improvised explosive device which contains radioactive material. The bomb is used to spread radiation across as wide an area as possible. The bomb is not a nuclear weapon and usually has minimal destructive power, its main purpose being to create a large enough blast to disperse the radioactive material. This material is usually nuclear waste from power stations. Materials most likely to be used in dirty bombs are Caesium-137, Strontium-90 and Americium-241. The actual damage that a dirty bomb could inflict is still the subject of a great deal of contradictory debate.