radiological weapon or radiological dispersion device (RDD) is any weapon that is designed to spread radioactive material with the intent to kill, and cause disruption upon a city or nation.
One version, known as a dirty bomb, is not a true nuclear weapon and does not yield the same explosive power. It uses conventional explosives to spread radioactive material, most commonly the spent fuels from nuclear power plants or radioactive medical waste.
Another version is the salted bomb, a true nuclear weapon designed to produce larger amounts of nuclear fallout than a regular nuclear weapon.