A dirty bomb is not a nuclear weapon per se since it does not use fissionable material.
Radioactive materials used may include Cesium-137, Strontium-90, Iodine-131, Uranium-235, Americium-241, Cobalt-60, Iridium-192, Plutonium-238, Radium-226.
Significance:
(1) The explosion of a dirty bomb is limited.
(2) The main threat is dispersion of radioactive material over a wide area. People at the epicenter may be exposed to both blast effect and lethal radiation.
(3) People with penetrating trauma associated with the bomb blast may harbor radioactive debris.
(4) Some sources of radioactive material may not be well-protected, such as radiation units in a hospital. This means that the radioactive materials can be collected locally.
