Radiological dispersal device

A radiological dispersal device, or dirty bomb, is a non-nuclear bomb that is designed to disperse radioactive material. It is generally comprised of 2 separate explosives with radioactive material sandwiched inside. Such RDDs appeal to terrorists because they require limited technical knowledge to build and deploy compared to a nuclear device. The size of the affected area and the level of destruction caused by an RDD would depend on the sophistication and size of the conventional bomb and other factors. The area affected could be placed off-limits to the public for several months during cleanup efforts. People who walk near the bomb before it explodes would be irradiated as well. If they get within 1 inch of a bomb containing 500 Ci of cesium-137 for 15 seconds, they would receive a dose of 9.16 Sieverts, which would have a 90% chance of killing the person. If the bomb was placed in a subway, and people spent 2 hours on it, anyone within 2.5 feet of the device will likely die, and sickness would occur within 12 feet. It could be left for a few weeks to not only kill more people, but make the terrorist less suspicious when it does detonate. Cleanup would be very hard. You would have to recover all of the 500 Ci after the explosion. It would likely never be clean again. The death toll would be in the hundreds, the injury toll in the thousands, and the people exposed in the tens of thousands. While no incidents have occurred where it was intentional, the Goiania incident was an accident, and the source's activity was around 1375 Ci. Lots of deaths and injuries resulted from it.

References

https://www.cdc.gov/nceh/radiation/emergencies/pdf/Infographic_Radiological_Dispersal_Device.pdf

http://radprocalculator.com/Gamma.aspx was used to calculate dose rate.