Answer to Question #2337 Submitted to "Ask the Experts"

Q

With all the talk about the effects of a dirty bomb, I am curious about how the contamination spreads from the original radioactive particle to, say, my driveway. If the original energy is gamma, how would that differ? That is, what is the process that transfers the radioactivity and what needs to be done to clean the affected area?

A

Actually, the radioactive particles ARE the contamination. When they settle out of the air onto your driveway, they are causing your driveway to become contaminated and, if you find a way to remove them, you are decontaminating your driveway.

There are three basic kinds of radiation: alpha, beta, and gamma. The major isotopes of concern are cobalt-60, cesium-137, and iridium-192, and they all give off gamma radiation. However, if someone used strontium-90, it gives off beta radiation, and uranium (such as depleted uranium) emits alpha particles.

What happens with a dirty bomb is that someone would pack some radioactive materials around an explosive device and use the explosives to blow the radioactive materials into the air. When they settle out on the ground or buildings, they cause the contamination. Once there, they must be removed to decontaminate your driveway or house, and you do this by cleaning them with water or by scrubbing them. However, whatever you clean up with will, itself, become contaminated, so you must treat the scrub brush or the wash water as radioactive. So cleanup is not necessarily an easy process.

I would expect that, in the event of a dirty bomb attack, the government will give instructions as to the best way to clean up and what to do with the contaminated decontamination equipment. Hopefully, though, there will not be such an attack.

You might be interested in the Nuclear Regulatory Commission's Fact Sheet on Dirty Bombs.



Andrew Karam, CHP, PhD