On May 8, 2002, the FBI captured Abdullah Al Muhajir, a U.S. citizen allegedly working with al Qaeda to set off a dirty bomb in an American city. This was unsettling news, to say the least. A dirty bomb is an explosive designed to spread dangerous radioactive material over a wide area. And when people hear "bomb" and "radioactive" in the same sentence, their minds jump to nuclear war pretty quickly.

It turns out that a dirty bomb's primary destructive power would probably be panic, not radiation damage. It's much closer to the power of an ordinary explosive than it is to the widespread destructive force of a nuclear bomb. But the fear of contamination could be debilitating, in the same way 2001's anthrax scare terrorized much of the American populace, even though only a few people were infected.

In this edition of HowStuffWorks, we'll find out what dirty bombs are and what they do. We'll also explore what might happen if one actually went off in a public area, and consider some of the consequences of this sort of attack.