That being said, a few grams of radioactive material improperly transported could probably cause more damage, contamination and poisoning wise, than the actual dirty bomb it was used in. Especially relatively easy to access older medical grade radiation emitting items or sources. This kinda shit actually seems to happens way more often than it should:
and of course all of this is miniscule to the history of government radiation accidents. Not to mention the fact that while the United States can bitch and whine as much as it wants about the danger of terrorists or countries we don’t like acquiring nukes or dirty bombs, the U.S. is still the only country in the world to ever use a nuclear weapon during war and against civilians (like, ya know, terrorists would), and more recently the only country to use DU ammunition near a civilian population.
ETA - Countries that have stockpiles of DU ammunition (source):
It is thought that between 17 and 20 countries have weapons incorporating depleted uranium in their arsenals. They include the U.S., the UK, France, Russia, China, India, Turkey, Saudi Arabia, Israel, Bahrain, Egypt, Kuwait, Pakistan, Thailand, Iraq and Taiwan.