[JustPiper]

Absolutely! Scuba Divers planting say a dirty nuke under a fuel barge in some East Coast port?

[jerseygirl]

Also, they might want to destroy the Statue of Liberty (symbolic value).

[Calpernia]

A dirty bomb blast will be effective in a very, very short area around the explosion.

They have three components to worry about:

blast
fragmentation
latent ionizing radiation

Fragments are parts of the bomb, what it was packed in, and anything laying loose around it. These fragments will loose speed and power at an amazing rate. Just because you're near it doesn't mean you're going to be hurt. Consider the bombers in Israel blowing themselves up with large charges and lots of intentional fragments (many times, nails are used) in crowded places. The vast majority of people there aren't hurt. 99% of the whole fragment danger period will last one or two seconds literally.

The good news for us is the contamination will lead cleanup crews (using a Geiger counter) to itself like a beacon. If you're exposed during the initial attack a warm shower and washing your clothes will erase the danger. You need long term exposure to a lot of this stuff to have it harm you twenty years from now.