Depends on the yield. It could blow up Chinatown, maybe. I'm assuming crude devices manufactured according to the same rough design as the Stanford grad student's design that was confiscated and classified 20 years ago, and yielding under 5 kilotons. At eight miles, a weapon like that would barely break glass windows in a house. Do a search for interactive weapons-effects pages on a competent search engine like Moonmist, Dogpile, or AskJeeves.
A military weapon, such as an ex-Soviet artillery round, would be a horse of a very different color.