Same thing goes for a dirty bomb detonated in the financial district or next to the Naked Cowboy in Times Square. Actually, even if you or your wife decided to walk around right after the detonation, the realistic danger to you is very low, all things considered. But people will be absolutely freaked out and not walking, but running over the bridges to get out of Manhattan. Like they say, a dirty bomb is primarily a psychological weapon, not a physical one, unless you happen to be physically blown up by the actual detonation (bye, bye, Naked Cowboy...). If you decide to wait it out inside for hours or a day, the air concentrations will diminish significantly and further lessen the already low risk when you finally venture out.

I commented on this particular topic in more depth in the past so I'll just link to that old post . Actually, that was an interesting thread in general so read through the whole thing.