text: Too many variables to consider, it's impossible to answer in this forum.  First of all, what do you mean by "nuclear bomb."  There are crude nuclear devices, which is called "dirty bomb."  A dirty bomb is basically a normal bomb with whole bunch of radioactive waste.  The explosion will send the particles into  the air, making SOME people die and thousands sick.  Also, decontainmenation would be a nightmare and public panic.  A small bomb could also be a tactical nuclear device.  Those are the so called "suitcase" bombs developed during the cold war.  They are, for the most part, not very effective.  Consider that it's very heavy and easy to detect by our current sensors in major cities.  If your definition of small is something like a "small" nuclear missile from states like.... say Iran/North Korea, then 25 mile radius will pretty much be wasted.  That being said, it's hard to denote a nuclear weapon by terrorist in NYC.  For starters, the Dept of Homeland Security has nuclear sensors around critical infrastuctures.  Nuclear signatures are VERY easy to detect, esp crude devices that could be used by a terrorist. There are tons of resources for this.  But it might be too difficult to explain to high school students.\n\nI don't know what the person below me is saying.  First, people in direct vincity of Nagasaki, all 120,000 of them, were VAPORIZED immediately. Second, WWII era nuclear weapons are like nothing of what we have now.  A single cold war era multi warhead ICBM missile could destory ALL life in the U.S East Coast.  A typical U.S. MIRV has ten sepearte warheads.  Don't think of this as ten different Nagaskais because EACH of those warheads are HUNDREDS of times more powerful than the "fatman" dropped on Japan.  A single U.S Trident U.S. submarine could destory a whole nation.