In my mind, the greatest threat, by far, from a terrorist using small nuclear devices is that they would want to get the biggest bang for the buck. The way to do that is to include in the package radioactive plutonium, (used to be very hard to come by, but with the fall of the Soviet Union, available) whether the device uses this plutonium as part of the nuclear explosion mechanism or not. Such a device would render a very large area, to include the area down wind totally uninhabitable for thousands of years. Radioactive plutonium, besides being an extremely poisonous substance in it's own right, has a half life in the many thousands of years.
That means that if an area containing radioactive plutonium has a radiation level of 1000 RDAs immediately after the detonation, it will be thousands of years before the radiation level is reduced by half, or 500 RDAs. Bye the way, 300 RDAs is the most exposure that we can handle for short periods of time; and it takes a while to recover from that level. For the purpose of the book: virtually any nuclear detonation will leave at least 1000 RDAs within the area of the fireball for a period of time that depends upon the materials from which it is constructed. Exposure to 1000 RDAs kills in a very short time. There is no treatment.
Offered by Ron.
Actually plutonium would probably pass right through the body in short order if ingested, but it only takes an amount of plutonium the size of a pollen grain to cause lethal cancer. Most plutonium in an explosion would be converted within a millionth of a second to other fissionable isotopes, also rain and weather would dilute radioactivity to where it would more like a couple hundred years of high radioactivity. A nastier version of the bomb was made by the soviets. The American bombs are more powerful but the soviet version had more severe biological impact above and beyond just the radiation effects.
Offered by Steve.