I did a little research...
Bikini Atoll (several islands) was subjected to 2 A-bomb tests like Nag & Hiro, in 1946; and 21 more tests in 1956 and 1958, the largest of which was about 15 megatons, while the smallest was around 10 kilotons. TheNag & Hiro were like 15 kilotons.
There were even more tests (about 40) on anothe Atoll in the Marshall Islands group.
The vast majority of the tests were surface or barge detonations. A couple were underground or airborne. They say there is more fallout from surface detonation than airborne, (and less destructive power)
The dangerous level of fallout travelled between 70 and 150 miles, although I'm sure if you were 200 miles away you wouldn't consider it safe. Detectible trace levels of radioactive material were found over 1000 miles away.
They allowed the natives to resettle in 1975, but soon removed them as it was still to dangerous. (17 civ turns) In 1998 the islands were declared safe to occupy, but you cannot safely eat a diet of locally grown food. (40 civ turns)
To me, this suggests that each nuke should only destroy and pollute one tile, and that pollution should have poisoning effects for about 20 years, and eliminate food production for 40 or more years. Engineers can mitigate, but as most have suggested, not make it all better in one turn!
Neutron weapons are tactical in nature and used to kill soldiers protected by armor. Neutron radiation blasts penetrate steel etc. while steel effectively blocks conventional nukes,(depending on proximity to ground zero) The "neutron bomb" that kills people and lets you walk into and use the city does not appear to exist.
There are also, although they may not have been built (trust no-one) cobalt and zinc bombs, which are the gift that lasts, providing a deadly dose of radiation for months / years after the blast. These could have strategic uses in a space game. (poisoning planets that you don't have the resources to develop but don't want your rivals to get)
Joker, you are a scary guy!
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