[aradox66]

I think OP meant "radioactive fallout" which would be the source of "long term radiation." Fission bombs scatter radioactive dust of uranium, plutonium, and fission byproducts that continue to emit harmful radiation for thousands of years.

A fusion bomb with no fission stage would have a massive radiation blast, but leave no radioactive fallout. 10 minutes after the bomb, radiation levels would be more or less back to background levels. Is my understanding.