“aren’t the Plutonium bombs of today different than the Uranium bomb of WWII? (in terms of long term environmental/health effects)”
Nagasaki (Fat Man) was a plutonium bomb.
Plutonium is ten times more toxic as a heavy metal (like lead or mercury), than it is as a radioactive element. So in a small area, a large dose is poisonous - but so much is consumed in the detonation, and residue is dispersed widely. Bottom line - not really an issue.
“Americans headed for Las Vegas to witness the distant mushroom clouds that could be seen from the downtown hotels. “
Winds from the test site didn’t go to Vegas. You could watch in safety. East of there, not quite so much.