Tell that to the people who lived in Europe at the time Chernobyl melt down when caesium 137 was spread over the continent.
'Scandinavian countries and other parts of the world were affected by the radioactive releases from Chernobyl. Caesium and other radioactive isotopes were blown by wind northward into Sweden and Finland and over other parts of the northern hemisphere to some extent. '
'Some 150,000 square kilometres in Belarus, Russia and Ukraine are contaminated and stretch northward of the plant site as far as 500 kilometres. An area spanning 30 kilometres around the plant is considered the “exclusion zone” and is essentially uninhabited'
