For a real life example: https://en.m.wikipedia.org/wiki/Goi%C3%A2nia_accident https://en.m.wikipedia.org/wiki/Goi%C3%A2nia_accident It was finally clocked as h

For a real life example: https://en.m.wikipedia.org/wiki/Goi%C3%A2nia_accident https://en.m.wikipedia.org/wiki/Goi%C3%A2nia_accident It was finally clocked as harmful 15 days after they got a hold of it, plenty of time for lots of people to get a lethal dose. And these people probably had at least some pop culture knowledge of nuclear radiation, compared to a distant primitive civilization who would have nothing.