I want to ask a question about a nuclear bomb, specifically about a myth I was told about holding your thumb up to the mushroom cloud to see if you're in range of radiation. Where would this be on topic? Biology, maybe?
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I'm guessing the "rule of thumb" you're referring to is the "extend your arm in direction of the mushroom, if your thumb is smaller than it, you're toast"? A claim like this is notable enough to be a fit, and with some research it could be an interesting question.
About your question specifically
It has actually already been asked on Skeptics: Is measuring the size of a nuclear cloud with your thumb an approximate indication of whether you're in the radiation zone?.
Thus, I don't recommend you ask it there, as it would only be a dupe, unless I've misunderstood what you were asking about; in which case, make sure to explain the difference between your question and this earlier one.