Reply to thread

Message: <blockquote data-quote="freyar" data-source="post: 6229209" data-attributes="member: 40227">Pb-210 is a product of a chain of decays starting with U-238, an isotope of uranium that's found pretty much everywhere on earth in varying quantities.  So Pb-210 is found basically everywhere as well.  I'm sure different lead mines will have slightly different amounts of Pb-210, but there's basically no way around getting Pb-210 when you mine lead.  We can separate it out (I think using centrifuging because its atomic weight is different than that of stable lead isotopes), but dark matter detection experiments have to be incredibly sensitive because the signal they're looking for is tiny.  So the labs are some of the most radiation-free places people can ever go, and it's pretty costly to purify the lead shielding to be as radiation-free as necessary.  However, the ingots that have been dug up centuries ago and lost undersea have been protected from new Pb-210 deposits and so are a lot cleaner than anything mined and processed today.This really has to do with strong medical standards.  I suspect (just a guess without having more information than that link) that there wasn't any "extra" Pb-210 in the radiation shielding, but the legal/medical requirements are such that the shielding has to be cleaner than anything found in nature.  That certainly happens.</blockquote>