Blog post: swansont: Lead, Rather than a Duck.

Since we are not asking "What else floats in water?"

Use of ancient lead in modern physics experiments ignites debate

Unfortunately the story really doesn't lay out the case for why ancient lead ballast falls into the category of "cultural heritage artifact" or why more than a small fraction of it would need to be preserved for study. Newly mined lead is contaminated with Pb-210, which has a half-life of about 22 years and is present because it's in the decay chain of U-238. So Pb that's been around for several hundred years (especially under water where it would better shielded against any kind of activation reaction) has been separated from the source of the unstable isotope that produces it (ultimately U-238, but realistically Ra-226, which is the "most recent" previous step along the decay chain with a half-life longer than a year) is more useful for shielding detectors, as it has essentially no sources of radiation that might cause spurious readings.
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