I didn't see this in the article, but is it correct to think that if the isotope decays after 23 years, the reason that natural lead contains it is because natural lead itself is some kind of decay product.
The isotope in question (Lead-210) is indeed a decay product of Uranium-238. However, not all lead is Pb-210, most of it is made of other, stable isotopes.
Since mining and refining lead removes the U-238 that would decay into more Pb-210, if you wait long enough (and shield it underwater), you get almost radiation-free lead, as the Pb-210 existing at the time of mining/refining eventually decays into non-radioactive Pb-206.
Yep, the isotope is constantly replenished by decay of heavier atoms. When it is mined these heavier atoms are removed. You just have to wait for the radioactive isotopes to decay.
