Afaik its always going to have some parts of uranium right? 50% after one half life, 25% after two half lives and it will keep on halving practically forever (or till the last atom decays). In the end it comes down to when you consider it a negligible amount.
I mean, yes, that's how it would work if there were an infinite number of atoms in the piece. There's a finite amount, though, so eventually there will be a point when all the atoms have completely decayed.
The normal lead we know but still special. Is the last stable element in the PSE and there is the theory that it's actually radioactive (unstable) but the decay is so slow that we probably never see a single atom of it decaying.
>Puts Iron-56 in a box.
>checks at the heat death if the universe
>still Iron-56
>mfw box also Iron-56