There are actually only 21 isotopes with "tens or hundreds of millennia" half-life listed on Wikipedia: https://en.wikipedia.org/wiki/List_of_radioactive_nuclid

There are actually only 21 isotopes with "tens or hundreds of millennia" half-life listed on Wikipedia: https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_by_half-life#109_seconds_(gigaseconds) https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_b...