Lead isotopes

Because of the radioactive displacement law, uranium and thorium both break down into different isotopes of lead. This was experimentally confirmed using unprecedentedly accurate methods for measuring weight, providing evidence for the isotope concept.
 Theodore William Richards United States 1913 Lead isotopes

Because of the radioactive displacement law, uranium and thorium both break down into different isotopes of lead. This was experimentally confirmed using unprecedentedly accurate methods for measuring weight, providing evidence for the isotope concept.