Carbon dating radiation
Coal, soot, and diamonds are all nearly pure forms of carbon.
In the example above, 500 atoms are "expected" to decay. It is just what will happen on average over the course of billions and billions of atoms.
This method for producing charcoal was known as early as the Roman civilization (509 476).
French physicist René Antoine Ferchault Reaumur (1683-1757) believed carbon might be an element.
Sometimes isotopes decay from one unstable isotope into another unstable isotope.
This can happen continuously in a long radioactive chain. As it decays, it transforms through a number of elements including thorium, radium, francium, radon, polonium, and bismuth.