In the transformations on the previous page, the greek symbol alpha indicates alpha-particle emission, and beta represents beta decay.

Excercise.
Write a few of the individual steps to check that mass number and charge are conserved.

In this series of breakdowns, uranium emits an alpha particle to become an unstable isotope of thorium, which goes via decay to protactinium and then to a different isotope of uranium. A series of a decays then descends through thorium, radium, radon, and polonium to an unstable lead isotope, and the process continues until a stable form of lead is reached. The entire decay chain represented on a p-n stability plot can be viewed on the previous page. Another decay chain leads from to , and a third chain, not shown, begins with and ends at . Lead is just at the upper end of the stable region, as seen on Page 29, and the heavier elements beyond it to the upper right decay spontaneously back to lead.