31.8

Radioactive Decay Series

When an unstable parent nucleus decays, the resulting daughter nucleus is sometimes also unstable. If so, the daughter then decays and produces its own daughter, and so on, until a completely stable nucleus is produced. This sequential decay of one nucleus after another is called a radioactive decay series. Examples 4, 5 and 6 discuss the first two steps of a series that begins with uranium :

Furthermore, Examples 8 and 9 deal with radon , which is formed down the line in the radioactive decay series. Figure 31-16 shows the entire series. At several points branches occur because more than one kind of decay is possible for an intermediate species. Ultimately, however, the series ends with lead , which is stable.

Figure 31-16 The radioactive decay series that begins with uranium and ends with lead . Half-lives are given in seconds (s), minutes (m), hours (h), days (d), or years (y). The inset in the upper left identifies the type of decay that each nucleus undergoes.

The series and other such series are the only sources of some of the radioactive elements found in nature. Radium , for instance, has a half-life of 1600 yr, which is short enough that all the created when the earth was formed billions of years ago has now disappeared. The series provides a continuing supply of , however.

Copyright © 2007 John Wiley & Sons, Inc. All rights reserved.