A brief description of radioactivity, its uses, and the problems caused by both natural and man-made varieties. Radioactivity is the energy released when unstable elements decay or when atoms are either split asunder (fission) or smashed together (fusion). The energy source can be the sun or naturally occurring uranium decaying into radon; more and more often, its sources come from the enterprises and accidents of man, with far-reaching results. The meltdown of the nuclear reactor at Chernobyl, for instance, was detected thousands of miles from the site--some of the aftereffects threatened the Finnish Laplanders' food chain. But even when great care is exercised, as at the Oak Ridge laboratory, unexpected contamination through the natural plant-animal food chain has occurred. We get too soon hot and too late smart. With nearly 50 books to their credit, the Milnes are veterans at researching and packaging information. Though atomic structure gets short shrift here (and is described so compactly that even those with some background may blink), and though more graphics would have clarified some topics--e.g., the relationship between various levels of roentgens, rems, and curies--the information is so important, and the facts presented so well chosen, that this belongs in most collections. Glossary; bibligraphy; index.