Begins with a description of the discovery of radioactivity and the historic research of such pioneers as the Curies and Rutherford. After a discussion of the interactions of &agr;, &bg;; and &ggr; rays with matter, the energetics of the different modes of nuclear disintegration are considered in relation to the Einstein mass-energy relationship as applied to radioactive transformations. Radiation detectors and radioactivity measurements are also discussed