Five experiments and nine activities are presented in this Unit 6 handbook. The experiments are related to random events, ranges of alpha and beta particles, half-lives, and radioactive tracers. The activities are concerned with the energy measurement in beta radiation, demonstration with sugar cubes, ionization by radioactivity, magnetic deflection of beta rays, exponential decay in concentrations, neutron detection problem analogue, chain reaction model, nuclear fission and fusion, and peaceful use of radioactivity. Self-directed instructions, demonstrations, and construction projects are stressed in these activities. The three chapters in the handbook are designed to correspond to three of the four chapters in the text. Notes on the film loop relating to collisions with an unknown object are provided. Also given are illustrations for explanation purposes. The work of Harvard Project Physics has been financially supported by: the Carnegie Corporation of New York, the Ford Foundation, the National Science Foundation, the Alfred P. Sloan Foundation, the United States Office of Education, and Harvard University. (CC)