Publisher Summary This chapter focuses on nuclear reactions, which are processes in which some change in the character of a nucleus takes place, either spontaneously as in radioactivity, or as the result of bombardment by a particle or ray. There are many similarities between the nuclear and chemical reactions, even though they occur in quite different energy regions and with different mechanisms. Individual particles are involved in each case—nucleons in nuclei and atoms in molecules, respectively. Conservation laws apply to each—that of charge, number of particles involved, and mass-energy. Reactions are similar in appearance. In contrast with charged particles, the neutron as a neutral particle need not have a high energy to penetrate the nucleus. Thus, neutrons are especially effective as projectiles for inducing nuclear reactions. The conservation of mass-energy is a firm requirement for any valid nuclear reaction. The total energy is made up of the rest energy—corresponding to a particle's mass at rest, and the kinetic energy of motion.