Radioactive Decay Kinetics

The number of nuclei in a radioactive sample that disintegrate during a given time interval decreases exponentially with time. Since radioactive decay represents the transformation of an unstable radioactive nuclide into a more stable nuclide, which may also be radioactive, it is an irreversible event for each nuclide. When a radionuclide decays, it does not disappear but is transformed into a new nuclear species of lower total energy and often differing Z, A, J, π, and soon. Some nuclides decay by more than one mode. Some nuclei may decay by either β +-decay or electron capture, others by α-decay or spontaneous fission, still others by γ-ray emission or internal conversion, etc. To fully discuss radioactivity, this chapter considers the consequences of the interaction of radiation with matter. The naturally occurring radionuclides can be classified as primordial, cosmogenic, and anthropogenic.