ABSTRACT
Radioactivity refers to the particles that are emitted from nuclei as a result of nuclear instability. Since the nucleus experiences an intense conflict between the two strongest forces in nature, it should not be surprising that there are many nuclear isotopes that are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation; however, there are several other varieties of radioactive decay. This entry presents the history of radioactivity discovery and defines the most important radioactivity parameters, as well as characterizes the natural and artificial radionuclides in the natural environment. Applications of radionuclides in science, radiology, and industry are also described, as well as the problem of radioactive pollution of the natural environment.
