radionuclides

Radionuclides are nuclides that possess an unstable combination of protons and neutrons, causing them to undergo radioactive decay to more stable configurations. Each radionuclide has a characteristic half-life, the time required for half of a sample to decay, and a specific decay scheme that can emit alpha, beta, and/or gamma radiation. They can be found both naturally and as products of human activity.

Natural radionuclides occur in the earth, atmosphere, and universe, such as uranium-238, thorium-232, potassium-40, and radon isotopes. Artificial radionuclides are produced in nuclear reactors, particle accelerators, or via nuclear reactions, including technetium-99m, iodine-131, cobalt-60, cesium-137, and americium-241. Radioactive decay can proceed through chains, with parent nuclides transforming into daughter nuclides that may also be radioactive. The activity of a sample is measured in becquerels (disintegrations per second) or curies, and the emitted radiation has energy that depends on the specific decay process.

Applications of radionuclides span medicine, industry, science, and dating. In medicine, diagnostic imaging uses gamma-emitting isotopes such as technetium-99m, while therapeutic radiopharmaceuticals deliver targeted radiation to diseased tissue. In industry and research, radionuclides serve as tracers, calibration sources, and in nondestructive testing. Long-lived radionuclides such as uranium-series isotopes and carbon-14 enable geological and archaeological dating.

Safety and regulation focus on minimizing exposure to ionizing radiation through shielding, containment, monitoring, and dose optimization. Waste management and environmental controls address the long-term handling of radioactive materials.