What Are Radioactive Materials?

Radioactive materials are substances that contain unstable atomic nuclei capable of undergoing spontaneous radioactive decay, emitting ionizing radiation in the form of alpha particles, beta particles, gamma rays, or other radiation types. The defining property of a radioactive material is the presence of radionuclides, which are isotopes whose nuclear configuration is not stable. Both naturally occurring and artificially produced radioactive materials exist, and they range from trace concentrations in soil and rock to highly concentrated forms produced in nuclear reactors and particle accelerators.

The study and management of radioactive materials draws from nuclear physics, radiochemistry, health physics, and materials science. The field encompasses the production, characterization, safe handling, and application of both natural radioisotopes and the more than three thousand known radioactive isotopes, of which only about eighty-four occur in nature.

Radioactive Isotopes

An isotope is a variant of a chemical element that shares the same number of protons but differs in neutron count, and a radioactive isotope (radioisotope) is one for which this nuclear configuration leads to instability. As the IAEA explains in its overview of radioisotopes, radioisotopes are critical to modern society with applications spanning medicine, environmental science, materials characterization, and national security. Naturally occurring radioactive materials (NORM) include uranium, thorium, radium, and radon, which appear in ores, building materials, and groundwater. Artificially produced radioisotopes are manufactured by bombarding target materials with neutrons in research reactors or with protons and other particles in cyclotrons. The U.S. Department of Energy Isotope Program manages the supply of specific radioisotopes required for medical and research purposes that cannot be obtained from natural sources. Some radioisotopes serve as electron sources or photon emitters in detection instruments; others are used as tracers in biological and environmental studies because their radiation provides a measurable signal at extremely low concentrations.

Classification and Handling

Radioactive materials are classified by activity level, physical form, and hazard category, which together determine handling requirements. Activity, measured in becquerels or curies, indicates the rate of decay; specific activity relates that rate to the mass of material. High-specific-activity materials require shielded containers, remote-handling tools, and controlled-environment facilities, while low-activity materials such as consumer-grade smoke detector sources can be handled under simpler administrative controls. Neutrino sources, a specialized category of radioactive material, rely on beta-decaying radionuclides such as chromium-51 or argon-37 to produce the intense neutrino fluxes required for reactor and solar neutrino experiments. The U.S. Nuclear Regulatory Commission (NRC) regulates the possession and use of byproduct materials, source materials, and special nuclear materials, requiring licensed facilities to follow documented radiation protection programs and maintain exposure records.

Production and Supply

Most research-grade and medical radioisotopes are produced in nuclear research reactors or accelerators, where target materials are irradiated and then chemically separated. The IAEA Bulletin on radioisotope applications documents how reactor-based production of molybdenum-99, the parent of technetium-99m, underpins millions of nuclear medicine procedures annually. Accelerator-produced isotopes, including fluorine-18 for PET scanning, must be manufactured near the point of use because their short half-lives preclude long-distance shipping. Supply chain reliability for medical radioisotopes has been a persistent international concern, driving investment in multiple production sites and new reactor designs.

Applications

Radioactive materials have applications in a wide range of fields, including:

• Nuclear medicine, for diagnostic imaging with technetium-99m and therapeutic treatment with lutetium-177 and actinium-225
• Industrial radiography and thickness gauging using gamma-emitting sources
• Well logging in the oil and gas industry to characterize geological formations
• Radiation processing for sterilizing medical devices, food irradiation, and polymer modification
• Scientific research, including radiocarbon dating, tracer studies, and fundamental nuclear physics experiments