Radionuclide
A radionuclide is an atom whose nucleus is unstable and decays by emitting radiation. Its decay can transform it into a different nuclide.
Radioactive decay: The spontaneous transformation of an unstable atomic nucleus, accompanied by particle or electromagnetic radiation. Radionuclide decay is a specific instance of this broader nuclear process.
Nuclide: A species of atom specified by its numbers of protons and neutrons, and sometimes its nuclear energy state. A radionuclide is a nuclide distinguished by an unstable nucleus.
Nuclear medicine: A medical specialty that uses radioactive substances for diagnosis, treatment, and research. It uses selected radionuclides to image organs or deliver radiation to disease.
Stable nuclide: A nuclide that has no observed spontaneous radioactive decay. It contrasts with radionuclides, whose nuclei undergo spontaneous decay.
Alpha decay: A nuclear decay that emits a helium-4 nucleus, reducing the parent nucleus’s atomic number by two. Heavy radionuclides can shed mass and charge through this emission.
Isotope: One of two or more nuclides of the same element, with equal proton numbers and different neutron numbers. Radioactive and stable isotopes can belong to the same chemical element.
Radiotracer: A detectable radioactive substance used to track the movement or distribution of a material in a system. Radionuclides can mark molecules so their paths can be measured.
Radioactive contamination: The unwanted presence of radioactive material on or within people, objects, or environments. Contamination describes where radioactive material is, not the identity of a radionuclide.
Beta decay: A nuclear decay in which a neutron or proton changes type through the weak interaction, emitting a beta particle. This process changes a radionuclide’s atomic number while often leaving its mass number unchanged.
Atomic nucleus: The dense central region of an atom, composed of protons and neutrons bound by the strong interaction. Its composition and energy state determine whether a radionuclide is unstable.