Radionuclides of Natural Origin
Radionuclides of Natural Origin : Radionuclides that occur naturally on Earth in significant quantities. The term is usually used to refer to the primordial radionuclides potassium-40, uranium-235, uranium238, thorium-232 and their radioactive decay products. Contrasted with radionuclides of artificial origin; also artificial radionuclides, anthropogenic radionuclides and human-made radionuclides