The nuclides generated during the decayThe spontaneous conversion of a nuclide into another nuclide... of the very long-lived natural radionuclides U-238 (half-lifeThe period during which half of the nuclei decay in a quanti... 4.5 bn years), U-235 (half-lifeThe period during which half of the nuclei decay in a quanti... 0.7 bn years) and Th-232 (half-lifeThe period during which half of the nuclei decay in a quanti... 14 bn years) are in turn radioactive, and therefore decayThe spontaneous conversion of a nuclide into another nuclide... again. Thus, the so-called decayThe spontaneous conversion of a nuclide into another nuclide... chains are created which end only when a non-radioactive nuclideA nuclide is a type of atom characterized by its proton numb... is formed. The uranium-radium decayThe spontaneous conversion of a nuclide into another nuclide... chain starts from U-238 and ends via 18 intermediate states at the stable lead-206. Uranium-235 is at the beginning of the uranium-actinium decayThe spontaneous conversion of a nuclide into another nuclide... chain leading via 15 radionuclides to lead-207. With ten intermediate states, the thorium decayThe spontaneous conversion of a nuclide into another nuclide... chain starting with thorium-232 and ending at lead-208 is the shortest.
Diagram natural decay chains
Uranium-radium chain Uranium-actinium chain Thorium chain