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For three elements (indium, tellurium, and rhenium) a very long-lived radioactive primordial nuclide is more abundant than a stable nuclide. The longest-lived radionuclide known, 128 Te, has a half-life of 2.2 × 10 24 years: 1.6 × 10 14 times the age of the Universe. Only four of these 35 nuclides have half-lives shorter than, or equal to ...
The half-life of thorium-232 (14 billion years) is more than three times the age of the Earth; thorium-232 therefore occurs in nature as a primordial nuclide.Other thorium isotopes occur in nature in much smaller quantities as intermediate products in the decay chains of uranium-238, uranium-235, and thorium-232.
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
It is the only fissile isotope that exists in nature as a primordial nuclide. Uranium-235 has a half-life of 703.8 million years. It was discovered in 1935 by Arthur Jeffrey Dempster. Its fission cross section for slow thermal neutrons is about 584.3 ± 1 barns. [1] For fast neutrons it is on the order of 1 barn. [2]
Tritium decays into helium-3 with a half-life of 12.3 years, so helium-3 can be produced by simply storing the tritium until it undergoes radioactive decay. As tritium forms a stable compound with oxygen ( tritiated water ) while helium-3 does not, the storage and collection process could continuously collect the material that outgasses from ...
(The more massive 209 Bi, long considered to be stable, actually has a half-life of 2.01×10 19 years.) 208 Pb is also a doubly magic isotope, as it has 82 protons and 126 neutrons. [6] It is the heaviest doubly magic nuclide known. A total of 43 lead isotopes are now known, including very unstable synthetic species.
At least 3,300 nuclides have been experimentally characterized [1] (see List of radioactive nuclides by half-life for the nuclides with decay half-lives less than one hour). A nuclide is defined conventionally as an experimentally examined bound collection of protons and neutrons that either is stable or has an observed decay mode .
), which has a half-life in excess of 1,000 trillion years. This nuclide occurs primordially, and has never been observed to decay to the ground state. (In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to 180 Hf (86%) or 180 W (14%).)