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Taking into account that all these nuclides must exist for at least 4.6 × 10 9 years, 146 Sm must survive 45 half-lives (and hence be reduced by 2 45 ≈ 4 × 10 13), 244 Pu must survive 57 (and be reduced by a factor of 2 57 ≈ 1 × 10 17), and 92 Nb must survive 130 (and be reduced by 2 130 ≈ 1 × 10 39).
The Solar System and Earth are formed from primordial nuclides and extinct nuclides. Extinct nuclides have decayed away, but primordial nuclides still exist in their original state (undecayed). There are 251 stable primordial nuclides, and remainders of 35 primordial radionuclides that have very long half-lives.
(t 1/2 = 4.5 × 10 9 years) of uranium is still fairly abundant in nature, but the shorter-lived isotope 235 U (t 1/2 = 0.7 × 10 9 years) is 138 times rarer. About 34 of these nuclides have been discovered (see List of nuclides and Primordial nuclide for details). The second group of radionuclides that exist naturally consists of radiogenic ...
The next group is the primordial radioactive nuclides. These have been measured to be radioactive, or decay products have been identified in natural samples (tellurium-128, barium-130). There are 35 of these (see these nuclides ), of which 25 have half-lives longer than 10 13 years.
One of the primordial nuclides is tantalum-180m, which is predicted to have a half-life in excess of 10 15 years, but has never been observed to decay. The even-longer half-life of 2.2 × 10 24 years of tellurium-128 was measured by a unique method of detecting its radiogenic daughter xenon-128 and is the longest known experimentally measured ...
An example of a nucleogenic nuclide is neon-21 produced from neon-20 that absorbs a thermal neutron (though some neon-21 is also primordial). [1] Other nucleogenic reactions that produce heavy neon isotopes are (fast neutron capture, alpha emission) reactions, starting with magnesium-24 and magnesium-25, respectively. [2]
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Neutron numbers for which there is a stable nuclide and a primordial radionuclide are 27 (50 V), 65 (113 Cd), 81 (138 La), 84 (144 Nd), 85 (147 Sm), 86 (148 Sm), 105 (176 Lu), and 126 (209 Bi). Neutron numbers for which there are two primordial radionuclides are 88 ( 151 Eu and 152 Gd) and 112 ( 187 Re and 190 Pt).