Primordial nuclide
Nuclear physics |
---|
In
Stability
All of the known 251 stable nuclides, plus another 35 nuclides that have half-lives long enough to have survived from the formation of the Earth, occur as primordial nuclides. These 35 primordial radionuclides represent isotopes of 28 separate elements.
).Because the
The seven shortest-lived primordial nuclides (i.e., the nuclides with the shortest half-lives) to have been experimentally verified are (7.0×108 years).
These are the seven nuclides with half-lives comparable to, or somewhat less than, the estimated age of the universe. (87Rb, 187Re, 176Lu, and 232Th have half-lives somewhat longer than the age of the universe.) For a complete list of the 35 known primordial radionuclides, including the next 28 with half-lives much longer than the age of the universe, see the complete list below. For practical purposes, nuclides with half-lives much longer than the age of the universe may be treated as if they were stable. 87Rb, 187Re, 176Lu, 232Th, and 238U have half-lives long enough that their decay is limited over geological time scales; 40K and 235U have shorter half-lives and are hence severely depleted, but are still long-lived enough to persist significantly in nature.
The longest-lived isotope not proven to be primordial
Nb
(3.5×107 years). 244Pu has been reported to exist in nature as a primordial nuclide,[2] although a later study did not detect it.[3] Taking into account that all these nuclides must exist for at least 4.6×109 years, 146Sm must survive 45 half-lives (and hence be reduced by 245 ≈ 4×1013), 244Pu must survive 57 (and be reduced by a factor of 257 ≈ 1×1017), and 92Nb must survive 130 (and be reduced by 2130 ≈ 1×1039). Mathematically, considering the likely initial abundances of these nuclides, primordial 146Sm and 244Pu should persist somewhere within the Earth today, even if they are not identifiable in the relatively minor portion of the Earth's crust available to human assays, while 92Nb and all shorter-lived nuclides should not. Nuclides such as 92Nb that were present in the primordial solar nebula but have long since decayed away completely are termed extinct radionuclides if they have no other means of being regenerated.[4]
Because primordial chemical elements often consist of more than one primordial isotope, there are only 83 distinct primordial
Naturally occurring nuclides that are not primordial
Some unstable isotopes which occur naturally (such as
C
and 3
H
), or (rarely) by such processes as geonuclear transmutation (neutron capture of uranium in the case of 237
Np
and 239
Pu
). Other examples of common naturally occurring but non-primordial nuclides are isotopes of radon, polonium, and radium, which are all radiogenic nuclide daughters of uranium decay and are found in uranium ores. The stable argon isotope 40Ar is actually more common as a radiogenic nuclide than as a primordial nuclide, forming almost 1% of the Earth's atmosphere, which is regenerated by the beta decay of the extremely long-lived radioactive primordial isotope 40K, whose half-life is on the order of a billion years and thus has been generating argon since early in the Earth's existence. (Primordial argon was dominated by the alpha process
A similar radiogenic series is derived from the long-lived radioactive primordial nuclide
Primordial elements
A primordial element is a
Naturally occurring stable nuclides
As noted, these number about 251. For a list, see the article list of elements by stability of isotopes. For a complete list noting which of the "stable" 251 nuclides may be in some respect unstable, see list of nuclides and stable nuclide. These questions do not impact the question of whether a nuclide is primordial, since all "nearly stable" nuclides, with half-lives longer than the age of the universe, are also primordial.
Radioactive primordial nuclides
Although it is estimated that about 35 primordial nuclides are
W
.[8] Similarly, all four primordial isotopes of lead are expected to decay to mercury, but the predicted half-lives are so long (some exceeding 10100 years) that such decays could hardly be observed in the near future. Nevertheless, the number of nuclides with half-lives so long that they cannot be measured with present instruments—and are considered from this viewpoint to be stable nuclides—is limited. Even when a "stable" nuclide is found to be radioactive, it merely moves from the stable to the unstable list of primordial nuclides, and the total number of primordial nuclides remains unchanged. For practical purposes, these nuclides may be considered stable for all purposes outside specialized research.[citation needed
List of 35 radioactive primordial nuclides and measured half-lives
These 35 primordial nuclides represent radioisotopes of 28 distinct chemical elements (cadmium, neodymium, osmium, samarium, tellurium, uranium, and xenon each have two primordial radioisotopes). The radionuclides are listed in order of stability, with the longest half-life beginning the list. These radionuclides in many cases are so nearly stable that they compete for abundance with stable isotopes of their respective elements. For three chemical elements, indium, tellurium, and rhenium, a very long-lived radioactive primordial nuclide is found in greater abundance than a stable nuclide.
The longest-lived radionuclide known, 128Te, has a half-life of 2.2×1024 years, which is 160 trillion times the
At the end of the list, two more nuclides have been added: 146Sm and 244Pu. They have not been confirmed as primordial, but their half-lives are long enough that minute quantities should persist today.
No. | Nuclide | Energy | Half- life (years) |
Decay mode |
Decay energy (MeV) |
Approx. ratio half-life to age of universe |
---|---|---|---|---|---|---|
252 | 128Te | 8.743261 | 2.2×1024 | 2 β− | 2.530 | 160 trillion |
253 | 124Xe | 8.778264 | 1.8×1022 | KK | 2.864 | 1.3 trillion |
254 | 78Kr | 9.022349 | 9.2×1021 | KK | 2.846 | 670 billion |
255 | 136Xe | 8.706805 | 2.165×1021 | 2 β− | 2.462 | 160 billion |
256 | 76Ge | 9.034656 | 1.8×1021 | 2 β− | 2.039 | 130 billion |
257 | 130Ba | 8.742574 | 1.2×1021 | KK | 2.620 | 87 billion |
258 | 82Se | 9.017596 | 1.1×1020 | 2 β− | 2.995 | 8.0 billion |
259 | 116Cd | 8.836146 | 3.102×1019 | 2 β− | 2.809 | 2.3 billion |
260 | 48Ca | 8.992452 | 2.301×1019 | 2 β− | 4.274, .0058 | 1.7 billion |
261 | 209Bi | 8.158689 | 2.01×1019 | α | 3.137 | 1.5 billion |
262 | 96Zr | 8.961359 | 2.0×1019 | 2 β− | 3.4 | 1.5 billion |
263 | 130Te | 8.766578 | 8.806×1018 | 2 β− | .868 | 640 million |
264 | 150Nd | 8.562594 | 7.905×1018 | 2 β− | 3.367 | 570 million |
265 | 100Mo | 8.933167 | 7.804×1018 | 2 β− | 3.035 | 570 million |
266 | 151Eu | 8.565759 | 5.004×1018 | α | 1.9644 | 360 million |
267 | 180W | 8.347127 | 1.801×1018 | α | 2.509 | 130 million |
268 | 50V | 9.055759 | 1.4×1017 | β+ or β− | 2.205, 1.038 | 10 million |
269 | 174Hf | 8.392287 | 7.0×1016 | α | 2.497 | 5 million |
270 | 113Cd | 8.859372 | 7.7×1015 | β− | .321 | 560,000 |
271 | 148Sm | 8.607423 | 7.005×1015 | α | 1.986 | 510,000 |
272 | 144Nd | 8.652947 | 2.292×1015 | α | 1.905 | 170,000 |
273 | 186Os | 8.302508 | 2.002×1015 | α | 2.823 | 150,000 |
274 | 115In | 8.849910 | 4.4×1014 | β− | .499 | 32,000 |
275 | 152Gd | 8.562868 | 1.1×1014 | α | 2.203 | 8000 |
276 | 184Os | 8.311850 | 1.12×1013 | α | 2.963 | 810 |
277 | 190Pt | 8.267764 | 4.83×1011[9] | α | 3.252 | 35 |
278 | 147Sm | 8.610593 | 1.061×1011 | α | 2.310 | 7.7 |
279 | 138La | 8.698320 | 1.021×1011 | β− or K or β+ | 1.044, 1.737, 1.737 | 7.4 |
280 | 87Rb | 9.043718 | 4.972×1010 | β− | .283 | 3.6 |
281 | 187Re | 8.291732 | 4.122×1010 | β− | .0026 | 3.0 |
282 | 176Lu | 8.374665 | 3.764×1010 | β− | 1.193 | 2.7 |
283 | 232Th | 7.918533 | 1.405×1010 | α or SF | 4.083 | 1.0 |
284 | 238U | 7.872551 | 4.468×109 | α or SF or 2 β− | 4.270 | 0.3 |
285 | 40K | 8.909707 | 1.251×109 | β− or K or β+ | 1.311, 1.505, 1.505 | 0.09 |
286 | 235U | 7.897198 | 7.038×108 | α or SF | 4.679 | 0.05 |
287 | 146Sm | 8.626136 | 1.03×108 | α | 2.529 | 0.008 |
288 | 244Pu | 7.826221 | 8.0×107 | α or SF | 4.666 | 0.006 |
List legends
- No. (number)
- A running positive integer for reference. These numbers may change slightly in the future since there are 251 nuclides now classified as stable, but which are theoretically predicted to be unstable (see Stable nuclide § Still-unobserved decay), so that future experiments may show that some are in fact unstable. The number starts at 252, to follow the 251 (observationally) stable nuclides.
- Nuclide
- Nuclide identifiers are given by their mass number A and the symbol for the corresponding chemical element (implies a unique proton number).
- Energy
- Mass of the average nucleon of this nuclide relative to the mass of a neutron (so all nuclides get a positive value) in MeV/c2, formally: mn − mnuclide / A.
- Half-life
- All times are given in years.
- Decay mode
α α decay β− β− decay K electron capture KK double electron capture β+ β+ decay SF spontaneous fission 2 β− double β− decay 2 β+ double β+ decay I isomeric transition p proton emission n neutron emission - Decay energy
- Multiple values for (maximal) decay energy in MeV are mapped to decay modes in their order.
See also
- Alpha nuclide
- Table of nuclides sorted by half-life
- Table of nuclides
- Isotope geochemistry
- Radionuclide
- Mononuclidic element
- Monoisotopic element
- Stable isotope
- List of nuclides
- List of elements by stability of isotopes
- Big Bang nucleosynthesis
References
- PMID 17124541.
- S2CID 4283169.
- .
- ^ P. K. Kuroda (1979). "Origin of the elements: pre-Fermi reactor and plutonium-244 in nature". .
- ISBN 9781466591745. Retrieved 13 July 2020.
- ^ H.-T. Shen; et al. "Research on measurement of 126Sn by AMS" (PDF). accelconf.web.cern.ch. Archived from the original (PDF) on 2017-11-25. Retrieved 2018-02-06.
- doi:10.1016/S0016-7037(98)00282-8)
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: CS1 maint: multiple names: authors list (link - ^ "Interactive Chart of Nuclides (Nudat2.5)". National Nuclear Data Center. Retrieved 2009-06-22.
- .