Primordial nuclide
Encyclopedia
In geochemistry
and geonuclear physics, primordial nuclides or primordial isotopes are nuclide
s found on the earth that have existed in their current form since before Earth
was formed. Only 288 such nuclides are known. All of the known 255 stable nuclides occur as primordial nuclides, plus another 33 nuclides that have half-lives long enough to have survived from the formation of the Earth. These 33 primordial radionuclides represent nuclides of 27 separate elements (cadmium
, neodynium, tellurium and uranium
each have two primordial radionuclides, and samarium
has three).
Due to the age of the Earth
of , this means that the half-life
of the given nuclides must be greater than about for practical considerations. For example, for a nuclide with half-life , this means 77 half-lives have elapsed, meaning that for each mole
of that nuclide being present at the formation of earth, only 6 atoms remain today.
The shortest-lived isotopes (i.e. isotopes with shortest half-lives) in the list of 33 radioactive primordial nuclides are:
These are the 6 nuclides with half-lives comparable to, or less than, the estimated age of the universe
. For a complete list of the 33 known primordial radionuclides, including the next 27 with half-lives much longer than the age of the universe, see the complete list in the section below.
The next longest-living nuclide after the end of the list given in the table is niobium-92
with a half-life of . (See list of nuclides for the list of all nuclides with half-lives longer than 60 minutes.) To be detected primordially, 92Nb
would have to survive at least 132 half-lives since the Earth's formation, meaning its original concentration will have decreased by a factor of 1040. To date, it has not been detected. It has been found that the next longer-lived nuclide, , with a half-life of is primordial, although just barely, as its concentration in a few ores is nearly 10−18 weight parts. Taking into account that all these nuclides must exist since at least , meaning survive 57 half-lives, their original number is now reduced by a factor of 257 which equals more than 1017.
Although it is estimated that about 33 primordial nuclides are radioactive (list below), it becomes very difficult to determine the exact total number of radioactive primoridals, because the total number of stable nuclides is uncertain. There exist many extremely long-lived isotopes whose half-lives are still unknown. For example, it is known theoretically that all isotope
s of tungsten
, including those indicated by even the most modern empirical methods to be stable, must be radioactive and can decay by alpha emission, but this could only be measured experimentally for . 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, the fact merely moves it from the stable to the unstable list of primordial nuclides, and the total number of primordial nuclides remains unchanged.
Because primordial chemical elements often consist of more than one primordial nuclide, there are only 84 distinguishable primordial chemical elements. Of these, 80 are stable and four are radioactive.
s such as and ), or (rarely) by such processes as geonuclear transmutation (neutron capture
of uranium in the case of ). Other examples of common naturally-occurring but non-primordial nuclides are radon
, polonium
, and radium
, which are all radiogenic nuclide
daughters of uranium decay and are found in uranium ores. A similar radiogenic series is derived from the long-lived radioactive primordial nuclide thorium-232. All of such nuclides have shorter half-lives than their parent radioactive primordial nuclides.
There are about 51 nuclides which are radioactive and exist naturally on Earth but are not primordial (making a total of fewer than 340 total nuclides to be found naturally on Earth).
for more information.
Note that half-lives are in seconds, and must be divided by 3.1556926 x 107 to obtain half-lives in years.
The longest has a half-life of 2.2 × 1024 years (160 million million times the age of the universe, which is about 4.32 x 1017 seconds). Only six of these 33 nuclides have half-lives shorter than, or equal to, the age of the universe. The remaining 27 have half-lives much longer. The shortest-lived primordial isotope so far detected has a half-life of only 80 million years, less than 2% of the age of the Earth and solar system.
A running positive integer for reference. These numbers may change slightly in the future as more of the 165 theoretically unstable nuclides are actually found to be unstable experimentally. The number starts at 256, to follow the 255 nuclides not yet found radioactive.
nuclide column
Nuclide identifiers are given by their mass number A and the symbol for the corresponding chemical element (implies a unique proton number). In the rare case that this is not the ground state
, this is indicated by a m for metastable appended to the mass number.
energy column
The column labeled "energy" denotes the mass of the average nucleon of this nuclide relative to the mass of a neutron (so all nuclides get a positive value) in MeV, formally: .
half-life column
All times are given in seconds ( = 1 year).
decay
mode column
decay energy column
Multiple values for (maximal) decay energy are mapped to decay modes in their order.
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
and geonuclear physics, primordial nuclides or primordial isotopes are nuclide
Nuclide
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state....
s found on the earth that have existed in their current form since before Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
was formed. Only 288 such nuclides are known. All of the known 255 stable nuclides occur as primordial nuclides, plus another 33 nuclides that have half-lives long enough to have survived from the formation of the Earth. These 33 primordial radionuclides represent nuclides of 27 separate elements (cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
, neodynium, tellurium and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
each have two primordial radionuclides, and samarium
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
has three).
Due to the age of the Earth
Age of the Earth
The age of the Earth is 4.54 billion years This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples...
of , this means that the half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of the given nuclides must be greater than about for practical considerations. For example, for a nuclide with half-life , this means 77 half-lives have elapsed, meaning that for each mole
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
of that nuclide being present at the formation of earth, only 6 atoms remain today.
The shortest-lived isotopes (i.e. isotopes with shortest half-lives) in the list of 33 radioactive primordial nuclides are:
- ..., , , , , and .
These are the 6 nuclides with half-lives comparable to, or less than, the estimated age of the universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...
. For a complete list of the 33 known primordial radionuclides, including the next 27 with half-lives much longer than the age of the universe, see the complete list in the section below.
The next longest-living nuclide after the end of the list given in the table is niobium-92
Isotopes of niobium
Naturally occurring niobium , element 41, is composed of one stable isotope . 93Nb is the lightest nuclide theoretically susceptible to spontaneous fission, and although this has never been observed, it makes niobium theoretically the lightest element with no stable isotope...
with a half-life of . (See list of nuclides for the list of all nuclides with half-lives longer than 60 minutes.) To be detected primordially, 92Nb
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
would have to survive at least 132 half-lives since the Earth's formation, meaning its original concentration will have decreased by a factor of 1040. To date, it has not been detected. It has been found that the next longer-lived nuclide, , with a half-life of is primordial, although just barely, as its concentration in a few ores is nearly 10−18 weight parts. Taking into account that all these nuclides must exist since at least , meaning survive 57 half-lives, their original number is now reduced by a factor of 257 which equals more than 1017.
Although it is estimated that about 33 primordial nuclides are radioactive (list below), it becomes very difficult to determine the exact total number of radioactive primoridals, because the total number of stable nuclides is uncertain. There exist many extremely long-lived isotopes whose half-lives are still unknown. For example, it is known theoretically that all isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s of tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, including those indicated by even the most modern empirical methods to be stable, must be radioactive and can decay by alpha emission, but this could only be measured experimentally for . 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, the fact merely moves it from the stable to the unstable list of primordial nuclides, and the total number of primordial nuclides remains unchanged.
Because primordial chemical elements often consist of more than one primordial nuclide, there are only 84 distinguishable primordial chemical elements. Of these, 80 are stable and four are radioactive.
Naturally occurring nuclides that are not primordial
Some unstable isotopes which occur naturally (such as , , and ) are not primordial, as they must be constantly regenerated. This occurs by cosmic radiation (in the case of cosmogenic nuclideCosmogenic nuclide
See also Environmental radioactivity#NaturalCosmogenic nuclides are rare isotopes created when a high-energy cosmic ray interacts with the nucleus of an in situ solar system atom, causing cosmic ray spallation...
s such as and ), or (rarely) by such processes as geonuclear transmutation (neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
of uranium in the case of ). Other examples of common naturally-occurring but non-primordial nuclides are radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
, polonium
Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
, and radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
, which are all radiogenic nuclide
Radiogenic nuclide
A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive, or stable.Radiogenic nuclides form some of the most important tools in geology...
daughters of uranium decay and are found in uranium ores. A similar radiogenic series is derived from the long-lived radioactive primordial nuclide thorium-232. All of such nuclides have shorter half-lives than their parent radioactive primordial nuclides.
There are about 51 nuclides which are radioactive and exist naturally on Earth but are not primordial (making a total of fewer than 340 total nuclides to be found naturally on Earth).
Primordial elements
There are 255 stable primordial nuclides and 33 radioactive primordial nuclides, but only 80 primordial stable elements (1 through 82, exclusive of 43 and 61) and four radioactive primordial elements (bismuth, thorium, uranium, and plutonium). The numbers of elements are smaller, because many primordial elements are represented by more than one primordial nuclide. See chemical elementChemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
for more information.
Naturally occurring stable nuclides
As noted, these number about 255. For a list, see the article list of stable isotopes. For a complete list noting which of the "stable" 255 nuclides may be in some respect unstable, see list of nuclides. 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 primordial also.List of 33 radioactive primordial nuclides and measured half-lives
These represent isotopes of 27 distinct chemical elements (five elements have more than one primordial isotope and one, samarium, has three). The radionuclides are listed in order of stability, with the longest half-life beginning the list.Note that half-lives are in seconds, and must be divided by 3.1556926 x 107 to obtain half-lives in years.
The longest has a half-life of 2.2 × 1024 years (160 million million times the age of the universe, which is about 4.32 x 1017 seconds). Only six of these 33 nuclides have half-lives shorter than, or equal to, the age of the universe. The remaining 27 have half-lives much longer. The shortest-lived primordial isotope so far detected has a half-life of only 80 million years, less than 2% of the age of the Earth and solar system.
List legends
no (number)A running positive integer for reference. These numbers may change slightly in the future as more of the 165 theoretically unstable nuclides are actually found to be unstable experimentally. The number starts at 256, to follow the 255 nuclides not yet found radioactive.
nuclide column
Nuclide identifiers are given by their mass number A and the symbol for the corresponding chemical element (implies a unique proton number). In the rare case that this is not the ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
, this is indicated by a m for metastable appended to the mass number.
energy column
The column labeled "energy" denotes the mass of the average nucleon of this nuclide relative to the mass of a neutron (so all nuclides get a positive value) in MeV, formally: .
half-life column
All times are given in seconds ( = 1 year).
decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
mode column
| α | α decay Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
| β− | β− decay Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
| K | electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
| KK | double electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... |
| β+ | β+ decay Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
| SF | spontaneous fission Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... |
| 2 | double β− decay Double beta decay Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted... |
| β+β+ | double β+ decay Double beta decay Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted... |
| I | isomeric transition Nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states... |
| p | proton emission Proton emission Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very... |
| n | neutron emission Neutron emission Neutron emission is a type of radioactive decay of atoms containing excess neutrons, in which a neutron is simply ejected from the nucleus. Two examples of isotopes which emit neutrons are helium-5 and beryllium-13... |
decay energy column
Multiple values for (maximal) decay energy are mapped to decay modes in their order.
| no | nuclide | energy | half-life (seconds) | decay mode | decay energy (MeV) | approx ratio half-life to age of universe |
|---|---|---|---|---|---|---|
| 256 | 128Te | 8.743261 | 2 | 2.530 | 160 million million | |
| 257 | 76Ge | 9.034656 | 2 | 2.039 | 130,000 million | |
| 258 | 82Se | 9.017596 | 2 | 2.995 | 8,000 million | |
| 259 | 116Cd | 8.836146 | 2 | 2.809 | 2,000 million | |
| 260 | 48Ca | 8.992452 | 2 β− | 4.274 , 0.0058 | 2,000 million | |
| 261 | 96Zr | 8.961359 | 2 β− | 3.4 | 1,000 million | |
| 262 | 209Bi | 8.158689 | α | 3.137 | 1,000 million | |
| 263 | 130Te | 8.766578 | 2 | 0.868 | 600 million | |
| 264 | 150Nd | 8.562594 | 2 | 3.367 | 600 million | |
| 265 | 100Mo | 8.933167 | 2 | 3.035 | 600 million | |
| 266 | 151Eu | 8.565759 | α | 1.9644 | 300 million | |
| 267 | 180W | 8.347127 | α | 2.509 | 100 million | |
| 268 | 50V | 9.055759 | β+ β− | 2.205 , 1.038 | 10 million | |
| 269 | 113Cd | 8.859372 | β− | 0.321 | 600,000 | |
| 270 | 148Sm Samarium Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3... |
8.607423 | α | 1.986 | 500,000 | |
| 271 | 144Nd | 8.652947 | α | 1.905 | 200,000 | |
| 272 | 186Os | 8.302508 | α | 2.823 | 100,000 | |
| 273 | 174Hf | 8.392287 | α | 2.497 | 100,000 | |
| 274 | 115In | 8.849910 | β− | 0.499 | 30,000 | |
| 275 | 152Gd | 8.562868 | α | 2.203 | 8,000 | |
| 276 | 130Ba | 8.742574 | KK | 2.620 | 5,000 | |
| 277 | 190Pt | 8.267764 | α | 3.252 | 60 | |
| 278 | 147Sm | 8.610593 | α | 2.310 | 8 | |
| 279 | 138La | 8.698320 | K β− | 1.737 , 1.044 | 7 | |
| 280 | 87Rb | 9.043718 | β− | 0.283 | 4 | |
| 281 | 187Re | 8.291732 | β− α | 0.0026 , 1.653 | 3 | |
| 282 | 176Lu | 8.374665 | β− | 1.193 | 3 | |
| 283 | 232Th | 7.918533 | α SF | 4.083 | 1 | |
| 284 | 238U | 7.872551 | α SF | 4.270 | 0.3 | |
| 285 | 40K | 8.909707 | β− K β+ | 1.311 , 1.505 , 1.505 | 0.09 | |
| 286 | 235U | 7.897198 | α SF | 4.679 | 0.05 | |
| 287 | 146Sm | 8.626136 | α | 2.529 | 0.008 | |
| 288 | 244Pu | 7.826221 | α SF | 4.666 | 0.006 |
See also
- Primordial element
- Table of nuclides sorted by half-life
- Table of nuclidesTable of nuclidesThe tables listed below provide information on the basic properties of all nuclides.* Neutron + Element 1 - Element 24 * Element 25 - Element 48 * Element 49 - Element 72...
- Isotope geochemistryIsotope geochemistryIsotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. Variations in the abundance of these isotopes, typically measured with an isotope ratio mass spectrometer or an accelerator mass spectrometer,...
- RadionuclideRadionuclideA radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
- Mononuclidic element
- Monoisotopic elementMonoisotopic elementA monoisotopic element is one of 26 chemical elements which have only a single stable isotope . A list is given in a following section....
- Stable isotopeStable isotopeStable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
- List of nuclides
- List of elements by stability of isotopes
- List of elements by nuclear stability