Nuclide

Nuclide

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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.

The word nuclide was proposed by Truman P. Kohman  in 1947. Doctor Kohman originally suggested nuclide as referring to a "species of nucleus" defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus.

Nuclides and isotopes


Designation Characteristics Example Remarks
Isotopes equal proton number ,
Isotones equal neutron number ,
Isobars equal mass number , , see beta 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...

Mirror nuclei
Mirror nuclei
Mirror nuclei is a term that refers to two different elemental isotopes with atomic numbers having difference of one, but with the same combined number of protons and neutrons that is with same mass number ....

neutron and proton number exchanged ,
Nuclear isomers different energy states , long-lived or stable


A set of nuclides with equal proton number (atomic number), i.e., of the same chemical element
Chemical 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...

 but different neutron number
Neutron number
The neutron number, symbol N, is the number of neutrons in a nuclide.Atomic number plus neutron number equals mass number: Z+N=A....

s, are called 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 the element. Particular nuclides are still often loosely called "isotopes", but the term "nuclide" is the correct one in general (i.e., when Z is not fixed). In similar manner, a set of nuclides with equal mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...

 A but different atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 are called isobars
Isobar (nuclide)
Isobars are atoms of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number but not in mass number. An example of a series of isobars would be 40S, 40Cl, 40Ar, 40K, and 40Ca...

 (isobar = equal in weight), and isotone
Isotone
Two nuclides are isotones if they have the same neutron number N, but different proton number Z. For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones. Similarly, S-36, Cl-37, Ar-38, K-39, and Ca-40 nuclei are all isotones of 20 because they all contain 20 neutrons...

s are nuclides of equal neutron number but different proton numbers. The name isotone has been derived from the name isotope to emphasize that in the first group of nuclides it is the number of neutrons (n) that is constant, whereas in the second the number of protons (p).

See the introduction to the article about isotopes for an explanation of the notation used for different nuclide or isotope types.

Nuclear isomer
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...

s are members of a set of nuclides with equal proton number and equal mass number (thus making them by definition the same isotope), but different states of excitation. An example is the two states of the single isotope shown among the decay scheme
Decay scheme
The Decay scheme of a radioactive substance is a graphical presentation of all the transitions occurring in a decay, and of their relationships.-Decay schemes of radioactive isotopes:...

s. Each of these two states (technetium-99m and technetium-99) qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes (an isotope may consist of several different nuclides of different excitation states).

The most long-lived non-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...

 nuclear isomer is the nuclide tantalum-180m, which has a 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...

 in excess of 1,000 trillion years. This nuclide occurs primordially, and has never been observed to decay to the different nuclide tantalum-180. (Incidentally, the ground state nuclide tantalium-180 does not occur primordially, since it is unstable with a half life of only 8 hours.)

There are about 255 nuclides in nature that have never been observed to decay. They occur among the 80 different elements that have one or more stable isotopes. See stable isotope
Stable isotope
Stable 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...

 and primordial nuclide
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...

. Unstable nuclides are radioactive and are called radionuclide
Radionuclide
A 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...

s. Their decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...

s ('daughter' products) are called 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...

s. About 255 stable and about 84 unstable (radioactive) nuclides exist naturally on Earth, for a total of about 339 naturally occurring nuclides on Earth.

Types of naturally occurring nuclides


Natural radionuclides
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...

 may be conveniently subdivided into three types. First, those whose half-lives
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...

 T1/2 are at least 2% as long as the age of the 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...

 (for practical purposes, these are difficult to detect with half-lives less than 10% of the age of the Earth) . These are remnants of nucleosynthesis
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...

 that occurred in stars before the formation of the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. For example, the isotope (T1/2 = ) of 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...

 is still fairly abundant in nature, but the shorter-lived isotope (T1/2 = ) is 138 times rarer. About 33 of these nuclides have been discovered (see list of nuclides and primordial nuclide
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...

 for details).

The second group of radionuclides that exist naturally consists of 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...

s such as (T1/2 = ), an isotope of 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 formed by radioactive 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...

. They occur in the decay chains of primordial isotopes of uranium or thorium. Some of these nuclides are very short-lived, such as isotopes of francium
Isotopes of francium
Francium has no stable isotopes. A standard atomic mass cannot be given. Its most stable isotope is 223Fr with a half-life of 22 minutes, which is also the only naturally occurring isotope, occurring in trace quantities as an intermediate decay product of 235U.Of elements whose most stable...

. There exist about 51 of these daughter nuclides that have half-lives too short to be primordial, and which exist in nature solely due to decay from longer lived radioactive primordial nuclides.

The third group consists of nuclides that are continuously being made in another fashion that is not simple spontaneous radioactive 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...

 (i.e., only one atom involved with no incoming particle) but instead involves a natural nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...

. These occur when atoms react with natural neutrons (from cosmic rays, 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...

, or other sources), or are bombarded directly with cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

s. The latter, if non-primordial, are called cosmogenic nuclide
Cosmogenic 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. Other types of natural nuclear reactions produce nuclides that are said to be nucleogenic
Nucleogenic
A nucleogenic isotope or nuclide, is one that is produced by a natural terrestrial nuclear reaction, other than a reaction beginning with cosmic rays . The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutron...

 nuclides.

An example of nuclides made by nuclear reactions, are cosmogenic (radiocarbon) that is made by cosmic-ray bombardment of other elements, and nucleogenic which is still being created by neutron bombardment of natural as a result of natural fission in uranium ores. Cosmogenic nuclides may be either stable or radioactive. If they are stable, their existence must be deduced against a background of stable nuclides, since every known stable nuclide is present on Earth primordially.

Artificially produced nuclides


Beyond the 339 naturally-occurring nuclides, more than 3000 radionuclides of varying half-lives have been artificially produced and characterized.

The known nuclides are shown in the chart of nuclides. A list of primordial nuclides is given sorted by element, at list of elements by stability of isotopes. A list of nuclides is also available, sorted by half-life, for the 905 nuclides with half-lives longer than one hour.

Summary table for numbers of each class of nuclides


This is a summary table for the 905 nuclides with half-lives longer than one hour, given in list of nuclides. Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.
Stability class Number of nuclides Running total
Running total
A running total is the summation of a sequence of numbers which is updated each time a new number is added to the sequence, simply by adding the value of the new number to the running total....

Notes on running total
Theoretically stable to all but proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...

90 90 Includes first 40 elements. Proton decay yet to be observed.
Energetically unstable to one or more known decay modes, but no decay yet seen. 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...

 possible for "stable" nuclides > niobium-93; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected.
165 255 Total of classically stable nuclides.
Radioactive primordial nuclide
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...

s.
33 288 Total primordial elements include bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...

, 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...

, thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

, plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, plus all stable nuclides.
Radioactive non-primordial, but naturally occurring on Earth. ~ 51 ~ 339 Carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

 (and other cosmogenic isotopes generated by cosmic rays); daughters of radioactive primordials, such as francium
Francium
Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.Actually the least unstable isotope, francium-223 It has the lowest electronegativity of all known elements, and is the second rarest naturally occurring element...

, etc., and nucleogenic
Nucleogenic
A nucleogenic isotope or nuclide, is one that is produced by a natural terrestrial nuclear reaction, other than a reaction beginning with cosmic rays . The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutron...

 nuclides from natural nuclear reactions that are other than those from cosmic rays (such as neutron absorption from spontaneous nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 or 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...

).
Radioactive synthetic (half-life > 1 hour). Includes most useful radiotracers. 556 905
Radioactive synthetic (half-life < 1 hour). >2400 >3300 Includes all well-characterized synthetic nuclides.

See also

  • Primordial element
  • Primordial nuclide
    Primordial nuclide
    In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...

  • List of nuclides sorted by half-life
  • Table of nuclides
    Table of nuclides
    The 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 geochemistry
    Isotope geochemistry
    Isotope 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,...

  • Radionuclide
    Radionuclide
    A 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...

  • Monoisotopic element
    Monoisotopic element
    A monoisotopic element is one of 26 chemical elements which have only a single stable isotope . A list is given in a following section....

  • Mononuclidic element
  • Stable isotope
    Stable isotope
    Stable 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 elements by stability of isotopes
  • List of elements by nuclear stability
  • Exotic nuclei