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A nuclide is a type (variety) of atoms , characterized by the two numbers that indicate how many protons and how many neutrons their atomic nuclei consist of. Sometimes the term also includes the energy state of the atomic nucleus, namely when it is sufficiently long-lived, i.e. i.e., nuclear isomers are counted as separate nuclides. Nuclides with the same number of protons belong to the same chemical element and are called the isotopes of this element. In this respect, nuclide is a generalization of the older term isotope.


The term nuclide was proposed by TP Kohman in 1947 . In 1952, Glasstone and Edlund formulated the difference between the terms nuclide and isotope in their book The elements of nuclear reactor theory : “Although the majority of the elements exist naturally as a mixture of isotopes, about 20 occur only as a single species. For this and other reasons it has been found desirable to introduce the term nuclide . It is used to describe an atomic species to be described by the composition of its atomic nucleus, that is, by the number of protons and neutrons it contains. An isotope is therefore one of a group of two or more nuclides that have the same number of protons, that is, the same atomic number but a different number of neutrons. An element like fluorine, of which only one species exists in nature, is said to form a single stable nuclide. "


A nuclide X is given the following formula:

Here is the element symbol , the mass number (nucleon number, i.e. the total number of protons and neutrons) and the atomic number ( atomic number , i.e. the number of protons). Any superscript at the top right of the element symbol denotes either an ionization state (ionic charge, e.g. "+", "2+") or an energetic state of excitation (e.g. in the form of an asterisk or an energy such as 4.4 MeV ) of the atom or - depending on the context - of the atomic nucleus. A stoichiometric index, i.e. the number of such atoms in the molecule of a compound, can be written down on the right. In nuclear physics, the number of neutrons in the nucleus is occasionally given at the bottom right , for example in the JANIS 4 core data viewer of the NEA .

Core isomers are identified by the lower case letter “m” (for “metastable”) without a space after the mass number (to differentiate between several isomers of a core, the “m” can be followed by a number, e.g. 152m1 Eu ).


(partly also ),

in simplified notations

60 Co or Co-60,
110m Ag, 110 Ag m or Ag-110m.

In the simplified notation, the atomic number is omitted; it is already determined by the element symbol.

In older literature (before about 1960) one can also find mass numbers written at the top right , e.g. B. 27 Co 60 or Co 60 .

Classes of nuclides

The different nuclides of one and the same chemical element, i.e. with the same number of protons, are called isotopes of this element. Until the international introduction of the term “nuclide” (approx. 1950), “isotope” was also used confusingly in the general meaning of atomic type; sometimes this still happens today (2018).

Nuclides with the same mass number are called isobars (from Greek for “equally heavy”), while nuclides with the same number of neutrons are isotons . Isomers are nuclides whose atomic nuclei are in different internal states with the same charge and the same number of masses. Unstable nuclides are radioactive and are called radionuclides .

designation Characteristic Examples Remarks
Isotopes same number of protons
Isotones same number of neutrons
Isobars same mass number see beta decay
Mirror cores Neutron number and proton number swapped Special case of the isobars
Isomers different inner states only long-lived states

There are 245 nuclides in nature, which according to the current state of knowledge are considered stable , and about 80 radionuclides. Over 3000 more radionuclides were artificially generated. In the case of some nuclides traditionally regarded as stable, the half-life is so long that their decay has only recently been discovered or is still being sought in experiments. As a result, the number of nuclides considered stable can decrease over time.

Nuclide maps give an overview of mass numbers, proton and neutron numbers and mostly also types of decay and half-lives of the known nuclides.

See also

Web links

Individual evidence

  1. A. D. McNaught, A. Wilkinson: nuclide . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . 2nd Edition. Blackwell Scientific Publications, Oxford 1997, ISBN 0-9678550-9-8 , doi : 10.1351 / goldbook.N04257 (English, .html corrected version (XML; 2006–) created by M. Nic, J. Jirat, B. Kosata; with updates from A. Jenkins -).
  2. ^ Truman Paul Kohman: Proposed New Word: Nuclide. In: American Journal of Physics Vol. 15, No. 4, 1947, pp. 356-357, doi: 10.1119 / 1.1990965 .
  3. ^ Samuel Glasstone, Milton C. Edlund: The elements of nuclear reactor theory . MacMillan, London 1952, pp. VII, 416 . P. 3.
  4. a b Standard DIN 1338: Formula notation and formula set. March 2011. p. 8, section 3.5 Atomic physics and chemical information on the symbols of the elements.
  5. Janis 4 - Java-based Nuclear Data Information System.
  6. Standard DIN 6814-4: Terms in radiological technology - Part 4: Radioactivity. October 2006. p. 13, Appendix A Explanations on the notation of nuclides.
  7. ^ Symbols, Units, Nomenclature and Fundamental Constants in Physics. (PDF) IUPAP , 1987, p. 9 , accessed on March 10, 2015 (English).
  8. Nudat database
  9. ^ J. Magill, G. Pfennig, R. Dreher, Z. Sóti: Karlsruher Nuklidkarte. 8th edition. Nucleonica GmbH, Eggenstein-Leopoldshafen 2012, ISBN 92-79-02431-0 (wall map) or ISBN 978-3-00-038392-2 (folding map), ISBN 92-79-02175-3 (accompanying brochure).