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Two
Two nuclide
A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state.
The word ''nuclide'' was coined by Truman ...
s are isotones if they have the same neutron number
The neutron number, symbol ''N'', is the number of neutrons in a nuclide.
Atomic number (proton number) plus neutron number equals mass number: . The difference between the neutron number and the atomic number is known as the neutron excess: . ...
''N'', but different proton number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
''Z''. For example, boron-12
Boron (5B) naturally occurs as isotopes and , the latter of which makes up about 80% of natural boron. There are 13 radioisotopes that have been discovered, with mass numbers from 7 to 21, all with short half-lives, the longest being that of , ...
and carbon-13 nuclei both contain 7 neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s, and so are isotones. Similarly, 36S, 37Cl, 38Ar, 39K, and 40Ca nuclei are all isotones of 20 because they all contain 20 neutrons. Despite its similarity to the Greek for "same stretching", the term was formed by the German physicist K. Guggenheimer K is the eleventh letter of the Latin alphabet.
K may also refer to:
General uses
* K (programming language), an array processing language developed by Arthur Whitney and commercialized by Kx Systems
* K (cider), a British draft cider manufact ...
by changing the "p" in "isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
" from "p" for "proton" to "n" for "neutron".
The largest numbers of observationally stable nuclides exist for isotones 50 (five: 86Kr, 88Sr, 89Y, 90Zr, 92Mo) and 82 (six: 138Ba, 139La, 140Ce, 141Pr, 142Nd, 144Sm). Neutron number
The neutron number, symbol ''N'', is the number of neutrons in a nuclide.
Atomic number (proton number) plus neutron number equals mass number: . The difference between the neutron number and the atomic number is known as the neutron excess: . ...
s for which there are no stable isotones are 19, 21, 35, 39, 45, 61, 89, 115, 123, and 127 or more. In contrast, the proton number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
s for which there are no stable isotopes are 43, 61, and 83 or more.via :File:NuclideMap_stitched.png; note also 
Isotopes of bismuth
Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as . Although bismuth-209 is now known to be unstable, it h ...
This is related to nuclear magic numbers, the number of nucleons forming complete shells within the nucleus, e.g. 2, 8, 20, 28, 50, 82, and 126. No more than one stable nuclide has the same odd neutron number, except for 1 (2H and 3He), 5 (9Be and 10B), 7 (13C and 14N), 55 (97Mo and 99Ru), and 107 (179Hf and 180mTa). Odd neutron numbers for which there is a stable nuclide and a primordial
Primordial may refer to:
* Primordial era, an era after the Big Bang. See Chronology of the universe
* Primordial sea (a.k.a. primordial ocean, ooze or soup). See Abiogenesis
* Primordial nuclide, nuclides, a few radioactive, that formed before ...
radionuclide
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...
are 27 (50V), 65 (113Cd), 81 (138La), 85 (147Sm), and 105 (176Lu). Neutron numbers for which there are two primordial radionuclides are 88 (151Eu and 152Gd) and 112 (187Re and 190Pt).
See also
*Isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s are nuclides having the same number of protons
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
: e.g. carbon-12 and carbon-13.
* Isobars are nuclides having the same mass number (i.e. sum of protons plus neutrons): e.g. carbon-12 and boron-12.
* Nuclear isomers are different excited states of the same type of nucleus. A transition from one isomer to another is accompanied by emission or absorption of a gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
, or the process of internal conversion. (Not to be confused with chemical isomers.)
Notes
{{Authority control Nuclear physics