Isotone

This article is about a concept in nuclear physics. For biochemistry, seeIsotonicity.For the mathematical meaning, seemonotonic function.

Nuclide half-lives colorcoded

Innuclear physics,isotonesarenucleidesof the differentchemical elements.They have the sameneutron number,but differentnucleon number(mass number) due to differentproton number(atomic number). For example,boron-12andcarbon-13nuclei both contain 7neutrons,and so are isotones. Similarly,³⁶S,³⁷Cl,³⁸Ar,³⁹K, and⁴⁰Ca nuclei are all isotones of 20 because they all contain 20 neutrons.

The term derives fromGreekἴσος (isos)'same' andτόνος (tonos)'tension' metaphorically suggesting the uniformity in one property (neutron count). It was formed by the German physicistK. Guggenheimerby changing the "p" in "isotope"from" p "for" proton "to" n "for" neutron ".

The largest numbers ofobservationally stablenuclides exist for isotones 50 (five:⁸⁶Kr,⁸⁸Sr,⁸⁹Y,⁹⁰Zr,⁹²Mo – noting also theprimordialradionuclide⁸⁷Rb) and 82 (six:¹³⁸Ba,¹³⁹La,¹⁴⁰Ce,¹⁴¹Pr,¹⁴²Nd,¹⁴⁴Sm – noting also the primordial radionuclide¹³⁶Xe).Neutron numbersfor which there are no stable isotones are 19, 21, 35, 39, 45, 61, 89, 115, 123, and 127 or more (though 21, 142, 143, 146, and perhaps 150 have primordial radionuclides). In contrast, theproton numbersfor which there are no stable isotopes are43,61,and83or more (83,90,92,and perhaps94have primordial radionuclides).This is related to nuclearmagic numbers,the number ofnucleonsforming completeshellswithin the nucleus, e.g. 2, 8, 20, 28, 50, 82, and 126. No more than one observationally stable nuclide has the same odd neutron number, except for 1 (²H and³He), 5 (⁹Be and¹⁰B), 7 (¹³C and¹⁴N), 55 (⁹⁷Mo and⁹⁹Ru), and 107 (¹⁷⁹Hf and^180mTa). In contrast, all even neutron numbers from 6 to 124, except 84 and 86, have at least two observationally stable nuclides. Neutron numbers for which there is a stable nuclide and a primordial radionuclide are 27 (⁵⁰V), 65 (¹¹³Cd), 81 (¹³⁸La), 84 (¹⁴⁴Nd), 85 (¹⁴⁷Sm), 86 (¹⁴⁸Sm), 105 (¹⁷⁶Lu), and 126 (²⁰⁹Bi). Neutron numbers for which there are two primordial radionuclides are 88 (¹⁵¹Eu and¹⁵²Gd) and 112 (¹⁸⁷Re and¹⁹⁰Pt).

The neutron numbers which have only onestable nuclide(compare:monoisotopic elementfor theproton numbers) are: 0, 2, 3, 4, 9, 11, 13, 15, 17, 23, 25, 27, 29, 31, 33, 37, 41, 43, 47, 49, 51, 53, 57, 59, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 84, 85, 86, 87, 91, 93, 95, 97, 99, 101, 103, 105, 109, 111, 113, 117, 119, 121, 125, 126, and the neutron numbers which have only one significant naturally-abundant nuclide (compare:mononuclidic elementfor theproton numbers) are: 0, 2, 3, 4, 9, 11, 13, 15, 17, 21, 23, 25, 29, 31, 33, 37, 41, 43, 47, 49, 51, 53, 57, 59, 63, 67, 69, 71, 73, 75, 77, 79, 83, 87, 91, 93, 95, 97, 99, 101, 103, 109, 111, 113, 117, 119, 121, 125, 142, 143, 146.

See also

• Isotopesare nuclides having the same number ofprotons:e.g. carbon-12 and carbon-13.
• Isobarsare nuclides having the samemass number(i.e. sum of protons plus neutrons): e.g. carbon-12 and boron-12.
• Nuclear isomersare different excited states of the same type of nucleus. A transition from one isomer to another is accompanied by emission or absorption of agamma ray,or the process ofinternal conversion.(Not to be confused withchemical isomers.)