Isotone

Nuclide halflives colorcoded. Neutron numbers for which there are no stable isotones include 19, 21, 35, 39, 45, 61, 71, 84, 89, 109, 115, 123, and 127 and up. In contrast, the only proton numbers for which there are no stable isotopes are 43, 61, and 83 and up.

This article is about a concept in nuclear physics. For biochemistry see isotonic. For the mathematical meaning, see monotone.

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. Despite its similarity to the Greek for "same stretching", the term was formed by replacing the "p" in "isotope" with "n" for "neutron".

See also

• Isotopes are nuclides having the same number of protons; 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, or the process of internal conversion. (Not to be confused with chemical isomers.)