isotone

[Alteration of ISOTOPE (with for replacing as though for).]

One of two or more atoms which display a constant difference A − Z between their mass number A and their atomic number Z. Thus, despite differences in the total number of nuclear constituents, the numbers of neutrons in the nuclei of isotones are the same. The numbers of naturally occurring isotones provide useful evidence concerning the stability of particular neutron configurations. For example, the relatively large number (six and seven, respectively) of naturally occurring 50- and 82-neutron isotones suggests that these nuclear configurations are especially stable. On the other hand, from the fact that most atoms with odd numbers of neutrons are anisotonic, one may conclude that odd-neutron configurations are relatively unstable. See also Nuclear structure.

One of several different nuclides having the same number of neutrons in their nuclei, but different mass numbers.

One of several nuclides having the same number of neutrons, but differing in number of protons in their nuclei.

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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. For example, Boron-12 and Carbon-13 both have 7 neutrons; S-36, Cl-37, Ar-38, K-39, Ca-40, these nuclei contain 20 neutrons each, etc. Isotones have a different number of protons

This is to be contrasted with

• Isotopes are nuclides having the same number of protons (Carbon-12 and Carbon-13)
• Isobars are nuclides having the same mass number; i.e. sum of protons plus neutrons; Carbon-12 and Boron-12. See Isobar (Contour line) for the meaning in the context of weather charts.
• 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.)

Etymology

The word "isotone" looks like Greek for "same stretching", but it actually is "isotope" with "p" for "proton" replaced by "n" for "neutron".

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