isotoni

Isotoni, in English isotones, are nuclides that have the same number of neutrons (N) but different numbers of protons (Z). Because the mass number is A = Z + N, isotones form families with different mass numbers along horizontal lines on the chart of nuclides.

On the chart of nuclides, isotones align along lines of constant N. This makes it possible to compare how changing the proton number while keeping N fixed influences nuclear properties such as binding energy, decay modes, and structure. The term reflects the biological-like idea of “equal neutrons” across a family of nuclides.

Examples illustrate common isotone chains. The N = 50 isotones include 90Zr, 92Mo, 94Ru, 96Pd, 98Cd, and 100Sn. Another well-known chain is N = 82, which includes 132Sn, 134Te, 136Xe, 138Ba, and 140Ce, among others. These chains show how nuclear properties evolve with increasing proton number while keeping neutron number constant. Some isotones are stable, while others are radioactive.

Isotones are used to study nuclear structure and the effects of neutron shells, including magic numbers, where nuclei exhibit greater stability. They complement related concepts such as isotopes (same Z, different N) and isobars (same A). Research on isotones helps test nuclear models, understand shell evolution, and explore trends in binding energy across the nuclear landscape.