Isobar (nuclide)

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons.

While the nuclei of these nuclides all contain 40 nucleons, they contain varying numbers of protons and neutrons.

For odd A, it is admitted that δ = 0 and the mass dependence on Z is convex (or on N or N − Z, it does not matter for a constant A).

In both aforementioned cases, a heavier nucleus decays to its lighter isobar.

This effect is also predicted (qualitatively) by other nuclear models and has important consequences.

Two observationally stable isobars exist for 36, 40, 46, 50, 54, 58, 64, 70, 74, 80, 84, 86, 92, 94, 96, 98, 102, 104, 106, 108, 110, 112, 114, 120, 122, 123, 124, 126, 132, 134, 136, 138, 142, 154, 156, 158, 160, 162, 164, 168, 170, 176, 180 (including a meta state), 192, 196, 198 and 204.

In this chart of nuclides , isobars occur along diagonal lines running from the lower right to upper left. The line of beta stability includes the observationally stable nuclides shown in black; disconnected 'islands' are a consequence of the Mattauch isobar rule .