For each isobar, there are between zero and three stable nuclides, dependent upon the number of mass minima, one or two. For the purposes of this graph, those nuclides which have very long halflives are classified as being stable. Many isobars with odd Atomic Weight, A, have only one stable isobar; whereas only those with even A can have two or three. If there are three 'stable' isobars, one of them will actually be unstable but with a very long halflife.

See Even Mass Beta Stability. and See Odd Mass Beta Stability.

There are no stable isobars of A=5 or 8, corresponding to Li-5 and He-5, or Li-8, Be-8 and B-8, because of alpha decay in these nuclides.

Note the distinctive alternate comb shape, due to the odd/even effect.

All isobars would have at least one stable member if it were not for alpha decay in some of them. Beryllium-8, which might be expected to be stable lying on the line of stability, is highly unstable, decaying with a half life of much less than 0.001 picosecond into two helium-4 nuclei. The fusion reactions within stars would proceed very much more rapidly and explosively if beryllium-8 did not have such a short existence.

The A=5 and A=8 isobars are the only isobars below A=211 for which there are no stable nuclides. Above A=209, there are very few isobars with stable members because of alpha decay, and the few that do exist are actually unstable with long halflives.