Isobars
Nuclides of different chemical elements that share the exact same mass number A (total number of nucleons) while having different atomic numbers Z.
Governing formula
A = Z + N = Constant
SI unit
Dimensionless Species
In depth
Isobars have different numbers of protons and neutrons (different Z and N), belonging to different chemical elements, but share nearly identical mass numbers. Beta decay transitions parent nuclides into daughter isobars.
Examples in the real world
Carbon-14 (Z=6, A=14) and Nitrogen-14 (Z=7, A=14) serving as nuclear isobars related by beta-minus decay.