Nuclear Stability
A measure of a nuclide's resistance to spontaneous radioactive decay, determined by the balance between nuclear strong attraction and proton Coulomb repulsion.
Governing formula
N/Z ≈ 1 (for light nuclei), N/Z ≈ 1.5 (for heavy nuclei)
SI unit
Dimensionless N/Z Ratio
In depth
Plotting neutron number N against proton number Z outlines the 'Band of Stability'. Light stable nuclei prefer N = Z, whereas heavy stable nuclei require extra neutrons (N/Z ~ 1.5) to dilute electrostatic repulsion between protons.
Examples in the real world
Lead-208 (82 protons, 126 neutrons) forming the heaviest naturally occurring stable double-magic nuclide.