Element Stability Proton (Z) v Neutron (N)

Element stability Proton (Z) v Neutron (N) number: From http://en.wikipedia.org/wiki/List_of_elements_by_stability_of_isotopes

Isotope half-lives. Note that the darker more stable isotope region departs from the line of protons (Z) = neutrons (N), as the element number Z becomes larger.