How do nuclear forces and electric repulsion affect the stability of a heavy nucleus?

The stability of a heavy nucleus is determined by the competition between the short-range, attractive strong nuclear force and the long-range, repulsive Coulomb force between protons.31

• Strong Nuclear Force: This attractive force acts only between the closest neighboring nucleons (protons and neutrons). It provides the cohesion necessary to hold the nucleus together against the disruptive effects of electrostatic repulsion.12
• Coulomb Repulsion: Because protons are positively charged, they exert a long-range repulsive force on one another. As the number of protons in a nucleus increases, this repulsion grows, acting to destabilize the nucleus.1

In heavy nuclei, the balance between these forces becomes precarious. To maintain relative stability as the number of nucleons increases, the nucleus requires an excess of neutrons to "dilute" the proton-to-proton repulsion. If a heavy nucleus is deformed, the Coulomb repulsion can eventually overcome the surface tension generated by the strong force, leading to nuclear fission, where the nucleus splits into two smaller, more stable fragments.1