Nuclear Potential

A nucleus packs several protons together within a volume only about $10^{-15}$ m across. Since all protons carry the same positive charge, the electrostatic (coulombic) repulsion between any two protons at that separation is large. If coulombic repulsion were the only force acting inside the nucleus, the protons would fly apart and no nucleus could exist at all -- yet nuclei plainly do exist, and are often extremely stable.

This tells us that a second, purely attractive force must also be at work inside the nucleus, strong enough to overcome the coulombic repulsion between protons at nuclear distances. This is the (strong) nuclear force, and it has a distinctive character: it acts over an extremely short range, essentially limited to the interior of the nucleus, and unlike the electrostatic force, it is completely independent of the charge on the nucleons involved. That means the strength of the attraction between two protons (p-p), between two neutrons (n-n), and between a proton and a neutron (p-n) are all equal. Collectively, these short-range p-p, n-n and p-n attractions constitute what is called the …