The Strong Nuclear Force and Binding Energy

It may seem strange that nuclei, being composed of positively charged protons and neutral neutrons packed very closely together, are able to exist. One might think that the large repulsive electrostatic forces between the protons should cause the nuclei of atoms to fly apart. Obviously, most nuclei are stable and thus there must exist some other force which binds them together. This force is known as the nuclear force and is an attractive force that acts between all nuclear particles at the short distances between them (about 2 x 10^-15 m). Within the nucleus, where the protons and neutrons are very close together, the nuclear force dominates the repulsive Coulomb force and holds the nucleus together.

One important illustration of the equivalence of mass and energy of Equation (13.2) has to do with what is called the binding energy of the nucleus. It is observed that the mass of any nucleus is always less than the sum of the masses of the individual constituent nucleons which make it up. The ``loss'' of mass which results when nucleons form a nucleus is attributed to a ``binding energy'', and is a measure of the strength of the strong nuclear force holding the nucleons together. In order to separate the nucleons, energy must be supplied to the nucleus. This is usually accomplished by bombarding the nucleus with high energy particles (atom smashing).