TABLE OF CONTENTS A variety of early experiments demonstrated that the character of the nuclear force differed markedly from any previously encountered in classical physics. However, a quantitative description of the nuclear force has turned out to be elusive. As we learned from atomic physics, where the correct level structure was found only after the classical Coulomb interaction between the nucleus and the electrons was extended to the atomic domain through quantum mechanics, knowing the properties of a force is only the first step in developing a theory of structure. Although neutrons and protons were known to be the nuclear constituents, the absence of a fundamental understanding of the nuclear force made it difficult to determine the structure of the nucleus. It is not surprising therefore that, instead of a theory, phenomenological models of the nucleus were constructed to accommodate the many remarkable experimental findings. In the following, we describe only a few such models. We should also keep in mind that, unlike the case of atomic physics, most of these nuclear models were proposed to explain only limited aspects of the data, which is precisely what they do.
The liquid drop model of the nucleus was one of the earliest phenomenological successes constructed to account for the binding energy of a nucleus. As we have already discussed, experiments revealed that nuclei were essentially spherical objects, with sizes that could be characterized by radii proportional to A 1/3, which suggested that nuclear densities were almost...
