NUCLEAR MODEL

any of several theoretical descriptions of the structure and function of atomic nuclei (the positively charged, dense cores of atoms). Each of the models is based on a plausible analogy that correlates a large amount of information and enables predictions of the properties of nuclei. Nuclear models can be classified into two main groups. In those of the first group, called independent-particle models, the main assumption is that little or no interaction occurs between the individual particles that constitute nuclei; each proton and neutron moves in its own orbit and behaves as if the other nuclear particles were passive participants. The shell nuclear model (q.v.) and its variations fall into this group. In a second group, called strong-interaction, or statistical models, the main assumption is that the protons and neutrons are mutually coupled to each other and behave cooperatively in a way that reflects the short-ranged strong nuclear force between them. The liquid-drop model and compound-nucleus model (qq.v.) are examples of this group. Other nuclear models incorporate aspects of both groups, such as the collective model (q.v.), which is a combination of the shell model and the liquid-drop model.