Four topics in theoretical physics; nuclear stopping power, heavy ion delta excitation, a Dirac spin symmetry, and classical scattering on an extended magnetic monopole

This thesis consists of four separate sections. The first develops a simple model of nuclear stopping power and compares the model predictions with another theoretical model and experimental observations. The second section is devoted to a phenomenological description of delta excitation in heavy ion charge exchange collisions based on a microscopic nucleon-delta potential. Some ambiguities in the formalism are discussed and clarified when possible. A comparison with experiment is made. The third section explores a spin symmetry in the Dirac equation in the presence of equal vector and scalar potentials. Implications for Dirac optical models of nucleon-nucleus scattering are discussed. The last section deals with the scattering of charged particles on extended magnetic monopoles using a formalism that maintains conservation of angular momentum while allowing violation of charge conservation.