Thermodynamical Models of Multifragmentation in Nuclear Systems.

Information and nucleation theories are used to build models of nuclear fragmentation in the context of a nuclear phase transition. I begin with a brief review of heavy-ion nuclear physics and a discussion of the different phases of nuclear matter. Next I look at combinatorics as it pertains to the fragmentation problem and discuss the use of weight functions and entropy. I derive the energy of a heated nuclear medium using the liquid drop model of Myers and Swiatecki as a basis. The energy is dependent on both the temperature and density of the system. The density can be related to the temperature through the coexistence curves, which are derived from an equation of state based on a Skyrme potential. Together, the energy and equation of state allow me to investigate fluctuations. Next I develop two models, beginning with a brief discussion of the general principles of thermodynamics upon which the models are founded and following with a derivation of the relevant equations. The models are used to calculate the size of fluctuations in the systems of interest; these are on the order of 2-30%. I also calculate multifragmentation yields and investigate the effects of varying different aspects of the models. Temperature plays a crucial role in determining the yields, as does the presence of particle excitations. In calculating the Coulomb energy one must be sure to include the effects of the gas phase. I close with a comparison of yields calculated using information theory with those from recent data. As expected the results indicate that further refinement of the models is necessary, and I identify what some of the most important refinements might be.