The Onset of Vaporization in GOLD-197 + GOLD-197 Collisions

Two bulk phase transitions exist in nuclear matter. At temperatures of the order of a few MeV up to a critical temperature of about 17 MeV, infinite neutral nuclear matter supports a mixed phase consisting of Fermi liquid droplets in coexistence with a nucleonic gas. At significantly higher temperatures of the order of 150 MeV, calculations within the standard model predict a deconfinement phase transition from hadronic matter to a quark-gluon plasma. One of the four major current thrusts in nuclear physics is the extraction of information about these basic phase transitions from nuclear collisions. Temperatures and densities relevant to the liquid gas phase transition can be momentarily attained in nuclear collisions at incident energies of E/A = 35-400 MeV. To search for the liquid -gas phase transition in a large system where signals of phase transitions are expected to be sharper, multifragment disintegrations in ^{197}Au + ^{197}Au collisions were investigated in this dissertation at incident energies of E/A = 100, 250 and 400 MeV. These measurements clearly indicate that the yields of intermediate mass fragments (IMF's; 3 <= Z <= 30) decrease significantly with the incident energy in central collisions, consistent with the onset of nuclear vaporization. These measurements were performed with an experimental array of considerable complexity, capable of providing considerable information about the dynamics of the collision. Measurements performed in this dissertation indicate the presence of a collective radial flow for central collisions that contain of the order of a third to a half of the total incident kinetic energy, thereby decreasing the energy available for thermal excitation. Measurements of the kinetic energy spectra also provide information about the mechanisms of energy deposition in peripheral collisions. Both fragment yields and energy spectra were compared to molecular dynamics calculations developed to predict these observations. These comparisons reveal significant shortcomings in these dynamical models.