Fragment distributions resulting from $\mathrm{Au}+\mathrm{Au}$ collisions at an incident energy of $E/A=600\mathrm{MeV}$ are studied. From the measured fragment and neutron distributions the mass and the excitation energy of the decaying prefragments were determined. A temperature scale was derived from observed yield ratios of He and Li isotopes. The relation between this isotope temperature and the excitation energy of the system exhibits a behavior which is expected for a phase transition. The nuclear vapor regime takes over at an excitation energy of 10 MeV per nucleon, a temperature of 5 MeV, and may be characterized by a density of 0.15–0.3 normal nuclear density.

Using symmetric ${}^{112}\mathrm{S}\mathrm{n}+{}^{112}\mathrm{S}\mathrm{n}$, ${}^{124}\mathrm{S}\mathrm{n}+{}^{124}\mathrm{S}\mathrm{n}$ collisions as references, we probe isospin diffusion in peripheral asymmetric ${}^{112}\mathrm{S}\mathrm{n}+{}^{124}\mathrm{S}\mathrm{n}$, ${}^{124}\mathrm{S}\mathrm{n}+{}^{112}\mathrm{S}\mathrm{n}$ systems at an incident energy of $E/A=50\mathrm{M}\mathrm{e}\mathrm{V}$. Isoscaling analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state. DOI: http://dx.doi.org/10.1103/PhysRevLett.92.062701 © 2004 The American Physical Society

Directed and elliptic flows of neutrons and light-charged particles were measured for the reaction ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector (LAND), combined with parts of the CHIMERA multidetector, the ALADIN Time-of-flight Wall, and the Washington University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA was used for complementary measurements of the isotopic composition and flows of light-charged particles. From the comparison of the elliptic-flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value $\gamma =0.72\pm 0.19$ is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of suprasaturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

A three parameter scaling relationship between isotopic distributions for elements with $Z\le 8$ has been observed. This allows a simple description of the dependence of such distributions on the overall isospin of the system. This scaling law (termed isoscaling) applies for a variety of reaction mechanisms that are dominated by phase space, including evaporation, multifragmentation, and deeply inelastic scattering. The origins of this scaling behavior for the various reaction mechanisms are explained. For multifragmentation processes, the systematics is influenced by the density dependence of the asymmetry term of the equation of state.

Isotopic distributions for light particles and intermediate mass fragments have been measured for ${}^{112}\mathrm{Sn}{+}^{112}\mathrm{Sn}$, ${}^{112}\mathrm{Sn}{+}^{124}\mathrm{Sn}$, ${}^{124}\mathrm{Sn}{+}^{112}\mathrm{Sn}$, and ${}^{124}\mathrm{Sn}{+}^{124}\mathrm{Sn}$ collisions at $E/A=50\mathrm{}\mathrm{MeV}$. Isotope, isotone, and isobar yield ratios are utilized to estimate the isotopic composition of the gas phase at freeze-out. Analyses within the equilibrium limit imply that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei. These observations suggest that neutron diffusion is commensurate with or more rapid than fragment production.