Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. 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.

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Multi-fragment decays of 129 Xe, 197 Au, and 238 U projectiles in collisions with Be, C, Al, Cu, In, Au, and U targets at energies between E/A = 400 MeV and 1000 MeV have been studied with the ALADIN forward-spectrometer at SIS. By adding an array of 84 SiCsI(Tl) telescopes the solid-angle coverage of the setup was extended to θ lab = 16 • . This permitted the complete detection of fragments from the projectile-spectator source.The dominant feature of the systematic set of data is the Z bound universality that is obeyed by the fragment multiplicities and correlations. These observables are invariant with respect to the entrance channel if plotted as a function of Z bound , where Z bound is the sum of the atomic numbers Z i of all projectile fragments with Z i ≥ 2. No significant dependence on the bombarding energy nor on the target mass is observed. The dependence of the fragment multiplicity on the projectile mass follows a linear scaling law.The reasons for and the limits of the observed universality of spectator fragmentation are explored within the realm of the available data and with model studies. It is found that the universal properties should persist up to much higher bombarding energies than explored in this work and that they are consistent with universal features exhibited by the intranuclear cascade and statistical multifragmentation models.

Isotope, isotone and isobar yield ratios are utilized to obtain an estimate of the isotopic composition of the gas phase, i.e., the relative abundance of free neutrons and protons at breakup. Within the context of equilibrium calculations, these analyses indicate that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei.

Recent measurements of pre-equilibrium neutron and proton transverse emission from 112,124 Sn+ 112,124 Sn reactions at 50 MeV/A have been completed at the National Superconducting Cyclotron Laboratory. Free nucleon transverse emission ratios are compared to those of A=3 mirror nuclei. Comparisons are made to BUU transport calculations and conclusions concerning the density dependence of the asymmetry term of the nuclear equation-of-state at sub-nuclear densities are made. The double-ratio of neutron-proton ratios between two reactions is employed as a means of reducing first-order Coulomb effects and detector efficiency effects. Comparison to BUU model predictions indicate a density dependence of the asymmetry energy that is closer to a form in which the asymmety energy increases as the square root of the density for the density region studied. A coalescent-invariant analysis is introduced as a means of reducing suggested difficulties with cluster emission in total nucleon emission. Future experimentation is presented.PACS numbers: 25.70.Mn,21.65.+f,26.62.+c The nuclear symmetry energy increases the masses of nuclei with very different neutron and proton concentrations and limits the neutron concentration and maximum neutron number N of any element. In the interior regions of neutron stars, where neutrons may comprise over 90% of the matter, the symmetry energy may contribute the bulk of the pressure supporting the star [1]. The nuclear equation-of-state at densities of 0.5≤ ρ ρ0 ≤10 (where ρ 0 is the nuclear saturation density) governs many of the neutron star macroscopic properties, including radius, moment of inertia, core structure [2], cooling rates, and the possible collapse of a neutron star into a black hole [3,4,5].Constraints on the symmetry energy at sub-saturation density have been obtained from measurements of the diffusion of neutrons and protons between nuclei of different asymmetry δ = (N-Z)/(N+Z) in peripheral collisions [6,7]. (Here N and Z are the relevant neutron and proton number of the nuclei.) Measurements of nuclear masses, isovector collective excitations and neutron skin measurements may also provide constraints at densities less than ρ 0 . Nevertheless, the density dependence of the symmetry energy is not known well enough to constrain the relevant neutron star properties. Using an alternative approach to improve present constraints, new measurements of the ratios of neutron and proton spectra in central heavy ion collisions are presented and compared to transport theory calculations. These calculations display a strong sensitivity to the density dependence of the symmetry energy, from which additional contraints may ultimately be derived [8] Using proton and neutron densities calculated from the non-linear relativistic mean-field theories as inputs, the dynamics of nucleon-nucleon collisions are calcuated. These calculations utilize nucleonic mean field potentials corresponding to an equation-of-state that can be expressed (at zero temperature) in terms of the mean energy of a nuc...