Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session J8: Minisymposium: Nuclei and Nuclear Matter at Non-Normal Density II |
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Sponsoring Units: DNP Chair: William Lynch, Michigan State University Room: Hyatt Regency Dallas Cumberland A |
Sunday, April 23, 2006 1:15PM - 1:51PM |
J8.00001: Mechanism of Isospin Equilibration in Semi-Peripheral Heavy Ion Reactions Invited Speaker: The BUU formalism with the inclusion of fluctuations was used to study a mechanism of isospin equilibration in semi-peripheral collisions of heavy ions close to the Fermi energy. In order to investigate the density dependence of the asymmetry term in the nuclear equation of state (i.e. the asy-stiffness of the equation of state) the calculations with different parametrization of this term were performed. It has been found that the low density interface between the interacting nuclei which develops in semi-peripheral collisions plays an important role in controlling the currents of neutrons and protons. The isospin transport is affected by an interplay between drift and diffusion being driven by differences in N/Z ratio and by density gradients. Both, the drift and the diffusion are sensitive to the asy-stiffness of the nuclear equation of state. A study of the isospin transport ratio shows that the experiment seems to favor a more asy-stiff equation of state and that a more asy-soft equation leads to a larger isospin equilibration. We may conclude that the charge equilibration measurements for semi-peripheral collisions provide an effective tool to investigate the properties of asymmetric nuclear matter. \newline \newline In collaboration with Massimo Di Toro, Maria Colonna, and Virgil Baran, LNS, Catania, Italy; and Hermann Wolter, University of Munich, Munich, Germany. [Preview Abstract] |
Sunday, April 23, 2006 1:51PM - 2:03PM |
J8.00002: Constraining properties of neutron stars with heavy-ion reactions Bao-An Li, Lie-Wen Chen, Che Ming Ko, Andrew W. Steiner Nuclear reactions induced by stable and/or radioactive neutron- rich nuclei provide the opportunity to pin down the equation of state of neutron-rich matter, especially the density ($\rho$) dependence of its isospin-dependent part, i.e., the nuclear symmetry energy $E_{\rm sym}$. A conservative constraint, $32 (\rho /\rho_{0})^{0.7} < E_{\rm sym}(\rho ) < 32(\rho /\rho _ {0})^{1.1}$, around the nuclear matter saturation density $\rho_0$ has recently been obtained from the isospin diffusion data in intermediate energy heavy-ion collisions. We review this exciting result and discuss its consequences and implications on nuclear effective interactions, radii and cooling mechanisms of neutron stars. [Preview Abstract] |
Sunday, April 23, 2006 2:03PM - 2:15PM |
J8.00003: Density dependence of the symmetry energy in the equation of state of asymmetric nuclear matter D.V. Shetty, S.J. Yennello, G.A. Souliotis The density dependence of the symmetry energy is an important ingredient in the equation of state of asymmetric nuclear mater. This currently unknown quantity is key to understanding the structure of systems as diverse as the atomic nuclei and neutron stars. Theoretical calculations predict wide variety of different forms of the density dependence of the symmetry energy. Results from various different measurements constraining this dependence will be presented. [Preview Abstract] |
Sunday, April 23, 2006 2:15PM - 2:27PM |
J8.00004: Nucleon Diffusion Observables in heavy ion reactions ManYee Tsang The study in heavy ion collision in the past years has focused on the understanding of the properties of bulk nuclear matter at densities above and below the saturation density. One promising observable to study the density dependence of the symmetry energy term in the nuclear Equation of State is the isospin diffusion. The idea is that the symmetry term in the nuclear EOS acts as the driving force that ``transports'' neutron and/or protons between the projectile and target during the multifragmentation process The isospin transport observable constructed with the isoscaling parameters has been used to constraint the equation of state which describes the dynamics of heavy ion reactions. In this talk, we will explore other observables that can be used to construct the isospin transport ratios. This work is supported by the National Science Foundation under Grant Number PHY-01-10253 [Preview Abstract] |
Sunday, April 23, 2006 2:27PM - 2:39PM |
J8.00005: Studying the symmetry energy of excited projectile-like sources August L. Keksis, M. Veselsky, G.A. Souliotis, E. Bell, J. Garey, M. Jandel, S. Parketon, C. Richers, A. Ruangma, D.V. Shetty, E.M. Winchester, S.J. Yennello Quasiprojectile, or projectile like, sources were reconstructed from the reactions 32 {\&} 45 MeV/nucleon 40Ar, 40Ca {\&} 48Ca on 112Sn {\&} 124Sn. The technique of isoscaling was used on the isotopic yields from these sources to determine the isoscaling parameter alpha. Alpha was also determined from the isotopic yields created by a hybrid model, which uses the Deep Inelastic Transfer, DIT, code to simulate the interaction stage and the Statistical Multifragmentation Model, SMM, to simulate the breakup stage of these quasiprojectile sources. The experimental results were compared to the theoretical results for various parameterizations of the symmetry energy used by the model. [Preview Abstract] |
Sunday, April 23, 2006 2:39PM - 2:51PM |
J8.00006: Exploring the Evolution of the Symmetry Energy of Hot fragments from the Compound Nucleus towards Bulk Multifragmentation G.A. Souliotis, A.S. Botvina, D.V. Shetty, A.L. Keksis, E. Bell, M. Jandel, M. Veselsky, S.J. Yennello High-resolution mass spectrometric data on the isotopic distributions of projectile-like fragments (heavy IMFs and heavy residues) from peripheral collisions of heavy neutron-rich beams (86Kr and 64Ni at 25MeV/nucleon) on a variety of targets are systematically compared with calculations of a hybrid model appropriate for this energy regime. The model consists of a well-tested deep-inelastic transfer model (DIT) for the dynamical stage of the collision and the latest version of the Statistical Multifragmentation model (SMM05) for the deexcitation stage. SMM05 allows the variation of the symmetry energy of hot primary fragments as a function of excitation energy (E*/A). The comparisons point to a gradual evolution (a linear decrease - to first approximation) of the symmetry energy coefficient of the binding energy from $\sim$25MeV/nucleon around E*/A=2 MeV/nucleon and below (essentially characterizing the compound nucleus regime) towards $\sim$15 MeV/nucleon at E*/A~4 MeV/nucleon (corresponding to mulk multifragmentation). Comparison of the present results with recent multifragmentation studies will be presented. Consequences of the observed gradual decrease of the symmetry energy to the distribution of hot exotic nuclei in the multifragmentation of neutron-rich systems and in supernova environments will be discussed. [Preview Abstract] |
Sunday, April 23, 2006 2:51PM - 3:03PM |
J8.00007: Neutron-Proton Transverse Emission Studies as a Signature of the Asymmetry Term of the Nuclear EOS Michael Famiano, William Lynch, Tsang Betty, Lee Sobotka, Robert Charity, Komarov Sergei, Andrew Rogers Neutron and proton transverse emission ratios are studied from the reactions $^{124}$Sn+${124}$Sn and $^{112}$Sn+$^{112}$Sn at 50 MeV/A as a signature of the density dependence of the asymmetry term of the nuclear EOS. Transverse neutron-proton emission ratios are compared to t/$^{3}$He ratios in the same framework. Results are compared to predictions from transport calculations, and future experiments are discussed. [Preview Abstract] |
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