Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session I8: Minisymposium: Nuclei and Nuclear Matter at Non-Normal Density I |
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Sponsoring Units: DNP Chair: Sherry J Yennello Texas A&M University Room: Hyatt Regency Dallas Cumberland A |
Sunday, April 23, 2006 10:30AM - 11:06AM |
I8.00001: Low Density Clustering in Near Fermi-Energy Collisions Invited Speaker: The nucleon collisions and thermal shock which occurs during near Fermi-Energy heavy ion collisions leads naturally to the production of nucleonic matter at sub-normal densities. Experiments suggest that average nuclear densities as low as $\sim $0.4 times normal density are reached. However there are large density fluctuations throughout the collision. In the early stages of the reaction the fluctuations are dynamically induced and lead to a decoupling of the momentum sphere of the initial participant matter from that of the remaining nucleons. This important feature of the dynamically evolving system manifests itself as kinematic differences between the early emitted light (gas) ejectiles and the remaining (liquid) matter. As the system relaxes toward equilibrium the two momentum spheres become more and more similar. Eventually the distinction is lost. The original kinematic differences can be exploited to probe the size and properties of the initial interaction zone, Such analyses reveal a large degree of alpha particle clustering at low densities. For densities near 0.025 normal density, temperature and density dependent symmetry energy coefficients have been derived from isoscaling analyses of the yields of nuclei with A {\#} 4 produced in the collisions of 35A MeV $^{64}$Zn + $^{92}$Mo and $^{197}$Au. The symmetry energies are much larger than those obtained in mean field calculations. They are in much better agreement with results of a recently proposed Virial Equation of State calculation. [Preview Abstract] |
Sunday, April 23, 2006 11:06AM - 11:18AM |
I8.00002: Breakup Densities of Hot Nuclei. Vic Viola Breakup densities of hot $^{197}$Au-like residues have been deduced from the systematic trends of Coulomb parameters required to fit intermediate-mass-fragment kinetic-energy spectra. The results indicate emission from nuclei near normal nuclear density below an excitation energy E*/A $\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $ 2 MeV, followed by a gradual decrease to a near-constant value of $\rho $/$\rho _{0} \quad \sim $ 3 for E*/A $\mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $ 5 MeV. Temperatures derived from these data with a density-dependent Fermi-gas model yield a nuclear caloric curve that is generally consistent with those derived from isotope ratios. [Preview Abstract] |
Sunday, April 23, 2006 11:18AM - 11:30AM |
I8.00003: Constructing the Phase Diagram of Infinite Nuclear Matter Luciano Moretto, Larry Phair, Jim Elliott, Kyrill Bugaev The low-energy portion of the phase diagram of finite nuclear matter has been obtained. This was achieved by analyzing the fragmentation yields of the EOS and ISiS collaborations using Fisher's droplet formalism corrected for finite size effects. The critical exponents, the surface energy coefficient, and the critical temperature associated with the liquid-vapor phase transition have all been extracted from the data. Using the ideal gas law, one can construct pressure-temperature and temperature-density coexistence curves for infinite nuclear matter. At much lower energies, compound nucleus reactions are also described by the Fisher formalism when one considers the ensemble average of first-chance emission of rare particles. A pressure-temperature correlation inferred from the mean emission times (measured by the ISiS collaboration) agrees very well with the pressure-temperature correlation inferred from the fragment yields. [Preview Abstract] |
Sunday, April 23, 2006 11:30AM - 11:42AM |
I8.00004: Cooling Dynamics in Multi-fragmentation processes William Lynch, T.X. Liu, M.J. van Goethem, X.D. Liu, R. Shomin, W.P. Tan, M.B. Tsang, G. Verde, A. Wagner, H.F. Xi, H.S. Xu, W.A. Friedman, S.R. Souza, R. Donangelo, B. Davin, Y. Larochelle, R.T. de Souza, V.E. Viola, R.J. Charity, L.G. Sobotka The energy spectra of the isotopes from Z=1-8 have been measured in the multifragmentation of Sn+Sn isotopes at E/A=50 MeV. Fragment energy spectra of neutron deficient isotopes are significantly more energetic than those of neutron rich isotopes of the same element. This trend is well beyond what can be expected for the bulk multi-fragmentation of an equilibrated system. It can be explained, however, if many of these fragments are evaporated from the surface of the system while it is expanding and cooling. [Preview Abstract] |
Sunday, April 23, 2006 11:42AM - 11:54AM |
I8.00005: Short timescale behavior of colliding heavy nuclei at intermediate energies Sylvie Hudan, Romualdo deSouza, Akira Ono Mid-peripheral collisions of two heavy-ions at intermediate energy are used to study the short-time scale behavior of colliding nuclei. The characteristics of clusters emitted by the excited projectile-like fragment (PLF$^{\ast })$ formed in such collisions allow the characterization of the system at relatively early times. In particular, alpha particles emitted from the PLF$^{\ast }$ exhibit a strong preference for emission towards the target-like fragment. The interplay of the initial deformation of the PLF$^{\ast }$ caused by the reaction, Coulomb proximity, and the rotation of the PLF$^{\ast }$ can result in the observed anisotropic angular distribution. A description of the collisions in the framework of antisymmetrized molecular dynamics calculations will be shown. [Preview Abstract] |
Sunday, April 23, 2006 11:54AM - 12:06PM |
I8.00006: Isotopic composition of the residues produced in the fragmentation of $^{124}$Xe and $^{136}$Xe projectiles Daniela Henzlova The evolution of the N/Z degree of freedom in the fragmenting system has become an important observable in investigations of the properties of nuclear systems under extreme temperatures and densities. With the use of the high-resolution magnetic spectrometer, the FRagment Separator (FRS), at GSI Darmstadt, the residues up to the heavy projectile, produced in the fragmentation of $^{124}$Xe and $^{136}$Xe projectiles in a lead target at 1AGeV, were isotopically identified. The full isotopic distributions and mean N/Z ratios measured in these reactions will be presented. The isotopic composition of the final residues reveals a clear sensitivity to the N/Z ratio of the projectile. The sensitivity of the final isotopic composition of the measured residues to the competing emission of light particles and more complex clusters during evaporation and to the thermal conditions at the freeze-out of the break-up stage is investigated. [Preview Abstract] |
Sunday, April 23, 2006 12:06PM - 12:18PM |
I8.00007: Reacceleration of the fragmentation residues in the reactions $^{197}$Au+$^{197}$Au/$^{27}$Al at 0.5 and 1 $A$ GeV Vladimir Henzl We present the results of the first experiments dedicated to the precise measurements of the longitudinal momenta of the projectile fragments in the reactions $^{197}$Au+$^{197}$Au at 0.5 and 1 $A$ GeV, and $^{197}$Au+$^{27}$Al at 0.5 $A$ GeV performed with the high-resolution magnetic spectrometer FRS at GSI-Darmstadt. It is observed, that projectile residues with masses above A$_{res} \quad >$ 150 produced in very peripheral collisions are decelerated in the reaction and follow the well established Morrissey systematic [1], however the mean velocities of the lighter residues level off, and progressively increase with decreasing mass and even reach a positive value with respect to the original projectile velocity (for A$_{res }<$ 85). The observed reacceleration phenomenon and its behavior with respect to the different beam energy and/or different collision geometry thus significantly improves our understanding of the spectator response to the participant blast which has been just recently theoretically predicted [2] and experimentally observed [3]. References: [1] D.J.Morrissey, Phys. Rev. C39, 460 (1989). [2] L.Shi, P.Danielewicz, and R.Lacey, Phys. Rev. C64, 034601 (2001). [3] M.V.Ricciardi et al., Phys. Rev. Lett. 90, 2123021 (2003). [Preview Abstract] |
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