Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session DD: Heavy Ion / Rare Isotope Reactions |
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Sponsoring Units: DNP Chair: B.M. Sherrill, National Superconducting Cyclotron Laboratory at Michigan State University Room: Gaylord Opryland Hermitage A |
Friday, October 27, 2006 2:00PM - 2:12PM |
DD.00001: Simulations of the ancillary silicon array for TIGRESS M. Porter-Peden, F. Sarazin, L. Erikson A highly segmented and compact silicon array is currently being designed to complement the TIGRESS gamma-ray array (TRIUMF-ISAC Gamma-ray Escape-Suppressed Spectrometer) at ISAC2. The silicon array fits in the inner volume of TIGRESS and is expected to be used in both Coulomb excitation and transfer reaction experiments. Simulations using GEANT4 are underway to optimize its configuration. At present, the layout of the array consists in two boxes made of four $\Delta$E-E telescopes in the forward angles and four E detectors in the backward angles. A CD detector covers the extreme backward angle. Simulations of a few case-experiments will be presented. This work is supported by the US department of Energy through Grant/Contract No. DE-FG03-93ER40789. [Preview Abstract] |
Friday, October 27, 2006 2:12PM - 2:24PM |
DD.00002: Symmetry Energy of Hot Heavy Fragments Produced in the Multifragmentation of Neutron-Rich Systems at Fermi Energies G.A. Souliotis, A.S. Botvina, D.V. Shetty, A.L. Keksis, M. Veselsky, S.J. Yennello Mass spectrometric data of the isotopic distributions of heavy projectile-like fragments (heavy IMFs: A=20-40 and heavy residues: A=40-60) from peripheral collisions of heavy neutron-rich beams on a variety of targets are systematically compared with model calculations appropriate for this energy regime (part of the data are presented in [1]). The model approach consists of a deep-inelastic transfer code (DIT) for the dynamical stage of the collision and the Statistical Multifragmentation model (SMM05) for the de-excitation stage. The comparisons indicate a gradual evolution of the symmetry energy coefficient of the binding energy of the hot primary fragments from 25 MeV around E*/A=2 MeV and below (compound nucleus regime) towards 15 MeV at about E*/A=4 MeV and above (bulk multifragmentation). The robustness of the above result to the input parameters of the calculation is explored in detail. Comparison of our calculations with literature data on heavy fragments at higher energies will also 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 core-collapse supernova environments will be discussed. [1] G.A. Souliotis et al, nucl-ex/0603006. [Preview Abstract] |
Friday, October 27, 2006 2:24PM - 2:36PM |
DD.00003: Symmetry energy, temperature, density and isoscaling parameter as a function of excitation energy in A $\sim$ 100 mass region D.V. Shetty, S.J. Yennello, G.A. Souliotis, A.L. Keksis, S.N. Soisson, B.C. Stein, S. Wuenschel Understanding the correlation between the temperature, density and symmetry energy of a nuclear system as it evolves with excitation energy is important for constructing the nuclear matter equation of state. Experimentally, the multifragmentation reaction provides the best possible means of studying nuclear matter at temperatures, densities and isospin (neutron$-$to$-$proton asymmetry) away from those of normal nuclear matter. Results from recent studies aimed at understanding this correlation will be presented; their relevance to the density dependence of the symmetry energy will be emphasized. [Preview Abstract] |
Friday, October 27, 2006 2:36PM - 2:48PM |
DD.00004: 3-D unrestricted TDHF fusion studies of spherical and deformed nuclei Sait Umar, Volker Oberacker We utilize the Time-Dependent Hartree-Fock (TDHF) method to calculate heavy-ion fusion cross sections for stable and neutron-rich nuclei. The calculations involve modern Skyrme forces, including all time-odd terms in the energy density functional, and are carried out on a large 3-D Cartesian lattice using the Basis-Spline collocation method. One of the appealing features of TDHF is that one can follow the time-evolution of the nuclear density distributions, resulting in either fusion or deep-inelastic reactions. We have studied both stable and neutron rich systems, such as the spherical systems $^{16}O+^{16}O$ and $^{16}O+^{28}O$ [Ref.1], and the spherical plus deformed system $^{16}O+^{22}Ne$ [Ref.2]. Within the framework of density-constrained TDHF [Ref.3], we have found a method to deduce the corresponding heavy-ion interaction potentials for these systems. Most recently, the TDHF code has been implemented on a massively parallel supercomputer; first results for the neutron-rich system $^{132}Sn+^{64}Ni$ will be presented. 1. A.S. Umar and V.E. Oberacker, Phys. Rev. C73, 054607 (2006) 2. A.S. Umar and V.E. Oberacker, nucl-th/0604010 3. A.S. Umar and V.E. Oberacker, nucl-th/0605084 [Preview Abstract] |
Friday, October 27, 2006 2:48PM - 3:00PM |
DD.00005: Neutron transfer and flow in reactions between heavy neutron-rich nuclei. Dan Shapira, Felix J. Liang, Carl J. Gross, Robert L. Varner, James R. Beene Two Step WKB calcualtions of nucleus nucleus capture were carried out. In our calcualtions we nvestigate the possibility of enhanced capture cross sectins for neutron rich heavy nuclei. The model calculation uses a systematic potential [1] that incorporates the effect of barrier distributions due to excitation and deformation in the entrance channel. Neutron transfer is treated in a semiclassical approximation [2][3]. The transfer form factor used in neutron transfer saturates at an internuclear distance where where neutron can flow freely between the two nuclear centers [4]. \newline \newline [1] K. Siwek-Wilczynska and J. Wilczynski Phys. Rev. {\bf C69}, 024611 (2004). \newline [2] V. Yu. Denisov Eur. Phys. {\bf A7}, 87 (2000). \newline [3] V. I. Zagrebaev Phys. Rev. {\bf C7}, 061601R (2003). \newline [4] P.H. Stelson Phys. Lett. {\bf B205}, 190 (1988). [Preview Abstract] |
Friday, October 27, 2006 3:00PM - 3:12PM |
DD.00006: Total cross sections for nucleon elastic scattering from stable and unstable nuclei at energies between 10 MeV and 1 GeV H.F. Arellano, H.V. von Geramb, M. Girod Parameter-free optical model potential results for total cross sections of nucleon elastic scattering are presented and discussed. The applications span over a wide energy range (10-1000 MeV) considering both stable and unstable nuclei. The study is based on \emph{in-medium} $g$-matrix full-folding optical model approach with the appropriate relativistic kinematic corrections needed for the higher energy applications. The effective interactions are based on realistic NN bare potentials supplemented with a separable non-Hermitian term to allow optimum agreement with current \emph{NN} phase-shift analyses, particularly to account for inelasticities above pion threshold$^{1)}$. The ground-state radial densities of the targets are obtained from Hartree-Fock-Bogoliubov calculations based on the finite range, density dependent Gogny force. Total cross sections and reaction cross sections are evaluated for neutron and proton scattering from $^{12-26}$O, $^{34-64}$Ca, $^{50-86}$Ni, $^{96-136}$Sn and $^{176-224}$Pb. The results for the stable nuclei as function of the energy are in reasonable agreement with the data. The systematics of the calculated cross sections as function of the target neutron number is also discussed. Supported in part by FONDECYT grant 1040938. \newline 1) H. F. Arellano and H. V. von Geramb, Phys. Rev C 66, 024602 (2002). [Preview Abstract] |
Friday, October 27, 2006 3:12PM - 3:24PM |
DD.00007: Population of Neutron-Unbound States from Direct Fragmentation Gregory Christian, Daniel Bazin, Nathan Frank, Alexandra Gade, Brage Golding, William Peters, Andrew Ratkiewicz, Andrew Stump, Andreas Stoltz, Michael Thoennessen, Matthew Kleber, Jason Miller, Jim Brown, Ted Williams, Joseph Fink, Paul DeYoung, Jerry Hinnefeld Fragmentation of a Calcium 48 beam was used to directly populate neutron-unbound states of nuclei located near the dripline. Neutron-rich fragments were detected with position sensitive detectors following a focusing quadruple triplet and a dipole magnet. The setup allowed for good isotopic separation and identification. Neutrons were detected in coincidence with the Modular Neutron Array (MoNA) located at zero degrees. Fragments from Z = 6 to Z = 12 with A/Z ranging from 2.0 to 2.7 were detected. From the relative velocity spectra of the neutrons and fragments information of the population of excited states in the different isotopes was extracted and will be presented. [Preview Abstract] |
Friday, October 27, 2006 3:24PM - 3:36PM |
DD.00008: Proximity decay and the Tidal effect A.B. McIntosh, R.T. de Souza, S. Hudan, C.J. Metelko, R. Alfaro, B.P. Davin, Y. Larochelle, H. Xu, L. Beaulieu, T. Lefort, R. Yanez, R. Charity, L.G. Sobotka, T.X. Liu, X.D. Liu, W.G. Lynch, R. Shomin, W.P. Tan, M.B. Tsang, A. Vander Molen, A. Wagner, H.F. Xi An excited nucleus can decay by emission of clusters. These clusters may be excited and themselves subsequently undergo particle decay. Peaks in the relative energy spectrum of the secondary decay products indicate resonance reflecting the discrete internal structure of the primary emitted cluster. Resonance spectroscopy can be used, for example, to determine the temperature of the initial source within a statistical approach. To date however, the effect of the field of the emitting nucleus on the decay of the cluster has been largely neglected. Tidal effects result in the correlation of the relative energy with emission angle as a function of the decay time. We explore the influence of the external Coulomb field on the decay of the first excited state of $^{8}$Be in the reaction $^{114}$Cd + $^{92}$Mo at E/A=50 MeV. Comparison of the experimental data with the predictions of a simple Coulomb trajectory model indicate that the interaction with the nuclear surface (proximity interaction) on the emitted cluster is not negligible. [Preview Abstract] |
Friday, October 27, 2006 3:36PM - 3:48PM |
DD.00009: Neutron to proton ratios of quasiprojectile and midrapidity emission in the $^{64}$Zn + $^{64}$Zn reaction at 45 MeV/nucleon D. Theriault, J. Gauthier, F. Grenier, F. Moisan, C. St-Pierre, R. Roy, B.P. Davin, S. Hudan, T. Paduszynski, R.T. de Souza, E. Bell, J. Garey, J. Iglio, A.L. Keksis, S. Parketon, C. Richers, D.V. Shetty, S.N. Soisson, G.A. Souliotis, B.C. Stein, S.J. Yennello Simultaneous measurement of both neutrons and charged particles emitted in the reaction $^{64}$Zn + $^{64}$Zn at 45 MeV/nucleon allows comparison of the neutron to proton ratio at midrapidity with that at projectile rapidity. The evolution of N/Z in both rapidity regimes with increasing centrality is examined. For the completely re-constructed midrapidity material one finds that the neutron-to-proton ratio is above that of the overall $^{64}$Zn + $^{64}$Zn system. In contrast, the re-constructed ratio for the quasiprojectile is below that of the overall system. This difference provides the most complete evidence to date of neutron enrichment of midrapidity nuclear matter at the expense of the quasiprojectile. [Preview Abstract] |
Friday, October 27, 2006 3:48PM - 4:00PM |
DD.00010: Fusion induced by radioactive $^{132}$Sn on $^{64}$Ni J.F. Liang, D. Shapira, C.J. Gross, R.L. Varner, J.R. Beene, A. Galindo-Uribarri, J. Gomez del Campo, P.A. Hausladen, P.E. Mueller, D.C. Radford, D.W. Straner, H. Amro, J.J. Kolata, J.D. Bierman, A.L. Caraley, K.L. Jones, Y. Larochelle, W. Loveland, D. Peterson The fusion excitation function for $^{132}$Sn on $^{64}$Ni was measured. The evaporation residues (ERs) were identified by their energy loss in an ionization chamber located at zero degrees and by time-of-flight. The fission fragments were detected by an annular double-sided silicon strip detector. The fragment-fragment coincidence and angular distributions were used to distinguish fission events from other reaction channels such as deep inelastic scattering. The fusion cross sections for $^{132}$Sn and $^{64}$Ni below the barrier are enhanced as compared to other stable Sn isotopes on $^{64}$Ni. Detailed data analysis and model comparisons will be presented. [Preview Abstract] |
Friday, October 27, 2006 4:00PM - 4:12PM |
DD.00011: The fusion of $^{9,11}$Li with $^{70}$Zn Walter Loveland, Radhika Naik, James Neeway, Peter Sprunger, A.M. Vinodkumar, Michael Trinczek, Marik Dombsky, Peter Machule, D. Ottewell, David Cross, K. Gagnon, W.J. Mills The fusion of $^{9,11}$Li with $^{70}$Zn was studied at the ISAC1 facility at TRIUMF. Beams of $^{9}$Li (11-14.5 MeV) struck $\approx$ 1 mg/cm$^{2}$ $^{70}$Zn targets in an evacuated scattering chamber. Beam intensities were monitored by measuring elastic scattering and by the use of a Faraday cup for $^{9}$Li while the $^{11}$Li beam was counted in a semiconductor detector placed behind the target. Typical $^{9}$Li beam intensities were 5 x 10$^{6}$ particle/s while the $^{11}$Li intensities were 800 particles/s. As and Ge evaporation residues were assayed using gamma and beta spectroscopy following post-irradiation chemical separation from the irradiated targets. A seven point excitation function for the $^{9}$Li + $^{70}$Zn reaction was measured and compared to coupled channels calculations. Due to the low $^{11}$Li beam intensity, only upper limits for fusion of $\approx$ 2b could be established for $^{11}$Li. [Preview Abstract] |
Friday, October 27, 2006 4:12PM - 4:24PM |
DD.00012: ABSTRACT WITHDRAWN |
Friday, October 27, 2006 4:24PM - 4:36PM |
DD.00013: Cross-section Measurements of $^{11}$B($n$, $n' \gamma$) M.S. Johnson, J.A. Becker, L.A. Bernstein, J.R. Cooper, P.E. Garrett, D.P. McNabb, W. Younes, M. Devlin, N. Fotiades, T.S. Hill, R.O. Nelson Excitation of high-energy states in $^{11}$B via inelastic neutron scattering is important to nuclear reaction studies. Measurements of the above reaction were conducted at LANL at the LANSCE facility. A 4.5~$mm$ thick target of $^{11}$B was bombarded with a continuum energy-spectrum of neutrons produced from a spallation source at the LANSCE facility at LANL. High-energy gamma-rays were measured using HPGe detectors in the GEANIE array. The neutron energies were determined by the time-of-flight technique. We will present and discuss results for the cross-section measurements of $^{11}$B($n$, $n' \gamma$). We will compare and contrast the results with previous measurements. [Preview Abstract] |
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DD.00014: Comparison of CDCC and Faddeev calculations for 11Be-p scattering A.C. Fonseca, A. Deltuva, A.M. Moro, F.M. Nunes The strong coupling between elastic and breakup channels in direct nuclear reactions involving halo type nuclei has lead to the development of CDCC calculations where an effective three-body problem is solved via the expansion of the full wave function in a selected set of continuum wave functions of a given pair subsystem Hamiltonian. Recent results [1] obtained with basis sets pertaining to two different pair subsystems lead to substantially different breakup cross sections. Given that the exact numerical solution of the Faddeev equations with two charged particles has recently become possible above three-body breakup threshold, we test CDCC by benchmarking calculations of the $p(^{11}{\rm Be},^{10}{\rm Be})pn$ breakup reaction with the corresponding exact solution of the Faddeev equations. The exact semi-inclusive cross section for the detection of $^{10}$Be at different energies or angles reveals that each CDCC calculation is only appropriate to describe specific regions of phase space. \newline \newline [1] A. M. Moro {\it et al.}, Nucl. Physics A{\bf {767}}, 138 (2006). [Preview Abstract] |
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