Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session DC: Nuclear Reactions/Rare Isotope Beams I |
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Chair: Sherry Yennello, Texas A&M University Room: 101 |
Thursday, October 27, 2011 10:30AM - 10:42AM |
DC.00001: Search for Heavy and Superheavy systems in $^{197}$Au +$^{232}$Th Collisions near the Coulomb Barrier Kris Hagel, Marina Barbui , Joseph Natowitz, Marcia Rodrigues, Kasia Schmidt, Roy Wada, Zbig Majka, Hua Zheng The possibility to produce very heavy elements in the reaction $^{197}$Au + $^{232}$Th at 7.5 MeV/nucleon has been investigated using the BigSol spectrometer at Texas A\&M. This experiment indicated the possibility to produce heavy elements of Z about 100, however a confirmation of this scenario would only come by detecting the high energy alpha particles emitted by the decaying heavy nuclei. In fact, very heavy nuclei are expected to decay to stable nuclei through alpha particle chains with energy around or above 10 MeV. A new experiment was performed to search for high energy alpha emission. The heavy reaction products in the angular range from 3$^{\circ}$ to 45$^{\circ}$ are implanted in a catcher foil. The particles emitted by the decaying implanted nuclei are detected using ${\Delta}$E-E telescopes in the backward position. The 7.5 AMeV 197Au beam from the K500 cyclotron at Texas A\&M was pulsed at different intervals in order to be able to identify species of different half-life. The events were recorded both in beam-on and beam-off conditions. The preliminary results will be shown. [Preview Abstract] |
Thursday, October 27, 2011 10:42AM - 10:54AM |
DC.00002: Isospin Dependence of Nucleon Exchange in 78,86Kr + 40,48Ca Reactions at E/A = 10 MeV Eric Henry, Wolf-Udo Schroder, Jan Toke, Michael Quinlan, Hardev Singh Preliminary results are presented of theoretical simulation calculations and experimental data obtained in the ISODEC experiment performed with the CHIMERA multi-detector array at LNS/Catania. One of the main objectives of this experiment measuring A, Z and energy of projectile and target remnants was to explore the isospin dependence of the flow of energy, mass and charge in damped nuclear reactions involving systems of very different initial isospin asymmetries. With a bombarding energy of E/A = 10 MeV the reaction systems approach the limits of an adiabatic nuclear response associated with a separation of relaxation time scales of macroscopic and microscopic degrees of freedom. However, non-equilibrium effects are expected to be still relatively weak, such that the effects of the driving forces underlying isospin relaxation are not masked by pre-equilibrium nuclear disintegration processes. [Preview Abstract] |
Thursday, October 27, 2011 10:54AM - 11:06AM |
DC.00003: Measurement of emitted tritons and 3Helium from 112,124Sn+112,124Sn collisions at Ebeam=50 MeV/ nucleon and 120 MeV/nucleon M. Youngs, D.D.S. Coupland, W.G. Lynch, M.B. Tsang, Z. Chajecki, R. Hodges, M. Kilburn, Fei Lu, J. Novak, A. Sanetullaev, J. Winkelbauer, Jenny Lee, M.A. Famiano, B. Giacherio, T.K. Ghosh, P. Russotto, G. Verde, C. Sfienti The nuclear symmetry energy affects many aspects of nuclear structure, nuclear astrophysics, and nuclear reactions. The spectral ratio of neutrons to protons from central heavy ion collisions is sensitive to the symmetry energy below saturation density, but is difficult to measure. t/3He ratios, however, provide an easier measurement, since neutron detection efficiency is not an issue. A recent experiment at NSCL/MSU has measured n/p ratios from collisions of 112,124Sn+112,124Sn at Ebeam=50 MeV/nucleon. In addition, t/3He ratios were measured at the same time. First results of the t/3He double ratios as well as systematic studies of theoretical calculations of n/p and t/3He double ratios will be discussed. [Preview Abstract] |
Thursday, October 27, 2011 11:06AM - 11:18AM |
DC.00004: Measurement of emitted neutrons and protons from 112,124Sn + 112,124Sn at Ebeam = 50 MeV/nucleon and 120 MeV/nucleon D.D.S. Coupland, M. Youngs, W.G. Lynch, M.B. Tsang, Z. Chajecki, R. Hodges, M. Kilburn, Fei Lu, J. Novak, A. Sanetullaev, J. Winkelbauer, Jenny Lee, M.A. Famiano, B. Giacherio, T.K. Ghosh, P. Russotto, G. Verde, C. Sfienti The nuclear symmetry energy affects many aspects of nuclear structure, nuclear astrophysics, and nuclear reactions. The spectral ratio of neutrons to protons from central heavy ion collisions is sensitive to the symmetry energy below saturation density, but previous measurements of the ratio have large uncertainties. In addition, transport model calculations of the ratio using the IBUU04 and ImQMD05 codes differ greatly, perhaps due to the effective mass splitting in the nuclear medium. A recent experiment at NSCL/MSU measured neutrons and protons emitted from central collisions of 112,124Sn + 112,124Sn at Ebeam = 50 MeV/nucleon to probe the symmetry energy, and at Ebeam = 120 MeV/nucleon to probe the mass splitting. First results will be presented and compared to transport model calculations. [Preview Abstract] |
Thursday, October 27, 2011 11:18AM - 11:30AM |
DC.00005: Isospin Observables from Fragment Energy Spectra Rachel Hodges, T.X. Liu, W.G. Lynch, M.B. Tsang, X.D. Liu, W.P. Tan, M.J. van Goethem, G. Verde, A. Wagner, H.F. Xi, H.S. Xu, M. Famiano, R.T. de Souza, V.E. Viola, R.J. Charity, L.G. Sobotka The energy spectra of light charged particles and intermediate mass fragments from $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at an incident energy of E/A=50 MeV have been measured with a large array of Silicon strip detectors. We used charged particle multiplicities detected in a near 4pi array to select data from the central collision region. We study isospin observables analogous to ratios of neutron and proton spectra, including double ratios and yield ratios of t/$^{3}$He and of asymmetries constructed from fragments with Z=3-8. Using the energy spectra, we can construct these observables as functions of kinetic energy and observe a large difference in the fragment observables if fragments contributing to sequential decays are included. [Preview Abstract] |
Thursday, October 27, 2011 11:30AM - 11:42AM |
DC.00006: Isotopic trends in dynamical breakup Sylvie Hudan, Romualdo de Souza, Alan McIntosh The simultaneous measurement of neutrons and charged particles produced in peripheral and mid-peripheral collisions in a heavy-ion cross-bombardment reaction $^{124,136}$Xe + $^{112,124}$Sn at E/A = 50 MeV is described. Dynamical decay in which the excited projectile-like fragment (PLF) decays on the timescale of its rotation is observed. Specifically, the dependence of the decay timescale on the charge-asymmetry of the binary split of the PLF is extracted. In addition, the correlation between the composition of the lighter fragment, the size of the lighter fragment, the velocity damping and the decay orientation is examined. [Preview Abstract] |
Thursday, October 27, 2011 11:42AM - 11:54AM |
DC.00007: Precision Measurement of Isospin Diffusion Jack Winkelbauer, R. Hodges, M.B. Tsang, W.G. Lynch, Z. Chajecki, D. Coupland, M. Youngs, F. Lu, A. Sanetullaev, R. Shane, S. Tangwancharoen, M. Famiano, S. George, T. Ghosh, J. Dunn, S. Dye, S. Nielsen, A. Ramos, R. Charity, L. Sobotka, J. Elson, T. Rana, M. el Houssieny In heavy-ion collisions, the tendency for isospin to drift from a neutron (proton) rich region to a neutron (proton) deficient region is sensitive to the density dependence of the symmetry energy. Until recently, most of the isospin diffusion results have been obtained with mid central to central collisions and different isospin observables have been used in experiment and in model simulations. To provide more accurate understanding of the dependence of isospin diffusion on impact parameters and different isospin observables, we have measured isotopic fragment and residue yields for $^{112,118,124}$Sn + $^{112,118,124}$Sn collisions at E/A=70 MeV. The measurements were carried out at the Coupled Cyclotron Facility at Michigan State University. Fragment yields were measured using the Large Area Silicon Strip Array (LASSA) and heavy residue yields emitted at the forward angles were measured using the S800 Spectrograph. Impact parameter was selected using the MSU Miniball-WU Miniwall phoswich array. Preliminary results will be presented. Work supported by the National Science Foundation under Grant PHY-0606007. [Preview Abstract] |
Thursday, October 27, 2011 11:54AM - 12:06PM |
DC.00008: Probing the dynamics of heavy ion collisions via two-particle correlations Z. Chajecki, V. Henzl, M. Kilburn, D. Henzlova, W.G. Lynch, D. Brown, D. Coupland, P. Danielewicz, C. Herlitzius, A. Rogers, A. Sanetullaev, J. Lee, B. Tsang, A. Vander Molen, M. Wallace, M. Youngs, Y. Sun, G. Verde, Z.S. Hudan, M. Famiano, R. deSouza, A. Chbihi, S. Lukyanov, L. Sobotka The angular and rapidity dependence of proton-proton correlations functions is studied in central 40Ca+40Ca and 48Ca+48Ca nuclear reactions at E=80 MeV/c. Measurements were performed with the HiRA detector complemented by the 4$\pi$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation function reflecting the different space-time extent of the source selected. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The estimate of the time scale of the fragmentation process is presented. The results are compared to the theoretical calculations from BUU transport model. This comparison emphasizes the importance of including the light clusters in the simulations to reproduce the experimental results. [Preview Abstract] |
Thursday, October 27, 2011 12:06PM - 12:18PM |
DC.00009: Towards quantum transport for central collisions of nuclei and of clouds of ultracold quantum gases Brent Barker, Arnau Rios, Pawel Danielewicz Efforts are on the way to develop a practical non-equilibrium Green's functions approach to central nuclear reactions. A truncation of the far off-diagonal elements of the spatial density matrix is implemented, resulting in speedup without affecting the evolution of the system close to the diagonal. The technique is applied to a simulation of collisions between quasi-1D Bose-Einstein condensates, using a modified Gross-Pitaevskii equation that allows inclusion of some transverse degrees of freedom in a one dimensional environment. [Preview Abstract] |
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