Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session R14: Nuclear Reactions |
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Sponsoring Units: DNP Chair: Robert Charity, Washington University, St Louis Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis G |
Monday, April 14, 2008 10:45AM - 10:57AM |
R14.00001: Differences in the Transverse Flow of $^{3}$H and $^{3}$He Fragments Z. Kohley, E. Bell, D.V. Shetty, G.A. Souliotis, S. Soisson, B. Stein, S. Wuenschel, L. May, S.J. Yennello The transverse flow of $^{3}$H and $^{3}$He fragments has been examined in the reactions of $^{58}$Fe+$^{58}$Fe and $^{58}$Ni+$^{58}$Ni at 45 MeV/u. The calculated flow parameters showed an increase in the flow for the $^{3}$He particles in comparison to the $^{3}$H for both systems. This difference in the transverse flow demonstrates a dependence of the flow parameter on the N/Z of the particle of interest. The results from $^{58}$Fe+$^{58}$Fe system are in qualitative agreement with previous theoretical predictions [1] in which the difference in the flow parameter between the $^{3}$He and $^{3}$H particles was shown to be sensitive to the density dependence of the symmetry energy. It may be possible to extract additional information from the differences in the $^{3}$H and $^{3}$He flow parameters through a comparison of the $^{58}$Fe+$^{58}$Fe and $^{58}$Ni+$^{58}$Ni systems. \newline [1] L. Scalone \textit{et al., }Phys. Lett. B \textbf{461, }9 (1999). [Preview Abstract] |
Monday, April 14, 2008 10:57AM - 11:09AM |
R14.00002: Search for the fade out of a collective enhancement of the nuclear level density L.G. Sobotka, S. Komarov, R.J. Charity, C.J. Chaira, W. Reviol, D.G. Sarantites, A.L. Caraley, M.P. Carpenter, D. Seweryniak The fade out of a collective enhancement of the nuclear level density is predicted (by an SU3 shell model) to give rise to a clear signature in the evolution of the spectral shape of evaporated charged particles with excitation energy. We have searched for this signature in the spectra of $\alpha $ particles emitted from $^{178}$Hf compound nuclei, with excitation energies between 54 and 124 MeV, formed in $^{18}$O + $^{160}$Gd fusion reactions. Gammasphere provided the ability to construct channel-specific $\alpha $-particle spectra and thus allow for a comparison to statistical model calculations on this basis. The expected clear signature of a rapid fade out of a collective enhancement is not found. The data are best reproduced by calculations which do not explicitly consider a collective enhancement and its fade out. [Preview Abstract] |
Monday, April 14, 2008 11:09AM - 11:21AM |
R14.00003: Detection of Neutrons and Charged-Particles emitted in Peripheral and Mid-Peripheral Collisions of $^{124,136}$Xe and $^{112,124}$Sn Nuclei at E/A = 50 MeV A.B. McIntosh, J. Black, S. Hudan, C.J. Metelko, R. Yanez, R.T. de Souza, A. Chbihi, M. Famiano, M.O. Fregeau, J. Gauthier, J. Moisan, R. Roy, S. Bianchin, C. Schwarz, W. Trautmann To investigate peripheral and mid-peripheral heavy ion collisions, neutrons and charged particles emitted in the cross-bombardment reactions $^{124,136}$Xe + $^{112,124}$Sn @ E/A = 50 MeV were measured. Projectile-like fragments at small angles (2.8$^{\circ}\le\theta\le$14.5$^{\circ}$) were identified by their atomic number and large velocity (V/V$_{beam}\ge$0.5) in the Si-Si-CsI(Tl)/PD array FIRST with high angular resolution ($\Delta\theta\approx$0.1$^{\circ}$). Intermediate mass fragments (IMF: Z$\ge$3) detected in FIRST were isotopically identified. At larger angles (30$^{\circ}\le\theta\le$45$^{\circ}$), light-charged particles and IMFs were isotopically identified in the silicon-strip array LASSA. With the DEMON array, pulse-shape discrimination and TOF were used to identify neutrons and measure their kinetic energies. Calibration of the charged particle detectors using fragmentation beams and electronic pulsers will be described. Elemental and isotopic resolution obtained with FIRST and LASSA will be shown; preliminary results will be presented. [Preview Abstract] |
Monday, April 14, 2008 11:21AM - 11:33AM |
R14.00004: Microscopic calculations of dynamics and N/Z equilibration in peripheral collisions below the Fermi energy. G.A. Souliotis, D.V. Shetty, S. Galanopoulos, S.J. Yennello A systematic study of heavy residues formed in peripheral collisions below the Fermi energy has been undertaken at Texas A\&M aiming at obtaining information on the mechanism of nucleon exchange and the course towards N/Z equilibration [1,2]. We expect to get insight on the dynamics and the nuclear equation of state by comparing our heavy residue data to detailed calculations using microscopic models of quantum molecular dynamics (QMD) type. We are performing calculations using two codes: the CoMD code of M. Papa, A. Bonasera [3] and the CHIMERA-QMD code of J. Lukasik [4]. Both codes implement an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon restoring the Pauli principle at each time step of the collision. CHIMERA-QMD uses a Pauli potential term to mimic the Pauli principle. Results of the calculations and comparisons with our residue data will be presented. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001). [4] J. Lukasik, Z. Majka, Acta Phys. Pol. B 24, 1959 (1993). [Preview Abstract] |
Monday, April 14, 2008 11:33AM - 11:45AM |
R14.00005: The influence of transport variables on isospin transport ratios Daniel Coupland, William Lynch, Pawel Danielewicz, Betty Tsang, Yingxun Zhang The influence of transport quantities on isospin equilibration in peripheral $^{112}$Sn+$^{112}$Sn, $^{112}$Sn+$^{124}$Sn, $^{124}$Sn+$^{112}$Sn, and $^{124}$Sn+$^{124}$Sn collisions is studied in the Boltzmann-Uehling-Uhlenbeck model. The isospin transport ratio constructed from the asymmetry of the projectile residue has been shown to contain information about the density dependence of the symmetry energy. However, the ratio also depends on the momentum dependence of the mean field, in-medium isospin nucleon-nucleon cross-sections, and the stiffness of the symmetry part of the equation of state (EOS). Our simulations will try to untangle the various effects and their influence on the extraction of the symmetry energy terms in the EOS. First results from the simulations and comparisons to other transport model calculations will be presented. This work is supported by the National Science Foundation under Grant PHY-0606007. [Preview Abstract] |
Monday, April 14, 2008 11:45AM - 11:57AM |
R14.00006: Isospin effects in two-particle correlation functions Vladimir Henzl, D. Henzlova*, M. Famiano*, M. Kilburn*, W. Lynch*, D. Coupland*, J. Elson*, C. Herlitzius*, S. Hudan*, J. Lee*, S. Lukyanov*, A. Rogers*, A. Sanetullaev*, R. de Souza*, L. Sobotka*, Z. Sun*, B. Tsang*, A. Vander Molen**, G. Verde*, M. Wallace*, M. Youngs* Dynamical and thermal properties of excited nuclear system produced during heavy ion collisions at intermediate incident energies can be studied by means of the intensity interferometry, which when applied to both charged particles (light charged particles and intermediate mass fragments) provide information about space-time properties of nuclear reactions. The shape of 2-particle correlation functions reflects the nature of the final state interaction and possible presence of a collective motion driven by the nuclear EoS. BUU simulations predict that the symmetry term of the EoS will affect the 2-proton correlation function, reflecting a more pronounced pre-equilibrium emission and shorter emission times when stiffer density dependence of the symmetry term is assumed. We will present preliminary results on the isospin effect on the 2-proton correlations measured in reactions $^{40,48}$Ca+$^{40,48}$Ca at 80$A $MeV. The experiment was performed at the NSCL/MSU using High Resolution Array (HiRA) in coincidence with the 4pi array. This work is supported by the National Science Foundation under Grant Nos. PHY-0606007 and PHY-9977707. [Preview Abstract] |
Monday, April 14, 2008 11:57AM - 12:09PM |
R14.00007: The influence of cluster emission and the symmetry energy on neutron - proton spectral double ratios William Lynch, Yingxun Zhang, Pawel Danielewicz, Michael Famiano, Zhuxia Li, Betty Tsang The emissions of neutrons, protons and bound clusters from central $^{124}$Sn+$^{124}$Sn and $^{112}$Sn+$^{112}$Sn collisions are simulated using the Improved Quantum Molecular Dynamics model for two different symmetry energy functions with different density dependencies. The calculated neutron -- proton spectral double ratios for these two systems are sensitive to the density dependence of the symmetry energy. The effect of cluster emission and comparisons to other transport calculations such as IBUU04 will be presented. This work is supported by the National Science Foundation under Grants PHY-0555893, PHY-0606007 and PHY 0216783. [Preview Abstract] |
Monday, April 14, 2008 12:09PM - 12:21PM |
R14.00008: Correlations between protons produced in the decay of $^{10}$C and $^{6}$Be states. R. Shane, K.M. Mercurio, R.J. Charity, J.M. Elson, L.G. Sobotka, M. Famiano, A. Wuosmaa, A. Banu, C. Fu, L. Trache, R.E. Tribble, A.M. Mukhamedzhanov This talk will present the 2-proton correlation data from recent secondary beam experiments using the MARS separator at TAMU. The experiment itself and the extracted decay paths for the previously known levels and a newly discovered level are described in a separate talk by K. Mercurio. The 2-proton relative-energy and relative-angle spectra for the $^{10}$C state at E*=6.6 MeV contain correlations that can be reproduced by R-matrix or Fadeev calculations but not sequential or three-body calculations. In the same experiment, we also collected kinematically complete data on $^{6}$Be ground-state decay. These data, as well as calculations from Grigorenko, will be presented in Jacobi ``T'' and ``Y'' coordinates. [Preview Abstract] |
Monday, April 14, 2008 12:21PM - 12:33PM |
R14.00009: Isoscaling studies of reconstructed quasi-projectiles in $^{24}$Mg, $^{40}$Ca+$^{112,124}$Sn reactions at 32 MeV/u Stratos Galanopoulos, G.A. Souliotis, A.L. Keksis, M. Veselsky, M. Jandel, D.V. Shetty, Z. Kohley, S. Soisson, B. Stein, S. Wuenschel, S.J. Yennello The isotopic distribution of the reaction products are sensitive observables in the study of the charge asymmetry term in the nuclear Equation of State, (nEOS) [1]. Studies on heavy-ion reactions near Fermi-energy region showed that the yield ratio of a given fragment coming from a neutron-rich vs a neutron deficient fragmenting system follows an exponential dependence with respect to the neutron and proton number of the fragments, an effect termed isoscaling (e.g. [2]). In this work, we study the isoscaling on $^{24}$Mg,$^{ 40}$Ca +$^{124,112}$Sn reacting systems from reconstructed quasi-projectile events (QP's), for the determination of the isoscaling parameter $\alpha $. The measurements were performed at the K500 Cyclotron accelerator of Texas A{\&}M University using $^{24}$Mg and $^{40}$Ca beams at 32 MeV/u. The projectile fragments were detected by the Forward Array Using Silicon Technology (FAUST) [3]. Properties of the reconstructed QP's were also systematically investigated (e.g. velocity and E$^{\ast }$/A$_{qp}$ distributions). \textbf{References} [1] M. Colonna \textit{et al}., Eur. Phys. J. A \textbf{30}, 165, (2006). [2] G. A. Souliotis \textit{et al}., Phys. Rev. C \textbf{73,} 024606 (2006). [3] F. Gimeno-Nogues \textit{et al}., Nucl. Instr. Meth. A \textbf{399}, 94 (1997). [Preview Abstract] |
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