Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session X10: Reactions: Rare Isotopes/Heavy Ions/Fission |
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Sponsoring Units: DNP Chair: C.W. Beausang, University of Richmond Room: Garden 1 |
Tuesday, May 3, 2011 10:45AM - 10:57AM |
X10.00001: Determining (n,$\gamma$) and (n,2n) cross sections for radioactive isotopes using surrogate reactions N.D. Scielzo, J.T. Burke, J.E. Escher Direct measurements of neutron-reaction cross sections on unstable nuclei are extremely challenging due to the difficulties associated with radioactive targets and neutron beams. The surrogate reaction method, an indirect approach which uses a combination of reaction modeling and experimentally-measured decay probabilities, is being used to determine (n,$\gamma$) and (n,2n) cross sections for short-lived nuclei where the compound nucleus of interest can be created through light-ion reactions on stable or long-lived targets. The STARS/LiBerACE silicon and germanium detector arrays were used to detect light ions and $\gamma$-rays in coincidence. Techniques are being explored to take into account the differences in angular momentum in the surrogate and neutron-induced reactions. Results for gadolinium and yttrium isotopes will be presented and some of the challenges associated with this technique will be discussed. [Preview Abstract] |
Tuesday, May 3, 2011 10:57AM - 11:09AM |
X10.00002: Reactions with deuterons within the CDCC formalism Neelam Upadhyay, Filomena Nunes The continuum discretized coupled channels (CDCC) method is applied to $(d\,,\,p)$ and $(p\,,\,d)$ reactions populating bound states of rare isotopes to better understand the role of the continuum. As a first example, we study the elastic and breakup channels in $^{10}Be\,(d\,,\,p)\,^{11}Be$ at low and intermediate energies. The deuteron incoming wave function is modeled as an effective three-body problem $p\,+\,n\,+\,^{10}Be$ and expanded using the CDCC method. The role of the deuteron spin and the $p\,-\,n$ interaction is investigated. The inverse reaction $^{11}Be\,(p\,,\,d)\,^{10}Be$ is also considered. Finally, a comparison to elastic scattering, breakup and transfer of deuterons on $^{12}C$ at similar energies is made. [Preview Abstract] |
Tuesday, May 3, 2011 11:09AM - 11:21AM |
X10.00003: ABSTRACT WITHDRAWN |
Tuesday, May 3, 2011 11:21AM - 11:33AM |
X10.00004: Monte Carlo Eikonal Scattering W.R. Gibbs, J.-P. Dedonder Eikonal multiple scattering theory in the form of the Glauber model is believed to be accurate for high-energy elastic scattering of heavy-ion systems. The evaluation of the full expression has only been done for the lightest systems with recourse often being made to an optical model model approximation. We evaluate the full expression without further approximation using a Monte Carlo representation of the nuclear density including the center-of-mass and Coulomb corrections. The center-of-mass correction remains very important for all nuclei investigated. The input to these calculations is the basic NN amplitude, characterized by four parameters, and the nuclear density. We have made calculations of a number of cases of elastic scattering using NN parameters taken from the VPI/GWU fits. Results of several calculations will be shown and compared with data. [Preview Abstract] |
Tuesday, May 3, 2011 11:33AM - 11:45AM |
X10.00005: Elliptic flow in Fermi-energy heavy-ion collisions and the nuclear equation of state Alan McIntosh, Aldo Bonasera, Stratos Galanopoulos, Kris Hagel, Zach Kohley, Larry May, Michael Mehlman, Dinesh Shetty, W.B. Smith, Sarah Soisson, George Souliotis, Brian Stein, Rahul Tripathi, Roy Wada, Sara Wuenschel, Sherry Yennello The nuclear equation of state, which describes the behavior of nuclear matter as a function of temperature and density, impacts the dynamics of supernovae explosions, the rapid synthesis of elements during these explosions, and properties of neutron stars. At present, the largest uncertainty in the equation of state is the density dependence of the symmetry energy. The elliptic flow in heavy ion collisions is predicted to be a sensitive probe of the symmetry energy. In the present work, we investigate the elliptic flow for isotopically resolved light charged particles produced in collisions of 70Zn+70Zn at E/A = 50MeV. The observed elliptic flows decrease with increasing collisions violence and increase with particle transverse momentum. The magnitude of the flow roughly scales with the number of nucleons. The flow after scaling differs between the species, which may be due in part to the symmetry energy. In the context of a dynamical model, CoMD, we investigate the impact of the density dependence of the symmetry energy on the flow of the light charged particles, particularly the mirror nuclei 3H and 3He. [Preview Abstract] |
Tuesday, May 3, 2011 11:45AM - 11:57AM |
X10.00006: Isoscaling, SMM and the symmetry energy: connecting the dots P. Marini, S.J. Yennello, A. Botvina, A. Bonasera, Z. Kohley, L.W. May, R. Tripathi, S. Wuenschel Nuclear symmetry energy plays a central role in both nuclear physics and astrophysics and is currently a topic of significant theoretical and experimental studies. Several observables in heavy ion collisions are known to be affected by the symmetry energy (Esym), but quantitative information is difficult to extract, due to secondary decay of excited primary fragments, which can distort signatures contained in primary fragment observables. The Statistical Multifragmentation Model (SMM) has been widely used for interpreting experimental data on multiple fragment production in different nuclear reactions and to extract information on the symmetry energy starting from secondary fragments. Isoscaling has been observed for the secondary fragments from $^{78,86}$Kr+$^{58,64}$Ni at $35$AMeV reactions, collected with NIMROD. A comparison to models is now needed to constrain Esym. In this contribution we will analyze SMM, paying special attention to the effects of the secondary de-excitation on the value of observables which can be extracted from experimental data and their correlation with input symmetry energy value in the model. Among the observables we will focus on the isoscaling parameter to figure out how the symmetry energy values, which can be extracted from it for both hot and cold fragments, are related. [Preview Abstract] |
Tuesday, May 3, 2011 11:57AM - 12:09PM |
X10.00007: The nucleus-nucleus reaction cross section at intermediate energy as a mean to constrain nuclear properties Francesca Sammarruca, Larz White The equation of state enters a variety of systems, all of which should be handled consistently, starting from the same microscopic nuclear interaction. Following this guideline, recently we have applied our (Dirac-Brueckner-Hartee-Fock) nuclear matter predictions to a broad spectrum of systems, ranging from neutron skins to neutron stars [1]. Presently, we are concerned with the nucleus-nucleus total reaction cross section, a fundamentally important quantity for testing nuclear models. The two main elements of the reaction input, the effective nucleon-nucleon cross sections and the density functions for the target and the projectile, are both sensitive to the equation of state. It is our plan to develop and test a set of ``tools'' which can then be applied to obtain information on exotic nuclei, such as their neutron distributions, or the medium dependence (including isospin- asymmetry dependence) of the nucleon-nucleon cross sections. \\[4pt] [1] F. Sammarruca, Int. J. Mod. Phys. E, Vol.19, 1259 (2010) [Preview Abstract] |
Tuesday, May 3, 2011 12:09PM - 12:21PM |
X10.00008: Impact parameter dependence of intermediate-mass fragment formation in Ca+Sn heavy-ion reactions at 45 AMeV Michael Quinlan, Iwona Pawelczak, Hardev Singh, Jan Toke, Udo Schroder Charged products produced in collisions of Ca and Sn at 45 AMeV were measured by the CHIMERA multi-detector. The kinematical relationships between the reaction products were analyzed. Events consistent with the binary split of the PLF were examined and found to show characteristics consistent with a non-equilibrium formation mechanism. In particular, two distinct event classes were found and appear to be sensitive to the centrality of the collision. A comparison of the data with a number of reaction models will be discussed. [Preview Abstract] |
Tuesday, May 3, 2011 12:21PM - 12:33PM |
X10.00009: On the 0.17-yoctosecond fission-time Christian Ythier, Sabet Hachem, Genevieve Mouze The rearrangement time of nuclear fission occurs within $0.17$ yoctosecond in a new state of nuclear matter characterized by the formation of closed shells of 82 and 126 nucleons [1] . The lifetime of the new phase can now be determined [2] on the basis of the prompt-neutron emission law [3]. Arguments are presented in favor of an ephemeral disappearance of the charge of the protons of the fissioning system, as if positive and negative W boson fields had to play a role in the formation of this new state. \\[4pt] [1] G. Mouze, S. Hachem and C.Ythier, arXiv:1006.4068 [nucl-ex] June 29, 2010; \\[0pt] [2] C.Ythier, S. Hachem and G. Mouze, arXiv:1101.1819 [nucl-ex] January 11,2011. \\[0pt] [3] J. Terrell, Phys.Rev 108 (1957)783. [Preview Abstract] |
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