Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session FF: Nuclear Reactions |
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Chair: Kris Hagel, Texas A&M University Room: Lamy |
Thursday, October 29, 2015 4:00PM - 4:12PM |
FF.00001: Mid-rapidity Emission in Reactions of Sn Isotopes at 26 MeV/nucleon J. Gauthier, M. Barbui, X. Cao, K. Hagel, J.B. Natowitz, R. Wada, S. Wuenschel Definitive studies of the properties of neutron rich nuclear matter are difficult. The experimental capabilities to carry out such experiments should be much improved as very neutron-rich beams become routinely available. Until then, selective exploitation of particular reaction mechanisms may offer some possibilities to probe such matter. Previous studies of collisions of Sn isotopes by the NIMROD collaboration provided evidence for creation of a highly neutron enriched mid-rapidity region [1]. Similar studies for other systems have led to different conclusions [2, 3]. We will report on a new study of these reactions in an attempt to clarify this situation. Our interest is driven by our efforts to probe the characteristics of low density neutron-rich clustered matter.\\[4pt] [1] D.V. Shetty et al., Phys. Rev. C 68, 054605 (2003).\newline [2] L. Sobotka et al., Phys. Rev. C 62, 031603 (2000).\newline [3] H. Xu et al., Phys. Rev. C 65, 061602 (2002). [Preview Abstract] |
Thursday, October 29, 2015 4:12PM - 4:24PM |
FF.00002: Near Fermi Energy reaction dynamics and clustering in alpha-conjugate systems Xiguang Cao, Katarzyna Schmidt, E.-J. Kim, K. Hagel, M. Barbui, S. Wuenschel, J.B. Natowitz, H. Zheng, N. Blando, A. Bonasera, G. Giuliani Theoretical study predicted that the self-organizing of alpha cluster is favored over deuteron below a critical density with moderate temperature, where the possible Bose-Einstein condensation (BEC) is expected to occur. However the experimental information about the alpha states at low density is scarce. It is natural to pursue experiments with $\alpha $ conjugate beams and advanced detection apparatus to explore the collective dynamics of alpha clustered systems at low density. Systematical experiments were carried out with 40Ca and 28Si beams at 10, 25, 35 MeV/u incident on 28Si, 12C, 40Ca and 180Ta targets, detected with the NIMROD-ISiS 4 Pi detector array. It is found that there is a strong neck-like emission, which consists mainly of alpha-like fragments. The characteristic of the $\alpha $ emission source is explored by shape analysis, multi-particle correlation and quantum fluctuation approaches. How these observables reveal the possible alpha BEC in low density and possible exotic toroidal and linear chain configurations made out of alpha clusters is discussed. [Preview Abstract] |
Thursday, October 29, 2015 4:24PM - 4:36PM |
FF.00003: Measurements of proton-proton correlations with the upgraded FAUST array (FAUSTUPS) Lauren Heilborn, Sherry Yennello The nuclear Equation of State (EoS) is important to a more fundamental understanding of nuclear matter, particularly as manifest in asymmetric systems, such as neutron stars. Proton-proton (pp) correlation functions have been predicted to be sensitive to the density-dependence of the Symmetry Energy in the EoS. In order to extract this relationship, the Forward Array Using Silicon Technology with Upgraded Position Sensitivity (FAUSTUPS) has recently been commissioned with position-sensitive silicons as the Delta-E detectors. In order to extract the position with a sensitivity of 200 um within a detector, a new method of position calibration for the array has been developed. Data has been collected from the reactions of 40Ar$+$70Zn,58Fe and 40Ca$+$58Ni at 40 MeV/nucleon. The three systems were chosen to include two that are the same total A, and two that are similar in total isospin content. Light charged particles have been measured, and preliminary results from this campaign will be shown. [Preview Abstract] |
Thursday, October 29, 2015 4:36PM - 4:48PM |
FF.00004: Rate of N-Z equilibration in a deformed nuclear system Andrea Jedele, A.B. McIntosh, S.J. Yennello The symmetry energy in the nuclear equation of state is a driving force for neutron-proton equilibration. The extent of equilibration is governed by the contact time and the gradient of the potential driving the equilibration. We have examined correlations between the largest two fragments (both isotopically identified) produced in collisions of 70Zn$+$70Zn at 35A MeV. Using the rotation angle as a clock, we observe a large difference in the average n-p asymmetry at short times. As time increases, the asymmetries converge toward each other, providing strong evidence for N-Z equilibration within a dynamically deformed quasi-projectile. [Preview Abstract] |
Thursday, October 29, 2015 4:48PM - 5:00PM |
FF.00005: Measurement of isospin diffusion from isoscaling of heavy fragment yields in 70 MeV/u Sn+Sn collisions Jack Winkelbauer, R.H. Showalter, M.B. Tsang, W.G. Lynch, Z. Chajecki, M.D. Youngs, D.D.S. Coupland, Fei Lu, A. Sanetullaev, R. Shane, S. Tangwancharoen, M. Famiano, S. George, R. Charity, L. Sobotka, J. Elson, R de Souza, Y Zhang Much effort has been undertaken recently to improve constraints on the symmetry energy term in the nuclear equation of state. Specifically, the behavior of the symmetry energy above and below saturation density plays a significant role in the properties of neutron stars, the structure of heavy nuclei, and the dynamics of nuclear reactions. The tendency for neutrons to drift from a neutron-rich region to a neutron-deficient region during a peripheral collision of heavy nuclei is known as isospin diffusion, and has been shown to be sensitive to the symmetry energy at sub-saturation densities. Isospin diffusion between projectiles of $^{112,118,124}$Sn at 70MeV/u and targets of $^{112,118,124}$Sn has been measured, using isoscaling ratios of heavy fragments as a tracer of the isospin content of the excited projectile-like fragment. The validity of using isoscaling as a surrogate for the isospin asymmetry will be discussed, and the associated isospin diffusion results will be presented. [Preview Abstract] |
Thursday, October 29, 2015 5:00PM - 5:12PM |
FF.00006: Using particle ratios to explore the limits of the thermodynamic model of heavy ion collisions Mike Youngs, Sherry Yennello The thermodynamic model of heavy ion collisions predicts the shape of particle spectra emitted from a source using a number of physical parameters. The chemical potential, which is one of these parameters, can be directly investigated by taking the ratio of spectra for a specific isotope from two different reaction systems. I will be discussing the effects of using the shapes of these ratios instead of integrated yields as well as differentiating between heavy residues and emitted fragments to explore the limits of this model. [Preview Abstract] |
Thursday, October 29, 2015 5:12PM - 5:24PM |
FF.00007: New prospects for characterizing the asymmetry dependence of the nuclear caloric curve Alan McIntosh, Sherry Yennello My recent measurements have demonstrated a dependence of the caloric curve on the neutron-proton asymmetry. If confirmed, this represents a new feature of the nuclear equation of state. These results were made possible by the complete isotopic reconstruction of excited quasi-projectiles produced in heavy ion collisions. I will discuss the isotopic reconstruction and multiple probes of the the temperature, which are the strengths of this measurement. I have conducted a new independent experiment to further study the asymmetry dependence of the caloric curve through fusion reactions. The new experiment and the status of the analysis will be discussed. [Preview Abstract] |
Thursday, October 29, 2015 5:24PM - 5:36PM |
FF.00008: Shannon information uncertainty and its application in heavy-ion collisions Chun-Wang Ma, J.B. Natowitz, Yi-Dan Song, Chun-Yuan Qiao The probes based on Shannon information have advantages in studying heavy-ion collisions since they do not require an equilibrium system, which can be used safely in an evolving reaction system. In the talk we will introduce the recent works studing heavy-ion collisions using information uncertainty probes. The analysis for the measured reactions will be presented. [Preview Abstract] |
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