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 PC: Nuclear Theory Far and Wide |
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Chair: Susan Seestrom, Los Alamos National Laboratory Room: Sweeney Ballroom B |
Saturday, October 31, 2015 10:30AM - 10:42AM |
PC.00001: Fission of Transactinide Elements Described in Terms of Generalized Cassian Ovals Nicolae Carjan, Fedor Ivanyuk The total deformation energy at scission for Z=100, 102, 104 and 106 isotopes is calculated using the Strutinsky procedure and nuclear shapes described in terms of Cassinian ovals generalized by the inclusion of three parameters: $\alpha_1$, $\alpha_4$ and $\alpha_6$. The corresponding fragment-mass distributions are estimated supposing they are due to thermal fluctuations in the mass asymmetry degree of freedom. For these four series of isotopes the experimentally observed transition from asymmetric to symmetric fission, that happens with increasing mass number A, is qualitatively reproduced. In lighter isotopes (e.g. $^{254}Fm$ and $^{254}Rf$) two mass-asymmetric fission modes are predicted to occur with comparable yields: one having compact and the other elongated scission configurations. On the other hand, in heavier isotopes (e.g. $^{264}Fm$ and $^{264}Rf$) the fragment-mass distributions are predicted to be narrow single-peaked around A/2 corresponding to essentially one mass-symmetric fission mode. The mass distributions are estimated separately for each fission mode, in order to display their inversion when A increases. Finally the distributions of the total kinetic energy of the fragments are calculated for the same isotopes. Qualitative agreement with data is obtained. [Preview Abstract] |
Saturday, October 31, 2015 10:42AM - 10:54AM |
PC.00002: Nuclear structure and dynamics with density functional theory Ionel Stetcu Even in the absence of \textit{ab initio} methods capable of tackling heavy nuclei without restrictions, one can obtain an \textit{ab initio} description of ground-state properties by means of the density functional theory (DFT), and its extension to superfluid systems in its local variant, the superfluid local density approximation (SLDA). Information about the properties of excited states can be obtained in the same framework by using an extension to the time-dependent (TD) phenomena. Unlike other approaches in which the nuclear structure information is used as a separate input into reaction models, the TD approach treats on the same footing the nuclear structure and dynamics, and is well suited to provide more reliable description for a large number of processes involving heavy nuclei, from the nuclear response to electroweak probes, to nuclear reactions, such as neutron-induced reactions, or nuclear fusion and fission. Such processes, sometimes part of integrated nuclear systems, have important applications in astrophysics, energy production, global security, etc. In this talk, I will present the simulation of a simple reaction, that is the Coulomb excitation of a $^{238}$U nucleus, and discuss the application of the TD-DFT formalism to the description of induced fission. [Preview Abstract] |
Saturday, October 31, 2015 10:54AM - 11:06AM |
PC.00003: Triaxial Nuclei: Floppy or Rigid? Weichuan Li, Stefan Frauendorf, Mark A. Caprio Triaxial nuclear shapes are interesting since they are so unusual in the nuclear chart. But whether triaxial nuclei are soft or rigid in shape is still a question. Softness of triaxial nuclei has primarily been studied in even-even nuclei. We study softness of triaxiality in odd-mass nuclei, using the core quasi-particle model, coupling an even-even core from the algebraic collective model with a quasi-particle in the spherical field. We want to know if the quasi-particle outside of the core influences the rigidness of the core and how it influences the core's properties. [Preview Abstract] |
Saturday, October 31, 2015 11:06AM - 11:18AM |
PC.00004: From hadrons to quarks: the neutron star equation of state Philip Powell, Gordon Baym, Tetsuo Hatsuda, Toru Kojo, Chris Pethick, Kota Masuda, Yifan Song, Tatsuyuki Takatsuka Astronomical measurements of neutron star masses and radii are beginning to provide the first significant constraints on the neutron star equation of state. Meanwhile, the recent discovery of neutron stars with masses in excess of two solar masses are posing challenges to conventional models of dense nuclear matter. We present a method for constructing a unified neutron star equation of state valid across a wide range of densities by incorporating the results of both nuclear potential models valid for $<2$ times nuclear density ($n_0$), and symmetry-based effective models of interacting quark matter, expected to be valid for $>(4-6)n_0$. We discuss processes favoring a gradual onset of quark degrees of freedom with increasing density and show that the possibility of quark-hadron continuity at low temperature is consistent with recent astronomical observations. In particular, we find that a smooth crossover between hadronic and quark matter at $\sim(2-3) n_0$, prevents the hyperonic-induced equation of state softening associated with convention nuclear models at $\sim4n_0$, which limits the maximum neutron star mass. Finally, we investigate parameter constraints of an effective quark model imposed by astronomical observation and discuss implications for the QCD phase diagram. [Preview Abstract] |
Saturday, October 31, 2015 11:18AM - 11:30AM |
PC.00005: Many-body correlation effects on the Bjorken-x dependence of cross section ratios off nuclei for Bjorken-x greater than 1 Athanasios Petridis, Allen Barr, Drew Fustin Many-body correlations in nuclei determine the behavior of cross section ratios off heavy over light nuclei especially for Bjorken-x greater than 1, obtained at Jefferson Lab. They can be described in terms of quark-cluster formation in nuclei due to wave-function overlapping, manifesting itself when the momentum transfer is high so that the partonic degrees of freedom are resolved. In clusters (correlated nucleons) the quark and gluon momentum distributions are softer than in single nucleons and extend to x greater than 1. The cluster formation probabilities are computed using a network-defining algorithm in which the initial nucleon density is either standard Woods-Saxon or is input from lower energy data while the critical radius for nucleon merging is an adjustable parameter. The exact choice of critical radius depends on the specific nucleus. Additional rescaling of the Bjorken-x is needed for bound nucleons. The calculations show that there is a dependence of the cross section ratios on the Bjorken-x. Detailed comparison with Jefferson-Lab data shows that model parameter values are consistent for all nuclei studied. Four-body correlations are needed to explain the experimental results even in the range of Bjorken-x between 2 and 3. [Preview Abstract] |
Saturday, October 31, 2015 11:30AM - 11:42AM |
PC.00006: New limits on intrinsic charm from a QCD global analysis Timothy Hobbs, Pedro Jimenez-Delgado, Timothy Londergan, Wally Melnitchouk We present a new global QCD analysis of parton distribution functions, allowing for possible intrinsic charm (IC) contributions in the nucleon inspired by recent model calculations on the light-front. The analysis makes use of the full range of available high-energy scattering data for $Q^2 \geq 1$~GeV$^2$ and $W^2 \geq 3.5$~GeV$^2$, including fixed-target proton and deuteron cross sections at lower energies that were excluded in previous global analyses. The expanded data set places more stringent constraints on the momentum carried by IC, with $\langle x \rangle_{_{\rm IC}}$ at most 0.5\% (corresponding to an IC normalization of $\sim 1\%$) at the 4$\sigma$ level for $\Delta\chi^2 = 1$. We also critically assess the impact of older EMC measurements of $F_2^c$ at large $x$, which favor a nonzero IC, but with very large $\chi^2$ values. [Preview Abstract] |
Saturday, October 31, 2015 11:42AM - 11:54AM |
PC.00007: Extreme deformations and clusterization at high spin in the $A\sim 40$ mass region Debisree Ray, Anatoli Afanasjev Recent revival of the interest to the study of superdeformation [1] and clusterization [2] in light nuclei has motivated us to undertake the study of extreme deformations in the $A\sim 32-50$ $N\sim Z$ nuclei. Unfortunately, at spin zero the predicted structures with extreme deformation are located at high excitation energies [2] which prevents their experimental observation. On the other hand, the rotation brings such structures closer to the yrast line [3] and, in principle, makes their observation possible with future generation of facilities such as GRETA. Thus, the systematic study of the extremely deformed structures and clusterization has been performed in the framework of cranked relativistic mean field theory. The major features of such structures, the spins at which they become yrast and the possiblities of their experimental observation will be discussed in this presentation.\\[4pt] [1] E.\ Ideguchi {\it et al}, Prog. Th. Phys. Supp. 196, 427 (2012). \\[0pt] [2] J.-P. Ebran, E.\ Khan, T.\ Niksic and D.\ Vretenar, Phys. Rev. C 90, 054329 (2014). \\[0pt] [3] A.\ V. Afanasjev and H.\ Abusara, Phys. Rev. C 78, 014315 (2008). [Preview Abstract] |
Saturday, October 31, 2015 11:54AM - 12:06PM |
PC.00008: Nuclear Cross Sections for Space Radiation Applications Charles Werneth, Khin Maung, William Ford, John Norbury, Michael Vera The eikonal, partial wave (PW) Lippmann-Schwinger, and three-dimensional Lippmann-Schwinger (LS3D) methods are compared for nuclear reactions that are relevant for space radiation applications. Numerical convergence of the eikonal method is readily achieved when exact formulas of the optical potential are used for light nuclei (A $\le $ 16) and the momentum-space optical potential is used for heavier nuclei. The PW solution method is known to be numerically unstable for systems that require a large number of partial waves, and, as a result, the LS3D method is employed. The effect of relativistic kinematics is studied with the PW and LS3D methods and is compared to eikonal results. It is recommended that the LS3D method be used for high energy nucleon-nucleus reactions and nucleus-nucleus reactions at all energies because of its rapid numerical convergence and stability for both non-relativistic and relativistic kinematics. [Preview Abstract] |
Saturday, October 31, 2015 12:06PM - 12:18PM |
PC.00009: Nuclear Barrier Height a Variable Potential Wave Due to Nuclear Vibrations Stewart Brekke Because the nucleus is vibrating, It is repeatedly changing position thereby causing the coulomb barrier height to vary over time. If the nucleus is considered as a point charge and vibrating, the distance between the nucleus and an incoming positive charge is repeatedly changing. The distance to the nucleus from an incoming charge is ${r+ A\cos2\pi ft}$. Therefore the nuclear barrier height is given by ${KE=kQ_1Q_2/(r + Acos2\pi ft)}$, where A is the average amplitude of nuclear vibration. If ${RMScos = 0.707}$, and ${r=0}$ at the point of contact of an incoming charge, the average nuclear barrier height is given by ${KE= kQ_1Q_2/ 0.707A}$. [Preview Abstract] |
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