Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session FD: Nuclear Theory in Many-Body Systems |
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Chair: Stefano Gandolfi, Los Alamos National Laboratory Room: Sweeny D |
Thursday, November 4, 2010 4:00PM - 4:12PM |
FD.00001: High Performance Algorithm for Non-Spurious Spin- and Parity-Dependent Nuclear Level Densitiy Roman Senkov, Mihai Horoi A new algorithm for calculating the spin- and parity-dependent shell model nuclear level densities using the moments method in the proton-neutron formalism was recently proposed. The algorithm was further improved to eliminate the spurious center-of-mass contributions from the level density. We will show results for some medium-mass nuclei and compare with exact shell model nuclear level density. The method can also be used to extract with good precision the ground state energy for very large shell model cases. Some application of the new algorithm to reaction rates for nuclei in the rp-process path will be presented. [Preview Abstract] |
Thursday, November 4, 2010 4:12PM - 4:24PM |
FD.00002: Preconditioning the Quantum Many-Body Problem Timour Ten, Joaquin Drut, Timo Lahde Modern algorithmic developments in Lattice Monte Carlo calculations, collectively referred to as Hybrid Monte Carlo (HMC), have dramatically improved the computational scaling of many-fermion simulations for large system volumes $V$. From the conventional $V^3$ or $V^2$ laws, we now know it is possible to reach $V^\alpha$ scaling with $\alpha\simeq 1.25$. However, the overall factor of the scaling law could and should be improved. This factor is determined in part by the number of iterations required for the solution of an ill-conditioned linear problem, which is repeatedly performed in HMC. In this contribution we present the results of a number of preconditioning strategies that accelerate and stabilize this linear problem for the case of strongly interacting non-relativistic fermions in $3+1$ dimensions. [Preview Abstract] |
Thursday, November 4, 2010 4:24PM - 4:36PM |
FD.00003: Compound-nuclear formation cross sections for neutrons on excited states of deformed nuclei F.S. Dietrich, I.J. Thompson, T. Kawano We have carried out coupled-channels calculations of the compound-nuclear formation cross sections on the ground and first-excited states of several nuclei with differing $K$-values for the ground-state band ($^{233}$U, $K=\frac{5}{2}$; $^{238}$U, $K=0$; and $^{239}$Pu, $K=\frac{1} {2}$). The compound formation cross section, which is the weighted sum of the transmission coefficients used in statistical reaction models, is the nonelastic cross section minus the sum of direct inelastic cross sections. We find that the ratio of the excited to ground-state cross section is very close to unity in all cases (within $\sim$0.1\%) over the incident energy range studied (1 keV to 20 MeV). This result requires that sufficient levels be coupled to ensure convergence (approximately 13 levels for odd-$A$ nuclei). The adiabatic model for scattering from deformed nuclei predicts compound formation cross sections that are independent of both the $K$ of the band and the excitation within the band. Our calculations show that the actual cross section ratios are very close to the adiabatic limit, even at very low incident energies. [Preview Abstract] |
Thursday, November 4, 2010 4:36PM - 4:48PM |
FD.00004: Time-dependent microscopic theory of $^{240}$Pu induced fission Walid Younes, Noel Dubray, Heloise Goutte We present fully microscopic dynamical calculations of low-energy $^{240}\textrm{Pu}$ fission. In this approach, a quantum-mechanical wave packet is constructed from constrained Hartree-Fock Bogoliubov solutions and evolved as a function of time from the first well to scission, using the Time-Dependent Generator Coordinate Method (TDGCM). The TDGCM provides a fully self-consistent framework to treat both the dynamic and static aspects of fission, as well as the interplay between single-particle and collective degrees of freedom which are central to the fission process. The only phenomenological input to the method is the effective interaction between the nucleons. The time evolution of the wave packet toward scission will be presented, and the calculation of fission-fragment properties (yields, kinetic and excitation energies, etc.) will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 4:48PM - 5:00PM |
FD.00005: Single-particle Energies of Superheavy Nuclei and Tests of Theory T.L. Khoo, F.P. Kondev, I. Ahmad, D. Seweryniak Superheavy nuclei (SHN) exist due to the stabilization from the shell-correction energy, which arises from gaps in the single-particle energies. Hence, knowledge of the single-particle energies is critical for understanding SHN. We have deduced the single-particle energies, which reproduce experimental 1-quasiparticle (qp) energies in odd-A Bk, Es, Cm and Cf nuclei, with corrections for the recoil term. Distinct shell gaps are evident at Z=100 and N=152. Comparisons with models reveal serious shortcomings in the single-particle energies of density functional theories, highlighting the need for improved effective interactions and questioning their predictions of magic gaps for SHN. In contrast, the single-particle spectrum from the ``universal'' Woods-Saxon potential gives fair agreement, provided deformation parameters (up to at least $\beta _{6})$ are chosen that minimize the total binding energy. Omission of $\beta _{6}$, for example, leads to diminution of the shell gaps and unreliable 1- and 2-qp energies. When properly defined, the Woods-Saxon potential applies for deformed shell-stabilized nuclei from Pu to Lr. [Preview Abstract] |
Thursday, November 4, 2010 5:00PM - 5:12PM |
FD.00006: Entrance Channel Dynamics of Hot and Cold Fusion Reactions Leading to Superheavy Elements Sait Umar, Volker Oberacker One of the most fascinating research areas involving low-energy nuclear reactions is the search for superheavy elements. Experimentally, two approaches have been used for the synthesis of these elements, one utilizing closed shell nuclei with lead-based targets (cold-fusion), the other utilizing deformed actinide targets with $^{48}$Ca projectiles (hot-fusion). In this talk we investigate the entrance channel dynamics for the reactions $\mathrm{^{70}Zn}+\mathrm{^{208}Pb}$ and $\mathrm{^{48}Ca}+\mathrm{^{238}U}$ using the fully microscopic time-dependent Hartree-Fock (TDHF) theory coupled with a density constraint~[1-3]. We calculate excitation energies and capture cross-sections relevant for the study of superheavy formations. We discuss the deformation dependence of the ion-ion potential for the $\mathrm{^{48}Ca}+\mathrm{^{238}U}$ system and perform an alignment angle averaging for the calculation of the capture cross-section. The results show that this approach can generate results in good agreement with experiment and other theories.\\[4pt] [1] Umar, Oberacker, PRC 74, 061601(R) (2006).\\[0pt] [2] Umar, Oberacker, EPJA 39, 243 (2009).\\[0pt] [3] Umar, Maruhn, Itagaki, and Oberacker, PRL 104, 212503. [Preview Abstract] |
Thursday, November 4, 2010 5:12PM - 5:24PM |
FD.00007: Nuclear viscosity and viscosity to entropy ratio Dani Fu, Aram Mekjian Both a classical and a quantum mechanical evaluation of the shear viscosity of hadronic matter is developed and compared. The classical evaluation involves the scattering angle produced by a potential while a quantum description is based on phase shifts from this potential. A hard sphere potential and an attractive square well potential are considered. The classical evaluation of the scattering angle can be cast into a form that has the structure of Snell's refraction law for an attractive potential. The limit of a large index of refraction gives the hard sphere result. The high wave number limit of the quantum result for a hard sphere has a scaling law associated with it. This scaling law is similar to a result which gives a factor of two increase of the hard sphere geometric scattering cross section. This increase is associated with diffraction of the wave around the sphere. The quantum mechanical evaluation is discussed in the unitary limit of infinite scattering length. In the limit of large scattering length the effective range to quantum thermal wavelength appears as a limiting scale. The viscosity to entropy density ratio is developed. Results are compared with the string theory limit for this ratio involving Planck's constant. [Preview Abstract] |
Thursday, November 4, 2010 5:24PM - 5:36PM |
FD.00008: Racah's method for general subalgebra chains M.A. Caprio, K.D. Sviratcheva, A.E. McCoy The method of infinitesimal generators (``Racah's method'') can be broadly and systematically formulated as a method applicable to the calculation of reduced coupling coefficients for a generic subalgebra chain $G\supset H$, provided the reduced matrix elements of the generators of $G$ and the recoupling coefficients of $H$ are known. In this talk, the method will be outlined, using the subalgebra chains of SO(5) as an example. Its applicability to problems in nuclear structure physics will be discussed. Supported by the US DOE (under grant DE-FG02-95ER-40934), the US NSF (under grants NSF-PHY-0500291, NSF-OCI-0904874, and NSF-PHY05-52843), and the Southeastern Universities Reasearch Association (SURA). [Preview Abstract] |
Thursday, November 4, 2010 5:36PM - 5:48PM |
FD.00009: Chiral 3N forces in neutron and nuclear matter Kai Hebeler We calculate the energy per particle and pressure in neutron and nuclear matter based on chiral nucleon-nucleon (NN) and three-nucleon (3N) interactions. For this we derive an effective density-dependent NN interaction from the leading order (NNLO) 3N interactions by averaging one particle over occupied states of the Fermi sea. We study saturation properties of nuclear matter, pairing gaps in finite nuclei and infinite nucleonic matter and the impact of 3N forces on properties of neutron stars. [Preview Abstract] |
Thursday, November 4, 2010 5:48PM - 6:00PM |
FD.00010: A unified force theory describing several two-particle systems from subatomic to cosmic Ken Naitoh Our previous report based on a quasi-stability concept applied to momentum conservation (K. Naitoh, JJIAM, 2001) revealed the reason why several particles such as biological cells, nitrogenous bases, and liquid droplets have the bimodal size ratios of about 2:3 and 1:1. The present paper extended with stochastic mechanics and indeterminacy principle also reveals the reason why a neutron impacting uranium 235 leads to the fusion of asymmetric and symmetric size ratios. This paper also clarifies the other asymmetric ratios related to the halo structure in atoms. Moreover, we show the reason why the models based on energy conservation and variation principle did not explain the fusion. The present theory can be applied for several levels of parcels from baryons to stars in the cosmos: specifically, at the level of nuclear force, van der Waals force, surface tension, and force of gravity. [Preview Abstract] |
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