Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session HD: Mini-symposium on Nuclei as Mesoscopic Systems II |
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Sponsoring Units: DNP Chair: Art Champagne, University of North Carolina Room: Gaylord Opryland Hermitage A |
Saturday, October 28, 2006 2:00PM - 2:36PM |
HD.00001: Neutron Stars Invited Speaker: The determination of the properties of matter inside of neutron stars constitutes a tremendous challenge for nuclear and many-body physics. Here I shall selectively review some of the recent developments in these fields, which concern nuclear processes in the crusts of neutron stars and new states and properties matter (hyperons, boson condensates, quark matter, superconductivity) at supernuclear densities encountered in the cores of neutron stars. Particular emphasis will be put on the physics inside of massive neutron stars. [Preview Abstract] |
Saturday, October 28, 2006 2:36PM - 2:48PM |
HD.00002: Nuclear Clusters in Astrophysics Alan H. Wuosmaa Alpha-cluster nuclei are prototypical mesoscopic systems that play significant roles in the most important nucleo-synthesis reactions forming the elements crucial to life on Earth, $^{12}$C and $^{16}$O. The production rates of these nuclei depend critically on the stellar environment, as well as detailed nuclear structure properties. The famous ``triple-alpha'' reaction that produces $^{12}$C, for example, proceeds through the well known excited $0^+_2$ state in $^{12}$C which possesses a well developed alpha-cluster character. In massive stars, the properties of and reactions involving cluster nuclei continue to strongly influence stellar evolution through processes such as $^{12}$C+$^{12}$C fusion. Current modeling of stellar evolution has evolved to a stage where new and better data are required to reduce the uncertainties in these theoretical predictions. I will review some of the important aspects of cluster nuclei in astrophysical environments, and discuss some ongoing experimental efforts to refine our knowledge of the rates of $^{12}$C production through the triple-alpha reaction, and $^{16}$O production via the $^{12}$C($\alpha, \gamma$)$^{16}$O reaction. Finally, I will discuss some of the challenges that are faced in understanding burning of heavier cluster nuclei in massive stars. Work supported by the U. S. Department of Energy, Office of Nuclear Physics under contracts DE-FG02-04R41320 and W-31-109-ENG38, and the National Science Foundation grants PHY01-10253 and PHY02-16783. [Preview Abstract] |
Saturday, October 28, 2006 2:48PM - 3:00PM |
HD.00003: Nuclear quantum phase transitions M.A. Caprio Quantum phase transitions in nuclei are discussed in relation to the properties of nuclei as mesoscopic systems. Recent results obtained within the framework of algebraic models, including investigations of quantum phase transitions at finite particle number, are summarized. Supported by the US DOE under grant DE-FG02-91ER-40608. [Preview Abstract] |
Saturday, October 28, 2006 3:00PM - 3:12PM |
HD.00004: Coupling between bosonic and fermionic degrees of freedom in $^{93}$Nb J.N. Orce, J.D. Holt, A. Linnemann, C.J. McKay Excited states in $^{93}$Nb can be regarded as resulting from the weak coupling of a $\pi 1g_{9/2}$ proton to a $^{92}_{40} $Zr core, and a $\pi 2p_{1/2}^{-1}$ proton-hole to a $^{94}_{42} $Mo core. These couplings result in two independent and unmixed one-phonon structures of opposite parity. The lack of mixing provides a good opportunity for a comprehensive analysis of the low-spin structure in this odd-mass nuclide. $^{93}$Nb has been studied using the $^{93}$Nb(n,n$^\prime$$\gamma$) reaction with neutron energies from 1.5 to 3 MeV, the $^{93}$Nb$\gamma$,$\gamma^\prime$) reaction with a bremsstrahlung end-point energy of 2.75 MeV, and $^{94}$Zr(p,2n$\gamma$$\gamma$)$^{93}$Nb reaction at bombarding energies ranging from 11.5 to 19 MeV. Excitation functions, lifetimes, and branching ratios were measured, and multipolarities and spin assignments were determined. The results from these experiments will be presented in this DNP meeting, including the proposed mixed-symmetry states at 1779.7 and 1840.6 keV, respectively, associated with the $\pi2{p^{-1}_{1/2}}\otimes(2_{1, {\rm MS}}^{+},^{94}$Mo) coupling. These assignments are derived from the observed $M1$ and $E2$ transition strengths to the 2${p_{1/2}^{-1}}$ symmetric one- phonon states, energy systematics, spins and parities, and comparison with shell model calculations. [Preview Abstract] |
Saturday, October 28, 2006 3:12PM - 3:24PM |
HD.00005: Band Termination in Heavy-Nuclei Mark Riley The generation of angular momentum (spin) is perhaps one of the most beautiful illustrations of finite particle number effects in nuclei. A deformed prolate nucleus can increase its spin by collective rotation about an axis perpendicular to its symmetry axis leading to I(I+1) quantum-rotor behavior and the observation of regular rotational bands. However, since the nucleus is a finite mesoscopic quantal system, such collective behavior must have an underlying microscopic basis which limits the spin that a particular nuclear configuration, or band, can generate. A combination of Coriolis and centrifugal forces, induced by rapid rotation, can break the valence pairs and align the individual nucleonic angular momentum along the collective rotation axis. These aligned nucleons move in equatorial orbits polarizing the nucleus, from its original prolate shape, towards an oblate one. Eventually the available spin is exhausted when all the valence nucleons outside a spherical, doubly magic core are aligned. This is known as valence-space ``band termination'' and is observed in gamma-ray emission spectra by the abrupt and characteristic end to a rotational band. High-spin terminating bands in heavy nuclei were first identified around Er-158, see Ref. [1] and references therein. Recent experimental data on this classic nucleus and its neighbors have greatly enhanced the band termination story and will be presented. [1] A.V. Afanasjev, D.B. Fossan, G.J. Lane, and I. Ragnarsson, Phys. Rep. 322, 1 (1999). [Preview Abstract] |
Saturday, October 28, 2006 3:24PM - 3:36PM |
HD.00006: Giant resonances in $^{112 \sim124}$Sn isotopes and the symmetry term in nuclear T. Li, U. Garg, P. V. Madhusudhana Rao, R. Marks, M. Fujiwara, S. Okumura, M. Yosoi, Y. Nakanishi, H. Hashimoto, K. Kawase, S. Terashima, M. Uchida, T. Kawabata, M. Itoh, T. Terazono, R. Matsuo, M. Ichikawa, H. Sakaguchi, T. Murakami, Y. Yasuda, Y Terashima, J. Zenihiro, Y. Iwao, H. Akimune Based on the same data on the giant monopole resonances, calculations within the non-relativistic and relativistic models predict for nuclear incompressibility $K_\infty$ values which are significantly different from one another, \textit{viz.}$\approx$220-235 and $\approx$250-270 MeV respectively. It appears that the solution of this puzzle requires a better determination of the symmetry energy at saturation point. We have investigated the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant dipole resonance (ISGDR) in Sn isotopes, using inelastic $\alpha$-particle of 400 MeV at extremely forward angles, including 0$^\circ$. The ISGMR and ISGDR strength distributions have been extracted from the background-free inelastic scattering spectra by using multipole-decomposition analysis. The implications of these results on the symmetry energy term will be discussed. [Preview Abstract] |
Saturday, October 28, 2006 3:36PM - 3:48PM |
HD.00007: Two-quasiparticle states in $^{252,254}$No and the stability of superheavy nuclei T.L. Khoo, S.K. Tandel, A. Robinson, D. Seweryniak, F.G. Kondev Two-quasiparticle (qp) states in shell-stabilized nuclei probe the levels that govern the stability of superheavy nuclei, test 2-qp energies from theory and, thereby, check their predictions of magic gaps. We have identified in $^{254}$No 2- and 4-qp isomers, with quantum numbers K$^{\pi }$ = 8$^{-}$ and (14$^{+})$, and a low-energy 2-qp K$^{\pi }$= 3$^{+}$ state, as well as a K$^{\pi }$ = 8$^{- }$isomer in$^{ 252}$No. The use of Woods-Saxon single-particle energies reproduces the experimental proton 2-qp energies in $^{254}$No. Some shortcomings in the 2-qp energies from self-consistent mean-field theories suggest that their predictions of magic gaps at Z=120 and 126 should be viewed with reservations. The resilient survival of superheavy nuclei with high Z, up to 118, well past the onset of spontaneous fission at Z=92, is an interesting phenomenon in nuclear and mesoscopic physics. This research was conducted by a collaboration from Argonne National Laboratory and the Universities of Massachusetts Lowell, Jyv\"{a}skyl\"{a}, K\"{o}ln, Liverpool, Maryland, Notre~Dame and Yale. [Preview Abstract] |
Saturday, October 28, 2006 3:48PM - 4:00PM |
HD.00008: The Symmetry Energy, Nuclei, and Neutron Stars Andrew Steiner The isospin symmetry energy, also known as the nuclear symmetry energy, is one of the key bridges between the description of heavy nuclei and neutron stars. Correlations among several observables that are connected to the symmetry energy will be discussed including the neutron skin thickness in heavy nuclei, the pressure of neutron-rich matter, the degree of isospin diffusion in intermediate-energy heavy-ion collisions, the radii of 1.4 solar mass neutron stars, and the threshold density for the direct Urca process. Particular attention will be paid to the critical density for the direct Urca process and how it can be modified by the isospin dependence of the symmetry energy. Connections to present neutron star observations and cooling data will be discussed. [Preview Abstract] |
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