Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session HA: New Symmetries in Nuclei |
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Sponsoring Units: DNP Chair: Bradley Sherrill, National Superconducting Cyclotron Laboratory at Michigan State University Room: Gaylord Opryland Tennessee C |
Saturday, October 28, 2006 2:00PM - 2:36PM |
HA.00001: Mixed Proton-Neutron Symmetry in the Valence Shell of Heavy Nuclei Invited Speaker: Three generic aspects determine the physics of atomic nuclei as specific examples of mesoscopic two-fluid quantum systems: collectivity (many-body aspect), shell structure (quantum aspect), and the isospin degree of freedom (two-fluid character). Their interplay and competition can be sensitively studied on phenomena that reflect these three aspects equally strongly such as collective isovector excitations of the valence shell of heavy nuclei. Such structures have been predicted previously, for instance, in the interacting boson model (IBM-2) in terms of mixed-symmetry states. New experimental approaches have been developed over the last few years for studying these off-yrast low-spin nuclear structures with mixed proton-neutron symmetry. The data will be reviewed and an outlook to the future development of the field will be attempted. [Preview Abstract] |
Saturday, October 28, 2006 2:36PM - 3:12PM |
HA.00002: The Transition Between Symmetry Phases in Nuclei Invited Speaker: The understanding of collective nuclear structure often relies upon a set of benchmarks or symmetries which describe idealized limits. The three standard benchmarks of nuclear structure, the vibrator, rotor, and $\gamma$-soft structure have been known for decades. Few nuclei actually manifest these symmetries, however, and the range of structures between them is extensive. Until recently, transitional nuclei were traditionally described by numerical diagonalization of a multi-parameter Hamiltonian. However, newly proposed critical point symmetries, X(5) and E (5), can now describe nuclei at the point of a phase transition from spherical to deformed shapes. The success of these analytic models has generated considerable interest in developing other simple models to describe a wider class of transitional nuclei. These models in fact, now provide analytic solutions to describe the entire range of nuclei between spherical and deformed shapes. The predictions of these models, along with traditional descriptions, will be presented. They show both excellent agreement and striking discrepancies with the data on most transitional nuclei. This work was supported by the U.S. DOE Grant No. DE-F602-91-ER-40609.\\ [Preview Abstract] |
Saturday, October 28, 2006 3:12PM - 3:48PM |
HA.00003: Magnetic Moment of $^{57}$Cu and shell breaking of the $^{56}$Ni core Invited Speaker: The nuclear magnetic moment of the ground state of $^{57}$Cu was deduced for the first time. Together with a known magnetic moment of the mirror partner, $^{57}$Ni, the spin expectation value, which is a contribution of nucleon spins to the magnetic moment, was extracted from the isoscaler part of magnetic moments. In the $sd$ shell, a systematic trend of the spin expectation value of isospin $T$ = 1/2 mirror nuclei has been observed. On the other hand, in the $fp$ shell, only a few mirror magnetic moments are known and therefore it is essential to measure more magnetic moments to explore the evolution of shell structure. Because $^{57}$Cu consists of the closed-shell $^{56}$Ni core plus one proton, the single-particle contribution is expected to be strong and any deviation from the shell model is a direct proof of shell breaking at $^{56}$Ni, which has been suggested [1] based on a systematic deviation between magnetic moments of odd-mass Cu isotopes and theoretical shell-model predictions. \\ From the resonance frequency, the magnetic moment was derived as $|\mu(^{57}{\rm Cu})| = (2.00 \pm 0.05) \mu_{\rm N}$ [2]. The $A$ = 57, $T$ = 1/2 spin expectation value was extracted as $\langle\Sigma\sigma_z\rangle = -0.78 \pm 0.13$. The small $\mu(^{57}$Cu) results in a large deviation and opposite sign from the shell-model calculations [3,4]. Considering the systematic behavior of the spin expectation value of $T$ = 1/2 nuclei in the $sd$ shell, the present result indicates a significant shell breaking at $^{56}$Ni with the neutron number $N$ = 28.\\ \noindent [1] V. V. Golovko {\it et al}., Phys. Rev. {\bf C 70}, 014312 (2004).\\ \noindent [2] K. Minamisono {\it et al}., Phys. Rev. Lett. {\bf 96}, 102501 (2006).\\ \noindent [3] D. R. Semon {\it et al}., Phys. Rev. {\bf C 53}, 96 (1996).\\ \noindent [4] M. Honma {\it et al}., Phys. Rev. {\bf C 69}, 034335 (2004). [Preview Abstract] |
Saturday, October 28, 2006 3:48PM - 4:24PM |
HA.00004: Aspects of nuclear pairing Invited Speaker: Pairing correlations between nucleons are known to be one of the major driving forces behind the nuclear many-body dynamics. The collective effects resulting from pairing play a crucial role in many nuclear properties. Despite a long history the methods of treating pairing along with corresponding questions and problems have constantly evolved. The role of pairing in exotic nuclei where superconducting phase competes with particle instability will be addressed in this presentation. Apart from this, the mesoscopic nature of the problem also accentuates other problems such as interplay of pairing and collective effects including rotations and deformations. The extended pairing phase transition, instability to large fluctuations and related thermodynamical properties are inseparable components of nuclear superconductivity. In this presentation I will explore these questions highlighting simultaneously the novel methods and techniques. The method of Exact Pairing (EP) is based on the algebraic treatment of pairing that relies on quasispin algebra. Recently the EP has evolved into a powerful technique that provides an exact numerical solution to the many-body problem. The EP serves as a foundation for understanding of manifestations of pairing in mesoscopic systems, and provides some answers to the above questions. The method allows for far-reaching extensions such as inclusion of collective dynamics within Random Phase Approximation, treatment of interactions beyond pairing and exploration of continuum of reaction states. Considering pairing within a rotating deformed proton emitter I will address its effect on particle emission. The kinematical suppression of the recoil, known as Coriolis attenuation, due to the superfluid nature of the rotating core is of special interest. [Preview Abstract] |
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