Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session R2: Nuclear Structure |
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Sponsoring Units: DNP Chair: Richard Casten, Yale University Room: Hyatt Regency Jacksonville Riverfront Grand 1 |
Monday, April 16, 2007 10:45AM - 11:21AM |
R2.00001: High-accurcay Penning trap mass measurements for nuclear structure and fundamental studies Invited Speaker: Like few other parameters, the mass of an atom, and its inherent connection with the atomic and nuclear binding energy is a fundamental property, a unique fingerprint of the atomic nucleus. For short-lived exotic atomic nuclei the importance of its mass ranges from the verification of nuclear models, nucleosynthesis studies, to a test of the Standard Model, in particular with regard to the weak interaction and the unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix [1]. The introduction of Penning traps into the field of mass spectrometry has made this method a prime choice for high-accuracy measurements on short-lived and stable nuclides. This is reflected in the large number of traps in operation, under construction, or planned world-wide. With the development and application of proper cooling and detection methods the trapping technique has the potential to provide the highest sensitivity and accuracy, even for very short-lived nuclides far from stability. The limits of mass measurements of exotic nuclei have been extended considerably by improving and developing on-line Penning trap mass spectrometers as, e.g., CPT at Argonne, ISOLTRAP at ISOLDE/CERN, JYFLTRAP at IGISOL/Jyv\"askyl\"a, LEBIT at MSU/East Lansing, and SHIPTRAP at GSI/Darmstadt. The precise determination of nuclear binding energies far from stability includes nuclei that are produced at rates of 100 ions/s and with half-lives well below 100\,ms. The mass resolving power reaches $10^7$ and the uncertainty of the resulting mass values has been pushed down to below $10^{-8}$. The presentation will describe the basics and recent progress made in ion trapping, cooling, and detection for high-accuracy Penning trap mass measurements. Special attention is devoted to the applications of accurate mass values for nuclear structure and fundamental studies. [1] K. Blaum, Phys.Rep. 425 (2006) 1. [Preview Abstract] |
Monday, April 16, 2007 11:21AM - 11:57AM |
R2.00002: The single-particle structure around $^{132}$Sn explored through the (d,p) reaction Invited Speaker: The nuclear shell model$^{1}$, originally developed by Maria Geoppert Mayer in 1949 (Nobel Prize 1963) has been used extensively to explain the structure of nuclei. The atomic shell model describes the increased stability observed when an electron shell is filled. Correspondingly, nuclei with magic numbers of protons or neutrons (2, 8, 20, 28, 50, 82, 126) display additional stability. Only ten nuclei to date have been observed which have these standard magic numbers for both neutrons and protons, of these, half are stable or very long-lived. Many changes have been observed in nuclei as we move away from the valley of stability and it is important, both to nuclear structure physics and to understanding the synthesis of nuclei in the cosmos, to understand how these changes affect single-particle states.$\backslash $One exotic doubly-magic nucleus which can be produced with sufficient intensity to perform reactions on it is $^{132}$Sn. Recent calculations$^{2}$ have shown that the structure around $^{132}$Sn may affect the freeze out of the rapid neutron capture (r-)process, believed to occur in supernovae, which is responsible for the production of about half the nuclear species heavier than iron. By adding a neutron to a beam of $^{132}$Sn via a transfer reaction, it is possible to study single-particle states beyond the double-shell closure. I will present results from a recent measurement of $^{133}$Sn via the $^{132}$Sn(d,p) reaction in inverse kinematics. \newline \newline [1] Maria Goeppert Mayer, \textit{Science} \textbf{145} 999 (1964). \newline [2] R. Surman and J. Engel, \textit{Phys. Rev. C}\textbf{ 64}, 035801 (2001). [Preview Abstract] |
Monday, April 16, 2007 11:57AM - 12:33PM |
R2.00003: Understanding proton-neutron mixed symmetry from microscopic internucleon interactions Invited Speaker: The atomic nucleus is perhaps the best-studied two-component quantum system in nature. When the two components (protons and neutrons) occupy different valence spaces, collective excitations of the valence-shell particles can arise which exhibit pronounced two-fluid character, and it is a fundamental problem to understand the microscopic origin of these ``mixed-symmetry" (MS) states. Since they are formed from a collective coupling of valence proton/neutron subsystems, MS states are expected to provide a unique probe of the effective valence shell proton-neutron interaction and be particularly sensitive to shell structures. In nearly-spherical nuclei in the mass A=90 and A=130 region, MS states are manifested as collective isovector quadrupole excitations and have recently received considerable experimental attention. This talk will focus on a theoretical program which attempts to describe and understand MS states from a microscopic shell model approach in which the low-momentum internucleon interaction $V_{{\rm low}\, k}$ is taken as the starting point. This work provided a comprehensive picture of MS states in an odd-mass nearly-spherical nucleus and played an instrumental role in the first experimental identification of MS states in such a nucleus, $^{93}$Nb. I will further discuss how the predicted evolution of MS properties reveals a restoration of collective MS structure in the mid-shell region, providing the first explanation for the existence of pronounced collective MS structures in weakly-collective nuclei. Throughout I will highlight the close connection between this work and ongoing experimental efforts. [Preview Abstract] |
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