Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session 2WA: Pre-Meeting Workshop: Exotic Nuclei: From the Laboratory to the Cosmos II |
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Sponsoring Units: DNP Chair: David Dean, Oak Ridge National Laboratory Room: Gaylord Opryland Bayou C |
Wednesday, October 25, 2006 2:00PM - 2:30PM |
2WA.00001: Probing shell structure using beta-delayed and isomeric gamma-ray spectroscopy at the NSCL Invited Speaker: I will review the results of recent measurements of beta-delayed and isomeric gamma rays from neutron-rich nuclides produced by fast fragmentation at the National Superconducting Cyclotron Laboratory at Michigan State University. The use of fast fragmentation allows for unambiguous mass and proton number assignments to each implanted fragment. The time and position correlations between fragment implantations and emitted beta particles, on an event-by-event basis, greatly reduce background and make the approach suitable for use with cocktail beams. The results to be discussed examined the systematic behavior of low- energy states in nuclides near the neutron shell closures at N = 20, 28, 50, and 82. This work was supported in part by the National Science Foundation grant PHY-01-10253. [Preview Abstract] |
Wednesday, October 25, 2006 2:30PM - 3:00PM |
2WA.00002: The Astrophysical Site of the r-process Invited Speaker: Over half the heavy elements with mass number A $>$ 100 are made by rapid neutron capture. However, the astrophysical site of this element synthesis is not yet known. There are a few sites under consideration, including core collapse supernovae, gamma ray bursts and neutron star mergers. I will discuss the prospects for obtaining an r-process in these cases, as well as the roles played by neutrinos and fission cycling. [Preview Abstract] |
Wednesday, October 25, 2006 3:00PM - 3:30PM |
2WA.00003: Break |
Wednesday, October 25, 2006 3:30PM - 4:00PM |
2WA.00004: The Role of the rp-Process in Accreting Neutron Stars Invited Speaker: Neutron stars in low mass X-ray binaries accrete enough material during their lifetimes to replace their entire crust. As the accreted material is pushed deeper and deeper into the star it undergoes a sequence of nuclear transformations. In the last ten years, the discovery of new observational phenomena has opened new windows onto these processes and the nuclei involved. In this talk, I will discuss what we're learning about nuclear burning on accreting neutron stars and the properties of the neutron star crust and core, concentrating on the important role of the heavy elements made in the rp-process. [Preview Abstract] |
Wednesday, October 25, 2006 4:00PM - 4:30PM |
2WA.00005: Reactions Induced by Neutron-Rich Nuclei Invited Speaker: Nuclear reactions involving the fusion of neutron-rich nuclei allow us to study the properties of halo or other loosely bound projectile nuclei, such as $^{6}$He and $^{11}$Li and to form and study the properties of the heaviest nuclei. In the latter case, the n-rich projectile allows us to reach nuclei with large neutron numbers, with resulting longer half-lives (qualitatively changing the study of the atomic physics and chemistry of these elements) along with allowing increased production cross sections due to lowered fusion barriers and higher survival probabilities. In four typical reactions $^{32,38}$S + $^{181}$Ta, $^{27,29,31}$Al + $^{197}$Au, $^{124,132}$Sn + $^{64}$Ni and $^{32,38}$S + $^{208}$Pb, one observes enhanced fusion cross sections and most interestingly, large and unanticipated shifts of the fusion barrier heights for the most n-rich projectiles. The systematics of these shifts are presented and compared to ideas of neutron flow in these reactions. In a related measurement for the $^{124,132}$Sn + $^{96}$Zr reaction, no evidence for increasing fusion hindrance with increasing isospin of the system was found. The implications of these results for the synthesis of heavy nuclei using radioactive beams are discussed. The interaction of $^{6}$He with $^{209}$Bi and $^{238}$U has been extensively studied. The fusion cross section is enhanced at sub-barrier energies and reduced above the barrier. Detailed calculations of the fusion excitation functions that consider breakup processes do reproduce the observed cross sections. The recent attempt to measure the fusion excitation functions for the $^{9,11}$Li + $^{70}$Zn reaction will be discussed. [Preview Abstract] |
Wednesday, October 25, 2006 4:30PM - 5:00PM |
2WA.00006: The Heaviest Exotic Nuclei in the Laboratory – Superheavy Nuclei Invited Speaker: How many more new elements can be synthesized? What are the nuclear and chemical properties of these exotic nuclei? Does the “Island of Stability” exist and can we ever explore the isotopes inhabiting that nuclear region? Some of the most fascinating questions about the limits of nuclear stability are confronted in the heaviest nuclei. This talk will focus on the current experimental research on the synthesis and characterization of superheavy nuclei with Z>112 from the Dubna/Livermore collaboration. Reactions using 48Ca projectiles from the U400 cyclotron and actinide targets (233,238U, 237Np, 242,244Pu, 243Am, 245,248Cm, 249Cf) have been investigated using the Dubna Gas Filled Recoil Separator in Dubna over the last 8 years. In addition, several experiments have been performed to investigate the chemical properties of some of the observed longer-lived isotopes produced in these reactions. A summary of the current status of the upper end of the chart of nuclides will be presented. [Preview Abstract] |
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