Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session Y11: Alchemy of the Heaviest Elements |
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Sponsoring Units: DNP Chair: Walter Loveland, Oregon State University Room: Marriott Tampa Waterside Room 7 |
Tuesday, April 19, 2005 1:30PM - 2:06PM |
Y11.00001: Super-Heavy Elements: Theoretical Perspective Invited Speaker: The superheavy nuclei represent the limit of nuclear mass and charge; they inhabit the remote corner of the nuclear landscape whose extent is unknown. The discovery of new elements with $Z\ge 110$ has brought much excitement to the atomic and nuclear physics communities. The very existence of nuclei that are so heavy hangs on a subtle balance between the attractive nuclear force and the disruptive Coulomb repulsion between protons that favors fission. In this work, we model the interplay between strong and electromagnetic interactions using the self-consistent energy density functional theory, which can describe the phenomenon of the spontaneous breaking of spherical symmetry. We predict that the long-lived superheavy elements can exist in a variety of shapes, including spherical, axial, and triaxial. In some cases, we anticipate the existence of metastable states and shape isomers that can affect decay properties; hence nuclear half-lives. [Preview Abstract] |
Tuesday, April 19, 2005 2:06PM - 2:42PM |
Y11.00002: Review of the Synthesis of the Heaviest Elements and Their Chemistry Invited Speaker: The heavy element group at Lawrence Livermore National Laboratory (LLNL) has a long tradition of nuclear and radiochemistry dating back to the 1950's. Some of the most exciting work has taken place in the last five years (in collaboration with the Flerov Laboratory of Nuclear Reactions in Dubna, Russia) with the discovery of four new elements - 113, 114, 115, and 116. By pushing the boundaries of the periodic table, we can start to answer some of the most fundamental questions of nuclear science, such as the locations of the next ``magic numbers'' of protons and neutrons, and the possibility of an ``Island of Stability'' where nuclides would have lifetimes much longer than those currently observed in the heaviest elements. We have already seen evidence of extra-stability in the heaviest nuclides, which leads to half-lives that are long enough for us to perform chemistry on these isotopes one atom at a time. Work is already underway on developing a chemical system designed to isolate element 114. These experiments will allow chemists to identify the chemical properties of element 114 and determine whether it truly behaves as a Group 14 element such as Sn or Pb. In this presentation, a brief history of the discovery of these new elements will be given as well as an introduction to the chemical experiments in progress. [Preview Abstract] |
Tuesday, April 19, 2005 2:42PM - 3:18PM |
Y11.00003: Structure and Formation of Heavy Shell-Stabilized Nuclei Invited Speaker: The heaviest nuclei represent systems at the limits of stability in charge, spin and excitation energy. They can exist only because the shell-correction energy lowers the ground-state energy, thereby creating a barrier against fission. The formation of these shell-stabilized nuclei is accompanied by electromagnetic emission. Despite minuscule cross sections ($<$1$\mu $b), in-beam $\gamma $-spectroscopic measurements have been possible, by combining large $\gamma $-ray detector arrays with mass analyzers, which uniquely identify the emitting nuclei. Measurements of the $\gamma $-ray total energy and multiplicity provide a measure of the fission barrier ($>$5 MeV) and also show that the nuclei can survive up to high angular momentum ($\sim $30$\hbar )$, although they are delicately bound. Hence, high partial waves are important in the synthesis of superheavy nuclei. The shell-correction energy arises from gaps in the single-particle energy spectrum. Hence, information on the latter is critical for understanding the heaviest nuclei, and is provided by the moments of inertia of rotational bands, the quasiparticle energies of odd-A nuclei and high-K isomers. The spectroscopic results on the heaviest nuclei (mainly on $^{252,253,254}$No, from experiments at Argonne and Jyv\"{a}skyl\"{a}) will be summarized and compared with the predictions of self-consistent relativistic mean-field theory. This comparison gives a picture of our current understanding about single-particle properties and pairing in the heaviest nuclei. [Preview Abstract] |
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