Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session DC: Mini-symposium on Nuclear Structure Theory and Experiments for Rare Isotopes II |
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Chair: Bruce Barrett, University of Arizona Room: Sweeny C |
Thursday, November 4, 2010 10:30AM - 10:42AM |
DC.00001: Electromagnetic transition rates in $^{70}$Ni and $^{72}$Ni David Miller, Lucia Cartegni, Robert Grzywacz, Mustafa Rajabali, Thomas Baugher, Daniel Bazin, Heather Crawford, Alexandra Gade, Geoff Grinyer, Hironori Iwasaki, Andrew Ratkiewicz, Philip Voss, Dirk Weisshaar, Krzysztof Starosta, Mathias Hackstein, Wolfram Rother A systematic study of Ni isotopes in the vicinity of doubly-magic $^{78}$Ni will help in the understanding of shell closure effects, isomerism, and single particle states in this region of the nuclear chart. An experiment was performed at National Superconducting Cyclotron Laboratory to measure electromagnetic transition rates in $^{70}$Ni and $^{72}$Ni populated by a one-proton knockout reaction of a Cu beam. The transition rates for the $2^+ \rightarrow 0^+$ and $4^+ \rightarrow 2^+$ transitions were determined using the Recoil Distance Method, particularly suited for picosecond lifetimes, using the Segmented Germanium Array coupled with the NSCL/K\"oln plunger at the target of the S800 spectrograph. The resulting lifetimes for the low lying transitions suggest a weaker core polarization for nickel isotopes above the N=40 subshell closure than previously suggested. [Preview Abstract] |
Thursday, November 4, 2010 10:42AM - 10:54AM |
DC.00002: New nuclide, $^{14}$F V.Z. Goldberg, B.T. Roeder, G.G. Chubarian, A.A. Alharbi, A. Banu, M.M. McCleskey, E. Simmons, G. Tabacaru, L. Trache, R.E. Tribble, G.V. Rogachev, E.D. Johnson, M.L. Avila, J.P. Mitchell, C. Fu Long ago the instability of $^{14}$F was estimated to be $\sim$2.58 MeV. Recently, properties of $^{14}$F and other 2s-d shell nuclei were calculated in the framework of an ab-initio approach. However, no experimental data are available on $^{14}$F. We used the Thick Target Inverse Kinematics method (TTIK) to study the excitation function for the $^{13}$O+p elastic scattering where $^{14}$F is the compound nucleus. The $^{13}$O (T$_{1/2}$ = 8.6 ms) secondary beam was made with intensity 5x10$^{3}$ pps via the $^{1}$H($^{14}$N,2n) reaction with a $^{14}$N primary beam at 38 MeV/u from the Texas A\&M Univ. cyclotron. To apply the TTIK method, we degraded the $^{13}$O energy to 11 MeV/u. As a result of the study, we obtain data on the ground and several excited states in $^{14}$F, their excitation energies, quantum characteristics and the widths of the resonances. The mass excess of $^{14}$F (M-E) was found to be 31960$\pm$50 keV. $^{14}$F appeared to be more stable than the corresponding estimations based on different extrapolations. Probably the unexpected lower instability is a result of rather pure single particle structure of the ground state in $^{14}$F. [Preview Abstract] |
Thursday, November 4, 2010 10:54AM - 11:06AM |
DC.00003: Ground-state neutron decay of $^{21}$C S. Mosby, M. Thoennessen, P. DeYoung The ground state of neutron-unbound $^{21}$C was measured for the first time in a neutron-fragment coincidence experiment at the National Superconducting Cyclotron Laboratory at Michigan State University. This is the heaviest neutron-unbound N = 15 nucleus and provides a measurement of the $\nu$(1s$_{1/2}$) - $\nu $(0d$_{5/2}$) shell gap in the presence of proton holes in the $p$ shell. $^{21}$C was produced via one-proton knockout from a $^{22}$N secondary beam at 69.7 MeV/u. The Modular Neutron Array (MoNA) was used to measure the time-of-flight and position of emitted neutrons, while $^{20}$C fragments were detected in a series of position and energy-sensitive detectors behind the MSU/FSU Sweeper magnet. The decay of $^{21}$C was then reconstructed event-by-event from the four-momentum vectors of the neutron and fragment. Preliminary results will be presented. [Preview Abstract] |
Thursday, November 4, 2010 11:06AM - 11:18AM |
DC.00004: Recent results for Be isotopes with JISP16 Pieter Maris, James Vary, Andrey Shirokov We present recent results from no-core full configuration calculations for Be isotopes up to mass 14 using a phenomenological two-body interaction, JISP16. We calculate the ground state energies (with numerical uncertainties) and low-lying spectra of both the natural and unnatural parity states. In addition to the binding energies we also discuss other observables such as dipole and quadrupole moments, as well as transition rates for select M1 and E2 transitions. [Preview Abstract] |
Thursday, November 4, 2010 11:18AM - 11:30AM |
DC.00005: Orbital dependent pairing and the structure of the lightest isotopes of tin Robert Grzywacz, Iain Darby, Jon Batchelder, Carrol Bingham, Lucia Cartegni, Carl Gross, Morten Hjorth-Jensen, David Joss, Sean Liddick, Witold Nazarewicz, Robert Page, Thomas Papenbrock, Mustafa Rajabali, Jimmy Rotureau, Krzysztof Rykaczewski, Stephen Padgett The island of alpha radioactivity near doubly magic $^{100}$Sn provides an opportunity to study properties of tin isotopes using the extreme selectivity of charge particle decay spectroscopy. In an experiment, which used the most advanced experimental spectroscopic techniques the $^{109}$Xe$\rightarrow$$^{105}$Te$\rightarrow$$^{101}$Sn alpha decay chain was studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge. The majority of the alpha decay branching ratio of the $^{105}$Te populates not the ground state but the first excited state in $^{101}$Sn leading to the revision of the established order of single particle levels. The in-depth analysis of this result with the state-of-the-art shell model calculations lead to surprising conclusions on the role of the pairing correlations in the lightest tin isotopes. [Preview Abstract] |
Thursday, November 4, 2010 11:30AM - 11:42AM |
DC.00006: Spin-triplet pairing in very large nuclei George Bertsch, Yuan Luo Spin-triplet pairing is expected to compete favorably against ordinary spin-single pairing when neutron and proton numbers are equal the nucleus becomes very large. Using empirically derived interactions, the spin-triplet region was found to start just beyond the domain of physically realizable nuclei*. We investigate here how the dominant pairing mode depends on nuclear deformation and neutron excess. We find that the spin-triplet pairing can persist to large deformations when N=Z and in spherical nuclei with some small neutron-proton asymmetry.\\[4pt] G.F. Bertsch and Y. Luo, Phys. Rev. C {\bf 81} 064320 (2010) [Preview Abstract] |
Thursday, November 4, 2010 11:42AM - 11:54AM |
DC.00007: Unified BCS-like model for pairing and alpha correlations Roman Sen'kov, Vladimir Zelevinsky Recent studies of nuclei far from stability set a problem of understanding the features of nuclear structure for systems with an unusual neutron-proton composition. Medium and heavy nuclei with $N$ close to $Z$, such as in the vicinity of $^{100}$Sn, give a unique example of a two-component fermionic system with coexisting pairwise and quartic correlations. To describe these collective effects we generalize the variational BCS ground state wave function including $p-p$, $n-n$, $p-n$ and $2p-2n$ components under the assumption of attractive interaction in time-conjugate orbitals. The analytical solution reveals the possibility of different condensates being a nuclear analog of the BCS-BEC crossover in mesoscopic physics. [Preview Abstract] |
Thursday, November 4, 2010 11:54AM - 12:06PM |
DC.00008: Estimation of pairing correlations for nuclear mass table evaluation Luis Robledo, George Bertsch Mean field models provide a well-justified theoretical approach to generate mass tables, but without some extension the energy misses the correlation energy associated with the restoration of broken symmetries such as angular momentum or particle number. The Lipkin-Nogami (LN) method is often used to treat the pairing correlation energy in mass table evaluations, mainly because of its simplicity. However, it has been found that in many nuclei pairing correlations are weak and the LN method, which is an approximation to the more sophisticated Particle Number Projection (PNP), fails. We propose an alternative to the LN method which can be safely applied in the regime of weak pairing correlations and is simpler than variation after projection (VAP) for the PNP. It is based on a Restricted VAP for PNP using the fluctuation on particle number as coordinate. We show that in the strong pairing correlation limit the LN method is recovered. The method is applied to the evaluation of the even-even nuclei mass table with the Gogny parametrization of the nuclear interaction. [Preview Abstract] |
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