Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session FC: Nuclear Structure A>150 |
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Chair: Fernando Montes, Michigan State University Room: Sweeney Ballroom B |
Thursday, October 29, 2015 4:00PM - 4:12PM |
FC.00001: Transfer of Neutrons from Deep Below the Fermi Surface via the (p,t) Reaction in the N=90 Region P. Humby, E. Wilson, C.W. Beausang, A. Simon, K. Gell, T. Tarlow, G. Vyas, T.J. Ross, R.O. Hughes, J.T. Burke, R.J. Casperson, J. Koglin, S. Ota, J.M. Allmond, M. McCleskey, E. McCleskey, A. Saastamoinen, R. Chyzh, M. Dag The $^{152,154}$Sm(p,t) reactions were used to investigate excited states populated by the transfer of neutrons from deep below the Fermi surface. States corresponding to the transfer of at least one neutron from below the N=82 shell closure are of particular interest since they provide a sensitive probe of the evolution of the shell closure with increasing deformation. In the present work, large quasi-discrete structures were observed in the triton energy spectra at excitation energies of 2-3~MeV and are interpreted in terms of the underlying Nilsson orbitals. The experiment utilized a 25~MeV proton beam from the K-150 cyclotron at the Cyclotron Institute of Texas A\&M University and the outgoing charged particles and $\gamma$ rays were detected using the STARLiTeR array. [Preview Abstract] |
Thursday, October 29, 2015 4:12PM - 4:24PM |
FC.00002: Application of the Oslo method to high resolution gamma spectra A. Simon, M. Guttormsen, A.C. Larsen, C.W. Beausang, P. Humby Hauser-Feshbach statistical model is a widely used tool for calculation of the reaction cross section, in particular for astrophysical processes. The HF model requires as an input an optical potential, gamma-strength function (GSF) and level density (LD) to properly model the statistical properties of the nucleus. The Oslo method is a well established technique to extract GSFs and LDs from experimental data, typically used for gamma-spectra obtained with scintillation detectors. Here, the first application of the Oslo method to high-resolution data obtained using the Ge detectors of the STARLITER setup at TAMU is discussed. The GSFs and LDs extracted from (p,d) and (p,t) reactions on \textsuperscript{152,154}Sm targets will be presented. [Preview Abstract] |
Thursday, October 29, 2015 4:24PM - 4:36PM |
FC.00003: Investigation of excited 0$^+$ states populated in the $^{162}Er$(p,t) reaction C. Burbadge, V. Bildstein, A. Diaz Varela, M. Dunlop, R. Dunlop, P.E. Garrett, D.S. Jamieson, D. Kisliuk, K.G. Leach, J. Loranger, A. MacLean, A. Radich, E. Rand, C.E. Svensson, G.C. Ball, S. Triambak, T. Faestermann, R. Hertenberger, H.- F. Wirth A continuing challenge in nuclear structure physics is the determination of the nature of low-lying excited 0$^+$ states. Various approaches have been implemented to interpret the occurence of these states, such as vibrational excitations in $\beta$ and $\gamma$ phonons or pairing excitations. One of the difficulties, however, in resolving the nature of these states is that there is a paucity of data; even the first excited state, 0$^+_2$, is not always known. Direct two-neutron transfer reactions are a useful tool for locating and investigating the nature of excited 0$^+$ states in well-deformed nuclei. Using the Q3D spectrograph at the Maier-Leibnitz Laboratory, the $N=92$ nucleus $^{160}$Er was studied via ($p,t$) reactions with a highly-enriched $^{162}$Er target. Strong population of the 0$^+_2$ state was observed with large cross sections greater than any other excited $0^+$ state. Preliminary results will be presented. [Preview Abstract] |
Thursday, October 29, 2015 4:36PM - 4:48PM |
FC.00004: Lifetime Measurements in $^{162}$Dy Clark Casarella, A. Aprahamian, S. Lesher, B. Crider, M. Lowe, E. Peters, F. Prados-Estevez, T. Ross, Z. Tully, S. Yates Historically, the rare-earth region of nuclei has been a fountainhead for nuclear structure phenomena. One of the more debated structure effects is the nature of excited 0+ bands in nuclei, and continues to be an outstanding challenge in nuclear structure physics; several interpretations exist, and we hope that lifetime measurements can help distinguish between them. $^{162}$Dy has an abundance of 0+ states with limited lifetime data; we have measured excitation functions, mean lifetimes, and angular distributions of gamma rays for excited states in $^{162}$Dy at the University of Kentucky Accelerator Laboratory. Low lying excited states were populated up to an excitation energy of E $<$ 3.2 MeV, where we will discuss the implications of the lifetimes under this energy threshold. This work was supported by the NSF under contract numbers PHY-1068192, PHY-1205412, and PHY-0956310. [Preview Abstract] |
Thursday, October 29, 2015 4:48PM - 5:00PM |
FC.00005: Particle-gamma studies with the new Hyperion array R.O. Hughes, J.T. Burke, S. Fisher, J. Parker, S. Ota, A. Ting, R.J. Casperson, E. McCleskey, A.B. Mcintosh, C.W. Beausang, E. Wilson, P. Humby Hyperion is a charged-particle and $\gamma $-ray spectroscopy array for low energy nuclear physics studies consisting of a highly segmented silicon telescope for charged particle detection surrounded by up to 14 HPGe ``clover'' $\gamma $-ray detectors. Hyperion was designed and built between March 2014 and May 2015 as a significant upgrade to the existing STARLiTeR array currently at Texas A{\&}M University Cyclotron Institute. The array was installed in May 2015 in preparation for its commissioning runs scheduled for September 2015. Hyperion will offer high particle-gamma and particle-gamma-gamma detection efficiencies and is intended to be used both for low energy structure studies and indirect measurements of neutron cross sections via the surrogate method. Details of the new array and the commissioning experiment focusing on $^{167,168,169}$Tm studies will be presented. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. Supported by DoE grant numbers DE-FG52-09NA29467 (TAMU), DE-NA0001801, DE-FG02-05ER41379 (UofR). [Preview Abstract] |
Thursday, October 29, 2015 5:00PM - 5:12PM |
FC.00006: Investigation of $^{198,200}$Hg isotopes A. Diaz Varela, E.T. Rand, P.E. Garrett, V. Bildstein, C. Burbadge, B. Hadinia, D.S. Jamieson, B. Jimeddorj, A.T. Laffoley, K.G. Leach, A.D. MacLean, A. Radich, C.E. Svensson, G.C. Ball, T. Faestermann, R. Hertenberger, H.-F. Wirth, B. Rebeiro, S. Triambak Limits on the electric dipole moment (EDM) continue to decrease for $^{199}$Hg, which provides the most stringent upper limit for a nuclear EDM to date. The $E3$ and $E1$ strength distributions to the ground state of $^{199}$Hg, and $E2$ transitions among excited states, would be ideal information to constrain theoretical models of the $^{199}$Hg Schiff moment. The high level density of $^{199}$Hg makes those determinations challenging, however similar information can be obtained from exploring surrounding even-even Hg isotopes. As part of a campaign to study the $^{198,200}$Hg isotopes, a number of experiments have been performed using the Q3D spectrograph at the Maier-Leibnitz Laboratory, with 22 MeV deuteron beams impinging on enriched Hg$^{32}$S targets. Inelastic scattering allows us to probe the desired $E2$ and $E3$ matrix elements, while the $^{198}$Hg$(d,p)$ and $^{200}$Hg$(d,t)$ reactions provide information on the neutron single-particle states of $^{199}$Hg. [Preview Abstract] |
Thursday, October 29, 2015 5:12PM - 5:24PM |
FC.00007: Prompt and Delayed Spectroscopy of Ac isotopes around $N=$126 S.S. Hota, G.J. Lane, M.W. Reed, A.J. Mitchell, A.E. Stuchbery, T. Kibedi, A.A. Akber, T.E. Eriksen, M.S. Gerathy, N. Palalani, T.R. Palazzo Nuclei above $Z=$82 and around $N=$126 are well described by the spherical shell model, with the attractive proton-neutron residual interactions and particle-octupole vibration coupling resulting in energy-favored, isomeric states occurring along the yrast line. Nuclei up to Z$=$88 are mostly well known [1], but information on Ac ($Z=$89) isotopes is limited. We report on high-spin, gamma-ray spectroscopy measurements of $^{214,215,216,217}$Ac performed at the Australian National University using the CAESAR array and fusion-evaporation reactions between $^{12}$C and $^{14,15}$N beams delivered by the 14UD accelerator incident on $^{204}$Pb and $^{209}$Bi targets. States up to 29/2$^{+}$ isomers were known previously in $^{215,217}$Ac [2,3], while only one gamma-ray has been assigned to each of $^{214,216}$Ac. New level schemes have now been constructed for $^{214,216}$Ac and those for $^{215,217}$Ac have been significantly extended. The results will be presented in detail together with semi-empirical shell model calculations that support the proposed level schemes. \\[4pt] [1] G. D. Dracoulis et. al., Phys. Rev. C 80, 054320 (2009).\\[0pt] [2] D. J. Decman et. al., Nuclear Physics A 436 (1985) 311-337.\\[0pt] [3] D. J. Decman et. al., Z. Phys. A 310, 55-59 (1983). [Preview Abstract] |
Thursday, October 29, 2015 5:24PM - 5:36PM |
FC.00008: Vibration and Rotation in N=150,152 Cf Nuclei P. Chowdhury, Y. Qiu, S.S. Hota, C.J. Lister, T.L. Khoo, R.V.F. Janssens, I. Ahmad, M.P. Carpenter, J.P. Greene, F.G. Kondev, T. Lauritsen, D. Seweryniak, S. Zhu Collective rotational bands with spins $>$ 20$\hbar$ have been populated in experiments on Z$\approx$100 nuclei via inelastic and transfer reactions with heavy beams. In this mass region, the coupling of rotations and vibrations is still waiting to be adequately explored. Nuclei here are expected to be especially fertile in non-quadrupole shape degrees of freedom. In addition to reflection-asymmetric octupole shapes, non-axial $\beta_{32}$ deformations have been predicted for N=150 nuclei in both mean-field and density functional theories, with $^{248}$Cf as a front-runner for the observation of such effects. Rotation-vibration couplings for higher order multipole shapes for these nuclei may provide a window to symmetries in superheavy nuclei. High-spin states in $^{248,250}$Cf nuclei were populated via inelastic and transfer reactions using a $^{208}$Pb beam incident on radioactive $^{249}$Cf and mixed $^{249,250,251}$Cf targets, with prompt $\gamma$ rays detected by the Gammasphere array. Octupole vibrations were identified in $^{248,250}$Cf, and extended to high spins. The results will be presented and discussed in the context of the emerging systematics of this region. [Preview Abstract] |
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