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 GF: Nuclear Structure: Around A=150 |
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Chair: Frank Dietrich, Lawrence Livermore National Laboratory Room: Kearney |
Friday, November 5, 2010 8:30AM - 8:42AM |
GF.00001: Investigation of octupole vibrations in even-even rare earth nuclei using (p,pg) M. Elvers, D. Savran, T. Ahn, V. Anagnostatou, N. Cooper, P. Goddard, A. Heinz, G. Ilie, D. Radeck, V. Werner, J. Endres, C. Kueppersbusch, A. Zilges, T. Ahmed, C. Deng, E. Jiang, N. Shenkov Octupole vibrations in even-even rare earth nuclei have been studied for the last decades but many questions still remain unresolved. An excellent method to excite those states is by means of inelastic proton and deuteron scattering as it has been done in plenty rare earth nuclei. In those experiments, however, only the energy of excited octupole states was measured but not the electromagnetic transitions. The branching ratios are crucial to obtain further information on the inner structure of those vibrations such as the mixing of the K quantum number. One drawback of this method is the occurrence of competing neutron evaporation reactions and hence the detection of the scattered particle is also needed. Hence, a new chamber has been developed at WNSL at Yale housing a five silicon detector array covering 10\% solid angle which was integrated in the YRAST setup. Using the new setup, the transitional nucleus $^{150}$Nd has been investigated in (p,p'$\gamma$). The band structure was extended and the level scheme was clarified. [Preview Abstract] |
Friday, November 5, 2010 8:42AM - 8:54AM |
GF.00002: ABSTRACT WITHDRAWN |
Friday, November 5, 2010 8:54AM - 9:06AM |
GF.00003: On transition strengths of E1, E2, {\&} E3 in the regions of mixed quadrupole-octupole collectivity John Rasmussen, Y.X. Luo, Joseph Hamilton, A.V. Ramayya, Raul Donangelo We review the main highlights of experiment and theory for the lowest three electric multipolarities, B(E1), B(E2), and B(E3), for nuclei where quadrupole and octupole collectivity may both occur. The principal regions of interest are around 6 to 12 protons and 6 to 12 neutrons beyond the doubly-closed shell nuclei $^{132}$Sn and $^{208}$Pb. We examine microscopic theoretical calculations\footnote{W. Zhang et al., Phys. Rev. \textbf{C 81}, 034302 (2010) and references therein.} in which deformations are driven by Nilsson orbitals near the Fermi energy. We also focus attention on recent experimental\footnote{P.E. Garrett et al., Phys. Rev. Letts. 103, 062501 (2009)} studies of $^{152}$Sm, where the ground band and associated K=1$^{-}$ band are mirrored by another 0$^{+}$ and 1$^{-}$ band about 0.7 MeV higher in energy. We suggest that a monopole pairing force alone is insufficient to cause this mirroring, and monopole-plus-quadrupole pairing or a more realistic nucleon-nucleon force is needed. [Preview Abstract] |
Friday, November 5, 2010 9:06AM - 9:18AM |
GF.00004: Low-Lying Negative-Parity Bands of $^{152}$Sm via Deuteron Inelastic Scattering S. Chagnon-Lessard, P.E. Garrett, J.C. Bangay, L. Bianco, K.G. Leach, A.A. Phillips, E.T. Rand, C.E. Svensson, G.C. Ball, T. Faestermann, R. Kr\"ucken, R. Hertenberger, H.F. Wirth Nuclei near N=90 and Z=64 have recently been suggested to be `tetrahedral-magic' [1]. One of the main signatures for tetrahedral symmetry is a vanishing quadrupole moment in low-lying negative-parity bands. This has the consequence that a rotational band possess very weak, or even vanishing, E2 matrix elements. With N=90 and Z=62, $^{152}$Sm is a potential candidate for relatively stable tetrahedral symmetry. Complementing studies of $^{156}$Dy [2], the structure of $^{152}$Sm has been investigated using deuteron inelastic scattering with a 22 MeV polarized deuterium beam at the MP tandem Van de Graaff accelerator of the TU/LMU Munich. The deuterons from the reaction were momentum analyzed using the Q3D spectrometer. Absolute cross sections and analyzing powers have been extracted for levels up to 2 MeV. The low-lying negative-parity bands are observed to be strongly populated, however detailed coupled-channel calculations are required before transition elements can be extracted due to the many possible population pathways. Details of the experiment and analysis will be presented. [1] J. Dudek et al., PRL \textbf{88}, 25 (2002). [2] D.J. Hartley et al., Bull. APS \textbf{54}, 10 (2009). [Preview Abstract] |
Friday, November 5, 2010 9:18AM - 9:30AM |
GF.00005: Precision intensities and angular correlation measurements in $^{152}$Sm E.A. McCutchan, C.J. Lister, S. Zhu, M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, D. Seweryniak The samarium isotopic chain shows great structural change dripline-to-dripline; evolving from deformed at the proton dripline, through spherical near stability before undergoing another transformation near N=90 when large prolate deformation re-emerges. Lying at the midpoint of this latter transition is $^{152}$Sm. Numerous models have been developed to explain $^{152}$Sm in terms of either being at the critical point of a phase transition, or in terms of coexisting shapes. To test the validity of these different models, a beta-decay experiment was performed at the ATLAS facility at Argonne. The decay of $^{152}$Eu to $^{152}$Sm was studied through gamma-ray spectroscopy using Gammasphere. An extremely large data set was collected, consisting of $>$ 7x10$^{9}$ gamma-gamma or higher fold events. This made possible a high precision measurement of energies and intensities and very definite angular correlation determinations. The new results resolve some previous experimental ambiguities and help to differentiate between theoretical models. Work supported by the DOE Office of Nuclear Physics under contract DE-AC02-06CH11357. [Preview Abstract] |
Friday, November 5, 2010 9:30AM - 9:42AM |
GF.00006: Particle-gamma studies of Gd isotopes by (p,p'), (p,d) and (p,t) reactions T.J. Ross, R.O. Hughes, C.W. Beausang, J.M. Allmond, J.T. Burke, L.W. Phair, N. Scielzo, C.T. Angell, M.S. Basunia, D.L. Bleuel, R.J. Casperson, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, J.J. Ressler An experiment was conducted using the STARS-LIBERACE array at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory to study Gd isotopes around the N=90 transition region. A 25 MeV proton beam was incident on $^{158/155/154}$Gd targets and used to populate states in $^{152-158}$Gd by (p,p'), (p,d) and (p,t) reactions. This experiment compliments our earlier work on $^{156}$Gd(p,x),[1]. The exit channel is selected by gating on charged particles using the STARS (Silicon Telescope Array for Reaction Studies) array, which also gives the excitation energy of the residual nucleus. Coincident gamma information is obtained using the LIBERACE (LIvermore BErkeley Array for Collaborative Experiments) clover detector array. Particle-gamma coincidence measurements provide a strong tool for probing the residual nucleus, [1]. Preliminary results pertaining to $^{158}$Gd will be presented. [1] J. M. Allmond et al. Phys. Rev. C 81, 064316 (2010) This work is supported in part via DOE grant numbers DE-FG02-05 ER41379 {\&} DE-FG52-06 NA26206(University of Richmond), DE-AC52 07NA27344(LLNL) and DE-AC02 05CH11231(LBNL). [Preview Abstract] |
Friday, November 5, 2010 9:42AM - 9:54AM |
GF.00007: Photon Strength Functions for $^{156, 157, 159}$Gd Bayarbadrakh Baramsai, G.E. Mitchell, A. Chyzh, D. Dashdorj, C. Walker, T.A. Bredeweg, A. Couture, R.C. Haight, M. Jandel, A.L. Keksis, J.M. O'Donnell, R.S. Rundberg, J.M. Wouters, J.L. Ullmann, D.J. Vieira, U. Agvaanluvsan, F. Becvar, M. Krticka In recent years the low energy behavior of the Photon Strength Function (PSF) has attracted much attention. A completely consistent description of this behavior is not available. The neutron capture $\gamma$-ray spectra measured by the DANCE detector array located at the Los Alamos Neutron Science Center has been used for the study of the PSF below the neutron separation energy. The radiative decay of the compound nuclei $^{156, 157, 159}$Gd has been measured. The spectra were simulated with the DICEBOX code. A variety of phenomenological models of the PSF were considered in the simulations. Comparison of the experimental and simulated spectra will be presented. [Preview Abstract] |
Friday, November 5, 2010 9:54AM - 10:06AM |
GF.00008: Particle-Gamma Studies of Transitional Gd Nuclei Via Light-Ion Reactions R.O. Hughes, T.J. Ross, C.W. Beausang, J.M. Allmond, J.T. Burke, L. Phair, C.T. Angell, M.S. Basunia, D.L. Bleuel, R.J. Casperson, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, J.J. Ressler, N.D. Scielzo Gd nuclei with N $\sim$ 90 are of great interest due to a rapid change from vibrational to rotational character. Numerous experiments that have studied these nuclei were limited to either pure $\gamma$-ray or pure charged-particle studies. Recently, a series of experiments have been carried out at the 88-Inch cyclotron at LBNL, which combine relatively high-efficiency $\gamma$-ray and charged-particle spectroscopy in the same experiment. A beam of 25 MeV protons was incident on enriched $^{154}$Gd, $^{155}$Gd, $^{156}$Gd and $^{158}$Gd targets. Charged particles from the (p,p'), (p,d), and (p,t) reaction channels were detected using a Si-telescope array (STARS) and the coincident gamma-rays (in $^{152-158}$Gd) were detected using the Liberace HPGe clover array. The relatively high particle-gamma efficiency, precise energy resolution (via the $\gamma$ rays), and particle-$\gamma$ angular information provides a precision tool for spectroscopic studies. Preliminary results will be presented. This work was supported in part by the DOE under grant Nos. DE-FG02-05 ER41379 \& DE-FG52-06 NA26206 (UR), DE-AC52 07NA27344 (LLNL), DE-AC02 05CH11231 (LBNL). [Preview Abstract] |
Friday, November 5, 2010 10:06AM - 10:18AM |
GF.00009: Possible tetrahedral band in $^{156}$Dy L.L. Riedinger, D.J. Hartley, D. Curien, J. Dudek, G. Duchene, B. Gall, M.A. Riley, X. Wang, C. Beausang, P.E. Garrett, W.D. Kulp, J.L. Wood, M.P. Carpenter, C.J. Chiara, F.G. Kondev, T. Lauritsen, E.A. McCutchan, S. Zhu, J. Sharpey-Schafer, J.M. Allmond, C.H. Yu, J. Simpson, V. Werner The lowest lying negative-parity band in $^{156}$Dy has been viewed as a K = 0$^{-}$ octupole-vibrational band, but could be tetrahedral in nature. To determine if this band is tetrahedral, the lifetimes of the states must be measured. We report a pilot study of the $^{26}$Mg($^{126}$Xe,5n) reaction using Gammasphere at Argonne's ATLAS facility, to learn if the states of interest would be populated in this reaction and to discover if any Doppler broadening could be observed, indicating a long lifetime for the band of interest. The states were populated in a low--statistics run and no Doppler broadening was observed, which is consistent with (but not conclusive for) tetrahedral symmetry. We are preparing a plunger measurement to disentangle the 2 ps population of this band from the lifetimes of the states in this debated K = 0$^{-}$ band, to learn if it is octupole vibrational (state lifetime around 0.5 ps) or tetrahedral (longer than a few ps). [Preview Abstract] |
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