Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session HD: Nuclear Structure III |
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Chair: Jutta Escher, Lawrence Livermore National Laboratory Room: Patio |
Friday, October 26, 2012 8:30AM - 8:42AM |
HD.00001: Lifetime measurement of the yrast 8$^{+}$ state in $^{70}$As Chris Morse, Hironori Iwasaki, Antoine Lemasson, Travis Baugher, Daniel Bazin, Jill Berryman, Alexandra Gade, Sean McDaniel, Andrew Ratkiewicz, Steven Stroberg, Phil Voss, Dirk Weisshaar, Kathrin Wimmer, Ryan Winkler, Alfred Dewald, Christoph Fransen, Adam Nichols, Robert Wadsworth In the A $\sim $ 70 region of the nuclear chart, the structure of excited nuclear states is sensitive to the occupation of the g$_{9/2}$ orbital. In particular, the excited states of the odd-odd nucleus $^{70}$As have been discussed in terms of the coupling of the valence proton and neutron to form two-particle configurations of $\pi $g$_{9/2}\nu $g$_{9/2}$ orbitals. To examine this, the lifetime of the 8$^{+}$ yrast state in $^{70}$As was measured using the gamma-ray line shape technique at the NSCL. Gamma-rays emitted at the reaction target position were measured with the SeGA HPGe array in coincidence with reaction residues detected in the S800 spectrometer. The transition strength of the lowest 8$^{+}$ level, which is among the excited states suggested to be part of these two-particle configurations, was obtained from the measured lifetimes. The validity of this assignment to a $\pi $g$_{9/2}\nu $g$_{9/2}$ configuration and the possible evolution of such high-spin orbitals in neutron-deficient As nuclei will be discussed in light of the present results. [Preview Abstract] |
Friday, October 26, 2012 8:42AM - 8:54AM |
HD.00002: Angular Correlations of $\gamma$-rays from $^{76}$As N. Cooper, V. Werner, E. Williams, C. Bernards, R.J. Casperson, A. Heinz, M. Marshall, J. Qian, M.K. Smith, J.R. Terry, R. Winkler, B.P. Crider, S.W. Yates The intermediate nucleus of the hypothetical neutrinoless double-beta ($0\nu 2\beta$) decay mode of $^{76}$Ge is $^{76}$As. Structural knowledge of this nucleus is important to the ongoing theoretical study of the $0\nu 2\beta$-decay mode. Energies and parities of many low-lying states of $^{76}$As are known; however, the only state of this nucleus with known spin is the ground state. The low-lying states of $^{76}$As have been studied in a $\gamma$-$\gamma$ angular correlations experiment at WNSL, Yale University. The $^{76}$Ge(p,n) reaction with 6 MeV incident protons was used to populate excited states of $^{76}$As. $\gamma$-rays were detected by a pair of LEPS detectors and 10 Compton-suppressed clover detectors mounted in the YRAST Ball array. Preliminary results will be presented. [Preview Abstract] |
Friday, October 26, 2012 8:54AM - 9:06AM |
HD.00003: Nuclear Structure Studies of $^{76}$Se and $^{76}$Ge with the $(n, n'\gamma)$ Reaction B.P. Crider, A. Chakraborty, A. Kumar, E.E. Peters, F.M. Prados-Est\'{e}vez, M.T. McEllistrem, S.W. Yates Experimental confirmation of neutrinoless double-beta decay (0$\nu\beta\beta$) would provide evidence of physics beyond the standard model by identifying the neutrino as its own anti-particle, \textit{i.e.}, a Majorana particle. Furthermore, such a confirmation would yield the absolute mass scale of neutrinos, provided that the nuclear matrix elements involved in the caculation are understood to a high degree of accuracy. A favorite candidate in the search for 0$\nu\beta\beta$ is the decay of $^{76}$Ge to $^{76}$Se, since $^{76}$Ge can act as a source of the decay as well as a high-resolution detector for the resultant events. In order to increase our knowledge of the structural properties of these nuclei, excitation function and $\gamma$-ray angular distribution measurements utilizing the $^{76}$Ge$(n, n'\gamma)$ and $^{76}$Se$(n, n'\gamma)$ reactions were performed at the University of Kentucky at neutron energies ranging from 2.0 MeV to 4.0 MeV. These measurements yield information on level spins and parities, level lifetimes, transition multipolarities, and transition probabilites. These results will be discussed in the context of structural features such as mixed-symmetry states and shape coexistence. [Preview Abstract] |
Friday, October 26, 2012 9:06AM - 9:18AM |
HD.00004: Measurement of the Isovector Giant Quadrupole Resonance of $^{89}$Y at HI$\gamma$S Mark Sikora, Gerald Feldman, Mohammad Ahmed, Jonathan Mueller, Luke Myers, Henry Weller, William Zimmerman The isovector giant quadrupole resonance (IVGQR) is challenging to characterize due to its broad width and low cross section relative to the nearby giant dipole resonance. The nearly 100 \% linearly polarized monochromatic photon beam available at the High Intensity $\gamma$-ray Source (HI$\gamma$S) provides a convenient method to study this collective state via Compton scattering. The interference of the E1 and E2 terms in the total elastic scattering amplitude provides enhanced sensitivity to the IVGQR parameters when measured simultaneously at forward and backward angles, significantly reducing the uncertainty in the extracted resonance parameters. We have performed such a measurement on $^{89}$Y over a photon energy range of 23-35 MeV. Scattered photons were detected by the 8 element HIGS NaI Detector Array (HINDA) at polar angles of 55$^{\circ}$ and 125$^{\circ}$, located in planes parallel and perpendicular to the plane of incident photon polarization. The out-of-plane to in-plane scattering ratio was measured as a function of beam energy at both polar angles, and the IVGQR parameters were determined from a least squares fit. Preliminary data will be presented along with the extracted resonance parameters for the IVGQR in $^{89}$Y. [Preview Abstract] |
Friday, October 26, 2012 9:18AM - 9:30AM |
HD.00005: High-spin states in $^{91,93}$Y N. Fotiades, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, W. Younes High-spin states in $^{91}$Y and $^{93}$Y were studied via prompt $\gamma$-ray spectroscopy. The data were obtained in two Gammasphere experiments at LBNL with reactions populating both isotopes as fission fragments following fission of much heavier compound nuclei. States with excitation energies up to 7~MeV were established in both isotopes above the previously known 9/2$^{+}$ isomers. Candidates for medium-spin negative parity states in $^{91}$Y are observed for the first time. The new states are compared with the first excited states in the neighboring N=52,54 isotones and with previous results on $^{91,93}$Y from fusion-evaporation reactions\footnote{D. Bucurescu, {\it et al.}, Phys. Rev. C {\bf 71}, 034315 (2005).} and multinucleon transfer reactions\footnote{D. Bucurescu, {\it et al.}, Phys. Rev. C {\bf 76}, 064301 (2007).} which were significantly enriched by the present measurement. The experimental results are compared to predictions from shell-model calculations. This work is supported in part by the U.S. Department of Energy and the National Science Foundation. [Preview Abstract] |
Friday, October 26, 2012 9:30AM - 9:42AM |
HD.00006: A New Investigation of $^{94}$Zr with the $(n,n'\gamma)$ Reaction E.E. Peters, A. Chakraborty, B.P. Crider, A. Kumar, M.T. McEllistrem, F.M. Prados-Est\'{e}vez, S.W. Yates Measurements of the low-lying structure of $^{94}$Zr with the $(n,n'\gamma)$ reaction revealed anomalous behavior not observed in other nuclei [1]. The B(E2) for the transition from the $2_2^+$ state at 1671.4 keV to the ground state was found to be larger than that from the $2_1^+$ to the ground state, 7.8(7) W.u. [1] vs. 4.9(3) W.u. [2], respectively. This nucleus then became the only example where such an inversion of the B(E2) strength occurs. Recently, we have carried out $(n,n'\gamma)$ measurements using metallic zirconium, zirconium (IV) oxide, and zirconium (IV) hydroxide samples of natural isotopic composition. The lifetime of the $2_2^+$ state was determined by the Doppler-shift attenuation method and the B(E2; $2_2^+ \rightarrow 2_1^+$) was obtained; the results differ significantly from those published [1]. A new analysis of the original $\gamma$-ray data [1] failed to reveal the source of this discrepancy. However, powder x-ray diffraction and scanning electron microscopy performed on each sample material, including that used previously [1], provide clues to the answer.\\[4pt] [1] E. Elhami \textit{et al.}, Phys. Rev. C {\bf75}, 011301(R) (2007). \newline[2] D. Abriola and A.A. Sonzogni, Nucl. Data Sheets {\bf197}, 2423 (2006). [Preview Abstract] |
Friday, October 26, 2012 9:42AM - 9:54AM |
HD.00007: Study of light tin isotopes via single-nucleon knockout reactions A. Ayres, K.L. Jones, T. Baugher, D. Bazin, J. Berryman, A. Bey, C. Bingham, L. Cartegni, G. Cerizza, A. Chae, A. Gade, R. Grzywacz, M.E. Howard, S. McDaniel, D. Miller, S. Padgett, S. Pain, A. Ratkiewicz, A. Shore, R. Stroberg, D. Weisshaar, K. Wimmer, R. Winkler Spectroscopic studies have been performed close to $^{100}$Sn, utilizing the S800 and CAESAR at the NSCL. These studies make use of a single neutron knockout reaction on $^{108}$Sn and $^{106}$Sn beams. The momentum distributions of the resulting residues indicate the $\ell$-value of the removed neutron and the spectroscopic factors for the even-mass nuclei. Additionally, $\gamma$-rays were measured in coincidence with the momentum distributions allowing the separation of the knockout channel where the residue is left in an excited state from the channel to the ground state. The odd-mass residue can then be characterized in terms of a hole in the d- or g- orbital with reference to the even-mass nucleus. The current status of the analysis will be presented. [Preview Abstract] |
Friday, October 26, 2012 9:54AM - 10:06AM |
HD.00008: Evidence for a smooth onset of deformation in the neutron-rich Kr isotopes Michael Albers, N. Warr, A. Blazhev, J. Jolie, K. Nomura, D. Muecher The aim of this work was to investigate the behaviour of the even-even Z=36 (Kr) isotopes in the phase transition region around A=100 by determining the energies of the 2$^{+}_{1}$ states and their E2 decay transition strengths to the ground state in $^{94}$Kr (N=58) and $^{96}$Kr (N=60). Information on the energies of the first excited 2$^{+}$ states exist only for the Kr isotopes up to N=58. For N=60, contradictory results on this observable were published recently. To clarify this contradiction several experimental runs were performed at the REX-ISOLDE facility at CERN, utilizing the high-efficiency MINIBALL $\gamma $-ray spectrometer and analyzing the emitted $\gamma $ -rays and scattered particles after the Coulomb-excitation reactions. The results of these experiments will be presented and discussed in the framework of the proton-neutron interacting boson model based on the constrained Hartree-Fock-Bogoliubov approach using the microscopic Gogny-D1M energy density functional. [Preview Abstract] |
Friday, October 26, 2012 10:06AM - 10:18AM |
HD.00009: Dipole Response of $^{76}$Ge P. Humby, N. Cooper, V. Werner, N. Pietralla, J. Beller, C. Romig, M. Zweidinger, J. Isaak, J. Bliss, M. Scheck, W. Tornow, G. Rusev, A.P. Tonchev, S.W. Yates, B.P. Crider, D. Savran, B. L\"oher The collective electric dipole resonance known as the pygmy dipole resonance has been investigated in the nucleus $^{76}$Ge using the photon scattering technique up to an endpoint energy of 9.2 MeV. The experiment was conducted at the S-DALINAC facility at Technische Universitat Darmstadt (TUD) using unpolarized bremsstrahlung photons. Three HPGe detectors with active BGO shields were used to observe the scattered gamma-rays. Spins and cross-sections of dipole-excited states have been extracted from the data. [Preview Abstract] |
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