Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session JG: Nuclear Structure IV |
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Chair: Volker Werner, Yale University Room: Newport News Marriott at City Center Pearl Salon III |
Saturday, October 13, 2007 2:00PM - 2:12PM |
JG.00001: Investigation of $^{152,153}$Dy Babak Shoraka, Volker Werner, Elizabeth McCutchan, Ho-Chiang Ai, Robert J. Casperson, Rick Casten, Andreas Heinz, Bernhard Huber, Robert Luettke, Jing Qian, Russ Terry, Elizabeth Williams, Ryan Winkler 152Dy is one of the most studied nuclei in the nuclear chart. Excited states in 152Dy (and 153Dy) were populated via the 124Sn(33S,Xn) reaction with the beam being delivered by the ESTU tandem accelerator at the Wright Nuclear Structure Laboratory. The New Yale Plunger Device (NYPD) was used in the SPEEDY array. Lifetimes are determined using the differential decay curve method from gamma-gamma coincidence data. First results will be presented. [Preview Abstract] |
Saturday, October 13, 2007 2:12PM - 2:24PM |
JG.00002: Triaxial Strongly Deformed bands in $^{163}$Tm X. Wang, R.V.F. Janssens, E.F. Moore, M.P. Carpenter, N.J. Hammond, T. Lauritsen, G. Mukherjee, D. Seweryniak, S. Zhu, U. Garg, Y. Gu, S. Frauendorf, T. Li, B.K. Nayak, N.S. Pattabiraman, S.S. Ghugre, R.S. Chakrawarthy, M. Whitehead, A.O. Macchiavelli A ``thin'' target experiment and a DSAM lifetime measurement were carried out with the reaction {\it $^{130}$Te($^{37}$Cl,4n)} using Gammasphere at LBNL and at ANL, respectively. It has been confirmed that the two new bands in $^{163}$Tm, interpreted as TSD bands based on particle-hole excitations, are associated with a larger deformation than the yrast sequences. The measured quadrupole transition moments will be compared with those of neighboring nuclei. Further, TAC calculations will be presented. They provide a natural explanation for the presence of wobbling bands in the Lu isotopes and the absence of such bands in all neighboring Tm, Hf and Ta nuclei. [Preview Abstract] |
Saturday, October 13, 2007 2:24PM - 2:36PM |
JG.00003: The Decay Pathways of a Triaxial Strongly Deformed (TSD) Band in $^{168}$Hf R.B. Yadav, W.C. Ma, H. Amro, P.G. Varmette, G.B. Hagemann, B. Herskind, K.A. Schmidt, G. Sletten, M. Carpenter, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, C.J. Lister, A. Bracco, S. Frattini, B. Million, J. Domscheit, H. H\"ubel, D.J. Hartley, L.L. Riedinger, S.W. $\O$deg{\aa}rd, S. Siem Following the discovery of the wobbling motion in $^{161-167}$Lu, TSD bands in the mass A $\sim$ 165 region have received considerable attention. Previously, three TSD bands were reported in $^{168}$Hf which is the first evidence for triaxial superdeformation in an even proton system [1]. However, none of the bands was linked to known levels. Consequently, the spin/parity, excitation energy, and intrinsic configurations of the bands remain unknown. Recently, we further analysed the $\gamma$-ray coincidence data obtained from the Gammasphere experiment at ANL using a self-supporting target. The decay pathways of TSD2 band to low-spin normal deformed structures have been established. The spin/parity of the band were determined. The results will be discussed based on cranked shell model calculations. Work supported by U.S. DOE grant DE-FG02-95ER40939. \newline [1] H. Amro et al., Physics Letters B 506 (2001) 39-44. [Preview Abstract] |
Saturday, October 13, 2007 2:36PM - 2:48PM |
JG.00004: Deviations from the Alaga rules in deformed Hf nuclei E.A. McCutchan, R.F. Casten, V. Werner, B. Shoraka, E. Williams Branching ratios from excited $K$ = 0,2 states in axially symmetric deformed nuclei can usually be described, in first order, using the Alaga rules. Some well-deformed nuclei, however, show significant deviations from the Alaga rules particulary when the first excited $K$ = 0 and 2 excitations are similar in energy. To further investigate this behavior, an experiment was performed to measure intensities from excited $K$ = 0,2 states in $^{172}$Hf. Low-lying non-yrast states of $^ {172}$Hf were populated in $\beta$ decay and studied through off-beam $\gamma$ ray spectroscopy. The $^{172}$Ta parent nuclei were produced through the $^{165}$Ho($^{12}$C, 5$n$) reaction. Results will be presented and compared to the systematics of the region. Work supported by U.S. DOE Grant No. DE-FG02-91ER-40609. [Preview Abstract] |
Saturday, October 13, 2007 2:48PM - 3:00PM |
JG.00005: Oblate collective rotation at high spins in neutron-rich, A$\approx $180 nuclei S.K. Tandel, U.S. Tandel, P. Chowdhury Neutron-rich isotopes in A$\approx $180 nuclei around the Hf region exhibit a confluence of conditions necessary for the realization of oblate collective rotation at high spins. The valence, high-j orbitals near the Fermi surface, for both protons and neutrons, have low $\Omega $ for oblate shapes in contrast to high-$\Omega $ values for prolate deformation. This situation favors oblate alignments over prolate, which leads to yrast, collective oblate shapes at high spins. Systematic calculations using both Woods-Saxon cranking and Ultimate Cranker have been performed to investigate this phenomenon, the results of which will be summarized. Excited states at high spins where oblate collective rotation is expected to become yrast are difficult to populate in these neutron-rich nuclei. The first experimental evidence of this phenomenon has been observed in $^{180}$Hf, which will be briefly discussed in this context. [Preview Abstract] |
Saturday, October 13, 2007 3:00PM - 3:12PM |
JG.00006: Insights into Nuclear Triaxiality from Interference Effects in $E2$ Matrix Elements J.M. Allmond, J.L. Wood, W.D. Kulp Recently, we have introduced [1] a triaxial rotor model with independent inertia and $E2$ tensors. The $E2$ matrix elements [2] of the osmium isotopes (186, 188, 190, and 192) are studied in the framework of this model (59 of 84 $E2$ matrix elements deviate by 30$\%$ or less). It is shown that interference effects in the inertia tensor ($K$-mixing) and the $E2$ tensor can lead to significant reductions in the diagonal $E2$ matrix elements. In some instances, the diagonal $E2$ matrix elements may decrease with increasing spin. Additionally, a sum rule for diagonal $E2$ matrix elements is shown and used to explore missing strength from $K$-admixtures. \newline \newline [1] J.L.~Wood, A-M.~Oros-Peusquens, R.~Zaballa, J.M.~Allmond, and W.D.~Kulp, Phys. Rev. C \textbf{70}, 024308 (2004). \newline [2] C.Y.~Wu, D.~Cline, T.~Czosnyka, A.~Backlin, C.~Baktash, R.M.~Diamond, G.D.~Dracoulis, L.~Hasselgren, H.~Kluge, et al., Nucl.~Phys.~\textbf{A607}, 178 (1996). [Preview Abstract] |
Saturday, October 13, 2007 3:12PM - 3:24PM |
JG.00007: Structure of the $4^{+}_{3}$ States in $^{186,188}$Os A.A. Phillips, P.E. Garrett, G.A. Demand, P. Finlay, K.L. Green, K.G. Leach, M.A. Schumaker, C.E. Svensson, J. Wong, R. Hertenberger, T. Faestermann, R. Kr\"{u}cken, H.-F. Wirth, L. Bettermann, N. Braun, D.G. Burke The structures of 4$^{+}_{3}$ states in the Os nuclei have been the subject of debate for the past several decades. Based on measured B(E2) values, they were interpreted in $^{186-192}$Os as K$^{\pi}$=4$^{+}$ two-phonon $\gamma$ vibrations, whereas inelastic scattering results, and single-proton transfer (d,$^{3}$He) and (t,$\alpha )$ imply a hexadecapole phonon description. Uncertainties in the (t,$\alpha )$ reaction mechanism, however, were cited as preventing a firm conclusion based on those data. To help clarify the nature of these K$^{\pi }$=4$^{+}$ bands, we have performed a ($^{3}$He,d) stripping reaction on targets of $^{185,187}$Re using 30 MeV $^{3}$He beams provided by the MP-tandem facility of the LMU/TUM in Garching. With an energy resolution of 13 keV, the deuterons were analyzed at 9 angles ranging from 5$^{\circ}$ to 50$^{\circ}$ with the Q3D spectrograph, and absolute cross sections were obtained for levels up to 3 MeV in excitation energy. Preliminary results will be presented. [Preview Abstract] |
Saturday, October 13, 2007 3:24PM - 3:36PM |
JG.00008: Detailed spectroscopy of $^{219}$Th W. Reviol, D.G. Sarantites, C.J. Chiara, O.L. Pechenaya, M. Montero, M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, C.J. Lister, D. Seweryniak, S. Zhu The previously unexplored nucleus $^{219}$Th has been studied, using the $^{198}$Pt($^{26}$Mg,5n) E$_{lab}$=128 MeV (ATLAS) fusion-evaporation reaction and the Gammasphere + HERCULES detector combination. The level scheme constructed from evaporation-residue selected $\gamma $--ray coincidence data has the following features: The ground state E2 sequence [neutron (g$_{9/2})^{3}$] shows a vibrational-like behavior. Another positive-parity E2 sequence is present and concurs with the picture of weak coupling of an h$_{11/2}$ neutron to the $^{218}$Th core. Among the set of negative-parity states is a short E2 sequence that forms, together with the h$_{11/2}$ sequence, an octupole-type band. The discussion will focus on the latter band structure. A trend for parity doublets in odd-mass Th nuclei will be presented. [Preview Abstract] |
Saturday, October 13, 2007 3:36PM - 3:48PM |
JG.00009: ABSTRACT WITHDRAWN |
Saturday, October 13, 2007 3:48PM - 4:00PM |
JG.00010: Alpha decay of $^{257}$Rf J. Qian, A. Heinz, R. Winkler, J. Vinson, R.V.F. Janssens, D. Peterson, D. Seweryniak, B. Back, M.P. Carpenter, G. Savard, A.A. Hecht, C.L. Jiang, T.L. Khoo, F.G. Kondev, T. Lauritsen, C.J. Lister, A. Robinson, X. Wang, S. Zhu, A.B. Gansworthy, M. Asai The excited states of heavy odd-even nuclei allow for the measurement of the single-particle energies of orbitals which play a major role in the shell stabilization of superheavy nuclei. Because production cross sections decrease with increasing mass and proton number, in-beam spectroscopy becomes increasingly difficult and the structure information becomes scarce. Here, we report on decay spectroscopy of $^{257}$Rf. The excited states of $^{257}$Rf and its daughter $^{253}$No can provide information on the single-particle structure near the deformed neutron shell $N=152$. $^{257}$Rf was produced in the fusion-evaporation reaction $^{50}$Ti + $^{208}$Pb at the Argonne Tandem Linac Accelerator System, using the Fragment Mass Analyzer. The mass/charge ratio of the recoils was used for the identification of the evaporation residues. The $\alpha$ decays together with $\alpha - \gamma$ coincidence in $^{257}$Rf and $^{253}$No were studied. The results will be compared with $N=151$ isotones. These data can test predictions of various models often used to predict the location of the next proton shell closure in the heaviest nuclei. This work was supported by the U.S. DOE under contract No. DE--AC02-- 06CH11357 and DE-FG02-91ER-40609. [Preview Abstract] |
Saturday, October 13, 2007 4:00PM - 4:12PM |
JG.00011: Technique for Angular Correlations and g-factor Measurements in Nuclei Produced in the Spontaneous Fission of $^{252}$Cf C. Goodin, A.V. Daniel, K. Li, A.V. Ramayya, N.J. Stone, J.K. Hwang, J.H. Hamilton, J.R. Stone, Y.X. Luo, J.O. Rasmussen, M.A. Stoyer, S.J. Zhu, G.M. Ter-Akopian, I.Y. Lee We present a new technique for measuring angular correlations between $\gamma$-rays emitted by the fragments from the spontaneous fission of $^{252}$Cf and measured with Gammasphere. For states with short lifetimes ($\leq$10ps), these correlations can be used to determine the spin and parity of unknown levels. For states with long lifetimes, the technique can be used to determine the g-factor of the level in question by measuring the attenuation of the correlation caused by rotation of the nucleus about the randomly oriented domains in an un-magnetized iron foil. Applying our new method to our set of triple coincidence data collected from the fission of $^{252}$Cf, we have been able to verify the spins of new levels in $^{138}$Cs, as well as new levels in $^{108,110,112}$Ru. We have also been able to reproduce the results of known g-factors for several nuclei, and the extremely high statistics ($\sim$10$^{11}$ events) of our data set will allow us to measure unknown g-factors of other excited states. Calculation of the relative detector efficiencies and the solid angle correction factor will be discussed as well as the procedures for the angular binning, peak fitting, and background subtraction. [Preview Abstract] |
Saturday, October 13, 2007 4:12PM - 4:24PM |
JG.00012: K isomers in Cm isotopes via deep-inelastic and transfer reactions U.S. Tandel, P. Chowdhury, S.K. Tandel, A.J. Knox, C.M. Wilson, I. Ahmad, M.P. Carpenter, J.P. Greene, S. Gros, R.V.F. Janssens, T.L. Khoo, F.G. Kondev, T. Lauritsen, C.J. Lister, D. Peterson, A. Robinson, D. Seweryniak, X. Wang, S. Zhu K isomers in $^{246}$Cm and $^{248}$Cm (Z = 96) were populated via deep-inelastic and transfer reactions using a $^{209}$Bi beam at $\sim $ 15{\%} above the Coulomb barrier, incident on a long-lived $^{248}$Cm target. This reaction mechanism has been employed for the first time in trans-plutonium nuclei to study high-K isomers. The out-of-beam data were collected using Gammasphere in different time regimes ranging from 80 microseconds up to 8 seconds to adjust to different isomer half-lives. The half-life of a known 8$^{-}$ isomeric state in $^{246}$Cm has been measured to be $\sim $ 1 s. A new high-K isomer with K$^{\pi }$ = (8$^{-})$ has also been discovered in $^{248}$Cm. These K$^{\pi }$ = 8$^{-}$ isomers have the same underlying neutron [624]7/2 x [734]9/2 configuration as is observed in the isotones $^{250}$Fm and $^{252}$No. These new data on high-K isomers will add to the limited knowledge of single-particle and pair-gap energies in heavy actinides. [Preview Abstract] |
Saturday, October 13, 2007 4:24PM - 4:36PM |
JG.00013: Radioactive Decay Energy Reactions Should Include Vibrational and Rotational Kinetic Energies Stewart Brekke In order to reconcile theory with experimental results energy relations of unstable nuclei should include vibrational and rotational kinetic energies. For alpha decay: $M_Pc^2 + 1/2I\omega_r^2 + (n +1/2)\hbar\omega_v +1/2M_Pv^2 = M_Dc^2 +1/2I\omega_r^2 +(n +1/2)\hbar\omega_v +1/2M_Dv^2 + M_\alpha c^2 +1/2I\omega_r^2 + (n +1/2)\hbar\omega_v +1/2M_\alpha v^2$. For beta decay: $M_Pc^2 + 1/2I\omega_r^2 +(n +1/2)\hbar\omega_v +1/2M_Pv^2 = M_Dc^2 + 1/2I\omega_r^2 + (n +1/2)\hbar\omega_v + 1/2M_Dv^2 + M_ec^2 +1/2I\omega_r^2 + (n+1/2)\hbar\omega_v + 1/2M_ev^2$. $1/2I\omega_r$ is the rotational kinetic energy and $(n +1/2)\hbar\omega_v$ is the vibrational kinetic energy. [Preview Abstract] |
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