Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session DG: Nuclear Structure II |
Hide Abstracts |
Chair: Eiji Ideguchi, CNS Univ.Tokyo Room: Kings 2 |
Thursday, October 15, 2009 7:00PM - 7:15PM |
DG.00001: Identification of new neutron-rich isotopes produced by in-flight fission of $^{238}$U at 345 MeV/u Tetsuya Ohnishi, Toshiyuki Kubo, Hiroyuki Takeda, Naoki Fukuda, Daisuke Kameda, Kensuke Kusaka, Atsushi Yoshida, Koichi Yoshida, Masao Ohtake, Naohito Inabe, Yoshiyuki Yanagisawa, Kanenobu Tanaka At RI Beam Factory (RIBF) at RIKEN Nishina Center, an in-flight radioactive isotope beam separator BigRIPS[1] was commissioned in 2007. Then we made a search for new isotopes using in-flight fission of a $^{238}$U beam at 345 MeV/u, and observed two new palladium isotopes $^{125}$Pd and $^{126}$Pd.[2] In November 2008, we revisited this experiment with improved experimental conditions and better tuning of BigRIPS. The intensity of the $^{238}$U beam was 1.6$\times$10$^9$ particle/sec on average, which was about 40 times higher than in 2007. The search was performed for three B$\rho$ settings that targeted different isotope regions. The achieved resolution of particle identification was good enough to well identify fission fragments even if some of them were not fully stripped. We observed more than 20 new isotopes with Z = 26 to 53, including $^{128}$Pd, which demonstrated the RI-beam production power of BigRIPS at RIBF. The details of the experiment will be reported. [1]T. Kubo, Nucl. Instr. and Meth. \textbf{B204}, 97(2003). [2]T. Ohnishi et al, J. Phys. Soci. Jpn. \textbf{77}, 083201(2008). [Preview Abstract] |
Thursday, October 15, 2009 7:15PM - 7:30PM |
DG.00002: Single-particle states in $^{112}$Cd probed with the $^{111}$Cd($\vec{d},p$) reaction P.E. Garrett, D. Jamieson, G.A. Demand, P. Finlay, K.L. Green, K.G. Leach, A.A. Phillips, C.S. Sumithrarachchi, C.E. Svensson, S. Triambak, J. Wong, G.C. Ball, R. Hertenberger, H.-F. Wirth, R. Kr\"ucken, T. Faestermann As part of a program of detailed spectroscopy of the Cd isotopes, the single-particle neutron states in $^{112}$Cd have been probed with the $^{111}$Cd($\vec{d},p$) reaction. Beams of polarized 22 MeV deuterons, obtained from the LMU/TUM Tandem Accelerator, bombarded a target of $^{111}$Cd. The protons from the reaction, corresponding to excitation energies up to 3 MeV in $^{112}$Cd, were momentum analyzed with the Q3D spectrograph. Cross sections and analyzing powers were fit to results of DWBA calculations, and spectroscopic factors were determined. The results from the experiment, and implications for the structure of $^{112}$Cd, will be presented. [Preview Abstract] |
Thursday, October 15, 2009 7:30PM - 7:45PM |
DG.00003: Properties of quadrupole-octupole coupled states in $^{116}$Cd from the (n, n$^{\prime}\gamma$) reaction C.S. Sumithrarachchi, P.E. Garrett, K.L. Green, M. Kadi, J. Jolie, N. Warr, S.W. Yates Negative-parity levels in the 2.4 MeV region, arising from the coupling of the 2$^{+}_{1}$ quadrupole and 3$^{-}_{1}$ octupole states, have been investigated with the (n, n$^{\prime}\gamma$) reaction. The measured $\gamma$-ray excitation functions, $\gamma$-$\gamma$ coincidences and angular distributions were utilized to characterize the decays of these states. The level lifetimes have been measured with the Doppler-shift attenuation method, and B(E1) and B(E2) values for the associated transitions have been determined. The enhanced B(E2) values for decay to the 3$^{-}$ octupole state from many of the candidate negative-parity states were observed to be consistent with the expected signature of quadrupole-octupole coupled states. The properties of these states will be compared with the systematics of quadrupole-octupole coupled states in Cd isotopes and IBM calculations. [Preview Abstract] |
Thursday, October 15, 2009 7:45PM - 8:00PM |
DG.00004: Collective and Non-Collective States in $^{116}$Cd J.C. Batchelder, H.K. Carter, E.H. Spejewski, J.L. Wood, D. Kulp, P.E. Garrett, K.P. Rykaczewski, J.C. Bilheux, D.W. Stracener, C.R. Bingham, R. Grzywacz, M.N. Tantawy, Y. Larochelle, D. Fong, J.H. Hamilton, J.K. Hwang, A.V. Ramayya, D.J. Hartley, W. Krolas, A. Piechaczek, E.F. Zganjar, J.A. Winger We have re-investigated the beta decay of the three isomers of $^{116}$Ag to levels in $^{116}$Cd at the HRIBF. Using the CARDS array at UNISOR, we have measured gamma-rays and conversion electrons and their decay times. Through the use of this information, we have been able to construct individual decay schemes for each isomer. Significant deviations are observed from expected U(5) symmetry in the 0$^+$ and 2$^+$ members of the previously assigned three-phonon quintuplet. We have identified candidates in $^{116}$Cd for the complete quadrupole-octupole quintuplet. The states are 5$^-$ at 2249.2 keV, 4$^-$ at 2340.1keV, 3$^-$ at 2392.1 keV, 1$^-$ at 2478.2 keV and 2$^-$ at 2519.2 keV. All show E2 transitions to the previously known 3$^-$ octupole state at 1921.7 keV. High-energy negative-parity states have been identified via their conversion electron data. These states are identified as possible broken pair states. This work is supported by the U. S. DOE contract DE-AC05-76OR00033 and others. [Preview Abstract] |
Thursday, October 15, 2009 8:00PM - 8:15PM |
DG.00005: Shell model calculation on Sn isotopes and evolution of shell structure Noritaka Shimizu, Takaharu Otsuka We perform shell model calculations of low-lying excited states of $^{100-132}$Sn even-even isotopes, and discuss the properties of the $E2$ transition probabilities of low-lying excited states. Recent improvements of rare isotope beam technique provide us with the experimental information of proton-rich tin isotopes towards $^{100}$Sn, especially $B(E2;0_1^+ \rightarrow 2_1^+)$ values of $^{106-114}$Sn. These $E2$ probabilities show unexpectedly large and inconsistent with the prediction of the large scale shell model calculation based on $G$-matrix prescription. In this work, we adopt rather schematic interaction such as pairing-plus-quadrupole interaction and monopole interaction, which is considered to play an important role in shell evolution of proton-rich nuclei around $^{100}$Sn and $Z=N=50$ shell gaps, with utilizing angular-momentum and number projection techniques and the Monte-Carlo shell model instead of traditional $n$-particle $n$-hole truncation. We demonstrates how the shell gap and $\nu 0h11/2$ intruder orbit evolve with decreasing neutron numbers of Sn isotopes, and discuss the origin of the anomalous behaviour of $E2$ transition probabilities. [Preview Abstract] |
Thursday, October 15, 2009 8:15PM - 8:30PM |
DG.00006: Evolution of the one-phonon mixed-symmetry state in the N=48 isotonic chain Linus Bettermann, Norbert Braun, Christoph Fransen, Stefan Heinze, Jan Jolie, Andreas Linnemann, Dennis Muecher, Ralf Schulze, Desiree Radeck, Ulrich Kneissl, Heinz-H. Pitz, Marcus Scheck In collective nuclei one can find excitations that are not fully symmetric with respect to the proton-neutron degree of freedom. Those states are called mixed-symmetry states and in vibrator-like nuclei their fundamental one-phonon excitation is the $2^+_{\mathrm{ms}}$ state. Near the $N=50$ shell closure $2^+_{\mathrm{ms}}$ states are well known in the light stable nuclei of the $N=52$ isotonic chain, while the data base in the $N=48$ chain is sparse. A nuclear resonance fluorescence experiment on $^{84}$Kr was performed at the University of Stuttgart and $\gamma \gamma$ coincidence measurements after fusion evaporation reactions on $^{90}$Mo and $^{88}$Zr at the Cologne Tandem accelerator to investigate the low spin structure and collectivity of these nuclei. We will present results concerning the identification of candidates for the $2^+_{\mathrm{ms}}$ state in all three nuclei and discuss these results in the framework of the Interacting Boson Model. Finally we will compare the $N=48$ with the $N=52$ isotonic chain. [Preview Abstract] |
Thursday, October 15, 2009 8:30PM - 8:45PM |
DG.00007: Low-spin excitations in $^{100}$Pd D. Radeck, L. Bettermann, A. Blazhev, C. Bernards, A. Dewald, C. Fransen, S. Heinze, J. Jolie, D. Muecher, T. Pissulla, K.O. Zell, O. Moeller In the context of investigating collectivity in the A=100 mass region the nucleus $^{100}$Pd was measured at the Cologne Tandem facility using the HORUS and the plunger setups. Detailed data exists for the N=52 isotones and the evolution of collectivity - especially of the symmetric and mixed-symmetric phonon states - was discussed. To extend the knowledge of the evolution in this region it is important to measure the N=54 isotones. Up to now the low-energy part of the excitation spectrum of $^{100}$Pd was known sparsely and only the lifetime of an $8^+$ isomer was known. Using the HORUS data the level scheme was extended, clarified and multipole mixing ratios were determined for the first time. The plunger experiment yielded lifetimes of the yrast states up to $12^+_1$. Both, the experimental excitation spectrum and electric transition strengths, were compared to predictions of theoretical models, i.e. the anharmonic vibrator model, the Interacting Boson Model and the shell model. A candidate for the one-phonon mixed-symmetry excitation $2^+_{1,\rm{ms}}$ was identified due to its dominating M1 transition to the symmetric $2^+_1$ state. The results will be presented and discussed. Supported by DFG, grant Jo 391/3-2 and US DOE DE-FG02-91ER40609. [Preview Abstract] |
Thursday, October 15, 2009 8:45PM - 9:00PM |
DG.00008: Evidence for Breakdown of Vibrational Motion in $^{110}$Cd Jack Bangay, Paul Garrett, Laura Bianco, Kyle Leach, Paul Finlay, Katie Green, Andrew Phillips, Evan Rand, Carl Svensson, Chandana Sumithrarachchi, James Wong $^{110}$Cd has long been considered an excellent example of a vibrational nucleus. However, recent work with other even-even Cadmium isotopes show a breakdown of vibrational motion at the 2 and 3-phonon level, suggesting the need for more precise measurements on $^{110}$Cd. The structure of $^{110}$Cd is studied with the ($n,n^{\prime}\gamma$) reaction performed at the University of Kentucky, as well as with the high statistics $\beta$-decay of $^{110}$In performed at the TRIUMF-ISAC facility using the 8$\pi$ spectrometer. Excitation funcions and angular distributions from the ($n,n^{\prime}\gamma$) reaction provide us with spectroscopic information on the level scheme, including level lifetimes and spins. This data is complemented by the $\gamma\gamma$ coincidences measured in the $^{110}$In $\beta$-decay that allows the observation of, or stringent limit on, weak, low-energy branches between levels at high excitation energy. Details of the analysis to date, including candidates for the full octupole-quadrupole coupled quintuplet, will be presented. [Preview Abstract] |
Thursday, October 15, 2009 9:00PM - 9:15PM |
DG.00009: Description of strong M1 transitions between 4$\mathbf{{}^{+}}$ states at N=52 within the sdg-IBM-2 R.J. Casperson, V. Werner, S. Heinze The interplay between collective and single-particle degrees of freedom for nuclei near the N=50 shell closure have recently been under investigation. In Molybdenum and Ruthenium nuclei, collective symmetric and mixed-symmetric structures have been identified, while in Zirconium, underlying shell-structure plays an enhanced role. The one-phonon 2${}^{+}$ mixed-symmetry state was identified from its strong M1 transition to the 2${}^{+}_{1}$ state. Similar transitions were observed between 4${}^{+}$ states in ${}^{94}$Mo and ${}^{92}$Zr, and shell model calculations indicate that hexadecapole excitations play a role. These phenomena will be investigated within the sdg-Interacting Boson Model-2 in order to gain a better understanding about the structure of the states involved, and to which extent the hexadecapole degree of freedom is important at relatively low energies. First calculations within this model, using an F-spin conserving Hamiltonian to disentangle symmetric and mixed- symmetric structures, will be presented and compared to data. [Preview Abstract] |
Thursday, October 15, 2009 9:15PM - 9:30PM |
DG.00010: Level density and radiative strength of $^{116,117}$Sn Andreas Schiller, Undraa Agvaanluvsan, Ann Cecilie Larsen, Rositsa Chankova, Magne Guttormsen, Gary E. Mitchell, Sunniva Siem, Alexander Voinov We have determined the level density and radiative strength function for energies less than the neutron separation energy for the isotopes $^{116,117}$Sn using the Oslo method. The excited nuclei were produced by the $(^3$He,$\alpha)$ and $(^3$He,$^3$He$^\prime)$ reactions, respectively, from a 38-MeV-$^3$He beam bombarding a highly enriched $^{117}$Sn target. The level densities show the characteristic near-exponential increase with energy and a factor 5 difference in magnitude due to the odd-even effect. Step structures which indicate successive pair breaking are superimposed the general trend. The radiative strength function of $^{117}$Sn shows a dramatic increase in slope above 4.5 MeV $\gamma$ energy. Connecting our data, from below the neutron separation energy to literature data above this value (obtained from the $(\gamma,n)$ reactions) suggests the presence of a pygmy resonance with a centroid just above the neutron separation energy of 7 MeV and about 5--10 times the strength of the M1 spin-flip resonance or 1--2\% of the TRK sum rule. [Preview Abstract] |
Thursday, October 15, 2009 9:30PM - 9:45PM |
DG.00011: DANCE (Detector for Advanced Neutron Capture Experiments) is a 4$\pi$ array of BaF$_2$ crystals installed at LANSCE, Lujan Center. Neutron capture measurements on $^{157}$Gd and $^{89}$Y nuclei were conducted using this facility. A. Chyzh, G. Mitchell, D. Vieira, T. Bredeweg, J. Ullmann, M. Jandel, A. Couture, A. Keksis, R. Rundberg, J. Wilhelmy, J. O'Donnell, B. Baramsai, R. Haight, J. Wouters, M. Krticka, W. Parker, J. Becker, U. Agvaanlusan DANCE (Detector for Advanced Neutron Capture Experiments) is a 4$\pi$ array of BaF$_2$ crystals installed at LANSCE, Lujan Center. Neutron capture measurements on $^{157}$Gd and $^{89}$Y nuclei were conducted using this facility. The absolute cross sections of the $^{89}$Y$(n,\gamma)$ reaction was measured for the first time ever in the neutron energy range of 10 eV -- 10 keV and improvements were made in the 10 -- 300 keV range. The error bars were significantly reduced and number of cross section points was increased since the past $^{89}$Y$(n,\gamma)$ experiments. The $^{157}$Gd$(n,\gamma)$ cross section was determined at $E_n$ = 20 eV -- 300 keV by normalizing the experimental DANCE data to a well known resonance taken from the ENDF/B-VII library. Computer simulations of the $^{157}$Gd$(n,\gamma)$ cascades and DANCE pulse height function were made using DICEBOX and GEANT4 codes and simulated $E_{sum}$ and $E_{\gamma}$ spectra are compared to the experimental DANCE data. Values of spin and photon strength function (PSF) of the $^{157}$Gd$(n,\gamma)$ resonances are provided in the range of $E_n$ = 2 -- 300 eV using spin dependence upon a $\gamma$-ray multiplicity. [Preview Abstract] |
Thursday, October 15, 2009 9:45PM - 10:00PM |
DG.00012: Multi-quasiparticle isomers involving proton-particle and neutron-hole configurations in $^{131}$I and $^{133}$I H. Watanabe, G.J. Lane, G.D. Dracoulis, A.P. Byrne, P. Nieminen, F.G. Kondev, K. Ogawa, M.P. Carpenter, R.V.F. Janssens, T. Lauritsen, D. Seweryniak, S. Zhu, P. Chowdhury The iodine isotopes with Z = 53 have attracted considerable interest because they exhibit a transition from more collective nature in the middle of the neutron shell to spherical shell-model structure as the number of neutrons increases toward the N = 82 closed shell. We have populated excited states in $^{131}$I$_{78}$ and $^{133}$I$_{80}$ using multi-nucleon transfer from $^{136}$Xe, with the aim of understanding the effect of neutron holes on nuclear structure. By means of time-correlated $\gamma $-ray coincidence spectroscopy and the measurement of $\gamma $-ray angular correlations, a J$^{\pi }$= 19/2$^{-}$ isomer at 1918 keV, with a half-life of 24(1) $\mu$s, has been identified in $^{131}$I, as well as nanosecond isomers with 23/2$^{+}$ in both isotopes. A T$_{1/2}$ = 25(3) ns isomer at 4308 keV in $^{131}$I is suggested to have J$^{\pi }$ = (31/2$^{-}$, 33/2$^{-})$ and is primarily attributed to the coupling of an odd proton in the d$_{5/2}$ or g$_{7/2}$ orbit with the ($\pi ^{2})_{0+}$ ($\nu $h$_{11/2}^{-3}$ d$_{3/2}^{-1})_{15-}$ configuration in $^{130}$Te responsible for the 15$^{-}$ isomer in that nucleus. In this presentation, the observed level properties will be compared with predictions of a shell-model calculation based on a j-j coupling scheme. [Preview Abstract] |
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