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 HG: Nuclear Structure III |
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Chair: E.A. McCutchan, Yale University Room: Newport News Marriott at City Center Pearl Salon III |
Saturday, October 13, 2007 9:00AM - 9:12AM |
HG.00001: Collective Band Structures in Neutron-Rich $^{108}$Mo Nucleus H.B. Ding, S.J. Zhu, J.H. Hamilton, A.V. Ramayya, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, I.Y. Lee, X.L. Che, J.G. Wang, Q. Xu High spin states in the neutron-rich $^{108}$Mo nucleus were studied by measuring prompt $\gamma $-rays following the spontaneous fission of $^{252}$Cf with the Gammasphere detector array. Our high statistics data, 5.7 x 10$^{11}$ triple coincidences, enabled us to see new bands. The ground-state band is confirmed, and the one-phonon $\gamma $-vibrational band is extended up to spin 12. Three new unexpected states are found to feed into the ground and one-phonon $\gamma $-band 6$^{+}$ and 8$^{+}$ states. A new collective band with a band head at 1422.4 keV is observed with energy spacing similar to the one-phonon $\gamma $-band and feeding only into this band. These data suggest its assignment as a two-phonon $\gamma $-vibrational band. Such bands are seen in $^{104,106}$Mo. Another new band is proposed as a two-quasi-proton excitation band. Systematic characteristics of the collective bands will be discussed. [Preview Abstract] |
Saturday, October 13, 2007 9:12AM - 9:24AM |
HG.00002: (p,t) Studies of Even-Even Pd Nuclei R. Winkler, R.F. Casten, C. Lambie-Hanson, A. Heinz, J. Qian, T. Faestermann, R. Graeger, R. Kr\"{u}cken, M. Mahgoub, H.-F. Wirth, N. Braun, S. Christen, R. Hertenberger Detailed studies of stable even-even Pd isotopes have been carried out using the two-neutron pickup reaction (p,t). The use of a Q3D spectrograph coupled with a high position resolution focal plane detector at the Maier-Leibnitz Laboratory of LMU and TU Munich was vital in the level energy, spin, and parity assignments of the populated low spin states. The spin and parity assignments were determined through comparison of angular distributions of the observed states with DWBA calculations. The results of this series of experiments, a near complete set of 0$^{+}$, 2$^{+}$, and 4$^{+}$ states below an excitation energy of 3.5 MeV for $^{102,106,108}$Pd, will be presented. Analysis including the comparison of the experimental results with theoretical predictions will be discussed. This work is supported by U.S. DOE Grant No. DE-FG02-91ER-40609. [Preview Abstract] |
Saturday, October 13, 2007 9:24AM - 9:36AM |
HG.00003: Hyperdeformation in the Cranked Relativistic Mean Field Theory Anatoli Afanasjev, C.W. Jang, J. Begnaud Since the discovery of superdeformation in 152Dy, nuclear hyperdeformation (HD) has been in the focus of attention of the nuclear structure community [1,2]. Recent observation of the very extended shapes in 108Cd (see Ref. [3] for theoretical analysis) and the observation of ridge-structures in 3-dimensional rotational mapped spectra in the A$\sim $120 mass region, having features consistent with hyperdeformation [2], have renewed interest in the study of hyperdeformation. Systematic search for hyperdeformation at high spin in the Z=40-60 part of nuclear chart has been performed within the framework of the cranked relativistic mean field (CRMF) theory. Available experimental data (108Cd, ridge-structures in the A$\sim $120 mass region) have been compared with the calculations. The CRMF results are also compared with those obtained in the macroscopic+microscopic method [1]: the similarities and differences are outlined. The detailed features of the HD bands have been studied. The regions most favoured for experimental observation of the HD discrete bands will be outlined. [1] N.Schunck, et al, Phys. Rev. C75, 054304 (2007), [2] B. Herskind et al, Phys. Scripta T125, 108 (2006), [3] A.V. Afanasjev et al, Phys.Rev. C 72. 031301(R) (2005). [Preview Abstract] |
Saturday, October 13, 2007 9:36AM - 9:48AM |
HG.00004: Systematic investigations of the stable Cd isotopes P.E. Garrett, K.L. Green, J.L. Wood, W.D. Kulp The Cd nuclei, especially the stable even-even isotopes have been well studied since they were suggested as paradigms of the vibrational, or $U(5)$, limit of the Interacting Boson Model (IBM). In addition to the normal quadrupole phonon states, in many cases suggested up to the three-phonon quintuplet, more deformed $2p4h$ intruder excitations have been established. Recent investigations with the $(n,n^{\prime}\gamma)$ reaction [1,2,3,4] have provided a wealth of information on the low-lying levels, including many lifetimes not previously known. Deviations in the transition $B(E2)$ values for low-spin states from those expected for $U(5)$ nuclei are observed to appear systematically across the Cd isotopes. We have performed detailed calculations using the IBM-2, and find that these deviations cannot be explained through considered mixings with the intruder excitations or mixed-symmetry states, indicating that some physics is missing in the description of these levels. \break \noindent [1] F. Corminboeuf {\it et al.}, Phys. Rev. C {\bf 63}, 014305 (2001).\hfill \break \noindent [2] P.E. Garrett {\it et al.}, Phys. Rev. C {\bf 75}, 014307 (2007).\hfill\break \noindent [3] D. Bandyopadhyay {\it et al.}, {\it to be published}. \hfill\break \noindent [4] M. Kadi {\it et al.}, Phys. Rev. {\bf 68}, 031306 (2003). \hfill [Preview Abstract] |
Saturday, October 13, 2007 9:48AM - 10:00AM |
HG.00005: Cd-128: ugly duckling or provocative young swan W.B. Walters, N. Hoteling, A.A. Hecht, P.F. Mantica, B.E. Tomlin, J. Pereira, A. Becerril, T. Fleckenstein, G. Lorusso, J.S. Pinter, J.B. Stoker, M. Quinn In this presentation, gamma ray spectra will be presented that arise from the decay of microsecond level isomers in $^{125,126,127,128,129}$Cd. These nuclei have been produced in fragmentation reactions at the NSCL, and identified using the beta counting system and SEGA gamma-ray detector array. Proposed level schemes for these nuclei will be shown that include the 2$^{+}$ and 4$^{+}$ energies for $^{126,128}$Cd that have been previously identified in radioactive decay. Emphasis will be on the structure of $^{128}$Cd for which the proposed 2$^{+}$ and 4$^{+}$ levels at 645 and 1428 keV, respectively, are far below the results from recent shell-model calculations. These structures are interpreted relative to the level structure of adjacent $^{115-124}$Cd $^{130}$Cd, $^{130}$In, and $^{125-134}$Sn isotopes. The possibility of weakened neutron-neutron and proton-neutron interaction strength will be discussed. [Preview Abstract] |
Saturday, October 13, 2007 10:00AM - 10:12AM |
HG.00006: ABSTRACT WITHDRAWN |
Saturday, October 13, 2007 10:12AM - 10:24AM |
HG.00007: Radioactive beam $g$-factor measurement of the 2$^+_1$ state of $^{132}$Te. N. Benczer-Koller, G. Kumbartzki, G. Gurdal, B. Krieger, C. Gross, R. Hatarik, P. O'Malley, S. Pain, L. Segen, N. Stone, A.E. Stuchbery, C. Baktash, D. Radford, C.-H. Yu, C. Bingham, M. Danchev, R. Grzywacz, R.V.F. Janssens The magnetic moment of the Coulomb-excited 2$^+_1$ state of $^{132}$Te has been measured by the transient field technique using the radioactive beam at HRIBF. Projectile excitation was induced in a C layer backed by either gadolinium or iron ferromagnetic foils. The de-excitation $\gamma$ ray was detected in a standard four-Clover Ge detector setup in coincidence with recoil C ions recorded in two forward Si detectors subtending angles 19$^\circ$ $<$ $\theta$ $<$ 47$^\circ$ above and below the beam axis. The viability of the technique has been demonstrated. Results will be presented and discussed. [Preview Abstract] |
Saturday, October 13, 2007 10:24AM - 10:36AM |
HG.00008: Test of Internal-Conversion Theory with Precise $\gamma $- and x-ray Spectroscopy: $^{134}$Cs$^{m}$,$^{ 137}$Ba, $^{139}$La N. Nica, J.C. Hardy, C. Balonek, V.E. Iacob, J. Goodwin, H.I. Park, W.E. Rockwell, M.B. Trzhaskovskaya We recently reported [1] a measurement of the ratio of $K$-shell internal conversion coefficients, \textbf{\textit{$\alpha$}}$_{K}$, for two transitions; the 127.5-keV $E$3 in $^{134}$Cs and the 661.7-keV$M$4 in $^{137}$Ba. Previous measurements of these \textbf{\textit{$\alpha $}}$_{K}$ values disagreed with calculations. Our new result for the ratio, 30.01(15), disagrees with, but is a factor of three more precise than, the previous average of all experimental results and is consistent with modern Dirac-Fock calculations that include the atomic vacancy in the daughter. This confirms our earlier conclusion [2] that this approach is the best one for $^{193}$Ir, a much heavier nucleus. In a new measurement we have now deduced the precise efficiency of our HPGe detector in the energy range of Cs-La K X-rays from the 165.9 keV,$ M1$ transition in $^{139}$La, for which the \textbf{\textit{$\alpha $}}$_{K}$ value can be reliably calculated and is nearly independent of whether the atomic vacancy is included or not. Based on this calibration, we have converted our ratio result into individual \textbf{\textit{$\alpha $}}$_{K}$ results for the transitions in $^{134}$Cs and $^{137}$Ba: viz. \textbf{\textit{$\alpha$}}$_{K}$(127.5)=2.745(16) and \textbf{\textit{$\alpha$}}$_{K}$(661.7)=0.0915(6). Both results are in good agreement with calculations that include the atomic vacancy. [1] N. Nica \textit{et al}., Phys. Rev. \textbf{C75}, 024308 (2007); [2] N. Nica \textit{et al}., Phys. Rev. \textbf{C70}, 054305 (2004). [Preview Abstract] |
Saturday, October 13, 2007 10:36AM - 10:48AM |
HG.00009: Search for mixed-symmetry states in $^{136}$Ba S. Mukhopadhyay, S.N. Choudry, B. Crider, E. Elhami, J.N. Orce, E.E. Peters, M. Scheck, M.T. McEllistrem, S.W. Yates The low-spin structure of $^{136}$Ba reactions was studied at the University of Kentucky with the (n,n$'\gamma$) reaction. The primary goal was the identification of the two-phonon mixed-symmetry states built on the first $2^+_{ms}$ at 2129 keV. Furthermore, the systematics and the quadrupole-octupole multi-phonon excitations received special focus. The excitation functions performed from 2.2 MeV to 3.9 MeV helped to determine the threshold for the $\gamma$-ray transitions and hence their placement in the level scheme. Lifetimes, spins, multipolarities, and branching ratios obtained from angular distributions at 2.5 MeV and 3.5 MeV will be presented. [Preview Abstract] |
Saturday, October 13, 2007 10:48AM - 11:00AM |
HG.00010: From chiral vibration to static chirality in $^{135}$Nd S. Mukhopadhyay, D. Almehed, U. Garg, S. Frauendorf, T. Li, P.V. Madhusudhana Rao, X. Wang, S.S. Ghugre, M.P. Carpenter, S. Gros, A. Hecht, R.V.F. Janssens, F.G. Kondev, T. Lauritsen, D. Seweryniak, S. Zhu Lifetimes were obtained in a DSAM measurement at Gammasphere, using the $^{100}$Mo($^{40}$Ar, 5n)$^{135}$Nd reaction. Electromagnetic transition probabilities have been measured for the intra- and inter-band transitions in the two sequences in the nucleus $^{135}$Nd that were previously identified as a composite chiral bands [1]. The measurements are in good agreement with results of a new combination of TAC and RPA calculations. The chiral character of the bands is affirmed and it is observed that their behavior is associated with a transition from a vibrational into a static chiral regime. [1] S. Zhu et al., Phys. Rev. Lett.91, 132501 (2003). [Preview Abstract] |
Saturday, October 13, 2007 11:00AM - 11:12AM |
HG.00011: Investigating g-bosons in low-lying mixed symmetry states of $^{140}$Nd R.J. Casperson, E. Williams, V. Werner, H. Ai, R.F. Casten, A. Heinz, E.A. McCutchan, J. Qian, R. Winkler, G. G\"{u}rdal, M. Chamberlain $^{140}$Nd was produced through the $^{141}$Pr(p,2n)$^{140}$Nd reaction using a 16 MeV proton beam from the Yale ESTU tandem accelerator. Angular correlation measurements were made in-beam using the newly reconfigured YRAST ball detector array, and will be used to identify the multipolarities of transitions between low-lying states. Low-lying mixed symmetry states in $^{140}$Nd will be identified, and the role of quadrupole and eventually hexadecapole degrees of freedom in these states will be investigated. Preliminary results will be presented. Work supported by US DOE under Grant Numbers DE-FG02-91ER-40609, DE-FG02-05ER-41379, and DE-FG02-88ER-40417. [Preview Abstract] |
Saturday, October 13, 2007 11:12AM - 11:24AM |
HG.00012: Search for Mixed Symmetry States in $^{138}$Nd J.R. Terry, V. Werner, H. Ai, R.J. Casperson, A. Heinz, B. Huber, R. L\"{u}ettke, E.A. McCutchan, J. Qian, B. Shoraka, E. Williams, R. Winkler Excited states of mixed proton-neutron symmetry have been observed in a number of nuclei--most notably and extensively in $^{94}$Mo [1]. Such states are characterized by strong $M1$ transitions to symmetric partner states and are typically observed at 2-3 MeV excitation in nuclides removed from a close shell by two particles and/or two holes. The neutron-deficient $^{138}$Nd has been populated by beta decay at the Wright Nuclear Structure Laboratory to search for mixed symmetry states four neutrons below the $N=82$ shell closure. Gamma-ray emissions are detected with an array of 8 HPGe clover detectors configured for angular correlations measurements and are analyzed to extract multipolarities and mixing ratios. Analysis is ongoing and results will be presented. This work is supported by the U.S. Dept. of Energy grant no. DE-FG02-91ER- 40609. \newline [1] C. Fransen et al. Phys. Rev. C 67 (2003) 024307 [Preview Abstract] |
Saturday, October 13, 2007 11:24AM - 11:36AM |
HG.00013: A search for low-lying mixed symmetry states in $^{140}$Nd E. Williams, R.J. Casperson, V. Werner, H. Ai, P. Boutachkov, R.F. Casten, M. Chamberlain, G. G\"{u}rdal, A. Heinz, E.A. McCutchan, J. Qian, R. Winkler Low-lying states in $^{140}$Nd were populated by $\beta^+$ decay from $^{140}$Sm. Subsequent $\gamma$ decays were observed off-beam at the YRAST Ball spectrometer at Yale University, which has recently been reconfigured for angular correlation studies. Angular correlation measurements will be used to search for possible low-lying mixed-symmetric $2^+$ states. Our results will shed more light on the evolution of mixed symmetry states in the N=80 isotones, as they seem to exhibit a strong dependence on the underlying shell structure. Preliminary results of this investigation will be presented. This work is supported by US DOE grant numbers DE-FG02-91ER-40609, DE-FG02-88ER-40417, DE-FG02-05ER-41379, and the US National Science Foundation. [Preview Abstract] |
Saturday, October 13, 2007 11:36AM - 11:48AM |
HG.00014: ABSTRACT WITHDRAWN |
Saturday, October 13, 2007 11:48AM - 12:00PM |
HG.00015: Shape Coexistence in Transitional Nuclei W.D. Kulp, P. Schmelzenbach, J.L. Wood, J.M. Allmond, K.S. Krane, J. Loats, C.J. Stapels, E.B. Norman The ``transitional'' nuclei near $N=90$ have long been a focus of experimental and theoretical investigations. We report on a program of study of the $N=90$ and $N=88$ nuclei with a focus on the structure of $^{150}$Sm elucidated through new high-statistics, precision $\gamma$-ray coincidence spectroscopy and $\gamma-\gamma$ angular correlation data from the radioactive decay of $^{150}$Pm ($T_{1/2} = 2.68$ h, $Q^- = 3454$ keV, $J^\pi = 1^-$) and $^{150m,g}$Eu ($T_{1/2} = 12.8$ h, $J^\pi = 0^-$ and $T_{1/2} = 36.9$ y, $J^\pi = 5^{(-)}$, respectively, $Q^+\mathrm{(g.s.)} = 2261$ keV). In particular, very weak key collective transitions (e.g., the $2^+_2 (1046) \rightarrow 4^+_1 (773)$ 272~keV $\gamma$ ray) are observed and precision $\delta(E2/M1)$ mixing ratios are extracted (determining $\Delta J = 0$ transitions). This data, when combined with published results from conversion electron measurements, two-neutron transfer studies, and Coulomb excitation supports the results from detailed multiple-spectroscopy studies of $^{152}$Sm [1] indicating that shape coexistence underlies the structure at $N=88, 90$. [1] W. D. Kulp, et al., arXiv:0706.4129 [nucl-ex]. [Preview Abstract] |
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