Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JF: Studies of Nuclear Symmetries |
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Sponsoring Units: DNP JPS Chair: Rick Casten, Yale University Room: Ritz-Carlton Hotel Plantation 3 |
Thursday, September 22, 2005 9:00AM - 9:15AM |
JF.00001: Possible E(5/4) Symmetry in $^{135}$Ba M.S. Fetea, R.B. Cakirli, R.F. Casten, D.D. Warner The case of a liquid drop with quadrupole deformation coupled to a particle with $j=3/2$ was recently presented as a special solution E(5/4) to dynamic supersymmetries of differential equations. This development prompted the search for odd-A candidates for an E(5/4) symmetry at the critical value of the spherical to $\gamma $-unstable transition. Energies and E2 transitions have been calculated for $^{135}$Ba in the Interacting Boson-Fermion Model, Particle Vibrator Model and in the Shell Model frameworks and compared with the E(5/4) predictions and with the data. A comparison of the results will be shown as well as an identification of key data that are needed. This work was supported by NSF Grant PHY 0204811, the Research Corporation, grant CC5494, and DOE Grant No. DE-FG02-91ER-40609. [Preview Abstract] |
Thursday, September 22, 2005 9:15AM - 9:30AM |
JF.00002: New band mechanism of doubly-odd nuclei in the medium-heavy mass region Koji Higashiyama In recent years, many experimental studies on the doubly-odd nuclei in the mass $A\sim 130$ region show two nearly degenerate $\Delta I=1$ bands built on the unique-parity $0h_{11/2}$ valence neutron and proton orbitals. From the theoretical side, these bands were extensively investigated in terms of mean field approaches. However, there was very few theoretical study which preserves both rotational symmetry and particle number conservation of the interactions. A few studies of them have been made using a pair-truncated shell model, where the shell model basis states are restricted to the collective subspace. This approach reproduced well experimental energy spectra and electromagnetic transitions of the doublet bands. From analysis of the wave functions and transition rates, it was found that the level scheme of the doubly-odd nuclei arises from different angular momentum configurations of the unpaired neutron and the unpaired proton, weakly coupled with the quadrupole collective excitations of the even-even part of the nucleus. In this talk, the results of these calculations will be presented and discussed. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JF.00003: Pair-truncated shell-model approach to the mass $A\sim 130$ region Naotaka Yoshinaga There exist two prominent features in even-even nuclei in the mass $A\sim 130$ region. First, low-lying states of these nuclei exhibit the $\gamma$ instability, which manifests in the energy staggering of even-odd spin states in the quasi-$\gamma$ bands and also in some forbidden $E2$ interband transition rates. Second, at high-spins yrast bands of these nuclei show anomalous behavior, the so-called backbending phenomenon. It arises due to band crossing between the ground-state band and s band originating from the alignment of two neutrons in the $0h_{11/2}$ orbital. For a description of both the low-lying states and backbending phenomena, we proposed a new version of the pair-truncated shell model, where the even-even nuclear states were constructed from angular momenta zero ($S$), two ($D$) and four ($G$) collective pairs, and non-collective $H$ pairs, which were made by two nucleons in the $0h_{11/2}$ orbitals. The model was applied to the even-even nuclei in this mass region, and reproduced well experimental energy spectra and electromagnetic properties. [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JF.00004: Deformation of excited states in collective nuclei using quadrupole shape invariants E. Williams, V. Werner Quadrupole shape invariants, formed by the isoscalar electric quadrupole operator, have been shown to provide a model- independent signature of nuclear deformation in a given eigenstate [1,2]. These invariants are of particular interest in cases where few lifetime data are available, as only a few absolute B(E2) values are needed to approximately determine the lowest quadrupole invariants for the ground state. In this work, we have extended earlier studies [3] of quadrupole shape invariants by investigating their general behavior for excited states and band structures in addition to the ground state, as well as exploring the behavior of these invariants at and between various limits of deformation (vibrational, rotational, and $\gamma$-soft) within the framework of the interacting boson model (IBA)-1. Preliminary results of this investigation will be presented. [1] K. Kumar. Phys. Rev. Lett. 28, 249 (1972). [2] D. Cline, Annu. Rev. Nucl. Part. Sci. 36, 683 (1986). [3] V. Werner et al. Phys. Rev. C, 61, 021301 (1999). Work supported by US DOE grant number DE-FG02-91ER-40609. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JF.00005: Investigating the B(E2) anomaly in $^{144}$Nd by relative Coulomb excitation C.R. Fitzpatrick, V. Werner, R.F. Casten, H. Ai, R.B. Cakirli, A. Heinz, E.A. McCutchan, D.A. Meyer, J. Qian, E. Williams, R. Winkler, G. G\"urdal Previous work has shown that for a few non-magic nuclei, B$_ {4/2}$ = B(E2; 4$_{1}^{+}$$\rightarrow$2$_{1}^{+}$)/B(E2; 2$_{1} ^{+}$ $\rightarrow$0$_{1}^{+}$) is less than one; this is anomalous in the context of collective models. $^{144}$Nd is a non-magic nucleus with a particularly low B$_{4/2}$ (0.73 $\pm$ 0.09) and as such merits further investigation. A Coulomb excitation experiment was carried out using the 20MV Tandem Van de Graff accelerator at Yale using $^{48}$Ti ions in the range 170-202 MeV on two composite targets: one a mix of $^{142}$Nd and $^{144}$Nd, the other a layered target of $^{148}$Sm and $^{144}$Nd. These data facilitate a relative measurement of B$_{4/2}$ for $^{144}$Nd, and also provide a check that the data in this region is self-consistent. Data analysis is in progress; results of this work will be presented. Work supported by US DOE grants DE-FG02-91ER-40609, DE-FG02- 88ER40417 and DE-FG03-03NA00081. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JF.00006: Investigation of Vibrational Structure using SAUTs Cornelius Beausang, R.B. Cakirli, R.F. Casten, V. Nikolova A recent paper by Cakirli et al. [1] investigating the vibrational structure of the nucleus $^{98}$Ru pointed out the importance that limits on intensities of Spin Allowed Unobserved Transitions (SAUTs) can have on the interpretation of specific levels and indeed the entire structure of the nucleus. SAUTs, refer to transitions, which are allowed by angular momentum selection rules, but whose intensities are too weak to be observed, between various levels of suggested multi-phonon multiplets. In some cases the ratio of B(E2) values, obtained from the intensity limits set from the non-observation of otherwise allowed transitions, e.g. between suggested levels of a three-phonon multiplet and levels in a two-phonon multiplet allowed for the reinterpretation of these states. In this work we undertake a (partial) survey of existing data in the literature to determine if meaningful, useful limits on SAUTS can aid in the interpretation of other vibrational and transitional nuclei.\newline \newline [1] R.B. Cakirili, et al., Phys. Rev. C \textbf{70 }044312 (2004) [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JF.00007: Ground-band doubling and chiral doublets in $^{110}$Ru J.H. Hamilton, S.J. Zhu, Y.X. Luo, J.O. Rasmussen, A.V. Ramayya, J.K. Hwang, Z. Jiang, Z. Zhang, R.Q. Xu, S.D. Xiao, X.L. Che, Y.N. U, W.C. Ma, J.D. Cole, I.Y. Lee, R. Donangelo Bands in neutron-rich $^{110}$Ru were reinvestigated by measuring high-fold prompt $\gamma $-ray coincidence events following the spontaneous fission of $^{252}$Cf with Gammasphere. The ground-state band and the $\gamma $-vibrational band have been confirmed and expanded with spin up to 20 h and 13 h respectively. Another side band built on a 10$^{+}$ state has been established. Its energies are nearly degenerate with the ground band. This is the first case of ground band doubling. Two new sets of $\Delta $I=1 negative parity bands are observed and have the characteristics of chiral vibrational bands. Evidence for their interpretation as chiral band doublets will be presented. These bands are very similar to chiral doublets we found in $^{106}$Mo. Preliminary data analysis indicates the possible presence of similar chiral band doublets in $^{112}$Ru. [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JF.00008: Proton-Neutron Mixed-Symmetry States of Vibrational Nuclei Near the $N=82$ Shell Closure Norbert Pietralla, T. Ahn, B. Bochev, A. Costin, K. Dusling, T.C. Li, S. Pontillo, G. Rainovski, Y. Rong Proton-neutron (pn) mixed-symmetry states (MSSs) have been defined in the pn-version of the interacting boson model (IBM- 2). They are quadrupole-collective structures with wave functions that contain antisymmetric parts with respect to the pn contribution. This makes them sensitive to isovector parts of the effective pn interaction in the valence shell. Multiphonon structures with mixed-symmetry have been discovered $[$1$]$ and studied in vibrational even-even nuclei near the $N=50$ shell closure. A program for investigating MSSs has been initiated at the Nuclear Structure Lab of SUNY at Stony Brook. We report on our identification of one-phonon $2^+_{1, {\rm ms}}$ MSSs of even-even vibrational nuclei near the $N=82$ shell closure with $^{136}$Ba, $^{136,138}$Ce, and $N=86$ isotones $[$2$]$ as examples. Experimental techniques, results, and consequences will be discussed. \\ $[$1$]$ N.~Pietralla {\it et al.}, Phys.~Rev.~Lett.~{\bf 83}, 1303 (1999); Phys. Rev. Lett.~{\bf 84}, 3775 (2000).\\ $[$2$]$ T.C.~Li, N.~Pietralla {\it et al.}, Phys.Rev.~C {\bf 71}, 044318 (2005). [Preview Abstract] |
Thursday, September 22, 2005 11:00AM - 11:15AM |
JF.00009: Investigation of 0$^+$ states in Rare Earth Region Nuclei D.A. Meyer, G. Graw, R. Hertenberger, H.-F. Wirth, R.F. Casten, P. von Brentano, D. Bucurescu, C.R. Fitzpatrick, S. Heinze, J.L. Jerke, J. Jolie, R. Kr\"{u}cken, M. Mahgoub, O. M\"{o}ller, D. M\"{u}cher, P. Pejovic, C. Scholl, V. Wood The nature of 0$^+$ excitations, especially in transitional and deformed nuclei, has recently attracted new attention with experiment studying $^{158}$Gd [1]. 15 additional nuclei in the rare earth region were studied via the (p, t) pickup reaction using the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. Outgoing tritons were recorded at three lab angles, and their relative cross sections are compared to those calculated using the distorted wave Born approximation (DWBA). Using the unique shape of the L = 0 angular distribution, more than double the number of 0$^+$ states than were previously known are identified. The distribution of 0$^+$ energies and cross sections is discussed. This work supported by the U.S. DOE under Grant No. DE-FG02- 91ER-40609, MLL, and DFG (C4-Gr894/2-3, Jo391/2-1). [1] S. R. Lesher, et al., Phys. Rev. C 66, 051305(R) (2002). [Preview Abstract] |
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