Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session LF: Nuclear Structure: Medium Mass A=100-150 |
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Chair: Paul Garrett, University of Guelph Room: Simmons Ballroom 4 |
Sunday, October 26, 2008 8:30AM - 8:42AM |
LF.00001: Investigation into the Low-Energy Structure of Ru Isotopes via \textit{G}-Factor Measurements M.J. Taylor, M.A. Bentley, N. Benczer-Koller, G. Kumbartzki, G. Gurdal, V. Werner, J. Qian, R. Winkler, A. Heinz, E. Williams, E.A. McCutchan, R. Casperson, A.E. Stuchbery, B. Shoraka, Z. Berant, R. Luttke An experiment was performed to investigate the low-energy structure of the even-A $^{96-104}_{44}$Ru isotopes. The experiment utilised the transient field technique combined with Coulomb excitation in inverse kinematics to measure the $g$ factors of the first excited 2$_{1}^{+ }$states. The transient field was calibrated through measurements of the known $g$(2$_{1}^{+})$ in $^{102}$Ru and $^{98}$Mo. The experiment constituted the first ever measurement of the $g$(2$_{1}^{+})$ for $^{96}$Ru as well more accurate relative measurements of the $g$(2$_{1}^{+})$ for $^{98,100,104}$Ru. Preliminary analysis of the data taken for $^{96}$Ru indicates a value for the $g$(2$_{1}^{+})$ close to the collective limit $Z/A $suggesting that the two neutrons and six proton holes outside of the $N=Z$=50 closed shells contribute equally to the 2$_{1}^{+}$ state wave function. The technique used, results and theoretical interpretations will be presented. [Preview Abstract] |
Sunday, October 26, 2008 8:42AM - 8:54AM |
LF.00002: Observation of an excited state in $^{101}$Sn via the $\alpha$-decay of $^{105}$Te Sean Liddick, Iain Darby, Robert Grzywacz, Krzysztof Rykaczewski, Robert Page, Carl Gross, Jon Batchelder The doubly magic nucleus $^{100}$Sn is a key test nucleus for the nuclear shell model. Required information in this region is knowledge of single-particle energies, particularly the energy separation between the $\nu d_{5/2}-\nu g_{7/2}$ orbitals. For the $^{100}$Sn region, the energy separation can be best extracted from the energy of the first excited state in $^{101}$Sn. In experiments performed at the HRIBF using the RMS $\alpha$-decay chains of $^{109}$Xe~$\rightarrow$~$^{105}$Te~$\rightarrow$~$^{101}$Sn~were observed following implants of $^{109}$Xe ions into a DSSD, fully instrumented with Digital Signal Processing, placed within the $\gamma$-array CARDS. Double $\alpha$-decay pulse shapes provide a unique and clean coincidence requirement which resulted in the observation of a $\gamma$-ray, interpreted as being emitted from the first excited state in $^{101}$Sn. These results will be presented and the implications for the single-particle level assignments will be discussed. [Preview Abstract] |
Sunday, October 26, 2008 8:54AM - 9:06AM |
LF.00003: Nuclear structure of $^{116}$Cd from the (n, n' $\gamma$) reaction C.S. Sumithrarachchi, P.E. Garrett, K.L. Green, M. Kadi, N. Warr, J. Jolie, S.W. Yates The nuclear structure of the Cd isotopes have been extensively studied with the aim of understanding the role of configuration mixing between multiphonon vibrational and intruder structures. The study of the low-lying levels in $^{116}$Cd is particularly important as it has been reported to possess a more complex nuclear structure than is predicted by the interacting boson model(IBM)[1]. The properties of multiphonon vibrational and intruder states in $^{116}$Cd 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 derive the level structure of $^{116}$Cd. The electromagnetic properties of levels in $^{116}$Cd and comparisons with IBM-2 calculations will be presented. \newline [1]. M. Kadi et al.,Phys. ReV. C 68, 031306(R) (2003). [Preview Abstract] |
Sunday, October 26, 2008 9:06AM - 9:18AM |
LF.00004: Precise Lifetime Measurement of $2^+_1$ State in $^{120}$Te by Recoil Distance Doppler Shift Method J.R. Terry, V. Werner, Z. Berrant, R.J. Casperson, A. Heinz, G. Henning, R. L\"{u}ttke, E.A. McCutchan, J. Qian, B. Shoraka, E. Williams, R. Winkler The lifetime of the first 2$^+$ state of $^{120}$Te has been measured using a combination of inverse-kinematics Coulomb excitation well below the Coulomb barrier and the recoil distance Doppler shift (RDDS) method. This technique yields lifetimes with uncertainties of approximately 2\%, due mostly to a large Doppler shift and nearly background-free gamma-ray spectra. The 2$^+_2$ and 4$^+_1$ excited states were also observed, providing a measure of the transition strengths to these states relative to the 2$^+_1$ state. Results are compared to calculations with and without $2p-2h$ proton intruder configurations across the $Z=50$ shell gap. This work is supported by the U.S. DOE under contract No. DE-FG02-91ER-40609. [Preview Abstract] |
Sunday, October 26, 2008 9:18AM - 9:30AM |
LF.00005: Spectroscopy of exotic $^{123,125}$Ag produced in fragmentation reactions Irina Stefanescu, W.B. Walters, N. Hoteling, P.F. Mantica, J. Pereira, J.S. Pinter, J.B. Stoker, B. Tomlin We extended the experimental knowledge in the mass-region around $^{132}$Sn by identifying the decay of high-spin isomers in the exotic odd-mass $^{123,125}$Ag. The two isotopes were produced at the NSCL laboratory by projectile fragmentation of a $^{136}$Xe beam at 120MeV/u directed onto a thick Be target. The NSCL Beta Counting System was used identify the secondary beam fragments. Prompt and delayed gamma-rays following the deexcitation of the fragments were detected with the SEGA array. Partial level schemes for $^{123,125}$Ag are proposed for the first time and compared with the results of shell-model calculations. [Preview Abstract] |
Sunday, October 26, 2008 9:30AM - 9:42AM |
LF.00006: High-spin states in $^{135}$Cs N. Fotiades, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, J.A. Becker, W. Younes High-spin states in $^{135}$Cs have been studied following the fission of the $^{226}$Th compound nucleus formed in a fusion-evaporation reaction ($^{18}$O at 91~MeV on $^{208}$Pb). The Gammasphere array was used to detect $\gamma$-ray coincidences. A sequence of transitions was observed in coincidence with the previously known 786.8-keV, $11/2^{+} \rightarrow 7/2^{+}$ transition from the 786.8-keV level of $^{135}$Cs extending the level scheme up to spin 23/2 and $\sim$3.3~MeV excitation energy. The assignment of this sequence to $^{135}$Cs is also supported by coincidences with known transitions in the complementary fragments. The observed experimental states are compared with states in the neighboring $^{137}$Cs nucleus, as well as with the states in the Z=54 core of $^{134}$Xe. The coupling of the odd proton occupying the $g_{7/2}$ orbital to the yrast states in $^{134}$Xe can account for the first excited states of $^{135}$Cs. This work was supported by the U.S. Department of Energy under Contracts No. DE-AC52-06NA25396 (LANL), DE-AC52-07NA27344 (LLNL) and AC03-76SF00098 (LBNL) and by the National Science Foundation (Rutgers). [Preview Abstract] |
Sunday, October 26, 2008 9:42AM - 9:54AM |
LF.00007: Study of low-lying excited states in $^{139}$La via the $\left(n,n^{\prime}\gamma\right)$ reaction S.F. Ashley, J.N. Orce, B. Crider, E. Elhami, M.T. McEllistrem, S. Mukhopadhyay, E. Peters, S.W. Yates An observable result of Pauli-blocking in atomic nuclei [1] is a reduction in the transition rates between equivalent phonon excitations in odd-A nuclei and even-even nuclei. In particular, studies of low-lying $J^{\pi}=1^-$ states in $^{141}$Pr [2,3], imply that the $B(E1: 1^- \rightarrow 0_1^+)$ values associated with decays from states with $[[2^+ \otimes 3^-]\otimes particle]_{J^{\pi}=1^-}$ configurations are $\sim 52-83\%$ of the $B(E1: 1^- \rightarrow 0_1^+)$ value associated with decay from the $[2^+ \otimes 3^-]_{J^{\pi}=1^-}$ state in $^{140}$Ce. This presentation will focus on lifetimes deduced from an angular-distribution measurement of $^{139}$La, via the $\left(n,n^{\prime}\gamma\right)$ reaction with E$_n = 2.0$ MeV, and a comparative interpretation of Pauli-blocking in $^{139}$La and $^{141}$Pr will be drawn.\\ $[1]$ V.G.~Soloviev, Theory~of~Atomic~Nuclei:~Quasiparticles~and~Phonons, IOP~Publishing~(Bristol,~United Kingdom), (1992)\\ $[2]$ M.~Scheck~et~al., Phys.~Rev.~C~\textbf{75}, 044313 (2007)\\ $[3]$ M.~Scheck~et~al., submitted to Phys.~Rev.~C [Preview Abstract] |
Sunday, October 26, 2008 9:54AM - 10:06AM |
LF.00008: g-factor measurements in $^{134}$Te and $^{140,142}$Xe Chris Goodin, K. Li, A.V. Daniel, N.J. Stone, A.V. Ramayya, J.H. Hamilton, Sh. Liu, J. Stone By using new techniques developed for measuring angular correlations with Gammasphere, the g-factor of the 4$^+$ state in $^{134}$Te has been measured for the first time. The g- factor measurement is compared to shell model predictions and good agreement is found between experiment and theory. The g-factors of 2$^+$ states in $^{140,142}$Xe are also measured for the first time with this method. g-factors in $^ {146}$Ba and $^{146,148}$Ce are measured to establish the method by comparison with previous values. The results are discussed in terms of IBM-2 and rotation-vibration models. [Preview Abstract] |
Sunday, October 26, 2008 10:06AM - 10:18AM |
LF.00009: Octupole correlations in light neutron-rich $^{143, 144}$La Y.X. Luo, J.H. Hamilton, J.O. Rasmussen, A.V. Ramayya, S.J. Zhu, J.K. Hwang Intensive investigations have shown strong evidence of octupole deformations and/or correlations in $^{142-148}$Ba, $^{144,146}$Cs and $^{145,147}$La. In the present work the high-spin level scheme of light neutron-rich $^{143}$La is expanded and that of $^{144}$La is proposed for the first time by measuring prompt gamma rays from the spontaneous fission of $^{252}$Cf at Gammasphere. B(E1)/B(E2) ratios, energy displacement $\delta $E(I) and the rotational frequency ratios $\omega ^{-}$(I)/$\omega ^{+}$(I) of the new parity-doublets of $^{143,144}$La indicate that octupole correlations also develop in these light neutron-rich La isotopes. Based on CSM calculations the band-crossings observed in a rotational frequency range of 0.31 to 0.34 MeV for the two even-parity bands in $^{143}$La are interpreted as due to alignment of a pair of $i_{13/2}$ neutrons in the nucleus. [Preview Abstract] |
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