Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session KD: Nuclear Structure V |
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Chair: Con Beausang, University of Richmond Room: Patio |
Friday, October 26, 2012 2:00PM - 2:12PM |
KD.00001: Utilizing angular distributions to measure the spin imparted to the continuum region of Gd nuclei by light-ion transfer reactions T.J. Ross, C.W. Beausang, R.O. Hughes, J.M. Allmond, C.T. Angell, M.S. Basunia, D.L. Bleuel, J.T. Burke, R.J. Casperson, J.E. Escher, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, L. Phair, J.J. Ressler, N.D. Scielzo, I.J. Thompson Historically it has proven extremely difficult to probe the properties of low-spin highly-excited states far above the yrast line in the bound quasi-continuum. We present the first measurement of the initial spin distribution of this region, following (p,d) and (p,t) reactions on $^{154}$Gd and $^{158}$Gd targets. The 25 MeV proton beam was provided by the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. A silicon telescope array, STARS, was used to detect light ions. We find that the spin transferred increases with excitation energy. Between 3 and 8 MeV, assuming a single dominant angular momentum transfer component, the measured angular distribution for the (p,d) reactions are well reproduced by DWBA calculations for $\Delta$L=4$\hbar$ transfer, whilst the (p,t) reactions are better characterized by $\Delta$L=5$\hbar$. A weighted combination of DWBA calculations, agrees excellently with experimental angular distributions. [Preview Abstract] |
Friday, October 26, 2012 2:12PM - 2:24PM |
KD.00002: Lifetime Measurements in $^{160}$Gd S.R. Lesher, I. Marsh, A. Aprahamian, C. Casarella, M. Smith, B.P. Crider, E.E. Peters, S.W. Yates The nature of low-lying excitations, K$^{\pi}=0^+$ bands in deformed nuclei remain enigmatic in the field, especially in relationship to quadrupole vibrations. One method of characterizing these states is by reduced transition probabilities, B(E2) values, a measure of the collectivity. These values can be measured directly by Coulomb excitation or calculated from measured lifetime values. Within the deformed region, there are five stable Gd isotopes, three of which have been studied to obtain B(E2) values, a fourth, $^{160}$Gd is the focus of this work. We have examined $^{160}$Gd with the (n,n$^{\prime}\gamma$) reaction and neutron energies up to 3.0 MeV to confirm known 0$^+$ states and to determine their lifetimes through DSAM measurements. Gamma-ray excitation functions and angular distribution measurements have been performed and preliminary results will be presented. [Preview Abstract] |
Friday, October 26, 2012 2:24PM - 2:36PM |
KD.00003: High-spin Spectroscopy in $^{163}$Hf R.B. Yadav, W.C. Ma, Q.A. Ijaz, J. Marsh, G.B. Hagemann, M. Carpenter, C. Hoffman, R.V.F. Janssens, F.G. Kondev, T. Lauritsen, S.F. Zhu, G. G\"{u}rdal, M. Alcorta, L.L. Riedinger, D. Hartley, S. Mukhopadhyay High-spin states of the odd-A nucleus $^{163}$Hf were populated through the $^{74}$Ge($^{94}$Zr,5n) reaction. Decay $\gamma$ rays were measured with the Gammasphere spectrometer array at ANL. Only two bands were known previously, the lowest one-quasiparticle band based on the neutron $i_{13/2}$ orbital and an excited negative-parity band (ABF) [1]. One band was extended to higher spin and more than eleven new bands observed, most of which were linked to each other. Spins and parities of levels were determined based on the measured multipolarities of $\gamma$ rays. The results will be discussed within the framework of cranked shell model calculations. \\[4pt] [1] K. P. Blume {\it et al}., Nucl. Phys. A 464, 445 (1987). [Preview Abstract] |
Friday, October 26, 2012 2:36PM - 2:48PM |
KD.00004: Identification of Triaxial Strongly Deformed Bands in $^{164}$Hf J.C. Marsh, W.C. Ma, Q.A. Ijaz, R.B. Yadav, G.B. Hagemann, R.V.F. Janssens, M.P. Carpenter, T. Lauritsen, S. Zhu, M. Alcorta, C. Hoffman, F.G. Kondev, G. G\"{u}rdal, L.L. Riedinger, D.J. Hartley, S. Mukhopadhyay A Gammasphere experiment has been performed at the ATLAS facility to search for triaxial strongly deformed (TSD) bands in $^{164}$Hf through the $^{94}$Zr($^{74}$Ge,4n) reaction. TSD bands, including families of wobbling bands, have been observed in several neighboring Lu and Ta isotopes and in $^{168}$Hf as well. Theoretical studies suggest that the elevated yrast line of $N=92$ isotope $^{164}$Hf may reduce the excitation energy of the predicted TSD structure relative to the normal deformed yrast line. This effect, together with the proton and neutron shell gaps at large triaxiality, makes $^{164}$Hf a better candidate for TSD structures. To date, two candidate TSD bands that are stronger and at lower spins than those in $^{168}$Hf [1] have been identified. Another new band was suggested to be associated with near-prolate shape with an enhanced deformation relative to normal deformed structures, similar to the ED bands systematically observed in heavier Hf isotopes in recent years.\\[4pt] [1] R. B. Yadav {\it et al.}, Phys. Rev. C {\bf 78}, 04316 (2008) and references therein. [Preview Abstract] |
Friday, October 26, 2012 2:48PM - 3:00PM |
KD.00005: Band Structures and Nucleon Alignments in $^{173,175}$W C.J. Guess, S.K. Tandel, P. Chowdhury, U. Shirwadkar, M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, C.J. Lister, D. Seweryniak, X. Wang, S. Zhu, D.J. Hartley Spectroscopic study of nuclei in the A$\sim$180 region is essential to better understand regional relationships between Nilsson orbitals. Highly excited rotational states in both nuclei were populated at Argonne National Laboratory via a 230 MeV $^{50}$Ti beam from the ATLAS accelerator incident on a $^{128}$Te target. The Gammasphere array was used to detect $\gamma$ decays from excited states. Rotational bands built on the level 1/2$^-$[521], p$_{3/2}$ in $^{173,175}$W have been extended to spins of 40 and 35$\hbar$ respectively, and bands built on the 7/2$^+$[633], i$_{13/2}$ configuration extended to 38 and 27$\hbar$ respectively. New sidebands in $^{173}$W have been observed in all previously-discovered bands. Alignments from i$_{13/2}$ neutron and h$_{11/2}$ proton crossings are consistent with predictions of Woods-Saxon cranking calculations. Experimental results and regional systematics will be presented. [Preview Abstract] |
Friday, October 26, 2012 3:00PM - 3:12PM |
KD.00006: In-beam and $\alpha$-decay studies of $^{180}$Tl F.G. Kondev, M.P. Carpenter, S. Zhu, R.V.F. Janssens, B.B. Back, P.F. Bertone, J. Chen, C.A. Chiara, C.J. Copos, J.P. Greene, G. Henning, C.R. Hoffman, B.P. Kay, T.L. Khoo, T. Lauritsen, E.A. McCutchan, C. Nair, A. Rogers, G. Savard, D. Seweryniak, D.J. Hartley We have carried out new spectroscopy studies of the $^{180}$Tl nuclide, in which a large electron-capture delayed fission branch was recently observed [1], by utilizing the $^{89}$Y + $^{92}$Mo symmetric reaction and the Argonne Fragment Mass Analyzer (FMA), in conjunction with the recoil-decay tagging technique. Prompt $\gamma$ rays were detected at the target position by Gammasphere and these were subsequently correlated with $\alpha$ decays measured using a Double-sided Silicon Strip Detector (DSSD) at the focal plane of FMA. In addition, an array of four Ge clover detectors surrounded the DSSD, thus allowing $\alpha-\gamma$ coincidences to be recorded. The obtained new results for $^{180}$Tl will be presented, together with those for the daughter nuclide $^{176}$Au.\\[4pt] [1] A.N. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010). [Preview Abstract] |
Friday, October 26, 2012 3:12PM - 3:24PM |
KD.00007: $\beta$-delayed $\gamma$-ray spectroscopy of $^{196}$Hg and its description within the extended supersymmetry C. Bernards, T. Ahmed, T. Ahn, C. Deng, M. Elvers, A. Heinz, S. Heinze, G. Ilie, E. Jiang, J. Jolie, R. Lee, D. Safran, N. Shenkov, T. Thomas, V. Werner The concept of nuclear structure SUSY has been observed and investigated in the Au-Pt mass region. It allows the simultaneous description of different nuclei forming so-called supermultiplets. All members of a supermultiplet are distinguished by a constant number of IBFM $\nu$- and $\pi$-bosons and -fermions. The most popular example is the `magic square' consisting of $^{194,195}$Pt and $^{195,196}$Au. Recently, efforts were made to investigate the expansion of the Au-Pt supermultiplets by a fifth member: the neighboring even-even Hg isotopes. For the square around $^{194}$Pt, this corresponds the 2-fermion--5-boson supermultiplet member $^{196}$Hg. We report on a $\gamma\gamma$ angular-correlation experiment to complete the data on low-spin states in $^{196}$Hg. It was performed at WSNL of Yale University using a 28-MeV proton beam activating an enriched $^{198}$HgS target. The $\gamma$-rays following the decay of the $\beta$-unstable $^{196}$Tl were observed off-beam with the YRAST-Ball Clover array. We present our results and discuss the description of $^{196}$Hg within the extended supersymmetry model. [Preview Abstract] |
Friday, October 26, 2012 3:24PM - 3:36PM |
KD.00008: Measurements of the neutron skin of $^{208}$Pb from parity violating electron scattering Jonathan Wexler We present the results for the thickness of the neutron skin of $^{208}$Pb from parity violating scattering asymmetry measurements using the Jefferson Lab polarized electron beam in experimental Hall A. Through parity violating elastic e-$^{208}$Pb reactions, the extraction of neutron distributions can be performed with relatively few theoretical uncertainties when compared to hadronic scattering techniques, providing clean access to previously poorly constrained parameters. A measurement of the $^{208}$Pb neutron skin provides insight into topics spanning the structure and symmetry energy of neutron rich nuclei and dense nuclear matter, and the equations of state for neutron stars. This talk will present the parity violating asymmetry and associated neutron skin thickness of $^{208}$Pb as well as planned measurements for improved precision and the prospects for $^{48}$Ca. [Preview Abstract] |
Friday, October 26, 2012 3:36PM - 3:48PM |
KD.00009: Measurement of $^{243}$Am(p,tf) as a surrogate for $^{240}$Am(n,f) R.J. Casperson, J.T. Burke, M. McCleskey, A. Saastamoinen, E. Simmons, A. Spiridon, A. Ratkiewicz, A. Blanc, M. Kurokawa, R.G. Pizzone The cross sections of (n,f) reactions are of interest in reactor modeling, but short-lived isotopes, such as $^{240}$Am, can be very difficult to measure. To avoid the enormous background created by such short-lived isotopes, we use the surrogate ratio method, which allows us to determine the ratio of an unknown cross section relative to a known one. In the case of $^{240}$Am(n,f), the ratio is relative to $^{235}$U(n,f), and we use (p,t) reactions to populate the relevant compound nuclei. We present preliminary results for measurements of $^{243}$Am(p,tf) and $^{238}$U(p,tf) using the STARLiTe detector system at the Texas A\&M University Cyclotron Institute. The performance of the recently commissioned data acquisition system will also be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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