Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session DF: Nuclear Structure II |
Hide Abstracts |
Chair: Krzysztof Piotr Rykaczewski, Oak Ridge National Laboratory Room: 104AB |
Thursday, October 27, 2011 10:30AM - 10:42AM |
DF.00001: Seniority, collectivity, and $B(E2)$ enhancement in $^{72}$Ni C.J. Chiara, I. Stefanescu, W.B. Walters, N. Sharp, M. Alcorta, M.P. Carpenter, G. G\"{u}rdal, C.R. Hoffman, R.V.F. Janssens, B.P. Kay, F.G. Kondev, T. Lauritsen, C.J. Lister, E.A. McCutchan, A.M. Rogers, D. Seweryniak, S. Zhu, B. Fornal, W. Kr\'{o}las, T. Paw\l at, J. Wrzesi\'{n}ski Gamma rays assigned to $_{28}^{72}$Ni$_{44}$\ have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV $^{76}$Ge beam and a $^{198}$Pt target. Using a combination of spectra produced by double gates on the known 454-, 843-, and 1095-keV members of the ground-state cascade, a coincident line at 199 keV has been identified and is tentatively assigned as the $8^{+}\rightarrow6^{+}$ transition. These $\gamma$-ray coincidences were observed only in prompt events, indicating an $8^{+}$ half-life below 20 ns and requiring a large $B(E2)$ enhancement compared to that expected from a seniority scheme. This value is consistent with models showing decay to a seniority $\nu=4,$ $6^{+}$ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV $2_{1}^{+}$ energy, as compared to the valence-symmetry counterpart $_{44}^{94}$Ru$_{50}$. [Preview Abstract] |
Thursday, October 27, 2011 10:42AM - 10:54AM |
DF.00002: Collectivity of Exotic Silicon Isotopes A. Ratkiewicz, A. Gade, T. Glasmacher, D. Weisshaar, G. Grinyer, D. Bazin, T. Baugher, S. Barlthelemy, B.A. Brown, C. Campbell, S. McDaniel, K. Meierbachtol, R. Meharchand, A. Signoracci, A. Spyrou, R. Stroberg, P. Voss, R. Winkler, P. Cottle, K. Kemper, D. Miller, A. Galindo-Uribarri, T. Otsuka, Y. Utsuno, E. Padilla-Rodal The determination of the electric quadrupole transition strength between the ground state and first excited state with spin-party of J$^{\pi }$=2$^{+}$ (the B(E2; 0$^{+}\rightarrow$ 2$^{+})$ value) in an even-even nucleus provides a measurement of the low-lying quadrupole collectivity. The B(E2) values for $^{34,36,38,40,42}$Si were measured via intermediate-energy Coulomb excitation at NSCL. The secondary beams were produced by fragmentation of $^{48}$Ca primary beam and guided onto a high-Z target. De-excitation gamma rays indicating the inelastic process were detected around the target position with the high efficiency scintillator array CAESAR in coincidence with scattered projectiles tracked on an event-by-event basis in the S800 spectrograph. The results comprise the first measurements of the quadrupole collectivity of $^{40}$Si and $^{42}$Si and probe the persistence of the $N$=28 magic number. The measured B(E2) values are compared to large-scale shell model calculations and provide insight into the evolution of shell structure and deformation in this region. [Preview Abstract] |
Thursday, October 27, 2011 10:54AM - 11:06AM |
DF.00003: Collectivity in neutron-rich Mn isotopes S.N. Liddick, S. Suchyta, N. Larson, B. Abromeit, M. Bolla, A. Ayres, A. Bey, C. Bingham, L. Cartegni, M. Madurga, M. Miller, M. Rajabali, R. Grzywacz, S. Paulauskas, S. Padgett, H.L. Crawford, I.G. Darby, K. Rykaczewski, S. Ilyushkin The rapid development of collectivity in the N = 40 region as protons are removed from the f$_{7/2}$ single-particle state is suggested by the dramatic drop in energy of the first excited $2^{+}$ state from $^{68}$Ni to $^{66}$Fe and the increase in B (E2) along the Fe isotopic chain. Recent large-scale shell model calculations which include the g$_{9/2}$ and d$_{5/2}$ single-particle states have attributed the increased collectivity in the Cr and Fe nuclei to the influence of multi- particle neutron excitations across N = 40. While a variety of experiments have focused on even-even nuclei, including Cr and Fe, very little is known about the odd-Z isotopes. To explore the influence of the intruder neutron g$_{9/2}$ and d$_{5/2}$ states, the beta decays of the Cr isotopes into the respective Mn nuclei were studied at the NSCL. Preliminary low-energy level structures for the Mn isotopes will be presented. [Preview Abstract] |
Thursday, October 27, 2011 11:06AM - 11:18AM |
DF.00004: Collectivity of Cr Isotopes Approaching N = 40 T. Baugher, A. Gade, D. Bazin, J.M. Cook, D.-C. Dinca, T. Glasmacher, W.F. Mueller, A. Ratkiewicz, D. Weisshaar, S. McDaniel, G. Grinyer, K. Walsh, R.V.F. Janssens, M.P. Carpenter, F.G. Kondev, S. Zhu, I. Stefanescu, E. Ricard-McCutchan, S. Freeman, A. Deacon, J.F. Smith, B. Kay, D. Sharp The reduced quadrupole transition probability, $B$($E$2;$0^+ \rightarrow 2^+$), provides a way to quantify low-lying collectivity in even-even nuclei. $B$($E$2) values for $^{58,60,62}$Cr were extracted using intermediate-energy Coulomb excitation at the NSCL. Cocktail beams containing $^{58,60,62}$Cr were produced in-flight and guided onto a high-$Z$ target. De-excitation gamma-rays tagging the inelastic process were detected in coincidence with the scattered particles using the high-purity germanium array SeGA and the S800 spectrograph. The measurement allowed the $B$($E$2) values of $^{60,62}$Cr to be extracted for the first time. Results are compared to large-scale shell-model calculations using a recent effective interaction developed for this region. [Preview Abstract] |
Thursday, October 27, 2011 11:18AM - 11:30AM |
DF.00005: ABSTRACT WITHDRAWN |
Thursday, October 27, 2011 11:30AM - 11:42AM |
DF.00006: Isomeric levels of nuclei near N = 40 S. Suchyta, S. Liddick, H. Crawford, G. Grinyer, A. Klose, P. Mantica, J. Pereira, A. Schneider, S. Vinnikova, C. Chiara, W. Walters, M. Carpenter, G. Gurdal, L. McCutchan, S. Zhu The neutron rich nuclei near N = 40 and Z $<$ 28 challenge our theoretical understanding of shell structure in this region.~ As protons are removed from the f$_{7/2}$ single-particle state, rapid changes in collectivity are observed and attributed to the influence of the neutron g$_{9/2}$ intruder orbital. Even the removal of two protons between $^{68}$Ni and $^{66}$Fe gives rise to a large drop by 1460 keV for the energy of the first excited 2$^{+}$ state from which an increase in collectivity has been inferred. The gamma-ray decay of isomeric states near N = 40 were studied at the NSCL to investigate nuclear structure in this region.~ We report the low level structures that were confirmed for $^{64}$Mn and newly proposed for $^{66}$Mn and $^{64}$V. [Preview Abstract] |
Thursday, October 27, 2011 11:42AM - 11:54AM |
DF.00007: Revisiting K-isomers in $^{176}$Hf via the $^{176}$Yb($\alpha$,4n) Reaction V.S. Prasher, A.Y. Deo, S. Hota, S. Lakshmi, P. Chowdhury, C.J. Guess, E.G. Jackson, V. Werner, T. Ahn, G. Ilie, V. Anagnostatou, N. Cooper, M. Elvers, P. Goddard, A. Heinz, D. Radeck, E. Williams High-K bands in $^{176}$Hf have been populated via the $^{176}$Yb($\alpha$,4n)$^{176}$Hf reaction at the WNSL tandem accelerator facility at Yale University using $\alpha$ beam energies of 41, 46 and 51 MeV. For the first time, fast beam pulsing was incorporated and tested with beam on-off periods of a few tens of $\mu$s. Known half lives of different high-K isomers in the Hf region [1] were measured to check the reliability of fast beam pulsing at WNSL for heavy ion spectroscopy. The population of 2-, 4-, and 6-qp isomers in $^{176}$Hf, with $t_{1/2}$= 9.6, 401 and 43 $\mu$s, respectively, is compared at different beam energies. The quest for states and isomers above the 22$^{-}$ 6-qp isomer[2] in $^{176}$Hf will also be discussed.\\[4pt] [1] T.L. Khoo et al., Phys. Rev. Lett. 28, 1717 (1972).\\[0pt] [2] G. Mukherjee et al., Phys. Rev. C82, 054316 (2010). [Preview Abstract] |
Thursday, October 27, 2011 11:54AM - 12:06PM |
DF.00008: $^{196}$Pt and the O(6) Symmetry E.A. McCutchan, C.J. Lister, M.P. Carpenter, G. Gurdal, G. Hennig, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, C. Nair, D. Seweryniak, S. Zhu, G. Rainovski, N. Pietralla, T. Moeller, C. Bauer, D. Cline, A.B. Hayes $^{196}$Pt is widely recognized as the textbook example of the O(6) symmetry of the Interacting Boson Model (IBM). Surprisingly, some of the unique IBM predictions for the O(6) limit have yet to be fully demonstrated in this nucleus. To rigorously test these predictions, a Coulomb excitation experiment was performed at the ATLAS facility at Argonne. Using a $^{196}$Pt beam at 850 MeV incident on a Carbon target, numerous low-spin, non-yrast states were populated. $\gamma$ rays were detected using Gammasphere operated in singles mode. From the measured intensities, the Gosia program was used to extract E2 matrix elements between states associated with the O(6) structure. Results will be discussed in terms of how closely the O(6) symmetry is followed in $^{196}$Pt. [Preview Abstract] |
Thursday, October 27, 2011 12:06PM - 12:18PM |
DF.00009: Precise measurements of lifetimes and deorientation in $^{92,94}$Zr using the Recoil Distance Doppler Shift method Matthew Hinton, Gabriela Ilie, Volker Werner, Tan Ahn, Nathan Cooper, Raphael Chevrier The lifetime for the $2_{1}^{+}$ state in $^{94}$Zr is known with only 20\% accuracy. In this region, involving proton and neutron sub-shell closures, it is highly desirable to know this value to greater precision, especially since $^{94}$Zr has the extraordinary case where the E2 excitation strength of the $2_{2}^{+}$ appears to be greater than that of the $2_{1}^{+}$. Therefore, we performed a lifetime measurement using the Recoil Distance Doppler Shift (RDDS) method and the New Yale Plunger Device. Beams of $^{92,94}$Zr, at energies of 245 MeV and 250 MeV, respectively, were Coulomb excited on a $^{24}$Mg target and $\gamma$-rays were measured in coincidence with the forward scattered Mg ions. Nuclear deorientation effects, due to hyperfine interactions, become increasingly important at the high charge states of the recoiling ions. In parallel to the RDDS measurement, the attenuation coefficients of the angular distributions were measured. The time dependence of these coefficients was used to calculate relative magnetic moments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700