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 DD: Nuclear Structure II |
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Chair: Siegfried Krewald, FZ Juelich Room: Patio |
Thursday, October 25, 2012 10:30AM - 10:42AM |
DD.00001: High-Precision Half-life Measurement for the Superallowed $\beta^+$ Emitter $^{14}$O Alex Laffoley High-precision measurements of superallowed Fermi beta decays between $0^+$ isobaric analog states have provided an invaluable probe of the Standard Model description of the electroweak interaction. Half-life measurements of the lightest of these, $^{10}$C and $^{14}$O, are of particular interest as the low-Z superallowed decays are most sensitive to a possible scalar current contribution. There are two primary methods for measuring the half-lives of $^{10}$C and $^{14}$O; one can directly count the beta particles or measure the gamma activity since both decay to an excited state of the daughter which then emit a characteristic gamma-ray. Comparing the experiments that detected the gamma-rays and those that perform beta counting measurements yield results that disagree with each other at the level of 0.11\% ($1.3\sigma$) for $^{14}$O and 0.13\% ($2.6\sigma$) for $^{10}$C. This provides motivation for a set of high-precision half-life measurements for $^{10}$C and $^{14}$O via both gamma-ray photopeak and direct beta counting techniques at TRIUMF to address the systematics between the methods used. The first of several experiments was performed at TRIUMF's ISAC facility in November 2011. This talk will highlight the importance and preliminary results of these measurements. [Preview Abstract] |
Thursday, October 25, 2012 10:42AM - 10:54AM |
DD.00002: Studies of the $\mathrm{^{19}O(d,p)^{20}O}$ reaction at {\sc resolut} D. Santiago-Gonzalez, I. Wiedenh\"over, M.L. Avila, L.T. Baby, J. Backer, J.C. Blackmon, E. Koshchiy, A.N. Kuchera, S. Kuvin, L.E. Linhardt, M. Matos, G.V. Rogachev The energetic location of the d$_{3/2}$--orbital in neutron-rich nuclei is of particular interest as it determines the location of the drip-line in the oxygen isotopes. Its behaviour has recently been discussed as a consequence of three-body forces [1]. Manifestations of such forces are traced through the location of the d$_{3/2}$ orbital, which closer to stability leads to highly excited states. In order to study the location and fragmentation of this orbital in $^{20}$O , we performed an experiment at the {\sc resolut} radioactive beam facility of the Florida State University accelerator laboratory. We produced a beam of the short-lived $^{19}$O isotope with an intensity of $1 \times 10^5$ pps, 65$\%$ purity and 4.11 MeV/u. This beam was used to study the spectroscopic factors of bound and unbound states of $^{20}$O using the $(d,p)$ reaction in inverse kinematics and components of the new {\sc anasen} detector array. We will present the methods used and compare our results with the ones recently published in [2].\\[4pt] [1] T. Otsuka et al., Phys. Rev. Lett 105, 032501 (2010)\\[0pt] [2] C. R. Hoffman et al., Phys. Rev. C 85, 054318 (2012) [Preview Abstract] |
Thursday, October 25, 2012 10:54AM - 11:06AM |
DD.00003: Unbound Excited States in $^{28}$Ne and $^{25}$F Jenna Smith, B. Alex Brown, Greg Christian, Shea Mosby, John F. Novak, Steven J. Quinn, Jesse Snyder, Artemis Spyrou, Michael J. Strongman, Michael Thoennessen, Thomas Baumann, Zachary Kohley, Joseph E. Finck, Calem R. Hoffman The neutron dripline has only been conclusively mapped out to $Z=8$. The unbound structure of isotopes with $Z>8$ has not been studied until recently, when multiple studies have focused on unbound states in neutron-rich fluorine isotopes. Unbound states in $^{28}$Ne and $^{25}$F were populated in the reaction of a 102 MeV/nucleon $^{29}$Na beam on a beryllium target. This is the first such state in $^{28}$Ne and the second such state in $^{25}$F. The measured decay energy of 32(22) keV in the $^{27}$Ne + $n$ system corresponds to an unbound excited state in $^{28}$Ne of 3.86(11) MeV. The decay energy of the $^{24}$F + $n$ system was measured as 300(170) keV, which places the second measured unbound state of $^{25}$F at 4.66(17) MeV. Measured decay energy spectra and a discussion of results will be presented. [Preview Abstract] |
Thursday, October 25, 2012 11:06AM - 11:18AM |
DD.00004: Collectivity in neutron-rich Cr isotopes S. Suchyta, S. Liddick, H. Crawford, G. Grinyer, N. Larson, J. Pereira, C. Prokop, A. Schneider, S. Vinnikova, C. Chiara, W. Walters, M. Carpenter, G. Gurdal, E. McCutchan, S. Zhu Collectivity rapidly develops in neutron-rich nuclei near N = 40 with Z $<$ 28 as protons are removed from the f$_{7/2}$ single-particle state. This collectivity has been inferred from large drops in the energy of the first excited 2$^{+}$ state in even-even Cr and Fe isotopes, as well as an increase in B(E2) along the Fe isotopic chain. Shell-model calculations that include the neutron g$_{9/2}$ and d$_{5/2}$ single-particle states indicate that the enhanced collectivity can be attributed to multi-particle neutron excitations across the N=40 gap. In the odd-odd nuclei, coexistence between spherical and deformed states has been proposed in the low-energy level structures of the Co and Mn isotopes. While recent studies of odd-A nuclei in this region have focused on the Co and Fe isotopes, less is known about the odd-A Cr isotopes. The structure of the odd-A Cr nuclei was investigated through the beta decay of neutron-rich V isotopes produced at the NSCL. The low-energy level schemes of the odd-A Cr isotopes will be presented and discussed. [Preview Abstract] |
Thursday, October 25, 2012 11:18AM - 11:30AM |
DD.00005: Shape Co-existence in Cr and Fe Isotopes Near $N$=40 M.P. Carpenter, R.V.F. Janssens, S. Zhu New data on the low- spin structure of neutron-rich Cr and Fe isotopes show a compression of the first 2$^{+ }$and 4$^{+}$ excitation energies relative to the lighter isotopes, suggesting the onset of collectivity associated with deformation. $B$(E2) values measured using Coulomb excitation and state lifetimes measured with a differential plunger also show an increase in collectivity as one approaches $N$=40 for the Fe and Cr isotopic chains. Recent shell- model calculations are able to reproduce the measured yrast level structure by including both $g_{9/2}$ and $d_{5/2}$ orbitals, which lie above the $N$=40 shell gap, in the model space of the calculations. Utilizing fusion evaporation reactions and Gammasphere, we have identified a number of rotational bands at high -spins in some of the lighter Cr and Fe isotopes. In addition, the moments of inertia associated with these bands, while all very similar, are dissimilar to the moments of inertia extracted for the ground state bands in the heavier Fe and Cr isotopes. This suggests that while the heavier isotopes display collectivity at low spin and excitation energy, mixing between the deformed states and the shell- model states distorts the deduced moments of inertia. In order to test this hypothesis, we have performed simple two-band mixing calculations assuming that the yrast bands of these neutron-rich Cr and Fe even-even isotopes result from mixing between spherical and deformed states. The results of these band mixing calculations will be presented. [Preview Abstract] |
Thursday, October 25, 2012 11:30AM - 11:42AM |
DD.00006: In-beam Gamma-ray spectroscopy of 43-46Cl Ragnar Stroberg, Alexandra Gade, Travis Baugher, Daniel Bazin, B. Alex Brown, Jonathan Cook, Thomas Glasmacher, Geoff Grinyer, Sean McDaniel, Andrew Ratkiewicz, Dirk Weisshaar The low-energy nuclear structure of the neutron-rich $^{43-46}$Cl isotopes is studied via in-beam $\gamma$-ray spectroscopy following the fragmentation of $^{48}$K projectiles on a $^{9}$Be target at intermediate beam energies. $\gamma\gamma$ coincidence information was used to construct level schemes for these neutron-rich nuclei. For the $N=28$ nucleus $^{45}$Cl, the lifetime of the first excited state at 130~keV was extracted via $\gamma$-ray line shape analysis, yielding an $M1$ strength an order of magnitude greater than that predicted by theory. The experimental data is compared to the results of large-scale shell-model calculations with effective interactions in the $sd$-$pf$ model space. [Preview Abstract] |
Thursday, October 25, 2012 11:42AM - 11:54AM |
DD.00007: Role of the $\nu $(g$_{9/2})$ orbital in the Ni isotopes Daniel S. Moerland, M. Albers, S. Zhu, J.V.F. Janssens, M. Alcorta, P.F. Bertone, M.P. Carpenter, C.R. Hoffman, F.G. Kondev, T. Lauritsen, C.J. Lister, E.A. McCutchan, C. Nair, A.M. Rogers, D. Seweryniak, T. Baugher, A. Gade, C.J. Chiara, P. Chowdhury, A.N. Deacon By analyzing and comparing the properties of high-spin structures, the evolution of the shape-driving effects of the $\nu $(g$_{9/2})$ orbital in the A$\approx $60 mass region can be inferred. In order to obtain information on those effects in the $^{60-65}$Ni isotopes from their behavior at high spin, an experiment was performed at ATLAS with Gammasphere and the Fragment Mass Analyzer (FMA). The Ni isotopes were produced by bombarding a 2 mg/cm$^{2}$-thick $^{26}$Mg target with a $^{48}$Ca beam at energies between 275 and 320 MeV. A and Z identification of the residues was achieved at the FMA focal plane. Signatures for collectivity and large deformation were found in several of the Ni isotopes of interest. The results will be presented and compared to observations in other nuclei of the region and to calculations. [Preview Abstract] |
Thursday, October 25, 2012 11:54AM - 12:06PM |
DD.00008: Collinear laser spectroscopy of stable $^{55}$Mn I in the BECOLA facility at NSCL A. Klose, P.F. Mantica, K. Minamisono, A. Schneider Laser spectroscopy was performed on stable $^{55}$Mn atoms using the collinear laser spectroscopy system of the BEam COoling and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory at Michigan State University. Mn$^{+}$ ions were extracted from a commercial ion source at 15~keV and neutralized in a Na vapor cell via charge-exchange reactions. The Mn atomic beam was co-propagated with laser light, and hyperfine spectra for both the ground and metastable states were measured by detecting laser-induced fluorescence. Analysis of the hyperfine spectra will be presented and future laser studies of other transition metal elements using BECOLA will be discussed. [Preview Abstract] |
Thursday, October 25, 2012 12:06PM - 12:18PM |
DD.00009: Level structure of $^{69}$Zn and the nature of yrast excitations near N=40 R.V.F. Janssens, S. Zhu, C.J. Chiara, W.B. Walters, M. Albers, M. Alcorta, P.F. Bertone, M.P. Carpenter, J.P. Greene, C.R. Hoffman, F.G. Kondev, N. Larson, S.N. Liddick, T. Lauritsen, C. Prokop, A.M. Rogers, D. Seweryniak, S. Suchyta The region of nuclei around $^{68}$Ni$_{40}$, with its closed proton shell and closed neutron harmonic-oscillator sub-shell, continues to be of much interest as recent data indicate that the stabilizing effects of the N=40 gap are rather localized in N and Z. There is evidence for the onset of collectivity and strong polarization of the $^{68}$Ni core in neighboring nuclei of the region. With two protons and one neutron hole in $^{68}$Ni, the structure of $^{69}$Zn provides an opportunity to learn about the nature of its yrast excitations, and to identify the orbitals responsible for polarization effects. Excited states in $^{69}$Zn were populated with deep-inelastic reactions of a $^{70}$Zn beam at 430 MeV on a thick 197Au target. A level scheme, with states built on the previously known 13.76(2)-hour isomer, will be presented, along with comparisons with the results of shell-model calculations. [Preview Abstract] |
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