Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session FM: Nuclear Structure A=60-100 |
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Chair: Riccardo Orlandi, JAEA Room: Hilton Queen's 6 |
Friday, October 26, 2018 9:00AM - 9:15AM |
FM.00001: Development of Optical Pumping Technique for Determination of Charge Radii and Nuclear Moments for Fe and Zr isotopes Jeremy Lantis, Kei Minamisono, David M Garand, Colton Kalman, Yuan Liu, Paul Mantica, Andrew Miller, Joel Zuzelski The first and second-row transition metals span an interesting region in the nuclear landscape, crossing both N = 28-50 neutron magic numbers as well as a debated subshell closure at N = 40. Of interest are charge radii and electromagnetic moments of Fe isotopes across N = 40 in the vicinity of 68Ni, where shape coexistence and rapid development of collectivity are suggested, and Zr isotopes, which have important implications for stewardship science. However, laser spectroscopy studies on transition metals are difficult due to low production rates and unfavorable electronic populations. An optical pumping technique is being developed at the BECOLA facility at NSCL/MSU to redistribute electronic populations to a favorable electronic state for laser spectroscopy. Simulation results for Fe and Zr, and current status of development will be discussed. |
Friday, October 26, 2018 9:15AM - 9:30AM |
FM.00002: Study of 68Co low-energy structure via β decay including fast-timing measurements Benjamin P. Crider, Christopher J Prokop, Sean N. Liddick, Mohammad Alshudifat, Akaa D Ayangeakaa, Michael P Carpenter, James J Carroll, Jun Chen, Christopher J Chiara, Helena David, Alex C Dombos, Shintaro Go, Robert K. Grzywacz, Jessica Harker, Robert V F Janssens, Nicole R Larson, Torben Lauritsen, Rebecca Lewis, Stephen Quinn, Francesco Recchia, Dariusz Seweryniak, Artemis Spyrou, Scott A Suchyta, William B Walters, Shaofei Zhu In neutron-rich nuclei near N = 40, the large energy separation of the νpf shell and the νg9/2 single-particle state is responsible for a subshell closure that has long been investigated for its impact on other nearby neutron-rich nuclei. Just beyond the N = 40 subshell closure, nuclei exhibit a sudden onset of collectivity as protons are removed from the πf7/2 single-particle state. This apparent fragility has been attributed to shape coexistence between spherical and prolate-deformed configurations. For 68Co, a recent β-decay study at NSCL concluded that the lowest-energy populated state was attributed to a deformed configuration, extending the presence of shape coexistence to this nucleus. This work reports on 68Co as determined from the analysis of new data from NSCL utilizing the selectivity of low-spin β decay from 68Fe to populate 68Co. An expanded schematic of the low-lying structure of 68Co including half-life information, particularly for the low-lying states, will be presented. |
Friday, October 26, 2018 9:30AM - 9:45AM |
FM.00003: Shape coexistence and isospin symmetry along N=Z Kathrin Wimmer The region of proton-rich nuclei around the N=Z offers a rich testing ground for various nuclear models. Rapid shape changes have been observed between from prolate deformation in 76Kr to an oblate ground state in 72Kr. Based on the comparison with its mirror nucleus 70Se, an oblate shape is expected for 70Kr. Breaking of isospin symmetry as well as the proximity to the proton drip line however, may lead to measurable differences in the excitation energy spectrum as well as the quadrupole collectivity of the A=70 mirror pair 70Kr and 70Se. 70Kr has been studied at the RIBF facility using Coulomb excitation and neutron removal reactions using the BigRIPS fragment separator to select 70-72Kr beams. Reaction products were identified in the ZeroDegree spectrometers, while emitted gamma-rays were detected in the DALI2 array. Detailed spectroscopic information on 70Kr and measurements of the B(E2) value will be presented and discussed in comparison to the mirror nucleus 70Se and theoretical calculations. These results give important insights in the evolution of shape coexistence and isospin symmetry across the N=Z line. |
Friday, October 26, 2018 9:45AM - 10:00AM |
FM.00004: Multiple band structures in $^{70}$Ge R.A. Haring-Kaye, S.I. Morrow, J. Doring, S.L. Tabor, K.Q. Le, P.R.P. Allegro, P.C. Bender, R.M. Elder, N.H. Medina, J.R.B. Oliveira, Vandana Tripathi High-spin states in $^{70}$Ge were studied using the $^{55}$Mn($^{18}$O,$p2n$) fusion-evaporation reaction at an energy of 50 MeV. Prompt $\gamma$-$\gamma$ coincidences were measured using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. An investigation of these coincidences resulted in the addition of 31 new transitions and the rearrangement of four others in the $^{70}$Ge level scheme, providing a more complete picture of the high-spin decay pattern involving multiple band structures. Spins were assigned based on directional correlation of oriented nuclei ratios, which many times also led to unambiguous parity determinations based on the firm assignments for low-lying states made in previous work. Total Routhian surface calculations, along with the observed trends in the experimental kinematic moment of inertia with rotational frequency, support the multi-quasiparticle configurations of the various crossing bands proposed in recent studies. The high-spin excitation spectra predicted by previous shell-model calculations compare favorably with the experimental one determined from this study. |
Friday, October 26, 2018 10:00AM - 10:15AM |
FM.00005: Coulomb excitation of transitional selenium at ReA3 Jack Henderson, Ching-Yen Wu, Alexandra Gade, Dirk W Weisshaar, Peter C Bender, Mark Spieker, John Ash, Robert Elder, Brandon Elman, Mara Grinder, Hironori Iwasaki, Elaine Kwan, Brenden Longfellow, Tea Mijatovic, Daniel Rhodes 72Se lies in a transitional region of the nuclear landscape, between well-established prolate nuclei around 74,76Se, and 70Se which has been found to exhibit oblate deformation. Calculations for 72Se predict a coexistence between prolate and oblate deformations, representing a transitional point in the selenium isotopic chain. The determination of the sign of deformation in 72Se is thus of considerable interest in order to experimentally localize this shape transition within the selenium isotopes. |
Friday, October 26, 2018 10:15AM - 10:30AM |
FM.00006: Probing Pair Correlations in 76Ge via Two-Proton Exchange Cross-Section Measurements Calvin R. Howell, David R. Ticehurst, B. Alex Brown, Dustin C. Combs, Alexander S. Crowell, Laurie C. Cumberbatch, Brent A. Fallin, Forrest Q.L. Friesen, Ronald C. Malone, Ian J. Thompson, Werner Tornow, Albert R. Young Cross-section measurements for the (3He, n) reaction on 74,76Ge have been performed at laboratory beam energies of 15 and 21 MeV for reaction angles from 0° to 18°. These data test the validity of the Bardeen-Cooper-Schrieffer (BCS) approximation for the wavefunctions of the ground states of the initial and final 0+ nuclei used in QRPA calculations of nuclear matrix elements for neutrinoless double beta (0νββ) decay of 76Ge [1]. The measured strength for transfer to the first 0+ excited state was less than 13% of the transfer to the ground state for both nuclei, suggesting that using the BCS approximation to describe the 76Se ground state in QRPA 0νββ calculations is valid. This result is consistent with recent (3He, n) cross-section measurements on these nuclei [1]. Fits to the cross-section angular distributions for transfer to the ground state using the DWBA code FRESCO provide information about the reaction mechanism and are sensitive to the optical model potential used in the calculations. The experimental method and results will be presented. [1] A. Roberts et al., Phys. Rev C 87, 051305(R) (2013). |
Friday, October 26, 2018 10:30AM - 10:45AM |
FM.00007: High eff. structure study of 77Ge nuclei from 77Ga β-decay Umesh Silwal, S.V. Ilyushkin, J.A. Winger, C.J. Gross, K.P. Rykaczewski, J.C. Batchelder, L. Cartegni, I.G. Darby, C. Goodin, R. Grzywacz, J.H. Hamilton, A. Korgul, W. Krolas, S.N. Liddick, C. Mazzocchi, S. Padgett, A. Piechaczek, M.M. Rajabali, D. Shapira, E.F. Zganjar Medium mass Ge nuclei exhibits interesting structural features like shape co-existence and tri-axial deformation in low-lying states which makes it an interesting case both from nuclear structure as well as astrophysical point of view. In this measurement, pure 77Cu beam was developed at the Holifield Radioactive Ion Beam facility of Oak Ridge National Lab and detailed β-decay studies of A = 77 decay chain was performed to understand the structure of corresponding daughter nuclei. Data on γ ray emission following β-decay, including βγ and γγ coincidences were recorded, and the gated γγ spectra were analyzed to identify the statistically significant coincidences in cascades. The proposed decay scheme of 77Ge nuclei contains a total of 39 energy levels occupying up to 3.2 MeV with the placement of 67 γ rays. Due to the purity of beam and high efficiency four clover HPGe detector used, this work has been able to significantly increase both the number of energy levels and transitions. Finally, shell model-calculations are used for comparison to the observed level density. |
Friday, October 26, 2018 10:45AM - 11:00AM |
FM.00008: Strong one-neutron emission from two-neutron inbound states in beta decays of $r$-process nuclei, $^{86, 87}$Ga Rin Yokoyama, Robert Grzywacz, Rasco Charlie, Nathan Brewer, Krzysztof P. Rykaczewski, Iris Dillmann, Jose Louis Tain, Shunji Nishimura Beta-delayed one- and two-neutron branching ratios ($P_{1n}$ and $P_{2n}$) are measured in the decay of $^{86}$Ga and $^{87}$Ga at the RI-beam Factory at RIKEN Nishina Center using a high-efficiency array of $^{3}$He neutron counters (BRIKEN). Large $P_{1n}$ values are observed in $^{87,86}$Ga compared to $P_{2n}$ which was not predicted by theoretical calculations [PRL117,092502(2016), PRC67,055802(2003), PRC93,025805(2016)]. Our shell model calculation explains the observed $P_{1n} > P_{2n}$ successfully only when combined with Hauser-Feshbach statistical model [Nucl.Phys.A913,51(2013)]. This result is the first experimental demonstration that competition between multi-particle emission channels has to be considered to predict the decay properties of multi-neutron emitters which must be included in the astrophysical $r$-process modeling. |
Friday, October 26, 2018 11:00AM - 11:15AM |
FM.00009: Search for super-allowed alpha decay around 100Sn region Shintaro Go, Yongchi Xiao, Robert K. Grzywacz, Andrei Andreyev, Michael Bentley, Kentaro Hirose, Hiroshi Ikezoe, David Jenkins, Romain Leguillon, Hiroyuki Makii, Chiara Mazzochi, Katsuhisa Nishio, Riccardo Orlandi, Costel Petrache, Krzysztof Piotr Rykaczewski, James Smallcombe, Bob Wadsworth The enhancement of alpha-decay probability for nuclei above 100Sn is expected since valence protons and neutrons above Z=N=50 occupy the same single-particle orbitals. The program to search for new alpha emitters in this region was initiated at JAEA Tandem Laboratory at Tokai, Japan. To detect an alpha decay chain from 112Ba->108Xe->104Te->100Sn, we developed a new implantation detector system. The detector combines the capability for the spacial recoil-decay correlations typically implemented with use of the Double sided Silicon Strip Detector, but is able to provide a very rapid response time due to used fo the fast scintillator. Proof of principle measurement was performed at the Recoil Mass Separator at JAEA Tandem accelerator. The performance of the detector and future plan to search for the alpha decay chain will be presented. |
Friday, October 26, 2018 11:15AM - 11:30AM |
FM.00010: Magnetic moment of isomeric state of 75Cu Yuichi Ichikawa Exotic nuclei with excess neutrons relative to stable ones often exhibit evolved shell structure and collectivity such as vibrated/deformed shapes, which compete with each other to express the actual structure. Here we show the precision analysis of this competition by focusing on the magnetic moment of an isomeric state of a neutron-rich nucleus 75Cu, where an intriguing shell evolution has been reported. The magnetic moment measurement was carried out at RIKEN RIBF, taking advantage of a spin-aligned RI beam produced with the two-step projectile fragmentation scheme recently proposed. The spin alignment as large as 30% was achieved by the two-step scheme incorporating an angular-momentum selecting proton removal from 76Zn to produce 75Cu. The magnetic moment of the isomeric state of 75Cu was determined by means of TDPAD method. In this talk, the experimental results will be presented. Discussion on the above competition at neutron-rich Cu isotopes, analyzed with the Monte-Carlo shell model calculation, will also be given. |
Friday, October 26, 2018 11:30AM - 11:45AM |
FM.00011: A detailed spectroscopic analysis using fusion evaporation reactions to study the high-spin structures in 179,180W and an analysis of nuclear structure in rapidly rotating Er, Yb, Hf and W nuclei K. A. Villafana, M. A. Riley, S. L. Miller, J. S. Baron, V. Tripathi, J. Simpson, D. J. Hartley, E. S. Paul High-spin states in 179;180W (Z = 74) were produced via fusion evaporation reactions. To produce the nuclei of interest, a 14C beam was impinged on a 1mg/cm2 170Er target, at beam energies of 75MeV and 68MeV respectively. The emitted γ-rays were detected using three escaped-suppressed clover detectors and seven single element escape-suppressed high-purity germanium detectors. As a result of this analysis, new decay transitions and new energy levels have been observed in both nuclei building on previously known structures [1, 2]. The analysis of this data using γ-γ and γ-γ-γ coincidences was done using the Radware analysis package [3]. Additionally, new systematic data in the A ≈ 180 region is also discussed, with an emphasis on the role that pair-blocking effects play during the rotation of the nucleus. This systematic investigation builds upon the classic findings of Garrett et al. [4] who investigated the critical band crossing frequencies of the first pair of i13/2 neutrons (AB) in rare-earth nuclei. The present work carries out a similar investigation for the second pair of aligning i13=2 neutrons (BC) at higher rotational frequencies [5].
[1] P. M. Walker et al., Phys. Rev. Lett. 67, 4 (1991). [2] P. M. Walker et al., Phys. Lett. B 309, 17 (1993). [3] D. C. Radford, Nucl. Instrum. Methods Phys. Res. A361, 297 (1995). [4] J. D. Garrett et al., Phys. Rev. Lett. 47, 75 (1981). [5] S. L. Miller, K. A. Villafana et al., To be published.
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