Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session KN: Nuclear Structure III |
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Chair: Calem Hoffman, Argonne National Laboratory Room: Salon K |
Wednesday, October 16, 2019 8:30AM - 8:42AM |
KN.00001: Investigating shape coexistence in $^{50,52,54}$Cr with E0 transitions and pair conversion spectroscopy Jackson Dowie, Tibor Kibedi, Ha Hoang, Kumar Raju, Eiji Ideguchi, Abraham Avaa, Vernon Chisapi, Pete Jones, Aqeel Akber, Ben Coombes, Tomas Eriksen, Matthew Gerathy, Timothy Gray, Greg Lane, Brendan McCormick, A.J. Mitchell, Andrew Stuchbery The phenomenon of shape coexistence, whereby excited states of an atomic nucleus exhibit shapes that deviate dramatically from their ground states, appears to be ubiquitous across the nuclear landscape. Electric monopole (E0) transitions, the only possible decay paths between $J^{\pi}$ = $0^{+}$ states, provide a unique probe into nuclear shape coexistence. The E0 strength is large when there is a large change in the nuclear mean-square charge radius, and when there is strong mixing between states of different deformation. The region between $^{40}$Ca and $^{56}$Ni is virtually unexplored from the perspective of E0 transitions. Only the $^{40,42,44,46}$Ca, $^{56,58,60}$Ni and $^{54}$Fe have been investigated; no work has been done on the Cr isotopes to date. The $0^{+}$ states and E0 transitions in $^{50,52,54}$Cr were investigated with the Super-e pair spectrometer at the ANU using beams from the 14UD tandem accelerator. We will present the first pair spectra for $^{50,52,54}$Cr and the E0 transition strengths for these nuclei. [Preview Abstract] |
Wednesday, October 16, 2019 8:42AM - 8:54AM |
KN.00002: Microscopic Calculations of Nuclear Level Densities with the Extrapolated Lanczos Method William Ormand, Alex Brown A new method for computing the density of states in nuclei making use of an extrapolated form of the tri-diagonal matrix obtained from the Lanczos method is presented. It will be shown that the global, average properties of the entire Lanczos matrix can be predicted from just four Lanczos iterations. The extrapolated Lanczos matrix (ELM) approach provides for an accurate computation of the density of states described within the configuration space. In many cases, this is sufficient to accurately calculate the density of states at, or near, the neutron separation energy, which is the region needed for Hauser-Feshbach calculations of radiative capture reactions. We will outline a procedure to analytically continue the extrapolated Lanczos matrix to the ground-state region. Validation with exact shell-model calculations will be shown and applications of the method will be demonstrated for $^{57}$Fe and $^{76}$Ge where comparison with experiment will be shown. We also demonstrate the $J$-dependence of the level density with the method and outline a procedure to extract the spin cutoff parameter. [Preview Abstract] |
Wednesday, October 16, 2019 8:54AM - 9:06AM |
KN.00003: On the nature of 0$^+$ states in $^{64}$Ni from Coulomb excitation David Little, Robert Janssens, Michael Jones, Daniel Ayangeakaa Recent experimental work on the doubly-magic nucleus $^{68}$Ni has shown that shape coexistence occurs despite its rigidly spherical ground state [1]. Several low-lying $0^+$ states have been discovered and attributed to different minima in the nuclear potential associated with oblate and prolate deformations. Consequently, it is important to question if such $0^+$ excitations can also occur in the most neutron-rich, stable Ni isotope, $^{64}$Ni, and whether or not they can be tied to shape coexistence. Two low-lying $0^+$ states have previously been observed in $^{64}$Ni, but additional information beyond their excitation energy and spin is needed in order to investigate their properties. A high-statistics Coulomb excitation experiment was performed at the ATLAS facility at ANL, where a $^{208}$Pb target was bombarded by a $^{64}$Ni beam at an energy of 272 MeV. The experimental setup involved the new GRETINA tracking array in conjunction with the Compact Heavy Ion COunter, CHICO2. Thirteen transitions were observed in $^{64}$Ni, including the 1521- and 1680-keV $\gamma$-rays associated with the de-excitation of the $0_2^+$ and $0_3^+$ states, respectively. B(E2) reduced transition probabilities were obtained for all observed states. [1] S. Leoni et al., PRL 118, 162502 (2017). [Preview Abstract] |
Wednesday, October 16, 2019 9:06AM - 9:18AM |
KN.00004: The structure of 72Ni via beta-delayed neutron spectroscopy of 72Co Andrew Keeler, Robert Grzywacz, S Go, T T King, M Madurga, S V Paulauskas, S Z Taylor, B Crider, S Liddick, R Lewis, J H Hamilton, C Zachary, E H Wang, N T Brewer, A Fialkowska, P D O'Malley, M Hall, M M Rajabali, S Illyushkin Studies of beta decays can give important insights into the structure of the nucleus. Measurements of closed-shell nuclei provide important benchmarks for structure models, which are used in simulations of r-process nucleosynthesis. This work studies beta decays and beta-delayed neutrons of 72Co produced at MSU's National Superconducting Cyclotron Laboratory using the Versatile Array of Neutron Detectors at Low Energy. To carry out this experiment, a novel position-sensitive scintillating detector was developed to enable the sub-nanosecond timing resolution that VANDLE requires, which silicon-based position-sensitive detectors would be unable to provide. A gamma spectroscopy setup including an HPGe Clover and LaBr3 HAGRiD detectors provides the necessary spectroscopic information for a full reconstruction of the 72Co decay strength. [Preview Abstract] |
Wednesday, October 16, 2019 9:18AM - 9:30AM |
KN.00005: Nature of triaxial deformation in $^{76}$Ge: A model-independent analysis A. D. Ayangeakaa, R. V. F. Janssens, David Little, D. J. Hartley The low-lying structure of $^{76}$Ge has become a subject of intense scrutiny ever since it was first suggested as a possible example of rigid triaxiality at low spin [1]. For decades, the experimental observation of such rigid structures has remained elusive and indeed, there has been a longstanding issue associated with whether axially asymmetric nuclei retain rigid-triaxial deformation in their ground-state configuration. In this study, an extensive, model-independent analysis of the nature of triaxial deformation in $^{76}$Ge has been performed following a high-statistics Coulomb excitation measurement with GRETINA and CHICO2. Shape parameters deduced on the basis of a rotational-invariant sum-rule analysis provided considerable insight into the underlying collectivity of the ground-state and $\gamma$ bands. Compelling evidence for low-spin, rigid-triaxial deformation in $^{76}$Ge based on the analysis of the statistical variance of the quadrupole asymmetry deduced from the measured $E2$ matrix elements will be presented. The relevance of these results for calculations aimed at providing, with suitable accuracy, the nuclear matrix elements relevant to neutrinoless double-beta decay will also be highlighted. [1] Y. Toh {\it et al.}, Phys. Rev. C87, 041304 (2013). [Preview Abstract] |
Wednesday, October 16, 2019 9:30AM - 9:42AM |
KN.00006: Level structure neutron-rich $^{80,82}$Se isotopes Anne Forney, William Walters Neutron-rich $^{80,82}$Se isotopes were studied using the Gammasphere Ge-detector array at ANL. Beams of $^{76}$Ge and $^{82}$Se were incident upon thick $^{238}$U and $^{208}$Pb targets in deep-inelastic reactions. The indication of triaxiality in $^{78}$Ge has recently been presented from a low-energy sequence of strictly $\Delta J=1$ transitions [1]. Isotonic $^{80}$Se exhibits none of the special features found in $^{78}$Ge. New data in $^{82}$Se will be presented to clarify $\beta$-decay studies [2,3], and angular-correlation measurements are used to strengthen spin and parity assignments in some cases. NuShellX calculations for the N = 46 and N = 48 isotones will be shown to test the $p_{3/2}f_{5/2}p_{1/2}g_{9/2}$ proton and neutron subspace [4]. [1] A. M. Forney, W. B. Walters, C. J. Chiara, R. V. F. Janssens, A. D. Ayangeakaa, J. Sethi, J. Harker, M. Alcorta, M. P. Carpenter, G. G\"urdal, C. R. Hoffman, B. P. Kay, F. G. Kondev, T. Lauritsen, C. J. Lister, E. A. McCutchan, A. M. Rogers, D. Seweryniak, I. Stefanescu, and S. Zhu. Submitted (2018). [2] J.V. Kratz, H. Franz, N. Kaffrell, G. Hermann. Nucl. Phys. A 250 13-37 (1975). [3] H. Gausemel, K. A. Mezilev, B. Fogelberg, P. Hoff, H. Mach, and E. Ramstr\"om Phys. Rev. C 70, 037301 (2004). [4] B.A. Brown and W.D.M. Rae. [Preview Abstract] |
Wednesday, October 16, 2019 9:42AM - 9:54AM |
KN.00007: Possible particle-hole intruder sequence in $^{\mathrm{83}}$Se$_{\mathrm{49}}$. William Walters, Anne Marie Forney A new sequence of higher-spin levels at 1266 (7/2$^{\mathrm{+}})$, 2407 (11/2$^{\mathrm{+}})$, 3689 (15/2$^{\mathrm{+}})$, and 4673 (19/2$^{\mathrm{+}})$ has been identified in the single-neutron-hole $^{\mathrm{83}}$Se$_{\mathrm{49}}$ nucleus. This sequence feeds into the 5/2$^{\mathrm{+}}$ level at 583 keV that is strongly populated in (d,p) reaction studies and considered as a 1-particle-2-hole state connected to the known d$_{\mathrm{5/2}}$ ground state of $^{\mathrm{85}}$Se$_{\mathrm{51}}$. The data were taken using Gammasphere at the ATLAS accelerator complex at Argonne National Laboratory following the interaction of a 630-MeV $^{\mathrm{82}}$Se beam with $^{\mathrm{208}}$Pb and $^{\mathrm{238}}$U targets. These and previously identified levels in $^{\mathrm{83}}$Se will be compared to shell-model calculations. [1] Richard A. Meyer, O. G. Lein III, and E. A. Henry, Phys. Rev. C \textbf{25}, 682 (1982). [2] Luis A Montestruque et al., Nucl. Phys. \textbf{A305}, 29 (1978). [3] Marie-Genevieve Porquet et al., Eur. Phys. J. A \textbf{39}, 295 (2009). [Preview Abstract] |
Wednesday, October 16, 2019 9:54AM - 10:06AM |
KN.00008: Investigating the first-forbidden beta-decay transitions of 92Rb and 96Y E.C. Good, S.M. Marley, N.D. Scielzo, K. Kolos, S. Padgett, E.K.M. Heckmaier, M.T. Burkey, M.P. Carpenter, J.A. Clark, P. Copp, B. DiGiovine, G. Savard, S. Zhu, J. Munson Nuclear reactors produce the highest flux of man-made antineutrinos from the beta decay of the fission products. The antineutrino flux can be measured using inverse beta decay reactions, and a deficit of roughly 5$\%$ is found when comparing to predictions which has been deemed the “reactor antineutrino anomaly.” The top two contributors to the detected antineutrino flux are $^{92}$Rb and $^{96}$Y, which both have first-forbidden 0- to 0+ transitions to the ground state that account for the majority of their intensities. These transitions are expected to have energy spectra closely resembling that of an allowed transition. However, currently there is no data to verify that assumption. To address this issue, we have studied the decays of $^{92}$Rb and $^{96}$Y using a set of silicon, plastic scintillator, and HPGe detectors at the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory. I will discuss the analysis of this experiment and its influence on understanding the shapes of these first-forbidden 0- to 0+ transitions. [Preview Abstract] |
Wednesday, October 16, 2019 10:06AM - 10:18AM |
KN.00009: Decays of neutron rich rubidium isotopes studied with Modular Total Absorption Spectrometer (MTAS) Darren Mckinnon, Robert Grzywacz, Bertis Rasco, Nathan Brewer, Krzysztof Rykaczewski, Aleksandra Fijalkowska, Marzena Wolinska-Cichocka, Marek Karny, Kathleen Goetz, Carl Gross, Daniel Stracener, Ed Zganjar, Jon Batchelder, Jeff Blackmon, Thomas King, Krzysztof Miernik, Stan Paulauskas, Mustafa Rajabali, Jeff Winger Total absorption spectroscopy is a highly efficient method for detecting gamma radiation from beta decay. The Modular Total Absorption Spectrometer (MTAS) consists of nearly one ton of NaI(Tl) and allows for the determination of beta-feeding distributions over the entire decay window. These studies provide unique insight into nuclear structure, properties of nuclear reactor decay heat, and the anti-neutrino spectrum for nuclear reactors. This presentation presents recent results from decays of neutron rich Rb isotopes in the transitional region near N$=$60 studied at the ORNL Tandem. In preparation for implementation of MTAS at CARIBU at Argonne National Laboratory, new auxiliary beam diagnostic detectors have been added to MTAS and preliminary results will be shown during the presentation. [Preview Abstract] |
Wednesday, October 16, 2019 10:18AM - 10:30AM |
KN.00010: Parametric correlations in energy density functionals A. Taninah, S. E. Agbemava, A. V. Afanasjev, P. Ring Density functional theories (DFT) are defined by underlying functionals. Some of those functionals depend on substantial number of parameters. However, the parametric correlations between them have not been studied before. Using covariant DFT as an example and statistical tools, we study such correlations for major classes of covariant energy density functionals. These include the non-linear meson-nucleon coupling (NL) model, the density dependent meson-exchange (DD-ME) model and point coupling (PC) model. Their functionals are defined by properties of spherical nuclei and nuclear matter properties. It turn out that parametric correlations exist between a number of parameters in all of those functionals. For example, linear parametric correlations exist between the $g_2$ and $g_3$ parameters which are responsible for the density dependence in the NL model [1]. Observed correlations effectively reduce the number of independent parameters to five or six dependent on the structure and the underlying physics of the functional. Thus, this is how many independent parameters could be defined in the CDFT using fitting protocols based on ground state and nuclear matter properties. \\[1][1] S. E. Agbemava, A.V. Afanasjev, A. Taninah, Phys. Rev. C 99, 014318 (2019). [Preview Abstract] |
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