Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session JB: Mini-Symposium on Nuclear Structure of the Ge and Se Isotopes |
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Chair: Hironori Iwasaki, National Superconducting Cyclotron Laboratory Room: Salon 2 |
Friday, October 27, 2017 10:30AM - 11:06AM |
JB.00001: Configuration interaction calculations for the region of $^{76}$Ge Invited Speaker: Alex Brown I will present a short history of the configuration interaction Hamiltonians that have been developed for the $ (0f_{5/2},1p_{3/2},1p_{1/2},0g_{9/2}) $ ($ jj44 $) model space. This model space is appropriate for the region of nuclei bounded by the nickel isotopes for $ Z=28 $ and the isotones with $ N=50 $. I will discuss results for the double-beta decay of $^{76}$Ge that lies in the $ jj44 $ region. I will show results for the structure of nuclei around $^{76}$Ge for some selected data from gamma decay, Gamow-Teller beta decay, charge-exchange reactions, one-nucleon transfer reactions, and two-nucleon transfer reactions. [Preview Abstract] |
Friday, October 27, 2017 11:06AM - 11:18AM |
JB.00002: Nuclear structure of 76Se from inelastic neutron scattering measurements Sharmistha Mukhopadhyay The low-lying, low-spin levels of $^{76}$Se were studied with the (n,n$'\gamma$) reaction. Gamma-ray excitation function measurements were performed at incident neutron energies from 2.0 to 3.5 MeV, and $\gamma$-ray angular distributions were measured at neutron energies of 2.4, 3.0 and 3.7 MeV. From these measurements, level spins, level lifetimes, $\gamma$-ray intensities, and multipole mixing ratios were determined. Interpreting the nuclear structure of the stable Se nuclei is challenging, with shape transitions, shape coexistence, and triaxiality in evidence. The low-lying structure of $^{76}$Se appears to be the most vibrational of the Se isotopes, with a two-phonon (0$^+$, 2$^+$, 4$^+$) triplet of collective states. In addition to these clearly collective excitations, we have identified and characterized a $4^+\rightarrow2^+\rightarrow 0^+$ cascade of two $E2$ transitions built on the first excited 0$^+$ state at 1122 keV. The picture for $^{76}$Se thus differs from $^{72}$Se and $^{74}$Se, and indicates that the configuration mixing of this coexisting band is less than exhibited in the other Se nuclei. Comparison of the low-lying level schemes of $^{76}$Ge and $^{76}$Se, the double-beta decay daughter, shows a marked difference. [Preview Abstract] |
Friday, October 27, 2017 11:18AM - 11:30AM |
JB.00003: Investigation of $^{76}$Ge structure via inelastic scattering studies B. P. Crider, S. Mukhopadhyay, B. A. Brown, S. F. Ashley, A. Chakraborty, A. Kumar, E. E. Peters, M. T. McEllistrem, F. M. Prados-Estévez, S. W. Yates The search for neutrinoless double-$\beta$ decay ($0\nu\beta\beta$) of $^{76}$Ge has led to renewed interest in the structure of this mass region, as structural information helps constrain calculations of the $0\nu\beta\beta$ nuclear matrix elements. The structure of many of the even-even Ge isotopes, including $^{76}$Ge, show interesting features, such as low-lying $0^+$ states that have been interpreted as evidence for shape coexistence, as well as indications of triaxiality. Of fundamental importance in understanding the nature of the excited states in $^{76}$Ge is the determination of transition strengths, which has been obtained through $^{76}$Ge(n,n$^{\prime}\gamma)$ studies at the University of Kentucky and the $^{76}$Ge$(\gamma,\gamma^{\prime})$ reaction at the High Intensity $\gamma$-Ray Source at Duke University. The measured transition strengths support the identification of band structure in $^{76}$Ge, a newly observed mixed-symmetry state, and the M1 scissors mode. [Preview Abstract] |
Friday, October 27, 2017 11:30AM - 11:42AM |
JB.00004: Nuclear deformation and searches of neutrinoless double-beta decay $(0\nu\beta\beta)$: A case study of $^{76}$Ge Robert V. F. Janssens, Akaa Daniel Ayangeakaa, ANL Collaboration, LLNL Collaboration, LLBL Collaboration, Maryland Collaboration Observation of neutrinoless double-beta decay ($(0\nu\beta\beta)$) would both demonstrate the Majorana nature of the neutrino and provide experimental access to its absolute mass scale. Over the last decade, wavefunction contributions for leading $(0\nu\beta\beta)$ candidates have been probed in a campaign of experiments utilizing transfer reactions to determine nucleon occupancies in a consistent way. While these studies have provided a great deal of information for comparison with theory, especially on contributions to the nuclear wavefunctions from competing orbitals, they lack sensitivity to the collective degrees of freedom which have been shown to be relevant in describing these nuclei. In this talk, we present results of a high-precision Coulomb excitation measurement of $^{76}$Ge, performed at Argonne National Laboratory using GRETINA and CHICO2. The results are compared with state-of-the-art shell model calculations and recently obtained $(n,n`\gamma)$ data, with emphasis on demonstrating the importance of nuclear deformation in determining the nuclear decay matrix elements. [Preview Abstract] |
Friday, October 27, 2017 11:42AM - 11:54AM |
JB.00005: Structural changes in $^{78}$Ge Anne M. Forney, W.B. Walters, J. Sethi, C.J. Chiara, A.D. Ayangeakaa, J. Harker, R.V.F. Janssens, S. Zhu, M.P. Carpenter, M. Alcorta, G. G\"{u}rdal, C.R. Hoffman, B.P. Kay, F.G. Kondev, T. Lauritsen, C.J. Lister, E.A. Mccutchan, A.M. Rogers$^{4}$, D. Seweryniak The nuclear structure of Ge isotopes when approaching the N=50 shell closure was investigated at the ATLAS facility at Argonne National Laboratory using the GAMMASPHERE detector array following deep-inelastic reactions. The structure of $^{78}$Ge appears to differ significantly from that observed in the stable $^{72,74,76}$Ge isotopes. In particular, a sequence of states linked by dipole transitions has been observed. It shows some properties suggestive of a gamma vibration, like in the lighter Ge isotopes, but the absence of quadrupole cross-over transitions is notable. Possible interpretations of this structure will be discussed. In addition, new information on the $^{80}$Ge nucleus will be presented, including clarification of spin assignments owing to the recently identified presence of two $\beta$-decaying isomers from $^{80}$Ga\footnote{D. Verney \it{et al.}, Phys. Rev C \textbf{87}, 054307 (2013).}. [Preview Abstract] |
Friday, October 27, 2017 11:54AM - 12:06PM |
JB.00006: Quadrupole collectivity beyond N = 50 in neutron- rich Se and Kr isotopes Brandon Elman, A. Gade, D. Barofsky, P. C. Bender, M. Bowry, M. Hjorth-Jensen, K. W. Kemper, S. Lipschutz, E. Lunderberg, N. Sachmpazidi, N. Terpstra, W. B. Walters, D. Weisshaar, A. Westerberg, S. J. Williams, K. Wimmer We will present results on measuring the $B(E2; 0^+_1 \rightarrow 2^+_n)$ strength for the neutron-rich $^{88,90}$Kr and $^{86}$Se isotopes from intermediate-energy Coulomb excitation. The electric quadrupole transition strengths to the first 2+ state complete, with considerably improved uncertainties, the evolution of quadrupole collectivity in the Kr and Se isotopes approaching $N = 60$, for which $^{90}$Kr and $^{86}$Se had previously been the most uncertain. We also report significant excitation strength to several higher lying 2+ states in the krypton isotopes. The results confirm shell model calculations in the $\pi(fpg)-\nu(sdg)$ shell with only a minimally tuned shell model setup that is based on a nucleon-nucleon interaction derived from effective field theory with effective charges adjusted to $^{86}$Kr. [Preview Abstract] |
Friday, October 27, 2017 12:06PM - 12:18PM |
JB.00007: Exploring single-hole state evolution near the $N=50$ shell closure Pei-Luan Tai, M. E. Howard, A. S. Adekola, J. A. Cizewski, B. Manning, L. J. Schradin, M. A. Famiano, D. Bazin, Z. Chajecki, D. Coupland, R. Hodges, J. Lee, W. Lynch, A. Sanetullaev, M. B. Tsang, J. Winkelbauer, M. Youngs, S. Ahn, K. Schmitt, D. W. Bardayan, K. Y. Chae, D. Shapira, T. K. Ghosh, R.R.C. Clement It is of interest to understand how nuclear structure evolves near the $N=50$ closed shell and towards more neutron-deficient nuclei. To obtain a more clear picture of the systematics of neutron-hole states in $N=49$ isotones, $^{83}_{34}$Se and $^{85}_{36}$Kr were produced through the one-neutron stripping $(p,d)$ reaction to populate single-neutron-hole states. The experiment was performed at the National Superconducting Cyclotron Laboratory with 35 MeV/u $^{84}$Se and 45.5 MeV/u $^{86}$Kr beams that impinged on C$_2$H$_4$ targets. The charged-particle detectors, HiRA, were used to identify emitted deuterons and measure their angles and energies; heavier recoils were identified and analyzed by the S800 Spectrograph. Preliminary PID maps, Q-value spectra and angular distribution will be presented. [Preview Abstract] |
Friday, October 27, 2017 12:18PM - 12:30PM |
JB.00008: Level structure of Ge-74 William B Walters, A. M. Forney, A. D. Ayangeakaa, J. Sethi, J. Harker, C. J. Chiara, R. V. F. Janssens, B. P. Kay, S. Zhu The current data for the level structure of Ge-74 from many sources will be~ \newline presented and supplemented by new data from multi-nucleon transfer reactions~using a wide range of beam and target combinations with Gammasphere. Data~will be presented to support a spin and parity assignment of 5$^{\mathrm{-}}$ for the~level at 2935.5 keV. Transitions between members of the proposed gamma band~and negative-parity levels will be shown and both kinds of structures~discussed in the context of the triaxiality described by Ragnarsson, Nilsson~and Sheline. Interpretations for the structure of the adjacent nuclei, Ge-72~and Ge-76 have been reported by Ayangeakaa et al., and Toh et al., respectively. \newline I. Ragnarsson, S. G. Nilsson, and R. K. Sheline, Physics Reports~\textbf{45}, 1 (1978). \newline A. D. Ayangeakaa et al., Phys. Lett. B \textbf{754}, 254 (2016). \newline Y. Toh et al., Phys. Rev. C \textbf{87}, 041304 (2013). \newline This work is supported by the U.S. Department of Energy, Office of Nuclear~Physics under Contract DE-AC02-06CH11357 and~under Grant DE-FG02-94ER40834. [Preview Abstract] |
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