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 KB: Nuclear Structure III |
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Chair: Mitch Allmond, Oak Ridge National Laboratory Room: Salon 2 |
Friday, October 27, 2017 2:00PM - 2:12PM |
KB.00001: Beta-Delayed Neutron Spectroscopy of 72Co with VANDLE Andrew Keeler, Robert Grzywacz, Thomas King, Steven Taylor, Stanley Paulauskas, Christopher Zachary Measurements of simple, closed-shell isotopes far from stability provide important benchmarks for nuclear models and are a key constraint in r-process calculations. In particular, r-process models are sensitive to beta decay lifetimes and branching ratios of these neutron-rich isotopes. In this experiment, the Versatile Array of Neutron Detectors at Low Energy (VANDLE) was used to observe decays of nuclei produced by the fragmentation of 82Se at the National Superconducting Cyclotron Laboratory (NSCL). The neutron and gamma emissions of 72Co were measured to map the beta strength distribution (S\textunderscore beta) above the neutron separation energy and infer the size of the Z$=$28 shell gap in the 78Ni region. An implantation detector made of a radiation-hardened, inorganic scintillator was used to correlate implanted ions with beta decays as well as provide a start signal for the neutron Time of Flight measurement. [Preview Abstract] |
Friday, October 27, 2017 2:12PM - 2:24PM |
KB.00002: Proton decay of ${}^{73}$Rb Andrew Rogers, C. Anderson, J. Barney, J. Estee, W.G. Lynch, J. Manfredi, H. Setiawan, R.H. Showalter, S. Sweany, S. Tangwancharoen, M.B. Tsang, J.R. Winkelbauer, K.W. Brown, J.M. Elson, C. Pruitt, L.G. Sobotka, Z. Chajecki, J. Lee Properties of nuclei beyond the proton drip-line are important for mass models, nuclear structure, and astrophysics. Weakly-bound or proton-unbound nuclei near the rp-process waiting points, such as the unbound $T_{z}=-\frac{1}{2}$ nucleus ${}^{73}$Rb, play a critical role in constraining calculations and observations of type I x-ray bursts. For instance, the rp process is greatly slowed near ${}^{72}$Kr ($N=Z$) due to its relatively long $\beta$-decay half life and inhibited proton capture. This waiting point, however, may be bypassed by sequential 2p-capture through ${}^{73}$Rb ~\textemdash~ a reaction which is sensitive to the ${}^{73}$Rb proton separation energy, $S_{\textrm{p}}$. Using invariant-mass spectroscopy, we have performed an experiment at NSCL to measure the decay of ${}^{73}$Rb$\rightarrow$p+${}^{72}$Kr in an attempt to directly determine $S_{\textrm{p}}({}^{73}\textrm{Rb})$. Analysis of reconstructed proton-emission spectra and decay signatures will be discussed. [Preview Abstract] |
Friday, October 27, 2017 2:24PM - 2:36PM |
KB.00003: Reporting the $\beta $-decay study of neutron rich $^{\mathrm{75}}$Zn into $^{\mathrm{75}}$Ga using LeRIBSS at HRIBF. Durga Siwakoti, S.V. Ilyushkin, J.A. Winger, K.P. Rykaczewski, C.J. Gross, J.C. Batchelder, L. Cartegni, I.G. Darby, R. Grzywacz, J.H. Hamilton, A. Korgul, S.N. Liddick, C. Mazzocchi, T. Mendez, S. Padgett, M.M. Rajabali, D. Shapira, W. Krolas, D.W. Stracener, E.F. Zganjar Recent updates on $\beta $ decay of $^{\mathrm{75}}$Zn into $^{\mathrm{75}}$Ga are presented with the decay scheme and structure of $^{\mathrm{75}}$Ga. The present study utilized a more efficient detector setup along with high purity of the $^{\mathrm{75}}$Cu beam in comparison to previous studies with a rate of over 2000 ions/s. The purity of beam which is obtained by using high-resolution isobar separator prevented any member of the decay chain from being dominant and allowed for comparisons of branching rations between the decays. The greater efficiency of the HPGe detector array meant more low energy $\gamma $-ray detection from the decays. The $\gamma $-$\gamma $ and $\beta $-$\gamma $ coincidence data obtained from the experiment were collected at the LeRIBSS (Low energy Radioactive Ion Beam Spectroscopy Station) and used to develop a revised decay scheme using an objective method. [Preview Abstract] |
Friday, October 27, 2017 2:36PM - 2:48PM |
KB.00004: Detailed$\beta $\textbf{-Decay Study of Neutron Rich }$^{\mathrm{\mathbf{76}}}$\textbf{Cu and Structure of }$^{\mathrm{\mathbf{76}}}$\textbf{Zn Isotope} U. Silwal, S.V. Ilyushkin, J. A. Winger, K. P. Rykacezewski, C. J. Gross, J. C. Batchelder, L. Cartegni, I. G. Darby, R. Grzywacz, J. H. Hamilton, A. Korgul, W. Krolas, S. N. Liddick, C. Mazzocchi, T. Mendez, S. Padgett, M. M. Rajabali, D. Shapira, D. W. Stracener, E. F. Zganjar The $\beta $ decay of neutron rich $^{\mathrm{76}}$Cu to levels in $^{\mathrm{76}}$Zn has been studied using 4-HPGe clover detectors at HRIBF of Oak Ridge National Lab. We have used a pure $^{\mathrm{76}}$Cu ion beam provided by the high resolution mass separator and data on $\gamma $-ray emission following $\beta $ decay including $\beta \gamma $ and $\gamma \gamma $ coincidences were obtained. Gated $\gamma \gamma $ spectra were analyzed to identify the statistically significant coincidences, and decay schemes have been developed for all daughter nuclei within the decay chain. Presented here is the case for $^{\mathrm{76}}$Cu $\beta $ decay. We have identified 58 $\gamma $ rays associated with this decay and have extended the decay scheme up to 5.6 MeV. Finally, we have compared this reconstructed decay scheme with shell-model calculations. [Preview Abstract] |
Friday, October 27, 2017 2:48PM - 3:00PM |
KB.00005: Direct measurement of beta-delayed neutron emission at and beyond doubly-magic $^{78}$Ni Rin Yokoyama An experiment aiming to measure the beta-neutron-gamma decay properties of nuclei around $^{78}$Ni produced by in-flight fission of a $^{238}$U beam at 345 MeV/u and selected by means of BigRIPS was recently performed using the BRIKEN setup [1]. The BRIKEN detector is composed of the AIDA implantation-decay array [2] as well as 140 $^{3}$He tubes and 2 HPGe clovers. The counting efficiency of a single beta-delayed neutron (${\rm \beta_{1n}}$) is above 60 %. About 24 ${\rm \beta_{1n}}$ values have been measured for the first time between $^{76}$Co and $^{96}$Br including the ${\rm \beta_{1n}}$ for $^{78}$Ni [3]. Over 20 nuclei that are expected to exhibit ${\rm \beta_{2n}}$ emission are within the studied region. An analysis of nuclear structure effects responsible for the observed ${\rm \beta_{1n}}/{\rm \beta_{2n}}$ competition should now be possible as well as performing the r-process simulations with a greatly enhanced set of experimental ${\rm \beta_{xn}}$ values. An overview of experiment and a discussion of some preliminary result will be presented. [1] A. Tarifeno-Saldivia et al., IOP Jour. of Instr. 2016. [2] C. Griffin et al., in Proc. of NIC XIII Conf., 7-11 July 2014, Debrecen, Hungary. [3] K. Rykaczewski et al., experiment RIBF 127R, RIKEN RIBF, May/June 2017. [Preview Abstract] |
Friday, October 27, 2017 3:00PM - 3:12PM |
KB.00006: Beta-delayed neutron emission from $^{94}$Rb at CARIBU Gemma Wilson, P Chowdhury, C Lister, T Brown, T Chillery, P Copp, E Doucet, M Carpenter, G Savard, S Zhu, AJ Mitchell Beta-delayed neutron emission studies are important in the astrophysical r-process, nuclear structure and for nuclear reactor safety and design. The probability of $\beta$-delayed neutron emission in $^{94}$Sr is 10.2(2)\%. Many of the $\gamma$ rays in $^{94}$Sr are misplaced, and an estimated 26\% are thought to be missing. Recently [1], substantial $\gamma$ strength from above the neutron separation energy in $^{94}$Sr has been reported. An experiment to understand this high-lying $\gamma$ strength was performed with the X-Array (a high-efficiency HPGe clover array), SCANS (Small CLYC Array for Neutron Scattering) and the SATURN decay station (Scintillator And Tape Using Radioactive Nuclei) for $\gamma$, fast-neutron and $\beta$-particle detection, respectively. Data from $\beta$ decay of $^{94}$Rb ions delivered from CARIBU were collected in a triggerless digital data acquisition system, with detected $\beta$, n, and $\gamma$ events correlated offline. A new $^{94}$Sr level scheme will be presented, with confirmation of new levels and transitions, in addition to evidence of $\gamma$ strength above the neutron separation energy. [1] J. L. Tain et al, Phys. Rev. Lett 115 (062502) 2015. [Preview Abstract] |
Friday, October 27, 2017 3:12PM - 3:24PM |
KB.00007: HAGRID/ VANDLE spectroscopy of Rb decays Thomas King, Robert Grzywacz, Steven Taylor, Stanley Paulauskas, Karl Smith Many neutron-rich isotopes that contribute in both decay heat production and r-process nucleosynthesis have substantial beta-delayed neutron branching ratios. Beta-delayed neutron emission is a relatively complicated mechanism which can leave the daughter in an gamma-emitting excited state. A comprehensive understanding of their energy output and decay strength, S\textunderscore beta, therefore requires the detection of both neutrons and gamma rays in coincidence. A series of measurements of delayed neutron precursors were performed at the On-Line Test Facility (OLTF) at the Oak Ridge National Laboratories using chemically selective ion sources and an enhanced VANDLE array. The main goal of this experiment was to revisit the decays of IAEA-marked priority precursors, including bromine, rubidium, cesium, and iodine, that are required to model the global properties in the fission of 238U [1].The unique data set, with neutron and gamma ray coincidences, benefited from the addition of a high-efficiency gamma-ray array, consisting of 16 LaBr3 crystals (HAGRiD), and a set of large volume NaI detectors to the VANDLE array. Characterization of and preliminary results from the new gamma-ray array for the decays of 94Rb and 97Rb will be presented.[1] IAEA BDN working group, private communication. [Preview Abstract] |
Friday, October 27, 2017 3:24PM - 3:36PM |
KB.00008: Evidence for shape coexistence in $^{96}$Y Enhong Wang, J.H. Hamilton, A.V. Ramayya, R. Han, C.J. Zachary, J.M. Eldridge, J.K. Hwang, N.T. Brewer, Y.X. Luo, J.O. Rasmussen, S.J. Zhu, G.M. Ter-Akopian, Yu.Ts. Oganessian The energy levels of neutron rich $^{96}$Y have been studied by analyzing the high statistics $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data from the spontaneous fission of $^{252}$Cf at Gammasphere. Twelve new transitions and 9 new levels in $^{96}$Y have been identified. Spins and parities are tentatively assigned according to the systematics and energy spacing. A small deformation with near spherical shape is proposed for $^{96}$Y ground state. A deformed rotational band has been established at about 1 MeV. Such result indicates shape coexistence of the $^{96}$Y nuclei. The results are consistent with the onset of very strong deformation at N=59 among Y isotopes. Shell model calculations are performed to explain the energy levels and are found to be in good agreement with experimental data. [Preview Abstract] |
Friday, October 27, 2017 3:36PM - 3:48PM |
KB.00009: $E2/M1$ Mixing Ratios in Transitions From the Gamma-Vibrational-Bands to the Ground-State-Rotational-Bands of $^{102,104,106,108}$Mo, $^{108,110,112}$Ru, and $^{112,114,116}$Pd Jonathan M. Eldridge, B. Fenker, C. Goodin, J. H. Hamilton, E. H. Wang, A. V. Ramayya, A. V. Daniel, G. M. Ter-Akopian, Y. X. Luo, J. O. Rasmussen, Yu. Ts. Oganesson, S. J. Zhu $E2/M1$ mixing ratios have been measured for transitions from states in the $\gamma$-vibrational-bands ($I^+_\gamma$) to states in the ground-state-bands ($I^+_g$ or $[I-1]^+_g$) of the neutron rich, deformed isotopes, $^{102,104,106,108}$Mo, $^{108,110,112}$Ru, and $^{112,114,116}$Pd, including from states as high as $9^+_\gamma$. These measurements were done using the GAMMASPHERE detector array, which, at the time of the experiment, had 101 working HPGe detectors, arranged at 64 different angles. A 62 $\mu$Ci source of $^{252}$Cf was placed inside GAMMASPHERE yielding $5.7\times10^{11}$ $\gamma-\gamma-\gamma$ and higher coincidence events. The angular correlation between the transitions from the $\gamma$-band to the ground band, and the pure E2 transitions within the ground band were then measured. These angular correlations yielded the mixing ratios, demonstrating that these transitions are all pure or nearly pure E2, in agreement with theory. In order to correct for possible attenuation due to the lifetime of the intermediate state in these correlations, the g-factors of the intermediate states needed to be known. Therefore, the g-factors of the $2^+_g$ states in the ground state band have been measured. [Preview Abstract] |
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