Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session JJ: Nuclear Astro III |
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Chair: Chris Ruiz, TRIUMF Room: Junior Ballroom A |
Saturday, October 15, 2016 10:30AM - 10:42AM |
JJ.00001: EMMA, a Recoil Mass Spectrometer for TRIUMF's ISAC-II Facility Barry Davids EMMA is a recoil mass spectrometer for TRIUMF's ISAC-II facility in the final stages of installation and commissioning. In this talk I will briefly review the spectrometer's design capabilities, describe recent progress in its installation and commissioning, and discuss plans for its initial experimental program. [Preview Abstract] |
Saturday, October 15, 2016 10:42AM - 10:54AM |
JJ.00002: Construction of the Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP) at Notre Dame Jacob Allen, Dan Bardayan, Drew Blankstein, Matthew Hall, Oscar Hall, James Kolata, Patrick O'Malley, Frederick Becchetti, Jeffery Blackmon, Steven Pain The study of nucleon transfer reactions gives information about many nuclei involved in astrophysical processes. The design and use of new detector systems improves our ability to accurately characterize these nuclei. The Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP) is a new helical orbit spectrometer being designed at the University of Notre Dame to study transfer reactions with high-energy light ion beams from the FN tandem accelerator. SSNAP incorporates a series of position-sensitive silicon detectors to be set on-axis inside the second TwinSol solenoid. SSNAP will be sensitive to light ions produced in different reactions and the charged-particle decay products from the exotic nuclei produced. Results of initial testing and future plans with this detector system will be shown in this presentation. [Preview Abstract] |
Saturday, October 15, 2016 10:54AM - 11:06AM |
JJ.00003: The CASPAR underground accelerator facility for the study of low energy nuclear astrophysics Daniel Robertson, Manoel Couder, Uwe Greife, Frank Strieder, Michael Wiescher The drive of nuclear astrophysics is to push the limits of reaction measurements into the burning regime of astrophysical interest. As current laboratory experiments approach the stellar burning window, the rapid drop off of cross-sections is a significant barrier and drives the need for higher intensity accelerators, more robust and isotopically enriched target material and lower background interference. The natural background suppression of underground accelerator facilities enables the extension of current experimental data to the lower energies needed. The CASPAR facility is the first and only underground accelerator facility in the US, focused on the study of low energy reactions of nuclear astrophysical interest. [Preview Abstract] |
Saturday, October 15, 2016 11:06AM - 11:18AM |
JJ.00004: Commissioning of the High Efficiency Total Absorption Spectrometer (HECTOR) C.S. Reingold, A. Simon, A. Spyrou, F. Naqvi, A. Dombos, A. Palmisano, T. Anderson, S.L. Henderson, S. Moylan, C. Seymour, M.A. Skulski, M.K. Smith, S.Y. Strauss, B. Vande Kolk P-process nucleosynthesis occurs in supernovae where the s-process seeds are present, and is responsible for the production of proton-rich nuclei. Photons from SN explosions induce characteristic ($\gamma$,n), ($\gamma$,p), and ($\gamma,\alpha$) reactions. These reactions are typically studied via the inverse reactions. For this purpose, the High Efficiency Total Absorption Spectrometer (HECTOR), a NaI(Tl) summing detector at the University of Notre Dame, was built. The array is designed to make precision cross section measurements for (p,$\gamma$) and ($\alpha,\gamma$) reactions. HECTOR is composed of 16 separate NaI(Tl) crystals and 32 photomultiplier tubes read by a digital data acquisition system, with gain-matching and summing done offline. The efficiency of HECTOR is about 52.7 (2.0)\% for a $^{60}$Co source. The commissioning run for HECTOR was performed via measurements of known resonances in the $^{27}$Al(p,$\gamma$)$^{28}$Si reaction to determine the efficiency of the array. The first results from HECTOR will be presented, as well as future plans with the array. [Preview Abstract] |
Saturday, October 15, 2016 11:18AM - 11:30AM |
JJ.00005: Verifying the Acceptance of St. George Christopher Seymour, Zach Meisel, Michael T. Moran, Gwenaelle Gilardy, Jaclyn Schmitt, Manoel Couder The St. George recoil separator at the University of Notre Dame will be used to measure radiative alpha capture reaction cross sections of astrophysical interest. Low reaction rates at energies found in stellar environments inhibit standard measurement techniques due to a relatively high gamma background. Recoil separators aim to eliminate this background problem by directly detecting the heavy reaction products. In order to conduct accurate measurements, the properties of the separator must be well understood. We have performed systematic measurements of the energy acceptance over the electric and magnetic rigidities of interest for St. George at zero degrees. We will report on those measurements and on the progress to determine the angular acceptance of the separator. [Preview Abstract] |
Saturday, October 15, 2016 11:30AM - 11:42AM |
JJ.00006: First Results From GRIFFIN: Half-Lives of Neutron Rich $^{128-130}$Cd Ryan Dunlop Half-lives of $N=82$ nuclei below doubly-magic $^{132}$Sn are key input parameters for any astrophysical $r$-process scenario and play an important role in the formation and shape of the second $r$-process abundance peak. Shell-model calculations for neutron-rich nuclei near the $N=82$ neutron shell closure that are not yet experimentally accessible have been performed by adjusting the quenching of the Gamow-Teller (GT) operator to reproduce the $^{130}$Cd half-life. The calculated half-lives of other nuclei in the region are known to be systematically too long. Recently, a shorter half-life for $^{130}$Cd was measured by the EURICA collaboration that resolves this discrepancy by scaling the GT quenching by a constant factor for all of the nuclei in the region. Distinguishing between these discrepant half-life measurements for $^{130}$Cd is thus of critical importance. We have measured the half-lives of $^{128-130}$Cd using the high-efficiency GRIFFIN $\gamma$-ray spectrometer at TRIUMF, which improves the precision of the $^{128,129}$Cd half-lives, and confirms the shorter half-life of $^{130}$Cd recently reported by the EURICA collaboration. Details of the GRIFFIN experiments will be presented and the implications of the resulting half-lives discussed. [Preview Abstract] |
Saturday, October 15, 2016 11:42AM - 11:54AM |
JJ.00007: Recent $\beta $-delayed neutron branching ratios of measurements with heavy nuclei. Roger Caballero-Folch, Iris Dillmann, Jorge Agramunt, Jose Luis Tain The understanding of the nuclear structure of the neutron-rich nuclei and several astrophysical phenomena, such as the r-process, is a challenge that need new experimental values to provide more realistic data inputs in theoretical models. The aim of this study is to achieve new $\beta $-delayed neutron branching ratios, Pn, of very neutron-rich nuclei. Experiments recently performed at the RIB facilities of GSI Darmstadt (Germany) and IGISOL in Jyv\"{a}skyl\"{a} (Finland) allowed to determine Pn values for heavier isotopes than those measured so far with a 4pi neutron detector based on $^{\mathrm{3}}$He counters. At GSI it was possible to measure $\beta $1n emitters for several Hg and Tl isotopes with masses beyond A\textgreater 200 and N\textgreater 126, and at IGISOL the $\beta $2n emitter $^{\mathrm{136}}$Sb, which represents an important leap in terms of mass since the heaviest known were around A\textasciitilde 150 for $\beta $1n and A\textasciitilde 100 for $\beta $2n. Results of P1n and P2n values will be presented, together with the new plans for $\beta $-delayed neutron emitter measurements at RIKEN (Japan). The BRIKEN project aims to measure more than a hundred of $\beta $1n, and many $\beta $2n and $\beta $3n emitters, a lot of them for the first time. These isotopes will be the most neutron-rich species measured so far. [Preview Abstract] |
Saturday, October 15, 2016 11:54AM - 12:06PM |
JJ.00008: Cross Section Measurements of ${}^{12}$C+${}^{16}$O Fusion Reaction at Stellar Energies Wanpeng Tan, X Fang, M Beard, G Gilardy, H Jung, Q Liu, S Lyons, D Robertson, K Setoodehnia, C Seymour, E Stech, B Vande Kolk, M Wiescher, R de Souza, S Hudan, V Singh, X Tang, E Uberseder $^{12}$C+$^{16}$O is one of the three fusion reactions ($^{12}$C+$^{12}$C, $^{12}$C+$^{16}$O, and $^{16}$O+$^{16}$O) that play an important role at the late stage of stellar evolution in massive stars. The previous meassurements of its cross section at low energies rely on the singles measurements of either gamma rays or charged particles. New measurement was conducted for the ${}^{12}$C+${}^{16}$O reaction at E$_{cm}$ = 3.64 - 4.93 MeV with the detection of both gammas and charged particles using the high intensity St ANA accelerator at the University of Notre Dame. The protons and alphas from the fusion evaporation were measured by a large area silicon strip detector array (SAND) while the gamma rays were detected by one large volume HPGe detector right after the target. Statistical model calculation were employed to interpret the experimental results. This provided a more reliable extrapolation for the 12C+16O fusion cross section, reducing substantially the uncertainty for stellar model simulations. [Preview Abstract] |
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