Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session GG: Nuclear Astrophysics: Experiment |
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Chair: Aaron Couture, Los Alamos National Laboratory Room: Peralta |
Friday, November 5, 2010 8:30AM - 8:42AM |
GG.00001: The breakout of the Hot CNO cycle via $^{18}$Ne resonant states S. Almaraz-Calderon, W. Tan, A. Aprahamian, B. Bucher, J. Gorres, A. Roberts, A. Villano, M. Wiescher, C. Brune, Z. Heinen, T. Massey, N. Ozkan, R.T. Guray, H. Mach The energy generation rate in the HCNO cycle is limited by the $\beta$ decay of the waiting point nuclei $^{14}$O and $^{15}$O. However, when the temperatures and densities are high enough (e.g. Novae and X-ray Bursts) it is possible to bypass them by p/$\alpha$ captures resulting in a thermonuclear runaway towards the rp-process. One of the two paths for breakouts from the HCNO cycle is the reaction chain $^{14}$O($\alpha$,p)$^{17}$F(p,$\gamma$)$^{18}$Ne($\alpha$,p), which proceeds through resonant states on $^{18}$Ne, making their reactions rates very sensitive on the partial and total widths, excitation energies and spins of such resonances. We studied the resonant states in $^{18}$Ne via $^{16}$O($^{3}$He,n) reaction. The neutrons were measured with an array of liquid scintillators using Time-of-Flight and pulse-shape discrimination techniques. The charged particles were detected in coincidence with neutrons by an array of silicon detectors, allowing us to measure $\alpha$, p, p' and 2p decay branching ratios. Tentative spin assignments were made in comparison with zero range DWBA calculations. This new information will be included in reaction network calculations to evaluate its impact on the nuclear energy generation that occurs in these stellar explosive environments. [Preview Abstract] |
Friday, November 5, 2010 8:42AM - 8:54AM |
GG.00002: Study of $^{19}$Ne levels of Importance to $^{18}$F production in Novae P.D. O'Malley, M.E. Howard, J.A. Cizewski, D.W. Bardayan, M.S. Smith, K.Y. Chae, S.T. Pittman, S.H. Ahn, R.L. Kozub, M. Matos, B. Moazen $^{18}$F is a relatively long-lived radioactive product of novae and its decay series is a direct probe of novae burning. The $^{18}$F(p,$\alpha)^{15}$O reaction dominates $^{18}$F destruction in novae but the rate is uncertain because the properties of important $^{19}$Ne levels have never been experimentally determined. There are several levels with uncertain spins and excitation energies that have only been estimated before. At ORNL, the $^{20}$Ne(p,d)$^{ 19}$Ne reaction was measured to study these important levels by using a 30 MeV beam of protons from the HRIBF tandem accelerator was used to bombard a carbon target implanted with $^{20}$Ne and outgoing particles were detected in a silicon strip detector array. Data will be shown and analysis discussed. [Preview Abstract] |
Friday, November 5, 2010 8:54AM - 9:06AM |
GG.00003: Study of the $^{19}$F($\alpha $,p)$^{22}$Ne reaction with an extended gas target K.Y. Chae, D.W. Bardayan, C.D. Nesaraja, M.S. Smith, S.H. Ahn, A. Ayres, A. Bey, K.L. Jones, S.T. Pittman, M.E. Howard, P.D. O'Malley, R.L. Kozub, M. Matos, B.H. Moazen, W.A. Peters Because of the astrophysical importance of measuring numerous ($\alpha $,p) reactions for explosive nucleosynthesis, we have developed a new approach using heavy ion beams incident on a He target and have measured the $^{4}$He($^{19}$F,$^{1}$H)$^{22}$Ne reaction as a first demonstration. $^{19}$F beams were produced at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL) and bombarded a large scattering chamber filled with helium gas. Using a newly built gas recirculator system, a windowless gas target was maintained at a constant He pressure of 9 Torr. Recoiling protons from the reactions were detected by a large area annular silicon strip detector array (SIDAR) which was configured in dE-E telescope mode. We measured the $^{19}$F($\alpha $,p) and $^{19}$F($\alpha $,p') excitation functions over the energy range of Ec.m.$\sim $1-2.1 MeV. Details of the experimental setup and a status report on the analysis will be presented. *Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. [Preview Abstract] |
Friday, November 5, 2010 9:06AM - 9:18AM |
GG.00004: Optical potential analysis for $^{26}$Al elastic scattering of protons and deuterons A. Bey, K.L. Jones, K.T. Schmitt, S.T. Pittman, S.H. Ahn, A. Ayres, R.L. Kozub, S. Graves, S. Strauss, D.W. Bardayan, K.Y. Chae, M.S. Smith, C.D. Nesaraja, W.A. Peters, P.D. O'Malley, A. Adekola, I. Spassova, M.E. Howard, D. Walter Destruction of $^{26}$Al in many explosive stellar environments is thought to proceed through the (p,$\gamma$) reaction. The effect of this reaction on the observed abundances of $^{26}$Al in the galaxy and its extinction in meteorites remains an open question. In this context, an experimental campaign has been carried at the HRIBF facility (ORNL) with a particular focus on studying the astrophysically involved single-particle levels of $^{27}$Si. Since the reliability of the spectroscopic information deduced from direct reactions lies on the validity of nuclear-reaction theories, it is essential to determine the best nucleon optical model potential parameters for the relevant targets. To this end, we have measured the elastic scattering of $^{26}$Al+p and $^{26}$Al+d in inverse kinematics at an incident energy of 117 MeV. Details about the experimental approach will be presented along with the preliminary results. [Preview Abstract] |
Friday, November 5, 2010 9:18AM - 9:30AM |
GG.00005: ABSTRACT WITHDRAWN |
Friday, November 5, 2010 9:30AM - 9:42AM |
GG.00006: A High-Precision Determination of the Astrophysical Rate for Production of $^{9}$Be C.W. Arnold, T.B. Clegg, H.J. Karwowski, G.C. Rich, J.R. Tompkins, C.R. Howell New cross section measurements of the astrophysically important $^{9}$Be($\gamma$,n) reaction have been made from 1.5 to 5.18 MeV. The measurements were made using the nearly monoenergetic circularly polarized $\gamma$-ray beam at Triangle Universities Nuclear Laboratory's High Intensity $\gamma$-ray Source. Measurements over narrow resonances employed beams with energy spread dE/E $\leq$ 1\%. The energy-dependent absolute efficiency of the neutron counter used in this work was measured to $\pm$ 3\% accuracy. New resonance parameters for the 4 lowest lying states in $^{9}$Be were determined. A new reaction rate for $\alpha + \alpha + n$ has been determined to better than $\pm$ 5\%. The present rate is $\sim$ 25\% larger than two widely accepted rates [1-2] in the temperature range important for r-process nucleosynthesis. The implications of this new rate on r-process and nuclear abundance predictions will be discussed.\\[4pt] [1] C. Angulo \textit{et al.} Nuc. Phys. A 656 (1999) 3-183. \\[0pt] [2] K. Sumiyoshi \textit{et al.} Nuc. Phys A 709 (2002) 467-486. [Preview Abstract] |
Friday, November 5, 2010 9:42AM - 9:54AM |
GG.00007: Measuring spin distributions in $^{95}$Mo(n,$\gamma$) and validation of the surrogate reaction A.S. Adekola, J.A. Cizewski, A. Couture, M. Devlin, M. Jandel, W.A. Peters, J. Burke, J.E. Escher Neutron capture cross sections on unstable nuclei are important quantities for understanding the synthesis of the heavy elements in stars and applications in nuclear energy and nuclear forensics. It is presently not possible to measure directly (n,$\gamma$) cross sections on nuclei with t$_{1/2}<$ 100 days. The (d, p$\gamma$) reaction is a candidate for an indirect or surrogate method to determine (n, $\gamma$) reaction cross sections on unstable nuclei. While neutron capture dominates at low $l$ values ($s$ and $p$ waves), charged particle reactions are expected to bring in more angular momentum. The $^{95}$Mo(n,$\gamma$) cross sections have been measured up to 200 keV. The $^{95}$Mo(n,$\gamma$) and $^{95}$Mo(d, p$\gamma$) reactions will be measured to determine the population of the yrast levels as a function of neutron energy and deduce the spin distributions for both (n,$\gamma$) and (d, p$\gamma$), respectively. The goal is to use the knowledge of the spin distributions in both (n,$\gamma$) and the surrogate (d, p$\gamma$) to develop a validated prescription to deduce (n,$\gamma$) cross sections from (d, p$\gamma$) measurements. In this talk, an overview of surrogate technique, our experimental approach and preliminary results of a commissioning $^{75}$As(d, p$\gamma$) experiment will be presented. [Preview Abstract] |
Friday, November 5, 2010 9:54AM - 10:06AM |
GG.00008: Astrophysical Implications of Recent Photos-Absorption Measurements Mary Beard, Burkhard K\"ampfer, Stephan Fraundorf, Ronald Schwengner, Michael Wiescher Photo-absorption cross sections are a fundamental ingredient in nuclear reaction model calculations. Recently, a set of photo-absorption cross sections, including a chain of Mo isotopes (A = 92 -- 100), have been measured at the Forschungszentrum Dresden using the ELBE accelerator. The impact of these photo-absorption cross section measurements on astrophysical reaction rates is discussed. [Preview Abstract] |
Friday, November 5, 2010 10:06AM - 10:18AM |
GG.00009: Using HiRA and the (p,d) Reaction to Explore Single-Hole State Evolution Near the N=50 Shell Closure M.E. Howard, A.S. Adekola, J.A. Cizewski, B. Manning, E. Merino, P.D. O'Malley, D. Bazin, Z. Chajecki, D. Coupland, R. Hodges, J. Lee, W. Lynch, A. Sanetullaev, M.B. Tsang, J. Winklebauer, M. Youngs, T.K. Ghosh, R.R.C. Clement, D.W. Bardayan, K.Y. Chae, D. Shapira, S.H. Ahn, K. Schmitt The 84Se(p,d)83Se and 86Kr(p,d)85Kr reactions at 45 MeV/u in inverse kinematics were measured at the National Superconducting Cyclotron Laboratory in May 2010, using the charged particle detector HiRA and the S800 spectrometer. The experiment described here is the first to utilize the entire HiRA array of 20 telescopes. The primary goal is to extract angular momentum quantum numbers and neutron spectroscopic factors for the ground and first excited states of 83Se. Measuring neutron single-hole states in the N=50 closed shell region will refine the nuclear Hamiltonians for the shell model description of heavier neutron-rich nuclei further from stability. This work is a model for future rare isotope beam experiments that could make meaningful contributions to r-process nucleosynthesis modeling. This work is supported in part by the U.S. National Science Foundation and Department of Energy. [Preview Abstract] |
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