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 DH: Nuclear Astro II |
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Chair: Reiner Kruecken, TRIUMF Room: Pavilion Ballroom C |
Friday, October 14, 2016 10:30AM - 10:42AM |
DH.00001: Alpha-capture reaction rates for 22Ne(alpha,n) via sub-Coulomb alpha-transfer Heshani Jayatissa, Grigory Rogachev, Yevgen Koshchiy, Vladilen Goldberg, Shadi Bedoor, Joshua Hooker, Curtis Hunt, Cordero Magana, Brian Roeder, Antti Saastamoinen, Alexandria Spiridon, Sriteja Upadhyayula Direct measurements of $\alpha$-capture reactions at energies relevant to astrophysics is extremely difficult to carry out due to the very small reaction cross section. The large uncertainties introduced when extrapolating direct measurements at high energies down to the Gamow energies can be overcome by measuring the Asymptotic Normalization Coefficients (ANC) of the relevant states using ($^{6}$Li,d) $\alpha$-transfer reactions at sub-Coulomb energies to reduce the model dependence. The study of the $^{22}$Ne($^{6}$Li,d) reaction was carried out at the Cyclotron Institute at Texas A$\&$M University. The $\alpha$-ANC measurements for the near $\alpha$-threshold resonances of $^{26}$Mg will provide constraints for the reaction rate of the $^{22}$Ne($\alpha$,n) reaction. [Preview Abstract] |
Friday, October 14, 2016 10:42AM - 10:54AM |
DH.00002: Measuring astrophysically relevant $^{\mathrm{36}}$Cl production cross sections Tyler Anderson, Michael Skulski, Karen Ostdiek, Wenting Lu, Adam Clark, Austin Nelson, Mary Beard, Philippe Collon The short-lived radionuclide $^{\mathrm{36}}$Cl (t$_{\mathrm{1/2}}^{\mathrm{\thinspace }}=$ 0.301 Ma) is known to have existed in the Early Solar System (ESS), and evaluating its production sources can lead to better understanding of the processes taking place in ESS formation and their timescales. The X-wind model is used to explain $^{\mathrm{36}}$Cl production via solar energetic particles from the young Sun, but is lacking empirical data for many relevant reactions. Bowers et al. (2013) measured the $^{\mathrm{33}}$S($\alpha $,p)$^{\mathrm{36}}$Cl cross section at various energies in the range of 0.70-2.42 MeV/A, and found them to be systematically under predicted by Hauser-Feshbach statistical model codes TALYS and NON-SMOKER, highlighting the need for more empirical data for these cross sections. Recent results of the re-measurement of the $^{\mathrm{33}}$S($\alpha $,p)$^{\mathrm{36}}$Cl reaction, providing greater coverage of the same energy range as Bowers et al., will be presented. Future plans for measurement of other $^{\mathrm{36}}$Cl producing reactions will also be discussed. [Preview Abstract] |
Friday, October 14, 2016 10:54AM - 11:06AM |
DH.00003: Study of the $^{18}$Ne($\alpha$,p)$^{21}$Na reaction with ANASEN and its importance in the breakout from the hot CNO cycle Maria Anastasiou, Ingo Wiedenhoever, L.T. Baby, N. Rijal, J.J. Parker, J.C. Blackmon, K.T. Macon, D.S. Gonzalez, Y. Koshchiy, G. Rogachev, J. Belarge, A. Kuchera The $^{18}$Ne($\alpha$,p)$^{21}$Na reaction provides a pathway for breakout from the hot CNO cycles to the rp-process in x-ray bursts and other astrophysical scenarios. However, the actual conditions under which the breakout occurs depend critically on the thermonuclear reaction rate. This rate has not been sufficiently determined yet over stellar temperatures on x-ray bursts and previous studies contradict each other in a significant way. We study the direct $^{18}$Ne($\alpha$,p)$^{21}$Na reaction with the Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN), using a helium gas target and an $^{18}$Ne radioactive beam. ANASEN is an active gas target detection system with the ability to measure excitation function using a single beam energy while the beam slows down in the target gas. Utilizing also the particle tracking capability of the experimental array the center of mass energy can be reconstructed at the reaction point. Preliminary results will be presented for the experiment performed in reaction energies relevant to those in the breakout leading to an x-ray burst. [Preview Abstract] |
Friday, October 14, 2016 11:06AM - 11:18AM |
DH.00004: A Low Energy Measurement of the $^{13}$C($\alpha$,n) Reaction Rebecca Toomey, Michael Febbraro, Steven Pain, Jolie Cizewski The slow neutron capture process (s process) is a key mechanism in heavy-element synthesis, reaching up to $^{209}$Bi. The s process creates elements along the line of beta-stability via neutron capture and beta decay in a low neutron flux environment in AGB stars. The dominant source of neutrons for the s process is the $^{13}$C($\alpha$,n) reaction. At the low energies occurring in these stellar conditions, this reaction cross section is very low, making direct measurement of the reaction rate difficult. Currently the state-of-the-art measurements using high-efficiency moderated neutron counter detectors have constrained this cross section down to approximately 300 keV - still well above stellar conditions, therefore requiring extrapolation of the S factor into the Gamow window ($\sim$140-230 keV). This talk will focus on the motivation and preparation for low-energy measurements of the $^{13}$C($\alpha$,n) reaction using a neutron spectroscopic technique with the aim of reducing uncertainties in current measurements, and also attempt measurements at lower energies. Background measurements and the characterisation of the experimental set up from the measurement of $^{13}$C($\alpha$,n) at higher energies at the University of Notre Dame will be presented. [Preview Abstract] |
Friday, October 14, 2016 11:18AM - 11:30AM |
DH.00005: Investigation of resonances in $^{20}$Mg: Implications for astrophysics and nuclear forces Jaspreet Randhawa, Rituparna Kanungo, Martin Alcorta, Christina Burbadge, Devin Burke, Greg Christian, Barry Davids, Julia Even, Greg Hackman, Jack Henderson, Shigeru Ishimoto, Satbir Kaur, Matthew Keefe, Reiner Kruecken, Jon Lighthall, Mohamad Moukaddam, Elizabeth Padilla-Rodal, Jenna Smith, Joseph Turko, Orry Workman $^{18}$Ne(2p,$\gamma$)$^{20}$Mg provides a possible pathway for breakout from the hot CNO cycles to the rp-process in type I X-ray bursts. This reaction rate is uncertain due to lack of any experimental information on the resonant states in $^{20}$Mg above proton emission threshold. Recent calculations using nuclear forces from chiral perturbation theory predict quite a different level structure for $^{20}$Mg with and without inclusion of three nucleon forces. These differences make study of $^{20}$Mg states important to constraint both nuclear theory and this reaction rate. We have investigated the excited states in $^{20}$Mg through inelastic deuteron scattering. The experiment was performed using the IRIS facility at TRIUMF,Canada. The $^{20}$Mg beam with an average intensity of 500 pps and energy of 8.5\textit{A} MeV was directed at novel thin windowless solid deuteron target. Experiment and initial observations will be discussed. [Preview Abstract] |
Friday, October 14, 2016 11:30AM - 11:42AM |
DH.00006: Study of 38Ca resonances in the 34Ar($\alpha$,p)37K reaction via proton scattering in 37K A. Lauer, C. Deibel, J. Blackmon, A. Hood, E. Good, K. Macon, D. Santiago, S. Pain, K. A. Chipps, T. Ahn, F. Montes, H. Schatz, W. Ong, j. Browne, K. Schmidt, G. Rogachev, S. Upadhyayula, S. Bedoor, J. Hooker, Y. Koshchiy, H. Jayatissa, I. Wiedenhoever, L. Baby, M. Anastasiou, N. Rijal The 34Ar($\alpha$,p)37K reaction is important in Type I X-ray bursts (XRBs), where nucleosynthesis proceeds through the $\alpha$,p and rp processes up to A$<$100. Waiting-point nuclei in XRBs (e.g. 34Ar) are in (p,$\gamma$)-($\gamma$,p) equilibrium and may stall the burst, but the ($\alpha$,p) reaction may provide a detour. We performed 37K+p elastic scattering to study the compound nucleus 38Ca at the ReA3 facility at the National Superconducting Cyclotron Laboratory using a 37K beam incident on a CH$_2$ target. Scattered protons were detected in telescopes of Si strip detectors, while coincident heavy recoils were detected in a gas ionization chamber. Experimental results will be presented and implications for XRB nucleosynthesis and observables discussed. [Preview Abstract] |
Friday, October 14, 2016 11:42AM - 11:54AM |
DH.00007: Study of resonances in $^{23}\mathrm{Mg}(p, \gamma)^{24}\mathrm{Al}$ via neutron transfer to analog states in $^{24}$Na Gregory Christian, Eames Bennett, Shuya Ota, Wilton Catford, Gavin Lotay, Adrien Matta, Ryan Wilkenson According to sensitivity studies, the $^{23}$Mg$(p,\gamma)^{24}$Al reaction has a significant influence on the production of the radionuclides $^{22}$Na and $^{26g}$Al in oxygen-neon novae. At nova temperatures, this reaction is thought to be dominated by a single resonance at $E_r \sim 480$ keV, whose strength has previously been measured using a radioactive $^{23}$Mg beam and recoil mass spectrometer. To further constrain the rate of this reaction, we have undertaken a spectroscopic study of the mirror states of $^{23}$Mg$(p,\gamma)^{24}$Al resonances, using the single-neutron transfer reaction $^{23}$Na$(d,p)^{24}$Na in inverse kinematics. The experiment utilized the TIARA silicon detector array coupled to four germanium clovers and the MDM magnetic spectrometer at the Texas A&M University Cyclotron Institute, serving as the commissioning experiment for the ``TIARA for Texas'' (T40) campaign at Texas A&M. In this talk, I will give an overview of the experimental setup; present preliminary results from the commissioning experiment; and discuss future plans for the T40 collaboration. [Preview Abstract] |
Friday, October 14, 2016 11:54AM - 12:06PM |
DH.00008: $^{20}$Ne($p,\gamma$)$^{21}$Na Cross Sections and the Astrophysical Impact Stephanie Lyons, Andreas Best, Ying Ying Chen, Richard deBoer, Gwen Gilardy, Joachim Goerres, Qian Liu, Alex Long, Zach Meisel, Mike Moran, Dan Robertson, Chris Seymour, Ed Stech, Bryant Van de Kolk, Michael Wiescher In stellar environments where T $>$ 0.05 GK, hydrogen burning may proceed via the NeNa cycle. $^{20}$Ne(p,$\gamma$)$^{21}$Na, the first reaction in the NeNa cycle, is thought to have the slowest reaction rate [1], thereby determine the timescale for the rest of the cycle. The stellar reaction rate for $^{20}$Ne(p,$\gamma$)$^{21}$Na is dominated by direct capture and the high energy tail of a sub-threshold resonance, as shown previously [2]. Measurements of the $^{20}$Ne(p,$\gamma$)$^{21}$Na cross section from E$_p$= 0.5-2.0 MeV were performed at the University of Notre Dame Nuclear Science Laboratory using the St. ANA 5U accelerator and the Rhinoceros extended gas target. The cross sections were measured relative to the E$_{c.m.}$=1113 keV resonance, whose strength was independently measured. The measured cross sections were then analyzed using R-matrix. The extrapolated astrophysical S-factors, as well as reaction rates will be presented.\\ 1. Iliadis et al. The Astrophysical Journal Supplement Series 134, 151 (2001).\\ 2. Rolfs et al. Nuclear Physics A 241, 480 (1975).\\ [Preview Abstract] |
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