Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session MB: Quiescent Stellar Burning |
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Chair: Frank Strieder, South Dakota School of Mines & Technology Room: Hilton Kohala 1 |
Saturday, October 27, 2018 2:00PM - 2:15PM |
MB.00001: First Measurement of the Neutron Capture Cross Sections of Stable Germanium Isotopes Alexander Laminack, Jeffery C Blackmon, Aaron J Couture, John Leonard Ullmann, Kevin T Macon, Ashley A Hood, Graeme Morgan, Erin Good, Scott T Marley, Catherine M Deibel, Gemma L Wilson Nearly half of all elements heavier than iron are created during the s-process. The s-process can be broken into main and weak components. Because the weak s-process occurs out of statistical equilibrium and the cross sections involved are small, each isotope serves as a bottleneck. Therefore the neutron capture cross sections radically affect the abundance of all isotopes downstream. Almost all stable Germanium isotopes lie along the weak s-process path and yet no neutron time-of-flight measurements of their cross sections have been made. In January 2018, the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science CEnter (LANSCE) was used to measure the neutron capture cross sections of 70Ge, 72Ge, and 73Ge. A follow up experiment to measure the cross sections of the remaining stable Germanium isotopes at the same facility is planned to occur in the near future. The results of these experiments, the astrophysical impact, and future work based on these results will be discussed. |
Saturday, October 27, 2018 2:15PM - 2:30PM |
MB.00002: Measurement of the 65Cu Neutron-Capture Cross Section for Constraining s-process Nucleosynthesis Christopher J Prokop, Aaron Couture, Shea Mosby, Gencho Y Rusev, John Leonard Ullmann Determining the origin of the elements in the observable universe requires detailed knowledge of the salient nuclear physics, such as neutron-capture cross-sections. Recently, the neutron-capture cross-sections of two isotopes, important for the s-process, 63,65Cu, have been called into question. A measurement from 2008 reduced the neutron-capture cross sections of 63,65Cu by ~65% and ~40%, respectively. However, a more recent measurement of 63Cu agrees well with the higher cross section from measurements prior to the 2008 work. This discrepancy is understood as a systematic bias in the 2008 measurement originating from the natural Cu backing material of the neutron production target not properly accounted for when determining the neutron flux. Moreover, it is likely the same systematic bias observed in the 2008 work for 63Cu is present for their 65Cu result as well, and the currently accepted neutron-capture cross section is far too low. Recently, neutron capture on 65Cu was measured using the Detector for Advanced Neutron Capture Experiments was performed at Los Alamos National Laboratory and preliminary results presently agree well with the older measurements. Analysis and results of this most recent measurement will be presented. |
Saturday, October 27, 2018 2:30PM - 2:45PM |
MB.00003: Commissioning and first measurements at the CASPAR underground accelerator facility Daniel Robertson, Axel Boeltzig, Tyler Borgwardt, Manoel Couder, Bryce Frentz, Uwe Greife, Mark Hanhardt, Thomas Kadlecek, Frank Strieder, Michael Wiescher The Compact Accelerator System for Performing Astrophysical Research (CASPAR) is the only U.S. deep underground accelerator facility, with a low-background environment created by 4300 m.w.e of overhead rock shielding, suitable for low-energy nuclear astrophysics measurements. Utilizing an electrostatic acceleration system covering the energy range 150 keV to 1.1 MeV for both 1H+ and 4He+ beams, crucial reactions of interest in stellar burning are accessible in the Gamow energy range. Commissioning measurements of the CNO-cycle reaction 14N(p,γ)15O are now complete, with results presented here. CASPAR now begins to focus on reactions of interest for the production of heavy elements through the s-process, primarily the neutron source reactions for both the main and weak s-process, 13C(α,n) and 22Ne(α,n) respectively. |
Saturday, October 27, 2018 2:45PM - 3:00PM |
MB.00004: Measurement of the 14N(p,γ)15O CNO cycle reaction at CASPAR Bryce Frentz, Daniel J Robertson, Ani Aprahamian, Axel Boeltzig, Tyler Borgwardt, Joachim Goerres, Mark Hanhardt, Thomas Kadlecek, Frank Strieder, Michael Wiescher The CNO cycle is the dominant energy source for large main sequence stars and significantly contributes to the hydrogen burning in asymptotic giant branch stars. Of the reactions in the CNO cycle, the 14N(p,γ)15O reaction is the slowest and therefore it regulates the energy production, lifetime, and abundance distribution of a given star. Measurements of this cross section show some large discrepancies and they are crucially inconsistent in the range of 300-600 keV, which is important for extrapolation to astrophysical energies. To address this problem, we have performed a measurement of this reaction at CASPAR, the first deep underground accelerator facility in the U.S., located on the 4850 ft. level of the Sanford Underground Research Facility in Western South Dakota. A proton beam impinged on TiN and ZrN targets at energies ranged from 270-1070 keV. The resulting cross-section information and its extrapolation to stellar burning energies will be presented. |
Saturday, October 27, 2018 3:00PM - 3:15PM |
MB.00005: R-matrix analyses of secondary γ-ray angular distributions for recent reaction studies at the University of Notre Dame Richard J DeBoer, Axel Boeltzig, Qian Liu, Kevin T Macon, Michael C F Wiescher, Carl Richard Brune, Michael T Febbraro, Kate L Jones, Jesus Pereira Lopez At the University of Notre Dame's Nuclear Science Laboratory we have recently studied 13C(α,n)16O as a background for neutrino experiments, 17O(α,n)20Ne for its role in the s-process and 10B(α,n)13N as a background for low energy underground nuclear astrophysics experiments at CASPAR and a possible key nucleosynthesis reaction in first generation stars. At the energies studied, all of these reactions produce secondary γ-rays from the population of excited states in the final nucleus. In many situations, especially when neutrons are the primary exit particle, detection of secondary γ-rays has several experimental advantages. These secondary γ-rays are in general anisotropic and measurements of the angular distributions give constraints on the spin-parities of populated resonances. We have performed a detailed experiment of this type for the 17O(α,n)20Ne reaction using the HAGRiD array. In this talk I will describe the analysis of these reactions using the R-matrix technique and giving benchmark calculations for the well-studied 15N(p,α)16O reaction. |
Saturday, October 27, 2018 3:15PM - 3:30PM |
MB.00006: Measuring the 13C(d,n)14N Cross Section—A Prominent Beam-Induced Background Reaction in Underground Nuclear Astrophysics Experiments Chad C. Ummel, Michael Febbraro, Eli Temanson, Mark E. Bannister, Kelly A. Chipps, Jolie A. Cizewski, Francesca Corrado, Charles C. Havener, Spencer Jones, Steven D. Pain, William A. Peters, David Walter The 13C(α,n)16O reaction is the primary source of neutrons for the main branch of the slow neutron capture process (s-process) of nucleosynthesis. Direct measurement of the cross section within the Gamow window is difficult due to low yields. Prior measurements have constrained the 13C(α,n)16O cross section down to 279 keV, but with large statistical uncertainties. These uncertainties, compounded by the unknown influence of a 1/2+ resonance in 17O near the α-capture threshold, make extrapolation into the Gamow window unreliable, necessitating additional measurements at low energies. Measurement is further complicated by beam-induced background from the 13C(d,n)14N reaction, resulting from deuterium contamination in the α-particle beams of most accelerators. At astrophysical energies, the 13C(d,n)14N cross section is many orders of magnitude greater than that of 13C(α,n)16O. Thus, a direct measurement of 13C(d,n)14N in the energy range of interest is needed. The 13C(d,n)14N cross section was accordingly measured at laboratory energies between 165 and 250 keV at Oak Ridge National Laboratory’s Multicharged Ion Research Facility. Preliminary results are discussed. |
Saturday, October 27, 2018 3:30PM - 3:45PM |
MB.00007: Understanding photoneutron sources for ultra-low background astrophysics measurements Michael T Febbraro, Steven D. Pain, Kelly A. Chipps, David G Walter, Rebecca Toomey, Axel Boeltzig, Daniel J Robertson, Daniel W. Stracener, Mark E Bannister, Michael Wiescher, Frank Strieder The 13C(α,n) and 22Ne(α,n) reactions, fueling the main and weak components of the s-process, are a top priority of current and upcoming underground astrophysical labs. This is driven by the need for ultra-low-background environments required for performing these very low yield measurements into the stellar burning regimes. Critical to the success of these measurements will be the characterization of ambient and beam-induced neutron background sources. One such background is photoneutron production from deuterium, induced by high-energy (>2.2 MeV) gamma rays, from beam-induced reactions or environmental background. A set of controlled experiments was performed at Oak Ridge National Laboratory and the CASPAR facility at SURF in an attempt to understand the impact of this reaction. Results of this study and implications for neutron counting and quasi-spectroscopic measurement approaches will be discussed. |
Saturday, October 27, 2018 3:45PM - 4:00PM |
MB.00008: Abstract Withdrawn
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Saturday, October 27, 2018 4:00PM - 4:15PM |
MB.00009: Elastic scattering of 3He + α with SONIK Devin Connolly, Som N Paneru, Jonathan Karpesky, Martin Alcorta, Carl Richard Brune, Michael Bowry, Barry S Davids, Matilda Delgado, Nicholas Esker, Jennifer Fallis, Adam Garnsworthy, Rekam Giri, Uwe Greife, Dave Hutcheon, Fitzpatrick Laddaran, Annika Lennarz, Matthew A Lovely, Chris Pearson, Chris Ruiz, Caleb Seeman Elastic scattering of 3He + α is of interest in analyses of 3He(α,γ)7Be, which has broad importance in big bang nucleosynthesis and solar neutrino physics. Phenomenologically, α(3He,3He)α can be used in global R-matrix analyses to extrapolate the 3He(α,γ)7Be astrophysical S-factor (S34) to energies of astrophysical interest. With respect to solar physics, 3He(α,γ)7Be, the initial reaction in the pp-II and pp-III chains, leads to the production of 7Be and 8B. Consequently, at solar energies S34 is almost directly proportional to the flux of νe emitted in the subsequent β - decays of 7Be and 8B. Thus it is critical to know S34 to a high degree of accuracy and precision. 3He + α elastic scattering was measured using the recently commissioned Scattering of Nuclei in Inverse Kinematics (SONIK) scattering chamber, a windowless, extended gas target surrounded by an array of collimated, ion implanted silicon charged particle detectors situated at TRIUMF, ISAC-I. Experimental techniques and preliminary results will be discussed. |
Saturday, October 27, 2018 4:15PM - 4:30PM |
MB.00010: Every Nucleus, When Created, Will Exhibit No Motion, Linear Motion, Rotational, and/or Vibratory Motion, Singly, or In Some Combination, Which May Later Be Modified By Outside Forces: A Natural Law. Stewart E Brekke Due to the excess energy of creation, a newly created nucleus may exhibit no motion, linear, rotational and/or vibrational motion, singly or in some combination. For example, in nuclear decay mpc2 +1/2mpv2+ 1/2Ipωp2 + 1/2 kp xp2 = mDc2 + 1/2mDvD2 + 1/2IDωD2 + 1/2kDxD2 + (particle mass-energy equivalence, linear, rotational and/or vibrational energies), as in all mechanical situations, every mass can have no motion, linear, rotational and/or vibratory motion singly or in some combination which later can be modified by external forces including newly formed nuclei sometimes even resulting from nuclear decay or common nuclear reactions. |
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