Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session X12: Nuclear Astrophysics II |
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Sponsoring Units: DNP Chair: Jeff Blackmon, Louisiana State University Room: Sheraton Plaza Court 1 |
Tuesday, April 16, 2019 10:45AM - 10:57AM |
X12.00001: Measuring the astrophysical 20Ne(p, γ)21Na rate at DRAGON Jonathan Karpesky, Devin S Connolly, Matthew A Lovely, Charlie Akers, Gregory Christian, Barry S Davids, Jennifer Fallis, Uwe Greife, Ulrike Hager, Dave Hutcheon, Alex Rojas, Chris Ruiz Understanding the abundance levels of isotopes produced in oxygen-neon (ONe) novae within our galaxy requires accurate measurements of nuclear reaction rates within their associated reaction network. During these cataclysmic events, the produced radioisotope 22Na is ejected into the interstellar medium and β-decays predominately to the first excited state in 22Ne leading to a characteristic 1.275 MeV gamma ray. To date, there has been no astronomical observation of this characteristic gamma ray that can be a potential probe into the physics occurring within novae. The production of 22Na in classical novae is limited by the 20Ne(p, γ)21Na nuclear reaction that sets the focus of this experiment. Using the DRAGON recoil separator, new measurements of the 20Ne(p, γ)21Na reaction are performed at lower energies closer to astrophysically relevant energy ranges. The aim is to reduce experimental uncertainties in the 20Ne(p, γ)21Na reaction rate in order to more accurately predict the production yield of 22Na in ONe novae and to measure the direct capture to the ground state in order to constrain the astrophysical S-factor. Experimental methods and results to be discussed. |
Tuesday, April 16, 2019 10:57AM - 11:09AM |
X12.00002: First measurement of low-energy resonances in the $^{24}$Mg($\alpha$,$p\gamma$)$^{27}$Al reaction Tan Ahn, Sebastian Aguilar, Richard J DeBoer, Daniel W Bardayan, Axel Boeltzig, Carl Richard Brune, Sean P Burcher, Kyungyuk Chae, Samuel Henderson, Kate L Jones, Jerome Kovoor, Kevin Macon, Khachatur Manukyan, Shea Mosby, Patrick D O'Malley, Maxime Renaud, Karl Smith, Wanpeng Tan, Bryant J Vande Kolk, Michael C F Wiescher Type Ia X-ray Bursts are energetic explosive events that we observe and understand through their light curves. The energy they generate comes from a complex network of nuclear reactions and a recent sensitivity study by Iliadis et al. finds that the $^{24}$Mg($\alpha$,$p$)$^{27}$Al reaction strongly affects the global energy release. Data on the direct measurement are scarce and the |
Tuesday, April 16, 2019 11:09AM - 11:21AM |
X12.00003: Constraining the νp-process through the study of neutron-induced charged-particle reactions on short-lived 56Ni Sean A Kuvin, Hye Young Lee, Christiaan Vermeulen, Kevin Bennett, Eva Birnbaum, Meiring Nortier, Georgios Perdikakis, Pelagia Tsintari The rate of the 56Ni(n,p)56Co reaction is a critical input for understanding the synthesis of heavy elements through the νp-process. However, there currently exists no experimental data for the reaction. This is due to the technical difficulties of producing a quality neutron beam at the relevant energies and in the fabrication of a short-lived 56Ni target (T1/2 ≈ 6 days). Both issues can be addressed by leveraging the unique capabilities of the Los Alamos Neutron Science Center (LANSCE), through target production and fabrication at the Isotope Production Facility and through the neutron beams that can be delivered to the Low Energy (n,z), LENZ, experiment station. To safely perform the (n,p) measurement with the highly radioactive target, we are developing an optimized detection system with guidance from a GEANT4 simulation. Progress towards the development of a 56Ni target, along with current and planned measurements with other nickel isotopes will be presented. |
Tuesday, April 16, 2019 11:21AM - 11:33AM |
X12.00004: Pulse shape discrimination of 3He proportional counters via rise time discrimination at CASPAR Tyler C Borgwardt, Axel Boeltzig, Manoel Couder, Bryce Frentz, Uwe Greife, August Gula, Mark Hanhardt, Thomas Kadlecek, Daniel J Robertson, Frank Strieder, Michael C F Wiescher Nuclear astrophysics experiments have the need to measure reactions at low energies in order to understand the reaction rates at stellar temperatures. The low yields at these energies have prompted the need for underground experiments to reduce the environmental background. Despite this reduction, experiments can still be limited by the intrinsic background of a detector. To address this problem, we have implemented pulse shape discrimination utilizing the rise time of the signal for the CASPAR neutron detector system. CASPAR is located at the 4850’ level of the Sanford Underground Research Facility (SURF) located in Western South Dakota and is the first deep underground accelerator facility in the United States. This pulse shape discrimination technique will be presented, along with some initial results of its application to recent low energy measurements of 11B(α,n)14N. |
Tuesday, April 16, 2019 11:33AM - 11:45AM |
X12.00005: Assembly and development of the prototype Single Atom Microscope Benjamin T Loseth, Ruoyu Fang, Jaideep Singh The Single Atom Microscope is an optical detection system under development for measuring the cross section of low yield nuclear reactions that are influential in nucleosynthesis. Under this system, the atomic products of the nuclear reaction are captured in a rare gas solid film that has been deposited on a cryogenically cooled transparent substrate. Once captured, the product atoms undergo resonant laser excitation and the emitted fluorescence light is optically imaged onto a sensitive CCD camera, at which point the product atoms can be individually counted. Single atom sensitivity is feasible due to the rare gas lattice surrounding the product atoms, which facilitates a large wavelength shift between the product atoms’ excitation and emission spectra as large as hundreds of nanometers. This detection scheme offers high efficiency, atomic selectivity, and most importantly is not sensitive to traditional sources of background. A prototype Single Atom Microscope has been assembled and an update on its’ testing and development will be presented, along with current status and future plans. |
Tuesday, April 16, 2019 11:45AM - 11:57AM |
X12.00006: A single fluid bubble chamber for measuring nuclear reaction rates of astrophysical importance. David Neto, Kevin Bailey, Jay F Benesch, Brandi Cade, Brad DiGiovine, Joseph M Grames, Alicia Hofler, Roy Holt, Reza Kazimi, Dave Meekins, Daniel Moser, Mathew Poelker, Tom O'Connor, Karl E Rehm, Seamus P Riordan, Riad S Suleiman, Rashi Talwar, Claudio Ugalde, Mike McCaughan Radiative capture reactions, such as (α,γ), (p,γ) and (n,γ), are of fundamental importance to the study of nucleosynthesis of elements in stellar cores, supernovae, etc. In the laboratory, these reactions are usually measured by bombarding gas targets or very thin films with particle beams. The low density of these targets and the sensitivity to background from environmental and cosmic sources can lead to long running times. In this contribution we explain a method - using a single fluid bubble chamber to measure nuclear reaction cross sections. The higher density of the fluid and measuring the time-reversed reaction increases the luminosity of the experiment by several orders of magnitude. We have measured the cross section of the photodisintegration process 19F(γ,α)15N by bombarding a superheated fluid of C3F8 with Bremsstrahlung γ rays produced from the electron injector at Jefferson Laboratory reaching cross sections of the time-reversed 15N(α,γ)19F reaction of about 80 picobarn. |
Tuesday, April 16, 2019 11:57AM - 12:09PM |
X12.00007: Measurement of 16O(e,e'α)12C: a new way to determine the 12C(α,γ)16O reaction rate at stellar energies Ivica Friščić The large uncertainty in the rate of the 12C(α,γ)16O reaction is the largest source of uncertainty in any stellar evolution model. With development of new high current energy-recovery linear accelerators (ERLs) and high density gas targets, measurement of the 16O(e,e'α)12C reaction close to threshold opens up a new approach to determine the 12C(α,γ)16O reaction rate with increased precision. The presentation will summarize a detailed study of this new approach and outline a conceptual experiment. Using direct reaction data and some realistic assumptions, the estimated statistical uncertainties in the low energy region will be shown, as well as the systematic uncertainty arising from the isotopic and chemical contamination in the oxygen gas. |
Tuesday, April 16, 2019 12:09PM - 12:21PM |
X12.00008: Investigating the impact of reaction rate uncertainties on Ti-44 and Ni-56 production in shock driven nucleosynthesis of core-collapse supernovae Shiv K Subedi, Zachary P Meisel, Grant Merz Recent observational advances have enabled high resolution mapping of Ti-44 in core-collapse supernova (CCSN) remnants. Comparisons between observations and 3D models provide stringent constraints on the CCSN mechanism. However, recent work has identified several uncertain nuclear reaction rates that influence Ti-44 and Ni-56 production in model calculations. We use MESA (Modules for Experiments in Stellar Astrophysics) as a tool to investigate the previously identified sensitivities of Ti-44 and Ni-56 production in CCSN to varied reaction rates. MESA is a code for modeling stellar evolution and stellar explosions in one-dimension. We will present our final results of the sensitivity study and our plans to reduce or remove uncertainties from the most significant reaction rates using direct and indirect measurement techniques at the Edwards Accelerator Lab at Ohio University.
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