Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session MD: Nuclear Astrophysics VII |
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Chair: Kay Kolos, LLNL Room: The Loft |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MD.00001: Abstract Withdrawn
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Wednesday, October 13, 2021 4:12PM - 4:24PM |
MD.00002: Precision mass measurements of neutron-rich nuclides using the Canadian Penning Trap mass spectrometer for studying the astrophysical r process Dwaipayan Ray, Guy Savard, Jason A Clark, Rodney Orford, Kumar S Sharma, Adrian A Valverde, Maxime Brodeur, Daniel P Burdette, Nathan Callahan, Biying Liu, Scott T Marley, Graeme Morgan, Louis Varriano, Gemma L Wilson, Xinliang L Yan The formation of about half of the nuclides with Z>26 is attributed to the astrophysical r process, of which our knowledge is still limited. Building models to reproduce the r-process elemental abundances relies on nuclear data with reduced uncertainties for these neutron-rich nuclides. Such data exist in limited quantity due to the difficulties in accessing those nuclides. Masses are an important input to such models. The CARIBU facility, at Argonne National Laboratory can produce beams of such neutron-rich nuclides using the spontaneous fission of a 252Cf source. The fragments are collected, cooled, bunched and purified, before being sent to the Canadian Penning Trap (CPT) mass spectrometer, where their masses are measured using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique. PI-ICR at the CPT has permitted mass measurements of long-lived isomers as well as weakly-produced nuclides from 252Cf fission, while regularly achieving precision of <5 keV/c2. A brief description of the apparatus and recent results will be presented. |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MD.00003: Experimental investigations of the (a,xn) reactions relevant for the r-process nucleosynthesis. Nabin Rijal, Fernando Montes, Sunghoon Ahn, Hendrik Schatz, Zachary P Meisel, Cody E Parker The fast-expanding neutron-rich neutrino-driven winds in the core-collapse supernovae are favorable scenarios for the nucleosynthesis of the light-heavy elements. Charge particle reactions, especially (a,xn), create seeds for the weak r-process populating abundances of near stable isotopes for the Sr-Ag range, for which there remains a large discrepancy between observed and predicted elemental abundances in the metal-poor halo stars. These abundances are significantly sensitive to the (a,xn) reaction rates. Only very few of these reactions had been measured in the energy range relevant for weak r-process astrophysical conditions. Theoretical calculations of reaction rates for such scenarios are very uncertain and model-dependent. In this talk, I will discuss three experiments that measured cross-sections of 85Br(a,xn),75Ga(a,xn), and 85Rb(a,xn) reactions using the HabaNERO detector at ReA3, NSCL, along with future possibilities at FRIB to measure and constrain other important (a,xn) reactions relevant for the r-process astrophysical conditions. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MD.00004: 82Se(d,pγ) with GODDESS for weak r-process nucleosynthesis Harrison E Sims, Jolie A Cizewski, Steven D Pain, Andrew Ratkiewicz The mass 80 peak of the r-process abundance pattern is believed to be the product of multiple possible astrophysical environments. Among these is a possible weak r-process that could occur in hot (~1GK) environments such as core-collapse supernovae. Neutron-capture rates on Se isotopes have been identified by Surman et al. [1] to have significant impact on final calculated abundance patterns. Stable 82Se lies between the 81 and 83 Se isotopes, which have significant impact on final abundances. However, the evaluated 82Se(n,γ) cross sections are inconsistent. Due to the close proximity to the N=50 shell closure, neutron-capture on 82Se probably proceeds via both direct and a compound nucleus (CN) processes. Direct-capture contributions can be deduced from spectroscopic factors of low-lying states in 83Se. To inform capture via a CN, the (d,pγ) reaction has recently be validated as surrogate for (n,γ) by Ratkiewicz et al [2]. To inform the competition between direct and compound nucleus (n,γ) processes near the weak r-process path, the (d,pγ) reaction was measured with GODDESS using 82Se beams from the ATLAS facility at ANL. Preliminary results will be presented. |
Wednesday, October 13, 2021 4:48PM - 5:00PM |
MD.00005: A new apparatus for indirect neutron capture measurements at LANSCE Athanasios Stamatopoulos, Paul E Koehler, Evelyn M Bond, Todd A Bredeweg, Aaron J Couture, Brad J DiGiovine, Michael E Fassbender, Anna C Hayes-Sterbenz, August L Keksis, Artem Matyskin, Donald K Parsons, Gencho Y Rusev, John L Ullmann, Cristian Vermeulen Direct measurements of radiative neutron capture rates for radionuclides at temperatures relevant to astrophysics can be extremely challenging. Therefore, indirect methods have been pursued and substantial effort has been devoted to quantifying systematic errors associated with these techniques. The Device for Indirect Capture Experiments on Radionuclides (DICER), a new apparatus that is being developed at the Los Alamos Neutron Science Center (LANSCE), explores the possibility of determining capture rates through the analysis of transmission data at the resolved resonance region. DICER and associated radionuclide production at the Isotope Production Facility (IPF), both at LANSCE, have been under development the last few years leading to the first measurement on a radioactive sample (88Zr, t1/2=83.4 days), which is planned for the summer of 2021. A description of the device and associated efforts will be discussed. |
Wednesday, October 13, 2021 5:00PM - 5:12PM |
MD.00006: Abstract Withdrawn
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Wednesday, October 13, 2021 5:12PM - 5:24PM |
MD.00007: Determining the 95Zr(n, γ) and 93Zr(n, γ) cross sections via 96Zr(p, p’) and 94Zr(p, p’) surrogate reactions Barbara S Wang, Craig S Reingold, Jason T Harke, Richard O Hughes, Jutta E Escher, Reto Trappitsch, Sean P Burcher, Emanuel V Chimanski, Wei Jia Ong, Michael R Savina, Danielle Z Shulaker, Aaron S Tamashiro, Peter K Weber, Brett H Isselhardt The surrogate-reaction method can improve our understanding of s-process nucleosynthesis. Branch-point nuclei are a crucial feature of the s-process that highly impact the elemental abundances. Knowing the (n, γ) cross sections of these nuclei allows for powerful constraints to be placed on the stellar conditions of the parent stars in which the elements originated. However, a large number of branch-point nuclei have half-lives on the order of months or less, making the use of direct-measurement techniques challenging, if not impossible. An experiment was performed in which the surrogate-reaction method was used to obtain the (n, γ) cross section for 95Zr (64-day half-life), whose branching has been observed in presolar stardust grains. Inelastic proton scattering from the stable isotope 96Zr served as the surrogate. The measurement was carried out at the Texas A&M University K150 Cyclotron. An enriched 96Zr foil was bombarded with 20-MeV protons. Scattered protons and coincident γ rays were measured with the LLNL Hyperion array, which consists of three segmented annular silicon detectors in a dE-E1-E2 configuration surrounded by an array of BGO Compton-suppressed HPGe Clover detectors. A benchmark was also performed using 94Zr(p, p’) to determine the 93Zr(n, γ) cross section, which has been previously measured via direct methods. Details of the experiment and preliminary results will be discussed. |
Wednesday, October 13, 2021 5:24PM - 5:36PM |
MD.00008: r-Process Radioisotopes from Near-Earth Supernovae and Kilonovae Xilu Wang, Adam M Clark, John Ellis, Adrienne Ertel, Brian Fry, Brian D Fields, Zhenghai Liu, Jesse Miller, Rebecca A Surman The astrophysical sites where r-process elements are synthesized remain mysterious: it is clear that neutron-star mergers (kilonovae, KNe) contribute, and some classes of core-collapse supernovae (SNe) are also likely sources of at least the lighter r-process species. The discovery of the live isotope Fe60 on the Earth and Moon over the past decades implies that one or more astrophysical explosions occurred near the Earth (within ~100pc) within the last few Myr, probably a SN. Intriguingly, several groups have reported evidence for deposits of Pu244, some overlapping with the Fe60 pulse, but pointing to a different origin like KNe. Motivated by the Pu244 observations, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble in which the Sun resides. This hypothesis is also consistent with the most recent Pu244 measurements by Wallner et al. (2021). |
Wednesday, October 13, 2021 5:36PM - 5:48PM |
MD.00009: Progress Towards a Single Atom Microscope for Nuclear Astrophysics Erin E White, Jaideep T Singh, Benjamin T Loseth, Roy A Ready, Thu Gibson, Abby Baratta, Keara Hayes The Single Atom Microscope (SAM) project aims to measure rare, low-yield nuclear reactions relevant to nuclear astrophysics. This novel detector technique involves capturing the product atoms in a cryogenically frozen and optically transparent noble gas solid and then counting the embedded atoms via laser-induced fluorescence and optical imaging. Due to the unique absorption and emission wavelengths of the product atoms—enabled by the lattice of noble gas atoms—optical filters can distinguish between them to select the wavelength range of interest, making single-atom sensitivity feasible. Rubidium atoms embedded in solid Krypton are being used for pilot measurements because they are laser-friendly and the system is astrophysically relevant—84Kr(p, γ)85Rb is a key branching point for determining the reaction flow in the p-process. Results from a preliminary experiment indicate that high energy Rb ions fully neutralize in Kr, which means single atom detection of neutral Rb is an appropriate, efficient path for measuring this specific nuclear reaction. Calibrating the brightness of Rb atoms in Kr is the next step towards achieving single atom sensitivity, which will complete the trinity of high efficiency, selectivity, and sensitivity required to measure nuclear reactions in a way that is complementary to other methods. |
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