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 ED: Nuclear Astrophysics II |
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Chair: Dwaipayan Ray, U. Manitoba Room: The Loft |
Tuesday, October 12, 2021 11:45AM - 11:57AM Not Participating |
ED.00001: Abstract Withdrawn
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Tuesday, October 12, 2021 11:57AM - 12:09PM |
ED.00002: The 19F(p,γ)20Ne and 19F(p,α)16O reaction rates and their effect on Calcium production in Population III stars from hot CNO breakout Richard J deBoer, Ondrea Clarkson, Aaron J Couture, Joachim Goerres, Falk Herwig, Ivano Lombardo, Phillip Scholz, Michael C F Wiescher First generation, or Population III, stars have a different evolution than those of later generations owing to their initial primordial abundance composition. Most notably, the lack of carbon, oxygen, and nitrogen, means that primordial massive stars must rely on the less efficient pp chains, thereby requiring the star to contract to reach temperatures high enough to eventually trigger 3α-reactions. Even when small amounts of the 12C(α,γ)16O reactions begin to feed the CNO mass range and enable the CNO cycle to generate energy, this occurs at higher temperatures compared to later stellar generations. It is currently controversial if the observed enhanced abundances of Ca in the most metal-poorstars could be a result of the high temperature H-burning conditions in the first massive stars. The level of this enrichment depends on the hot breakout path from the CNO cycles via the 19F(p,γ)20Ne reaction. In this work, the rates of both the 19F(p,γ)20Ne and competing 19F(p,α)16O reactions are re-evaluated using phenomenological R-matrix, simultaneously considering several 19F(p,γ)20Ne, 19F(p,α)16O, and 19F(p,p)19F data sets, in order to better characterize the rate uncertainties. It is found that the rate uncertainty for 19F(p,γ)20Ne reaction is considerably larger than previously reported. This is the result of undetermined interferences between observed resonances, a possible threshold state, possible subthreshold states, direct capture, and higher lying resonances. Additional experimental measurements are therefore needed to determine if 19F(p,γ)20Ne CNO breakout is responsible for Ca enrichment in metal poor stars. |
Tuesday, October 12, 2021 12:09PM - 12:21PM |
ED.00003: Measurement of the low energy resonances in $^{22}\rm{Ne}(\alpha,\gamma)^{26}\rm{Mg}$ reaction Shahina Shahina, Michael C F Wiescher, Daniel Robertson, Joachim Goerres, Anna Simon, Edward J Stech, Manoel Couder, Frank Strieder, Philipp Scholz, Orlando Gomez, Rebeka Kelmar, Alexander C Dombos, August Gula, Thomas Kadlecek, Mark Hanhardt ${^{13}\rmC(a,n)^{16}\rmO}$ and $^{22}\rm{Ne}(\alpha,n)^{25}\rm{Mg}$ are considered the two important neutron sources for the s-process, but there is still uncertainty about the total available neutron flux for the s-process. ${^{13}\rmC(a,n)^{16}\rmO}$ determines the neutron production in AGB stars while $^{22}\rm{Ne}(\alpha,n)^{25}\rm{Mg}$, which occurs during core helium and carbon shell burning, acts as the primary neutron source in massive stars. But the $\Nean$ reaction has a negative Q-value $= -478\pm 0.05$ keV and hence operates only at high temperatures, e.g., the peak of helium burning, and during C-shell burning (if sufficient $^{22}\rm{Ne}$ is available). Moreover, the neutron-producing role of $^{22}\rm{Ne}(\alpha,n)^{25}\rm{Mg}$ is complicated by the competing $^{22}\rm{Ne}(\alpha,\gamma)^{26}\rm{Mg}$ reaction, which has a positive Q-value $=10614.74\pm 0.03$ keV and therefore starts operating at relatively lower temperatures, before $^{22}\rm{Ne}(\alpha,n)^{25}\rm{Mg}$ can kick in. Hence it is important to investigate the reaction rate of $^{22}\rm{Ne}(\alpha,\gamma)^{26}\rm{Mg}$ in order to put quantitative constraints on the neutron production for the weak s-process. It was experimentally observed by the direct measurements that the reaction rate for $^{22}\rm{Ne}(\alpha,\gamma)^{26}\rm{Mg}$ is strongly impacted by the low energy resonance at $\rmE_{\alpha}$(lab) = 828 keV, but the recent indirect measurements show that the resonance at $\rmE_{\alpha}$(lab) = 653 keV can appreciably impact the $^{22}\rm{Ne}(\alpha,\gamma)^{26}\rm{Mg}$ reaction rate. The measurement of both these resonances was performed at Sanford Underground Research facility (SURF), CASPAR. Preliminary analysis of the resonance strengths for these two resonances will be presented. |
Tuesday, October 12, 2021 12:21PM - 12:33PM |
ED.00004: Measurement of low-energy resonances in the 22Ne(α,n)25Mg Reaction Thomas Kadlecek, Frank Strieder, Daniel Robertson, Orlando J Olivas-Gomez, Rebeka Kelmar, Mark Hanhardt, Manoel Couder, Michael C F Wiescher The 22Ne(α,n)25Mg reaction is a key neutron source for the slow neutron-capture process. The reaction rate at stellar energies is most likely dominated by a resonance at 832 keV. Due to low resonance strengths at lower energies only upper limits have been previously determined for resonances below 832 keV. Recent measurements were completed for the strengths of resonances at 832 keV and below. These measurements utilized the Compact Accelerator System for Performing Astrophysical Research (CASPAR), located on the 4850-feet level of the Sanford Underground Research Facility (SURF). |
Tuesday, October 12, 2021 12:33PM - 12:45PM |
ED.00005: Using MUlti-Sampling Ionization Chamber (MUSIC) for a direct measurement of the 22Mg(α,p)25Al reaction Heshani Jayatissa, Melina Avila, Tan Ahn, Calem R Hoffman, Johnson Liang, Zachary P Meisel, Wei Jia Ong, Karl E Rehm, Daniel Santiago-Gonzalez, Tsz Leung Tang, Gemma L Wilson, Claus Muller-Gatermann, Jie Chen, David Neto, Claudio Ugalde, Athanasios * Psaltis Type I X-ray burst (XRB) nucleosynthesis involves processes such as the triple-α reaction, the rp-process, and the (α,p) process. The dominant (p,γ) nucleosynthesis flow in XRBs halts at several waiting point nuclei such as 22Mg, 24-26Si, 28-30S and 34Ar due to (p,γ)-(γ,p) equilibrium. The XRB nucleosynthesis flow can bypass these waiting points via (α,p) reactions. However, the present uncertainties in the relevant (α,p) reaction rates at these waiting points hinder the ability to accurately predict the light curve and ash composition of XRBs. For these waiting point nuclei, the 22Mg(α,p)25Al reaction has been identified as an important reaction bypassing the waiting points for XRB nucleosynthesis. Thus, it is crucial to constrain the reaction rate of the 22Mg(α,p)25Al reaction at astrophysical energies. To this end, we have performed a direct measurement of the 22Mg(α,p)25Al reaction cross section in inverse kinematics using a 22Mg beam from the RAdioactive Ion SeparatOR (RAISOR) and the MUlti-Sampling Ionization Chamber (MUSIC) at Argonne National Laboratory. Preliminary results from this measurement will be discussed. |
Tuesday, October 12, 2021 12:45PM - 12:57PM |
ED.00006: Studying Sodium Production in Globular Clusters via the 23Na(3He,d)24Mg Reaction Caleb A Marshall, Kiana Setoodehnia, John H Kelly, Federico E Portillo Chaves, Giulia Cinquegrana, Amanda Karakas, Richard Longland Globular clusters are dense, gravitationally bound collections of hundreds of thousands of stars. Our theories of stellar evolution, at the present time, cannot account for the observed anticorrelation between sodium and oxygen in cluster stars. While the astrophysical site of these so called abundance anomalies is still unknown, this chemical signature indicates the in situ processing of |
Tuesday, October 12, 2021 12:57PM - 1:09PM |
ED.00007: Measurement of the $^{18}$O($\alpha$,n)$^{21}$Ne reaction for nuclear astrophysics. Rebecca Toomey, Michael T Febbraro, Richard J deBoer, Gwenaelle Gilardy, Harrison E Sims, Steven D Pain, August Gula, Luis A Morales, Sebastian Aguilar, Samuel L Henderson, Aaron J Couture The formation of supernova carbonaceous dust is thought to originate from the inner He-rich zones of massive stars. We can study the isotopic abundances of these presolar grains to gain insight into explosive stellar nucleosynthesis. Analysis of presolar grains from the Orgueil meteorite found that $^{18}$O had an isotopic enrichment of up to 98,000% over terrestrial abundance, in addition to high spatial correlation with hotspots of $^{15}$N. A potential cause of this is that during explosive He-shell burning, the bulk of neutrons required for $^{15}$N production are sourced from the $^{18}$O($\alpha$,n)$^{21}$Ne reaction. Previous measurements of this reaction, performed almost 60 years ago, have varying levels of uncertainty and contain no branching ratio or partial cross section information. To address this, a high-resolution study of the $^{18}$O($\alpha$,n)$^{21}$Ne reaction was conducted at the University of Notre Dame over the energy range E$_{\alpha}$ = 2-8 MeV. Outgoing neutrons from this reaction were detected with ODeSA and secondary gamma rays were detected with 2 HPGe detectors from the LANL GEANIE array. Preliminary partial differential cross sections and neutron angular distributions will be presented. |
Tuesday, October 12, 2021 1:09PM - 1:21PM |
ED.00008: Fusion cross-section measurements in the Ne-Mg region to constrain pycnonuclear burning in the neutron star crust Jaspreet S Randhawa, Tan Ahn, Dan W Bardayan, James J Kolata, Patrick D O'Malley Pycnonuclear reactions occur in a highly dense matter when nuclei are frozen in lattice structures. One such site is the crust of accreting neutron stars where the pycnonuclear reactions serve as an important heat source. Various studies have shown that the fusion of neutron-rich isotopes of Ne and Mg are most important among the pycnonuclear reactions in neutron star crusts. In the absence of any data on these fusion reaction cross-sections, theoretical cross-sections remain highly uncertain. A program has been initiated at the University of Notre Dame to measure the fusion cross-sections in the Ne-Mg region using the Notre Dame (ND)-Cube, a newly commissioned active-target Time Projection Chamber (TPC). We will discuss the use of Ne-based gas mixtures as a target gas where the high gain has been achieved using the thick gas electron multipliers. Preliminary results from the first study of 20Ne+24Mg fusion cross-sections will be discussed. These measurements demonstrate the capabilities of TPCs as a highly efficient system to measure cross-sections below the fusion barrier and therefore provide a stringent test of theoretical model predictions. Future plans to measure the fusion cross-sections along the neon isotopic chain will be discussed. |
Tuesday, October 12, 2021 1:21PM - 1:33PM |
ED.00009: Abstract Withdrawn |
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