Bulletin of the American Physical Society
Fall 2022 Meeting of the APS Division of Nuclear Physics
Volume 67, Number 17
Thursday–Sunday, October 27–30, 2022; Time Zone: Central Daylight Time, USA; New Orleans, Louisiana
Session EE: Nuclear Astrophysics II |
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Chair: Philip Adsley, Texas A&M University Room: Hyatt Regency Hotel Celestin C |
Friday, October 28, 2022 10:30AM - 10:42AM |
EE.00001: Reaction Networks as a Many-Body Problem Sayani Ghosh, Bradley S Meyer States or species and the reactions among them make up a reaction network. In the network, the abundances of species or the probabilities of states can be tracked as the reactions evolve in time by standard numerical techniques. In this work we look at a reaction network as a many body problem. The states or species make up this multi-level system and the energies are calculated from the branchings of a directed graph. The edges of the graph are reaction rates and the vertices are the states or species. We think of this problem in terms of the Matrix Forest Theorem where the constraints on the rate matrix are interpreted in terms of matrix minors. This approach allows us to compute an energy spectrum for the network, and we are able to understand the evolution of the network as transitions among different levels in the spectrum. We apply this approach to understand network equilibrium, dynamic equilibrium, quasi-static equilibrium, and reaction freeze out, especially in nucleosynthetic systems in stellar environments. Our approach can help clarify the governing role of particular reactions in element formation processes. |
Friday, October 28, 2022 10:42AM - 10:54AM |
EE.00002: Extrapolating Mixture Density Network predictions: application to the astrophysical r-process Mengke Li, Matthew R Mumpower, Trevor M Sprouse, Amy E Lovell, Arvind Mohan, Bradley S Meyer Understanding the origin of elements in our Universe is one of the outstanding questions in science. The astrophysical rapid neutron capture process (r-process) is believed to be responsible for creating half of the heavy isotopes up to bismuth and all of thorium and uranium. In modeling the r-process, masses are used as a basis for nuclear input for the network calculations. In previous studies, the relation between the r-process abundance and the mass model has been investigated, and it was found that different mass models have strong influences on the calculated abundance pattern. However, the uncertainty of the calculated r-process abundance either comes from different mass models or arises from varying individual masses within the same range. Here, we use a sophisticated Machine Learning based mass model utilizing the probabilistic Mixture Density Network (MDN) to predict masses. This method accurately predicts the masses with root mean square around 300 keV and also provides quantified uncertainties of each mass. We simulate the r-process abundance pattern that arise from the application of our MDN mass model. The MDN model encodes complex correlations among nuclei, so we use this information to estimate abundance uncertainties. |
Friday, October 28, 2022 10:54AM - 11:06AM |
EE.00003: Radiative decay branching ratio of Hoyle state in 12C Zifeng Luo, Grigory V Rogachev, Marina Barbui, Jack E Bishop, Grigor Chubaryan, Vladilen Z Goldberg, Emily Harris, Heshani Jayatissa, Evgeniy Koshchiy, Michael J Roosa, Antti Saastamoinen, Dustin P Scriven The triple-alpha process is one of the most important reactions in nuclear astrophysics. It is a sequence of two reactions a) α+α →8Be(g.s.) and b) 8Be+α ⇔ γ+12C leading to the production of carbon. The second reaction proceeds through a special excited 0+ state at 7.65 MeV excitation energy in 12C, the so-called Hoyle state. The reaction rate of the triple-alpha process is proportional to ΓαΓrad/(Γα+Γrad) ≈ Γrad since Γα≫Γrad. One way to establish the Γrad is to measure the branching ratio for electromagnetic decay and utilize the known partial width Γπ (E0) for the electron-positron pair production. Recent measurement of branching ratio for electromagnetic decay is more than 3σ away from the adopted value. Our work is to verify the result by measuring the total radiative decay branching ratio of Hoyle state in 12C. |
Friday, October 28, 2022 11:06AM - 11:18AM |
EE.00004: Successful νp-process in neutrino-driven outflows in core-collapse supernovae Amol V Patwardhan, Alexander Friedland, Payel Mukhopadhyay The origin of the relatively high solar system abundances of certain proton-rich isotopes in the 9092,94Mo and 96,98Ru, as a well as to predict the correct abundance ratios of these isotopes to other p-nuclides. These difficulties became more dire with the recent calculations that took into account in-medium effects enhancing the rate of the triple-α reaction. Here, we revisit the problem and present explicit examples of calculations, with 13 and 18 M⊙ progenitor masses, in which both the required absolute yields of the Mo and Ru p-nuclides and the observed isotopic ratios are successfully reproduced, even with the enhanced triple-α rates taken into account. The models are characterized by entropy-per-baryon values in the 80-to-90 range and by subsonic outflow profiles. Optimal conditions for the νp-process are reached at different post-bounce times for different progenitor masses, but always within the first 2-3 seconds after the start of the explosion. To obtain the required entropy values at this stage of the explosion---given the available nuclear equations of state---requires a relatively heavy PNS. This suggests that the Mo and Ru p-nuclides observed in the Solar System were made in CCSN explosions characterized by an extended accretion stage. At the same time, the νp-process yields are found to vary significantly with the PNS mass and with the outflow character. |
Friday, October 28, 2022 11:18AM - 11:30AM |
EE.00005: Testing the Effects of Astrophysical Reaction Rate Libraries on Stellar Models John E Pedersen, Amber C Lauer-Coles The proper modeling of many astrophysical processes require a thorough understanding of the nuclear reactions that govern them. In particular, the rate at which these reactions proceed is critical to accurate modeling. Reaction rates have been formulated both through experimental measures and theoretical calculations. Along with the nuclear network that describes how each isotope interacts with each other, they form the basis for necessary calculations the model must run. In an attempt to store all the individual reaction rates in one place, and to keep them up to date, several different libraries have been created. These databases are independent efforts that lack standard practices between them and ongoing stewardship of the database. The goal of this project is to highlight the variation in results when using different reaction rate libraries, illustrating the need for cooperation. Computationally robust stellar models of X-Ray Bursts will be run in Modules for Experiments in Stellar Astrophysics (MESA), which blends the reaction rate libraries into the models itself. Several astrophysical variables of interest, such as isotope abundance and features of the light curve, will be analyzed for each model using varying reaction rate libraries. Any inconsistency in results will be discussed along with suggestions for unified efforts with the intent to establish a standard for compiling astrophysical reaction rates. |
Friday, October 28, 2022 11:30AM - 11:42AM |
EE.00006: Isobar-analogue reactions 6Li(p,γ)7Be and 6Li(n,γ)7Li relevant to the 6Li/7Li ratio Alessya S Tkachenko, Nataliya A Burkova, Sergey B Dubovichenko, Roman Y Kezerashvili In the framework of the modified potential cluster model with forbidden states formulated in [1] the isobar-analogue 6Li(p,γ)7Be and 6Li(n,γ)7Li reactions in the temperature range from 0.01 to 10 T9 are studied. While the dominant sources that determine the 6Li/7Li ratio are 4He(d,γ)6Li and 4He(t,γ)7Li processes, a qualitative feature of the reactions of radiative capture of neutrons 6Li(n,γ)7Li and protons 6Li(p,γ)7Be(e-ν)7Li can lead to a redistribution of lithium isotopes in the 6Li/7Li balance. These reactions are included in the calculations of the mass fractions as “destructive” for the 6Li isotope. The contribution of the isobar-analogue 6Li(p,γ)7Be and 6Li(n,γ)7Li reactions into the 6Li/7Li balance is estimated from the corresponding rates of these processes, the astrophysical S-factor for 6Li(p,γ)7Be is calculated and compared with the available experimental data and calculations done within different models. Cross-sections for 6Li(p,γ)7Be and 6Li(n,γ)7Li calculated using [1] are in reasonable agreement with experimental data. |
Friday, October 28, 2022 11:42AM - 11:54AM |
EE.00007: Can a nearby supernova explain the 10Be excess in the Early Solar System? Jaspreet Randhawa, Andre Sieverding, D. Zetterberg, Richard J deBoer, Tan Ahn, R. Mancino, Gabriel Martinez-Pinedo, William R Hix Excess of 10Be in the meteorites has mostly been studied in the context of non-thermal, in-situ nucleosynthesis due to cosmic rays or Solar energetic particles from Sun in its early phase. Recently, a low mass core-collapse supernova has been postulated as a possible source of 10Be. However, in CCSNe a major uncertainty for the production of 10Be in CCSNe is the 10Be(p,α)7Li reaction rate. We will show that a newly found resonance state in 11B (Er ~ 190 keV) is the single-most important state in the Gamow window which increases the reaction rate by many orders of magnitude. As the new reaction rate decreases the 10Be yield, we will show that low mass CCSN is unlikely to produce enough 10Be to explain the observed excess in meteorites. Remaining uncertainties in 10Be(p,α)7Li reaction rate and experimental plans to further constrain this reaction rate will be discussed. |
Friday, October 28, 2022 11:54AM - 12:06PM |
EE.00008: Measurements of 12C+12C fusion reaction at Notre Dame Wanpeng Tan, Orlando Gomez, August Gula, Kevin Lee, Ashabari Majumdar, Shane Moylan, Shahina Shahina, Michael C F Wiescher, Eli F Aguilera, David Lizcano, Enrique Martinez-Quiroz, Juan Morales-Rivera Carbon and oxygen burning reactions, in particular, 12C+12C, are believed to be important for late stellar burning phases. The strength of these fusion reactions could also determine the ignition, burning, and nucleosynthesis pattern in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. Various experimental work and developments related to measurement of these reaction rates have been carried out at University of Notre Dame. In particular, 12C+12C and 12C+16O fusion experiments with SAND (a silicon detector array) have been conducted at the high-intensity St. ANA accelerator with particle-gamma coincidence and differential target techniques. New results of 12C+12C cross sections at low energies relevant to nuclear astrophysics will be reported and compared with other recent measurements using different approaches. Its impact on the carbon burning process under astrophysical scenarios will be discussed as well. |
Friday, October 28, 2022 12:06PM - 12:18PM |
EE.00009: Measurement of Near-Threshold Resonances in 9B for Big Bang Nucleosynthesis Gordon W McCann, Ingo Wiedenhoever, Lagy T Baby, Jeffery C Blackmon, William D Braverman, Keilah Davis, Catherine M Deibel, Juan C Esparza, Kenneth G Hanselman, Kevin T Macon, David He, Rachel M Shaffer, Scott T Marley, Khang H Pham, Vignesh Sitaraman, Balakrishnan Sudarsan, Eli S Temanson, Gemma L Wilson The Primordial Lithium Problem remains one of the largest discrepancies between calculation and observation for Standard Big Bang Nucleosynthesis (SBBN), where the calculated value of the 7Li abundance is a factor of 3-4 times larger than the observed value. To alleviate this tension, nuclear reactions which could potentially destroy mass-7 nuclei must be investigated. Of particular interest is the reaction 7Be+d→2α+p; resonances in the 9B compound near the deuteron threshold have been the subject of some investigation. Recent measurements using the Super Enge Split-Pole Spectrograph (SESPS) and the Silicon Array for Branching Ratio Experiments (SABRE) at Florida State University, a potential resonance in 10B(3He, α)9B→7Be+d was identified at even lower resonance energy than the previously known 16.8 MeV resonance in 9B. Subsequently, a repeat investigation with additional emphasis on the p+8Be branch was performed to further investigate this structure. Results and impact on SBBN will be discussed. |
Friday, October 28, 2022 12:18PM - 12:30PM |
EE.00010: Direct measurement of the low energy resonances in 22Ne(α,γ)26Mg reaction Shahina Shahina, Daniel Robertson, Manoel Couder, Orlando Gomez, August Gula, Mark Hanhardt, Thomas Kadlecek, Rebeka Kelmar, Philipp Scholz, Anna Simon, Edward Stech, Frank Strieder, Michael C F Wiescher, Joachim Goerres The 22Ne(α,γ)26Mg is an important reaction in stellar helium-burning environments as it competes directly with one of the main neutron sources for the s-process, the 22Ne(α,n)25Mgreaction. The reaction rate of the 22Ne(α,γ)26Mg is dominated by the low energy resonances at Eαlab = 650 and 830 keV respectively. The Eαlab = 830 keV resonance has been measured previously, but there are some uncertainties in the previous measurements. We confirmed the measurement of the Eαlab = 830 keV resonance using implanted 22Ne targets and obtained a resonance strength of ωγ = 35 ± 4 μeV, and provide a weighted average of the present and previous measurements of ωγ = 35 ± 2 μeV with reduced uncertainties. We also attempted to measure the strength of the predicted resonance at Eαlab = 650 keV directly for the first time and found an upper limit of ωγ < 0.1 μeV for the strength of this resonance. In addition, we also measured the Eplab = 851 keV resonance in 22Ne(p,γ)23Na, and obtained a resonance strength of ωγ = 9.2 ± 0.7 eV with significantly lower uncertainties compared to previous measurements. |
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