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1. Nuclear Reactions in Astrophysics: A Review of Useful Probes for Extracting Reaction Rates

   https://doi.org/10.1146/annurev-nucl-020620-063734  

   Nunes, F.M. ; Potel, G. ; Poxon-Pearson, T. ; Cizewski, J.A. ( October 2020 , Annual Review of Nuclear and Particle Science)

   null (Ed.)

   Astrophysical simulations require knowledge of a wide array of reaction rates. For a number of reasons, many of these reaction rates cannot be measured directly and instead are probed with indirect nuclear reactions. We review the current state of the art regarding the techniques used to extract reaction information that is relevant to describe stars, including their explosions and collisions. We focus on the theoretical developments over the last decade that have had an impact on the connection between the laboratory indirect measurement and the astrophysical desired reaction. This review includes three major probes that have been, and will continue to be, widely used in our community: transfer reactions, breakup reactions, and charge-exchange reactions. 

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2. Experiments probing clustering effects in explosive nucleosynthesis

   https://doi.org/10.3389/fphy.2023.1123868  

   Bardayan, D. W. ( February 2023 , Frontiers in Physics)

   Nuclear clustering affects the nucleosynthesis occurring in a number of astrophysical environments. Highly-clusterized nuclear states typically occur near particle thresholds and therefore can produce dramatic impacts on the nuclear reaction rates. This is especially true for astrophysical explosions that are driven by the consumption of helium as fuel. Such burning can occur in X-ray bursts, supernovae type Ia, and core-collapse supernovae for instance. This article will focus on the explosive astrophysical events in which nuclear clustering is most important, will discuss the types of information and tools necessary to estimate the astrophysical reaction rates, and will discuss example experiments at Notre Dame and other facilities that have or will be performed to measure the critical nuclear data needed for such estimates. 

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3. Constraining Nucleosynthesis in Neutrino-driven Winds: Observations, Simulations, and Nuclear Physics

   https://doi.org/10.3847/1538-4357/ac7da7  

   Psaltis, A. ; Arcones, A. ; Montes, F. ; Mohr, P. ; Hansen, C. J. ; Jacobi, M. ; Schatz, H. ( August 2022 , The Astrophysical Journal)

   Abstract A promising astrophysical site to produce the lighter heavy elements of the first r -process peak ( Z = 38 − 47) is the moderately neutron-rich (0.4 < Y e < 0.5) neutrino-driven ejecta of explosive environments, such as core-collapse supernovae and neutron star mergers, where the weak r -process operates. This nucleosynthesis exhibits uncertainties from the absence of experimental data from ( α , xn ) reactions on neutron-rich nuclei, which are currently based on statistical model estimates. In this work, we report on a new study of the nuclear reaction impact using a Monte Carlo approach and improved ( α , xn ) rates based on the Atomki-V2 α optical model potential. We compare our results with observations from an up-to-date list of metal-poor stars with [Fe/H] < −1.5 to find conditions of the neutrino-driven wind where the lighter heavy elements can be synthesized. We identified a list of ( α , xn ) reaction rates that affect key elemental ratios in different astrophysical conditions. Our study aims to motivate more nuclear physics experiments on ( α , xn ) reactions using the current and new generation of radioactive beam facilities and also more observational studies of metal-poor stars. 

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4. An Improved Method for Coupling Hydrodynamics with Astrophysical Reaction Networks

   https://doi.org/10.3847/1538-4357/ac8478  

   Zingale, M. ; Katz, M. P. ; Nonaka, A. ; Rasmussen, M. ( August 2022 , The Astrophysical Journal)

   Abstract Reacting astrophysical flows can be challenging to model, because of the difficulty in accurately coupling hydrodynamics and reactions. This can be particularly acute during explosive burning or at high temperatures where nuclear statistical equilibrium is established. We develop a new approach, based on the ideas of spectral deferred corrections (SDC) coupling of explicit hydrodynamics and stiff reaction sources as an alternative to operator splitting, that is simpler than the more comprehensive SDC approach we demonstrated previously. We apply the new method to a double-detonation problem with a moderately sized astrophysical nuclear reaction network and explore the time step size and reaction network tolerances, to show that the simplified-SDC approach provides improved coupling with decreased computational expense compared to traditional Strang operator splitting. This is all done in the framework of the Castro hydrodynamics code, and all algorithm implementations are freely available. 

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5. Nucleosynthesis of "Light" Heavy Nuclei in Neutrino-driven Winds. Role of ( α,n ) reactions

   https://doi.org/10.1088/1742-6596/1668/1/012033  

   Pereira, J. ; Arcones, A. ; Bliss, J. ; Montes, F. ( January 2020 , ArXivorg)

   Neutrino-driven winds following core collapse supernovae have been proposed as a suitable site where the so-called light heavy elements (between Sr to Ag) can be synthetized. For moderately neutron-rich winds, ( α,n ) reactions play a critical role in the weak r process, becoming the main mechanism to drive nuclear matter towards heavier elements. In this paper we summarize the sensitivity of network-calculated abundances to the astrophysical conditions, and to uncertainties in the ( α,n ) reaction rates. A list of few ( α,n ) reactions were identified to dominate the uncertainty in the calculated elemental abundances. Measurements of these reactions will allow to identify the astrophysical conditions of the weak r process by comparing calculated/observed abundances in r-limited stars. 

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