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 KD: Nuclear Astrophysics V |
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Chair: Alicia Palmisano, UTK Room: The Loft |
Wednesday, October 13, 2021 11:30AM - 11:42AM |
KD.00001: Fission in White Dwarfs as a New Supernova Mechanism I Matthew E Caplan, Charles J Horowitz White dwarf stars cool and eventually begin to crystallize in their cores. The freezing temperature of this Coulomb plasma of ionized nuclei is proportional to Z5/3 (nuclear charge Z) due to the high Coulomb energies, so the first solids that form in a C/O white dwarf may be greatly enriched in actinides. We estimate that the solids may be so enriched in actinides, especially uranium, that they could support a fission chain reaction. This reaction could ignite carbon burning and lead to the explosion of an isolated WD in a thermonuclear supernova (SN Ia). Our mechanism could potentially explain SN Ia with sub-Chandrasekhar ejecta masses and short delay times. |
Wednesday, October 13, 2021 11:42AM - 11:54AM |
KD.00002: Fission in White Dwarfs as a New Supernova Mechanism II Charles J Horowitz, Matthew E Caplan The first solids that form as a white dwarf (WD) starts to crystallize are expected to be greatly enriched in actinides. Previously [PRL 126, 1311010] we found that these solids might support a nuclear fission chain reaction that could ignite carbon burning and provide a new Type Ia supernova (SN Ia) mechanism involving an isolated WD. Here we explore this fission mechanism in more detail and calculate the final temperature and density after the chain reaction and discuss several possibly open physics questions for this mechanism. |
Wednesday, October 13, 2021 11:54AM - 12:06PM |
KD.00003: Quantified Nuclear Mass Model for Nuclear Astrophysics Simulations Rahul Jain, Leo Neufcourt, Witold Nazarewicz, Samuel A Giuliani Nuclear mass is a fundamental property of the nucleus. Nuclear binding energies determine the particle drip lines where the nuclear landscape ends as well as the Q-values of nuclear reactions. As a result, they are a key ingredient in astrophysical models and simulations. We are, however, limited in our ability to experimentally measure the complete mass table and have to rely on theory to carry out extrapolations. Since global mass models are fitted to known experimental data and then used to predict masses over the whole nuclear chart, assessing their uncertainties in regions far from stability is a non-trivial task. This makes it difficult to quantify the impact of the uncertainties of nuclear masses in astrophysical simulations involving exotic nuclei. To overcome this limitation, we present a model-based mass extrapolation technique where we model the binding energy residuals with fully Bayesian Gaussian Process Regression. The statistically corrected predictions obtained from 11 different global nuclear models are then combined via Bayesian model averaging, according to their experimental evidence. This leads us to a quantified mass model providing uncertainties and covariances that can be used for astrophysical modeling and sensitivity studies. |
Wednesday, October 13, 2021 12:06PM - 12:18PM |
KD.00004: Applying machine learning to a Maxwellian-averaged n-capture cross section for improved estimates Amber C Lauer-Coles, David A Brown Neutron-capture cross sections are relevant to many nuclear physics fields. These fields depend on the accuracy of both the existing measurements, as well as estimated values for unmeasured nuclei. For many applications the most relevant nuclear quantities are unmeasured, and will remain so for some time. The result is almost total reliance on estimates, with varying levels of success due to assumptions that, while necessary, might not be supported by the physics. As such, new methods are always of interest. Current methods include diverse theoretical formulations of mass, level density, and neutron separation energy. These often focus on a single nuclear quantity or bulk property (such as mass model), which heavily weights that quantity's importance by default. This work attempts to improve estimates of neutron capture cross sections, especially where few or no measurements exist by applying the predictive capability of machine learning (ML). As the neutron fluence in many applications can be treated as a weighted sum of Maxwellian spectra, we use machine learning to develop a regression model for the temperature dependence of the Maxwellian averaged-cross section, coupled to additional physical quantities where known. The methods and early results will be discussed. |
Wednesday, October 13, 2021 12:18PM - 12:30PM |
KD.00005: Contribution of Collapsars and Hypernovae to the origin and early evolution of heavy element explosive nucleosynthesis Grant J Mathews, Yuta Yamazaki, Hirozaku Sasaki, Motohiko Kusakabe, Toshitaka Kajino In spite of years of effort many aspects of the origin and evolution of heavy elements in nature are yet to be understood. In this talk we will summarize the current status of models for both the formation of r-process nucleosynthesis and the p-process. We describe state-of the art developments of supernova and binary neutron star evolution in both the r-process and p-process nucleosynthesis. In particular, we will highlight the emerging evidence for the important role of hypernovae (energetic supernovae) and collapsars(jets from the collapse of massive stars to a black hole). We highlight how these events may play a key role in the origin and early evolution of explosive heavy-element nucleosynthesis. |
Wednesday, October 13, 2021 12:30PM - 12:42PM |
KD.00006: Corrected Beta-Equilibrium in Neutron Star Mergers Ziyuan Zhang, Mark Alford, Alexander Haber, Steven P Harris In the neutrino-transparent regime of neutron star mergers, where the temperature is about 1 to 10 MeV, the traditional cold beta equilibrium condition is incorrect. We calculate the correction term, which is the isospin chemical potential, and it reaches 20 to 30 MeV, depending on the equation of state. In order to do so, we improve the existing direct Urca rate calculations using a relativistic dispersion relation and compute the full twelve-dimensional phase space integral. |
Wednesday, October 13, 2021 12:42PM - 12:54PM |
KD.00007: Response function for supernova and neutron star crust with chiral effective theory Eunkyoung Shin, Jeremy W Holt, Ermal Rrapaj, Sanjay K Reddy We have been studied dynamic response function in an environment of supernova and static response function for neutron star crust. We use different cutoff energies (414, 450, and 500 MeV) at dynamic response function in chiral effective theory. We use nuclear potential from chiral effective theory with 2N and 3N interaction to describe microscopic nucleon-nucleon interaction in static response function. We check the effect of 2N and 3N force in a variety of densities and transferred momentum from neutrinos to pure neutron matter. We checked 2N interaction is opposite to 3N interaction at low momentum. The effect of 2N and 3N disappeared in high momentum. While q is zero, the effect of 3N force in ChEFT is negligible at low densities. 3N force canceled out by 2N at higher densities. Similar phenomena are detected in the equation of state. The equation of state is repulsive for 3N and attractive for 2N. The response is sensitive to choose the nuclear potential. Therefore, I emphasize the importance of nuclear potential. |
Wednesday, October 13, 2021 12:54PM - 1:06PM |
KD.00008: Applying Bayesian Methods to R-Matrix Predictions of Nuclear Reaction Observables Daniel M Odell, Carl R Brune, Daniel R Phillips, Som N Paneru, Maheshwor Poudel, Richard J deBoer In order to develop reliable predictions, the need to prioritize the comprehensive uncertainty quantification of nuclear structure and reaction predictions has only become stronger over that past several years. In line with this broader effort, I will present the results of our recent work to apply R-matrix theory to low-energy, nuclear reactions with Bayesian methods. First, I will present our analysis of the t(d,n)⍺ reaction, the results of which provide a more accurate prediction of the S factor at solar energies. Second, I will discuss our efforts to produce an accurate, well-understood prediction for the 3He–⍺ total capture S factor at solar energies from an analysis of a recent scattering measurement at TRIUMF alongside previously analyzed data. I will also cover our attempts to resolve discrepancies between the analyses of 3He–⍺ capture and scattering data. Finally, I will preview the future of Bayesian methods and R-matrix theory and similar undertakings. |
Wednesday, October 13, 2021 1:06PM - 1:18PM |
KD.00009: Fresh approaches to using solar isotopic abundances to determine heavy element origins Nicole Vassh, Matthew R Mumpower, Benoit Côté, Gail C McLaughlin, Rebecca A Surman For more than 60 years the solar isotopic abundances have been providing clues to the astrophysical origins of elements. Although the era of multi-messenger astronomy presents new paths to understanding single events, the solar abundances still serve as the key informant of the contributions of a given site to the enrichment of the Solar System. We will discuss recent methods to evaluate both the last and dominant source of heavy r-process elements. To evaluate the dominant source in a modern way, statistical methods offer a fresh and innovative approach. We apply such techniques to the r-process rare-earth abundance peak due to its high sensitivity to the nuclear properties of lanthanides as well as the astrophysical environment in which heavy element synthesis occurs. We will present the most recent results which derive the masses capable of forming the rare-earth peak in accretion disk winds as well as neutron star merger dynamical ejecta. When considering the last source of r-process enrichment, traces of radioactive isotopes in meteorites are a promising avenue. We will present results which demonstrate the diagnostic power of the abundance ratio of two particularly special radioactive isotopes and compare their ratio in meteorites to predicted nucleosynthetic abundances in neutron star mergers and rare supernovae. We will also describe how the latest precision measurements and upcoming experiments are in a prime position to illuminate key nuclear properties which affect these studies. |
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