Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session KD: Nuclear Astrophysics II |
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Chair: Melina Avila, ANL |
Saturday, October 31, 2020 8:30AM - 8:42AM |
KD.00001: Identifying important X-ray burst reactions using stellar modelling in MESA Amber Lauer, Brittney Contreras, Ian Lapinski, Arthur Champagne Type I x-ray bursts occur on accreting neutron stars via the (r,p) process during thermonuclear runaway up to the A=100 region. Studying these bursts will help in understanding the underlying star and its unknown physics. Unfortunately many of the reactions involve unstable nuclei that are difficult to produce for use in experiments. Thus, sensitivity studies are a useful steering mechanism to guide the experimental community and optimize the application of resources. We have begun such a study, based on a model of an accreting neutron star using Modules for Experiments with Stellar Astrophysics, which incorporates a nuclear reaction network of 305 species and 3000 reactions, including (n,g), (n,p), (n,a), (p,g), (a,p), (a,g), and weak reactions. A series of models is calculated in which a single reaction rate is varied to test its effect on features of the model, such as observables and abundances. From this we can identify the most useful and important reactions to the X-ray burst environment and the (r-p) process. This talk will discuss the process and preliminary results including the coarse-resolution study and its implications for the second round, currently under analysis, where actual uncertainties of key reaction rates are implemented, as well as future implications. [Preview Abstract] |
Saturday, October 31, 2020 8:42AM - 8:54AM |
KD.00002: Sensitivity Studies of Nuclear Reaction Rates for Type-I X-Ray Burst Chowdhury Irin Sultana, Jessica Borowiak, Jacob Elliott, Alfredo Estrade, Bradley S. Meyer, Hendrik Schatz Type-I X-ray bursts are frequently occurring thermonuclear runaways on the surface of an accreting neutron star. The different nuclear reactions that empower the cataclysmic event play a key role in model-observation comparison. We investigate the effect of the uncertainties in the nuclear reactions using ONEZONE model for a set of different compositions of the material accreted from the companion star. We obtain conditions at burst ignition by simulating the settling process of the accreted material with a full reaction network and compare results to a semi-analytical model. Afterward, we perform a sensitivity of the X-ray burst by varying proton and alpha-induced reaction rates in JINA REACLIBV2.2 within representative nuclear physics uncertainties. We will present the result for the sensitivity to nuclear reactions that have an impact on the X-ray burst light curve and ash production. This result will benefit future experimental work to understand the structure of accreted neutron stars. [Preview Abstract] |
Saturday, October 31, 2020 8:54AM - 9:06AM |
KD.00003: Ab initio reactions for X-ray burst nucleosynthesis Alexis Mercenne, Kristina Launey, Tomas Dytrych, Jutta Escher, Jerry Draayer We present the latest results of the symmetry-adapted resonating group method (SA-RGM), a microscopic \textit{ab initio} approach for nuclear reactions for light to medium-mass nuclei. It builds upon the \textit{ab initio} RGM framework, but in addition, the internal cluster wave functions are calculated using the symmetry-adapted no-core shell model. It takes advantage of group theoretical methods, such as SU(3) and symplectic symmetries, to reorganize and reduce the dimensionality of the model space, consequently making solutions for heavier nuclei feasible. The SU(3) algebra is suited for RGM-type calculations as well, since it naturally takes antisymmetry and cluster correlations into account. In this presentation, I will discuss the SA-RGM formulation and its applications to nuclear reactions for intermediate-mass nuclei from an \textit{ab initio} perspective. This will be illustrated with the latest results on phase shifts for single nucleon projectile on ${ { }^{ 4 } }$He, ${ { }^{ 16 } }$O and ${ { }^{ 20 } }$Ne targets, as well as a study of the nucleon radiative capture on ${ { }^{ 23 } }$Al of significance to astrophysics. [Preview Abstract] |
Saturday, October 31, 2020 9:06AM - 9:18AM |
KD.00004: Probing Alpha Clustering for X-ray Burst Nucleosynthesis in a Symmetry-Adapted Framework Alison Dreyfuss, Kristina Launey, Jutta Escher, Grigor Sargsyan, Robert Baker, Tomas Dytrych, Jerry Draayer I discuss a new framework for studying clustering and determining alpha partial widths, asymptotic normalization coefficients (ANC), and alpha-capture reaction rates for narrow resonances, using symmetry-adapted wave functions. I will demonstrate the method through the well-studied $^{\mathrm{20}}$Ne system, by calculating the overlap between the $^{\mathrm{16}}$O$+$alpha cluster configuration and states in $^{\mathrm{20}}$Ne calculated in two different symmetry-adapted no core shell model formalisms. I will focus on the 5.79-MeV 1- state in $^{\mathrm{20}}$Ne and its alpha partial width, and discuss the $^{\mathrm{16}}$O(alpha, gamma)$^{\mathrm{20}}$Ne reaction rate at astrophysical temperatures. This ultimately is used to explore impacts on simulated X-ray burst abundance patterns. [Preview Abstract] |
Saturday, October 31, 2020 9:18AM - 9:30AM |
KD.00005: Quest for $\alpha$-cluster states to constrain the ($\alpha$,p) reactions in type-I X-ray bursts using active-targets Jaspreet Singh Randhawa, Tan Ahn, Wolfgang Mittig, Yassid Ayyad, Daniel Bazin, Saul Beceiro-Novo, Jie Chen, Nathan Watwood, Samuel Henderson, D. Bardayan, Patrick O'Malley, Sebastian Aguilar, Maxime Renaud, James Kolata Type-I X-ray bursts are powered by the nuclear burning, e.g. hot CNO cycles, $\alpha p$-process, $rp$-process. To constrain the $\alpha p$-process, direct measurements of reaction cross sections in the Gamow window is required. However, for any direct measurement of such reactions restricted to only higher energies, extrapolations to the Gamow window need detailed information on nuclear structure especially the near-threshold $\alpha$-cluster states. Time projection chambers used in active target mode provides an ample detector system for performing the resonant elastic scattering in inverse kinematics to explore cluster states. Use of pure He and H$_{2}$ gases as target aided by the thick GEMs, offers nearly background-free measurement. We will present the initial observation from simultaneous measurement of $^{17}$F($\alpha$,p) and $^{17}$F($\alpha, \alpha$) with pAT-TPC with pure helium gas. The new active target being developed at the University of Notre Dame and plans to use this detector for resonant $\alpha$-scattering to explore the alpha-cluster states in the astrophysics will be discussed. [Preview Abstract] |
Saturday, October 31, 2020 9:30AM - 9:42AM |
KD.00006: Study of States Near E$_x=6$ MeV in $^{18}$Ne Using $^{17}$F(p,p) B Sudarsan, L E Linhardt, J C Blackmon, C M Deibel, H E Gardiner, K T Macon, L T Baby, I Wiedenhöwer The $^{14}$O($\alpha$,p)$^{17}$F reaction rate has a strong influence on the light curve of Type I X-ray bursts. At temperatures lower than 1 GK, this rate is dominated by states in $^{18}$Ne with $E_x\sim6$ MeV. The RESOLUT radioactive-ion beam facility at FSU was used to study $^{18}$Ne resonances around $E_x\sim6$ MeV using $^{17}$F$+p$ scattering in inverse kinematics. We report a combined R-matrix analysis of data from our experiment with data from an earlier study\footnote{J. Hu et al., Phys.Rev.C \textbf{85} 025803(2014)} of the same reaction that covered a broader energy range but with poorer resolution. We will report constraints that can be placed on the spin-parity of resonances and proton partial widths that are important for the $^{14}$O($\alpha$,p)$^{17}$F reaction rate. Results will be compared to information from other reaction studies in the literature. [Preview Abstract] |
Saturday, October 31, 2020 9:42AM - 9:54AM |
KD.00007: Study of $^{\mathrm{57}}$Zn $\beta $-delayed proton emission and its impact on the $^{\mathrm{56}}$Ni rp-process waiting point Mansi Saxena A strong bypass circumventing $^{56}$Ni waiting point and diverting the rp-process flow through the path $^{55}$Ni(p,$\gamma$)$^{56}$Cu(p,$\gamma$)$^{57}$Zn($\beta^{+})$$^{57}$Cu(p,$\gamma$)$^{58}$Zn has been proposed \footnote{W.-J. Ong, et. al, Phy. Rev C {\bf 95} 055806 (2017).}. The $^{56}$Ni(p,$\gamma$) and $^{56}$Cu(p,$\gamma$) reaction rates calculated with the recently measured mass of $^{56}$Cu \footnote {A.A.Valverde, et. al, Phy. Rev Lett. {\bf 120} 032701 (2018).} show that the rp-process flow can redirect around the $^{56}$Ni waiting point. However, the dominant source of uncertainty regarding the strength of this bypass is the $\beta^{+}$-delayed proton emission decay branch of $^{57}$Zn, having a present estimate of 78$\pm$17\% \footnote {B. Blank et. al, Eur. Phys. J. A {\bf 31} 262-272 (2007).}. We measured $\beta$-delayed proton emission of $^{\mathrm{57}}$Zn at the National Superconducting Cyclotron Laboratory using implantation in a DSSD surrounded by a clover array for p-$\gamma$-coincidences. We substantianlly improved the precision for the proton-emission branching ratio and identified new $\gamma$-ray transitions that each correspond to the exotic $\beta$-$\gamma$-p decay mode. These results, along with the impact on the rp-process flow will be discussed [Preview Abstract] |
Saturday, October 31, 2020 9:54AM - 10:06AM |
KD.00008: Determination of the $^{60}$Zn Level Density from Neutron Evaporation Spectra Doug Soltesz Nuclear reactions of interest for astrophysics often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $\beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. Our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He,n) measured at the Edwards Accelerator Laboratory. We compared this level density to theoretical predictions, including phenomenological, microscopic, and shell model based approaches. We find that the $^{60}$Zn level density is somewhat lower than expected for excitation energies under rp-process conditions. This includes a plateau within the level density from roughly 5-6 MeV excitation energy, which is in disagreement with the usual expectation of exponential growth and all theoretical predictions we explored. A determination of the spin distribution at relevant energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate. [Preview Abstract] |
Saturday, October 31, 2020 10:06AM - 10:18AM |
KD.00009: Improved treatment of neutron star cooling via modified Urca Process Ziyuan Zhang, Mark Alford Most neutron stars cool predominately via the modified Urca process, in which emitted neutrinos carry away energy. The traditional treatment for the in-medium nucleon propagator in the modified Urca process uses crude approximations. We reformulate the propagator by including the nucleon self-energy and examine the effect of this new propagator on the neutrino emissivity due to the modified Urca process. [Preview Abstract] |
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