Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session H17: The Nucleosynthesis of Proton-Rich Isotopes in Classical NovaeFocus Live
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Sponsoring Units: DNP Chair: Kelly Chipps, Oak Ride National Laboratory Room: Delaware A |
Sunday, April 19, 2020 10:45AM - 11:21AM Live |
H17.00001: Informing (p,$\gamma )$ rates using the (d,p) reaction Invited Speaker: S.D. Pain Proton capture rates via low-lying proton resonances are of astrophysical interest for understanding galactic chemical evolution, energy generation and production rates of individual radionuclides. These reactions are difficult to measure directly, especially for reactions on radioactive nuclei which dominate the reaction network in explosive scenarios, due to limited beam intensities and the small proton widths. While the (d,n) reaction can be used to constrain these rates indirectly by determining energies, J$^{\mathrm{\pi }}$ assignments, and spectroscopic factors of proton resonances, practical considerations of neutron measurement for inverse kinematics reactions currently limit the applicability of the technique. Alternatively, the (d,p) reaction can be used to determine these properties for the mirror neutron states in the conjugate nucleus with improved resolution and detection efficiency. Using ORRUBA and GODDESS, we have initiated a campaign of such measurements on astrophysically-interesting self-conjugate (N$=$Z) nuclei in the sd shell. The technique, results of benchmarking against direct measurements of $^{\mathrm{26}}$Al(p,$\gamma )$, and the application of the technique to $^{\mathrm{30}}$P(p,$\gamma )$ and $^{\mathrm{38}}$K(p,$\gamma )$ will be presented, along with plans for future measurements at FRIB. [Preview Abstract] |
Sunday, April 19, 2020 11:21AM - 11:33AM Live |
H17.00002: Spin and parities of 19Ne states of astrophysical interest Federico Portillo Chaves, Kiana Setoodehnia, Caleb Marshall, Richard Longland Observations of classical nova ejecta show discrepancies with theoretical predictions, particularly for the quantity of material ejected by the explosion. This discrepancy could be resolved with the detection of $\gamma$ rays originating from $^{18}$F. However, theoretical predictions of the flux of these $\gamma$ rays are limited by large uncertainties in the $^{18}$F destruction rates. These uncertainties are caused mainly by the incomplete knowledge of the influence of low energy resonances on the cross section for the main $^{18}$F destruction reaction $^{18}$F(p,$\alpha$)$^{15}$O. In this work we searched for states in the compound nucleus ($^{19}$Ne) relevant at nova temperatures and determined their spin and parities (J$^{\pi}$) when possible. In particular, we found that the state at 6.130 MeV (a proton sub-threshold resonance at E$_{CM}$=-280 keV) has a J$^{\pi}$=3/2$^+$, which opens the possibility for interference in the cross section with the well known broad resonances at E$_{CM}$ = 332 keV and 665 keV. We will present our experimental results and will highlight their effect on the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate. [Preview Abstract] |
Sunday, April 19, 2020 11:33AM - 11:45AM Live |
H17.00003: First measurement with GADGET: $^{\mathrm{23}}$Al $\beta $ decay and $^{\mathrm{22}}$Na production in novae Christopher Wrede, M. Friedman, T. Budner, D. Perez-Loureiro, E. Pollacco, J. Jose, B. A. Brown, M. Cortesi, C. Fry, B. Glassman, J. Heideman, M. Janasik, M. Roosa, J. Stomps, J. Surbrook, P. Tiwari Novae are expected to produce the radionuclide $^{\mathrm{22}}$Na, leading to the emission of a 1.275-MeV $\gamma $ ray. Next generation $\gamma $-ray space telescopes will likely provide unique constrains on nova models by observing this $\gamma $-ray line. An important input to models of $^{\mathrm{22}}$Na production in novae is the rate of the destructive $^{\mathrm{22}}$Na(p,$\gamma )^{\mathrm{23}}$Mg reaction. The rate is dominated by one resonance, whose strength can be measured directly or constructed from measurements of its branching ratio and lifetime. We have determined the proton branching ratio to be 5 times lower than the most precise literature value by measuring the $\beta $ delayed proton decay of $^{\mathrm{23}}$Al using the Gaseous Detector with Germanium Tagging (GADGET) at NSCL. Considering this new measurement along with two discrepant direct measurements we argue that the lifetime of this resonance should be re-measured. A 1D hydrodynamic code has been used to model a series of nova explosions on oxygen-neon white dwarfs, from which different $^{\mathrm{22}}$Na yields have been obtained for several nuclear-data inputs for the $^{\mathrm{22}}$Na(p, $\gamma )^{\mathrm{23}}$Mg reaction rate. [Preview Abstract] |
Sunday, April 19, 2020 11:45AM - 11:57AM Live |
H17.00004: Spectroscopic studies on $^{39}$Ca for classical nova endpoint nucleosynthesis Johnson Liang, Alan Chen, Athanasios Psaltis, Christopher Wrede, Lijie Sun, Tamas Budner, Cathleen Fry, Pranjal Tiwari, Marius Anger, Shawn Bishop, Thomas Faestermann, Ralf Hertenberger, Dominik Seiler, Hans-Friedrich Wirth, Richard Longland, Caleb Marshall, Federico Portillo, John Kelley In classical nova nucleosythesis repeated proton capture reactions and beta-decays produce proton-rich isotopes and the endpoint of this nucleosynthesis typically occurs in nuclei close to A $\sim$ 40. There is currently a discrepancy between the observed and predicted isotopic abundances in this mass region. One particular reaction, $^{38}$K(p,$\gamma$)$^{39}$Ca is important in this regard. Nova simulations show that this reaction can alter the isotopic abundances of $^{38}$Ar, $^{39}$K, and $^{40}$Ca significantly when the reaction rate is varied by its maximum uncertainty. Thus, it is important to constrain uncertainties of this reaction rate to accurately predict isotopic abundances. Although a recent direct measurement has reduced the reaction rate uncertainty, more measurements precisely probing the low energy resonances within the Gamow window would help this effort. To that end, I will present important levels in $^{39}$Ca with experiments performed at the Maier Leibnitz Laboratory and TUNL. [Preview Abstract] |
Sunday, April 19, 2020 11:57AM - 12:09PM Live |
H17.00005: Investigating the $^{38}$K($p$,$\gamma$)$^{39}$Ca reaction rate in novae via the energy levels of $^{39}$Ca Matthew Hall, Daniel Bardayan, Travis Baugher, Alex Lepailleur, Steven Pain, Andrew Ratkiewicz While it is known that the endpoint of nucleosynthesis in nova explosions is around $^{40}$Ca, discrepancies exist between the modeled and observed abundances of nuclei near the endpoint. Uncertainties in the $^{38}$K($p$,$\gamma$)$^{39}$Ca reaction rate could be one source of the discrepancy. Accurate calculation of the rate depends on knowledge of three $\ell=0$ resonances, which correspond to $J^\pi=5/2^+$ excited states in $^{39}$Ca above the $^{38}$K+$p$ threshold. Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies (GODDESS) was used to study these excited states via the $^{40}$Ca($^3$He,$\alpha$)$^{39}$Ca reaction at Argonne National Laboratory. Three excited states with energies of 6156.2(16), 6268.8(22), and 6470.8(19) keV were found by studying the $\gamma$-$\alpha$ coincidences in the measurement, corresponding to three suspected $J^\pi=5/2^+$ states. Their impact on the $^{38}$K($p$,$\gamma$)$^{39}$Ca reaction rate was investigated and these results will be discussed. [Preview Abstract] |
Sunday, April 19, 2020 12:09PM - 12:21PM On Demand |
H17.00006: Studying reactions important to classical nova nucleosynthesis with the Super Enge Split-Pole Spectrograph at Florida State University E.C. Good, C.M. Deibel, S. Balakrishnan, J.C. Blackmon, K. Davis, A.D. Hood, A. Laminack, R. Malecek, K.M. Macon, K. Pham, B. Asher, L. Baby, C. Benetti, N. Gerken, K. Hanselman, E. Lopez Saavedra, G. McCann, E. Temanson, E. Rubino, J. Perello, A. Morelock, C. Esparza, I. Wiedenhoever First science runs at the Super Enge Split-Pole Spectrograph (SE-SPS) at Florida State University utilizing the Silicon Array for Branching Ratio Experiments (SABRE) have been conducted to study excited states corresponding to resonances of interest to nuclear reactions in proton-rich nuclei. These reactions are of importance for classical nova nucleosynsthesis. SABRE was used in conjunction with the SPS and its gas-filled focal plane detector to determine states populated in the nuclei of interest and their decay branching ratios, which are needed for the calculation of nuclear reaction rates. I will discuss measurements for the 38K(p,gamma)39Ca reaction via a study of 40Ca(3He,alpha)39Ca*(p)38K, among other results. [Preview Abstract] |
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