Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session JC: Nuclear Astrophysics II |
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Chair: Greg Christian, Texas A&M University Room: Sweeney Ballroom B |
Friday, October 30, 2015 10:30AM - 10:42AM |
JC.00001: Moving towards first science with the St. George recoil separator Zachary Meisel, G.P.A. Berg, G. Gilardy, M. Moran, J. Schmitt, C. Seymour, E. Stech, M. Couder The St. George recoil mass separator has recently been coupled to the 5MV St. Ana accelerator at the University of Notre Dame's Nuclear Science Lab. St. George is a unique tool designed to measure radiative alpha-capture reactions for nuclei up to A$=$40 in inverse kinematics in order to directly obtain cross sections required for astrophysical models of stellar and explosive helium burning. Commissioning of St. George is presently taking place with primary beams of hydrogen, helium, and oxygen. In this presentation, results will be shown for the measured energy acceptance of St. George, which compare favorably to COSY results when employing the calculated optimal ion-optical settings. Additionally, future plans will be discussed, such as assessing the angular acceptance of St. George and the re-integration of HiPPO at the separator target position to provide a dense, windowless helium gas-jet target. [Preview Abstract] |
Friday, October 30, 2015 10:42AM - 10:54AM |
JC.00002: Measurement campaign for astrophysically relevant $^{36}$Cl production cross sections Tyler Anderson, Michael Skulski, Karen Ostdiek, Wenting Lu, Mary Beard, Philippe Collon The short-lived radionuclide $^{36}$Cl (t$_{1/2} = $ 0.301 Ma) is known to have existed in the Early Solar System (ESS), and evaluating its production sources can lead to better understanding of the processes taking place in ESS formation and their timescales. The x-wind production model is used to explain $^{36}$Cl production via solar energetic particles from the young Sun, but is lacking empirical data for many relevant reactions. Bowers et al. (2013) measured the cross section of $^{33}$S($\alpha $,p)$^{36}$Cl at various energies in the range of 0.70-2.42 MeV/A, and found them to be systematically under predicted by statistical Hauser-Feshbach model codes TALYS and NON-SMOKER, highlighting the need for more empirical data for these cross sections. A recent paper by Mohr (2013) called these results in to question, prompting the re-measurement of the cross section for $^{33}$S($\alpha $,p)$^{36}$Cl at new energies in the same energy range as Bowers et al. This talk will also discuss two further planned measurements of cross sections suggested by Bowers et al. to be the next most significant in $^{36}$Cl production. [Preview Abstract] |
Friday, October 30, 2015 10:54AM - 11:06AM |
JC.00003: Further Exploration of the $^{33}$S($\alpha $,p)$^{36}$Cl Reaction Cross Section Michael Skulski, Tyler Anderson, Mary Beard, Philippe Collon, Wenting Lu, Karen Ostdiek Short-lived radionuclides (SLRs) are extant from the Early Solar System (ESS) and useful for dating products of ESS processes. The SLR $^{36}$Cl was potentially produced by solar energetic particles incident on gas and dust in the protoplanetary disk. Measurement of the cross section of the reaction $^{33}$S($\alpha $,p)$^{36}$Cl, which contributes significantly to the abundance of $^{36}$Cl, is an important input in solar irradiation models regarding the determination of elemental abundances, and is thus of great interest. In a previous measurement performed by Bowers et al. (2013), the cross section of this reaction was studied using a combination of activation of a $^{4}$He gas cell and analyzing the produced $^{36}$Cl via Accelerator Mass Spectrometry (AMS) over an energy range of 0.7 -- 2.42 MeV/A. The result of this measurement was a significantly higher yield of $^{36}$Cl than predicted by Hauser-Feshbach cross section calculations. In light of the paper by Mohr (2013), the same activation was repeated at the University of Notre Dame at intermediate energies to study the cross section further, using the same combination of activation and AMS. The results of this measurement will be presented. [Preview Abstract] |
Friday, October 30, 2015 11:06AM - 11:18AM |
JC.00004: Direct measurement of several resonance strengths and energies in $^{34}$S$(\alpha,\gamma)^{38}\!$Ar within the $T\,=\,2.2$ GK Gamow window with DRAGON D. Connolly, P. O'Malley, C. Akers, A.A. Chen, G. Christian, B. Davids, L.E. Erikson, J. Fallis, B.R. Fulton, U. Greife, Ulrike Hager, D.A. Hutcheon, S. Ilyushkin, A.M. Laird, A. Mahl, C. Ruiz Radiative $\alpha$ capture on $^{34}$S can impact nucleosynthesis in several astrophysical environments, including oxygen burning, explosive oxygen burning (Type II supernovae), and Type Ia supernovae. However, there exist discrepancies in the literature for the resonance strengths of two strong resonances within the Gamow window for oxygen burning temperatures ($E_{0}\,\pm\,\Delta/2\,=\,3183\,\pm\,897$ keV at $T\,=\,2.2$ GK). Previous measurements suffered from systematic uncertainties inherent in the experimental technique. Furthermore, there are several states in $^{38}$Ar in the energy range of interest for which no $^{34}$S + $\alpha$ resonance strength/energy measurements have been performed. This measurement was performed in inverse kinematics at the DRAGON recoil separator at TRIUMF in BC, Canada. DRAGON's experimental technique allows direct measurement of quantities such as stopping power and resonance energy, alleviating the need for external inputs and reducing uncertainty. This talk will discuss DRAGON's experimental technique, analysis methods and results. [Preview Abstract] |
Friday, October 30, 2015 11:18AM - 11:30AM |
JC.00005: An indirect study of the $^{44}$Ti($\alpha$,p)$^{47}$V stellar rate using high precision $^{50}$Cr(p,t)$^{48}$Cr reaction measurements A. Long, G.P.A. Berg, Y. Chen, M. Couder, J. Goerres, Z. Meisel, M. Wiescher, P. Adsley, P. Papka, J.J. van Zyl, R. Neveling, F.D. Smit, L. Pellegri Observations of $^{44}$Ti ejecta in core-collapse supernova by space-based $\gamma$-ray telescopes may provide a powerful probe into the underlying core-collapse explosion mechanisms. $^{44}$Ti is believed to be produced just outside the collapsed core within regions undergoing $\alpha$-rich freeze out and its synthesis is critically sensitive to temperature, density, and Y$_{e}$ evolution. Present sensitivity studies have shown that the most influential reaction governing the synthesis of $^{44}$Ti in this scenario is the $^{44}$Ti($\alpha$,p)$^{47}$V reaction. Direct measurements of this reaction within the relevant astrophysical energies has proven difficult and therefore very little experimental information exist. The $^{44}$Ti($\alpha$,p)$^{47}$V reaction reaction rate will depend strongly on the exact characteristics and number of natural parity states in $^{48}$Cr that fall within the Gamow window. We have performed high energy-resolution zero-degree coincident measurements of the $^{50}$Cr(p,t)$^{48}$Cr reaction at iThemba LABS with the motivation of precisely identifying energies and spins of ($\alpha$,p) resonances in $^{48}$Cr. Preliminary results will be presented. [Preview Abstract] |
Friday, October 30, 2015 11:30AM - 11:42AM |
JC.00006: Elastic and inelastic scattering of neutrons from $^{56}$Fe Anthony Paul Ramirez, M.T. McEllistrem, S.H. Liu, S. Mukhopadhyay, E.E. Peters, S.W. Yates, J.R. Vanhoy, T.D. Harrison, B.G. Rice, B.K. Thompson, S.F. Hicks, T.J. Howard, D.T. Jackson, P.D. Lenzen, T.D. Nguyen, R.L. Pecha The differential cross sections for elastic and inelastic scattered neutrons from $^{56}$Fe have been measured at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator) for incident neutron energies between 2.0 and 8.0 MeV and for the angular range 30$^{\circ}$ to 150$^{\circ}$. Time-of-flight techniques and pulse-shape discrimination were employed for enhancing the neutron energy spectra and for reducing background. An overview of the experimental procedures and data analysis for the conversion of neutron yields to differential cross sections will be presented. These include the determination of the energy-dependent detection efficiencies, the normalization of the measured differential cross sections, and the attenuation and multiple scattering corrections. Our results will also be compared to evaluated cross section databases and reaction model calculations using the TALYS code. [Preview Abstract] |
Friday, October 30, 2015 11:42AM - 11:54AM |
JC.00007: Toward a Measurement of the Half-Life of 60Fe for Stellar and Early Solar System Models Karen Ostdiek, Tyer Anderson, William Bauder, Matthew Bowers, Philippe Collon, Wenting Lu, Daniel Robertson, Michael Skuski, Sam Austin, John Greene, Walter Kutschera, Michael Paul, Anthony Wallner Radioisotopes, produced in stars and ejected through core collapse supernovae, are important for constraining stellar and early Solar System models. The presence of these isotopes, specifically $^{60}$Fe, can identify progenitors of SN types, give evidence for nearby SNe, and can be a chronometer for ESS events. The $^{60}$Fe half-life, which has been in dispute in recent years, can have an impact on calculations for the timing for ESS events, the distance to nearby SN, and the brightness of individual, non-steady state $^{60}$Fe $\gamma$ ray sources in the Galaxy. To measure such a long half life, one needs to simultaneously determine the number of atoms in and the activity of an $^{60}$Fe sample. We have undertaken a half-life measurement at Notre Dame and have successfully measured the activity of our $^{60}$Fe sample using the isomeric decay in $^{60}$Co rather than the traditional $^{60}$Co grow-in decay. This will then be coupled with the results of the $^{60}$Fe concentration measurement of our sample using Accelerator Mass Spectrometry (AMS). I will present the most recent results of both measurements. [Preview Abstract] |
Friday, October 30, 2015 11:54AM - 12:06PM |
JC.00008: In-flight proton breakup of ${}^{73}$Rb A.M. Rogers, C. Anderson, J. Barney, J. Estee, W.G. Lynch, J. Manfredi, H. Setiawan, R.H. Showalter, S. Sweany, S. Tangwancharoen, M.B. Tsang, J.R. Winkelbauer, K.W. Brown, J.M. Elson, C. Pruitt, L.G. Sobotka, Z. Chajecki, J. Lee Properties of nuclei beyond the proton drip-line are important for mass models, astrophysics, and nuclear structure. Weakly-bound or proton-unbound nuclei near the rp process waiting-points, in particular, play a critical role in constraining calculations and observations of type I x-ray bursts. The relatively slow $\beta$-decay of ${}^{72}$Kr, for instance, may be bypassed significantly by 2p-capture reactions through ${}^{73}$Rb. This process, however, depends sensitively on the ${}^{73}$Rb proton separation energy, $S_{\textrm{p}}$. While recent measurements of ${}^{65}$As and ${}^{69}$Br have reduced uncertainties in the reaction sequence, the ${}^{72}$Kr waiting point still remains largely unconstrained. We have performed an experiment at NSCL to measure, using invariant-mass spectroscopy, the decay of ${}^{73}$Rb$\rightarrow$p+${}^{72}$Kr in an attempt to determine $S_{\textrm{p}}({}^{73}\textrm{Rb})$. Preliminary results from our recent ${}^{73}$Rb decay experiment will be presented. [Preview Abstract] |
Friday, October 30, 2015 12:06PM - 12:18PM |
JC.00009: Resolving Urca cooling reaction layers in neutron stars Alex Deibel Reaction network calculations predict that the crust of an accreting neutron star should host Urca reactions: $e^{-}$-capture/$\beta^{-}$-decay cycles that cool the crust through neutrino emission. Neutron star transients offer an opportunity to test this prediction. During accretion outbursts, the crust of a neutron star transient reaches temperatures above $T > 2 \times 10^{8}$ K where Urca cycling is expected to balance the accretion-driven crust heating. However, post-outburst thermal evolution models of the hottest transient MAXI J0556-332 have shown that the Urca cooling reactions must take place deeper in the star than predicted, or must be absent entirely, in order to fit quiescent observations. In order to reconcile the predictions from nuclear reaction networks and post-outburst thermal evolution models, we model the Urca reaction layer with higher resolution than ever before. This modeling allows us to incorporate measured $e^{-}$-capture rates and follow the temperature evolution of the reaction layer on relatively small scales. These developments in reaction layer modeling will not only help delineate the effects of Urca cooling on neutron star crusts, but will aid in incorporating Urca cooling in X-ray burst models. [Preview Abstract] |
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