Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session HF: Nuclear Astrophysics: Nuclear Reactions |
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Chair: Michael Wiescher, University of Notre Dame Room: Garden III |
Friday, October 26, 2012 8:30AM - 8:42AM |
HF.00001: Fusion cross section of $^{3}$He$(\alpha,\gamma)^{7}$Be Antonios Kontos, Joachim G\"orres, Andreas Best, Richard deBoer, Ethan Uberseder, Michael Wiescher The $^3$He$(\alpha, \gamma)^7$Be reaction is important for the neutrino production in the sun's core and the production of $^7$Li during the big bang nucleosynthesis. Due to the low level density of $^7$Be, the reaction mechanism is dominated by a strong direct capture component at the relevant energies. Recent experiments have improved the uncertainty of the reaction but some discrepancies still exist. In the present work, a relatively wide energy window was measured, $E_{CM} = 0.300-1.450$ MeV, by detecting the prompt gamma-rays from the reaction. The experiments were carried out at the Nuclear Science Laboratory, University of Notre Dame and utilized a compact helium jet gas target (HIPPO) to ensure a sufficiently high gamma-ray detection efficiency. The results are compared with literature. [Preview Abstract] |
Friday, October 26, 2012 8:42AM - 8:54AM |
HF.00002: Enhancement of the Triple-Alpha Reaction Rate in Hot, Dense Environments Sam M. Austin, Richard H. Cyburt In typical helium-burning stars, the rate of the triple-alpha (3$\alpha )$ reaction depends primarily on the radiative width of the 0$^{+ }$ state at 7.65 MeV in $^{12}$C (the Hoyle state) as observed in the laboratory. At sufficiently high temperatures (T) and densities ($\rho )$, however, interaction with particles in the astrophysical environment can induce de-excitation of the Hoyle state. This effectively increases the relevant width of the Hoyle state and thereby the 3$\alpha $ rate. The strength of these processes is given by the inverse of inelastic scattering rate leading to the Hoyle state. The strength of some of these processes can be obtained from experiment. Earlier measurements of excitation of the Hoyle state by inelastic proton and alpha scattering showed that these enhancements can be significant. This is not possible for induced de-excitation from the Hoyle state to the 2$^{+}$ state at 4.44 MeV; inelastic scattering from the excited 2$^{+}$ state to the Hoyle state is not measurable. Given possible ranges of T and $\rho $ one anticipates that only de-excitation by protons, neutrons and alpha particles might be important. There is no information at relevant energies for neutrons. In the present work we have used experimental cross sections where available, supplemented by TALYS calculations to provide cross sections for unobservable (2$^{+}$ to 0$^{+})$ cross sections or unobserved energy ranges. We find that enhancements can be significant in reactions preceding the r-process in supernovae. [Preview Abstract] |
Friday, October 26, 2012 8:54AM - 9:06AM |
HF.00003: R-matrix analysis of 16O reactions Richard deBoer, Joachim Goerres, Paul LeBlanc, Ethan Uberseder, Michael Wiescher, Gianluca Imbriani Over the last 60 years, a large amount of experimental nuclear data has been obtained for reactions which probe the $^{16}$O compound nucleus near the alpha and proton separation energies, the energy regimes most important for nuclear astrophysics. Difficulties and inconsistencies in past analysis of the individual reaction data prompt a more complete global analysis with the first aim of determining the level of consistency between the wide variety of experimental data. The global analysis has been performed using a multiple entrance/exit channel \textit{R}-matrix framework. Over the wide range of experimental data considered, a high level of consistency is found between the many different data sets, resulting in a single consistent \textit{R}-matrix fit which describes the broad level structure of $^{16}$O below $E_x$ = 13.5 MeV. The resulting fit is used to re-investigate our current understanding of the reaction components which contribute to the low energy cross sections of $^{15}$N + $p$ and $^{12}$C + $\alpha$ reactions. Work has begun on establishing a better estimate of the reaction rate uncertainties by performing a Monte Carlo analysis on the many data sets considered. [Preview Abstract] |
Friday, October 26, 2012 9:06AM - 9:18AM |
HF.00004: ABSTRACT WITHDRAWN |
Friday, October 26, 2012 9:18AM - 9:30AM |
HF.00005: Measurement of the $^{26g}$Al(d,p)$^{27}$Al Reaction to Constrain the $^{26g}$Al Destruction Reaction Rate Steven Pain Detailed observations of the 1809-keV $\gamma$ ray from the beta decay of $^{26}$Al within the galaxy has provided an insight into ongoing nucleosynthesis. Understanding the abundance of $^{26}$Al requires knowledge of the production and destruction rates for $^{26}$Al. For temperatures where the ground-state and metastable state of $^{26}$Al are decoupled, the $^{26}$Al(p,$\gamma$)$^{27}$Si reaction, which is determined by states near the proton threshold in $^{27}$Si, contributes to the destruction rate. Though the strengths of many of these resonances have been measured directly, there remain uncertainties for the lowest resonances, which are relevant for giant star temperatures. We have measured mirror states in $^{27}$Al to inform the $^{27}$Si structure, via the $^{26}$Al(d,p)$^{27}$Al reaction in inverse kinematics at the HRIBF. A beam of $\sim$5 million $^{26}$Al per second impinged on a $\sim$150 $\mu$g/cm$^2$ CD$_2$ target. Proton ejectiles were detected in the SIDAR and ORRUBA silicon detector arrays. Details of the experimental setup and results will be presented. This work was supported in part by the US Department of Energy Office of Science and the National Science Foundation. [Preview Abstract] |
Friday, October 26, 2012 9:30AM - 9:42AM |
HF.00006: ABSTRACT WITHDRAWN |
Friday, October 26, 2012 9:42AM - 9:54AM |
HF.00007: Measurement of the $\mathrm{^{25}Al(d,n)^{26}Si(p)}$ reaction at RESOLUT: Spectroscopy of $l=0$ and $l=1$ resonances Jessica Baker, Ingo Wiedenhover, Alexander Rojas, Lagy Baby, Sean Kuvin, Patrick Peplowski, Daniel Santiago-Gonzalez, Georgios Perdikakis, Dennis Gay Studies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest $l=0$ and $l=1$ resonances is the most important step to determine reaction rates in the astrophysical $rp$--process path. In an experiment performed at the {\sc resolut} radioactive beam facility of Florida State University, we have studied the $\mathrm{^{25}Al(d,n)^{26}Si}$ reaction in inverse kinematics to establish the spectrum of the lowest $l=0$ and $l=1$ resonances. The spectrum is consistent with a previous experiment using the same reaction at {\sc resolut} [1] and results obtained from recent stable beam experiments [2]. [Preview Abstract] |
Friday, October 26, 2012 9:54AM - 10:06AM |
HF.00008: Systematic study of (p,$\gamma )$ and ($\alpha $,$\gamma )$ reactions on Nickel isotopes Anna Simon The stable neutron-deficient isotopes of the elements from Se to Hg are synthesized during so called p-process. The modeling of p-process nucleosynthesis requires a large network of thousands of nuclear reactions involving stable nuclei as well as unstable, proton-rich nuclides. However, there are still very few charged-particle cross sections determined experimentally, despite big experimental efforts in recent years. Thus, the p-process rates involving charged projectiles are still based on theoretical cross sections obtained from modern Hauser--Feshbach statistical model calculations. It is crucial not only to measure cross sections for reactions that were shown to be particularly important for the p-process but also to provide systematic information on the (p,$\gamma )$ and ($\alpha $,$\gamma )$ reactions for nuclei beyond iron in order to put constraints on the theoretical models. Here, the recent investigation of (p,$\gamma )$ and ($\alpha $,$\gamma )$ reactions on stable Nickel isotopes will be presented. The obtained results will be compared to theoretical calculations that are commonly used in astrophysical models. [Preview Abstract] |
Friday, October 26, 2012 10:06AM - 10:18AM |
HF.00009: Cross section measurements of the $^{74}$Ge(p,$\gamma )$ and $^{90}$Zr(p,$\gamma )$ reactions Stephen Quinn, Sean Liddick, Anna Simon, Artemis Spyrou, Benjamin Stefanek, Manoel Couder, Joachim Gorres, Antonios Kontos, Daniel Robertson, Ed Stech, Wanpeng Tan, Michael Wiescher, Paul DeYoung, Graham Peaslee The p-nuclei are a group of stable, neutron-deficient isotopes whose production cannot be explained by neutron capture processes. Instead, nucleosynthesis is favored to occur via the p-process, in which high stellar temperatures lead to a series of photodisintegration reactions, their inverse capture reactions, and $\beta ^{+}$ decays on existing seed nuclei. Current p-process network calculations do not accurately reproduce the observed abundance pattern of the p-nuclei, particularly for the lightest masses. In an effort to improve our understanding of the nucleosynthesis of the lightest p-nuclei, the $^{74}$Ge(p,$\gamma )$ and $^{90}$Zr(p,$\gamma )$ reactions were recently measured using the FN Tandem Accelerator at the University of Notre Dame in combination with the NSCL SuN detector. Cross section results at astrophysically relevant energies will be presented and compared with theoretical calculations. [Preview Abstract] |
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