Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session D8: Nuclear Astrophysics I |
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Sponsoring Units: DAP Chair: Henric Krawczynski, Washington University at St. Louis Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Promenade A |
Saturday, April 12, 2008 1:30PM - 1:42PM |
D8.00001: Fusion reactions of nuetron rich nuclei in dense matter Helber Dussan, Charles Horowitz Fusion reactions play a key role in stellar evolution. The astrophysical S factor (or its associated fusion cross section) is important to know reaction rates, study chemical composition and temperature profiles of the star, as well as rate of production of heavy elements. There is not too much experimental information for the low energy fusion cross section of very neutron rich light nuclei. Using a simple barrier penetration model, we calculated the S factor for fusion reactions of neutron rich nuclei ($^{24}O + ^{24}O$, $^{28}Ne + ^{28}Ne$ and $^{12}C +$ a range of Oxygen isotopes up to $^{24}O$). These results provide a lower limit for the fusion cross sections, since the dynamics of the neutron skin of neutron rich nuclei could enhance the penetration of the Coulomb barrier. [Preview Abstract] |
Saturday, April 12, 2008 1:42PM - 1:54PM |
D8.00002: Study of the $^{13}$C({\it d,n$_{0,1}$})$^{14}$N reaction below $E_{cm}$ = 400 keV Eric Clinton, M.W. Ahmed, S.S. Henshaw, B.A. Perdue, P.N. Seo, S. Stave, H.R. Weller, P.P. Martel, R.H. France III, R.M. Prior, M.C. Spraker Several poorly understood reactions may contribute to heavy element inhomogeneous nucleosynthesis. Among these reactions, $^{13}$C({\it d,n}) has been studied in order to better understand the dynamics of this reaction and the proper way to extrapolate its S-factor. We have made detailed measurements of the angular distributions of the cross sections and the vector analyzing power for the {\it n$_{0}$} and the {\it n$_{1}$} reaction groups in the $E_{cm}$ range from 250 to 400 keV. The atomic beam polarized ion source and the TUNL mini-tandem supplied polarized deuterium beams which struck a thick, enriched $^{13}$C target. Nine organic liquid scintillator (BCI-501) neutron detectors were placed at forward and backwards angles. Angular coverage was from 0$^{\circ}$ to 158$^{\circ}$ with two detectors at $\pm$ 90$^{\circ}$ to control systematic effects. The data will be compared to the predictions of the direct reaction model. [Preview Abstract] |
Saturday, April 12, 2008 1:54PM - 2:06PM |
D8.00003: Experimental Tests of Quasiparticle Plasma State Momentum Distribution Predictions in Metal-Hydrides David Koltick, Yeong Kim An experiment is proposed to search for power law fall off of the momentum distribution of protons in a metal hydride at equilibrium temperatures near the proton interstitial binding energy. A p$^{-8}$ power law falls off is predicted at scales $pc/kT>\mbox{10 to 100}$by Galitskii and Yakimets [1] and Kim and Zubarev [2], using calculations based on quasiparticle plasma state calculations. Similar behavior is observed in high energy hadronic particle distributions at scales $P_\bot /m_\pi \sim \mbox{10 to 100.}$ The experiments scatter a pulsed beam of thermal neutrons from a metal-hydride target at $\sim $1000\r{ } K. The experimental signature for power law tails is the uniform angular scattering of the neutron beam to higher energies in the 10 eV and higher energy range. The experiment is designed to search for quasiparticle like behavior to a level of 10$^{-10}$. \begin{enumerate} \item V.M. Galitskii and V.V. Yakimets, J. Exp. Theoret. Phys. (U.S.S.R.) \textbf{51}, 957 (1966). \item Y.E. Kim and A.L. Zubarev, Japanese J. of Applied Physics \textbf{45}, L552 (2006); \textbf{46},1656 (2007). \end{enumerate} [Preview Abstract] |
Saturday, April 12, 2008 2:06PM - 2:18PM |
D8.00004: Effects of nuclear molecular configurations on the astrophysical S-factor for $^{16}$O + $^{16}$O Alexis Diaz-Torres, Leandro R. Gasques, Michael Wiescher The impact of nuclear molecular configurations on the astrophysical S-factor for $^{16}$O + $^{16}$O is investigated within the realistic two-center shell model based on Woods-Saxon potentials. These molecular effects refer to the formation of a neck between the interacting nuclei and the radial dependent collective mass parameter. It is demonstrated that the former is crucial to explain the current experimental data with high accuracy and without any free parameter, whilst in addition the latter predicts a pronounced maximum in the S-factor. In contrast to very recent results by Jiang et al., the S-factor does not decline towards extremely low values as energy decreases. [Preview Abstract] |
Saturday, April 12, 2008 2:18PM - 2:30PM |
D8.00005: Super-Reflection in Fluid Discs David Tsang, Dong Lai In differentially rotating discs with no self-gravity, density waves cannot propagate around the corotation, where the wave pattern rotation speed equals the fluid rotation rate. Waves incident upon the corotation barrier may be super-reflected (commonly referred to as corotation amplifier), but the reflection can be strongly affected by wave absorptions at the corotation resonance/singularity. The sign of the absorption is related to the Rossby wave zone very near the corotation radius. We derive the explicit expressions for the complex reflection and transmission coefficients, taking into account wave absorption at the corotation resonance. We show that depending on the sign of the gradient of the specific vorticity of the disc, $\zeta=\kappa^2/(2\Omega\Sigma)$ (where $\Omega$ is the rotation rate, $\kappa$ is the epicyclic frequency, and $\Sigma$ is the surface density), the corotation resonance can either enhance or diminish the super-reflectivity, and this can be understood in terms of the location of the Rossby wave zone relative to the corotation radius. Our results provide the explicit conditions (in terms of disc thickness, rotation profile and specific vorticity gradient) for which super-reflection can be achieved. Global overstable disc modes may be possible for discs with super-reflection at the corotation barrier. [Preview Abstract] |
Saturday, April 12, 2008 2:30PM - 2:42PM |
D8.00006: Gamma Strength Function for {\it p}-process Nucleosynthesis Calculations C.T. Angell, S. Hammond, H.J. Karwowski, E. Kwan, G. Rusev, A. Tonchev, J.H. Kelley, A. Makinaga, H. Utsunomiya The Gamma Strength Function (GSF) is a key component for calculating photodisintegration reaction rates used for the {\it p}-process modeling. During the {\it p}-process, the nucleus can be thermally excited lowering the effective threshold of photodisintegration. To calculate the reaction rates for excited states, the GSF is taken from an extrapolation of the low-energy tail of the giant dipole resonance. A new technique for determining the GSF using nuclear resonance flourescence was developed, and measurements were taken for $^{142}$Nd and $^{150}$Nd at E$_{\gamma}$= 4 -- 9 MeV. The experiment was done at the HIGS facility using a polarimeter consisting of four clover detectors. The results will be presented, and the impact on {\it p}-process calculations will be discussed. [Preview Abstract] |
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