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 H15: Nuclear Astrophysics II |
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Sponsoring Units: DNP Chair: Hendrik Schatz, Michigan State University Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis H |
Sunday, April 13, 2008 8:30AM - 8:42AM |
H15.00001: The Astrophysical $^{187}$Re$^{187}$Os Ratio: Measurement of the $^{187}$Re(n, 2n $\gamma$)$^{186m}$Re Destruction Cross Section J.H. Kelley, D.B. Masters, S. Hammond, H.J. Karwowski, E. Kwan, A. Hutcheson, A.P. Tonchev, W. Tornow, F.G. Kondev, S. Zhu We have initiated a program to measure neutron-induced cross sections on $^{187}$Re using monoenergetic neutron beams and an array of HPGe $\gamma$-ray detectors at TUNL. Our emphasis is on measuring transitions in the $^{187}$Re(n, 2n ) reaction that populate the long-lived isomeric state, $^ {186m}$Re. These data are needed to decrease uncertainties in the $^{187} $Re/$^{187}$Os cosmochronometer, which dates the $r$-process nucleosynthesis. Results from a first run using a pulsed 12 MeV neutron beam will be presented, and an overview of planned measurements that will measure the excitation function making use of both prompt $\gamma$-ray detection and activation techniques will be given. [Preview Abstract] |
Sunday, April 13, 2008 8:42AM - 8:54AM |
H15.00002: A Study of the $^{14}$C(?,?) Reaction Rate Through the ANC Technique E.D. Johnson, G.V. Rogachev, A.M. Mukhamedzhanov, A. Aguilar, P. Bender, T. DeVore, G.V. Goldberg, K.W. Kemper, S. Lee, L. Miller, J. Mitchell, P. Peplowski, M. Perry, R. Reynolds, A. Rojas The astrophysical significance of the $^{14}$C(?,?) reaction is due to its involvement in the NCO chain. The NCO chain is thought to trigger He flashes in white dwarf stars, and is also thought to be a neutron source for the s-process in low mass stars [L. Buchmann et al., The Astrophys. Journ. 324 (1988), M. Hashimoto et al., The Astrophys. Journ. 307 (1986)]. Recently the ANC of the 3$^{-}$, 6.4 MeV, near threshold state in $^{18}$O was measured via a sub-Coulomb, inverse kinematics ?-transfer reaction at the Florida State University J.D. Fox Superconducting Accelerator Laboratory. The $^{14}$C(?,?) reaction rate at stellar temperatures is highly dependent upon the structure of this 3$^{-}$ state. As shown in E.D. Johnson et al. PRL 97 (2006) the measured ANC can be used to calculate the $^{14}$C(?,?) reaction rate without any dependence on nuclear models. [Preview Abstract] |
Sunday, April 13, 2008 8:54AM - 9:06AM |
H15.00003: Effects on $^{18}$F production in novae from changes in the $^{17}$O(p,$\alpha$)$^{14}$N rate B.H. Moazen, J.C. Blackmon, D.W. Bardayan, K.Y. Chae, K. Chipps, C.P. Domizioli, R. Fitzgerald, U. Greife, W.R. Hix, K.L. Jones, R.L. Kozub, E.J. Lingerfelt, R.J. Livesay, C.D. Nesaraja, S.D. Pain, L.F. Roberts, J.F. Shriner Jr., M.S. Smith, J.S. Thomas The properties of a resonance at 183 keV are important for understanding the $^{17} $O(p,$\alpha$)$^{14}$N and $^{17}$O(p,$\gamma$)$^{18}$F reaction rates at nova temperatures and was recently reported to significantly increase the (p,$\alpha$) reaction rate. A method involving the bombardment of a hydrogen filled target chamber was recently developed at ORNL for measuring the strength and energy of (p, $\alpha$) resonances and was applied to measure this resonance in $^{17}$O(p,$ \alpha$)$^{14}$N. The strength of the resonance was confirmed and post-processing nova nucleosynthesis simulations show the new $^{17}$O(p,$\alpha$)$^{14}$N reaction rate significantly decreases $^{18}$F production in low mass ONeMg novae but has little effect on more energetic novae [Moazen et. al. Phys. Rev. C 75 065801 (2007)]. Results and astrophysical implications will be presented as well as future plans to measure $^{18}$F(p,$\alpha$)$^{15}$O with this technique. ORNL is managed by UT Battelle for the US DOE [Preview Abstract] |
Sunday, April 13, 2008 9:06AM - 9:18AM |
H15.00004: Spin assignments of $^{22}$Mg through a $^{24}$Mg(p,t)$^{22}$Mg measurement K.Y. Chae, B.W. Bardayan, J.C. Blackmon, B.H. Moazen, K. Chipps, R. Hatarik, K.L. Jones, R.L. Kozub, J.F. Liang, C.D. Nesaraja, P.D. O'Malley, C. Matei, S.D. Pain, S.T. Pittman, M.S. Smith The $^{18}$Ne(alpha,p)$^{21}$Na reaction plays a crucial role in the (alpha,p) process, which leads to the rapid proton capture process in X-ray bursts. The reaction rate depends upon properties of $^{22}$Mg levels above the alpha threshold at 8.14 MeV. Despite recent studies of these levels, only the excitation energies are known for most with no constraints on the spins. We have studied the $^{24}$Mg(p,t)$^{22}$Mg reaction at the ORNL Holifield Radioactive Ion Beam Facility, and by measuring the angular distributions of outgoing tritons, hope to provide the first experimental constraints on the spins of astrophysically-important $^{18}$Ne(alpha,p)$^{21}$Na resonances. Details of the experiment and a report of the current stage of the analysis will be presented. * This work was supported in part by the US DOE and the NSF. [Preview Abstract] |
Sunday, April 13, 2008 9:18AM - 9:30AM |
H15.00005: Experimental Exploration of $^{69}Br$ and the rp-Process $^{68}Se$ Waiting Point A.M. Rogers*, M.A. Famiano*, M.S. Wallace*, M.-J. van Goethem*, F. Delaunay*, W.G. Lynch*, M.B. Tsang*, M. Mocko*, J. Lee*, R.T. de Souza*, S. Hudan*, L.G. Sobotka*, R.J. Charity*, J. Elson*, S. Lobastov, D. Shapira, D. Bazin, A. Gade, G. Verde* To realistically model the rp-process, experimental data along the proton dripline are required. Of particular interest is the $^{68}Se$ waiting point region where proton capture is inhibited. The reaction rate for the 2p-capture process $^{68}Se + 2p\rightarrow^{70}Kr$ depends exponentially on the Q-value, which is poorly constrained. We have performed an experiment to measure Q-values of proton unbound states of nuclei, specifically $^{69}Br$, at the NSCL Coupled Cyclotron Facility. The experiment is designed to reconstruct the decays of proton unbound nuclei such as $^{69}Br$ by detecting the decay protons using the MSU High Resolution Array (HiRA) in coincidence with a heavy residue, e.g. $^{68}Se$, which is measured in the S800 spectrograph. Details of the experimental setup as well as preliminary experimental results will be presented. [Preview Abstract] |
Sunday, April 13, 2008 9:30AM - 9:42AM |
H15.00006: Mass Measurements of Proton-Rich Isotopes between Mo and Pd using the Canadian Penning Trap Mass Spectrometer J. Fallis, K.S. Sharma, H. Sharma, G. Savard, A.F. Levand, T. Sun, J.A. Clark, C. Deibel, A. Parikh, C. Wrede, D. Lascar, R. Segel, S. Caldwell, M. Sternberg, J. Van Schelt, F. Buchinger, J.E. Crawford, S. Gulick, J.K.P. Lee, G. Li, N.D. Scielzo, A.A. Hecht In our understanding of the origin of elemental abundances the means of producing the observed abundances of $^{92}$Mo and $^{94}$Mo have long been unknown. These ``light p'' nuclei cannot be adequately produced by the classic p-process alone. The $\nu$p-process however, which occurs due to the neutrino wind in core collapse supernovae explosions, involves both proton-capture and neutron-capture reactions and can produce $^{92}$Mo and $^{94}$Mo. The final abundances of these isotopes depend directly on the values of the proton separation energies, S$_{p}$, along the reaction path of this process. Recent mass measurements performed with the Canadian Penning Trap Mass Spectrometer have dramatically reduced the uncertainties of S$_{p}$ values of proton-rich nuclei between Mo and Pd. These measurements and the resulting implications for both the $\nu$p-process path and the $^{92}$Mo/$^{94}$Mo abundance ratio will be discussed. This work was supported by grants from NSERC, Canada and the U.S. DOE, Nucl. Phys. Div.,under Contract W-31-109-ENG-38 [Preview Abstract] |
Sunday, April 13, 2008 9:42AM - 9:54AM |
H15.00007: Thermal Conductivity of Accreting Neutron Stars Crusts. Liliana Caballero, Charles Horowitz Many Neutron Stars in binary systems exhibit X-ray outbursts. Cooling times after a burst depend on where in the crust heating from thermonuclear and pycnonuclear reactions occur, and the crust's thermal conductivity. The thermal conductivity depends on electrons scattering from nuclei. We use molecular dynamics simulations to determine the structure of the crust when large numbers of impurities are present. We find a regular lattice, instead of an amorphous solid, with a large thermal conductivity. This high conductivity may require additional heating from pycnonuclear reactions in order to explain the ignition temperatures of superburts. [Preview Abstract] |
Sunday, April 13, 2008 9:54AM - 10:06AM |
H15.00008: Nuclear Matter at High Density and Finite Temperature Abhishek Mukherjee, Geoff Ravenhall, Jaime Morales, Vijay Pandharipande The equation of state of bulk nuclear matter is one of the most important microscopic inputs in the understanding of supernovae explosions and cooling of proto-neutron stars. This talk will describe calculations of the equation of state of nuclear matter at finite temperature based on the variational principle and correlated basis functions, and using modern realistic two body (Argonne v18) and three body (Urbana IX) nuclear forces. This work is a generalization of the Akmal-Pandharipande-Ravenhall equation of state to finite temperatures. The behavior of some other important physical quantities including the effective mass will also be discussed. [Preview Abstract] |
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