Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session H11: Nuclear Astrophysics |
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Sponsoring Units: DNP Chair: Artemis Spyrou, Michigan State University Room: Embassy F |
Sunday, April 1, 2012 10:45AM - 10:57AM |
H11.00001: Alpha production via electromagnetic dissociation John W. Norbury Light ions produced from the interactions of galactic cosmic rays (GCR) provide a significant contribution to the space radiation environment inside spacecraft. Among the most important light ions are alpha particles. In relativistic nucleus-nucleus collisions, which are the type of collisions relevant for GCR interactions, light ions are produced from both strong and electromagnetic forces. Electromagnetic dissociation (EMD) is the process whereby a virtual photon from one nucleus knocks out a particle from the other nucleus. Therefore, in predicting space radiation environments one must include a correct description of alpha production via EMD. A calculation of this process, using a theoretical photonuclear model, is presented and compared to experimental data. [Preview Abstract] |
Sunday, April 1, 2012 10:57AM - 11:09AM |
H11.00002: $^{18}$O($p$,$\gamma$)$^{19}$F resonance strength measurement at low energies Matthew Buckner, Christian Iliadis, John Cesaratto, Chris Howard, Thomas Clegg, Arthur Champagne, Stephen Daigle As a 0.4M$_{\bigodot}$ $\leq$ M $\leq$ 8M$_{\bigodot}$ approaches the end of its stellar evolution, it will enter the asymptotic giant branch (AGB) stage and ascend the giant branch one final time. During the AGB stage, a star experiences significant mass loss, and grain condensation occurs in the stellar atmosphere. A subset of presolar oxide grains recovered from comet and meteorite samples can be attributed to this stellar environment; these grains feature $^{18}$O depletion that cannot be explained by existing AGB stellar models. An extra mixing process referred to as ``cool bottom processing" (CBP) was proposed by Wasserburg et al. (1995) for low-mass AGB stars. The $^{18}$O depletion observed in these presolar grains may result from the $^{18}$O+$p$ process during CBP. A low energy, unobserved, narrow resonance exists within the ($p$,$\gamma$) reaction that may affect thermonuclear reaction rates near the CBP temperature regime. Though the E$_{R}^{lab}$ = 95 keV resonance strength ($\omega\gamma$) has been constrained previously, measurements at the Laboratory for Experimental Nuclear Astrophysics (LENA) have improved the resonance strength upper limit. The effect this improvement has on $^{18}$O($p$,$\gamma$)$^{19}$F thermonuclear reaction rates will be discussed. [Preview Abstract] |
Sunday, April 1, 2012 11:09AM - 11:21AM |
H11.00003: The Simulation of a Nuclear Astrophysics Detection System Christopher Howard, Arthur Champagne, Christian Iliadis The Laboratory for Experimental Nuclear Astrophysics (LENA), which is part of TUNL, houses a gamma-ray spectrometer designed for directly measuring stellar fusion reactions. The detection systems are made up of multiple detectors, taking advantage of multi-photon coincidence counting in order to reduce environmental background. This talk will describe the various methods of coincidence gating and associated Geant4 simulations. A number of examples will be presented and discussed: point source data, in-beam data, and an extended source -- the detection of aluminum-26 in a meteorite fragment. [Preview Abstract] |
Sunday, April 1, 2012 11:21AM - 11:33AM |
H11.00004: Experimental techniques to use the $(d,n)$ reaction for spectroscopy of low-lying proton-resonances Sean Kuvin, Ingo Wiedenh\"over, Lagy T. Baby, Jessica Baker, Daniel Santiago-Gonzalez, Georgios Perdikakis, Dennis Gay, Imeh Ebong 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. At the {\sc resolut} facility, we have used the $(d,n)$ reaction to populate the lowest $p$-- resonances in $^{26}$Si, and demonstrated the usefulness of this approach to populate the resonances of astrophysical interest [1]. In order to establish the $(d,n)$ reaction as a standard technique for the spectroscopy of astrophysical resonances, we have developed a compact setup of low-energy Neutron-detectors, {\sc resoneut} and tested it with the stable beam reaction $\mathrm{^{12}C(d,n)^{13}N}$ in inverse kinematics. Performance data from this test-experiment and future plans for this setup will be presented. \\[4pt] [1] P.N. Peplowski {\it et al.} Phys.Rev.{\bf C 79}, 032801 (2009) [Preview Abstract] |
Sunday, April 1, 2012 11:33AM - 11:45AM |
H11.00005: The commissioning of a summing NaI(Tl) (SuN) gamma detector Anna Simon Proton rich nuclei more massive than iron cannot be produced by s- or r-processes, as the $\beta $-decay of neutron rich seed nuclei stops at the valley of stability. The most favorable scenario for the creation of these nuclei is a chain of photodisintegration reactions, namely ($\gamma $,p), ($\gamma $,$\alpha )$ and ($\gamma $,n), the so called p-process. The p-process can be studied via the reverse reactions, radiative capture. To develop a more lucid picture of the p-process through this capture process at energies relevant to astrophysical environments a summing NaI(Tl) (SuN) gamma detector has been commissioned and developed at the NSCL. SuN is a 16x16 in. cylindrical barrel divided into eight optically separated segments, each of which contains three photomultipliers. The segmentation of the crystal as well as a high summing efficiency (about 70{\%} for 60-Co) make the detector a perfect tool for investigation of (p,$\gamma )$ and ($\alpha $,$\gamma )$ reactions during inverse kinematics experiments. Utilizing radioactive beams from the ReA3 facility, SuN will provide a great opportunity for precise measurement of p-process relevant reactions cross sections for proton rich nuclei. Results of the first measurements utilizing the SuN detector and various beams from a Van de Graaff accelerator at the University of Notre Dame will be presented. [Preview Abstract] |
Sunday, April 1, 2012 11:45AM - 11:57AM |
H11.00006: R-Process Nucleosynthesis in the Neutrino Pair Heated Collapsar MHD Jet Grant Mathews, Ko Nakamura, Sasumu Sato, Seiji Harikae, Toshitaka Kajino The collapsar scenario is a model for long-duration gamma ray bursts (GRBs). It is also a possible site for r-process nucleosynthesis. We present numerical r-process calculations in the context of a MHD + neutrino pair heated collapsar simulation. This model begins with relativistic magnetohydrodynamic simulations including ray-tracing neutrino transport to describe the development of the black hole accretion disk and the heating of the funnel region to produce a relativistic jet. The late time evolution of the jet then utilizes axisymmetric special relativistic hydrodynamics to follow the temperature, entropy, electron fraction, and density for representative test particles flowing with the jet from temperatures of $9 \times 10^9$ to $3 \times 10^8$ K. The evolution of nuclear abundances from nucleons to heavy nuclei for representative test particle trajectories was solved in a large nuclear reaction network. We show that a robust $r$-process successfully occurs within the collapsar jet outflow and argue that sufficient mass is ejected within the flow to account for the observed r-process abundance distribution along with the large dispersion in r-process elements observed in metal-poor halo stars. [Preview Abstract] |
Sunday, April 1, 2012 11:57AM - 12:09PM |
H11.00007: $^{176}$Lu/$^{175}$Lu thermometry for Oklo natural reactors: a new look at old data Chris Gould, Eduard Sharapov Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures $T_O$, which in turn impacts Oklo bounds on the time variation of the fine structure constant $\alpha$. We revisit results for reactor zone RZ10 in light of new astrophysical measurements of the isomer branching ratio $B^g$ in $^{175}$Lu neutron capture at 5 and 25 keV. We recalculate predictions for $T_O$ as a function of $B^g$ using realistic models of the Oklo neutron flux. We find $T_O = 100 \pm 30$ C using a new value of $B^g$, in contrast to $350 < T_O < 500 $ C using the evaluated value at thermal energy. Lutetium thermometry can be applicable to analyses of Oklo reactor data, but a better measurement of $B^g$ with thermal neutrons is needed to confirm the reliability of temperature predictions. [Preview Abstract] |
Sunday, April 1, 2012 12:09PM - 12:21PM |
H11.00008: High Amplitude Bulk Viscosity of Dense Matter and Probing the Phases of Dense matter with Neutron Star Physics Simin Mahmoodifar, Mark Alford, Kai Schwenzer Neutron stars are the only laboratory for studying cold ultra-dense matter. Since the density at the core of a neutron star is extremely high one could expect the existence of exotic matter such as degenerate quarks, boson condensate and etc in the core. Studying the transport properties of the different phases of dense matter that can occur in a compact star is important because transport properties such as viscosity, emissivity, heat capacity and etc, in addition to depending on the equation of state of matter, also depend on the low-energy degrees of freedom and therefore can discriminate between different phases more efficiently. In this talk I will present our results for the high amplitude bulk viscosity of dense matter and I will explain how spin-down evolution of neutron stars can be used as a probe of the phases of matter at low temperatures and high densities. [Preview Abstract] |
Sunday, April 1, 2012 12:21PM - 12:33PM |
H11.00009: Bulk viscosity of strange quark matter Xinyang Wang, Igor Shovkovy It is known that the interior of neutron stars is made of very dense baryonic matter, but our knowledge regarding the actual state of such matter is incomplete. The way to test the idea regarding the presence of quark matter inside stars is to make predictions regarding physics processes that affect observable features of stars. Bulk viscosity is one of important properties which determines the suppression of the rotational instabilities. In this talk, I will introduce the bulk viscosity of strange quark matter by taking into account the interplay between the nonleptonic and semileptonic week processes. The result is very important in order to relate accessible observables of compact stars to their internal composition. [Preview Abstract] |
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