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 JF: Nuclear Astrophysics: Core Collapse and Collapsed Stars |
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Chair: Sanjay Reddy, Institute for Nuclear Theory, University of Washington Room: Garden III |
Friday, October 26, 2012 10:30AM - 10:42AM |
JF.00001: Unique first-forbidden $\beta$-decay rates for neutron-rich nickel and zinc isotopes in stellar matter Jameel-Un Nabi The structure of neutron-rich nuclei has grown interest with the development of modern techniques enabling access to the exotic regions of the nuclide chart. In astrophysical environments, when allowed Gamow-Teller(GT) transitions are unfavored, first-forbidden transitions become important especially in medium heavy and heavy nuclei. Particularly in case of neutron-rich nuclei, GT transitions tend to be Pauli blocked and first-forbidden transitions are favored. In this meeting I would like to present the microscopic calculation of unique first-forbidden stellar $\beta$-decay rates and the associated $\beta$-decay half-lives for a number of neutron-rich nickel and zinc isotopes using the pn-QRPA theory. Comparison of the total half-lives will also be made with the measured half-lives and other theoretical calculations wherever possible. The temperature and density profiles were chosen for the advanced nuclear burning stages of the presupernova and supernova star. The results for total beta decay half-lives, for these neutron-rich nuclei, are found to be in much better agreement with the measured results and show marked improvement over the calculated half-lives where only allowed GT transitions were considered. The calculated rates are of special importance for core-collapse simu [Preview Abstract] |
Friday, October 26, 2012 10:42AM - 10:54AM |
JF.00002: Mass measurements along the r-process path at CARIBU Guy Savard, Jason Clark, Jon Van Schelt, Dan Lascar, Anthony Levand, Bruce Zabransky, Kumar Sharma The CARIBU facility is now operational and a large body of new mass measurements around the N=82 waiting point has been accumulated. The masses of over 70 neutron-rich isotopes from the heavy Californium fission peak have been measured with the CPT Penning trap mass spectrometer yielding a typical accuracy of 10 keV/c2. The most neutron-rich masses show significant deviations from either masses measured by other means when available or from extrapolated values from the last Atomic Mass Evaluation when no measurements where available. The system used for these measurements will be briefly described and an analysis of the modification to the delay for the r-process in this region when taking into accounts the new masses will be presented. [Preview Abstract] |
Friday, October 26, 2012 10:54AM - 11:06AM |
JF.00003: Sensitivity of the r-process to individual beta decay rates Rebecca Surman, J. Cass, G. Passucci, A. Aprahamian Beta decay rates have long been known to be crucial pieces of nuclear data for calculations of r-process nucleosynthesis. In light of experimental advances that have pushed measurement capabilities closer to the classic r-process path, we revisit the role of individual beta decay rates in a range of potential main r-process scenarios. We consider hot r-processes characterized by $(n,\gamma)$-$(\gamma,n)$ equilibrium and steady beta flow, freezeout from equilibrium, ana cold r-processes where $(n,\gamma)$-$(\gamma,n)$ equilibrium is established briefly if at all. We point out the nuclei in each of these scenarios whose beta decay rates have the greatest impact on the overall r-process abundance pattern and describe the mechanisms by which this influence occurs. [Preview Abstract] |
Friday, October 26, 2012 11:06AM - 11:18AM |
JF.00004: Neutrino-Induced Production of Beryllium in Core-Collapse Supernovae Projjwal Banerjee, Wick Haxton, Alexander Heger, Yong-Zhong Qian We present two new mechanisms for neutrino-induced production of $^9$Be in core-collapse supernovae. The first mechanism operates in the shocked material close to the core of low-mass progenitors of $\sim 8 M_\odot$. The second mechanism operates in He shells of progenitors of $\sim 11-15 M_\odot$. While the first mechanism is independent of metallicity, the second mechanism operates only at metallicities $\la 10^{-3}$ the solar value. We explore the sensitivity of both mechanisms to neutrino emission spectra, flavor oscillations, and the explosion energy. We find that the observed Be abundances at low metallicities can be accounted for by these two mechanisms and discuss similar mechanisms that may produce Be at higher metallicities. [Preview Abstract] |
Friday, October 26, 2012 11:18AM - 11:30AM |
JF.00005: Neutrino Pair Emission from Hot Nuclei During Stellar Collapse Wendell Misch, Alex Brown, George Fuller We present the results of shell model calculations that show that particle-hole repulsion helps enhance the rate of neutral current de-excitation of thermally excited nuclei into neutrino-antineutrino pairs. Our calculations indicate that this process is the dominant source of low energy neutrino pairs near the onset of neutrino trapping during stellar collapse. [Preview Abstract] |
Friday, October 26, 2012 11:30AM - 11:42AM |
JF.00006: Structure of the Highly Magnetized Neutron Star Crust Joseph Hughto, Charles Horowitz, Jose Pons Sharma \& Reddy recently investigated how the potential between two ions at high density is modified by the presence of a very strong magnetic field. If the field is high enough, only the first Landau level is filled and this leads to an anisotropic potential with magnetic screening. We take this potential and use Molecular Dynamics to model the crust of a magnetar. We determine the structure of the highly magnetized crust and also compute various transport properties. [Preview Abstract] |
Friday, October 26, 2012 11:42AM - 11:54AM |
JF.00007: ABSTRACT WITHDRAWN |
Friday, October 26, 2012 11:54AM - 12:06PM |
JF.00008: r-modes in Quark Stars with a Crystalline Superconducting Crust Gautam Rupak, Prashanth Jaikumar The r-mode instability in rotating compact objects provide strong constraints on the equation of state of dense matter. Calculations with quark matter in the color-flavor-locked (CFL) phase with or without kaon condensation indicate that the viscous damping in the superfluid matter due to Goldstone-Nambu boson scattering is not sufficient to explain the observed rotation rates in cold compact objects. We consider a star composed of a core made of CFL quark matter and a thin crust of crystalline color superconducting quark matter. The decay of the r-modes at the boundary with the crust that has a high shear modulus provides additional damping mechanism that can make the theoretical model compatible with observation. [Preview Abstract] |
Friday, October 26, 2012 12:06PM - 12:18PM |
JF.00009: Molecular dynamics simulations of nuclear pasta Andre da Silva Schneider, Joe Hughto, Don Berry, Charles Horowitz The study of supernovae requires understanding the properties of matter at a large range of densities and temperatures. At subnuclear densities of about $10^{14}$ g/cm$^3$ nucleons, protons and neutrons, become the relevant degrees of freedom. Both nucleons interact via a short-range nuclear force. Meanwhile, protons also interact via a long range Coulomb force. Because of competition between these two forces nucleons arrange themselves in a variety of complex shapes known as \textit{nuclear pasta}. In the present work we describe a simple semiclassical model for the nucleon interactions and use large scale molecular dynamics simulations to study the \textit{nuclear pasta}. [Preview Abstract] |
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