Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session K9: Nuclear Astrophysics |
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Sponsoring Units: DNP Chair: Carlos Bertulani, Texas A&M University Commerce Room: 250A |
Sunday, April 17, 2016 1:30PM - 1:42PM |
K9.00001: Cross-section measurements of $^7Be+d \rightarrow p+\alpha+\alpha$ and $^7Li+d \rightarrow n+\alpha+\alpha$ with ANASEN and their implication in the Standard Big Bang Nucleosynthesis(SBBN). Nabin Rijal, Ingo Wiedenhover, L.T. Baby, J. Belarge, S. Kuvin, J.C. Blackmon, K.T. Macon, D. Santiago-Gonzalez, E. Koshchiy, G. Rogachev Astrophysically observed $^7Li$ is 3-4 times less than predicted by current models of SBBN. The nuclear reaction $^7Be+d$ at energies relevant to SBBN, has been discussed as a possible means to destroy mass-7 nuclei. We investigate the $^7Be+d$ reaction at SBBN energies using a radioactive $^7Be$ beam and deuterium gas target inside ANASEN (Array for Nuclear Astrophysics Studies with Exotic Nuclei). ANASEN is an active target detector system which tracks the charged particles using a position sensitive proportional counter and 24-SX3 and 4-QQQ position sensitive Silicon detectors, all backed up by CsI detectors. The experiment measures a continuous excitation function by slowing down the beam in the target gas down to zero energy. Our set-up provides a high detection efficiency for all relevant reaction channels. We also performed an experiment for the mirror nuclear reaction $^7Li+d$ with ANASEN in solid target mode as well as in gas target mode. The preliminary results of these experiments along with details of ANASEN will be presented. [Preview Abstract] |
Sunday, April 17, 2016 1:42PM - 1:54PM |
K9.00002: Bubble Chamber : A novel technique for measuring thermonuclear rates at low energies R. Talwar, J. Benesh, B. DiGiovine, J. Grames, R. J. Holt, G. Kharashvili, D. Meekins, D. Moser, M. Poelkar, K. E. Rehm, A. Robinson, A. Sonnenschein, M. Stutzman, R. Suleiman, C. Tennant, C. Ugalde Adopting ideas from dark matter search experiments, we have found that a superheated liquid in a bubble detector is sensitive to recoils produced by $\gamma$-ray beams impinging on the nuclei in the liquid. Such a target-detector system has a density factor of four orders of magnitude higher than conventional gas targets and is practically insensitive to the $\gamma$-ray beam itself. Also, since photodisintegration reactions have approximately two orders of magnitude higher cross-sections than direct particle capture reactions, such a technique can pave the way towards measuring these reactions within the stellar Gamow window. In an effort to study the $^{16}$O($\gamma,\alpha$)$^{12}$C system using the bubble chamber technique, the first test of the superheated N$_2$O liquid with a low-energy bremsstrahlung beam at JLab has been completed. This test has been performed to understand the background contributions from $^{17}$O and $^{18}$O nuclei in N$_2$O. The experimental technique, results and future plans will be presented. [Preview Abstract] |
Sunday, April 17, 2016 1:54PM - 2:06PM |
K9.00003: \A{31}Cl beta decay and the \A{30}P\pg\A{31}S reaction rate in nova nucleosynthesis Michael Bennett, C. Wrede, B. A. Brown, S. N. Liddick, D. PĂ©rez-Loureiro The \A{30}P\pg\A{31}S reaction rate is critical for modeling the final isotopic abundances of ONe nova nucleosynthesis, identifying the origin of presolar nova grains, and calibrating proposed nova thermometers. Unfortunately, this rate is essentially experimentally unconstrained because the strengths of key \A{31}S proton capture resonances are not known, due to uncertainties in their spins and parities. Using a \A{31}Cl beam produced at the National Superconducting Cyclotron Laboratory, we have populated several \A{31}S states for study via beta decay and devised a new decay scheme which includes updated beta feedings and gamma branchings as well as multiple states previously unobserved in \A{31}Cl beta decay. Results of this study, including the unambiguous identification due to isospin mixing of a new $l = 0$, $J^\pi = 3/2^+$ \A{31}S resonance directly in the middle of the Gamow Window, will be presented, and significance to the evaluation of the \A{30}P\pg\A{31}S reaction rate will be discussed. [Preview Abstract] |
Sunday, April 17, 2016 2:06PM - 2:42PM |
K9.00004: Measuring Th, U and Pb abundances in the ancient r-process star HE1523-0901, and neutron-star mergers as the site of the r-process Invited Speaker: Anna Frebel Some old metal-poor Galactic stars formed from material enriched in the hehaviest elements made in the r-process, enabling stellar age measurements. In the case of star HE 1523-0901, an age of 13.2 Gyr was previously derived from multipe abundance ratios involving Th, U and other heavy stable elements. A new measurement of the total produced Pb strongly constraints the various Pb production channels in the r-process that occur in addition to the decay component by the Th and U decay. We find good agreement with current "waiting point" models for the production of elements in the actinide region. These observational constraints will improve r-process modelling of the heaviest n-rich nuclei. Together with results of the "r-process galaxy" Reticulum II (Ji et al. 2016), constraint are now available on neutron-star mergers as the site of the r-process. It remains to be seen if halo r-process stars like HE1523-0901 share the same nucleosynthetic origin [Preview Abstract] |
Sunday, April 17, 2016 2:42PM - 2:54PM |
K9.00005: Influence of neutrinos on r-process nucleosynthesis in black hole--neutron star mergers Jonas Lippuner, Luke F. Roberts, Matthew D. Duez, Joshua A. Faber, Francois Foucart, James C. Lombardi, Christian D. Ott, Marcelo Ponce During a black hole--neutron star merger, baryonic material can be dynamically ejected. Because this ejecta is extremely neutron-rich, the r-process rapidly synthesizes heavy nuclides as the material expands and cools. This can contribute to galactic chemical evolution of the r-process elements and lead to a short-lived optical transient, called a kilonova, powered by the radioactive decay of the heavy nuclides. We use the nuclear reaction network {\it SkyNet} to model r-process nucleosynthesis under varying levels of neutrino irradiation by post-processing tracer particles in the ejecta of a full numerical relativity simulation of a black hole--neutron star merger. We find the ejected material robustly produces the second and third r-process peaks, whose abundances remain unchanged even for very high neutrino luminosities, due to the rapid velocities of the outflow. Nonetheless, we find that neutrinos can have an impact on the detailed abundance pattern by significantly enhancing the amount of material produced in the first peak around $A\sim78$. Electron neutrinos are captured by neutrons to produce protons while neutron capture is occurring. These protons rapidly form low-mass seed nuclei, a fraction of which eventually ends up in the first peak after neutron capture ceases. [Preview Abstract] |
Sunday, April 17, 2016 2:54PM - 3:06PM |
K9.00006: ABSTRACT MOVED TO X4.003 |
Sunday, April 17, 2016 3:06PM - 3:18PM |
K9.00007: Pairing in high-density neutron matter including short- and long-range correlations Dong Ding, Arnau Rios, Helber Dussan, Willem Dickhoff, Sam Witte, Artur Polls To address open questions in neutron star phenomenology, pairing gaps of $^1S_0$ and $^3P_2-^3F_2$ channels in a wide range of densities has been calculated using three different interactions (AV18 CDbonn N3LO). Traditionally, the Bardeen-Cooper-Schrieffer(BCS) approach has been used to compute gaps from bare nucleon-nucleon interactions. Here, we incorporate the influence of short- and long-range correlations in the pairing gaps. Short-range correlations (SRC) are treated including the appropriate fragmentation of single-particle states, and they suppress the gaps substantially. Long-range correlations(LRC) dress the pairing interaction via density and spin modes, and provide a relatively small correction. Results are relevant and parametrized in a user friendly way for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A. [Preview Abstract] |
Sunday, April 17, 2016 3:18PM - 3:30PM |
K9.00008: Outflows from neutron star merger remnant disks: nucleosynthesis and kilonovae Rodrigo Fernandez, Jonas Lippuner, Luke Roberts, Alexander Tchekhovskoy, Francois Foucart, Brian Metzger, Daniel Kasen, Eliot Quataert The accretion disk formed in a neutron star merger can drive powerful winds on timescales of 100ms to seconds after coalescence. The wind material is more strongly irradiated by neutrinos than the dynamical ejecta, and hence has a less neutron-rich composition, with implications for $r$-process element synthesis and the radioactively-powered kilonova transient. This talk will present preliminary results from projects aimed at quantifying (1) the nucleosynthesis yield from disks around hypermassive neutron stars, (2) the effect of MHD turbulence on mass ejection when a black hole sits at the center, and (3) the interaction between disk wind and dynamical ejecta when the relative masses of these components vary. [Preview Abstract] |
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