Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session CG: Mini-Symposium on Weak Interactions in Astrophysics |
Hide Abstracts |
Chair: Hendrik Schatz, Michigan State University Room: 105AB |
Thursday, October 27, 2011 8:30AM - 9:06AM |
CG.00001: Measurement of Gamow-Teller transitions from $^{56}$Ni Invited Speaker: Masaki Sasano Electron-capture (EC) and $\beta $-decay play important roles in type-II and type-Ia supernovae. They occur through the Gamow-Teller (GT) and Fermi transitions in nuclei, which are extensively studied to reliably estimate the weak-interactions rates. Experimentally, a powerful probe to study GT transitions has been provided by the charge-exchange reactions at intermediate energies such as the (p,n), ($^{3}$He,t) rections. They can selectively excite the GT transitions in a wide excitation energy region. Until recently, such studies have been restricted to stable nuclei because of difficulties in inverse-kinematics measurements with rare isotope beams. In this talk, we present the first study with a rare isotope using the $^{56}$Ni(p,n)$^{56}$Cu reaction at 110 MeV/u in inverse kinematics with a newly developed Low-Energy Neutron Detector Array (LENDA) in combination with the S800 spectrometer. $^{56}$Ni is produced in large abundances during the pre-explosion phase of core-collapse supernovae and considered to be as one of the most important contributors to the change in the electron-to-baryon ratio in core-collapse supernovae. In addition, to study the GT transition in $^{56}$Ni serves as a stringent test of the effects of the N=Z=28 core not being inert on GT transitions for a large number of nearby nuclei in the Fe region. [Preview Abstract] |
Thursday, October 27, 2011 9:06AM - 9:18AM |
CG.00002: A Long, Cold, Early $r$-process? $\nu$-induced Nucleosynthesis in He Shells Revisited Projjwal Banerjee, Wick Haxton, Yong-Zhong Qian We reexamine a $\nu$-driven $r$-process mechanism in the He shell of a core-collapse supernova with low initial metallicity. We use the hydrodynamic code KEPLER to calculate the nucleosynthesis both before and after the passage of shock, in recent pre-supernova models. We find that for an inverted neutrino mass hierarchy, $A\sim 130$ and 195 abundance peaks can be produced over $\sim 20$--50~s for initial metallicities $\leq 10^{-3}$ the solar value. The mechanism is sensitive to the amount of $^{28}$Si and $^{32}$S present in the He shell in the pre-supernova model, as well as on the $\nu$ emission model and oscillations. We discuss the implications of this early $r$-process which could alter interpretations of abundance data from metal-poor stars. [Preview Abstract] |
Thursday, October 27, 2011 9:18AM - 9:30AM |
CG.00003: Evidence for an Inverted Neutrino Mass Hierarchy from the T2K $\theta_{1 3}$ Result and $\nu$-Process Nucleosynthesis Grant Mathews, Toshitaka Kajino, Wako Aoki, Wataru Fujiya The synthesis of $^{11}$B and $^{7}$Li via neutrino-induced nucleon emission (the $\nu$-process) is sensitive to the neutrino mass hierarchy if the $\theta_{1 3}$ mixing angle is large enough. This arises because, when there is significant 13 mixing, the average electron neutrino energy for the charged-current neutrino reactions is larger for a normal mass hierarchy than for an inverted hierarchy. This mixing occurs in the carbon shell and hence affects the nucleosynthesis of $^{11}$B and $^{7}$Li in the helium shell of core-collapse supernovae. Recent constraints on $\theta_{1 3}$ from the T2K collaboration indicates that indeed $\theta_{1 3}$ is large enough to induce substantial mixing. Moreover, there is also recent recent evidence from SiC $X$ grains in meteorites for the existence of $\nu$-process $^{11}$B and $^{7}$Li encapsulated in some grains. We show here that these two new results hint at a marginal ($1 \sigma$) preference for an inverted neutrino mass hierarchy. The analysis of more $X$ grains enriched in Li and B could substantially improve this limit. [Preview Abstract] |
Thursday, October 27, 2011 9:30AM - 9:42AM |
CG.00004: Probing the origins of $^{19}$F with the $^{19}$F (t, $^{3}$He) $^{19}$O charge exchange reaction Amanda Prinke, R.G.T. Zegers, Sam M. Austin, D. Bazin, J.M. Deavin, R. Meharchand, K. Meierbachtol, G. Perdikakis, M. Sasano, L.L. Valdez, A. Cole, Y. Fujita, M. Nagashima, C.J. Guess, G.W. Hitt, Y. Shimbara Nuclear charge-exchange experiments are frequently used to extract Gamow-Teller strengths relevant to astrophysics. This talk will discuss one such recent measurement of the Gamow-Teller strength via the $^{19}$F (t, $^{3}$He) $^{19}$O* reaction at 115 MeV/u. The experiment was performed at the National Superconducting Cyclotron Laboratory using a secondary triton beam, and the $^{3}$He ejectiles were momentum-analyzed in the S800 magnetic spectrometer. The extracted Gamow-Teller strength distribution from this experiment can be directly related to $^{19}$O* beta decay to $^{19}$F. This weak interaction rate may contribute to the astrophysical abundance of $^{19}$F. Additionally, the experimental results will be compared to shell-model calculations in the sd-shell. [Preview Abstract] |
Thursday, October 27, 2011 9:42AM - 9:54AM |
CG.00005: Computational Resources for Including Nuclear Physics in Astrophysical Simulations Evan O'Connor, Christian D. Ott Simulations of core-collapse supernovae have long included detailed nuclear physics such as finite-temperature equations of state (EOS) and neutrino interactions. Computational simulations of relativistic astrophysical systems such as Black Hole (BH) - Neutron Star (NS) binaries and NS-NS binaries are also beginning to include these nuclear physics inputs. We present a set of open-source, computational tools to aid in the incorporation of nuclear physics into simulations. At stellarcollapse.org, we provide EOS tables and the associated drivers needed to quickly, smoothly, and efficiently integrate all publicly available finite-temperature EOS tables into astrophysical simulations. We also have recently begun compiling, and present here, an open-source library of neutrino interactions relevant for computational simulations of relativistic astrophysical systems. The ultimate goal of NuLib is to provide a computationally efficient and complete resource of neutrino interactions for physics benchmarking and code validation. NuLib will also provide a venue for nuclear theorists to make available to the computational community new or improved neutrino interactions. [Preview Abstract] |
Thursday, October 27, 2011 9:54AM - 10:06AM |
CG.00006: Nuclear reactions in the crust of an accreting neutron star Kit Yu Lau, A.V. Afanasjev, M. Beard, E. Brown, L.R. Gasques, S. Gupta, W.R. Hix, K.L. Kratz, P. Moller, H. Schatz, A. Steiner, M. Wiescher, D.G. Yakovlev Recently there have been many discoveries from observations of accreting neutron stars in x-ray binaries. Many of the observed phenomena such as superbursts or the cooling of quasi-persistent transients during their quiescent state are affected by the thermal properties and the composition of the crust. To model the nuclear energy release and crust compositions, we run a consistent nuclear reaction network that follows the evolution of an accreted fluid element from the atmosphere down to the inner crust, where free neutrons exist in beta-equilibrium. We take into account a majority of the most important nuclear processes including electron capture, neutron capture, neutron emissions, $\beta $ decay, and pycnonuclear fusion reactions. Our calculations show that pycnonuclear fusion reactions can occur at a shallower depth than previously thought, depending on the nuclear mass model used. [Preview Abstract] |
Thursday, October 27, 2011 10:06AM - 10:18AM |
CG.00007: Determining Electron-capture Rates of pf-shell Nuclei in Explosive Stellar Environments A.L. Cole, A.C. Dombos, R.G.T. Zegers, Sam M. Austin, B.A. Brown, L. Valdez, S. Gupta, G.W. Hitt The electron-capture rates on pf-shell nuclei are required to model the evolution of core-collapse and thermonuclear supernovae. The majority of these rates are determined from calculated Gamow-Teller strength (B(GT)) distributions, as it's not feasible to measure the B(GT) distributions for all pf-shell nuclei. We present preliminary results of a systematic comparison between the electron-capture rates of 13 pf-shell nuclei determined from experimental B(GT) distribution measurements and the electron-capture rates of nuclei determined only from calculated B(GT) distributions, as measurements do not exist. The B(GT) distribution calculations were performed with the shell model using two different interaction Hamiltonians. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700