Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session CG: Nuclear Astrophysics: Nucleosynthesis |
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Chair: Jeff Blackmon, Oak Ridge National Laboratory Room: Peralta |
Thursday, November 4, 2010 8:30AM - 8:42AM |
CG.00001: Measuring $^{3}$He($^{3}$He,2p)$^{4}$He and t(t,2n)$^{4}$He reactions near 10 keV at inertial confinement fusion facilities D.P. McNabb, R.N. Boyd, D.T. Casey, J.A. Frenje, S. Hatchett, C.K. Li, A. Mackinnon, P.W. McKenty, P. Navratil, R.D. Petrasso, S. Quaglioni, T.C. Sangster, F.H. Seguin Nuclear reactions at stellar energies are often obtained through extrapolations from higher energy data, or in low-background experiments such as those at the LUNA underground laboratory. However, even when measurements are possible, TN rates in burning plasmas are inherently different from those in beam-target experiments. The fusing nuclei are surrounded by bound electrons in accelerator experiments, whereas they occupy mainly continuum states in the plasma environment of a star. We will discuss plans to measure the bare-nuclear cross section and particle production spectra for the $^{3}$He($^{3}$He,2p)$^{4}$He fusion, a key reaction in the solar proton-proton chain, and the analogue T(t,2n)$^{4}$He reaction. Challenging issues of characterizing background proecess and plasman conditions will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 8:42AM - 8:54AM |
CG.00002: Low energy measurements of the 12C(a,g) reaction with a bubble chamber Claudio Ugalde, Brad Digiovine, Kevin Gullikson, Roy Holt, Dale Henderson, Ernst Rehm, Andrew Sonnenschein, Arthur Champagne, Rajarshi Raut, Gencho Rusev, Anton Tonchev, Neil Sturchio Hydrostatic helium burning in stars is dominated be the 3$\alpha$ and the 12C($\alpha,\gamma)$ processes. While the former is thought to be reasonably well understood, the latter has eluded even the most sensitive laboratory measurements. This reaction not only has a strong influence on the nucleosynthesis of most elements of the periodic table, but also determines the structure and evolution of subsequent stellar burning stages and explosive scenarios. We have devised a technique for measuring the 12C($\alpha,\gamma)$ reaction with a considerable improvement in sensitivity from previous experiments. Adopting ideas from dark matter search experiments with bubble chambers, we have found that a superheated water vessel would be sensitive to $\alpha$ particle and 12C recoils produced from a $\gamma$ ray impinging on 16O nuclei. The main advantage of the new target-detector system is a density as high as a factor of 10,000 over conventional gas targets. Also, the detector would be virtually insensitive to the $\gamma$ ray beam itself, thus allowing us to detect only the products of the reaction of interest. [Preview Abstract] |
Thursday, November 4, 2010 8:54AM - 9:06AM |
CG.00003: Studying the triple - $\alpha$ reaction in hyperspherical harmonic approach Ngoc Nguyen, Filomena Nunes The triple-$\alpha$ reaction is studied by using hyperspherical harmonic (HH) method [1]. Starting from three body model, we determine the $2^+$ state and the $0^+$ resonance as well as the quadrupole strength function B(E2). The triple-$\alpha$ reaction rate are calculated. We also carefully consider the contributions of the nonresonant continuum states to the reaction rate at low temperature ($T \le 10^8 K$). The results are compared with [2,3].\\[4pt] [1] I. J. Thompson, F. M. Nunes, B. V. Danilin, Comput.Phys.Comm. {\bf 161, 87-107 (2004).}\\[0pt] [2] K.Ogata, M.Kan, M.Kamimura, Prog. Theor. Phys. {\bf 122, 1055 (2009).}\\[0pt] [3] R. de Diego, E. Garrido, D.V. Fedorov, A.S. Jensen, {\bf arXiv:1005.5647v1.} [Preview Abstract] |
Thursday, November 4, 2010 9:06AM - 9:18AM |
CG.00004: Determination of the stellar reaction rates of $^{17}$O($\alpha$,n)$^{20}$Ne and $^{17}$O($\alpha, \gamma$)$^{21}$Ne Andreas Best, Sascha Falahat, Joachim Goerres, Michael Wiescher The reaction $^{16}$O(n, $\gamma)^{17}$O acts a neutron poison in the weak s-process by reducing the number of available neutrons in the stellar burning environment. The captured neutrons can be re-emitted into the stellar environment via the reaction $^{17}$O(n, n)$^{20}$Ne, weakening the poisoning effect of $^{16}$O. This channel competes with the reaction $^{17}$O($\alpha, \gamma)^{21}$Ne, so that in order to determine the strength of $^{16}$O as a neutron poison it is important to know the reaction of both channels. Only limited information is available on the $^{16}$O($\alpha, n)^{20}$Ne and especially on the $^{16}$O($\alpha, \gamma)^{21}$Ne reaction, which leads to large uncertainties in the determination of the abundance production of the weak s-process. The $(\alpha, n)$ channel has been measured in the energy range from 900 keV to 2300 keV using a high efficiency 4$\pi$ neutron detector. To improve the efficiency determination of the detector the $(\alpha, n_1)$ channel has been measured separately via gamma-ray spectroscopy and the detector response to the resulting neutron energy distribution has been modeled in a Geant4 simulation. An initial measurement of the $(\alpha, \gamma)$ channel has been successfully completed and a second experiment using the new 5 HPGe detector array GEORGINA is in planning. Results of the finished experiments and the planned experiment will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 9:18AM - 9:30AM |
CG.00005: Recent measurements at DRAGON Ulrike Hager The DRAGON recoil separator facility at TRIUMF measures radiative alpha and proton capture reactions of astrophysical importance in inverse kinematics. This is done using radioactive and stable ion beams produced and accelerated using the ISAC (Isotope Separator and ACcelerator) facility. Over the last few years, the DRAGON collaboration has embarked on a programme to measure a variety of reactions considered vital to the understanding of various astrophysical scenarios. During the last year two such measurements were conducted, namely $^{17}$O($\alpha$,$\gamma$)$^{21}$Ne and $^{33}$S($p$,$\gamma$)$^{34}$Cl. The $^{17}$O($\alpha$,$\gamma$)$^{21}$Ne reaction plays a potentially important part in the $s$-process, as the $^{17}$O($\alpha$,$\gamma$) / $^{17}$O($\alpha$,$n$) reaction rate ratio determines the efficiency of $^{16}$O as a neutron poison through the $^{16}$O($n$,$\gamma$)$^{17}$O reaction. The $^{33}$S($p$,$\gamma$)$^{34}$ reaction is important for understanding certain elemental abundances in Oxygen Neon (ONe) Novae. Nucleosynthesis calculations predict as much as 150x the solar abundance of $^{33}$S in the ejecta of ONe novae. The overproduction factor may, however, vary by factors of at least 0.01 -- 3 due to uncertainties in the $^{33}$S($p$,$\gamma$)$^{34}$Cl reaction rate at nova temperatures. [Preview Abstract] |
Thursday, November 4, 2010 9:30AM - 9:42AM |
CG.00006: A Study of ${ }^{12}C({ }^{12}C,n){ }^{23}Mg$ Brian Bucher, Justin Browne, Adam Alongi, Xiao Fang, Alexander Moncion, Katherine O'Connor, Wanpeng Tan, Xiaodong Tang The ${ }^{12}C({ }^{12}C,n){ }^{23}Mg$ reaction may be a significant neutron source for the weak s-process, which occurs in massive stars and is largely responsible for the elements iron through strontium. It has been studied with the FN Tandem Van de Graaff accelerator at the University of Notre Dame using beta and gamma spectroscopy. Measurements have been made at center-of-mass energies ranging from 6.5 MeV down to 3.5 MeV. Only one other data set reaches this low in energy (Dayras et al. 1977), so it is important to check these results and attempt to push the measurements towards lower energies, in order to more accurately predict the reaction rate in astrophysical environments. Preliminary results of the new measurements, along with a comparison to previous measurements, will be presented at the conference. [Preview Abstract] |
Thursday, November 4, 2010 9:42AM - 9:54AM |
CG.00007: Measurement of the NP Elastic Cross Section by Neutron Transmission Brian Daub, Michael Kovash, Vladimir Henzl, Khayrullo Shoniyozov There are very few previous measurements of the cross section for neutron-proton elastic scattering at energies between 200 and 500 keV. To improve this situation, we used a pulsed proton beam from the Van de Graaff accelerator at the University of Kentucky to produce 200-800 keV neutrons via the $^7$Li(p,n)$^7$Be reaction. We determined the total n-p elastic cross section by measuring the transmission of the neutron beam in samples of CH$_2$ and carbon, using a BC501 liquid scintillator. The cross section obtained by taking ratios between normalized sample-in and sample-out yields is independent of both detector efficiency and dead time. [Preview Abstract] |
Thursday, November 4, 2010 9:54AM - 10:06AM |
CG.00008: Discovery of the Grand Unified Theory Radhakrishnan Nair I have discovered the Grand Unified Theory which unites quantum with classical mechanics. This discovery is based on a geocentric universe, the myth of empty space, four states of matter in three dimensional space and space-time exponentiation, instead of space-time curvature. [Preview Abstract] |
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