Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session HD: Mini-Symposium on Radioactive Beams and Observations in Nuclear Astrophysics I |
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Chair: Ani Aprahamian, University of Notre Dame Room: Newport News Marriott at City Center Grand Salon IV |
Saturday, October 13, 2007 9:00AM - 9:36AM |
HD.00001: Signatures of the r- and rp-processes Invited Speaker: The astrophysical r- and rp-processes leave important signatures in the cosmic pattern of elemental abundances and in the observed features of astrophysical events such as X-ray bursts and cooling transient X-ray binaries. A wealth of new observational data has been collected on these signatures over the last years, providing new clues and also puzzles related to some key questions in nuclear astrophysics. This has greatly increased the need for reliable nuclear physics to enable interpretation of the observational data. I will review the progress in observations, the important open questions related to the r- and rp-processes, and the prospects of addressing the nuclear physics problems with radioactive beam experiments. [Preview Abstract] |
Saturday, October 13, 2007 9:36AM - 9:48AM |
HD.00002: Rp-process and r-process Studies with Radioactive Beams at ATLAS Hye Young Lee, M. Notani, K.E. Rehm, J.P. Greene, D. Henderson, R.V.F. Janssens, C.-L. Jiang, R.C. Pardo, J.P. Schiffer, N.J. Goodman, J.C. Lighthall, S.T. Marley, A. Wuosmaa, L.J. Jisonna, R.E. Segel, N. Patel, M. Paul, X.D. Tang For astrophysical interests, measurements with various radioactive beams using the in-flight method have been performed at ATLAS. In order to compensate the low cross sections, detection techniques with high efficiencies have been developed using silicon strip detectors in coincidence with the Enge split-pole spectrograph. Among the on-going projects, the $^{27}$Si(d,t)$^{26}$Si reaction has been measured in inverse kinematics using a radioactive $^{27}$Si beam to study spins and parities of levels above the proton threshold which are important for the rp-process path. To investigate the possible impact of neutron capture reactions with light nuclei in r-process, results from (d,p) measurements as surrogates for (n,$\gamma )$ studies will be also discussed. \textit{This work was supported in part by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 and by the NSF Grant No. PHY-02-16783 (Joint Institute for Nuclear Astrophysics).} [Preview Abstract] |
Saturday, October 13, 2007 9:48AM - 10:00AM |
HD.00003: Nuclear Astrophysics and ISAC: Past and Future Lothar Buchmann The past and future in the field of Nuclear Astrophysics at ISAC will be discussed. [Preview Abstract] |
Saturday, October 13, 2007 10:00AM - 10:12AM |
HD.00004: Laboratory Measurements of Explosive Nucleosynthesis P.D. Parker, J.A. Caggiano, J.A. Clark, C.M. Deibel, R. Lewis, A. Parikh, C. Wrede The determination of reaction rates involving radioactive nuclei is essential for understanding explosive nucleosynthesis. This can involve direct studies using radioactive beams (e.g., $^{13}$N, $^{17}$F, $^{21}$Na, etc.) and/or indirect studies of the properties of residual systems and their particle decays (e.g., $^{19}$Ne*$\leftrightarrow ^{18}$F+p, $^{27}$Si*$\leftrightarrow ^{26m}$Al+p, $^{31}$S*$\leftrightarrow ^{30}$P+p, etc.). Examples of these types of studies and their complementarity will be discussed. [Preview Abstract] |
Saturday, October 13, 2007 10:12AM - 10:24AM |
HD.00005: The impact of the $^{26}$Al$^{m}$(p,$\gamma )^{27}$Si reaction rate on the destruction of $^{26}$Al in ONe novae Catherine Deibel, Jac Caggiano, Jason Clark, Rachel Lewis, Anuj Parikh, Peter Parker, Christopher Wrede Evidence of ongoing nucleosynthesis of $^{26}$Al ($\tau _{1/2}$ = 7.2 x 10$^{5}$ yr) in our galaxy has been observed in the form of the 1.809 MeV $\gamma $-ray resulting from $^{25}$Mg(p,$\gamma )^{26}$Al$^{g.s.}(\beta ^{+ }\nu _{e})^{26}$Mg$^{\ast }$ [1]. The $^{25}$Mg(p,$\gamma )$ reaction can also produce $^{26}$Al$^{m}$, the short lived ($\tau _{1/2 }$= 6.3 s), 0$^{+}$, isomeric state of $^{26}$Al, which $\beta ^{+}$-decays to $^{26}$Mg$^{g.s.}$ only and must be treated separately from $^{26}$Al$^{ g.s.}$ at peak temperatures typical in novae (T$_{9 }\approx $ .1 - .35)[2]. Since $^{26}$Al(p,$\gamma )^{ 27}$Si competes with the $\beta ^{+}$-decay of $^{26}$Al in novae, resonances in $^{26}$Al$^{g.s./m}$(p,$\gamma )^{ 27}$Si may have a significant impact on $^{26}$Al production. We have used the $^{28}$Si(p,d)$^{ 27}$Si, $^{28}$Si($^{3}$He,$\alpha )^{ 27}$Si$^{\ast }$(p)$^{ 26}$Al, and $^{27}$Al($^{3}$He,t)$^{ 27}$Si$^{\ast }$(p)$^{ 26}$Al reactions to study the $^{26}$Al(p,$\gamma )^{ 27}$Si reaction. Several previously unpublished levels in $^{27}$Si and proton decay branching ratios will be reported. Their impact on the $^{26}$Al(p,$\gamma )^{ 27}$Si reaction rate and the nucleosynthesis of $^{26}$Al in ONe novae will be discussed. \newline [1] Diehl, R. \textit{et al.}, A{\&}A, \textbf{449} (2006) 1025. \newline [2] Ward, R.A. and Fowler, W.A., ApJ, \textbf{238} (1980) 266. [Preview Abstract] |
Saturday, October 13, 2007 10:24AM - 10:36AM |
HD.00006: Searching for resonances in the unbound $^{6}$Be nucleus K.Y. Chae, D.W. Bardayan, J.C. Blackmon, A.E. Champagne, J.J. Das, R.P. Fitzgerald, V. Guimaraes, K.L. Jones, M.S. Johnson, R.L. Kozub, R.J. Livesay, Z. Ma, C.D. Nesaraja, S.D. Pain, M.S. Smith, J.S. Thomas, D.W. Visser Knowledge of the $^{3}$He($^{3}$He,2p)$^{4}$He reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low energy resonance in the $^{3}$He+$^{3}$He system or electron screening. In the $^{6}$Be nucleus, however, no excited states have been observed above the first 2$^{+}$ state at E$_{x}$ = 1.67 MeV up to 23 MeV, even though several are expected. The d($^{7}$Be,t)$^{6}$Be reaction has been studied for the first time to search for resonances in the $^{6}$Be nucleus using radioactive $^{7}$Be beam at the ORNL Holifield Radioactive Ion Beam Facility. Details of the experiment and a report of the current stage of the analysis will be presented. [Preview Abstract] |
Saturday, October 13, 2007 10:36AM - 10:48AM |
HD.00007: Structure of $^8$B through $^7$Be+p scattering J.C. Blackmon, R.J. Livesay, U. Greife, D.W. Bardayan, K.Y. Chae, A.E. Champagne, C. Diebel, R. Fitzgerald, M.S. Johnson, K.L. Jones, R.L. Kozub, Z. Ma, C.D. Nesaraja, S.D. Pain, F. Sarazin, J.F. Shriner, Jr., D.W. Stracener, M.S. Smith, J.S. Thomas, D.W. Visser, C. Wrede Cross sections for $^7$Be+p elastic and inelastic scattering were measured at the HRIBF. Beams of $^7$Be at 17 incident energies betweeen E$_{cm}$=0.5-3.4 MeV bombarded CH$_2$ targets. Scattered protons were detected in a silicon-strip detector array covering $\theta_{cm}$=70$^{\circ}$-150$^{\circ}$. We have performed a multi-level R-matrix analysis of the combined cross sections (about 400 data points) to determine properties of states in $^8$B. The inelastic scattering data provide evidence for positive-parity states that were previously unobserved but were predicted by theory. Results and implications will be discussed. [Preview Abstract] |
Saturday, October 13, 2007 10:48AM - 11:00AM |
HD.00008: The ${}^{16}$N $\beta$-delayed $\alpha$ decay : Today and Tomorrow Xiaodong Tang The ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O is one of the most important reactions in nuclear astrophysics. The best determination of the S factor relies on three different experiments, the elastic scattering of $\alpha$ off ${}^{12}$C, the $\alpha$ capture reaction on ${}^{12}$C and the ${}^{16}$N $\beta$ delayed $\alpha$ decay. In this talk, I will review the current status of the existing ${}^{16}$N decay experiments. I will also discuss the possible ${}^{16}$N experiments in the near future to achieve more accurate S factor. [Preview Abstract] |
Saturday, October 13, 2007 11:00AM - 11:12AM |
HD.00009: Reaction Rates for Neutron Capture Reactions on Light sd-shell Nuclei Mary Beard, Michael Wiescher, Alberto Mengoni, B. Alex Brown Reaction rates of neutron capture cross sections on light nuclei are of great importance to a wide variety of astrophysical nucleosynthesis scenarios. Where experimental data is not available, theoretical estimates of these rates provide a vital basis for inputs into a spectrum of stellar scenarios. Neutron capture reaction rates have been calculated for a range of light sd-shell nuclei, stretching into the neutron rich. The context for the reaction rate calculation has been a hybrid model of compound and direct capture model, where necessary nuclear data, when absent from the literature, has been provided by theoretical shell model calculations. [Preview Abstract] |
Saturday, October 13, 2007 11:12AM - 11:24AM |
HD.00010: Single particle states in $^{131}$Sn and the r-process R.L. Kozub, J.F. Shriner, Jr., A. Adekola, D.W. Bardayan, J.C. Blackmon, F. Liang, C.D. Nesaraja, D. Shapira, M.S. Smith, K.Y. Chae, K.L. Jones, Z. Ma, B.H. Moazen, K. Chipps, L. Erikson, J.A. Cizewski, R. Hatarik, S.D. Pain, C. Matei, W. Krolas, T.P. Swan Recent r-process calculations suggest the $^{130}$Sn(n,$\gamma$)$^{131}$Sn reaction rate plays a pivotal role in nucleosynthesis, engendering global effects on isotopic abundances over a wide mass range.$^1$ Direct neutron capture is likely the dominant reaction in the r-process near the N=82 closed shell, and the reaction rate is thus strongly impacted by the properties of single particle states in this region. We have acquired (d,p) reaction data in the A$\sim$132 region in inverse kinematics using $\sim$630 MeV beams (4.85 MeV/u for $^{130}$Sn) and CD$_2$ targets. An array of Si strip detectors, including SIDAR and an early implementation of the new ORRUBA, was used to detect reaction products. Preliminary excitation energies and angular distributions have been extracted for the strongest states observed in $^{131}$Sn, and DWBA calculations have been performed to determine $\ell$-values. A status report on analysis and results will be presented. \newline $^1$J. Beun, G. C. McLaughlin, W. R. Hix, and R. Surman, in prep. (2007). \newline Research supported by the U. S. Dept. of Energy, the National Science Foundation, and the LDRD program at ORNL. [Preview Abstract] |
Saturday, October 13, 2007 11:24AM - 11:36AM |
HD.00011: TOF Mass Measurements of Very Exotic Nuclides: an Input for Astrophysical Calculations M. Mato\v{s}, A. Estrade, M. Amthor, D. Bazin, A. Becerril, T. Elliot, D. Galaviz, A. Gade, G. Lorusso, F. Montes, J. Pereira, M. Portillo, A.M. Rogers, H. Schatz, A. Stolz, A. Aprahamian, D. Shapira, E. Smith, S. Gupta, M. Wallace Atomic masses play a crucial role in many nuclear astrophysics calculations. Very exotic nuclei can be accessed by time-of- flight techniques at radioactive beam facilities. The NSCL facility provides a well-suited infrastructure for TOF mass measurements of very exotic nuclei. At this facility, we have recently implemented a~TOF-B$\rho$ technique and performed mass measurements of neutron-rich nuclides in the Fe region, important for calculations of the r-process and processes occurring in the crust of accreting neutron stars. Description of the TOF technique, results and future plans related to nuclear astrophysics will be presented. [Preview Abstract] |
Saturday, October 13, 2007 11:36AM - 11:48AM |
HD.00012: NERO-The Neutron Emission Ratio Observer Giuseppe Lorusso, Jorque Pereira, Paul Hosmer, Karl Ludvig Kratz, Fernando Montes, Paul Reeder, Peter Santi, Hendrik Schatz The Neutron Emission Ratio Observer (NERO), has been constructed for the use at the National Superconducting Cyclotron Laboratory to work in conjunction with the NSCL Beta Counting System in order to detect $\beta $-delayed neutrons. The design of the detector provides high and flat efficiency for a wide range of neutron energies, as well as a low neutron background. [Preview Abstract] |
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