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 KF: Nuclear Astrophysics: Nuclear Structure |
Hide Abstracts |
Chair: Ani Aprahamian, University of Notre Dame Room: Garden III |
Friday, October 26, 2012 2:00PM - 2:12PM |
KF.00001: Leading E1 and M1 contributions to radiative neutron capture on lithium-7 Lakma Fernando, Renato Higa, Gautam Rupak We provide a model-independent calculation of the radiative neutron capture on lithium-7 over an energy range where the contribution from the 3+ resonance becomes important by using halo effective field theory. We describe how the couplings in the EFT Lagrangian are constrained from available data on low-lying bound and resonance states. We also present power counting arguments that establish a hierarchy for electromagnetic one- and two-body currents. Our model independent results quantify the current uncertainties in nuclear theory in the single particle approximation. [Preview Abstract] |
Friday, October 26, 2012 2:12PM - 2:24PM |
KF.00002: $^{18}$Ne level structure and the $^{14}$O($\alpha$,p) reaction rate Wanpeng Tan, S. Almaraz-Calderon, A. Aprahamian, B. Bucher, A. Roberts, M. Wiescher, C. Brune, T. Massey, N. Ozkan, R. Guray, H. Mach On one of the hot CNO waiting points, the $^{14}$O($\alpha$,p) reaction plays an important role in explosive hydrogen burning environments like X-ray bursts. It proceeds through the resonances (above the alpha-decay threshold) in $^{18}$Ne. The level structure of $^{18}$Ne above the alpha-decay threshold has been studied using the $^{16O}$($^3$He,n) reaction at Notre Dame. A coincidence measurement of neutrons and charged particles decaying from populated states in $^{18}$Ne has been made. Decay branching ratios were measured for six resonances and used to calculate the $^{14}$O($\alpha$,p)$^{17}$F reaction rate. The new experimental information combined with previous experimental and theoretical information provides a more accurate calculation of the reaction rate. [Preview Abstract] |
Friday, October 26, 2012 2:24PM - 2:36PM |
KF.00003: Stellar neutron sources and s-Process in Massive Stars R. Talwar, G.P.A. Berg, L. Bin, M. Couder, R. deBoer, X. Fang, H. Fujita, Y. Fujita, J. Goerres, K. Hatanaka, T. Itoh, T. Kadoya, A. Long, Y. Masaru, Y. Matsuda, K. Miki, A. Tamii, M. Wiescher Potential stellar neutron sources for the s-process in massive stars are associated with $\alpha $-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the buildup of the neutron sources $^{22}$Ne, and $^{26}$Mg during the helium-burning phase in stars. A critical influence on these reactions is expected to come from low-energy resonances at stellar energies between 300 keV and 1500 keV. It is possible that these resonances are characterized by a pronounced cluster structure near the $\alpha $-threshold. Direct measurements of capture reactions to study the cluster structure are handicapped by the Coulomb barrier and limited detector resolutions. Hence, inelastic $\alpha $-scattering on these nuclei has been used as an alternative tool to probe into the level structure. In reference to this, the experiment performed using the Grand Raiden Spectrometer at RCNP, Osaka will be discussed and preliminary results will be presented. [Preview Abstract] |
Friday, October 26, 2012 2:36PM - 2:48PM |
KF.00004: ABSTRACT WITHDRAWN |
Friday, October 26, 2012 2:48PM - 3:00PM |
KF.00005: The level Structure of $^{30}$S and its Astrophysical Implications S. Almaraz-Calderon, A. Aprahamian, G.P.A. Berg, W.P. Tan, M. Wiescher The level structure of $^{30}$S plays a fundamental role in understanding the nucleosynthesis processes of proton-rich nuclei in explosive scenarios. Thermonuclear runaway processes like Novae and X-ray bursts are driven by the rp- and $\alpha$p- processes, transferring proton-rich material from the Hot CNO cycle up to mass 40. Two of the key reactions in such processes, the $^{26}Si(\alpha,p)^{29}P$ and $^{29}P(p,\gamma)^{30}S$ are expected to proceed through resonance states in $^{30}$S, making the reaction rates very sensitive to the structure of $^{30}$S. We studied the level structure of $^{30}$S via the $^{28}Si(^{3}He,n)$ and $^{32}S(p,t)$ reactions. Important experimental information on energy levels, decay branching ratios and tentative spin assignments were extracted to calculate the $^{29}P(p,\gamma)^{30}S$ and $^{26}Si(\alpha,p)^{29}P$ reaction rates. Several levels between the proton- and alpha- thresholds were observed for the first time. The $^{29}P(p,\gamma)^{30}S$ reaction rate was re-evaluated using the new experimental information and compared with previous estimates. Levels above the alpha threshold have been measured for the first allowing us to calculate the experimental $^{26}Si(\alpha,p)^{29}P$ reaction rate and to compare it with theoretical calculations. [Preview Abstract] |
Friday, October 26, 2012 3:00PM - 3:12PM |
KF.00006: Low-lying structure of the N=49 nucleus $^{81}$Ge S. Ahn, K.L. Jones, S.T. Pittman, D.W. Bardayan, K.Y. Chae, C.D. Nesaraja, S.D. Pain, M.S. Smith, A.S. Adekola, J.A. Cizewski, S. Hardy, M.E. Howard, B. Manning, P.D. O'Malley, W.A. Peters, I. Spassova, K.A. Chipps, J.C. Blackmon, M. Matos, B.C. Rasco, R.L. Kozub The study of low-lying levels of nuclei near closed shells elucidates the evolution of nuclear shell structure far from stability, and also affects estimates of heavy element nucleosynthesis in supernova explosions. Currently, there is little experimental data for the relevant unstable nuclei. This is particularly the case on the the neutron-rich side, where changes in the shell structure are expected near the drip line. The low-lying levels of the N=49 nucleus $^{81}$Ge have been studied by measuring the $^{80}$Ge(d,p)$^{81}$Ge transfer reaction at 310 MeV (3.875 MeV/u) in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The excitation energies and the angular distributions of low-lying levels were measured. The experimental setup and the preliminary result on the data analysis will be presented. [Preview Abstract] |
Friday, October 26, 2012 3:12PM - 3:24PM |
KF.00007: Electron-Capture on Excited States of pf-shell Nuclei in Stellar Environments A.L. Cole, T.S. Anderson, A.C. Dombos, A.K. Schooley, R.G.T. Zegers, Sam M. Austin, B.A. Brown, L. Valdez, S. Gupta, G.W. Hitt, O. Fawwaz At stellar temperatures and densities electron-capture rates on ground and excited states of pf-shell nuclei can influence the dynamics of core-collapse and thermonuclear supernovae. For 13 pf-shell nuclei, we have completed a comparison between Gamow-Teller strength distributions and the corresponding electron-capture rates determined from measurements and those determined from shell model and QRPA calculations. Both of these measured and calculated electron-capture rates assumed that the parent nuclei were in the ground state. We now explore the effect that including excited states has on the calculated electron-capture rates and present preliminary results. [Preview Abstract] |
Friday, October 26, 2012 3:24PM - 3:36PM |
KF.00008: Beta-delayed neutron spectroscopy using an ion trap R.M. Yee, N.D. Scielzo, S. Caldwell, J.A. Clark, J.P. Greene, D. Lascar, A.F. Levand, G. Li, E.B. Norman, S. Padgett, M. Pedretti, A. Perez-Galvan, G. Savard, R.E. Segel, K.S. Sharma, M.G. Sternberg, J. Van Schelt, B.J. Zabransky Beta-delayed neutron emission is of interest to both pure and applied nuclear physics communities. For example, branching ratios are needed to determine how the short-lived neutron-rich isotopes synthesized in the astrophysical r-process decay back to stability. Also, neutron energy spectra are required for the design of nuclear reactors. Reliable measurements of beta-delayed neutron properties can be performed with high precision using a combination of sophisticated ion-trapping techniques and modern radiation-detection systems. When a radioactive ion decays in the trap, the recoil-daughter nucleus and emitted particles emerge from the $<$1 mm$^{3}$ trap volume with minimal scattering and propagate unobstructed through vacuum. These properties allow the momentum and energy of the emitted neutron to be precisely reconstructed from the nuclear recoil. Spectroscopy of beta-delayed neutrons can be performed with high efficiency and energy resolutions approaching 3{\%}. The current status of a campaign to measure delayed neutron properties of interest to nuclear reactors and r-process nucleosynthesis will be discussed. [Preview Abstract] |
Friday, October 26, 2012 3:36PM - 3:48PM |
KF.00009: Single Particle states in $^{131,133}$Sn and r-process nucleosynthesis Michael Smith, Shisheng Zhang, Ray Kozub, Goran Arbanas The (d,p) transfer reaction was recently used with radioactive $^{130}$Sn and $^{132}$Sn beams to determine four strong single-particle bound levels in $^{131,133}$Sn. These levels have strikingly similar excitation energy spacings that have not yet been addressed by a theoretical nuclear structure model. Information on these single particle bound levels, as well as on resonant levels above the neutron capture threshold, are also needed to determine the $^{130,132}$Sn neutron capture cross sections -- and their corresponding thermonuclear reaction rates -- which (in the case of $^{130}$Sn) significantly impacts the synthesis of heavy elements in the r-process in supernovae. We used the analytical continuation of the coupling constant (ACCC) method based on a relativistic mean field theory with BCS approximation to self-consistently calculate single-particle bound and resonant levels for $^{131,133}$Sn. Our results for the single particle bound and resonant levels in $^{131,133}$Sn will be presented, along with our level densities and the implications for neutron capture cross sections for r-process studies. [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