Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session H7: Nuclear Astrophysics |
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Sponsoring Units: DNP Chair: Kate Jones, University of Tennessee Room: Delaware A |
Sunday, February 14, 2010 10:45AM - 10:57AM |
H7.00001: New Equation of State for Supernova Simulations Gang Shen, Chuck Horowitz In this work, we calculate the equation of state (EoS) of nuclear matter for a wide range of temperatures, densities, and proton fractions for use in supernova and neutron star merger simulations. We employ a full relativistic mean field (RMF) calculation for matter at intermediate density and high density, and the Virial expansion of a nonideal gas for matter at low density. This is an improvement over the Lattimer-Swesty equation of state, that uses a simple liquid drop model, and the H. Shen and Toki equation of state, that uses the Thomas Fermi and variational approximations. We use the RMF parameter set NL3, and approximate the unit cell for non-uniform nuclear matter as a spherical Wigner-Seitz cell, wherein the mean fields of nucleons are solved fully self-consistently. The Virial gas consists of neutrons, protons, alpha particles, and 8980 species of nuclei with masses from FRDM mass tables. As the density decreases, the mean field results match smoothly to the Virial gas. At very low density, the Virial expansion reduces to nuclear statistical equilibrium. We tabulate the resulting EoS at over 100,000 grid points in the temperature range $T$ = 0 $\sim$ 80 MeV, the density range $n_B$ = 10$^{-8}$ $\sim$ 1.6 fm$^{-3}$, and the proton fraction range $Y_P$ = 0 $\sim$ 0.56. This table will soon be available for supernova and neutron star merger simulations. [Preview Abstract] |
Sunday, February 14, 2010 10:57AM - 11:09AM |
H7.00002: A Study of the $^{12}C$ + $^{12}C$ Fusion Reactions at Astrophysically Relevant Energies J. Zickefoose, J. Schweitzer, T. Spillane, D. Schuermann, Y. Guan, H.-W. Becker, C. Rolfs, F. Strieder, M. De Cesere, N. De Cesere, A. Di Leva, F. Terrasi, L. Gialanella, G. Imbriani, B. Limata The fusion reactions $^{12}C$($^{12}C$,p)$^{23}Na$ and $^{12}C$($^{12}C$,$\alpha$)$^{20}Ne$ are the relevant nuclear processes in the carbon burning phase of stellar evolution. The stellar mass required to ignite carbon depends on the fusion reaction rates at the Gamow energy. The measurement of carbon burning reaction rates near the Gamow energy has been limited by hydrogen contamination in the carbon targets. Thus current estimates of the reaction rates rely heavily on extrapolation from higher energies that does not include resonances. We extended the lower energy limit by a novel technique to strongly reduce the hydrogen background for both gamma ray and charged particle measurements. The current experiment intends to further extend the lower energy limit by utilizing ultra low hydrogen content targets. Experimental procedures, results, and the impact for reaction rates will be discussed. [Preview Abstract] |
Sunday, February 14, 2010 11:09AM - 11:21AM |
H7.00003: Differential Cross Section Measurements for Elastic and Inelastic Scattering of Neutrons from Neon Sean MacMullin, Reyco Henning, Mary Kidd, Werner Tornow, Calvin Howell Neutron backgrounds are a significant concern to experiments that attempt to directly detect Weakly Interacting Massive Particle (WIMP) dark matter. Until now, there was insufficient data available for the interactions of neutrons with neon, which is a candidate detection medium for such experiments. Neutron elastic and inelastic scattering from neon of natural abundance was investigated at the Triangle Universities Nuclear Laboratory. A pulsed beam of 8.0 MeV neutrons, incident on a high pressure gas target, was created with the 10 MV Tandem Van de Graaff accelerator using the $^2$H$(d,n)^3$He reaction. The cross section was measured using a time-of-flight technique for angles from 22$^{\circ}$ to 154$^{\circ}$. Details of the experimental technique and differential cross section results will be presented. [Preview Abstract] |
Sunday, February 14, 2010 11:21AM - 11:33AM |
H7.00004: Spin assignments to excited states in $^{22}$Na through a $^{24}$Mg(p,$^{3}$He)$^{22}$Na reaction measurement K.Y. Chae, D.W. Bardayan, J.C. Blackmon, J.F. Liang, C.D. Nesaraja, M.S. Smith, B.H. Moazen, K.L. Jones, S.T. Pittman, K.A. Chipps, R. Hatarik, P.D. O'Malley, S.D. Pain, R.L. Kozub, C. Matei The $^{21}$Ne(p,$\gamma$)$^{22}$Na reaction is part of the NeNa cycle, which is important for the nucleosynthesis of Ne and Na isotopes in stellar explosions such as novae. This reaction also influences the production of $^{22}$Na which $\gamma$ ray astronomers are searching for with the INTEGRAL satellite to help diagnose the nova mechanism. This reaction proceeds through levels in $^{22}$Na above the proton threshold at 6.739 MeV. Despite numerous previous studies, the spins and parities are not well known for many levels that may dominate the rate. We measured the $^{24}$Mg(p,$^{3}$He)$^{22}$Na reaction using 41 and 41.5 MeV proton beams and a 500 $\mu$g/cm$^{2}$ $^{24} $Mg target at the Holifield Radioactive Ion Beam Facility to better constrain the spins of important levels. Recoiling $^{3} $He particles were detected by a segmented silicon detector array at 16 angles simultaneously. By comparing the angular distributions of $^{22}$Na levels and DWBA calculations, we are able to constrain the spins and parities of astrophysically important $^{21}$Ne(p,$\gamma$)$^{22}$Na resonances. Experimental details and a status report on the analysis will be presented. * This work was supported in part by the US DOE and the NSF. [Preview Abstract] |
Sunday, February 14, 2010 11:33AM - 11:45AM |
H7.00005: Proton Capture Reactions on 46Ti, 64Zn, 114Sn and 116Sn relevant to rp-Process Ravin Kodikara, Michael Famiano, Brenna Giacherio, V. Subramanian, Asghar Kayani Radiative proton capture reactions relevant to rp-process on 46Ti, 64Zn, 114Sn and 116Sn were investigated at the Western Michigan University accelerator facility. Targets were irradiated with a monoenergetic proton beam within the energy range (1-4) MeV. Decay of daughter products was measured using two HPGe coaxial gamma detectors. (p,g)cross-sections of 114Sn were measured for the first time while 116Sn and 64Zn cross sections were measured at a wide energy range compared to previous attempts. S-factors and thermonuclear reaction rates were calculated and compared with results from the MOST and NON-SMOKER codes. At higher energies 114Sn(p,g)115Sb results were in better agreement with the theory, indicating that any possible disagreement at lower energies may be due to shell closure effects in the Sn nuclei for the proton induced reactions. [Preview Abstract] |
Sunday, February 14, 2010 11:45AM - 11:57AM |
H7.00006: Structure of $^{69}$Br and the rp-process in X-ray bursts Caroline Nesaraja, Michael Smith The long (35.5 sec.) positron decay lifetime of $^{68}$Se, coupled with the low estimated probability of proton capture into $^{69}$Br, make $^{68}$Se a waiting point in the rp-process powering explosions in X-ray binaries. The thermonuclear reaction flow in X-ray bursts (XRB) depends sensitively on the properties of $^{69}$Br, especially whether or not the ground state is proton bound [1]. Recent studies of the mass of $^{68}$Se and the decay of $^{69}$Br prompt a reassessment of the $^{69}$Br properties relevant for rp-process burning in XRB. In our current project to evaluate the structure of nuclei with mass 69, we will focus on $^{69}$Br. Our assessment, which will be included in the ENSDF database at the U.S. National Nuclear Data Center, will be used to generate a new reaction rate for proton capture on $^{68}$Se, and subsequently for new X-ray burst nucleosynthesis calculations. \\[4pt] [1] H.Schatz et al., Phys. Rep. \textbf{294}, 167 (1988) [Preview Abstract] |
Sunday, February 14, 2010 11:57AM - 12:09PM |
H7.00007: Identification of $\mu $s isomers in the $^{100}$Sn region Ana Becerril, Mathew Amthor, Thomas Baumann, Daniel Bazin, Jill Berryman, Heather Crawford, Alfredo Estrade, Alexandra Gade, Thomas Ginter, Carol Guess, Marc Hausmann, Milan Matos, Giuseppe Lorusso, Paul Mantica, Rhiannon Meharchand, Kei Minamisono, Fernando Montes, George Perdikakis, Jorge Pereira, Mauricio Portillo, Hendrik Schatz, Karl Smith, Joshua Stoker, Andreas Stolz, Remco Zegers New $\mu $s isomeric states have been identified in proton-rich nuclei in the vicinity of the doubly-magic nucleus $^{100}$Sn. The nuclei of interest were produced and studied at NSCL by fragmentation of a 120 MeV/u $^{112}$Sn primary beam on a $^{9}$Be target and selected with the A1900 Fragment Separator in conjunction with the Radio Frequency Fragment Separator system. The ions were implanted into the NSCL Beta Counting System and were correlated with their subsequent decays on an event-by-event basis. Prompt and $\beta $-delayed $\gamma $ rays were identified with the Segmented Germanium Array. Experimental details and preliminary results will be presented. Comparison to shell model predictions will also be discussed. [Preview Abstract] |
Sunday, February 14, 2010 12:09PM - 12:21PM |
H7.00008: Enabling Environmental Background Reduction for Nuclear Astrophysics Measurements with Pulsed Proton Beams Matthew Buckner, John Cesaratto, Thomas Clegg, Bret Carlin Benefits accrue when nuclear reactions relevant to astrophysical processes are studied with low-energy \textit{pulsed} proton beams. Because Coulomb repulsion reduces the nuclear reaction rate, continuous backgrounds often dominate the signal of interest. Pulsing the beam can reduce these backgrounds by gating data collection electronics. Target lifetime can become short when the target current increases, so pulsing the beam to limit the average current while raising the peak pulsed current offers a way to optimize S/N. At TUNL's Laboratory for Experimental Nuclear Astrophysics, remote LabVIEW-controlled, pulsed proton-beam operation has been extended to a new ECR source by pulsing the beam extraction HV power supplies. Target proton currents $>$ 1mA DC are available between 100 and 190 keV, and pulsed operation has been demonstrated at 15 keV. Work is underway to extend pulsed operation to energies between 100 and 190 keV and to begin initial experiments with this new capability. Latest results will be reported. [Preview Abstract] |
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