Bulletin of the American Physical Society
79th Annual Meeting of the APS Southeastern Section
Volume 57, Number 16
Wednesday–Saturday, November 14–17, 2012; Tallahassee, Florida
Session HC: Nuclear Physics II |
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Chair: John Shriner, Tennessee Technological University Room: DoubleTree Adams-Park |
Friday, November 16, 2012 10:45AM - 10:57AM |
HC.00001: Giant Monopole Energies from a Constrained Relativistic Mean-Field Approach Wei-Chia Chen, Jorge Piekarewicz Most nuclear energy density functionals (EDFs) are calibrated using exclusively data from nuclear experiments performed under normal nuclear densities and isospin asymmetries. Thus, when extrapolated to the extreme, the predictions differ significantly from model to model. In this work, we develop a constrained relativistic mean-field approach to compute giant monopole energies of nuclei with various isospin asymmetries. The results are compared against those obtained from a relativistic random phase approximation and excellent agreement is found. These results make viable the use of giant monopole energies into the calibration scheme of future nuclear EDFs. [Preview Abstract] |
Friday, November 16, 2012 10:57AM - 11:09AM |
HC.00002: Four-fold data analysis of $^{252}$Cf fission products E.H. Wang, N.T. Brewer, J.H. Hamilton, A.V. Ramayya, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, S.J. Zhu, G.M. Ter-Akopian, Yu.Ts. Oganessian Prompt gamma-ray 4-fold data were built to collect 2$\times $10$^{11}$ $\gamma -\gamma -\gamma -\gamma $ quadruple- and higher-fold $\gamma $ -coincidence events from the spontaneous fission of $^{252}$Cf with Gammasphere detector arrays. The nuclei $^{106}$Nb, $^{142}$La, Ba and Gd have been studied with these data. By using the new 4-fold data, we confirmed several weak tentative transitions in $^{106}$Nb, $^{142}$La, Ba, $^{148}$Ce which were observed previously from the $\gamma -\gamma $ -$\gamma $ triple cube. Some new transitions in $^{106}$Nb, $^{142}$La were identified by our new 4-fold data. Cascades in $^{145}$Ba are much clearer in four-fold data than the previous triple coincidence data. We will continue to study other nuclei by our 4-fold data with lower background than the previous triple cube. We thank M. Riley for urging us to build the 4-fold data set to get more accurate intensities. [Preview Abstract] |
Friday, November 16, 2012 11:09AM - 11:21AM |
HC.00003: ANC measurement on ($^6$Li,d) reactions M.L. Avila, G.V. Rogachev, E. Koshchiy Direct measurement of many astrophysically important reactions cannot be done due to small cross sections. An alternative can be to obtain the Asymptotic Normalization Coefficient (ANC) as an effective method to determine the astrophysical S factor. Combination of the sub-Coulomb $\alpha$-transfer reaction and application of the ANC technique in the analysis of the experimental data practically eliminates all dependence of the result on model parameters, making this approach a very valuable tool for studies of astrophysically important reaction rates. In this study we report the ANC measurements of near threshold states for ($^6$Li,d) reactions performed at sub-Coulomb energies at the Florida State University Tandem-LINAC facility. The reactions that were studied using this technique are $^{16}$O($^6$Li,d)$^{20}$Ne, $^{13}$C($^6$Li,d)$^{17}$O and $^{12}$C($^6$Li,d)$^{16}$O. [Preview Abstract] |
Friday, November 16, 2012 11:21AM - 11:33AM |
HC.00004: The recent study of the structure of $^{31}$Si Pei-Luan Tai, L. Hamilton, P. Bender, S. Tabor, V. Tripathi, C. Hoffman, R. Clark, P. Fallon, A. Macchiavelli, S. Paschalis, M. Petri, M. Carpenter, R.V.F. Janssens, T. Lauritsen, E. McCutchan, D. Seweryniak, S. Zhu, C. Chiara, X. Chen, W. Reviol, D. Sarantites $^{31}$Si was produced through the $^{18}$O ($^{18}$O, $\alpha$n) reaction at the beam energy of 25 MeV, which preferentially populates the high spin states. The $\alpha$ particles were detected in Microball and the multiple $\gamma$-ray coincidences were detected by Gammashpere. There are 11 newly observed states and 22 new discovered $\gamma$ transitions. A strong competition is seen between negative-parity {}``intruder'' states and positive-parity pure s-d states. Shell model calculations agree relatively well with both groups of states. Kinematic correction code for recoil is under development. [Preview Abstract] |
Friday, November 16, 2012 11:33AM - 11:45AM |
HC.00005: Study of Neutron Deficient $^{9}$C Joseph Belarge, G.V. Rogachev, J. Blackmon, I. Wiedenhover, L. Baby, E.D. Johnson, A.N. Kuchera, E. Koshchiy, J. Lai, L. Linhardt, K. Macon, M. Matos, D. Santiago-Gonzalez Development of theoretical framework that allows the combination of nuclear structure calculations with the continuum is an important objective of modern nuclear theory [1,2]. Due to the low binding energy of exotic isotopes even the lowest excited states are unbound and therefore it is essential to take the continuum into account. We studied the structure of the lightest bound carbon isotope, $^{9}$C, through $^{8}$B+p resonance scattering using the new active target detector ANASEN [3]. The experiment was performed at the John D. Fox Superconducting Accelerator Laboratory at FSU. A rare isotope beam of $^{8}$B ions was produced using the radioactive nuclear beam facility RESOLUT. Pure hydrogen gas was used as a target and also as an active medium for the gas proportional counters of the ANASEN detector. The analysis of the p+$^{8}$B excitation functions was performed using the R-Matrix approach. The preliminary results will be presented.\\[4pt] [1] A. Volya, Phys. Rev. C {\bf79}, 044308 (2009).\\[0pt] [2] S. Quaglioni and P. Navr\'atil, PRL {\bf101}, 092501 (2008).\\[0pt] [3] M. Matos, et al., Proc. Intern. Symposium on Nuclei in the Cosmos XI, July 19-23 2010, Heidelberg, Germany, p.226(2010) [Preview Abstract] |
Friday, November 16, 2012 11:45AM - 11:57AM |
HC.00006: High Spin Structures in 25Na Justin VonMoss, Samuel Tabor, Vandana Tripathi, Peter Bender, Alexander Volya, Pei-Luan Tai High-spin states in $^{25}$Na were populated in the $^{9}$Be ($^{18}$O, pn) reaction using a 35 MeV $^{18}$O beam from the John D. Fox Superconducting Accelerator Laboratory at Florida State University. Gamma rays were detected using the FSU compton-supressed germanium array in coincidence with protons from the reaction. Two new states and seven new gamma transitions were observed. Additionally a doublet has been identified which a resolves conflict in the published works. Unobserved, and highly excited particle-hole states have been predicted using shell model calculations. [Preview Abstract] |
Friday, November 16, 2012 11:57AM - 12:09PM |
HC.00007: Measurement of the $^{25}$Al(d,n)$^{26}$Si(p) reaction at RESOLUT: Spectroscopy of $l=0$ and $l=1$ resonances Jessica Baker, Ingo Wiedenhover, Alexander Rojas, Lagy Baby, Sean Kuvin, Patrick Peplowski, Daniel Santiago-Gonzalez, Georgios Perdikakis, Dennis Gay Studies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest $l=0$ and $l=1$ resonances is the most important step to determine reaction rates in the astrophysical $rp$--process path. In an experiment performed at the {\sc resolut} radioactive beam facility of Florida State University, we have studied the $\mathrm{^{25}Al(d,n)^{26}Si}$ reaction in inverse kinematics to establish the spectrum of the lowest $l=0$ and $l=1$ resonances. The spectrum is consistent with a previous experiment using the same reaction at {\sc resolut} [1] and results obtained from recent stable beam experiments [2]. \\[4pt] [1] P.N. Peplowski et al. Phys.Rev C 79, 032801 (2009)\\[0pt] [2] K.A. Chipps et al. Phys.Rev C 28, 045803 (2010) [Preview Abstract] |
Friday, November 16, 2012 12:09PM - 12:21PM |
HC.00008: The Proto-neutron star crust studied with an Ising approach Karim Hasnaoui, Jorge Piekarewicz The thermodynamics of the proto-neutron stars crust is studied in this project. Obtaining information on the star matter thermodynamics will enhance the understanding of physical phenomena involved in the cooling of proto-neutron stars, and the formation of type II supernovae. The main goals of this project is to understand qualitatively, how the different structures of the crust, such as the well known {\sl ``nuclear pasta''} or the liquid and gas phases can be formed as function of the proton fraction $X_{p}$, the density $\rho$, or the temperature $T$. For this purpose, we have developed a classical model based on a Ising/Lattice-gas approach, where the short range nuclear interaction and the long range Coulomb interaction have been included. We are now able to perform simulation for a very large number of particles, and we will show that the signals of phase transitions between the {\it pasta} structures and the gas phase as function of the different conditions previously mentioned, can be clearly identified on the structure form factor $S(k)$, but also on the heat capacity $C_{v}$. [Preview Abstract] |
Friday, November 16, 2012 12:21PM - 12:33PM |
HC.00009: Monte Carlo simulation of secondary electron emission in the Nab experiment Chatham David McLaughlin The Nab experiment aims at a precise measurement of $a$, the electron neutrino correlation parameter and $b$ the Fierz interference term in neutron $\beta$ decay. The measurement is to be performed at the Spallation Neutron Source (SNS) in Oak Ridge, TN using a asymmetric magneto-electrostatic spectrometer. One of the main challenges is the detection of the low energy proton resulting from the $n \to e^- p \bar{\nu}_{e}$ decay. This can be accomplished in two ways: by placing the detector itself at a negative potential to accelerate the protons. Alternatively we detect the secondary emission electrons (SEEs), from multiple passages of the proton through a thin ($\sim$100nm) foil in front of the detector. The foil is at a high negative potential. The Poisson distributed SEEs are detected in segmented Si detectors with virtually no adverse effects due to the detector's thin dead surface layer. Initial Monte Carlo simulation of the problem using GEANT4 indicates a mean of 8.7 secondary electrons are generated using a Al foil at -30kV. While most are immediately reabsorbed, a median of 2 electrons is detected per proton. Other suitable foil materials can increase the number of detected SEEs. Representative results of a full simulation in both detection modes will be presented. [Preview Abstract] |
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