Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session JC: Nuclear Physics II |
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Chair: Paul Cottle, Florida State University Room: Crystal Ballroom C |
Friday, October 21, 2011 1:30PM - 1:42PM |
JC.00001: New Levels in $^{162}$Gd Brayton Doll, 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 We've measured prompt gamma rays from the fission fragments of the spontaneous fission of $^{252}$Cf in Gammasphere. The data from the experiment have high statistics with 5.7*10$^{11}$ triple and higher gamma coincidences. We examined levels in $^{162}$Gd in this data set which shows very consistent I(I+1) level spacing in the yrast band. This demonstrates consistency with a rotational nucleus that has a large quadrupole deformation. this is common for nuclei in between closed spherical shells. To find new levels and gamma transitions, we looked at triple coincidence gates in the Radware software in which we see population of yrast states up to 16+. We found new evidence for proposed collective bands in this isotope. Results will be discussed. [Preview Abstract] |
Friday, October 21, 2011 1:42PM - 1:54PM |
JC.00002: Octupole correlations in Ba and Ce nuclei N.T. Brewer, W.A. Yzaguirre, J.H. Hamilton, A.V. Ramayya, S.H. Liu, C. Goodin, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, S.J. Zhu, G.M. Ter-Akopian, A.V. Daniel $\gamma -$rays from the Spontaneous Fission of~$^{252}$Cf were measured with Gammasphere and have given great insight into the structure of neutron rich nuclei. We have examined high-spin states and the $\gamma $-transitions associated with octupole correlations in$^{143-146}$Ba and~$^{148}$Ce. Coexisting quadrupole/octupole deformation is characterized by two $\Delta $I = 1 rotational bands with opposite parities. The states in these two rotational bands are described by a quantum number called simplex with s$^{2}$ = (-1)$^{A}$. In~$^{143}$Ba, the levels are extended to 43/2$^{+}$~with a total of six new levels along with two new transitions. In~$^{144}$Ba, we have placed new levels including three E1 transitions and 8 linking transitions to the s = +1 band to give more definitive evidence for the s = -1 band. Six new levels are found in~$^{145}$Ba. For~$^{144}$Ba and $^{148}$Ce we have, for the first time in even-even isotopes, confirmed the spin/parity of some s = -1 levels using angular correlations. [Preview Abstract] |
Friday, October 21, 2011 1:54PM - 2:06PM |
JC.00003: Neutron emission asymmetries from linearly polarized $\gamma$ rays on $^{nat}$Cd, $^{nat}$Sn, and $^{181}$Ta W. Clarke Smith, Gerald Feldman Azimuthal asymmetries in neutron yields produced by bombarding targets with linearly polarized photons via ($\gamma$,$n$), ($\gamma$,2$n$), and ($\gamma$,$f$) reactions are being investigated as a possible means of identifying various nuclear isotopes. The High Intensity $\gamma$-ray Source (HI$\gamma$S) at Duke University provides nearly monochromatic, circularly or linearly polarized $\gamma$ rays with high intensity by Compton backscattering free-electron-laser photons from stored electrons. Linearly polarized $\gamma$ rays produced by HI$\gamma$S were incident on $^{nat}$Cd, $^{nat}$Sn, and $^{181}$Ta targets at six energies $E_{\gamma}$ between 11.0 and 15.5 MeV and emitted neutrons were detected both parallel and perpendicular to the plane of polarization by an array of 18 liquid-scintillator detectors at angles in the range $\theta=55^{\circ}$--$142^{\circ}$. Detected neutrons were distinguished from Compton scattered photons by pulse-shape-discrimination and timing cuts, and their energies ($E_n$) were determined using time-of-flight information over a 0.5 m flight path. The characteristic plots of $R_n$, the ratio of neutron counts parallel to neutron counts perpendicular to the plane of the incident $\gamma$-ray polarization, against $E_n$ were constructed for each value of $E_{\gamma}$ and $\theta$ and then compared to those for other targets studied at HI$\gamma$S, including fissile nuclei $^{235}$U and $^{238}$U. [Preview Abstract] |
Friday, October 21, 2011 2:06PM - 2:18PM |
JC.00004: Sensitivity of the Reaction Cross Section Calculation in the Glauber Theory Framework to the Parameters of Random Number Generation John Wilson To extract the nuclear size information, the experimentally measured interaction cross-section is compared to cross-sections calculated in the framework of Glauber theory or in its various approximations. These calculations are usually performed using a Monte Carlo technique. In the presented paper, we discuss the sensitivity of the reaction and interaction cross sections' calculation to the parameters of the Metropolis-Hasting algorithm which is used to produce nucleon coordinates distributed according to the chosen nuclear density distribution. We evaluate generated sequence of the random nucleon coordinates using lag-1 autocorrelation, correlation of multiple data sets, and running first and second moments. We show that an non-optimal Metropolis-Hasting proposal distribution increases uncertainty of the cross section calculation. The obtained dependence of the accuracy of the determined nuclear density parameters on the various statistical diagnostics of the Metropolis-Hasting for the various types of nuclear density distributions is also discussed. [Preview Abstract] |
Friday, October 21, 2011 2:18PM - 2:30PM |
JC.00005: From Finite Nuclei to Neutron Stars Wei-Chia Chen, Jorge Piekarewicz We will discuss attempts to build a relativistic density functional using constraints from both finite nuclei and neutron stars. The calibration of the model will proceed through a standard minimization of a quality chi-square measure. Moreover, by studying the model-parameter landscape around the minimum we will be able to provide meaningful theoretical error bars as well as to uncover correlations between physical observables. [Preview Abstract] |
Friday, October 21, 2011 2:30PM - 2:42PM |
JC.00006: Neutrino oscillations: latest mixing parameters David Ernst, Bernadette Cogswell, David Latimer, Jesus Escamilla Roa Assuming three neutrinos, the neutrino oscillation mixing parameters are extracted from a global analysis of the Super-K atmospheric, MINOS disappearance and appearance neutrino, CHOOZ, T2K, KamLAND, and all solar data. MINOS anti-neutrino data is not included. The full oscillation probabilities are used so that we can address the question of the sign of $\theta_{13}$. How to extract the allowed confidence level regions without assuming Gaussian statistics is explain. The probability that $\theta_{13}$ is negative will be given, as well as the probability that Double CHOOZ and Daya Bay will measure a non-zero value of $\theta_{13}$. Correlations between $\theta_{13}$ and $\theta_{23}$ will be examined. [Preview Abstract] |
Friday, October 21, 2011 2:42PM - 2:54PM |
JC.00007: Independent Benchmarking of a Hybrid Monte Carlo Cross Section Code Nathan DeLauder, Lawrence Townsend Understanding the effects of high-energy neutron interactions with certain materials is of considerable interest to the field of space radiation protection. Due to the expected radiation environment, neutron production and interactions with spacecraft materials will result in neutrons that can cause significant biological risk to crewmembers. For investigating incident particle interactions with target materials, an existing statistical model code (ALICE2008) was used for determining the particle spectra from a hybrid Monte Carlo simulation (HMS) of pre-compound nuclear decay. Presented is a comparison of neutron reaction cross-section results from ALICE2008 to reported values from widely accepted sources to benchmark the code for this specialized use with targets of interest. [Preview Abstract] |
Friday, October 21, 2011 2:54PM - 3:06PM |
JC.00008: Derivation of the Abrasion-Ablation Model Using Corrections to the Phase Function Santosh Bhatt, Lawrence Townsend The analytical abrasion-ablation model has been used for the quantitative predictions of the neutron and light ion spectra from nucleus-nucleus and nucleon-nucleus collisions. The abrasion stage of the current model is based on the Glauber's multiple scattering theory and applies the small angle approximation which assumes the longitudinal momentum transfer for the scattering amplitude to be small, where the expansion of the scattering amplitude is only considers first order terms. However the validity of the small angle approximations for the current model is not clear for light ions and nucleons. In this work, we have re-derived the phase functions, $\chi $, for the calculation of nuclear cross-sections using a perturbation approach and expanded Fourier-Bessel arguments of scattering amplitude in terms of Legendre polynomials, thus eliminating the small angle approximation. We have computed the differential cross-section for various projectile-target data sets at different energies for different scattering angles and compared our results with the usual Glauber model. [Preview Abstract] |
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