Bulletin of the American Physical Society
75th Annual Meeting of the Southeastern Section of APS
Volume 53, Number 13
Thursday–Saturday, October 30–November 1 2008; Raleigh, North Carolina
Session EA: Nuclear Physics I |
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Chair: Paul Huffman, North Carolina State University Room: Holiday Inn Brownstone Roosevelt |
Thursday, October 30, 2008 3:45PM - 3:57PM |
EA.00001: Measurement of the $^{2}$H(n,np)n Cross Section in the SCRE Configuration A. Couture, T. Clegg, B. Crowe, D. Markoff, L. Cumberbatch, C. Howell, A. Crowell, J. Esterline, B. Fallin, R. Pedroni To try to understand differences between earlier measurements and theoretical predictions, we are currently measuring the $^{2}$H(n,np)n cross section at both 19 and 16 MeV in the Symmetric Constant Relative Energy (SCRE) configuration [1]. In the neutron-deuteron (nd) breakup reaction, the SCRE configuration occurs when, in the center of mass frame, the three outgoing nucleons all have the same energy and their final momenta all lie in the same plane separated by 120 degrees. We are measuring two special cases of this configuration; one where the plane contains the incident beam, another where the plane is perpendicular to the incident beam. The neutron beam is produced by the $^{2}$H(d,n)$^{3}$He reaction. The breakup reaction target consists of a CD$_{2}$ foil located in a scattering chamber with two charged particle detection arms, each containing an E-$\Delta $E telescope. We are detecting the proton and one of the neutrons in coincidence. Experimental details and the status of our experimental measurements will be described. [1] W. Glockle, et al., Physics Reports \textbf{274 }(1996) 107. [Preview Abstract] |
Thursday, October 30, 2008 3:57PM - 4:09PM |
EA.00002: An Investigation of the $^{48}$Ca($\gamma$,n) Cross Section between 9.5 and 15.3 MeV J.R. Tompkins, C.W. Arnold, H.J. Karwowski, G. Rich, L.G. Sobotka, C.R. Howell A 2.7 g $^{48}$Ca target enriched to 92.4\% was probed using an incident $\gamma$-ray beam of $\sim$2\% energy resolution generated at the TUNL High Intensity $\gamma$-Ray Source (HI$\gamma$S). Prior to the experiment, no direct measurements had been made using a quasi-monoenergetic $\gamma$-ray beam. Cross sections for the ($\gamma$, n) reaction, normalized to the known D($\gamma$, n) reaction cross sections,\footnote{W.Jaus and W.S.Woolcock, \textit{Nucl. Phys.} \textbf{A}608 (1996) 399.} were measured to a precision of less than $\pm$6\% at 34 different energies between 9.5 and 15.3 MeV using a $^{3}$He proportional counter for neutron detection. The $\gamma$-ray energies span the region from the neutron emission threshold, across previously identified M1 strength, and up the low-energy edge of the E1 Giant Dipole Resonance. Neutron emission dominates the region though a few excited states in the daughter nucleus are populated. The experimental data will be presented as will the initial interpretation of this excitation function. [Preview Abstract] |
Thursday, October 30, 2008 4:09PM - 4:21PM |
EA.00003: Experience with the UNC Polarized $^3$He Target Timothy Daniels, Thomas Clegg, Alex Couture, Charles Arnold We discuss our experience with the UNC polarized $^3$He target\footnote{T. Katabuchi \textit{et al.}, Rev. Sci. Instrum. \textbf{76}, 033503 (2005)} to collect for p+$^3$He spin-correlation coefficients below 6 MeV. The use of a compact, enclosed external polarizer was convenient in a general-purpose accelerator target room, but made optimization and improvement difficult. The target initially used spin-exchange with Rb to achieve $\sim$30\% polarization in 24hr with a T1 of 36hr, before the original optical pumping cell was destroyed. The wide variation in performance, both individually and over time, of the 10 replacement cells we fabricated included the deterioration of T1 in individual cases after optical pumping and reversing the magnetic holding field, but no clear difference between GE-180 and Pyrex cells. The best replacement cell yielded $\sim$20\% polarization with a 15hr T1. Cells using a mixture of Rb and K gave similar results,\footnote{A. Couture \textit{et al.}, Bull. Am. Phys. Soc.,\textbf{51} No. 8, 20 (2006)} though they reached saturation polarization in $\sim$12hrs. A frequency-narrowed 30W diode laser\footnote{C. W. Arnold \textit{et al.}, Bull. Am. Phys. Soc. \textbf{51}, no 8, 20 (2006)} produced similar results to those of the 60W broadband diode laser. [Preview Abstract] |
Thursday, October 30, 2008 4:21PM - 4:33PM |
EA.00004: The $\beta$ decays of $^{75,77}$Cu S.V. Ilyushkin, J.A. Winger, K.P. Rykaczewski, C.J. Gross, D. Stracener, R. Grzywacz, S.N. Liddick, I. Darby, S. Padgett, J.C. Batchelder, E.F. Zganjar The newly designed Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS) at the HRIBF was implemented in order to study properties of neutron-rich nuclei. Isotopes of interest are produced by proton-induced fission in a uranium carbide target. Ions are separated using the high-resolution injector magnet and delivered to LeRIBSS, which consists of a universal detector support and a new fast moving tape collector. Using negative ions and adjusting the high-resolution magnet slits and field allowed us to obtain high purity beams with good rate. In particular a rate of about 3000 pps was reached for $^{75}$Cu. Results of beta and beta-delayed neutron decay studies of $^ {75,77}$Cu will be discussed. Funded by DOE grant DE-FG02- 96ER41006. [Preview Abstract] |
Thursday, October 30, 2008 4:33PM - 4:45PM |
EA.00005: Nuclear Fragmentation Model Evaluation Ryan Norman, Steve Blattnig The semiempirical nuclear abrasion-ablation model NUCFRG2 was recently updated to include the qualitative even-odd effect for fragment charge production seen in experiments and the addition of alpha cluster knockout. In this talk, we present a comparison of the updated NUCFRG2 model cross sections with recent experimental cross sections and give a discussion of the results. [Preview Abstract] |
Thursday, October 30, 2008 4:45PM - 4:57PM |
EA.00006: Light Ion Production Improvements in the NUCFRG2 Semiempirical Nuclear Fragmentation Model: Preliminary Results Sirikul Sriprisan, Ryan Norman, Lawrence Townsend The nuclear interaction model used in the space radiation transport/shielding codes developed at NASA Langley Research Center is the NUCFRG2 semiempirical model. Previous versions of this model used simple approximations to generate yields of light ion fragments (Z = 1,2). In an attempt to improve the accuracy of the light ion yields, a coalescence formalism is incorporated into NUCFRG2. In this work, the modifications to the NUCFRG2 model are described and preliminary results for light ion yields presented. [Preview Abstract] |
Thursday, October 30, 2008 4:57PM - 5:09PM |
EA.00007: Modeling and Design of a Gadolinium Based Neutron Detector David Ticehurst, Jeromy Tompkins, Hugon Karwowski The goal is to measure the partial cross sections for ($\gamma $, xn) and ($\gamma $, f) on the actinides with the ultimate objective of developing and refining a method for the $\gamma $-ray interrogation of fissionable material. These measurements require the construction of a highly segmented neutron detector to record multiple neutrons emitted following photodisintegration and fission. Each detector segment will use a gadolinium-loaded liquid organic scintillator optically coupled to a photomultiplier tube. Gadolinium has one of the highest thermal neutron capture cross sections (49 kb), therefore its presence in the detector will greatly enhance neutron detection efficiency. A prototype detector of 3 L volume has been constructed and modeled using Geant4, a Monte Carlo based program.\footnote{S.Agostinelli et al., \textit{Nucl. Instr. and Meth}. \textbf{A}506, 250, (2003).} The detector model and conclusions developed from it along with the results from testing the prototype detector will be presented. [Preview Abstract] |
Thursday, October 30, 2008 5:09PM - 5:21PM |
EA.00008: Isotopic shifts in light Kr nuclei and evidence of N=36 magicity near the rp-process path J.K. Sharma, M.M. Sharma Neutron-deficient Kr isotopes play an important role in the rp- process nucleosynthesis.\footnote{H. Schatz et al., Phys. Rep. 294 (1998) 167.} The isotope $^{72}$Kr has been described variously as a waiting-point nucleus. We have examined the experimental data on isotopic shifts in light Kr nuclei close to the proton drip line within the framework of the relativistic mean-field theory. Using the Lagrangian model with the vector self-coupling of $\omega$ meson,\footnote{M.M. Sharma, A.R. Farhan, S. Mythili, Phys. Rev. C61 (2000) 054306.} it is shown that $^{72}$Kr is oblate in its ground-state, which exhibits a shape-coexistence with a prolate shape. It is shown that the negative isotopic shift for $^{72}$Kr provides an evidence for a neutron shell closure at $N=36$. This is affirmed by the presence of a shell gap in the single-particle spectrum in the deformed space. This lends credence to the isotope $^{72}$Kr as being a waiting-point nucleus in the rp-process path. [Preview Abstract] |
Thursday, October 30, 2008 5:21PM - 5:33PM |
EA.00009: High Spin States in $^{139,140,142}$Cs Shaohua Liu, J.H. Hamilton, A.V. Ramayya, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, S.J. Zhu The high spin excited states of neutron-rich nuclei $^{139,140,142}$Cs are investigated from a study of the prompt $\gamma$ rays emitted in spontaneous fission of $^{252}$Cf with the Gammasphere detector array. Eight new $\gamma$ transitions and a new side band in $^{139}$Cs are observed here. Seven new $\gamma$ transitions, involving two new levels at lower spins and one at high spins, in $^{140}$Cs are identified. The level scheme of $^{142}$Cs is rebuilt and eleven new $\gamma$ transitions, one new side band and four low energy transitions in $^{142}$Cs are observed here. Angular correlation measurements are planed to confirm or assign the spins of levels in these three nuclei. Theoretical calculations are needed to interpret the new observed structures of $^{140, 142}$Cs. [Preview Abstract] |
Thursday, October 30, 2008 5:33PM - 5:45PM |
EA.00010: Nonlinear Tunneling and Nuclear Decay Christa Labadorf, Eugene Chaffin Recent astrophysical data have indicated a possible variation of the proton-electron mass ratio $\mu $ = m$_{p}$/m$_{e}$. Attributing the variation to a change in the strength of the nuclear force, we take into account nonlinear inteactions, such as those originally proposed in 1955 by Johnson and Teller, and examine the resulting change in nuclear half lives. Our Mathematica calculations show the effect of the nonlinear terms by solving the three-dimensional nonlinear Schrodinger equation in a model applied to a typical nucleus. We match the radial wavefunction and its derivative for the interior of the nucleus to the Coulomb wavefunctions on the exterior of the nucleus in a generalization of the procedure originally used by Pieronne and Marquez, 1978, but without the nonlinear interactions. The results indicate that the nonlinear interactions, in cases where the number of nodes in the radial wavefunction is poised on a change from one value to another, can cause a large change in half-life for a small change in the strength of the nuclear force. [Preview Abstract] |
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