Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session FE: Nuclear Reactions: Light Ions |
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Chair: Ian Thompson, Lawrence Livermore National Laboratory Room: Simmons Ballroom 1 |
Saturday, October 25, 2008 8:30AM - 8:42AM |
FE.00001: Refinement of Global Phase-Shift Analysis for $p+^3He$ Elastic Scattering Using Spin-Correlation Coefficients Tim Daniels, Charles Arnold, John Cesaratto, Thomas Clegg, Alexander Couture, Astrid Imig, Hugon Karwowski As part of an investigation of the A=4 system, we measured the spin-correlation coefficients A$_{yo}$, A$_{oy}$, A$_{yy}$, and A$_{xx}$ for p-$^{3}$He elastic scattering at E$_{lab}$ of 2.3, 2.7, 4.0, and 5.5 MeV and $\Theta _{lab}$ between 30$^{\circ}$ and 150$^{\circ}$. The data were taken using TUNL's atomic beam polarized ion source and our spin-exchange optical pumping polarized $^{3}$He target\footnote{T. Katabuchi \textit{et al.,} Rev. Sci. Instrum. 76, 033503 (2005)}. We aim to resolve ambiguities in the phase shifts of George and Knutson\footnote{E.A. George and L.D. Knutson, Phys Rev C 67, 027001 (2003)}, which seem most sensitive to A$_{xx}$ and A$_{yy}$ at the lowest of these energies. Our measurements will be shown with phase-shift-analysis solutions, as well as some discussion of systematic effects related to the steering of charged particles by the target's magnetic field. [Preview Abstract] |
Saturday, October 25, 2008 8:42AM - 8:54AM |
FE.00002: Spectroscopic Factors From the Single Neutron Pickup Reaction $^{64}$Zn$(\vec{\mathrm{d}}$,t) Kyle Leach, P.E. Garrett, G.A. Demand, P. Finlay, K.L. Green, A.A. Phillips, C.S. Sumithrarachchi, C.E. Svensson, S. Triambak, G.C. Ball, T. Faestermann, R. Kr\"ucken, H.-F. Wirth, R. Herten-Berger A great deal of attention has recently been paid towards high precision superallowed $\beta$-decay ${\cal F}t$ values. With the availability of extremely high precision $(<0.1\%)$ experimental data, the precision on ${\cal F}t$ is now limited by the $\sim1\%$ theoretical corrections.\footnote{I.S. Towner and J.C. Hardy, Phys. Rev. C \textbf{77}, 025501 (2008).} This limitation is most evident in heavier superallowed nuclei (e.g. $^{62}$Ga) where the isospin-symmetry-breaking correction calculations become more difficult due to the truncated model space. Experimental data is needed to help constrain input parameters for these calculations, and thus experimental spectroscopic factors for these nuclei are important. Preliminary results from the single-nucleon-transfer reaction $^{64}$Zn$(\vec{\mathrm{d}}$,t)$^{63}$Zn will be presented, and the implications for calculations of isospin-symmetry breaking in the superallowed $\beta^+$ decay of $^{62}$Ga will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 8:54AM - 9:06AM |
FE.00003: The development of single-nucleon pickup reactions with fast, exotic beams as a spectroscopic tool S. McDaniel, A. Gade, P. Aldrich, D. Bazin, J.M. Cook, C. Aa. Diget, K.W. Kemper, T. Glasmacher, A. Ratkiewicz, K. Siwek, J.A. Tostevin, D. Weisshaar One-nucleon knockout reactions are an established tool to track the evolution of nuclear shell structure away from stability by probing single-\emph{hole} states. Currently, fast-beam, heavy-ion induced \emph{pickup} reactions are being developed that provide, in a similar way, the complementary structure information by probing single-\emph{particle} states. At the NSCL, several proton and neutron pickup reactions centered around the proton-rich isotope $^{50}$Fe were investigated: $^9$Be($^{49}$Mn,$^{50}$Fe)X, $^9$Be($^{50}$Fe,$^{51}$Fe)X, and $^9$Be($^{48}$Cr,$^{49}$Mn)X. Information from these reactions, including the effects of target variation ($^9$Be versus $^{12}$C), will help develop the one-nucleon pickup reaction into a tool for nuclear structure physicists. [Preview Abstract] |
Saturday, October 25, 2008 9:06AM - 9:18AM |
FE.00004: The statistical decay properties of Gadolinium isotopes using the DANCE array D. Dashdorj, G. Mitchell, B. Baramsai, R. Chankova, A. Chyzh, C. Walker The gadolinium isotopes are interesting for reactor applications as well as for medicine and astrophysics. There are seven stable isotopes of gadolinium with varying deformation. Decay $\gamma$ rays following neutron capture on Gd isotopes are detected by the DANCE array, which is located at flight path 14 at the Lujan Neutron Scattering Center at Los Alamos National Laboratory. The high segmentation and close packing of the detector array enable $\gamma$-ray multiplicity measurements. The calorimetric property of the DANCE array coupled with the neutron time-of-flight technique enables one to gate on a specific resonance of a specific isotope in the time-of-flight spectrum and obtain the summed energy spectrum for that isotope. The singles $\gamma$-ray spectrum for each multiplicity can be separated by their DANCE cluster multiplicity. Various photon strength function models are used for comparison with experimentally measured DANCE data and provide insight for understanding the statistical decay properties of deformed nuclei. [Preview Abstract] |
Saturday, October 25, 2008 9:18AM - 9:30AM |
FE.00005: Determining the ($n$,$\gamma )$ cross section of $^{153}$Gd using surrogate reactions Nicholas Scielzo The astrophysical $s$-process creates isotopes through a series of low-energy ($n$,$\gamma )$ reactions and beta decays. Direct measurements of the ($n$,$\gamma )$ cross sections for unstable nuclei are extremely challenging due to the challenges presented by radioactive targets and low intensity neutron beams. The surrogate reaction technique can be used to circumvent these difficulties by creating the same compound nucleus through light-ion reactions on a stable target. We have collected data to determine the low-energy ($n$,$\gamma )$ cross section for the unstable nucleus $^{153}$Gd by bombarding a stable $^{154}$Gd target with protons to create the desired $^{154}$Gd* compound nucleus. The STARS/LiBerACE silicon and clover germanium detector arrays were used to detect $\gamma $-rays in coincidence with the scattered protons. Additional cross section measurements using $^{156}$Gd and $^{158}$Gd targets are compared to direct measurements of the ($n$,$\gamma )$ cross sections for $^{155}$Gd and $^{157}$Gd to check the technique. The current status of the analysis will be presented. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344. [Preview Abstract] |
Saturday, October 25, 2008 9:30AM - 9:42AM |
FE.00006: (n,$\gamma$) by the Internal Surrogate Ratio Method: A Benchmark using $^{235}$\textrm{U}(d,p) J.M. Allmond The Surrogate Reaction Technique, first proposed in 1970 [1], has recently been under investigation by a Richmond / LLNL / LBNL / Yale collaboration. These studies are currently performed at LBNL using the STARS and LiBerACE detector arrays. Both absolute [1] and ratio [2] methods have been employed to circumvent technical challenges presented by the fabrication of unstable targets and by the production of high-flux neutron beams. The $^{235}$\textrm{U}(d,p) surrogate reaction at 21~MeV benchmarks the (n,$\gamma$) cross section by use of the \textit{internal ratio method} (same compound nucleus but different exit channel). The present study marks the first benchmark of the internal ratio method. Previous tests of the Surrogate Ratio Method have focused on determining (n,f) cross sections using the \textit{external ratio method} (different compound nucleus but same exit channel). Results of this study are presented.This work was performed under the auspices of the U.S. Department of Energy under contract numbers DE-FG52-06NA26206 (UR), DE-AC52-07NA27344 (LLNL), and DE-AC02-05CH11231 (LBNL).\\ {[1]}J.D. Cramer and H.C. Britt, Nucl. Sci. Eng. \textbf{41}, 177 (1970). \\ {[2]}C. Plettner, \textit{et~al.}, Phys. Rev. C \textbf{71} 051602 (2005). [Preview Abstract] |
Saturday, October 25, 2008 9:42AM - 9:54AM |
FE.00007: Chemical Equilibration Involving Decaying Particles in the Early Universe Inga Kuznetsova, Takeshi Kodama, Johann Rafelski We study kinetic master equations involving chemical reactions comprising the decay of particles in a thermal bath. We consider both, the decay channel into two particles, and the inverse process, the fusion of two thermal particles into one. We derive chemical equilibrium condition for the particle density. We evaluate the thermal invariant rate using as input the free space (vacuum) decay time. We consider examples, how decay time of some hadrons changes in hadronic medium, as compared to vacuum. These considerations are of interest both in heavy ions collisions applications and towards the understanding of hadron evolution in the early Universe. We consider here the reaction $\pi^{0}\leftrightarrow \gamma+\gamma$ as one of examples. [Preview Abstract] |
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