Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session DA: Photonuclear Reactions at Low and High Energies |
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Chair: Lei Guo, Los Alamos National Laboratory Room: Sweeny A |
Thursday, November 4, 2010 10:30AM - 10:42AM |
DA.00001: Two-Body Photodisintegration of $^{3}$He between 7 and 16 MeV W. Tornow, H.J. Karwowski, J.H. Kelley, R. Raut, G. Rusev, S.C. Stave, A.P. Tonchev Data are reported for the two-body photodisintegration cross section of $^{3}$He between 7 and 16 MeV in 1 MeV energy steps. The measurements were performed at TUNL's High-Intensity Gamma-ray Source (HIGS) using mono-energetic photon beams. A $^{3}$He/Xe high-pressure gas scintillator served as target and detector. A NaI detector was used for the incident photon flux determination. Our data are in good agreement with recent theoretical calculations, but differ significantly from the majority of the previous data, including the recent data of Naito \textit{et al}. [1] obtained with a mono-energetic photon beam and a time-projection chamber. \\[4pt] [1] S. Naito\textit{ et al}., Phys. Rev. C\textbf{ 73}, 034003 (2006). [Preview Abstract] |
Thursday, November 4, 2010 10:42AM - 10:54AM |
DA.00002: The Two-Body Photodisintegration Reaction $^{4}$He($\gamma $,p)$^{3}$H between 22 and 30 MeV R. Raut, M.W. Ahmed, A.C. Crowell, G. Rusev, S.C. Stave, A.P. Tonchev, W. Tornow, J.H. Kelley The $^{4}$nucleus is often considered as the link between the classical few-body systems and more complex nuclei. Only recently it became possible to calculate the photoabsorption cross section of $^{4}$with realistic nucleon-nucleon potential models. However, the experimental situation is still as controversial as it was a quarter century ago. Using TUNL's HIGS facility, the two-body photodisintegration cross section of $^{4}$He into a proton and triton was measured between 22 and 30 MeV in 0.5 MeV energy steps. High-pressure $^{4}$He/Xe gas scintillators of various compositions served as targets and detectors. Pure Xe gas scintillators were used for background measurements. A NaI detector was employed for the incident photon flux determination. Our data are in fairly good agreement with recent theoretical calculations of the Trento group [1], but differ significantly from the majority of the previous data, including the recent data of Shima \textit{et al}. [2] obtained with mono-energetic photon beams and a time-projection chamber. \\[4pt] [1] S. Quaglioni \textit{et al}., Phys. Rev. C \textbf{69}, 044002 (2004). \\[0pt] [2] T. Shima \textit{et al., }Phys. Rev. C \textbf{72}, 044004 (2005). [Preview Abstract] |
Thursday, November 4, 2010 10:54AM - 11:06AM |
DA.00003: The 2-Body Photodisintegration Reaction $^{4}$He($\gamma $,n)$^{3}$He below 30 MeV J.H. Kelley, R. Raut, G. Rusev, S.C. Stave, A.P. Tonchev, W. Tornow The charge-symmetric reactions $^{4}$He($\gamma $,p)$^{3}$H and $^{4}$He($\gamma $,n)$^{3}$He are of special interest in few-body physics. Although they have been studied for half a century, the data for these classical breakup reactions scatter widely. For the $^{4}$He($\gamma $,n)$^{3}$He reaction case, it is advantageous to detect the $^{3}$He particles rather than the associated neutrons. The most recent approach used a time-projection chamber [1] for the $^{3}$He detection, but these data disagree considerably from those obtained via neutron detection [2]. In an attempt to clarify the situation, we measured the cross section of the $^{4}$He($\gamma $,3He)n 2-body breakup reaction below E$\gamma $=30 MeV at TUNL's HIGS facility using high-pressure $^{4}$He/Xe gas scintillators of various composition ratios. The challenge in this approach is to separate the pulses from the low-energy $^{3}$He ions, which are not mono-energetic, from those produced by Compton scattered electrons at the low pulse-height side and those from the $^{4}$He($\gamma $,p)$^{3}$H reaction at the high pulse-height side. First results will be compared to existing data and theoretical calculations. [1] T. Shima\textit{ et al}., Phys. Rev. C\textbf{ 72}, 044004 (2005). [2] B. Nilsson \textit{et al}., Phys. Rev. C \textbf{75}, 014007 (2007). [Preview Abstract] |
Thursday, November 4, 2010 11:06AM - 11:18AM |
DA.00004: Fission Fragment Studies from Near-Barrier Photo-Fission of Uranium M.J. Tuffley, M.S. Johnson, J.M. Hall, D.P. McNabb, M.W. Ahmed, S. Stave, H.R. Weller, J.M. Mueller, H. Karwowski, J. Tompkins We have performed near-barrier photo-fission measurements on uranium at the High Intensity Gamma-ray Source (HIGS) at TUNL. Offline gamma-ray measurements of the activated targets were performed to identify decaying fission fragments and determine their concentrations. Fission fragment analysis can be utilized to help validate the overall fission cross-section determination. The distribution of the fission fragments is expected to be a function of the incident photon energy, especially near the fission threshold. The offline gamma rays were measured with an HPGe detector at the HIGS facility. We measured the gamma ray spectra of the activated targets as a function of time. These spectra were then analyzed to determine the lifetimes of the fragments. We will present the results of our analysis and discuss future prospects. [Preview Abstract] |
Thursday, November 4, 2010 11:18AM - 11:30AM |
DA.00005: Observation of second-order radiative transitions in nuclei Robert Chrien Second order nuclear radiative transitions have been observed in the decay of $^{137}$Ba from a $^{137}$Cs source. Such a decay is expected from second order perturbation theory at a level of 1/$ \alpha )^2$ , or about $10^-4$. Second order transitions have been observed before only in the special case of $0^+$ to $0^+$ transitions where there is no competing first order transition. In the present work, transitions, which proceed via unspecified virtual states in $^{137}$Ba and consist of various multipole mixtures, are reported. It is expected that these new data will stimulate further research into this long-neglected area of nuclear research. [Preview Abstract] |
Thursday, November 4, 2010 11:30AM - 11:42AM |
DA.00006: Polarization Measurements of the Recoil Proton in $H(\vec{\gamma},\vec{p})\pi^0$ reaction Wei Luo, Mark Jones, Lubomir Pentchev Perturbative QCD theory predicts that the polarization components of the proton above the baryon resonance region should have a smooth dependence of $E_{\gamma}$, and approach limits established by hadron helicity conservation in the $H(\vec{\gamma},\vec{p})\pi^0$ reaction. Published data shows strong variation of the polarization variables above $2 \mbox{ GeV}$, which could be a sign of high-mass resonances. We present preliminary results for the $\pi^{0}$ photo-production from Jefferson Lab Hall C experiments E04-108, E04-019, E07-002 and Hall A experiment E99-114, which all measured the polarization observables of the recoil proton with high statistics. Our data extends the polarization measurements of $\pi^{0}$ photo-production up to $E_{\gamma}=5.7 \mbox{ GeV}$, with four momentum transfers up to 8.5 GeV$^2$. The results show consistency with published data up to $4.1 \mbox{ GeV}$. We will discuss the interpretation of these results. [Preview Abstract] |
Thursday, November 4, 2010 11:42AM - 11:54AM |
DA.00007: Light Vector Meson Photoproduction off of $^1$H at Jefferson Lab and $\rho$-$\omega$ Interference in the Leptonic Decay Channel Michael Paolone, Chaden Djalali, Rakhsha Nasseripour, Dennis Weygand, Mike Wood Recent studies of light vector meson production in heavy nuclear targets has generated interest in $\rho$-$\omega$ interference in the leptonic decay channel. An experimental study of the elementary process provides valuable input for theoretical models and calculations. In experiment E04-005, high statistics photoproduction data has been taken in Jefferson Lab's CLAS detector with tagged photon energies up to 5 GeV incident on a LH$_2$ target. Preliminary results of the $e^{+}e^{-}$ decay channel, with emphasis on the $\rho$-$\omega$ interference region, will be shown and compared to similar experimental data of photoproduction off of heavier nuclear targets ($^2$H to Pb) from Jefferson Lab experiment E01-112. [Preview Abstract] |
Thursday, November 4, 2010 11:54AM - 12:06PM |
DA.00008: Cross Section Measurement of $^2$H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations A. Couture, T.B. Clegg, C.R. Howell, S. Tajima, A. Crowell, J. Esterline, B. Fallin, L. Cumberbatch, B. Crowe, D. Markoff, R. Pedroni We have made cross-section measurements of neutron-deuteron breakup at an incident neutron energy of 16 MeV. The scattered proton was detected in coincidence with one of the neutrons and their energies were determined via time-of-flight techniques. Target-beam luminosity is obtained from n-d elastic scattering performed concurrently with the main experiment by detecting the scattered deuteron. Our current measurements are of two special cases of the Symmetric Constant Relative Energy Configuration: the space-star and the coplanar star. Data are compared with theoretical predictions [1] through Monte Carlo calculations which smear point geometry predictions over the finite beam, target, and detectors. Preliminary results for the space star are in agreement with previous experimental measurements [2] and are at least 20\% larger than theoretical predictions. \\[4pt] [1] H Witala and W Gl\"{o}ckle. J. Phys. G: Nucl. Part. Phys. 37 064003 (2010). \\[0pt] [2] C.R. Howell, Nucl. Phys. A 689, 298c (2001). [Preview Abstract] |
Thursday, November 4, 2010 12:06PM - 12:18PM |
DA.00009: A measurement of the differential cross section for the reaction $\gamma^{*} n \to \pi^{-} p$ from deuterium Jixie Zhang, Gail Dodge Differential cross sections for exclusive $\pi^{-}$ electro-production from the neutron in the reaction e+d $\rightarrow$ e$'$+$\pi^{-}$+p+p$_{r}$ have been measured over a broad kinematics range. The experiment was performed using a newly built radial time projection chamber (RTPC) and the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The RTPC detector was specially built to detect low energy recoil protons and had a valid momentum acceptance from 67 to 250 MeV/c. Electron scattering data were taken with beam energies of 2.1, 4.2 and 5.3 GeV using a 7 atm gaseous deuterium target. The differential cross sections for D$(e, e'\pi^{-}p)$p have been extracted, with the proton detected either by the CLAS or by the RTPC. The structure functions $\sigma_{\mbox{\tiny{T}}} + \varepsilon \sigma_{\mbox{\tiny{L}}}$, $\sigma_{\mbox{\tiny{LT}}}$ and $\sigma_{\mbox{\tiny{TT}}}$ are also extracted and compared to MAID and SAID predictions. [Preview Abstract] |
Thursday, November 4, 2010 12:18PM - 12:30PM |
DA.00010: Further Developments in Two-Body Bound-State problem in Light-Front Dynamics Yukihisa Tokunaga Solving the relativistic bound-state problem is an important task in nuclear physics. Even the two-body bound-state problem has been solved only under a certain approximation due to the nonperturbative nature. The two-body Bethe-Salpeter equation in the Wick-Cutkosky model was often solved in the ladder approximation without including the cross-ladder contribution, although many different and more accurate treatments of the numerical method to solve the bound-state problem have been developed nowadays. In this presentation, we use the light-front dynamics (LFD) to solve the two-body bound-state problem and extend the light-front ladder approximation to include the cross-ladder contribution. Using the variational principle, we present the numerical result of the binding energy versus the coupling constant including the particle and antiparticle effect to the cross-ladder contribution and show the attractive nature of this effect. To find the bound-state system where this effect is significant, we discuss the case with different masses of two scalar particles and also with the exchange particle of non-zero mass to compare the effect in the Coulomb potential vs. the Yukawa potential. [Preview Abstract] |
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