Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session H8: Nuclear Reactions |
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Sponsoring Units: DNP Chair: Peggy McMahan, Lawrence Berkeley National Laboratory Room: Hyatt Regency Dallas Cumberland A |
Sunday, April 23, 2006 8:30AM - 8:42AM |
H8.00001: Electron scattering on halo nuclei Carlos Bertulani The inelastic scattering of electrons on weakly-bound nuclei is studied with a model based on the long range of the bound state wavefunction and on the effective-range expansion for the continuum wavefunctions. Three mechanisms have been considered: (a) dissociation of halo nuclei by high energy electrons, (b) dissociation by electrons present target, and (c) Coulomb dissociation. It is shown that the properties of halo nuclei can be studied in electron-radioactive colliders using the electro-disintegration process. A comparison with fixed-target experiments is also performed. [Preview Abstract] |
Sunday, April 23, 2006 8:42AM - 8:54AM |
H8.00002: The Search for Target Structure Effects in Elastic Scattering K.W. Kemper, O.A. Momotyuk, B.T. Roeder, N. Keeley, K. Rusek In elastic scattering, the question occurs as to how to separate details of the target structure from those of the projectile when using both standard optical potentials and semi-microscopic potentials in detailed coupled channels calculations. We will show that by graphing the cross section and analyzing power data as a function of momentum transfer rather than scattering angle that it is possible see regions of momentum transfer where effects arise from the projectile alone and regions where the target contribution must be accounted for. For light mass systems, these effects are more easily observed in the data by plotting the scattering cross section with respect to momentum transfer rather than the normally used ratio to Rutherford. The analysis of data for the elastic scattering of polarized $^{7}$Li from targets of $^{6}$Li, $^{7}$Li and $^{12}$C will be presented. A similar analysis of previously published data for $^{6}$He (1) and $^{6}$Li (2) elastic scattering from $^ {12}$C will also be presented.\\ (1) V. Lapoux et al. Phys. Rev. C66, 034608 (2002)\\ (2) A. Nadasen et al. Phys. Rev. C47, 674 (1993)\\ This work was supported in part by the U.S. National Science Foundation and the State of Florida. [Preview Abstract] |
Sunday, April 23, 2006 8:54AM - 9:06AM |
H8.00003: Tidal Effects in the Resonance decay of light clusters Romualdo deSouza, Alan Mcintosh, Sylvie Hudan, Carl Metelko An excited nucleus can decay by emission of clusters. These clusters may be excited and themselves subsequently undergo particle decay. Peaks in the relative energy spectrum of the secondary decay products indicate resonance reflecting the discrete internal structure of the primary emitted cluster. Resonance spectroscopy can be used, for example, to determine the temperature of the initial source within a statistical approach. To date however, the effect of the field of the emitting nucleus on the decay of the cluster has been largely neglected. Tidal effects result in the correlation of the relative energy with emission angle as a function of the decay time. We explore the influence of the external Coulomb field on the decay of the first excited state of $^{8}$Be in the reaction $^{60}$Ni + $^{100}$Mo at E/A=11 MeV. Experimental results will be compared with the predictions of a simple Coulomb trajectory model. [Preview Abstract] |
Sunday, April 23, 2006 9:06AM - 9:18AM |
H8.00004: Surrogate Measurement of the $^{237}$U(n, f) Reaction Cross Section H. Ai, C.W. Beausang, L. Ahle, L.A. Bernstein, J.T. Burke, J.A. Church, K. Moody, E.B. Norman, W. Younes, D. Bleuel, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, M.A. McMahan, L.W. Phair, E. Rodriguez-Vieitez, S. Sinha, M. Wiedeking The surrogate method of estimating reaction cross section, by inferring from the reaction probability of a different reaction that forms the same excited compound nucleus, has been established to be reliable by recent works. Using this method, the goal of this measurement is to estimate the (n, f) cross section on the short lived $^{237}$U through the measurement of the ($\alpha$, $\alpha$'f) reaction probability of the long lived $^{238}$U. The $^{238}$U($\alpha$, $\alpha$'f) experiment was performed at LBNL with the STARS detector (Silicon Telescope Array for Reaction Studies.) Preliminary analysis on the estimation of the $^{237}$U(n, f) reaction cross section will be presented. This work was supported by U.S. DOE Grant No. DE-FG02-05ER41379, DE-FG-05NA25929, and Contract No. W-7405-Eng-48, DE-AC03-76SF0098. [Preview Abstract] |
Sunday, April 23, 2006 9:18AM - 9:30AM |
H8.00005: Statistical model calculations of heavy-ion induced fusion-fission reactions Scott McCalla, John Lestone Statistical model calculations of heavy-ion induced fusion-fission reactions are performed with fission barrier heights, and potential curvatures, at both the equilibrium and saddle points, determined as a function of the total spin, $J$, the spin about the symmetry axis, $K$, and the nuclear temperature, $T$, in a self-consistent manner. The fission saddle points are correctly determined by finding the minimum in the system entropy as a function of deformation along the fission path. It is shown that if the saddle points are incorrectly determined using the turn points in the $T$=0 potential energy surfaces, that erroneous conclusions can be made regarding the viscosity of nuclear matter. When fission is modeled correctly, vast amounts of heavy-ion induced fission-probability and particle-emission data are consistent with the fission of fully equilibrated systems with the nuclear viscosity determined via the surface plus window dissipation model of Nix and Sierk. [Preview Abstract] |
Sunday, April 23, 2006 9:30AM - 9:42AM |
H8.00006: Characterizing deuteron breakup on thin targets at 20 MeV Kristen Brown, M.A. McMahan, Darren Bleuel, Lawrence Heilbronn, Larry Phair, John Keith III, L.A. Bernstein, Larry Ahle, Jason Burke, Jennifer Church, Bethany Lyles, Ian Thompson The breakup of a deuteron in the Coulomb field of a larger nucleus is a well-known phenomenon that has been studied for many decades. Deuteron breakup also has the potential of generating a forward-focused, relatively monoenergetic neutron beam at fluxes which are useful for many applications, including reactions on radioactive targets. However, most previous studies of this process have taken place at higher energies (Ed $\ge $ 56 MeV) and using thick targets. In order to evaluate the efficacy of deuteron breakup as a neutron source, we have studied the break-up process by measuring proton energy spectra -- with and without neutron coincidence -- from 2 - 9\r{ } in the laboratory using STARS (Silicon Telescope Array for Reaction Studies), on thin targets of Ti and Ta. Proton energy spectra and cross sections will be presented. [Preview Abstract] |
Sunday, April 23, 2006 9:42AM - 9:54AM |
H8.00007: Sub-threshold neutron-induced fission cross sections of $^{240, 242}$Pu Fredrik Tovesson, Tony Hill The $^{240, 242}$Pu(n,f) cross sections have been measured with a moderated spallation target at the Lujan facility at Los Alamos Neutron Science Center (LANSCE). In this experiment the cross section was measured from thermal energies up to the onset of the fission threshold at a few hundred keV. There are plans to extend the investigated energy range by using the WNR facility, where an un-moderated spallation target produces neutrons up to hundreds of MeV. The capture and fission cross sections for $^{240, 242}$Pu are important for fast reactor applications and are being measured in support of the Advanced Fuel Cycle Initiative (AFCI). The feasibility of measuring fission cross sections over this large energy rang has already been shown for $^{237}$Np, and the present work is the first step towards measuring more short-lived isotopes. These Pu-isotopes are alpha-emitters, and $^{240}$Pu has a half-life of only 6560 years. It was shown that the present experimental technique was suitable for handling targets with this high activity. [Preview Abstract] |
Sunday, April 23, 2006 9:54AM - 10:06AM |
H8.00008: The Zero Degree Calorimeter for CMS. Jeff Wood The Zero Degree Calorimeter (ZDC) is a device currently in the construction stages for use in nuclear research at the Large Hadron Collider (LHC) which is expected to operate by 2007. The ZDC will be used for both particle physics and nuclear physics research is scheduled at LHC. The ZDC itself will consist of plates at 45 degree angles relative to the beam and will be made of tungsten. Between these plates, there are plates of fiber optics that collect light. The events from colliding beams within the ZDC release Cherenkov light which the fibers then pick up. These many fibers will be fed into a photomultiplier tube with a time resolution of about 25 nanoseconds, the period at which events are expected. One of the problems discussed shall be the tendency of the quartz-based optical fibers to darken over time, so calibration is also necessary. The calibration mechanism will involve injecting a known amount of light into the ZDC itself so that a comparison can be made with the amount of light that is received by the photomultiplier tube. The challenge is creating an injection system resilient enough to withstand a highly radiative environment that will be also compatible with the resolution of the photomultiplier tube. [Preview Abstract] |
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