Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session DB: Mini-symposium on Stewardship Science II |
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Sponsoring Units: DNP Chair: Lee Bernstein, Lawrence Livermore National Laboratory Room: Gaylord Opryland Tennessee A |
Friday, October 27, 2006 2:00PM - 2:36PM |
DB.00001: Activities of the Center of Excellence for Radioactive Ion Beam Studies for Stewardship Science Invited Speaker: The Center of Excellence for Radioactive Ion Beam Studies for Stewardship Science is a consortium of universities, Oak Ridge Associated Universities, and Oak Ridge National Laboratory, led by Rutgers University. The purpose of this project, funded by the NNSA/DP Academic Alliance for Stewardship Science program, is to use radioactive ion beams to study low-energy nuclear reactions of importance to stewardship science, as well as to prepare future researchers in applied nuclear science. These studies are enabled by the plethora of unstable accelerated beams available at the Holifield Radioactive Ion Beam Facility at Oak Ridge. The initial measurements use neutron-rich beams of uranium fission fragments to study the neutron-transfer (d,p) reaction, a possible surrogate of neutron capture reactions. We also develop new radioactive ion beams of interest to nuclear structure, nuclear astrophysics, and stewardship science. This talk will present an overview of the activities of the Center and the available facilities, describe initial results of a (d,p) reaction with a fission fragment beam, and outline activities proposed for the near term. In collaboration with H.K. Carter, ORAU. [Preview Abstract] |
Friday, October 27, 2006 2:36PM - 2:48PM |
DB.00002: Reaction Mechanisms for (d,p) on Exotic Nuclei Neil Summers, Filomena Nunes, Ian Thompson Transfer reactions are typically analyzed using DWBA reaction theory. The structure of the exotic nuclei of affects the (d,p) cross section through overlaps of the relevant many body wave functions. In standard DWBA theory this overlap is approximated by a single particle wave function, where the core is considered inert. Then the cross section is scaled by the spectroscopic factor. Transfer to excited states and even continuum states for weakly bound nuclei can also be considered. This ``standard'' reaction theory neglects many things. On top of multi-step effects which can be investigated using a coupled channels approach, the single particle nature of the final states and the assumption that the core is inert are two approximations that can now be examined using an extension of the coupled channels approach called XCDCC (eXtended Continuum Discretized Coupled Channels). We use XCDCC to study Be10(d,p)Be11 and Be11(p,d)Be10 reactions and the effects of couplings. We examine the continuum states of Be11 where we can now model resonances built on excited core components. We compare our results with various sets of data and draw general conclusion important for (p,d) and (d,p) reactions. [Preview Abstract] |
Friday, October 27, 2006 2:48PM - 3:00PM |
DB.00003: Radioactive Ion Beams for Stewardship Science Andreas Kronenberg, H.K. Carter, E.H. Spejewski Measurements of particular reaction sequences that influence the cumulative fission yield of specific fission products of interest for stewardship science as well as for nuclear reactions on radiochemical detectors used in testing nuclear devices are often not accessible with radioactive targets because of short half-lives, high specific activities or availability of sufficient target material. Therefore, a possible surrogate reaction for (n,$\gamma )$ is the neutron transfer in (d,p) or (d,p$\gamma )$ reactions, which can be measured with ion beams of short-lived radioactive species in inverse kinematics. The Center of Excellence for Radioactive Ion Beam Studies for Stewardship Science is developing experimental techniques for measuring (d,p) reactions. Therefore, a strong component of our center is the development of accelerated radioactive ion beams such as 48V, 73,74As, 92,94,95Sr, 82Ge, 132,134Sn, Zr, Mo, Tc, and others. Some of these beams had not been available before, because the elements are refractory, or some beams require higher beam intensity or purity. Beam development techniques include different actinide targets, e.g. ThO2, molecular sideband formation, e.g. for Sr and possibly charge-exchange processes. This talk will consider specific beams of interested for our center. This research was sponsored by the NNSA under Stewardship Science Academic Alliance program through DOE Cooperative Agreement {\#} DE-FC03-3NA00143. [Preview Abstract] |
Friday, October 27, 2006 3:00PM - 3:12PM |
DB.00004: Development of the Oak Ridge Rutgers University Barrel Array S.D. Pain, J.A. Cizewski, R. Hatarik, K.L. Jones, M. Sikora, J.S. Thomas, D.W. Bardayan, J.C. Blackmon, C.J. Nesaraja, M.S. Smith, J. Howard, R.L. Kozub, J. James, R.J. Livesay, A. Gaddis, M.S. Johnson, B.H. Moazen The development of high quality RIBs, such as those at the HRIBF at ORNL, has made possible the performance of transfer reactions on unstable nuclei. Measurements of (d,p) reactions on n-rich fission fragments yield data on nuclear structure away from stability, are of importance to stewardship science and are of astrophysical interest due to the proximity to suggested r-process paths. Experimentally, (d,p) reactions on heavy ($Z$=50) fission fragments are complicated by the strongly inverse kinematics and low beam intensities. Ejectile detection with high resolution in position and energy, a high dynamic range and a high solid angular coverage is required. The Oak Ridge Rutgers University Barrel Array (ORRUBA) is currently under development for such measurements, providing a high solid angular coverage for angles forward and backward of 90 degrees. Resistive strip silicon detectors are used to obtain high- precision position and energy measurement, and $\Delta$E-E particle identification is employed at angles forward of $\theta_{lab}$ = $90^{\circ}$. The array's scientific motivation and technical aspects will be presented, along with a report of the first measurements performed with an early implementation of ORRUBA. [Preview Abstract] |
Friday, October 27, 2006 3:12PM - 3:24PM |
DB.00005: Results from (d,p) measurements in inverse kinematics at the HRIBF K.L. Jones, R.L. Kozub The Center of Excellence for Radioactive Ion Beam Studies has begun a program of (d,p) transfer experiments on fission fragment beams. These types of measurements probe the structure of nuclei away from stability, providing critical information for neutron-capture network models. The doubly-magic nuclei are used as bench marks for structure models. However, few exotic doubly-magic nuclei are available for in depth study, such as can be made using transfer reactions. Understanding the evolution of single-particle structure of nuclei close to the magic numbers, but away from the valley of stability, is crucial for improving models of the nucleus. This, in turn, provides critical information for neutron-capture network models. Fission fragment beams in the 132Sn region are available at Coulomb barrier energies at the Holifield Radioactive Ion Beam Facility (HRIBF). A major focus of our studies is on nuclei around the doubly-magic 132Sn nucleus. We have made a proof of principle study of (d,p) reactions in inverse kinematics in the A$\sim $132 region using a stable beam of 124Sn [1]. Results from the test measurement and the status of two experiments using radioactive 130Sn and 132Sn beams will be presented. [1] K.L. Jones et al., Phys. Rev. C 70, 067602 (2004). [Preview Abstract] |
Friday, October 27, 2006 3:24PM - 3:36PM |
DB.00006: Benchmarking ($d,p\gamma$) as surrogate reaction for ($n,\gamma$) R. Hatarik, J.A. Cizewski, K. Jones, S.D. Pain, T. Swan, D.W. Bardayan, J.C. Blackmon, L.A. Bernstein, J.T. Burke, F.S. Dietrich, J.E. Escher, M.S. Johnson, R. Kozub, A. Kronenberg Neutron capture cross sections on unstable nuclei are important for many applications in nuclear structure and astrophysics. Measuring these cross sections directly is a major challenge and often impossible. In the surrogate reaction technique a desired cross section can be extracted by measuring a different (surrogate) reaction that produces the same compound nucleus. In contrast to neutron capture, a neutron transfer cross section can be measured in inverse kinematics, which allows to measurements of cross sections on short lived-species. To test the feasability of using a ($d,p\gamma$) reaction as a surrogate for ($n,\gamma$), $^{143}$Nd and $^{145}$Nd have been chosen. The goal of this benchmark experiment is to reproduce the known neutron capture cross sections ratio of these isotopes. [Preview Abstract] |
Friday, October 27, 2006 3:36PM - 3:48PM |
DB.00007: Cross section measurements of $^{9}\mbox{Be}(\alpha, \mbox{n})^{12}\mbox{C}$ Z. Heinen, A. Adekola, C.R. Brune, S.M. Grimes, H. Hadizadeh, M.J. Hornish, T.N. Massey, C. Matei, A. Voinov The $^{9}\mbox{Be}(\alpha, \mbox{n})^{12}\mbox{C}$ reaction has a large cross section and hence is useful in applications as a neutron source. This reaction is also a key step in the formation of $^{12}\mbox{C}$ in neutron-rich environments, such as the ejecta of type-II supernovae. Using the 4.5-MV tandem accelerator at Ohio University, the differential cross section of $^{9}\mbox{Be}(\alpha, \mbox{n})^{12}\mbox{C} $ has been measured for an incident energy of $E_{\alpha}$ = 4.5 MeV. The time-of-flight method was used with a flight path of 30 m. A 15-$\mu \mbox{m}$-thick target of $^{9}\mbox{Be}$ was used. This thickness yielded broad peaks in the neutron energy spectra which allowed the energy dependence of the cross section to be inferred for $2 \leq E_{\alpha} \leq 4.5$ MeV. Using a beam swinger apparatus, neutrons were detected at laboratory angles of $0^{\circ}$, $15^{\circ}$, $35^{\circ}$, $40^{\circ}$, $60^{\circ}$, $88^{\circ}$, $110^{\circ}$, $120^{\circ}$, $130^ {\circ}$, and $145^{\circ}$. Neutrons associated with the ground state and the first two excited states of $^{12}\mbox{C}$ were measured. I will present the cross section data and discuss its implications. [Preview Abstract] |
Friday, October 27, 2006 3:48PM - 4:00PM |
DB.00008: Radiative strength functions and spin measurements for $^{95,96}$Mo from radiative neutron capture Steven Sheets, U. Agvaanluvsan, M. Krticka, G.E. Mitchell, J.A. Becker, J.L. Ullmann, T.A. Bredeweg, J.M. O'Donnell, R. Reifarth, R.S. Rundberg, David Vieira, J.M. Wouters Statistical properties in $^{95,96}$Mo have been measured using the multiplicity of $\gamma$-rays following neutron capture. Below the neutron separation energy an unusual enhancement in the radiative strength function (RSF) of Fe and Mo isotopes has been reported. We provide a new measurement of the RSF and compare our results with those obtained from two-step cascade measurements. An improved spin assignment for resonances in $^{96}$Mo is given. [Preview Abstract] |
Friday, October 27, 2006 4:00PM - 4:12PM |
DB.00009: ABSTRACT WITHDRAWN |
Friday, October 27, 2006 4:12PM - 4:24PM |
DB.00010: Neutron induced reactions of $^{150}$Sm and influence of spin distribution in the pre-equilibrium process D. Dashdorj, G.E. Mitchell, U. Agvaanluvsan, J.A. Becker, J.R. Cooper, P.E. Garrett, C.Y. Wu, W. Younes, T. Kawano, M. Chadwick, M. Devlin, N. Fotiades, R.O. Nelson Cross-section measurements were made of prompt $\gamma$-ray production as a function of incident neutron energy (E$_n$ = 1 to 35 MeV) on an enriched (95.6$\%$) $^{150}$Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center facility. The prompt-reaction $\gamma$ rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The preequilibrium reaction process is important at high energies. The spin distribution transferred in preequilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These preequilibrium spin distributions were incorporated into a new version of the Hauser-Feshbach statistical reaction code GNASH and the $\gamma$-ray production cross sections were calculated and compared with experimental data. The difference in the partial $\gamma$-ray cross sections using spin distributions with and without preequilibrium effects will be discussed. [Preview Abstract] |
Friday, October 27, 2006 4:24PM - 4:36PM |
DB.00011: Production of Neutron-Rich Isotopes from ThO$_{2}$ Targets E.H. Spejewski, A. Kronenberg, H.K. Carter, D.W. Stracener The Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory provides radioactive-ion beams for research in nuclear and astrophysics. An essential function is to produce a variety of radioactive species to meet the intensity, energy, and purity requirements of specific experiments. The primary production method has been proton-induced fission of uranium. However, production rates in the mass 80-95 region are expected to be higher from proton-induced fission of thorium. [1] In particular, $^{82}$Ge is expected to increase by an order or magnitude [2], and $^{92}$Sr yields should increase. Our first series of online experiments using a dense ThO$_{2}$ powder target, nevertheless, produced yields roughly a factor of 10 less than for UC$_{x}$ targets. Porous targets of ThO$_{2 }$have been produced and extensive yield measurements performed. Results from the different ThO$_{2}$ targets are compared to each other and to yields from some UC$_{x}$ targets. In order to obtain some understanding of these results, holdup-time measurements have been made on some chemical elements. [1] T. Ohtsuki, et al., Phys Rev C40 (1989) 2144. [2] V. Rubchenya, private communication. [Preview Abstract] |
Friday, October 27, 2006 4:36PM - 4:48PM |
DB.00012: Fission Fragment Spectroscopy Using a Frisch-Gridded Chamber in RPI's Lead Slowing-Down Spectrometer Catherine Romano A double sided Frisch-gridded fission chamber for use in RPI's Lead Slowing-Down Spectrometer (LSDS) is being developed at Rensselaer Polytechnic Institute. Placing this fission chamber in the high neutron flux of the LSDS allows measurements of neutron induced fission cross sections, as well as the mass and kinetic energy of the fission fragments of various isotopes. The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is deposited on a thin polyimide film located in the center of the cathode. Samples are made by dissolving small amounts of actinides in solution, placing the solution on the films and allowing the solution to evaporate. The anode signal and the sum of the anode and grid signals are collected by the data acquisition system. These values are used to calculate the angle of emission of the fission fragments which is then used to determine their energies and masses. RPI's LSDS is a 75 ton, 1.8m cube of lead. The RPI 60MeV Linac creates neutrons through a ($\gamma $,n) reaction when the electrons interact with a tantalum target inside the lead spectrometer. The resulting neutron flux is about 4 orders of magnitude larger than an equivalent resolution time-of-flight experiment. The high neutron flux allows for the measurement of isotopes that are not available in large quantities (sub-micrograms) or with small fission cross sections (microbarns). In collaboration with Ezekiel Blain, Zack Goldstein, Yaron Danon and Robert Block at Rensselaer Polytechnic Institute. Funded by Stewardship Science Academic Alliance, National Nuclear Security Agency. [Preview Abstract] |
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