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 FB: Mini-Symposium: Nuclear Physics Research and Connections to Nuclear Energy I |
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Chair: Lee Schroeder, Lawrence Berkeley National Laboratory Room: Room 208 |
Saturday, October 25, 2008 8:30AM - 9:06AM |
FB.00001: Basic Nuclear Physics Research Needs for Nuclear Energy Invited Speaker: Basic nuclear physics research will play a central role in the development of the future nuclear facilities. Federal requirements for higher efficiencies, lower operating and construction costs, and advanced safeguards can all be impacted by the quality of nuclear data used in the fuel cycle calculations for design and licensing. Uncertainties in the underlying nuclear data propagate to uncertainties in integral and operational parameters, which drive margins and cost. Department of Energy (DOE) programs are underway to help develop the necessary nuclear research infrastructure. The Nuclear Energy office of DOE leads the development of new nuclear energy generation technologies to meet energy and climate change goals and advanced, proliferation resistant nuclear fuel technologies that maximize energy from nuclear fuel, while maintaining and enhancing the national nuclear infrastructure. These activities build on important work started over the last three years to deploy new nuclear plants in the United States by early in the next decade, and to develop advanced, next-generation nuclear technology. In this talk, I will discuss some of the foreseen opportunities and needs for basic nuclear research in nuclear energy. [Preview Abstract] |
Saturday, October 25, 2008 9:06AM - 9:18AM |
FB.00002: Determining cross sections for low-energy neutron capture reactions via the Surrogate method Jutta Escher, Frank Dietrich, Nicholas Scielzo, Christian Forssen The {\em Surrogate Nuclear Reactions} method, an indirect approach for determining compound-nuclear reaction cross sections, has recently received renewed attention. The method has primarily been employed to determine (n,f) cross sections for various actinides, including unstable isotopes. Cross sections for other reactions, in particular (n,$\gamma$) reactions on short-lived targets, are of interest as well, but are more difficult to extract from Surrogate measurements. This contribution will focus on the prospects for employing the Surrogate method to obtain neutron-capture cross sections for applications in the areas of astrophysics and nuclear energy. Progress made in understanding the impact and treatment of the spin mismatch between the desired (neutron-induced) and Surrogate reactions will be summarized. Calculations will be presented that assess the validity of employing various approximate treatments in the interpretation of Surrogate measurements and insights gained from recent experiments will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 9:18AM - 9:30AM |
FB.00003: Measuring the $^{239}$U(n,f) cross section using a two neutron transfer surrogate reaction Jason Burke Measuring fission cross sections of unstable short lived actinides has been a difficult challenge to experimental physicists for decades. Cross sections for neutron induced reactions are essential for basic and applied science fields of study such as nuclear astrophysics and nuclear reactor design. Surrogate reactions offer an alternative approach to direct measurements. I will present our work on the surrogate two neutron transfer reaction $^{238}$U($^{18}$O,$^{16}$O)$^{240}$U used to obtain the fission cross section of $^{239}$U(n,f) by comparing it to the known $^{235}$U(n,f) cross section obtained via the $^{234}$U($^{18}$O,$^{16}$O)$^{236}$U reaction. This work was performed under the auspices of the U.S. Department of Energy under contract numbers DE-AC52-07NA27344 (LLNL), DE-AC02-05CH11231 (LBNL) and DE-FG52-06NA26206 (UR). [Preview Abstract] |
Saturday, October 25, 2008 9:30AM - 9:42AM |
FB.00004: Surrogate reactions on fission fragments for nuclear energy R. Hatarik, J.A. Cizewski, W.A. Peters, D.W. Bardayan, S.D. Pain Neutron capture cross sections on unstable nuclei are important for many applications in nuclear structure, astrophysics, for the advanced fuel cycle initiative and other applied programs. Measuring these cross sections directly is impossible for short lived species and theoretical calculations often do not have the required accuracy. An alternative approach is to measure the neutron transfer reaction (d,p$\gamma$), which can be done using radioactive beams and CD$_2$ targets and has been demonstrated to be a surrogate for (n,$\gamma$). This talk would present the status of (d,p$\gamma$) measurements with radioactive ion beams and prospects for measurements with fission fragments. [Preview Abstract] |
Saturday, October 25, 2008 9:42AM - 9:54AM |
FB.00005: Benchmarking the Surrogate Ratio Method Using the {\boldmath $\alpha$,$\alpha$}'f) reaction S.R. Lesher, L.A. Bernstein, J.T. Burke, D.L. Bleuel, F.S. Dietrich, J.E. Escher, B.F. Goldblum, K.J. Moody, E.B. Norman, N.D. Scielzo, H. Ai, C.W. Beausand, R.M. Clark, P. Fallon, J. Gibelin, I.Y. Lee, A.O. Macchiavelli, M.A. McMahan, L. Phair, E. Rodriguez-Vieitez, M. Wiedeking The Surrogate Ratio Method is a technique that can be used to obtain neutron induced reaction cross sections on unstable nuclei. Using the 88-Inch Cyclotron at LBNL and the Silicon Telescope Array for Reaction Studies (STARS), $^{234}$U and $^{236}$U were excited via inelastic $\alpha $ particle scattering. Fission events from the decay of these nuclei were detected in coincidence with the alpha particles. The ratio of their fission probabilities was compared to the known $^{233}$U(n,f) / $^{235}$U(n,f) cross-section ratio and found to agree over an excitation energy range of 7 -- 25 MeV. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344 and Grant Nos. DE-FG52-06NA26206 and DE-FG02-05ER41379. This work was also supported by the Director, Office of Science, Office of Nuclear Physics of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. [Preview Abstract] |
Saturday, October 25, 2008 9:54AM - 10:06AM |
FB.00006: How Can the Accuracy of Neutron Nonelastic Cross Sections be Improved? Frank Dietrich The nonelastic cross section for incident neutrons is particularly important for applications because it directly determines the sum of all reaction processes other than elastic scattering, and is closely related to the compound-nucleus formation cross section. Scatter in available measurements of the nonelastic cross section shows that this quantity is not known very accurately ($\approx$5--10\%). We will show examples of this, together with results from a new technique that shows promise of reducing uncertainties to $\approx$2--3\% in the range of a few MeV to a few tens of MeV [1]. Comparison of results using this technique on Fe, Pb, Th, and U with optical model calculations suggests that optical potentials are not reliable for predicting nonelastic cross sections to better than $\approx$5\%, even when they reproduce total cross sections well ($\approx$1\%). We will suggest a limited set of high-accuracy measurements of nonelastic cross sections that could be made to guide the further development of optical models that are able to predict nonelastic cross sections reliably. \newline [1] F. S. Dietrich, J. D. Anderson, R. W. Bauer, and S. M. Grimes, Phys. Rev. C{\bf 68}, 064608 (2003). [Preview Abstract] |
Saturday, October 25, 2008 10:06AM - 10:18AM |
FB.00007: A Gas Electron Multiplier (GEM) Detector for Fast Neutron Imaging C.C. Jewett, M. McMahan, J. Cerny, L. Heilbronn, M. Johnson We have built a Gas Electron Multiplier (GEM) detector for detection of fast neutrons at Lawrence Berkeley National Laboratory. The detector consists of a 0.0625 inch thick polypropylene neutron converter, three GEM foils and a grid of 16 readout pads on a printed circuit board. In this talk, we present images of the GEM detector, the results of tests with $^{60}$Co, AmBe sources and our neutron beam, and a comparison between the proposed fast neutron GEM detector and a fast neutron $^{238}$U fission chamber we purchased. One of the advantages of the GEM detector over the fission chamber is the fact that it provides the x-y position information of the neutrons. [Preview Abstract] |
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