Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session JH: Mini-Symposium on Applications of Nuclear Physics IV |
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Chair: Lee Schroeder, Lawrence Berkeley National Laboratory and TechSource-Inc Room: General Kearny |
Friday, October 30, 2015 10:30AM - 10:42AM |
JH.00001: Measurement of the $^{242}$Pu neutron capture cross section M.Q. Buckner, C.Y. Wu, R.A. Henderson, B. Bucher, T.A. Bredeweg, B. Baramsai, A. Couture, M. Jandel, S. Mosby, J.M. O'Donnell, J.L. Ullmann, A. Chyzh Precision (n,f) and (n,$\gamma$) cross sections are important for the network calculations of the radiochemical diagnostic chain for the U.S. DOE's Stockpile Stewardship Program. $^{242}$Pu(n,$\gamma$) cross section is relevant to the network calculations of Pu and Am. Additionally, new reactor concepts have catalyzed considerable interest in the measurement of improved cross sections for neutron-induced reactions on key actinides. To date, little or no experimental data has been reported on $^{242}$Pu(n,$\gamma$) for incident neutron energy below 50 keV. A new measurement of the $^{242}$Pu(n,$\gamma$) reaction was performed with the DANCE together with an improved PPAC for fission-fragment detection at LANSCE during FY14. The relative scale of the $^{242}$Pu(n,$\gamma$) cross section spans four orders of magnitude for incident neutron energies from thermal to $\approx $ 30 keV. The absolute scale of the $^{242}$Pu(n,$\gamma$) cross section is set according to the measured $^{239}$Pu(n,f) resonance at 7.8 eV; the target was spiked with $^{239}$Pu for this measurement. The absolute $^{242}$Pu(n,$\gamma$) neutron capture cross section is $\approx$ 30{\%} higher than the cross section reported in ENDF for the 2.7 eV resonance. Latest results to be reported. [Preview Abstract] |
Friday, October 30, 2015 10:42AM - 10:54AM |
JH.00002: Gamma-Ray Emission Spectra as a Constraint on Calculations of $^{234,236,238}$U Neutron-Capture Cross Sections J.L. Ullmann, M. Krticka, T. Kawano, T.A. Bredeweg, B. Baramsai, A. Couture, R.C. Haight, M. Jandel, S. Mosby, J.M. O'Donnell, R.S. Rundberg, D.J. Vieira, J.B. Wilhelmy, J.A. Becker, C.Y. Wu, A. Chyzh Calculations of the neutron-capture cross section at low neutron energies (10 eV through 100's of keV) are very sensitive to the nuclear level density and radiative strength function. These quantities are often poorly known, especially for radioactive targets, and actual measurements of the capture cross section are usually required. An additional constraint on the calculation of the capture cross section is provided by measurements of the cascade gamma spectrum following neutron capture. Recent measurements of $^{234,236,238}$U(n,$\gamma$) emission spectra made using the DANCE 4$\pi$ BaF$_2$ array at the Los Alamos Neutron Science Center will be presented. Calculations of gamma-ray spectra made using the DICEBOX code and of the capture cross section made using the CoH$_3$ code will also be presented. These techniques may be also useful for calculations of more unstable nuclides. [Preview Abstract] |
Friday, October 30, 2015 10:54AM - 11:06AM |
JH.00003: Improved Modeling of Prompt Fission Neutron Spectra for Nuclear Data Evaluations Denise Neudecker, Patrick Talou, Toshihiko Kawano, Albert C. Kahler, Morgan C. White The prompt fission neutron spectra (PFNS) of major actinides such as $^{239}$Pu and $^{235}$U are quantities of interest for nuclear physics application areas including reactor physics and national security. Nuclear data evaluations provide recommended data for those application areas based on nuclear theory and experiments. Here, we present improvements made to the effective models predicting the PFNS up to incident neutron energies of 30 MeV and their impact on evaluations. These models describe relevant physics processes better than those used for the current US nuclear data library ENDF/B-VII.1. In addition, the use of higher-fidelity models such as Monte Carlo Hauser-Feshbach calculations will be discussed in the context of future PFNS evaluations. (LA-UR-15-24763) [Preview Abstract] |
Friday, October 30, 2015 11:06AM - 11:18AM |
JH.00004: Complete event simulations of nuclear fission Ramona Vogt For many years, the state of the art for treating fission in radiation transport codes has involved sampling from average distributions. In these average fission models energy is not explicitly conserved and everything is uncorrelated because all particles are emitted independently. However, in a true fission event, the energies, momenta and multiplicities of the emitted particles are correlated. Such correlations are interesting for many modern applications. Event-by-event generation of complete fission events makes it possible to retain the kinematic information for all particles emitted: the fission products as well as prompt neutrons and photons. It is therefore possible to extract any desired correlation observables. Complete event simulations can be included in general Monte Carlo transport codes. We describe the general functionality of currently available fission event generators and compare results for several important observables. [Preview Abstract] |
Friday, October 30, 2015 11:18AM - 11:30AM |
JH.00005: The LANL/LLNL Program to Measure Prompt Fission Neutron Spectra at LANSCE Robert Haight, Ching Yen Wu, Hye Young Lee, Terry Taddeucci, Shea Mosby, John O'Donnell, Nikolaos Fotiades, Mattew Devlin, John Ullmann, Ronald Nelson, Stephen Wender, Morgan White, Clell Solomon, Denise Neudecker, Patrick Talou, Michael Rising, Brian Bucher, Matthew Buckner, Roger Henderson Accurate data on the spectrum of neutrons emitted in neutron-induced fission are needed for applications and for a better understanding of the fission process. At LANSCE we have made important progress in understanding systematic uncertainties and in obtaining data for $^{235}$U on the low-energy part of the prompt fission neutron spectra (PFNS), a particularly difficult region because down-scattered neutrons go in this direction. We use a double time-of-flight technique to determine energies of incoming and outgoing neutrons. With data acquisition via waveform digitizers, accidental coincidences between fission chamber and neutron detector are measured to high statistical accuracy and then subtracted from measured events. Monte Carlo simulations with high performance computers have proven to be essential in the design to minimize neutron scattering and in calculating detector response. Results from one of three approaches to analyzing the data will be presented. [Preview Abstract] |
Friday, October 30, 2015 11:30AM - 11:42AM |
JH.00006: High-Resolution Correlated Fission Product Measurements of $^{235}$U$(n_{th},f)$ with SPIDER Dan Shields The SPIDER detector (SPectrometer for Ion DEtermination in fission Research) has obtained high-resolution, moderate-efficiency, correlated fission product data needed for many applications including the modeling of next generation nuclear reactors, stockpile stewardship, and the fundamental understanding of the fission process. SPIDER simultaneously measures velocity and energy of both fission products to calculate fission product yields (FPYs), neutron multiplicity ($\nu$), and total kinetic energy (TKE). These data will be some of the first of their kind available to nuclear data evaluations. An overview of the SPIDER detector, analytical method, and preliminary results for $^{235}$U$(n_{th},f)$ will be presented. LA-UR-15-20130 [Preview Abstract] |
Friday, October 30, 2015 11:42AM - 11:54AM |
JH.00007: Reducing Uncertainties in Neutron-Induced Fission Cross Sections Using a Time Projection Chamber Brett Manning Neutron-induced fission cross sections for actinides have long been of great interest for nuclear energy and stockpile stewardship. Traditionally, measurements were performed using fission chambers which provided limited information about the detected fission events. For the case of $^{239}$Pu(n,f), sensitivity studies have shown a need for more precise measurements. Recently the Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) has developed the fission Time Projection Chamber (fissionTPC) to measure fission cross sections to better than 1\% uncertainty by providing 3D tracking of fission fragments. The fissionTPC collected data to calculate the $^{239}$Pu(n,f) cross section at the Weapons Neutron Research facility at the Los Alamos Neutron Science Center during the 2014 run cycle. Preliminary analysis has been focused on studying particle identification and target and beam non-uniformities to reduce the uncertainty on the cross section. Additionally, the collaboration is investigating other systematic errors that could not be well studied with a traditional fission chamber. [Preview Abstract] |
Friday, October 30, 2015 11:54AM - 12:06PM |
JH.00008: Mass Yields and Average Total Kinetic Energy Release in Fission for $^{235}$U, $^{238}$U, and $^{239}$Pu Dana Duke Mass yield distributions and average total kinetic energy ($\overline{TKE}$) in neutron induced fission of $^{235}$U, $^{238}$U, and $^{239}$Pu targets were measured with a gridded ionization chamber. Despite decades of fission research, our understanding of how fragment mass yields and $\overline{TKE}$ depend on incident neutron energy is limited, especially at higher energies (above 5-10 MeV). Improved accuracy in these quantities is important for nuclear technology as it enhances our simulation capabilities and increases the confidence in diagnostic tools. The data can also guide and validate theoretical fission models where the correlation between the fragment mass and TKE is of particular value for constraining models. The Los Alamos Neutron Science Center - Weapons Neutron Research (LANSCE - WNR) provides a neutron beam with energies from thermal to hundreds of MeV, well-suited for filling in the gaps in existing data and exploring fission behavior in the fast neutron region. The results of the studies on target nuclei $^{235}$U, $^{238}$U, and $^{239}$Pu will be presented with a focus on exploring data trends as a function of neutron energy from thermal through 30 MeV. Results indicate clear evidence of structure due to multi-chance fission in the $\overline{TKE}$. [Preview Abstract] |
Friday, October 30, 2015 12:06PM - 12:18PM |
JH.00009: Using Ultracold Neutrons to Characterize Fission Fragment Induced Sputtering Leah Broussard, Mark Makela, Chris Morris One of the modern challenges in nuclear science and technology is the understanding of the nature of fission fragment damage to material and the resulting ejection of matter as the fragments pass through the surface, with implications to stockpile stewardship and nuclear energy. We have demonstrated a new technique that can be used to characterize the sputtered material with knowledge of the location of the originating fission event. Due to their very high fission cross sections, ultracold neutrons ($\sim$100 neV energy) can be used to control the depth at which fission takes place using their energy or the material enrichment. This effort represents one of the first practical applications of ultracold neutrons, which to date have been primarily used to explore questions in fundamental particle physics. We will present results of demonstration measurements including first limits on the total and fission cross sections for 100 neV scale neutrons and the status of the development of this new capability. [Preview Abstract] |
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