Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session KJ: Applications of Nuclear Physics |
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Chair: Kris Starosta, Simon Fraser University Room: Junior Ballroom A |
Saturday, October 15, 2016 2:00PM - 2:12PM |
KJ.00001: Sensitivity of $^{252}$Cf(sf) Neutron Observables to $\mathtt{FREYA}$ Inputs Ramona Vogt, Jorgen Randrup, Patrick Talou Within the framework of the fission event generator $\mathtt{FREYA}$, (Fission Reaction Event Yield Algorithm) we have studied the sensitivity of various neutron observables to the yield distribution $Y(A,Z,{\rm TKE})$ used as input to the code. Concentrating on the spontaneous fission of $^{252}$Cf, we generate a large number of different input yield distributions by performing simultaneous variations in the mass and charge yields as well as the kinetic energy distribution, governed by yield covariance matrices established from experimental data sets. For each of these input yield distributions, we then use $\mathtt{FREYA}$ to generate a large sample of complete fission events from which we extract various neutron observables, in particular the neutron multiplicity distribution, and the neutron spectrum associated with each multiplicity. On this basis, we are able to determine the sensitivity of those observables to the uncertainties in the input yield distribution obtained experimentally. This kind of study can be applied to any other case of interest and the information obtained can help to establish any needs and target accuracies required for further measurements to ensure reliable data validation. [Preview Abstract] |
Saturday, October 15, 2016 2:12PM - 2:24PM |
KJ.00002: Reducing Uncertainties in Neutron Induced Fission Cross Sections via a Time Projection Chamber Joshua Magee Neutron induced fission cross sections of actinides are of great interest in nuclear energy and stockpile stewardship. Traditionally, measurements of these cross sections have been made with fission chambers, which provide limited information on the actual fragments, and ultimately result in uncertainties on the order of several percent. The Neutron Induced Fission Fragment Tracking Experiment collaboration (NIFFTE) designed and built a fission Time Project Chamber (fission TPC), which provides additional information on these processes, through 3-dimensional tracking, improved particle identification, and in-situ profiles of target and beam non-uniformities. Ultimately, this should provide sub-percent measurements of (n,f) cross-sections. During the 2015 run cycle, measurements of several actinides were performed at the Los Alamos Neutron Science Center (LANSCE) Weapons Neutron Research (WNR) facility. An overview of the fission TPC will be given, as well as the current progress towards a sub-percent measurement of the $^{239}$Pu/$^{235}$U (n,f) cross-section ratio. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Saturday, October 15, 2016 2:24PM - 2:36PM |
KJ.00003: Energy and Angular Correlations of Fission Products William Peters, M. S. Smith, S. D. Pain, M. Febbraro, A. Galindo-Uribarri, K. L. Jones, K. Smith, R. Grzywacz, E. Temanson, J. A. Cizewski Despite the discovery of fission nearly 80 years ago and its importance to nuclear energy, national security, and astrophysics; there are very few measurements that correlate multiple fission products. A proof-of-principle experiment is underway at Oak Ridge National Lab to measure the energy and angle correlation between prompt fission neutrons, gamma rays, and fragments in time-coincidence. The angular and energy spectrum of the prompt neutrons and$/$or gamma rays with respect to fragment mass, could reveal new details concerning the energy balance between these products and will be essential for benchmarking advanced fission models. An array of neutron and gamma-ray detectors is positioned opposite dual time-of-flight detectors and a total-energy detector to determine one fragment mass. Preliminary results from a spontaneous $^{252}$Cf source will be presented, along with plans for future improvements. [Preview Abstract] |
Saturday, October 15, 2016 2:36PM - 2:48PM |
KJ.00004: Measurement of neutron-induced reactions on $^{242m}$Am M. Q. Buckner, C.-Y. Wu, R. A. Henderson, B. Bucher, A. Chyzh, T. A. Bredeweg, B. Baramsai, A. Couture, M. Jandel, S. Mosby, J. L. Ullmann Neutron-induced reaction cross sections of $^{242m}$Am were measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. A new neutron-capture cross section was determined relative to a simultaneous measurement of the well-known $^{242m}$Am(n,f) cross section. The (n,$\gamma$) cross section was measured from thermal to an incident energy of 1 eV. Our new $^{242m}$Am fission cross section was normalized to ENDF/B-VII.1 and agreed well with the (n,f) cross section reported in the literature from thermal energy to 1 keV. The capture-to-fission ratio was determined from thermal energy to E$_{n}$ = 0.1 eV, and it was found to be (n,$\gamma$)/(n,f) = 26(4)$\%$ compared to 19$\%$ from ENDF/B-VII.1. Our latest results will be reported. [Preview Abstract] |
Saturday, October 15, 2016 2:48PM - 3:00PM |
KJ.00005: DT High Energy Measurements and Comparison of Multiple Spectra in a He-4 Gas Neutron Detector Hannah E. Gardiner, Ting Zhu, Sasmit Gokhale, Cody Parker, Andrea Richard, Thomas Massey, James E. Baciak, Andreas Enqvisst, Kelly A. Jordan Neutron spectroscopy is important for a variety of applications to nuclear energy, national security, and basic science research. Currently, organic scintillator neutron detectors are used as a diagnostic tool for neutron spectroscopy in DT fusion research. However, these neutron measurements generate contaminants in common organics from deuteron or carbon break-up that affects the light output spectrum. A potential solution to this problem is to use a He-4 fast neutron gas scintillator detector system. He-4 has excellent gamma rejection due to a low charge density, pulse shape discrimination, and lower light yield and deposited energy from gamma interactions. The detector will also not degrade due to high intensity background gamma radiation. The detector was irradiated with 14.1 MeV neutrons at the Edwards Accelerator Lab at Ohio University. We report on the effectiveness of the He-4 detector system to measure the resulting high energy neutrons and compare this spectrum to other neutron spectra taken with this detector. [Preview Abstract] |
Saturday, October 15, 2016 3:00PM - 3:12PM |
KJ.00006: Development of a High- Brightness, Quasi- Monoenergetic Neutron Source at LLNL for Nuclear Physics Applications M.S. Johnson, S.G. Anderson, D. Bleuel, P.J. Fitsos, D. Gibson, J.M. Hall, R. Marsh, B. Rusnak Lawrence Livermore National Laboratory is developing a high-brightness, quasi-monoenergetic neutron source. The intensity of the neutron source is expected to be 10$^{\mathrm{11}}$ n/s/sr with energies between 7 MeV and 10 MeV at 5{\%} bandwidth at 0-degrees. This energy region is important for the study of neutron-induced reactions, nuclear astrophysics, and nuclear structure. For example, for neutrons between 1 and 10 MeV, the capturing states are below the GDR in many nuclei and the dominant reactions are compound and direct capture. The intensity and energy selection of the source makes it appealing for measurements of sparse targets at specific energies. We will present an array of nuclear physics measurements that will benefit from this source. The source is also of interest to generating activated targets for decay-out studies or for target production for other reaction-based measurements, e.g. fusion-evaporation reactions. Other usage examples include practical applications for imaging of very dense objects such as machine parts. For this presentation, we will discuss our method to use (d,n) production reaction on deuterium in a windowless gas target system. This approach is required because of the large power of the 7 MeV, 300$\mu $A deuteron beams. We will discuss our facility and its capabilities. [Preview Abstract] |
Saturday, October 15, 2016 3:12PM - 3:24PM |
KJ.00007: C$^{7}$LYC Scintillators and Fast Neutron Spectroscopy P. Chowdhury, T. Brown, E. Doucet, C.J. Lister, G.L. Wilson, N. D'Olympia, M. Devlin, S. Mosby Cs$_2$LiYCl$_6$ (CLYC) scintillators detect both gammas and neutrons with excellent pulse shape discrimination. At UML, fast neutron measurements with a 16-element 1"x1" CLYC array show promise for low energy nuclear science. CLYC detects fast neutrons via the $^{35}$Cl(n,p) reaction (resolution $<$10$\%$ at $<$8 MeV). In our $^7$Li-enriched C$^7$LYC, the thermal neutron response from the $^6$Li(n,$\alpha$)t reaction is virtually eliminated [1]. The low intrinsic efficiency of CLYC for fast neutrons ($<1\%$) is offset by increased solid angle with the array placed near the target, since TOF is not needed for energy resolution. The array was tested at LANL for measuring elastic and inelastic neutron scattering on $^{56}$Fe. The incident energy from the white neutron source was measured via TOF, and the scattered neutron energy via the pulse height in CLYC. The array was also tested at CARIBU for measuring beta-delayed neutrons. Larger CLYC crystals are now a reality. Measurements with the first 3" x 3" C$^7$LYC crystal are in progress at UML. Results will be discussed in the context of constructing a C$^7$LYC array at FRIB for reaction and decay spectroscopy of neutron-rich fragments.\\ 1. N. D'Olympia et al., Nucl. Inst. Meth. A694, 140 (2012), and A763, 433 (2014). [Preview Abstract] |
Saturday, October 15, 2016 3:24PM - 3:36PM |
KJ.00008: Photo-fission Product Yield Measurements at E$_\gamma $=13 MeV on $^{235}$U, $^{238}$U, and $^{239}$Pu. W. Tornow, M. Bhike, S. W. Finch, FNU Krishichayan, A. P. Tonchev We have measured Fission Product Yields (FPYs) in photo-fission of $^{235}$U, $^{238}$U, and $^{239}$Pu at TUNL's High-Intensity Gamma-ray Source (HI$\gamma $S) using mono-energetic photons of E$_\gamma $=13 MeV. Details of the experimental setup and analysis procedures will be discussed. Yields for approximately 20 fission products were determined. They are compared to neutron-induced FPYs of the same actinides at the equivalent excitation energies of the compound nuclear systems. In the future photo-fission data will be taken at E$_\gamma $=8.0 and 10.5 MeV to find out whether photo-fission exhibits the same so far unexplained dependence of certain FPYs on the energy of the incident probe, as recently observed in neutron-induced fission, for example, for the important fission product $^{147}$Nd [1].\newline M. E. Gooden \textit{et al.}, Nucl. Data Sheets {\bf 131}, 319 (2016). [Preview Abstract] |
Saturday, October 15, 2016 3:36PM - 3:48PM |
KJ.00009: New results from Compton spectrometer experiments Amanda Gehring, Michelle Espy, Todd Haines, Timothy Webb Over the past three years, a Compton spectrometer has successfully measured the x-ray spectra of intense radiographic sources. In this method, a collimated beam of x-rays incident on a convertor foil ejects Compton electrons. A collimator in the entrance to the spectrometer selects the forward-scattered electrons, which enter the magnetic field region of the spectrometer. The position of the electrons at the magnet's focal plane is proportional to the square root of their momentum, allowing the x-ray spectrum to be reconstructed. The spectrometer is a neodymium-iron magnet which measures spectra in the less than 1 MeV to 20 MeV energy range. In addition, a new spectrometer has been constructed that is a samarium-cobalt magnet with a calculated energy range of 50 keV to 4 MeV. The spectrometers have been fielded at both continuous and pulsed power facilities. Recent experimental results will be presented. [Preview Abstract] |
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