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FIGARO : measuring neutron emission spectra with a white neutron source /.

Description: Neutron emission spectra from reactions induced by fast neutrons are of importance in basic physics and applications. Very few data are available in the literature over a wide range of incident neutron energies such as produced with a white neutron source. The FIGARO facility at the WNR/LANSCE neutron source has been established to measure such neutron emission over a range of incident neutron energies from 1 to over 100 MeV. Using the time-of-flight technique twice (once to determine the incident neutron energy and again to determine the outgoing neutron energy), we are measuring neutron emission spectra for several reactions such as (n,n') and (n,f). Neutron emission from inelastic scattering gives information on the level density of excited states of the target nucleus. Our first measurements are on structural materials such as iron.
Date: January 1, 2002
Creator: Haight, Robert C.; O'Donnell, J. M.; Zanini, L.; Devlin, M. & Rochman, D. (Dimitri)
Partner: UNT Libraries Government Documents Department

MEASUREMENT OF THE AVERAGE ENERGY AND MULTIPLICITY OF PROMPT-FISSION-NEUTRONS FROM 238U(n,f) AND 237 Np(n,f) FROM 1 TO 200 MeV.

Description: Taking advantage of the neutron source of the LANCSE, it has been possible to obtain a measure of the velocity distribution and the number of prompt-neutrons emitted in the neutron-induced fission of {sup 238}U and {sup 237}Np over a broad incident neutron energy range. The mean kinetic energy was extracted and is shown as the function of the incident-neutron energy. We confirm here the observation, for both reactions, of a dip around the second chance fission which is explained by the lower kinetic energy of the pre-fission neutrons. Such a observation is reproduced by Los Alamos model as implemented at Bruyeres le Chatel and by the Maslov model. As far as the neutron multiplicity is concerned, a similar dip is observed. However, such a behavior is not present in data measured by other groups.
Date: June 28, 2007
Creator: TAIEB,J.; GRANIER, T.; ETHVIGNOT, T.; DEVLIN, M.; HAIGHT, R.C.; NELSON, R.O. et al.
Partner: UNT Libraries Government Documents Department

The FIGARO Facility at Los Alamos : capabilities and first results /

Description: A new beam line at the fast neutron spallation source at Los Alamos Neutron Science Center has been constructed for studies of neutron-induced reactions producing gamma rays, internal conversion electrons or neutrons. This facility, called FIGARO (Fast neutron-Induced GAmma-Ray Observer), follows on the great successes of GEANIE (described in other contributions to this Conference), by detecting de-excitation gamma rays with high-resolution germanium detectors. FIGARO has fewer gamma-ray detectors than GEANIE, but instead offers other features including: extremely good collimation of the neutron beam for background reduction, a flexible experimental area to optimize detection efficiency and to allow evaluation of other detectors such as ICEBALL-II for internal conversion electrons, inclusion of neutron detectors for the study of neutron-gamma coincidences, beam time to relieve the scheduling pressure on GEANIE, and a PC-based data acquisition system. Our initial measurements include level density studies through 59Co(n,xgamma) reactions to complement our previous 59Co(n,xalpha) measurements, reaction studies of MeV neutrons on 99Tc with the goal of determining cross sections relevant to transmutation and neutron transport in the design of facilities to incinerate nuclear waste, and an assessment of measuring internal conversion electrons, rather than gamma rays, produced by neutron excitation of actinides.
Date: January 1, 2001
Creator: Devlin, M. J. (Matthew J.); Zanini, L.; O'Donnell, J. M.; Aprahamian, A. (Ani); Saladin, J. X. & Haight, Robert C.
Partner: UNT Libraries Government Documents Department

148-Gd cross section measurements for accelerator target facilities

Description: In a series of experiments at LANSCE's WNR facility, 148Gdp roduction was measured for 600- and 800-MeV protons on tungsten, tantalum, and gold. These experiments used 3 pm thin W, Ta, and Au foils and 10 pm thin A1 activation foils, Spallation yields were determined for many short-lived and long-lived spallation products with these foils using gamma and alpha spectroscopy.
Date: January 1, 2002
Creator: Corzine, R. K. (R. Karen); Pitcher, E. J. (Eric J.); Devlin, M. J. (Matthew J.) & Hertel, N. E. (Nolan E.)
Partner: UNT Libraries Government Documents Department

Gamma-ray production cross sections in multiple channels for neutron induced reaction on 48Ti for En=1 to 200 MeV

Description: Prompt {gamma}-ray production cross sections were measured on a {sup 48}Ti sample for incident neutron energies from 1 MeV to 200 MeV. Partial {gamma}-ray cross sections for transitions in {sup 45-48}Ti, {sup 45-48}Sc, and {sup 43-45}Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial {gamma}-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the LANSCE/WNR facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, pre-equilibrium emission and direct reaction mechanisms are included. Overall the model calculations of the partial {gamma}-ray cross sections are in good agreement with measured values.
Date: July 6, 2006
Creator: Dashdorj, D; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A et al.
Partner: UNT Libraries Government Documents Department

Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections

Description: Prompt {gamma}-ray production cross section measurements were made as a function of incident neutron energy (En = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These preequilibrium spin distributions were incorporated into the Hauser-Feshbach statistical reaction code GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. Neutron inelastic scattering populates 150Sm excited states either by (1) forming the compound nucleus {sup 151}Sm* and decaying by neutron emission, or (2) by the incoming neutron transferring energy to create a particle-hole pair, and thus initiating the pre-equilibrium process. These two processes produce rather different spin distributions: the momentum transfer via the pre-equilibrium process tends to be smaller than in the compound reaction. This difference in the spin population has a significant impact on the {gamma}-ray de-excitation cascade and therefore in the partial {gamma}-ray cross sections. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects was significant, e.g., for the 558-keV transition between 8{sup +} and 6{sup +} states the calculated partial {gamma}-ray production cross sections changed by 70% at E{sub n} = 20 MeV with inclusion of the spin distribution of pre-equilibrium process.
Date: April 16, 2007
Creator: Dashdorj, D; Kawano, T; Mitchell, G E; Becker, J A; Agvaanluvsan, U; Chadwick, M et al.
Partner: UNT Libraries Government Documents Department

Neutron induced inelastic cross sections of 150Sm for En = 1 to 35 MeV

Description: Cross-section measurements were made of prompt gamma-ray production as a function of incident neutron energy (E{sub n} = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) 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 {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Partial {gamma}-ray cross sections were predicted using the Hauser-Feshbach statistical reaction code GNASH. Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These pre-equilibrium spin distributions were incorporated into a new version of 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 pre-equilibrium effects is discussed.
Date: August 16, 2006
Creator: Dashdorj, D; Mitchell, G E; Kawano, T; Becker, J A; Agvaanluvsan, U; Chadwick, M B et al.
Partner: UNT Libraries Government Documents Department

Spin distribution in neutron induced preequilibrium reactions

Description: The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E{sub n} {approx} 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through {gamma}-ray spectroscopy. Cross-section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy (E{sub n} = 1 to 250 MeV) on a {sup 48}Ti 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 {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations 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 is significant.
Date: October 4, 2005
Creator: Dashdorj, D; Kawano, T; Chadwick, M; Devlin, M; Fotiades, N; Nelson, R O et al.
Partner: UNT Libraries Government Documents Department

Lead Slowing Down Spectrometer Status Report

Description: This report documents the progress that has been completed in the first half of FY2012 in the MPACT-funded Lead Slowing Down Spectrometer project. Significant progress has been made on the algorithm development. We have an improve understanding of the experimental responses in LSDS for fuel-related material. The calibration of the ultra-depleted uranium foils was completed, but the results are inconsistent from measurement to measurement. Future work includes developing a conceptual model of an LSDS system to assay plutonium in used fuel, improving agreement between simulations and measurement, design of a thorium fission chamber, and evaluation of additional detector techniques.
Date: June 7, 2012
Creator: Warren, Glen A.; Anderson, Kevin K.; Bonebrake, Eric; Casella, Andrew M.; Danon, Yaron; Devlin, M. et al.
Partner: UNT Libraries Government Documents Department

Lead Slowing-Down Spectrometry for Spent Fuel Assay: FY12 Status Report

Description: Executive Summary The Office of Nuclear Energy, Fuel Cycle R&D, Material Protection and Control Technology (MPACT) Campaign is supporting a multi-institutional collaboration to study the feasibility of using Lead Slowing Down Spectroscopy (LSDS) to conduct direct, independent and accurate assay of fissile isotopes in used fuel assemblies. The collaboration consists of Pacific Northwest National Laboratory (PNNL), Los Alamos National Laboratory (LANL), Rensselaer Polytechnic Institute (RPI), Idaho State University (ISU). There are three main challenges to implementing LSDS to assay used fuel assemblies. These challenges are the development of an algorithm for interpreting the data with an acceptable accuracy for the fissile masses, the development of suitable detectors for the technique, and the experimental benchmarking of the approach. This report is a summary of the progress in these areas made by the collaboration during FY2012. Significant progress was made on the project in FY2012. Extensive characterization of a “semi-empirical” algorithm was conducted. For example, we studied the impact on the accuracy of this algorithm by the minimization of the calibration set, uncertainties in the calibration masses, and by the choice of time window. Issues such a lead size, number of required neutrons, placement of the neutron source and the impact of cadmium around the detectors were also studied. In addition, new algorithms were developed that do not require the use of plutonium fission chambers. These algorithms were applied to measurement data taken by RPI and shown to determine the 235U mass within 4%. For detectors, a new concept for a fast neutron detector involving 4He recoil from neutron scattering was investigated. The detector has the potential to provide a couple of orders of magnitude more sensitivity than 238U fission chambers. Progress was also made on the more conventional approach of using 232Th fission chambers as fast neutron detectors. For benchmarking measurements, ...
Date: October 1, 2012
Creator: Warren, Glen A.; Anderson, Kevin K.; Casella, Andrew M.; Danon, Yaron; Devlin, M.; Gavron, A. et al.
Partner: UNT Libraries Government Documents Department

Ternary particles with extreme N/Z ratios from neutron-induced fission

Description: The existing ternary fission models can well reproduce the yields of the most abundant light charged particles. However, these models tend to significantly overestimate the yields of ternary particles with an extreme N/Z ratio: {sup 3}He, {sup 11}Li, {sup 14}Be, etc. The experimental yields of these isotopes were investigated with the recoil separator LOHENGRIN down to a level of 10{sup {minus}10} per fission. Results from the fissioning systems {sup 233}U (n{sub th}, f), {sup 235}U(n{sub th},f), {sup 239}Pu(n{sub th},f) {sup 241}Pu(n{sub th},f) and {sup 245}Cm(n{sub th},f) are presented and the implications for the ternary fission models are discussed.
Date: May 16, 2000
Creator: Koster, U.; Faust, H.; Friedrichs, T.; Oberstedt, S.; Fioni, G.; Grob, M. et al.
Partner: UNT Libraries Government Documents Department

Fast-neutron-induced fission studied by gamma-spectroscopy.

Description: Prompt gamma-ray and x-ray spectroscopy techniques are being employed to study fast-neutron-induced fission of actinides to determine independent (pre-beta-decay) yields for a wide range of product nuclides. Data are acquired using the GEANIE high-resolution gamma-ray spectrometer at the LANSCE/WNR unmoderated spallation neutron source providing neutrons with energies from below 1 MeV to over 400 MeV. Three different techniques (identification by characteristic gamma rays, by gamma-gamma coincidences, and by fission-gamma coincidences) are being used to gather complementary data sets from which detailed fission yields can be extracted. From these data, mass and charge distributions are determined over a wide incident-neutron energy range. The phenomena of interest include the transition from asymmetric to symmetric fission, the competition between neutron and gamma-ray emission, nuclear structure effects in fission and the angular momentum imparted to the fission products. Results for 238U and 236U are presented.
Date: January 1, 2002
Creator: Nelson, R. O. (Ronald O.); Fotiadis, N. (Nikolaos); Devlin, M. J. (Matthew J.); Johns, G. D. (Glen D.); Ethvignot, T. (Thierry); Granier, T. (Thierry) et al.
Partner: UNT Libraries Government Documents Department

Lead Slowing-Down Spectrometry for Spent Fuel Assay: FY11 Status Report

Description: Executive Summary Developing a method for the accurate, direct, and independent assay of the fissile isotopes in bulk materials (such as used fuel) from next-generation domestic nuclear fuel cycles is a goal of the Office of Nuclear Energy, Fuel Cycle R&D, Material Protection and Control Technology (MPACT) Campaign. To meet this goal, MPACT supports a multi-institutional collaboration to study the feasibility of Lead Slowing Down Spectroscopy (LSDS). This technique is an active nondestructive assay method that has the potential to provide independent, direct measurement of Pu and U isotopic masses in used fuel with an uncertainty considerably lower than the approximately 10% typical of today’s confirmatory assay methods. This document is a progress report for FY2011 collaboration activities. Progress made by the collaboration in FY2011 continues to indicate the promise of LSDS techniques applied to used fuel. PNNL developed an empirical model based on calibration of the LSDS to responses generated from well-characterized used fuel. The empirical model demonstrated the potential for the direct and independent assay of the sum of the masses of 239Pu and 241Pu to within approximately 3% over a wide used fuel parameter space. Similar results were obtained using a perturbation approach developed by LANL. Benchmark measurements have been successfully conducted at LANL and at RPI using their respective LSDS instruments. The ISU and UNLV collaborative effort is focused on the fabrication and testing of prototype fission chambers lined with ultra-depleted 238U and 232Th, and uranium deposition on a stainless steel disc using spiked U3O8 from room temperature ionic liquid was successful, with improving thickness obtained. In FY2012, the collaboration plans a broad array of activities. PNNL will focus on optimizing its empirical model and minimizing its reliance on calibration data, as well continuing efforts on developing an analytical model. Additional measurements are planned at LANL ...
Date: August 1, 2011
Creator: Warren, Glen A.; Casella, Andrew M.; Haight, R. C.; Anderson, Kevin K.; Danon, Yaron; Hatchett, D. et al.
Partner: UNT Libraries Government Documents Department

The EBEX Experiment

Description: EBEX is a balloon-borne polarimeter designed to measure the intensity and polarization of the cosmic microwave background radiation. The measurements would probe the inflationary epoch that took place shortly after the big bang and would significantly improve constraints on the values of several cosmological parameters. EBEX is unique in its broad frequency coverage and in its ability to provide critical information about the level of polarized Galactic foregrounds which will be necessary for all future CMB polarization experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a resolution of less than 8 arcminutes over four focal planes each of 4. diffraction limited field of view at frequencies up to 450 GHz. The experiment is designed to accommodate 330 transition edge bolometric detectors per focal plane, for a total of up to 1320 detectors. EBEX will operate with frequency bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a rotating achromatic half-wave plate. EBEX is currently in the design and construction phase, and first light is scheduled for 2008.
Date: January 6, 2005
Creator: Oxley, P.; Ade, P.; Baccigalupi, C.; deBernardis, P.; Cho, H-M.; Devlin, M.J. et al.
Partner: UNT Libraries Government Documents Department

Measurement and analysis of quadruple ({alpha}{gamma}{gamma}) angular correlations for high spin states of {sup 24}Mg.

Description: The high-lying, {alpha}-decaying states in {sup 24}Mg have been studied by measuring the complete decay path of {alpha} and {gamma} emissions using five segmented Silicon detectors in conjunction with GAMMASPHERE. The authors analyzed the ({alpha}{gamma}) triple angular correlations and, for the first time, ({alpha}{gamma}{gamma}) quadruple correlations. The data analysis is based on a new Fourier transformation technique. The power of the technique is demonstrated.
Date: October 30, 2000
Creator: Wiedenhover, I.; Wuosmaa, A. H.; Lister, C. J.; Carpenter, M. P.; Janssens, R. V. F.; Amro, H. et al.
Partner: UNT Libraries Government Documents Department

Partial (gamma)-Ray Cross Sections for the Reaction 239Pu(n,2n(gamma)i) and the 239Pu(n,2n) Cross Section

Description: Absolute partial {gamma}-ray cross sections for production of discrete {gamma} rays in the {sup 239}Pu(n,2n{gamma}i){sup 238}Pu reaction have been measured. The experiments were performed at LANSCE/WNR on the 60R flight line. Reaction {gamma}-rays were measured using the large-scale Compton-suppressed array of Ge detectors, GEANIE. The motivation for this experiment, an overview of the partial {gamma}-ray cross-section measurement, and an introduction to the main experimental issues will be presented. The energy resolution of the Ge detectors allowed identification of reaction {gamma} rays above the background of sample radioactivity and fission {gamma} rays. The use of planar Ge detectors with their reduced sensitivity to neutron interactions and improved line shape was also important to the success of this experiment. Absolute partial {gamma}-ray cross sections are presented for the 6{sub 1}{sup +} {yields} 4{sub 1}{sup +} member of the ground state rotational band in {sup 238}Pu, together with miscellaneous other {gamma}-ray partial cross sections. The n,2n reaction cross section shape and magnitude as a function of neutron energy was extracted from these partial cross sections using nuclear modeling (enhanced Hauser-Feshbach) to relate partial {gamma}-ray cross sections to the n,2n cross section. The critical nuclear modeling issue is the ratio of a partial cross section to the reaction channel cross section, and not the prediction of the absolute magnitude.
Date: September 14, 2001
Creator: Beacker, J.A.; Bernstein, L.A.; Younes, W.; McNabb, D.P.; Garrett, P.E.; Archer, D. et al.
Partner: UNT Libraries Government Documents Department