10 Matching Results

Search Results

Advanced search parameters have been applied.

Xe-135 Production from Cf-252

Description: 135Xe is a good indicator that fission has occurred and is a valuable isotope that helps enforce the Comprehensive Test Ban Treaty. Due to its rather short half life and minimal commercial interest, there are no known sources where 135Xe can be purchased. Readily available standards of this isotope for calibrating collection and analytical techniques would be very useful. 135Xe can be produced in the fissioning of actinide isotopes, or by neutron capture on 134Xe. Since the neutron capture cross section of 134Xe is 3 mB, neutron capture is a low yield, though potentially useful, production route. 135Xe is also produced by spontaneous fission of 252Cf. 252Cf has a spontaneous fission rate of about 6 x 1011 s-1g-1. The cumulative yield from the spontaneous fission of 252Cf is 4.19%; and the competing neutron capture reaction that depletes 135Xe in thermal reactor systems is negligible because the neutron capture cross-section is low for fast fission neutrons. At the INL, scientists have previously transported fission products from an electroplated 252Cf thin source for the measurement of nuclear data of short-lived fission products using a technique called He-Jet collection. We have applied a similar system to the collection of gaseous 135Xe, in order to produce valuable standards of this isotope.
Date: March 1, 2012
Creator: McGrath, C. A.; Houghton, T. P.; Pfeiffer, J. K. & Hague, R. K.
Partner: UNT Libraries Government Documents Department

Actinide Targets for Neutron Cross Section Measurements (C)

Description: The Advanced Fuel Cycle Initiative (AFCI) and the Generation IV Reactor Initiative have demonstrated a lack of detailed neutron cross-sections for certain "minor" actinides, those other than the most common (235U, 238U, and 239Pu). For some closed-fuel-cycle reactor designs more than 50% of reactivity will, at some point, be derived from “minor” actinides that currently have poorly known (n,g) and (n,f) cross sections. A program of measurements under AFCI has begun to correct this. One of the initial hurdles has been to produce well-characterized, highly isotopically enriched, and chemically pure actinide targets on thin backings. Using a combination of resurrected techniques and new developments, we have made a series of targets including highly enriched 240Pu, and 242Pu. Thus far, we have electrodeposited these actinide targets. In the future, we plan to study reductive distillation to achieve homogeneous, adherent targets on thin metal foils and polymer backings. As we move forward, separated isotopes become scarcer, and safety concerns become greater. The chemical purification and electodeposition techniques will be described.
Date: April 1, 2006
Creator: Baker, J. D. & McGrath, C. A.
Partner: UNT Libraries Government Documents Department

Development of Neutron Probes for Characterization of Hazardous Materials in the Sub-surface Medium

Description: Neutron probes are being developed at the Idaho National Engineering and Environmental Laboratory (INEEL) for the detection, identification and quantification of hazardous materials in the ground. Such materials include plutonium, uranium, americium, chlorine and fluorine. Both a Neutron Gamma (NG) probe and a Prompt Fission Neutron (PFN) probe are being developed. The NG probe is used primarily for nuclide identification and quantification measurements. The PFN is used mostly for the detection and measurement of fissile material, but also for the determination of thermal neutron macroscopic absorption cross sections of the various elements comprising the ground matrix. Calibration of these probes will be carried out at the INEEL using an indoor facility that has been designed for this activity.
Date: May 15, 2002
Creator: Keegan, R.P.; McGrath, C.A. & Lopez, J.C.
Partner: UNT Libraries Government Documents Department

Gamma-ray production cross sections from neutron interactions with iron.

Description: The initial purpose of this experiment was to provide a consistent data base of neutron-induced gamma-ray production cross sections over a large energy range for use in estimating elemental composition of the martian surface by observing gamma rays produced by cosmic ray interactions on the planet's surface [Bo02]. However, these data should be useful for other projects such as oil-well logging, accelerator transmutation of nuclear waste, shielding calculations, gamma-ray heating for nuclear reactors and verification of nuclear model calculations and databases. The goal of the measurements was to collect data on the strongest gamma rays from many samples of interest. Because of the available beam time this meant that many of the measurcments were rather short. Despite the short running time the large samples used and the good beam intensity resulted in very satisfactory results. The samples, chosen mainly as common constituents of rock and soil and measured in the same few week period, include: B&, BN, C, Al, Mg, Si, S, Cay Ti, Cr, Mn, and Fe. Be was also used as a neutron scatterer that only produces one gamma ray (478 keV from 7Li) with appreciable intensity. Thus Be can serve as a measure of neutron-induced backgrounds. In this first paper we present results for Fe.
Date: January 1, 2002
Creator: Nelson, R. O. (Ronald O.); Laymon, C. M. (Charles M.); Wender, S. A. (Stephen A.); Drake, D. M. (Darrell M.); Drosg, Manfred; Bobias, S. G. (S. George) et al.
Partner: UNT Libraries Government Documents Department

Nuclear Science at GEANIE

Description: GEANIE at LANSCE/WNR combines the precision energy resolution of germanium detectors with the advantages of a white source providing neutrons with energies 1 < E{sub n}(MeV) < 250 to address a variety of topics in nuclear physics. The authors present the analysis of two data sets, n+{sup 235}U and n+{sup 92}Mo, acquired at GEANIE during the 1998 beam cycle. These data showcase the breadth of subjects under study at this facility, including the spectroscopy of stable and near-stable nuclei, reaction dynamics, fission studies, and the relative population of isomer and ground states in neutron-induced reactions.
Date: December 17, 1999
Creator: Younes, W.; Becker, J.A.; Bernstein, L.A.; Garrett, P.E.; McNabb, D.P.; McGrath, C.A. et al.
Partner: UNT Libraries Government Documents Department


Description: The recovery of Cs and Sr from acidic solutions by solvent extraction has been investigated. The goal of this project was to develop an extraction process to remove Cs and Sr from high-level waste in an effort to reduce the heat loading in storage. Solvents for the extraction of Cs and Sr separately have been used on both caustic and acidic spent nuclear fuel waste in the past. The objective of this research was to find a suitable solvent for the extraction of both Cs and Sr simultaneously from acidic nitrate media.
Date: October 3, 2004
Creator: Riddle, C.L.; Baker, J.D.; Law, J.D.; McGrath, C.A.; Meikrantz, D.H.; Mincher, B.J. et al.
Partner: UNT Libraries Government Documents Department

Transition from Asymmetric to Symmetric Fission in the 235U(n,f) Reaction

Description: Prompt {gamma} rays from the neutron-induced fission of {sup 235}U have been studied using the GEANIE spectrometer situated at the LANSCE/WNR ''white'' neutron facility. Gamma-ray production cross sections for 29 ground-state-band transitions in 18 even-even fission fragments were obtained as a function of incident neutron energy, using the time-of-flight technique. Independent yields were deduced from these cross sections and fitted with standard formulations of the fragment charge and mass distributions to study the transition from asymmetric to symmetric fission. The results are interpreted in the context of the disappearance of shell structure at high excitation energies.
Date: July 19, 2001
Creator: Younes, W; Becker, J A; Bernstein, L A; Garrett, P E; McGrath, C A; McNabb, D P et al.
Partner: UNT Libraries Government Documents Department

Preliminary Report on the Population of the 235U T1/2=25-Minute Isomer by the (Nu,Nu'Gamma)Reaction

Description: The population cross section of the T{sub 1/2} = 25-minute, E{sub x} = 76.8-keV isomer in {sup 235}U via the {sup 235}U(n,n{prime}{gamma}) reaction has been estimated in the E{sub n} = 2.1-20-MeV range. Gamma rays populating both isomer and ground states were detected using the GEANIE spectrometer at the LANSCE/WNR ''white-source'' neutron facility. Partial {gamma}-ray cross sections were obtained as a function of incident neutron energy, using {gamma}-ray spectroscopy and the time-of-flight technique. A correction for unobserved transitions was applied to the measured partial cross sections using the Hauser-Feshbach code GNASH to produce population cross sections for the isomer- and ground-state levels. The deduced isomer population cross section at E{sub n} = 2.1 MeV is 1.1(1) b, and the isomer-to-ground state population ratio decreases from 0.9 to 0.06 over the E{sub n} = 2.1-20-MeV range. The details of the measurement and recommendations to improve the current results are discussed.
Date: October 9, 2002
Creator: Younes, W; Britt, H C; Becker, J A; Bernstein, L A; Garrett, P E; McGrath, C A et al.
Partner: UNT Libraries Government Documents Department

Neutron-Induced Partial Gamma-Ray Cross-Section Measurements with GEANIE at LANSCE/WNR

Description: GEANIE is the first large-scale Ge detector array used in conjunction with a high-energy neutron spallation source. GEANIE consists of eleven Compton-suppressed planar detectors, nine suppressed and six unsuppressed co-axial detectors. Spallation neutrons are provided by the LANSCE/WNR facility, and reaction neutron energies are determined via time-of-flight. neutron flux is monitored in-beam with a fission chamber. GEANIE at LANSCE/WNR currently emphasizes the measurement of partial gamma-ray cross sections as a function of neutron energy. Absolute cross section measurements require a complete understanding of array performance. Important effects include intrinsic detector efficiency, beam and detector geometry corrections, target attenuation, and deadtime. Measurements and calculations of these effects will be presented for the specific cases of iron and actinide targets. The use of radioactive targets incurs a large deadtime penalty. In order to increase data throughput they are making plans to move to a triggerless data acquisition system. These modifications and other improvements to the electronics for better timing will be discussed.
Date: January 10, 2000
Creator: McNabb, D.P.; Becker, J.A.; Archer, D.; Bernstein, L.A.; Garrett, P.E.; McGrath, C.A. 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