56 Matching Results

Search Results

Advanced search parameters have been applied.
in creator/contributor: "Hanson, A."  
Results: 1 - 24 next

Torsion and quantum gravity

Description: It is suggested that the absence of torsion in conventional gravity could in fact be dynamical. A gravitational Meissner effect might produce instanton-like vortices of nonzero torsion concentrated at four-dimensional points; such torsion vortices would be the gravitational analogs of magnetic flux vortices in a type II superconductor. Ordinary torsion-free spacetime would correspond to the field-free superconducting region of a superconductor; a dense phase of ''torsion foam'' with vanishing metric but well defined affine connection might be the analog of a normal conductor. 14 references.
Date: September 1, 1978
Creator: Hanson, A.J. & Regge, T.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

The Assessment of Geometrical Effects on Compton Profile Measurements

Description: Energy dispersive measurements of Compton scattered x rays for analyses have become important with the development of high efficiency, high energy resolution detectors for 50--200 keV x rays. The Compton scattered x ray peak is an inherently broad peak resulting in part from the momentum distribution of the target electrons, referred to as the Compton profile. Hence, information from the width of the Compton peak can be used to study the momentum distribution. The actual peak width also depends on geometrical and attenuation effects. We have begun to assess the geometrical effects and present some of the results. 2 refs., 3 figs.
Date: October 1988
Creator: Gigante, G. E. & Hanson, A. L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Transition Core Properties during Conversion of the NBSR from HEU to LEU Fuel

Description: The transition of the NBSR from HEU to LEU fuel is challenging due to reactivity constraints and the need to maintain an uninterrupted science program, the mission of the NBSR. The transition cannot occur with a full change of HEU to LEU fuel elements since the excess reactivity would be large enough that the NBSR would violate the technical specification for shutdown margin. Manufacturing LEU fuel elements to represent irradiated fuel elements would be cost prohibitive since 26 one-of-a-kind fuel elements would need to be manufactured. For this report a gradual transition from the present HEU fuel to the proposed LEU fuel was studied. The gradual change approach would follow the present fuel management scheme and replace four HEU fuel elements with four LEU fuel elements each cycle. This manuscript reports the results of a series of calculations to predict the neutronic characteristics and how the neutronics will change during the transition from HEU to LEU in the NBSR.
Date: October 31, 2013
Creator: L., Hanson A. & D., Diamond
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Prompt Neutron Lifetime for the NBSR Reactor

Description: In preparation for the proposed conversion of the National Institute of Standards and Technology (NIST) research reactor (NBSR) from high-enriched uranium (HEU) to low-enriched uranium (LEU) fuel, certain point kinetics parameters must be calculated. We report here values of the prompt neutron lifetime that have been calculated using three independent methods. All three sets of calculations demonstrate that the prompt neutron lifetime is shorter for the LEU fuel when compared to the HEU fuel and longer for the equilibrium end-of-cycle (EOC) condition when compared to the equilibrium startup (SU) condition for both the HEU and LEU fuels.
Date: June 24, 2012
Creator: Hanson, A.L. & Diamond, D.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Planning the HEU to LEU Transition for the NBSR

Description: A study has been carried out to understand how the NIST research reactor (NBSR) might be converted from using high-enriched uranium (HEU) to using low-enriched uranium (LEU) fuel. An LEU fuel design had previously been determined which provides an equilibrium core with the desirable fuel cycle length - a very important parameter for maintaining the experimental, scientific program supported by the NBSR. In the present study two options for getting to the equilibrium state are considered. One option starts with the loading of an entire core of fresh fuel. This was determined to be unacceptable. The other option makes use of the current fuel management scheme wherein four fresh fuel elements are loaded at the beginning of each cycle. However, it is shown that without some alterations to the fuel cycle, none of the transition cores containing both HEU and LEU fuel have sufficient excess reactivity to operate the reactor for the optimum length. It was determined that operating the first mixed cycle for a sufficiently reduced length of time provides the excess reactivity which enables subsequent cycles to be run for the desired number of days.
Date: September 12, 2011
Creator: Hanson, A.L. & Diamond, D.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Calculation of Design Parameters for an Equilibrium LEU Core in the NBSR

Description: A plan is being developed for the conversion of the NIST research reactor (NBSR) from high-enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel. Previously, the design of the LEU fuel had been determined in order to provide the users of the NBSR with the same cycle length as exists for the current HEU fueled reactor. The fuel composition at different points within an equilibrium fuel cycle had also been determined. In the present study, neutronics parameters have been calculated for these times in the fuel cycle for both the existing HEU and the proposed LEU equilibrium cores. The results showed differences between the HEU and LEU cores that would not lead to any significant changes in the safety analysis for the converted core. In general the changes were reasonable except that the figure-of-merit for neutrons that can be used by experimentalists shows there will be a 10% reduction in performance. The calculations included kinetics parameters, reactivity coefficients, reactivity worths of control elements and abnormal configurations, and power distributions.
Date: September 30, 2011
Creator: Hanson, A.L. & Diamond, D.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Calculation of Kinetics Parameters for the NBSR

Description: The delayed neutron fraction and prompt neutron lifetime have been calculated at different times in the fuel cycle for the NBSR when fueled with both high-enriched uranium (HEU) and low-enriched uranium (LEU) fuel. The best-estimate values for both the delayed neutron fraction and the prompt neutron lifetime are the result of calculations using MCNP5-1.60 with the most recent ENDFB-VII evaluations. The best-estimate values for the total delayed neutron fraction from fission products are 0.00665 and 0.00661 for the HEU fueled core at startup and end-of-cycle, respectively. For the LEU fuel the best estimate values are 0.00650 and 0.00648 at startup and end-of-cycle, respectively. The present recommendations for the delayed neutron fractions from fission products are smaller than the value reported previously of 0.00726 for the HEU fuel. The best-estimate values for the contribution from photoneutrons will remain as 0.000316, independent of the fuel or time in the cycle.The values of the prompt neutron lifetime as calculated with MCNP5-1.60 are compared to values calculated with two other independent methods and the results are in reasonable agreement with each other. The recommended, conservative values of the neutron lifetime for the HEU fuel are 650 {micro}s and 750 {micro}s for the startup and end-of-cycle conditions, respectively. For LEU fuel the recommended, conservative values are 600 {micro}s and 700 {micro}s for the startup and end-of-cycle conditions, respectively. In all three calculations, the prompt neutron lifetime was determined to be longer for the end-of-cycle equilibrium condition when compared to the startup condition. The results of the three analyses were in agreement that the LEU fuel will exhibit a shorter prompt neutron lifetime when compared to the HEU fuel.
Date: March 6, 2012
Creator: L., Hanson A. & D., Diamond
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

DETERMINATION OF INVENTORIES AND POWER DISTRIBUTIONS FOR THE NSBR.

Description: This memo presents the details of the methodology for developing fuel inventories for the NBSR along with power distributions predicted with this set of inventories. Several improvements have been made to the MCNP model of the NBSR since a set of calculations was performed in 2002 in support of the NBSR relicensing and SAR update. One of the most significant changes in the model was to divide the fuel elements into upper and lower halves so the effects of uneven burn between the two halves (due to the shim arms) can be determined. The present set of power distributions are provided for comparison with the previous safety analyses.
Date: September 12, 2005
Creator: HANSON, A.L. & DIAMOND, D.J.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

A Neutronics Methodology for the NIST Research Reactor Based on MCNXP

Description: A methodology for calculating inventories for the NBSR has been developed using the MCNPX computer code with the BURN option. A major advantage of the present methodology over the previous methodology, where MONTEBURNS and MCNP5 were used, is that more materials can be included in the model. The NBSR has 30 fuel elements each with a 17.8 cm (7 in) gap in the middle of the fuel. In the startup position, the shim control arms are partially inserted in the top half of the core. During the 38.5 day cycle, the shim arms are slowly removed to their withdrawn (horizontal) positions. This movement of shim arms causes asymmetries between the burnup of the fuel in the upper and lower halves and across the line of symmetry for the fuel loading. With the MONTEBURNS analyses there was a limitation to the number of materials that could be analyzed so 15 materials in the top half of the core and 15 materials in the bottom half of the core were used, and a half-core (east-west) symmetry was assumed. Since MCNPX allows more materials, this east-west symmetry was not necessary and the core was represented with 60 different materials. The methodology for developing the inventories is presented along with comparisons of neutronic parameters calculated with the previous and present sets of inventories.
Date: May 16, 2011
Creator: Hanson, A. & Diamond, D.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Application of synchrotron radiation to x-ray fluorescence analysis of trace elements

Description: The development of synchrotron radiation x-ray sources has provided the means to greatly extend the capabilities of x-ray fluorescence analysis for determinations of trace element concentrations. A brief description of synchrotron radiation properties provides a background for a discussion of the improved detection limits compared to existing x-ray fluorescence techniques. Calculated detection limits for x-ray microprobes with micrometer spatial resolutions are described and compared with experimental results beginning to appear from a number of laboratories. The current activities and future plans for a dedicated x-ray microprobe beam line at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory are presented.
Date: August 1, 1986
Creator: Gordon, B.M.; Jones, K.W. & Hanson, A.L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Determination of surface oxide compositions on Alloy 600 using Rutherford backscattering

Description: The surface composition of oxides formed on Alloy 600 under conditions similar to those in the primary side of PWR heat exchangers has been studied as a function of potential using Rutherford backscattering and proton inelastic scattering. Electropolished samples of Alloy 600 were exposed at several potentials to a solution of 0.18M H/sub 3/BO/sub 3/(2000 ppM B) with 0.28M LiOH (1.4 ppM Li) at 300/sup 0/C for 450 hours. The potentials relative to an internal hydrogen electrode ranged from -.09 to 750 mV. RBS analysis showed little or no oxide formation on samples exposed at 0 mV. Above 0 mV oxide layers formed whose thicknesses increased with potential. In addition the RBS showed a significantly enhanced concentration of aluminum and silicon in oxide. Both the oxygen and the sum of the aluminum and silicon content appeared to maintain a fixed surface concentration independent of the oxide thickness. Boron and lithium concentration were analyzed with proton inelastic scattering. No lithium was found in any sample. The boron concentration was found to follow the thickness of the oxide.
Date: January 1, 1984
Creator: Hanson, A.L.; Isaacs, H.S. & Kraner, H.W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Characterization of Alloy 600 surfaces after exposure to a caustic environment

Description: The surface morphology and compositions of as-received and electropolished Alloy 600 surfaces have been studied using scanning electron microscopy and /sup 4/He/sup +/ Rutherford Backscattering. The samples were exposed to 1% NaOH with 1% Na/sub 2/CO/sub 3/ solutions over a range of potentials. The as-received surfaces did not show any distinctive changes whereas the electropolished surfaces were markedly dependent on the underlying metal. Between -90 and 70 mV, relative to a nickel/hydrogen electrode, the active surface showed a distinct grain boundary and grain orientation dependent etching. These surfaces were also covered by a nickel layer which decreased in thickness with potential from 100 nm at -90 mV and was not observable at 70 mV. At 170 and 225 mV a highly stressed oxide was observed which spalled off entire grains. These surfaces would be expected to show a dependence on temperature cycling. At higher potentials at and above 270 mV duplex surface oxides with high nickel outer layers and high chromium inner layers were observed.
Date: January 1, 1983
Creator: Isaacs, H.S.; Kraner, H.W. & Hanson, A.L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Applications of nuclear analytical methods to materials analysis

Description: Nuclear analytical methods have now become important in the characterization of many types of materials and have been shown to be an extremely important extension of many more common methods. To illustrate the breadth of their use, some recent Brookhaven experiments are described that deal with the depth distribution of hydrogen in Nb-H alloys, the diffusion of Mo in graphite at high temperatures, and the measurement of Al and Si concentrations in zeolite catalysts. It is hoped that the presentation of these illustrative examples will serve as a stimulus and encouragement for the further application of nuclear analytical methods.
Date: January 1, 1982
Creator: Jones, K.W.; Hanson, A.L. & Kraner, H.W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Effect of Shim Arm Depletion in the NBSR

Description: The cadmium shim arms in the NBSR undergo burnup during reactor operation and hence, require periodic replacement. Presently, the shim arms are replaced after every 25 cycles to guarantee they can maintain sufficient shutdown margin. Two prior reports document the expected change in the 113Cd distribution because of the shim arm depletion. One set of calculations was for the present high-enriched uranium fuel and the other for the low-enriched uranium fuel when it was in the COMP7 configuration (7 inch fuel length vs. the present 11 inch length). The depleted 113Cd distributions calculated for these cores were applied to the current design for an equilibrium low-enriched uranium core. This report details the predicted effects, if any, of shim arm depletion on the shim arm worth, the shutdown margin, power distributions and kinetics parameters.
Date: February 22, 2013
Creator: H., Hanson A.; N., Brown & Diamond, D.J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Planning the HEU to LEU Transition for the NBSR

Description: A study has been carried out to understand how the NIST research reactor (NBSR) might be converted from using high-enriched uranium (HEU) to using low-enriched uranium (LEU) fuel. An LEU fuel design had previously been determined which provides an equilibrium core with the desirable fuel cycle length—a very important parameter for maintaining the experimental, scientific program supported by the NBSR. In the present study two options for getting to the equilibrium state are considered. One option starts with the loading of an entire core of fresh fuel. This was determined to be unacceptable. The other option makes use of the current fuel management scheme wherein four fresh fuel elements are loaded at the beginning of each cycle. However, it is shown that without some alterations to the fuel cycle, none of the transition cores containing both HEU and LEU fuel have sufficient excess reactivity to enable reactor operation for the required amount of time. It was determined that operating the first mixed cycle for a sufficiently reduced length of time provides the excess reactivity which enables subsequent transition cycles to be run for the desired number of days.
Date: October 24, 2011
Creator: Hanson, A.L. & Diamond, D.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Local Burn-Up Effects in the NBSR Fuel Element

Description: This study addresses the over-prediction of local power when the burn-up distribution in each half-element of the NBSR is assumed to be uniform. A single-element model was utilized to quantify the impact of axial and plate-wise burn-up on the power distribution within the NBSR fuel elements for both high-enriched uranium (HEU) and low-enriched uranium (LEU) fuel. To validate this approach, key parameters in the single-element model were compared to parameters from an equilibrium core model, including neutron energy spectrum, power distribution, and integral U-235 vector. The power distribution changes significantly when incorporating local burn-up effects and has lower power peaking relative to the uniform burn-up case. In the uniform burn-up case, the axial relative power peaking is over-predicted by as much as 59% in the HEU single-element and 46% in the LEU single-element with uniform burn-up. In the uniform burn-up case, the plate-wise power peaking is over-predicted by as much as 23% in the HEU single-element and 18% in the LEU single-element. The degree of over-prediction increases as a function of burn-up cycle, with the greatest over-prediction at the end of Cycle 8. The thermal flux peak is always in the mid-plane gap; this causes the local cumulative burn-up near the mid-plane gap to be significantly higher than the fuel element average. Uniform burn-up distribution throughout a half-element also causes a bias in fuel element reactivity worth, due primarily to the neutronic importance of the fissile inventory in the mid-plane gap region.
Date: January 2013
Creator: Brown, N. R.; Hanson, A. L. & Diamond, D. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

PHYLOGENOMICS - GUIDED VALIDATION OF FUNCTION FOR CONSERVED UNKNOWN GENES

Description: Identifying functions for all gene products in all sequenced organisms is a central challenge of the post-genomic era. However, at least 30-50% of the proteins encoded by any given genome are of unknown function, or wrongly or vaguely annotated. Many of these 'unknown' proteins are common to prokaryotes and plants. We accordingly set out to predict and experimentally test the functions of such proteins. Our approach to functional prediction is integrative, coupling the extensive post-genomic resources available for plants with comparative genomics based on hundreds of microbial genomes, and functional genomic datasets from model microorganisms. The early phase is computer-assisted; later phases incorporate intellectual input from expert plant and microbial biochemists. The approach thus bridges the gap between automated homology-based annotations and the classical gene discovery efforts of experimentalists, and is much more powerful than purely computational approaches to identifying gene-function associations. Among Arabidopsis genes, we focused on those (2,325 in total) that (i) are unique or belong to families with no more than three members, (ii) are conserved between plants and prokaryotes, and (iii) have unknown or poorly known functions. Computer-assisted selection of promising targets for deeper analysis was based on homology .. independent characteristics associated in the SEED database with the prokaryotic members of each family, specifically gene clustering and phyletic spread, as well as availability of functional genomics data, and publications that could link candidate families to general metabolic areas, or to specific functions. In-depth comparative genomic analysis was then performed for about 500 top candidate families, which connected ~55 of them to general areas of metabolism and led to specific functional predictions for a subset of ~25 more. Twenty predicted functions were experimentally tested in at least one prokaryotic organism via reverse genetics, metabolic profiling, functional complementation, and recombinant protein biochemistry. Our approach predicted and validated ...
Date: January 3, 2012
Creator: V, DE CRECY-LAGARD & D, HANSON A
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Some uncertainties associated with preparation of standards in organic matrix

Description: Until recently no techniques which have multielement detection capability, high sensitivity and good spatial resolution in relatively thick tissue sections have existed. The use of proton induced x-ray emission /PIXE/ and synchrotron radiation induced x-ray emission /SRIXE/ using proton and x-ray microbeams changed this situation. However there are some difficulties with the existing standards for quantitatively calibrating the trace elements concentration in biological materials. For the purpose of our experiments a special technique of standard production was applied. 7 refs., 1 tab., 1 fig.
Date: January 1, 1986
Creator: Cholewa, M.; Hanson, A.L.; Jones, K.W.; McNally, W.P. & Fand, I.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Resistivity changes in superconducting-cavity-grade Nb following high-energy proton irradiation

Description: Niobium superconducting rf cavities are proposed for use in the proton LINAC accelerators for spallation-neutron applications. Because of accidental beam loss and continual halo losses along the accelerator path, concern for the degradation of the superconducting properties of the cavities with accumulating damage arises. Residual-resistivity-ratio (RRR) specimens of Nb, with a range of initial RRR`s were irradiated at room temperature with protons at energies from 200 to 2000 MeV. Four-probe resistance measurements were made at room temperature and at 4.2 K both prior to and after irradiation. Nonlinear increases in resistivity simulate expected behavior in cavity material after extended irradiation, followed by periodic anneals to room temperature: For RRR = 316 material, irradiations to (2 - 3) x 10{sup 15} p/cm{sup 2} produce degradations up to the 10% level, a change that is deemed operationally acceptable. Without. periodic warming to room temperature, the accumulated damage energy would be up to a factor of ten greater, resulting in unacceptable degradations. Likewise, should higher-RRR material be used, for the same damage energy imparted, relatively larger percentage changes in the RRR will result.
Date: December 1, 1997
Creator: Snead, C.L. Jr.; Hanson, A. & Greene, G.A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

Reassessment of selected factors affecting siting of Nuclear Power Plants

Description: Brookhaven National Laboratory has performed a series of probabilistic consequence assessment calculations for nuclear reactor siting. This study takes into account recent insights into severe accident source terms and examines consequences in a risk based format consistent with the quantitative health objectives (QHOs) of the NRC`s Safety Goal Policy. Simplified severe accident source terms developed in this study are based on the risk insights of NUREG-1150. The results of the study indicate that both the quantity of radioactivity released in a severe accident as well as the likelihood of a release are lower than those predicted in earlier studies. The accident risks using the simplified source terms are examined at a series of generic plant sites, that vary in population distribution, meteorological conditions, and exclusion area boundary distances. Sensitivity calculations are performed to evaluate the effects of emergency protective action assumptions on the risk of prompt fatality and latent cancers fatality, and population relocation. The study finds that based on the new source terms the prompt and latent fatality risks at all generic sites meet the QHOs of the NRC`s Safety Goal Policy by margins ranging from one to more than three orders of magnitude. 4 refs., 17 figs., 24 tabs.
Date: February 1997
Creator: Davis, R. E.; Hanson, A. L.; Mubayi, V. & Nourbakhsh, H. P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Determination of light elements in amalgam restorations. [Dental amalgam]

Description: Rutherford backscattering has been used to measure the major elemental compositions in the near-surface regions of freshly prepared and used samples of dental amalgam. A depletion from bulk stoichiometry of the major elements, which indicates an accumulation of lighter elements on the surface of the materials, has been observed. Increases in the F, Na, Cl, P, O, C, and N concentrations between freshly prepared samples and used samples were measured by observation of gamma rays produced by proton and deuteron induced reactions.
Date: January 1, 1982
Creator: Hanson, A.L.; Jones, K.W.; Kraner, H.W.; Osborne, J.W. & Nelson, G.V.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department

Concentration profile of hydrogen near the surface of niobium

Description: Samples hydrided in two different ways were investigated. The materials used were thin foils (50 ..mu..m, MARZ grade) of niobium, 10 x 25 mm in size. The two methods of hydriding produced different surface conditions which were the subject of the present investigation. One method consisted of the following procedures. The samples were outgassed and cleaned in UHV to remove virtually all the interstitial impurities from the bulk and surface. A small spot of Pd was then deposited onto the clean surface of the niobium in situ in the UHV-system by evaporation from a hot Pd filament. The second method of hydriding was similar to that used by most investigators of metal-hydrogen systems. A sample is placed in the hydriding unit and allowed to absorb a premeasured amount of hydrogen while cooling from approx. 800 C where the surface oxide is dissolved into the bulk. In order to study the effect of a poor vacuum in the hydriding unit, samples were heated to 800 C in different base pressures prior to the admission of hydrogen. One sample was heated in 1 x 10/sup -5/ Torr oxygen.
Date: January 1, 1982
Creator: Pick, M.A.; Hanson, A.; Jones, K.W. & Goland, A.N.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department

X-ray fluorescence with synchrotron radiation

Description: X-ray fluorescence (XRF) has long been used to make measurements of trace element concentrations in biological materials with very high sensitivity. It has not been previously possible to work with micrometer spatial resolutions because of the relatively low brightness of x-ray tubes. This situation is much improved by using synchrotron storage ring x-ray sources since the brightness of the synchrotron source is many orders of magnitude higher than is obtained with the most intense tube sources. These intense sources open the possibility of using the XRF technique for measurements with resolutions of approximately cellular dimensions. A description of a current research project at Brookhaven which uses synchrotron radiation induced x-ray emission (SRIXE) is presented to illustrate a specific application of the method in biology. 1 ref., 4 figs.
Date: March 1, 1986
Creator: Jones, K.W.; Gordon, B.M.; Hanson, A.L.; Pounds, J.G. & Schidlovsky, G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department