20 Matching Results

Search Results

Advanced search parameters have been applied.

NMR spectroscopic investigations of surface and interlayer species on minerals, clays and other oxides

Description: The behavior of chemical species adsorbed on solid surfaces and exchanged into clay interlayers plays a significant role in controlling many natural and technologically important processes, including rheological behavior, catalysis, plant growth, transport in natural pore fluids and those near anthropogenic hazardous waste sites, and water-mineral interaction. Adsorption and exchange reactions have been the focus of intense study for many decades. Only more recently, however, have there been extensive spectroscopic studies of surface species. Among the spectroscopic methods useful for studying surface and exchanged species (e.g., infrared, X-ray photoelectron spectroscopy [XPS] and X-ray absorption spectroscopy [XAS]), nuclear magnetic resonance spectroscopy (NMR) has the considerable advantage of providing not only structural information via the chemical shift and quadrupole coupling constant but dynamical information in the Hz-mHz range via lineshape analysis and relaxation rate measurements. It is also possible to obtain data in the presence of a separate fluid phase, which is essential for many applications. This paper illustrates the range of applications of NMR methods to surface and exchanged species through review of recent work from our laboratory on Cs in clay interlayers and Cs, Na and phosphate adsorbed on oxide surfaces. The substrate materials used for these experiments and our long-term objectives are related to problems of geochemical interest, but the principals and techniques are of fundamental interest and applicable to a wide range of technological problems.
Date: July 1, 1996
Creator: Kirkpatrick, R. J.; Yeongkyoo Kim; Weiss, C. A. & Cygan, R. T.
Partner: UNT Libraries Government Documents Department

The sorption behavior of Cs and Cd onto oxide and clay surfaces

Description: The sorption of Cs and Cd on model soil minerals was examined by complementary analytical and experimental procedures. X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy were used to characterize the chemical and physical nature of Cs-reacted soil minerals. Cd and Cs adsorption isotherms for kaolinite were also measured at variable pH and temperature to establish likely reaction stoichiometries, while atomic force microscopy (AFM) was used to characterize the microtopography of the clay surface. XPS analyses of Cs-exchanged samples show that Cs is sorbed at mineral surfaces and at the interlayer site of smectite clays, although the spectral resolution of XPS analyses is insufficient to differentiate between basal, edge or interlayer sites. {sup 133}Cs MAS-NMR results also show that Cs is adsorbed primarily in an interlayer site of montmorillonite and on edge and basal sites for kaolinite. Cd adsorption isotherms on kaolinite were found to be additive using Al{sub 2}0{sub 3} + Si0{sub 2} Cd binding constants. AFM quantification of kaolinite crystallites suggest that edges comprise up to 50% of the BET surface area, and are consistent with NMR and surface charge results that Cs an Cd adsorption occur primarily at edge sites.
Date: March 1, 1995
Creator: Westrich, H.R.; Cygan, R.T.; Brady, P.V.; Nagy, K.L.; Anderson, H.L. & Kirkpatrick, R.J.
Partner: UNT Libraries Government Documents Department

Measurement of the Parity Violating Asymmetry A

Description: The weak pion-nucleon coupling constant H{sub {pi}}{sup 1} remains poorly determined, despite many years of effort. The recent measurement of the {sup 133}Cs anapole moment has been interpreted to give a value of H{sub {pi}}{sup 1} almost an order of magnitude larger than the limit established in the {sup 18}F parity doublet experiments. A measurement of the gamma ray directional asymmetry A{sub {gamma}} for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine H{sub {pi}}{sup 1} independent of nuclear structure effects. However, since the predicted asymmetry is small, A{sub {gamma}} {approximately} 5 x 10{sup {minus}8}, systematic effects must be reduced to < 5 x 10{sup {minus}9}. The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors.
Date: December 4, 1998
Creator: Wilburn, W. S.; Bazhenov, A.; Blessinger, C. S.; Bowman, J. D.; Chupp, T. E.; Coulter, K. P. et al.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT OF PROTOTYPE TITANATE ION EXCHANGE LOADED MEMBRANES FOR STRONTIUM, CESIUM AND ACTINIDE DECONTAMINATION FROM AQUEOUS MEDIA

Description: We have successfully incorporated high surface area particles of titanate ion exchange materials (monosodium titanate and crystalline silicotitanate) with acceptable particle size distribution into porous and inert support membrane fibrils consisting of polytetrafluoroethylene (Teflon{reg_sign}), polyethylene and cellulose materials. The resulting membrane sheets, under laboratory conditions, were used to evaluate the removal of surrogate radioactive materials for cesium-137 and strontium-90 from high caustic nuclear waste simulants. These membrane supports met the nominal requirement for nonchemical interaction with the embedded ion exchange materials and were porous enough to allow sufficient liquid flow. Some of this 47-mm size stamped out prototype titanium impregnated ion exchange membrane discs was found to remove more than 96% of dissolved cesium-133 and strontium-88 from a caustic nuclear waste salt simulants. Since in traditional ion exchange based column technology monosodium titanate (MST) is known to have great affinity for the sorbing of other actinides like plutonium, neptunium and even uranium, we expect that the MST-based membranes developed here, although not directly evaluated for uptake of these three actinides because of costs associated with working with actinides which do not have 'true' experimental surrogates, would also show significant affinity for these actinides in aqueous media. It was also observed that crystalline silicotitanate impregnated polytetrafluoroethylene or polyethylene membranes became less selective and sorbed both cesium and strontium from the caustic aqueous salt simulants.
Date: May 30, 2008
Creator: Oji, L; Keisha Martin, K & David Hobbs, D
Partner: UNT Libraries Government Documents Department

Chemical evolution of leaked high-level liquid wastes in Hanford soils

Description: A number of Hanford tanks have leaked high level radioactive wastes (HLW) into the surrounding unconsolidated sediments. The disequilibrium between atmospheric C0{sub 2} or silica-rich soils and the highly caustic (pH > 13) fluids is a driving force for numerous reactions. Hazardous dissolved components such as {sup 133}Cs, {sup 79}Se, {sup 99}Tc may be adsorbed or sequestered by alteration phases, or released in the vadose zone for further transport by surface water. Additionally, it is likely that precipitation and alteration reactions will change the soil permeability and consequently the fluid flow path in the sediments. In order to ascertain the location and mobility/immobility of the radionuclides from leaked solutions within the vadose zone, the authors are currently studying the chemical reactions between: (1) tank simulant solutions and Hanford soil fill minerals; and (2) tank simulant solutions and C0{sub 2}. The authors are investigating soil-solution reactions at: (1) elevated temperatures (60--200 C) to simulate reactions which occur immediately adjacent a radiogenically heated tank; and (2) ambient temperature (25 C) to simulate reactions which take place further from the tanks. The authors studies show that reactions at elevated temperature result in dissolution of silicate minerals and precipitation of zeolitic phases. At 25 C, silicate dissolution is not significant except where smectite clays are involved. However, at this temperature CO{sub 2} uptake by the solution results in precipitation of Al(OH){sub 3} (bayerite). In these studies, radionuclide analogues (Cs, Se and Re--for Tc) were partially removed from the test solutions both during high-temperature fluid-soil interactions and during room temperature bayerite precipitation. Altered soils would permanently retain a fraction of the Cs but essentially all of the Se and Re would be released once the plume was past and normal groundwater came in contact with the contaminated soil. Bayerite, however, will retain significant amounts of ...
Date: May 19, 2000
Creator: NYMAN,MAY D.; KRUMHANSL,JAMES L.; ZHANG,PENGCHU; ANDERSON,HOWARD L. & NENOFF,TINA M.
Partner: UNT Libraries Government Documents Department

NEUTRON CROSS SECTION EVALUATIONS OF FISSION PRODUCTS BELOW THE FAST ENERGY REGION

Description: Neutron cross section evaluations of the fission-product isotopes, {sup 95}Mo, {sup 99}Tc, {sup 101}Ru, {sup 103}Rh, {sup 105}Pd, {sup 109}Ag, {sup 131}Xe, {sup 133}Cs, {sup 141}Pr, {sup 141}Nd, {sup 147}Sm, {sup 149}Sm, {sup 150}Sm, {sup 151}Sm, {sup 152}Sm, {sup 153}Eu, {sup 155}Gd, and {sup 157}Gd were carried out below the fast neutron energy region within the framework of the BNL-KAERI international collaboration. In the thermal energy region, the energy dependence of the various cross-sections was calculated by applying the multi-level Breit-Wigner formalism. In particular, the strong energy dependence of the coherent scattering lengths of {sup 155}Gd and {sup 157}Gd were determined and were compared with recent calculations of Lynn and Seeger. In the resonance region, the recommended resonance parameters, reported in the BNL compilation, were updated by considering resonance parameter information published in the literature since 1981. The s-wave and, if available, p-wave reduced neutron widths were analyzed in terms of the Porter-Thomas distribution to determine the average level spacings and the neutron strength functions. Average radiative widths were also calculated from measured values of resolved energy resonances. The average resonance parameters determined in this study were compared with those in the BNL and other compilations, as well as the ENDF/B-VI, JEF-2.2, and JENDL-3.2 data libraries. The unresolved capture cross sections of these isotopes, computed with the determined average resonance parameters, were compared with measurements, as well as the ENDF/B-VI evaluations. To achieve agreement with the measurements, in a few cases minor adjustments in the average resonance parameters were made. Because of astrophysical interest, the Maxwellian capture cross sections of these nuclides at a neutron temperature of 30 keV were computed and were compared with other compilations and evaluations.
Date: May 11, 2000
Creator: OH,S.Y.; CHANG,J. & MUGHABGHAB,S.
Partner: UNT Libraries Government Documents Department

ISOMERIC CROSS-SECTION RATIOS FOR SOME (n,$gamma$) AND (/cap alpha/,XN) REACTIONS

Description: Isomeric cross section ratios for several nuclear reactions in the medium mass region were measured. The cross section ratios of isomers produced by the thermal neutron irradiation of Se/sup 60/, Rh/sup 103/, Pd/sup 106/ TE/sup 128/ and Cs/s up 133/ were measured. Isomeric cross section ratios for the formation of the isomeric pair In/sup 110/ and In/sup 110m/, produced in the Ag/ sup 107/ ( alpha ,n) and the Ag/sup 109/ ( alpha ,3n) reactions were also measured at several energies of the incoming projectile. He ions were accelerated to a maximum energy of 43 Mev. The relative amounts of the isomers produced in the reactions were determined by scintillation counting. In the case of the In/sup 110/ isomers the efficiencies of the scintillation counter for detecting each isomer were measured, so that absolute cross sections as well as cross section ratios could be determined for these isomers. The isomeric cross section ratios were also calculated theoretically using a statistical model, in which angular momentum effects were included. By comparing experimentally measured cross section ratios for the formation of isomeric pairs to the calculated ratios, information about the dependence of the nuclear level density on angular momentum was obtained. (auth)
Date: August 1, 1961
Creator: Bishop, C.T.
Partner: UNT Libraries Government Documents Department

Lower limit for the average angular momentum leading to fusion

Description: The existence of a finite and essentially energy-independent lower limit for the average angular momentum leading to fusion at energies well below the Coulomb barrier has been experimentally confirmed. We report the observation of this angular momentum limit for the systems {sup 12}C + {sup 128}Te, {sup 7}Li + {sup 133}Cs, and {sup 3}He + {sup 136}Ba. We find that the predicted values of {bar l} are consistent with experiment. The expected variation of {bar l} with entrance channel is also observed. 3 refs., 2 figs.
Date: October 1, 1989
Creator: DiGregorio, D.E.; Lesko, K.T.; Harmon, B.A.; Norman, E.B.; Pouliot, J.; Sur, B. et al.
Partner: UNT Libraries Government Documents Department

SEMI-ANNUAL SUMMARY RESEARCH REPORT IN PHYSICS FOR JANUARY THROUGH JUNE 1957

Description: Deviations from the allowed spectrum shape observed in P/sup 32/ beta - decay are discussed. Coincidence data taken on Yb/sup 169/ and Tb/sup 160/ are reviewed. The directional correlation function for the 357 to 82 kcv gamma cascade in Cs/sup 133/ following Ba/sup 133/ electron capture decay was determined. The detection of trace oxygen impuritics in metals by the beta activity from x-ray bombardment appears feasible. Results obtained in tests of this mcthod are reported. A pulse heating method for measuring the high- temperature specific heats of metals was developed and applied to Fe in the temperature range 25 to 1000 deg C. The results of electrical resistivity measurements made on Ni and Ni-alloys at temperatures between 25 and 1000 deg C are plotted. Discussions of the semiconducting properties of Mg/sub 2/Si and Mg/ sub 2/Ge single crystals are included. (For preceding period see ISC-833.) (D.E.B.)
Date: September 11, 1957
Partner: UNT Libraries Government Documents Department

End of life fission product distributions in F-1 experiment fuel rods

Description: Fission product migration and end-of-life distributions were examined in the F-1 (X094) series of sealed, mixed-oxide fuel rods irradiated in the fast flux of EBR-II. Cesium, rubidium, iodine, and strontium data obtained from axial gamma scanning, mass spectrometry, and radiochemical analyses are presented. The results show significant migration of cesium, probably as both a volatile species and as the noble gas precursor. Cesium metal species leaving the fuel region accumulate predominately at the fuel-blanket interface. Volatile cesium reaching the fission product traps is readily sorbed by the charcoal.
Date: May 1, 1980
Creator: Goodin, D.T.; Langer, S. & Bell, W.E.
Partner: UNT Libraries Government Documents Department