1,741 Matching Results

Search Results

Advanced search parameters have been applied.

Elemental analysis of water and air solids by neutron activation analysis

Description: Instrumental neutron activation analysis was used to determine the elemental concentrations in water and air solids samples collected on Nucleopore and Whatman filters from the Walker Branch Watershed. The results from this study show that the trace element concentrations removed by water from the watershed vary seasonally, as well as geographically. The data point up the usefulness and versatility of absolute neutron activation analysis. The NBS Standard Orchard Leaves were assayed in a similar manner, and good agreement was obtained between results here and standard values. (auth)
Date: January 1, 1975
Creator: Bate, L.C.; Lindberg, S.E. & Andren, A.W.
Partner: UNT Libraries Government Documents Department

Neutron activation techniques for the measurement of trace metals in environmental samples

Description: Neutron activation techniques for measuring trace metals in fresh waters, seawater, marine organisms, sediments, and atmospheric particulates are discussed. Principles of neutron activation analysis, neutron irradiation facilities and procedures, and sample preparation including preconcentration and postirradiation separations are outlined. (109 references) (LK)
Date: January 1, 1974
Creator: Robertson, D.E. & Carpenter, R.
Partner: UNT Libraries Government Documents Department

Provenance studies of Sgraffiato and Late Green Glazed wares from Siraf, Iran

Description: Results of neutron activation analyses of 23 elements in ceramic archaeological specimens are given. Various wares are divided into the following categories: early Sgraffiato, late Sgraffiato, late Green A, late Green B, and Samarra ware. Results are given on the following elements: Al, Ca, Dy, Mn, Na, K, U, Sm, La, Ti, Lu, Co, Sc, Fe, Cs, Cr, Ni, Eu, Ce, Hf, Ta, Th, and Yb. (JGB)
Date: March 1, 1975
Creator: Michel, H.V.; Asaro, F. & Frierman, J.D.
Partner: UNT Libraries Government Documents Department

The Determination of Trace Amounts of Uranium by Neutron Activation Analysis

Description: Abstract: "The determination of trace concentrations of uranium in synthetic materials, ores, soils and water by neutron radioactivation analysis is described. The principles of the activation analysis method as applied to trace uranium determination, the processing of irradiated specimens, and some examples of the results obtained by this method of analysis are discussed in this paper."
Date: August 24, 1953
Creator: Mahlman, H. A. & Leddicotte, G. W.
Partner: UNT Libraries Government Documents Department

Analytical comparison of various Egyptian soils, clays, shales, and some ancient pottery by neutron activation

Description: as a basis for classiftcation of clays and for tracing the origin of the parent materials used in pottery manufacturing, Nine pottery specimens were analyzed as a very preliminary test of the potential of correlation between clay and pottery compositions. (LK)
Date: January 1, 1973
Creator: Tobia, S.K. & Sayre, E.V.
Partner: UNT Libraries Government Documents Department

Pathways for C—H Activation and Functionalization by Group 9 Metals

Description: As fossil fuel resources become more and more scarce, attention has been turned to alternative sources of fuels and energy. One promising prospect is the conversion of methane (natural gas) to methanol, which requires an initial activation of a C-H bond and subsequent formation of a C-O bond. The most well studied methodologies for both C-H activation and C-O bond formation involve oxidation of the metal center. Metal complexes with facile access to oxidation states separated by four charge units, required for two subsequent oxidations, are rare. Non-oxidative methods to perform C-H bond activation or C-O bond formation must be pursued in order for methane to methanol to become a viable strategy. In this dissertation studies on redox and non-redox methods for both C-H activation and C-O bond formation are discussed. In the early chapters C-O bond formation in the form of reductive functionalization is modeled. Polypyridine ligated rhodium complexes were studied computationally to determine the properties that would promote reductive functionalization. These principles were then tested by designing an experimental complex that could form C-O bonds. This complex was then shown to also work in acidic media, a critical aspect for product stabilization. In the later chapters, non-oxidative C-H activation is discussed with Ir complexes. Both sigma bond metathesis and concerted metalation deprotonation were investigated. For the former, the mechanism for an experimentally known complex was elucidated and for the latter the controlling factors for a proposed catalyst were explored.
Date: May 2015
Creator: Pahls, Dale R.
Partner: UNT Libraries

Near-Monodisperse Ni-Cu Bimetallic Nanocrystals of Variable Composition: Controlled Synthesis and Catalytic Activity for H2 Generation

Description: Near-monodisperse Ni{sub 1-x}Cu{sub x} (x = 0.2-0.8) bimetallic nanocrystals were synthesized by a one-pot thermolysis approach in oleylamine/1-octadecene, using metal acetylacetonates as precursors. The nanocrystals form large-area 2D superlattices, and display a catalytic synergistic effect in the hydrolysis of NaBH{sub 4} to generate H{sub 2} at x = 0.5 in a strongly basic medium. The Ni{sub 0.5}Cu{sub 0.5} nanocrystals show the lowest activation energy, and also exhibit the highest H{sub 2} generation rate at 298 K.
Date: July 22, 2008
Creator: Zhang, Yawen; Huang, Wenyu; Habas, Susan E.; Kuhn, John N.; Grass, Michael E.; Yamada, Yusuke et al.
Partner: UNT Libraries Government Documents Department

Prompt gamma activation analysis (PGAA) and short-lived neutron activation analysis (NAA) applied to the characterization of legacy materials

Description: Without quality historical records that provide the composition of legacy materials, the elemental and/or chemical characterization of such materials requires a manual analytical strategy that may expose the analyst to unknown toxicological hazards. In addition, much of the existing legacy inventory also incorporates radioactivity, and, although radiological composition may be determined by various nuclear-analytical methods, most importantly, gamma-spectroscopy, current methods of chemical characterization still require direct sample manipulation, thereby presenting special problems with broad implications for both the analyst and the environment. Alternately, prompt gamma activation analysis (PGAA) provides a'single-shot' in-situ, non-destructive method that provides a complete assay of all major entrained elemental constituents.1-3. Additionally, neutron activation analysis (NAA) using short-lived activation products complements PGAA and is especially useful when NAA activation surpasses the PGAA in elemental sensitivity.
Date: February 13, 2008
Creator: Firestone, Richard B; English, G.A.; Firestone, R.B.; Perry, D.L.; Reijonen, J.P.; Leung, Ka-Ngo et al.
Partner: UNT Libraries Government Documents Department

Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO

Description: The shape dependence of the catalytic reduction of NO by CO on Rhodium nanopolyhedra and nanocubes was studied from 230-270 C. The nanocubes are found to exhibit higher turnover frequency and lower activation energy than the nanopolyhedra. These trends are compared to previous studies on Rh single crystals.
Date: July 13, 2009
Creator: Renzas, J.R.; Zhang, Y.; Huang, W. & Somorjai, G.A.
Partner: UNT Libraries Government Documents Department


Description: A description of the ORNL neutron activation analytical service is presented. Techniques and measurement limits are also discussed as well as general applications. (J.R.D.)
Date: July 1, 1959
Creator: Leddicotte, G.W. & Reynolds, S.A.
Partner: UNT Libraries Government Documents Department

Neutron Activation and Other Analytical Data for Plutonic Rocks from North America and Africa: Appendix D. Microfiche Tables

Description: Tables of data containing the results of a literature search, a limited chemical analytical program, and visits to three alkaline-rock localities to accompany a report of the findings of establishing criteria for determining if a site had uranium resource potential. The criteria were applied to various sites in the U.S.; those results are also reported, with additional information about ongoing study.
Date: 1978
Creator: Price, Van; Fay, W. M. & Cook, J. R.
Partner: UNT Libraries Government Documents Department

The Identification and Determination of Trace Amounts of Rare Earth Elements in Graphite by Neutron Activation

Description: Abstract: "A method is described for the identification and quantitative determination of trace amounts of rare earths in graphite by measurement of the energies and decays of the activities induced by neutron irradiation. The specific rare earth elements identified are europium and samarium. During the development of this method, the half-lives of Eu-152 and Sm-153 were determined. These are reported as 9.32 +/- 0.04 hours and 46.34 +/- 0.23 respectively."
Date: September 1, 1949
Creator: Ross, A. M.
Partner: UNT Libraries Government Documents Department

Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Description: Methane and dinitrogen are abundant precursors to numerous valuable chemicals such as methanol and ammonia, respectively. However, given the robustness of these substrates, catalytically circumventing the high temperatures and pressures required for such transformations has been a challenging task for chemists. In this work, computational studies of various transition metal catalysts for methane C-H activation and N2 activation have been carried out. For methane C-H activation, catalysts of the form LnM=E are studied, where Ln is the supporting ligand (dihydrophosphinoethane or β-diketiminate), E the activating ligand (O, NCH3, NCF3) at which C-H activation takes place, and M the late transition metal (Fe,Co,Ni,Cu). A hydrogen atom abstraction (HAA) / radical rebound (RR) mechanism is assumed for methane functionalization (CH4 à CH3EH). Since the best energetics are found for (β-diket)Ni=O and (β-diket)Cu=O catalysts, with or without CF3 substituents around the supporting ligand periphery, complete methane-to-methanol cycles were studied for such systems, for which N2O was used as oxygen atom transfer (OAT) reagent. Both monometallic and bimetallic OAT pathways are addressed. Monometallic Fe-N2 complexes of various supporting ligands (LnFe-N2) are studied at the beginning of the N2 activation chapter, where the effect of ligand on N2 activation in end-on vs. side-on N2 isomers is discussed. For (β-diket)Fe-N2 complexes, the additional influence of diketiminate donor atom (N(H) vs. S) is briefly addressed. The remainder of the chapter expands upon the treatment of β-diketiminate complexes. First, the activation and relative stabilities of side-bound and end-bound N2 isomers in monometallic ((β-diket)M-N2) and bimetallic ((β-diket)M-N2-M(β-diket)) first row transition metal complexes are addressed. Second, the thermodynamics of H/H+/H- addition to (β-diket)Fe-bound N2, followed by subsequent H additions up to release of ammonia, is discussed, for which two mechanisms (distal and alternating) are considered. Finally, the chapter concludes with partial distal and alternating mechanisms for H addition to N2 ...
Date: May 2010
Creator: Pierpont, Aaron
Partner: UNT Libraries