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Abstract  

Assessment of the long-term performance of nuclear melt glass under saturated conditions provides insight into factors controlling radionuclide release into groundwater. Melt glass samples were collected from an underground nuclear detonation cavity at the Nevada Test Site that was in contact with groundwater for more than 10 years. The samples were made into thin sections and the distribution of alpha-activity mapped using CR-39 plastic detectors. The melt glass is visually heterogeneous and the results of the alpha-track radiography indicate that the highest alpha-activity is associated with areas of dark colored glass. Analyses of the thin sections by alpha-spectrometry show the prominent actinide species to be 238Pu, 239,240Pu and 241Am. Scanning electron microprobe analysis of the bulk glass shows conspicuous alteration layers lining internal vesicle surfaces in the glass. X-ray diffraction patterns for the alteration phases are consistent with clay mineral compositions. Glass dissolution models indicate these layers are too thick to have formed at ambient temperatures over the 10 year period in which they remained in a saturated environment. This implies the alteration layers likely formed at temperatures higher than ambient during cooling of the cavity following the underground detonation. Mobilization of this clay alteration layer as colloidal particles in groundwater represents a potential source of actinide release into the environment.

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Abstract  

Let R denote the purely infinite simple unital Leavitt path algebra L(E). We completely determine the pairs of positive integers (c, d) for which there is an isomorphism of matrix rings M c (R) ≌ M d (R), in terms of the order of [1 R ] in the Grothendieck group K 0(R).

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Abstract  

This paper describes the measurement of210Bi by Cerenkov counting in a commercial liquid scintillation counter. The counting efficiency in water is 0.17 counts per second per Becquerel (17%). When the enhancers Triton X-100 (15% v/v) and sodium salicylate (1% m/v) are added to the solution the counting efficiency for210Bi increases from 17% to 75%. The210Po daughter of210Bi causes interference of 0.85 counts per second per Becquerel in the presence of the enhancers but not in water. When210Bi and210Po are present in secular equilibrium the total counting efficiency is 160%. When210Bi and210Po are not in secular equilibrium the210Po can be removed immediately before counting by plating onto silver foil. The use of the enhancers gives a substantial increase in counting efficiency compared to counting in water. Compared with solutions used in liquid scintillation counting the enhancer solution is inexpensive and can be disposed of without environmental hazard.

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Abstract  

Theft, illegal possession, smuggling, or attempted unauthorized sale of nuclear and radiological materials remains a worldwide problem. The Nuclear Smuggling International Technical Working Group (ITWG) has adopted a model action plan to guide investigation of these cases through a systematic approach to nuclear forensics. The model action plan was recently documented and provides recommendations concerning incident response, collection of evidence in conformance with required legal standards, laboratory sampling and distribution of samples, radioactive materials analysis, including categorization and characterization of samples, forensics analysis of conventional evidence, and case development including interpretation of forensic signatures.

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Abstract  

We have developed a sequential extraction technique for determining the geochemical partitioning of Am, Pu, and U in soils and sediments. Stable element analyses were combined with radiometric measurements to determine the most probable geochemical host phases of these actinides in reference sediment IAEA-135.241 Am results indicate an association with carbonate minerals and organic matter. The extraction profile of238U was similar to that of refractory elements Al, Ti, and K.239/240Pu data suggest a fractionation of Pu into Fe-bearing phases of varying solubility. The reproducibility of the method was quite good (replicates agreed to within 10% at a 95% confidence level).

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A prediction from the herbivore optimization hypothesis is that for every combination of site/habitat type and plant community type there is a grazing intensity that causes a maximum increase in above-ground net primary productivity compared with the ungrazed control. NPP is defined as the rate of change in green, herbaceous biomass per unit time per unit area. We tested this hypothesis in the primary summer range of  a growing population of wood bison (Bison bison athabascae) within the Mackenzie Bison Sanctuary, Northwest Territories, Canada. Plots (0.5 x 0.5 m) in graminoid meadows dominated by awned sedge (Carex atherodes) were either clipped at 3 cm, exposed to wood bison grazing, temporarily protected for 3 weeks, or permanently protected. This resulted in the removal of 100%, 0-79%, 0-79% or 0%, respectively, of shoot tissue available to wood bison. NPP of meadows clipped twice at 3 cm in 1986 was the same as control NPP at 5 study sites. In 1987, only the 2 most productive study sites of 1986 were intensively examined: plots clipped once in early summer increased in NPP by 120% and 133% compared to controls; NPP of meadows grazed by wood bison increased by 200% compared to controls at the most productive site, but remained the same as controls at the less productive site. Therefore, the herbivore optimization hypothesis was accepted at the 2 most productive sites in 1987, but rejected at all 5 study sites in 1986. In 1987, the standing crop of dead material was 258% and 142% higher in controls than in grazed plots at the 2 most productive sites. We think this dead material was responsible for the lower NPP observed in control plots.

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Abstract  

Data from the quasi-elastic transfer reaction products140La and92mNb exhibit near zero effective ranges, flat excitation functions over large energy ranges and Q independent yields. These features are used to characterise quasi elastic reactions via the target-like product.

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A new tin dithiocarbamate containing sulphur bridges, di-μ-sulphidobis [bis(N,N-diethyldithiocarbamato)tin(IV)], has been isolated from the thermal decomposition of tetrakis(N,N-diethyldithiocarbamato)tin(IV). A dimeric structure is proposed on the basis of results from mass spectrometry, infrared spectroscopy, thermal analysis and vapour pressure osmometry.

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Abstract  

Water-soluble metal-binding polymers in combination with ultrafiltration are shown to be an effective method for selectively removing dilute actimide ions from acidic solutions of high ionic strength. The actinide-binding properties of commercially available water-soluble polymers and several polymers which have been reported in the literature were evaluated. The functional groups incorporated in the polymers were pyrrolidone, amine, oxime, and carboxylic, phosphonic, or sulfonic acid. The polymer containing phosphonic acid groups gave the best results with high distribution coefficients and concentration factors for241Am(III) and238Pu(III)/(IV) at pH 4 to 6 and ionic strengths of 0.1 to 4.

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