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[en] A portable, rapid, and sensitive assessment of sub-clinical organophosphorus (OPs) agent exposure based on reactivation of cholinesterase (ChE) from OP-inhibited ChE using rat saliva (in vitro) was developed using an electrochemical sensor coupled with a microflow-injection system. The sensor was based on a carbon nanotube (CNT)-modified screen printed carbon electrode (SPE), which was integrated into a flow cell. Due to the extent of inter-individual ChE activity variability, ChE biomonitoring often requires an initial base-line determination (non-inhibited) of enzyme activity which is then directly compared with activity after OP exposure. This manuscript described an alternative strategy where reactivation of the phosphorylated enzyme was exploited to enable measurement of both inhibited and baseline ChE activity (i.e. after reactivation) in the same sample. The use of CNT makes the electrochemical detection of the products from enzymatic reactions more feasible with extremely high sensitivity and at low potentials. Paraoxon was selected as a model OP compound for in vitro inhibition studies. Some experiment parameters, (e.g. inhibition and reactivation times), have been optimized such that, 92-95% ChE reactivation can be achieved over a broad range of ChE inhibition (5-94%) with paraoxon. The extent of enzyme inhibition using this electrochemical sensor correlates well with conventional enzyme activity measurements.
[en] Anomalous cross-reactions with the dihydro- and tetrahydro-reduced metabolites of norethindrone were observed utilizing antisera raised against norethindrone-3-bovine serum albumin. Whereas displacement of 3H-norethindrone from the antiserum by the metabolites was generally minimal, where one of the metabolites was used as radiotracer, displacement by the metabolites was equal to or greater than that achieved by norethindrone. This unexpected finding was examined for its usefulness in developing a radioimmunoassay system for norethindrone metabolites in plasma. The sensitivity of the resulting standard curve was such as to permit quantitation of pg amounts of the reduced metabolites
[en] Document available in extended abstract form only. In the context of nuclear waste management, long-term safety assessments have shown that selenium-79, released from the solid waste matrix, could be one of the major isotopes contributing to the global radioactivity potentially reaching the biosphere. Selenium has a quite complex speciation, with four main oxidation states, depending on both the pH and the redox potential of the surrounding environment. Sorption onto minerals can strongly affect the availability and the mobility of selenium. It is thus of great importance to be able to characterize both at a macroscopic and a microscopic level the different processes (retention, reduction, surface precipitation,...) that can potentially take place. Regarding the multi-barrier concept considered for deep underground storage of high level and long-lived radionuclides, clays are candidates as host rock as well as backfill materials. The main phases constituting clay rocks are minerals such as montmorillonite, bentonite, or illite, but also other compounds like iron oxides, titanium oxide, pyrite, calcite and organic matter. It has already been shown that clays and iron oxides can sorb and reduce selenium(VI) and selenium(IV). Thus, sorption experiments of selenium(VI) and selenium(IV) onto kaolinite and illite have been performed. Kaolinite and illite have been investigated since they are abundant and well crystallized clay mineral in soils. To get a better understanding of involved sorption mechanisms, a combination of both macroscopic and microscopic measurements have been used. Kaolinite KGa1-b from the Clay Mineral Society repository has been used without further pretreatment. Illite du Puy (France) has been purified in order to remove auxiliary and minor phases to get a homo-ionic 'Na-illite' clay. Then, batch experiments aiming at studying the sorption behaviour of selenium(VI) and selenium(IV) onto kaolinite and illite have been performed in NaCl and NaClO4. Preliminary results show that clays have higher affinity towards selenium(IV) compared to selenium(VI), which is an agreement with former studies on iron and aluminium oxides. The influence of the suspensions pH, as well as the ionic strength effect has been investigated. All the experiments have been performed under anoxic conditions in a glove box under N2 atmosphere (O2 < 1 ppm). Selenium speciation in solution has been checked using Hydride Generation-Atomic Absorption Spectroscopy measurements. The oxidation state of the selenium species once sorbed onto the kaolinite and illite surface has been evidenced using X-Ray Photoelectron Spectroscopy. Electrophoresis measurements have also been performed during this work. Comparison between the zeta potential of the kaolinite and illite surfaces before and after selenium oxyanions retention has been done, to check whether the sorption takes place by chemical bonding formation or rather by electrostatic attraction. Finally, ATR-FTIR measurements have been performed using an ATR ZnSe crystal. By comparison with former IR measurements concerning selenato and selenito-ligands containing complexes as well as phases with sorbed selenium species, the fashion binding of selenium(VI) and selenium(IV) onto kaolinite and illite has been evidenced. (authors)
[en] Binary and ternary surface complexes of U(VI) and Np(V) on gibbsite were spectroscopically identified. Se(VI) forms two different types of outer-sphere complexes depending on the solid metal oxide. (author)
[en] The impact of elevated temperature (25 to 80 C) on the complexation of Cm(III) by phosphate was investigated by time-resolved laser induced fluorescence spectroscopy (TRLFS). Using the specific ion interaction theory (SIT), the complexation constants at infinite dilution (log β ) were obtained. Finally, using the van't Hoff equation, positive enthalpy of reaction (ΔRH ) and entropy of reaction (ΔRS ) were derived.
[en] Transportation packages for fissile material are required by 10 CFR Part 71 (Ref. 1) to be evaluated for criticality safety assuming fresh water in-leakage. Criticality safety analyses for spent nuclear fuel transportation packages have typically been performed with the conservative assumption that the fuel is unburned. This assumption, in general, results in a large margin of subcriticality, and reduces the number or initial enrichment of spent fuel assemblies which may be transported in a package. In an effort to make spent fuel transportation packages more efficient, applicants for certificates of compliance under 10 CFR Part 71 have increasingly sought credit for the reduction in reactivity that occurs with spent fuel burnup, or burnup credit, in their criticality safety analyses. NRCs Div. of Spent Fuel Storage and Transportation published Interim Staff Guidance 8 (ISG-8), 'Burnup Credit in the Criticality Safety Analyses of PWR Spent Fuel in Transport and Storage Casks, ' in May of 1999 (Ref. 2), with subsequent revisions in July of 1999 (Ref. 3) and September of 2002 (Ref. 4). This document provides guidance regarding acceptable approaches to burnup credit criticality analyses for intact spent PWR assemblies in transportation packages. This paper will detail the technical basis supporting the current recommendations in ISG-8, including that for: 1) the licensing basis limits and model assumptions, 2) acceptable validation techniques for isotopic depletion and criticality codes, 3) the determination of burnup credit loading curves, and 4) the assigned burnup loading value. Additionally, this paper will discuss staff considerations for a potential revision to ISG-8, which may incorporate new data and computational techniques available for isotopic depletion and criticality code validation, as well as potential alternatives to in-pool burnup measurements to prevent assembly mis-loads. (authors)
[en] Nickel-63 is a low energy beta-emitter needing a radiochemical separation before β-counting. Several papers described the separation and the detection of 63Ni in environmental samples. The method used in our work was first developed by SKWARZEC and HOLM. The main steps of this separation are the selective precipitation of nickel with dimethylglyoxime (DMG) and the use of the non-sorption of nickel on anion resin in hydrochloric acid solutions. In this paper, a new step is added to eliminate high quantities of calcium and magnesium phosphate disturbing the iron hydroxide precipitation step. The procedure has been applied to soft water samples: sediments, plants and fishes. The chemical yields are 60, 70 and 20%, respectively. The detection limit of 63Ni by liquid scintillation spectrometer is 10 mBq. (author)
[en] Sorption of selenium (IV) and aqueous silicates onto Magnetite (Fe3O4) has been investigated, with initial concentration of aqueous silicates under solubility limit of amorphous silica. By using the double diffuse layer model (DDLM), the adsorption constants for selenium (IV) and H4SiO4 onto Magnetite have been determined from those experimental observations. Then, by using those surface complexation constants, prediction curves of the sorption of selenium (IV) in the presence of aqueous silicates onto Magnetite have been calculated. Finally, laboratory experiments were performed, confirming the ability of the DDLM to predict the competition effect observed experimentally between selenium (IV) and aqueous silicates for the surface sites of Magnetite. (authors)
[en] Full text of publication follows: In the context of an underground repository, silicates would be one of the major species found in water. Dissolved silicates would come from clays and silica (present as an impurity in many minerals) as well as from the degradation of glass canisters. Studies of their sorbing properties are nevertheless rather scarce in the literature although their presence on solid surfaces can modify surface sites availability and surface charge, which can influence global surface reactivity of solids. Furthermore, sorption of dissolved silicates on corrosion products of the metallic containers that could be used in the underground repository, could increase the solubility of the glass canisters. The aim of this work was to evaluate the role of the dissolved silicates in such a context, by studying their sorption on magnetite, hematite and goethite, chosen as model materials for corrosion products. Both experimental and modeling approach have been used, including XPS and Moessbauer measurements (to investigate possible alteration of the magnetite surface during experiments) as well as potentiometric titration data and sorption experiments. For goethite, the sorption edge showed that the sorption is maximum between pH 9 and 10. Saturation experiments allowed us to make the hypothesis of 1 Si atom sorbed on 1≡FeOH site. For magnetite, maximum sorption of silicates was located between pH 7 and 8, which corresponds to the pH of interstitial water in the underground laboratory of Bure in France. Sorption experiments were then modeled using surface complexation models (Fiteql 4.0 code). A structural study is under progress, using IR and Raman spectroscopies, in order to check the proposed mechanisms. (authors)
[en] Triple point, defined as the junction of metal, dielectric, and vacuum, is the location where electron emission is favored in the presence of a sufficiently strong electric field. To exploit triple point emission, metal-oxide-junction (MOJ) cathodes consisting of dielectric ''islands'' over stainless steel substrates have been fabricated. The two dielectrics used are hafnium oxide (HfOx) for its high dielectric constant and magnesium oxide (MgO) for its high secondary electron emission coefficient. The coatings are deposited by ablation-plasma-ion lithography using a KrF laser (0-600 mJ at 248 nm) and fluence ranging from 3 to 40 J/cm2. Composition and morphology of deposited films are analyzed by scanning electron microscopy coupled with x-ray energy dispersive spectroscopy, as well as x-ray diffraction. Cathodes are tested on the Michigan Electron Long-Beam Accelerator with a relativistic magnetron, at parameters V=-300 kV, I=1-15 kA, and pulse lengths of 0.3-0.5 μs. Six variations of the MOJ cathode are tested, and are compared against five baseline cases. It is found that particulate formed during the ablation process improves the electron emission properties of the cathodes by forming additional triple points. Due to extensive electron back bombardment during magnetron operation, secondary electron emission also may play a significant role. Cathodes exhibit increases in current densities of up to 80 A/cm2, and up to 15% improvement in current start up time, as compared to polished stainless steel cathodes