Multi-Laboratory Results for the Cathodoluminescence Emission Spectrum from a Synthetic Zircon Standard

The Standards Committee of the Society for Luminescence Microscopy and Spectroscopy (SLMS) circulated doped zircon crystals as a standard for comparison of cathodoluminescence (CL) emission spectra obtained at different laboratories. Eleven laboratories have submitted spectra acquired from this standard. The crystals are synthetic zircons doped with 1.4 wt.% of Dy2O3 The participating laboratories used a variety of CL instrumentation including cold cathode optical micro-scope attachments, hot cathode optical microscope attachments, and EMPA/SEM-based systems. Two laboratories provided both uncorrected and corrected spectra. All other spectra are uncorrected. A variety of different spectrometers/spectrographs and detector systems were used. Photomultiplier tubes (PMTs), photo diode arrays, intensified photo diode arrays, and charge coupled devices (CCDs) are represented among the final results. The laboratories with apparently the best resolving power reported 8 peaks in the multiplet at 485 nm. The spectra submitted by some laboratories showed only a single peak at this position. The wavelength scale calibrations were compared by noting the wavelength of the most intense peak in the 485 multiplet. This varied from 476.3 nm to 489 nm among the eleven laboratories. The systems have different overall transmission and detection functions: a combination of the influence of the transmission of the viewing window (typically leaded-glass), the microscope, the fiber optics coupling (if used), the response of the grating and spectrometer/spectrograph, and the detector response. As an initial test of this variation, the ratio of the peak maximum intensity at 575 nm to that at 485 nm was compared. This ratio varied from 0.6 to 3.93 among the eleven laboratories

UO2 CORROSION IN HIGH SURFACE-AREA-TO-VOLUME BATCH EXPERIMENTS

Unsaturated drip tests have been used to investigate the alteration of unirradiated UO{sub 2} and spent UO{sub 2} fuel in an unsaturated environment, such as may be expected in the proposed repository at Yucca Mountain. In these tests, simulated groundwater is periodically injected onto a sample at 90 C in a steel vessel. The solids react with the dripping groundwater and water condensed on surfaces to form a suite of U(VI) alteration phases. Solution chemistry is determined from leachate at the bottom of each vessel after the leachate stops interacting with the solids. A more detailed knowledge of the compositional evolution of the leachate is desirable. By providing just enough water to maintain a thin film of water on a small quantity of fuel in batch experiments, we can more closely monitor the compositional changes to the water as it reacts to form alteration phases

Genesis and evolution of the San Manuel iron skarn deposit (Betic Cordillera, SW Spain)

The San Manuel magnesian skarn is an iron deposit hosted in dolomitic marbles from a tectonic slice imbricated within the Ronda peridotites, in the westernmost part of the Betic Cordillera, Spain. According to the dominant mineral assemblage, the skarn is subdivided into three different zones, (1) forsterite +/- calcite skarn, (2) calcite +/- chlorite +/- serpentine skarn, and (3) Ca-amphibole skarn. The main ore in the skarn is a similar to 2.5 m thick, massive ore body situated in the middle of the sequence. In this paper, we firstly report a comprehensive major to trace element composition, texture, microstructure, and mineralogy characterization for zoned magnesioferritemagnetite grains of the San Manuel deposit using a combination of (1) laser ablation inductively coupled plasma mass spectrometer, (2) focused ion beam combined with transmission electron microscopy, and (3) electron back-scattered diffraction. We have defined four different magnesioferrite-magnetite generations. A complete sequence of zoning includes cores of magnesioferrite (Mag-1; MgO up to 10.6 wt%) overprinted by three successive generations of magnetite, namely Mag-2, Mag-3, Mag-4. Mag-2 (MgO < 4 wt%), hosts composite forsterite +/- calcite +/- chlorite inclusions, consistently with high Si, Ca, and Sr (average: 8204 ppm, 8980 ppm, and 49 ppm respectively) contents detected by in situ laser ablation inductively coupled plasma (LA-ICP-MS). Mag-3 replacing former Mag-1 and Mag-2 includes nanometric spinel and gahnite exsolutions detected by focused ion beam combined with a transmission electron microscope (FIB-TEM), which is consistent with its high Al, Ti, V, and Ga (average: 5073 ppm, 368 ppm, and 20 ppm, respectively) trace element concentration. Mag-4 is the Fe-richest magnetite (up to 94.16 wt% FeOtotal) forming the outermost rims in magnetite grains, and exhibiting the lowest total trace element contents. Approaches in temperature estimations employing magnetitespinel exsolutions in Mag-3 suggest that the minimum temperature of the prograde stage reached temperatures below 700 degrees C, whereas Mag-4 should be formed during the retrograde stage. Magnetite microstructure studied by electron backscatter diffraction (EBSD) suggests Mag-4 formation under fluid-assisted dynamic conditions, which is consistent with the tectonic evolution of the emplacement. We propose that the San Manuel deposit formed by pulsed hydrothermal fluids derived from anatexis of crustal rocks during peridotite emplacement, promoting reequilibration processes that led to the magnesioferrite-magnetite zoning

Development and Testing of a Glass Waste Form For the Immobilization of Plutonium

The United States has declared about 50 metric tons of weapons-grade Pu surplus to national security needs. The President has directed that this Pu be placed in a form that provides a high degree of proliferation resistance in which the surplus Pu is both unattractive and inaccessible for use by others [I]. Three alternatives are being evaluated for the disposal 2048 of this material: (1) use of the Pu as a fuel source for commercial reactors; (2) immobilization, where Pu is fixed in a glass or ceramic matrix that also contains or is surrounded by highly radioactive material; and (3) deep bore hole, where Pu is emplaced at depths of several kilometers. The immobilization alternative is being directed by the staff at Lawrence Livermore National Laboratory (LLNL). The staff at ANL are assisting by developing a glass for the immobilization of Pu and in the corrosion testing of glass and ceramic material prepared both at ANL and at other DOE laboratories. As part of this program, we have developed an ATS glass into which 5-7 wt percent Pu has been dissolved. The ATS glass was engineered to accommodate high Pu loading and to be durable under conditions likely to accelerate glass reactions in the geological environment during long-term storage

Development and Testing of a Glass Waste Form for the Immobilization of Plutonium

The United States has declared about 50 metric tons of weapons-grade Pu surplus to national security needs. The President has directed that this Pu be placed in a form that provides a high degree of proliferation resistance in which the surplus Pu is both unattractive and inaccessible for use by others [I]. Three alternatives are being evaluated for the disposal 2048 of this material: (1) use of the Pu as a fuel source for commercial reactors; (2) immobilization, where Pu is fixed in a glass or ceramic matrix that also contains or is surrounded by highly radioactive material; and (3) deep bore hole, where Pu is emplaced at depths of several kilometers. The immobilization alternative is being directed by the staff at Lawrence Livermore National Laboratory (LLNL). The staff at ANL are assisting by developing a glass for the immobilization of Pu and in the corrosion testing of glass and ceramic material prepared both at ANL and at other DOE laboratories. As part of this program, we have developed an ATS glass into which 5-7 wt percent Pu has been dissolved. The ATS glass was engineered to accommodate high Pu loading and to be durable under conditions likely to accelerate glass reactions in the geological environment during long-term storage

GABAA receptors as molecular targets of general anesthetics: identification of binding sites provides clues to allosteric modulation

PurposeThe purpose of this review is to summarize current knowledge of detailed biochemical evidence for the role of γ-aminobutyric acid type A receptors (GABA(A)-Rs) in the mechanisms of general anesthesia.Principal findingsWith the knowledge that all general anesthetics positively modulate GABA(A)-R-mediated inhibitory transmission, site-directed mutagenesis comparing sequences of GABA(A)-R subunits of varying sensitivity led to identification of amino acid residues in the transmembrane domain that are critical for the drug actions in vitro. Using a photo incorporable analogue of the general anesthetic, R(+)etomidate, we identified two transmembrane amino acids that were affinity labelled in purified bovine brain GABA(A)-R. Homology protein structural modelling positions these two residues, αM1-11' and βM3-4', close to each other in a single type of intersubunit etomidate binding pocket at the β/α interface. This position would be appropriate for modulation of agonist channel gating. Overall, available information suggests that these two etomidate binding residues are allosterically coupled to sites of action of steroids, barbiturates, volatile agents, and propofol, but not alcohols. Residue α/βM2-15' is probably not a binding site but allosterically coupled to action of volatile agents, alcohols, and intravenous agents, and α/βM1-(-2') is coupled to action of intravenous agents.ConclusionsEstablishment of a coherent and consistent structural model of the GABA(A)-R lends support to the conclusion that general anesthetics can modulate function by binding to appropriate domains on the protein. Genetic engineering of mice with mutation in some of these GABA(A)-R residues are insensitive to general anesthetics in vivo, suggesting that further analysis of these domains could lead to development of more potent and specific drugs

Basis of the Gabamimetic Profile of Ethanol

This article summarizes the proceedings of a symposium held at the 2005 Research Society on Alcoholism meeting. The initial presentation by Dr. Wallner provided evidence that selected GABAA receptors containing the δ subunit display sensitivity to low intoxicating ethanol concentrations and this sensitivity is further increased by a mutation in the cerebellar α6 subunit, found in alcohol-hypersensitive rats. Dr. Mameli reported that ethanol affects γ-aminobutyric acid (GABA) function by affecting neural circuits that influence GABA release. Dr. Parsons presented data from electrophysiological and microdialysis investigations that ethanol is capable of releasing GABA from presynaptic terminals. Dr. Morrow demonstrated that systemic ethanol increases neuroactive steroids in brain, the absence of which alters various functional responses to ethanol. Dr. Criswell presented evidence that the ability of ethanol to increase GABA was apparent in some, but not all, brain regions indicative of regional specificity. Further, Dr. Criswell demonstrated that neurosteroids alone and when synthesized locally by ethanol act postsynaptically to enhance the effect of GABA released by ethanol in a region specific manner. Collectively, this series of reports support the GABAmimetic profile of acutely administered ethanol being dependent on several specific mechanisms distinct from a direct effect on the major synaptic isoforms of GABAA receptors

Quantifying garnet-melt trace element partitioning using lattice-strain theory: New crystal-chemical and thermodynamic constraints

Many geochemical models of major igneous differentiation events on the Earth, the Moon, and Mars invoke the presence of garnet or its high-pressure majoritic equivalent as a residual phase, based on its ability to fractionate critical trace element pairs (Lu/Hf, U/Th, heavy REE/light REE). As a result, quantitative descriptions of mid-ocean ridge and hot spot magmatism, and lunar, martian, and terrestrial magma oceans require knowledge of garnet-melt partition coefficients over a wide range of conditions. In this contribution, we present new crystal-chemical and thermodynamic constraints on the partitioning of rare earth elements (REE), Y and Sc between garnet and anhydrous silicate melt as a function of pressure (P), temperature (T), and composition (X). Our approach is based on the interpretation of experimentally determined values of partition coefficients D using lattice-strain theory. In this and a companion paper (Draper and van Westrenen this issue) we derive new predictive equations for the ideal ionic radius of the dodecahedral garnet X-site,