Abstract. The electrical conductivity of a partial melt is influenced by many factors, including melt conductivity, crystalline conductivity, and melt fraction, each of which is influenced by temperature. We have performed measurements of bulk conductivity as a function of temperature of an Fo80-basalt partial melt between 684 ø and 1244øC at controlled oxygen fugacity. Melt fraction and composition variations with temperature calculated using MELTS [Ghiorso and Sack, 1995] indicate that the effect on melt conductivity of changing melt composition is balanced by changes in temperature (T). Thus bulk conductivity as a function of T or melt fraction in this system can be calculated assuming a constant melt conductivity. The bulk conductivity is well mod-

is the most promising. SrI 2 (Eu) emits into the Eu 2+ band, centered at 435 nm, with a decay time of 1.2 µs and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3% FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramics fabrication allows production of Gadolinium-and Terbium-based garnets which are not growable by melt techniques due to phase instabilities. While scintillation light yields of Cerium-doped ceramic garnets are high, light yield non-proportionality and slow decay components appear to limit their prospects for high energy resolution.We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance energy resolution.

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The complex electrical properties of poly crystalline San Carlos olivine compacts were measured over the range of frequency l0−4–104Hz from 800° to 1400°C under controlled oxygen fugacity. The impedance data display a strong frequency dependence that is evidenced most clearly when the results are displayed in the complex impedance plane. A parameterized model of the frequency dependent electrical response using equivalent electrical circuits is presented. Two distinct conduction mechanisms of the sample are observed: grain interior and grain boundary conduction. Each occurs over a different range of frequency. The resistance of each mechanism adds in series resulting in a lower total DC conductivity for polycrystalline olivine than for either mechanism separately. The total DC conductivity is dominated by the grain interior conductivity above 1200°C, whereas the grain boundary conductivity has the strongest influence below 1000° C. Impedance spectra of natural dunite samples exhibit a similar type of frequency dependence. The grain interior conductivity displays a change in slope at 1344°C and has activation energies of 1.45 eV (800°–1344°C) and 4.87 eV (>1344°C). The grain boundary conductivity has an activation energy of 2.47 eV. In these cases, the ƒO2 for each experimental run was controlled at that of the wustite‐magnetite oxygen buffer. Experiments on samples with different grain sizes reveal no dependence of DC conductivity on grain size for either mechanism, although the relaxation time and real relative permittivity of the grain boundary mechanism are dependent on grain size. Because of the electrical response observed at low frequencies, care must be taken in the inversion of electromagnetic field observations using laboratory measurements made in the kilohertz range since they may not be the same as DC measurements. Impedance measurements must be performed over a range of relatively low frequencies to assess the role of grain boundaries on the overall electrical response of polycrystalline materials.

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[1] The electrical conductivity (s) was measured for a single crystal of San Carlos olivine (Fo 89.1 ) for all three principal orientations over oxygen fugacities 10 À7 < f O 2 < 10 1 Pa at 1100, 1200, and 1300°C. Fe-doped Pt electrodes were used in conjunction with a conservative range of f O 2 , T, and time to reduce Fe loss resulting in data that is $0.15 log units higher in conductivity than previous studies. At

[1] Bulk electrical conductivity and impedance spectroscopy of single crystal and polycrystalline San Carlos olivine with carbon or iron sulfide impurities on grain boundaries were measured at 1GPa and 350°C-1200°C in a piston cylinder apparatus. The addition of 0.1 wt% ($0.16 vol%) C causes series-type grain boundary impedance in the samples that slightly decreases the bulk conductivity of the system. In contrast, the addition of 1.0 vol% sulfide results in conductivity much higher than plain olivine, but still lower than that of a fully interconnected sulfide phase. The sulfide is partially connected on the grain boundaries and edges and has reached the electrical percolation threshold. The effect adding sulfide is similar to the effect of adding 0.01% -0.1% H to olivine. It may not always be necessary to have hydrogen or connected melt or fluid to account for anomalously high conductivity in some parts of the mantle or crust. Citation: Watson, H. C., J.

[1] We examine permeable flow through porous materials using volcanic pyroclasts with simple pore geometries. Laminar lattice-Boltzmann (LB) fluid flow simulations through 3-D synchrotron x-ray microtomographic images allow us to model fluid flow through anisotropic pumiceous volcanic samples (tube pumice). We find a good correspondence between calculated permeability (using both simple approximations and LB simulations) and maximum laboratory permeability measured parallel to the direction of vesicle elongation in most tube pumice samples. Moreover, this comparison demonstrates that small vesicles control fluid flow through the pore structure of tube pumice, even when large, but isolated, vesicles are present. However, neither simple approximations nor LB models for flow through small tomographic volumes can adequately model permeable flow perpendicular to vesicle elongation or in material with complex geometries. This mismatch illustrates current limitations in both resolution of x-ray tomography for delicate pumice structures and shows the importance of scale in LB calculations.