The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Imed Ghiloufi - One of the best experts on this subject based on the ideXlab platform.
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Optical Emission Spectroscopy Measurements and Simulation of Radioelement Volatility During Radioactive Waste Treatment by Plasma
Plasma Chemistry and Plasma Processing, 2011Co-Authors: Imed Ghiloufi, Christophe GiroldAbstract:An optical emission spectroscopy (OES) method has been used to measure the concentration above the melt of some Radioelements, ^137Cs, ^60Co and ^106Ru during the vitrification of radioactive wastes by thermal plasma. This method allows the study of non homogeneous optically thin plasmas exhibiting a symmetry plane without sophisticated tomographic systems. Local plasma temperatures above the melt have been evaluated using measured relative intensities of spectral lines of the plasma-forming gas. Radioelement concentrations in the plasma are deduced from the intensity ratio of the Radioelement–gas spectral lines. A computer model is used to simulate the volatility of ^137Cs, ^60Co and ^106Ru, during the treatment of radioactive wastes by thermal plasma. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. In this study, the OES measurements and the computer model allowed the determination of this Radioelement volatility depending on the parameters like plasma current, and the nature of atmosphere furnace. The results of the model are compared to those obtained by OES measurements.
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Study of ^239Pu, ^144Ce, and ^90Sr Behavior During Radioactive Wastes Treatment by Thermal Plasma Technology
Plasma Chemistry and Plasma Processing, 2009Co-Authors: Imed GhiloufiAbstract:A computer model is used to study the volatility of some Radioelements (Cerium, Plutonium and Strontium) during radioactive wastes treatment by thermal plasma technology. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. The model enables the determination of the effects of various parameters (e.g., temperature, plasma current, and presence of oxygen in the carrier gas) on the Radioelement volatility. The obtained results indicate that any increase in molten bath temperature causes an increase in the Radioelement volatility. It is also found that the oxygen flux in the carrier gas strengthens the Radioelement incorporation in the containment matrix. For electrolyses effects, an increase in the plasma current increases both the vaporization speed and the vaporized quantities of ^239Pu, ^144Ce, and ^90Sr.
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Simulation of Radioelement volatility during the vitrification of radioactive wastes by arc plasma.
Journal of hazardous materials, 2008Co-Authors: Imed GhiloufiAbstract:Abstract A computer model is used to simulate the volatility of some Radioelements cesium (137Cs), cobalt (60Co), and ruthenium (106Ru) during the radioactive wastes vitrification by thermal plasma. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. The model enables the determination of the effects of various parameters (e.g., temperature, plasma current, and matrix composition) on the Radioelement volatility. The obtained results indicate that any increase in molten bath temperature causes an increase in the cobalt volatility; while ruthenium has a less obvious behavior. It is also found that the oxygen flux in the carrier gas supports the Radioelement incorporations in the containment matrix, except in the case of the ruthenium which is more volatile under an oxidizing atmosphere. For electrolyses effects, an increase in the plasma current considerably increases both the vaporization speed and the vaporized quantities of 137Cs and 60Co. The increase of silicon percentage in the containment matrix supports the incorporation of 60Co and 137Cs in the matrix. The simulation results are compared favorably to the experimental measurements obtained by emission spectroscopy.
Kirsty A. Beckett - One of the best experts on this subject based on the ideXlab platform.
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OBSERVATIONS ON THE CORRELATION BETWEEN URANIUM AND THORIUM Radioelement CHANNELS IN WESTERN AUSTRALIA AIRBORNE RADIOMETRIC SURVEYS.
2015Co-Authors: Kirsty A. BeckettAbstract:In Australia, natural Radioelement maps of potassium (K), thorium (Th) and uranium (U) are routinely generated from gamma-ray spectrometry data. Whether airborne or ground, the procedure for converting the gamma-ray spectra from airborne detectors to Radioelement concentrations remains the same, as these procedures have been established over the past three decades. The development and acceptance of thes
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OBSERVATIONS ON THE CORRELATION BETWEEN URANIUM AND THORIUM Radioelement CHANNELS IN WESTERN AUSTRALIA AIRBORNE RADIOMETRIC SURVEYS.
2004Co-Authors: Kirsty A. BeckettAbstract:INTRODUCTION In Australia, natural Radioelement maps of potassium (K), thorium (Th) and uranium (U) are routinely generated from gamma-ray spectrometry data. Whether airborne or ground, the procedure for converting the gamma-ray spectra from airborne detectors to Radioelement concentrations remains the same, as these procedures have been established over the past three decades. The development and acceptance of these procedures has not been one-sided, with various scientists arguing the benefits and shortcomings of many different processing techniques (e.g., Clarke et al. 1972, Gunn 1978, Grasty & Minty 1995 Minty 1997, Allyson & Sanderson 1998, Minty et al. 1998, Dickson & Taylor 2000, Billings et al. 2003). The outcomes of these rigorous scientific pursuits are encapsulated in the International Atomic Energy Agency (IAEA) July 2003 publication "Guidelines for Radioelement mapping using gamma ray spectrometry". The radiometric products delivered from all commercial processing companies in Australia reflect these guidelines, with final acquisition products delivered as gridded Radioelement maps of %K, eTh, eU, and total count (total gammaray dose rate).
Ana-catalina Plesa - One of the best experts on this subject based on the ideXlab platform.
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Hemispheric Dichotomy in Lithosphere Thickness on Mars Caused by Differences in Crustal Structure and Composition
Journal of Geophysical Research. Planets, 2018Co-Authors: Melanie Thiriet, Chloé Michaut, Doris Breuer, Ana-catalina PlesaAbstract:Estimates of the Martian elastic lithosphere thickness suggest small values of similar to 25 km during the Noachian for the southern hemisphere and a large present-day difference below the two polar caps (\textgreater= 300 km in the north and \textgreater110 km in the south). In addition, young lava flows suggest that Mars has been volcanically active up to the recent past. We run Monte Carlo simulations using a 1-D parameterized thermal evolution model to investigate whether a north/south hemispheric dichotomy in crustal properties and composition can explain these constraints. Our results suggest that 55-65% of the bulk Radioelement content are in the crust, and most of it (43-51%) in the southern one. The southern crust can be up to 480 kg/m(3) less dense than the northern one and might contain a nonnegligible proportion of felsic rocks. Our models predict a dry mantle and a wet or dry crustal rheology today. This is consistent with a mantle depleted in Radioelements and volatiles. We retrieve north/south surface heat flux of 17.1-19.5 mW/m(2) and 24.8-26.5 mW/m(2), respectively, and a large difference in lithospheric temperatures between the two hemispheres (170-304 K in the shallow mantle). This difference could leave a signature in the seismic signals measured by the future InSight mission.
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NUCM2 Monte Carlo results - wet crust and dry mantle rheology
2018Co-Authors: Melanie Thiriet, Chloé Michaut, Ana-catalina Plesa, Doris BreuerAbstract:Monte Carlo results for NUCM2 simulations (Figure 9b)Rheology = dry mantle and wet crust, diffusion creepFiles:Each line of the files (scores, thickness, enrichment factor and crustal Radioelement content) corresponds to a model with given crustal parameters (crustal thickness in meters and enrichment factor) and the results obtained for this model.Gaussian scores for the three constraints on elastic thickness are given in the files "score". To compute scores between 0 and 1, these scores have to be divided by the maximum of the corresponding gaussian (given in "Gaussian_maximum.csv": in order for the Noachian, the Southern polar cap and the Northern polar cap)The file "MeltFormation" gives the difference in meters between the depth of the stagnant lid and the depth of melt formation in the Southern hemisphere. Models with present-day formation in the South are those where this difference is lower than 100 km.The percentage of Radioelement contained in the Northern and Southern crusts are given in files "RadioelementContents".
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UCM Monte Carlo results - wet crust and dry mantle rheology
2018Co-Authors: Melanie Thiriet, Chloé Michaut, Ana-catalina Plesa, Doris BreuerAbstract:Monte Carlo results for UCM simulations (Figures 6a-b-c-d, 7a and 9a). Rheology = dry mantle and wet crust, diffusion creepFiles:Each line of the files (scores, thickness, enrichment factor and crustal Radioelement content) corresponds to a model with given crustal parameters (crustal thickness in meters and enrichment factor) and the results obtained for this model.Gaussian scores for the three constraints on elastic thickness are given in the files "score". To compute scores between 0 and 1, these scores have to be divided by the maximum of the corresponding gaussian (given in "Gaussian_maximum.csv": in order for the Noachian, the Southern polar cap and the Northern polar cap)The file "MeltFormation" gives the difference in meters between the depth of the stagnant lid and the depth of melt formation in the Southern hemisphere. Models with present-day formation in the South are those where this difference is lower than 100 km.The percentage of Radioelement contained in the Northern and Southern crusts are given in files "RadioelementContents".
Olwen Williams-thorpe - One of the best experts on this subject based on the ideXlab platform.
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Radioelement distribution in the Tertiary Lundy Granite (Bristol Channel, UK)
Geological Magazine, 1995Co-Authors: R. S. Thorpe, Andrew G. Tindle, Olwen Williams-thorpeAbstract:The Radioelement distribution and content of the Lundy granite, a coarse-grained megacrystic granite of Tertiary age, has been measured using a portable gamma-ray spectrometer in order to assess fractionation and alteration processes in the granite. Results indicate a systematic variation of K, Th and U (with a few notable exceptions) that follows a partially concentric distribution to lower concentrations inland. The plateau region of the island (particularly the southern half) is relatively depleted in all Radioelements. Over the island, measurements of K vary from 1.3–4.9 wt %, Th varies from 5.0–20.3 ppm and U varies from 2.0–12.5 ppm. A petrographic, electron microprobe and autoradiography examination of the granite indicates that the Radioelements mainly reside in discrete major and accessory minerals, of which K-feldspar (K), biotite (K), monazite (Th), xenotime (U), tungsteniferous columbite (U) and uraninite (U) are the most important. Uraninite is rare, being preserved only in fresh samples which come mainly from abandoned quarries. Mass balance modelling indicates that up to 76.6% of uranium could reside in uraninite and where this has been leached by secondary processes such as hydrothermal alteration or weathering then the present Radioelement content no longer reflects the original rock composition. Fission track evidence is presented to show the pathways along which uranium has been mobilized from or within the granite. Secondary sites of Radioelements include fractures cross-cutting all major minerals (but especially quartz), grain boundaries, altered cores of plagioclase feldspar and occasionally yellowy brown mixed chlorite/smectite replacement product after biotite. Biotite itself may exhibit secondary tracks along cleavage traces. Combined effects of crystal fractionation (primary variation) and secondary alteration best explain the distribution of Radioelements, with K controlled by fractionation of the major phases K-feldspar and biotite, Th by fractionation of the accessory mineral monazite (±xenotime and uraninite) and U contents by uraninite and tungsteniferous columbite. Secondary processes have removed much of the uraninite leaving behind indeterminate Fe—U material along fractures and residual U (and Th) enrichment within altered major minerals. There is some evidence to suggest that late Radioelement-bearing fluids precipitated monazite and uraniferous zircon along fractures during the waning stages of magmatic activity.
Pete Burnard - One of the best experts on this subject based on the ideXlab platform.
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Production, Release and Transport of Noble Gases in the Continental Crust
Reviews in Mineralogy and Geochemistry, 2002Co-Authors: Chris J. Ballentine, Pete BurnardAbstract:Noble gases within the crust originate from three main sources: the atmosphere, introduced into the crust dissolved in groundwater; the mantle, in regions of magmatic activity; and those produced in the crust by the result of radioactive decay processes. The continental crust contains approximately 40% of the terrestrial Radioelements (Rudnick and Fountain 1995) that produce noble gases and, after the mantle and the atmosphere, forms the third major terrestrial noble gas reservoir (neglecting the core). In addition to these sources, contributions from interplanetary dust particles (IDP), cosmic ray interaction with the crustal surface and anthropogenic noble gases can in some cases be a significant source of noble gases in crustal materials. The use of noble gases to understand the role of fluids in different geological settings relies on their low natural abundance and chemical inertness. The low abundance of noble gases in crustal systems and their distinct isotopic character means that contributions from these different sources can often be resolved and quantified. With this, information is gained about the source of associated fluids, the environment from which they originated the physical manner in which they have been transported to the sampling site and the different phases that may have interacted within the crustal fluid system. This is only possible, however, with a detailed understanding of the processes that control the concentration and isotopic composition of the noble gases in different crustal environments. The first part of this chapter deals with the three different mechanisms of noble gas production within the crust—radiogenic, nucleogenic, fissiogenic (Fig. 1⇓). We show how production ratios are affected not only by the source region Radioelement concentration, but in the case of nucleogenic reactions, also by the spatial distribution and concentration of the target elements. For completeness we consider cosmogenic noble gas production rates and Interplanetary …
