The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Ulrich H. Faul - One of the best experts on this subject based on the ideXlab platform.
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Melt retention and segregation beneath mid-ocean ridges.
Nature, 2001Co-Authors: Ulrich H. FaulAbstract:Geochemical models of melting at mid-ocean ridges-particularly those based on trace elements and Uranium-Decay-Series isotopes-predict that melt segregates from the matrix at very low porosities, of order 0.1%. Some of these models also require that the melt ascends rapidly. But these predictions appear to conflict with seismic data obtained by the mantle electromagnetic and tomography (MELT) experiment. These data reveal, beneath the East Pacific Rise (at 17 degrees S), a region of low velocities several hundred kilometres wide, which is best explained by the presence of 1-2% melt, distributed on a grain scale in disk-shaped geometries. Here I show that these apparently contradictory constraints can be reconciled by taking into account the geometry and resulting permeability of the intergranular network of melt, together with the changing character of the melt as it ascends. A deep, volatile-rich melt with low viscosity and density is mobile at 0.1% porosity, but basaltic melt only becomes mobile at a porosity above 1%. While the volumetric contribution of the volatile-rich melt to the erupted basalts is small, the isotopic disequilibria (except for radium) generated by porous flow of this melt are preserved if melt transport is rapid at the onset of high-productivity melting. Also, because of incomplete extraction, some melt is retained in a broad zone, consistent with the MELT observations.
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Melt retention and segregation beneath mid-ocean ridges
Nature, 2001Co-Authors: Ulrich H. FaulAbstract:Geochemical models of melting at mid-ocean ridges—particularly those based on trace elements and Uranium-Decay-Series isotopes—predict that melt segregates from the matrix at very low porosities^ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , of order 0.1%. Some of these models also require that the melt ascends rapidly^ 3 , 5 . But these predictions appear to conflict with seismic data obtained by the mantle electromagnetic and tomography (MELT) experiment^ 9 . These data reveal, beneath the East Pacific Rise (at 17 °S), a region of low velocities several hundred kilometres wide, which is best explained by the presence of 1–2% melt, distributed on a grain scale in disk-shaped geometries^ 10 . Here I show that these apparently contradictory constraints can be reconciled by taking into account the geometry and resulting permeability of the intergranular network of melt, together with the changing character of the melt as it ascends. A deep, volatile-rich melt with low viscosity and density is mobile at 0.1% porosity, but basaltic melt only becomes mobile at a porosity above 1%. While the volumetric contribution of the volatile-rich melt to the erupted basalts is small, the isotopic disequilibria (except for radium) generated by porous flow of this melt are preserved if melt transport is rapid at the onset of high-productivity melting. Also, because of incomplete extraction, some melt is retained in a broad zone, consistent with the MELT observations.
Karl K. Turekian - One of the best experts on this subject based on the ideXlab platform.
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The effect of weathering regime on Uranium Decay Series and osmium in two soil profiles
GEOCHEMICAL JOURNAL, 2004Co-Authors: S. Krishnaswami, G. A. Williams, William C. Graustein, Karl K. TurekianAbstract:Two soil profiles from the United States with radically different emplacement and climatic histories were analyzed for U, Th and members of the 238U Decay Series (234U, 230Th, 226Ra, 210Pb), 137Cs and osmium isotopes. The arid New Mexico profile is developed on an approximately 250, 000 years old colluvium while the temperate New Hampshire profile is formed on till after the last glaciation at about 10, 000 years ago. Both the profiles show significant 234U/238U 230Th/234U and 226Ra/230Th disequilibria, however, in the New Hampshire profile, the disequilibria are far more pronounced in mid-depths (20–50 cm). High Os concentration with highly radiogenic 187Os/188Os is another characteristic of the mid-depths of the New Hampshire profile. This layer, particularly at about 30–40 cm depth has the characteristics of a soil developed on black shale, as evidenced from both the high U and Os concentrations and the large excess of 230Th over 238U. This profile clearly shows that the regolith on which the contemporary soil is developing was not homogeneous. The presence of measurable excess 226Ra activity over 230Th activity in both profiles suggests the need for a source of 226Ra external to the regolith in both cases. Atmospheric deposition of 226Ra is a possible source for this 226Ra excess and brings to light the important role of atmospheric deposition of nuclides and their transport in the soil profile in pedogenic processes. It also shows that regolith developed by glacial processes need not be homogeneous, thereby confounding the understanding of vertically modified soil profiles.
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Uranium Decay Series
Reviews in Mineralogy and Geochemistry, 2003Co-Authors: Karl K. TurekianAbstract:The discovery of the 238U Decay chain, of course, started with the seminal work of Marie Curie in identifying and separating 226Ra. Through the work of the Curies and others, all the members of the 238U Decay chain were identified. An important milestone for geochronometrists was the discovery of 230Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years!) The application of the 238U Decay chain to the dating of deep sea sediments was by Piggott and Urry in 1942 using the “Ionium” method of dating. Actually they measured 226Ra (itself through 222Rn) assuming secular equilibrium had been established between 230 …
Clemens Walther - One of the best experts on this subject based on the ideXlab platform.
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Impact of former Uranium mining activities on the floodplains of the Mulde River, Saxony, Germany.
Journal of environmental radioactivity, 2015Co-Authors: Stefan Bister, Jonny Birkhan, Torben Lüllau, Maruta Bunka, A. Solle, C. Stieghorst, Beate Riebe, Rolf Michel, Clemens WaltherAbstract:The Mulde River drains the former Uranium mining areas in Saxony (Germany), which has led to a large-scale contamination of the river and the adjacent floodplain soils with radionuclides of the Uranium Decay Series. The objective of the investigation is to quantify the long-term effect of former Uranium mining activities on a river system. All of the investigated environmental compartments (water, sediment, soil) still reveal an impact from the former Uranium mining and milling activities. The contamination of water has decreased considerably during the last 20 years due to the operation of water treatment facilities. The Uranium content of the sediments decreased as well (on average by a factor of 5.6), most likely caused by displacement of contaminated material during flood events. Currently, the impact of the mining activities is most obvious in soils. For some of the plots activity concentrations of >200 Bq/kg of soil were detected for Uranium-238. Alluvial soils used as grassland were found to be contaminated to a higher degree than those used as cropland.
Stefan Bister - One of the best experts on this subject based on the ideXlab platform.
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Impact of former Uranium mining activities on the floodplains of the Mulde River, Saxony, Germany.
Journal of environmental radioactivity, 2015Co-Authors: Stefan Bister, Jonny Birkhan, Torben Lüllau, Maruta Bunka, A. Solle, C. Stieghorst, Beate Riebe, Rolf Michel, Clemens WaltherAbstract:The Mulde River drains the former Uranium mining areas in Saxony (Germany), which has led to a large-scale contamination of the river and the adjacent floodplain soils with radionuclides of the Uranium Decay Series. The objective of the investigation is to quantify the long-term effect of former Uranium mining activities on a river system. All of the investigated environmental compartments (water, sediment, soil) still reveal an impact from the former Uranium mining and milling activities. The contamination of water has decreased considerably during the last 20 years due to the operation of water treatment facilities. The Uranium content of the sediments decreased as well (on average by a factor of 5.6), most likely caused by displacement of contaminated material during flood events. Currently, the impact of the mining activities is most obvious in soils. For some of the plots activity concentrations of >200 Bq/kg of soil were detected for Uranium-238. Alluvial soils used as grassland were found to be contaminated to a higher degree than those used as cropland.
S. Chalupnik - One of the best experts on this subject based on the ideXlab platform.
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radium balance in discharge waters from coal mines in poland the ecological impact of underground water treatment
Radioprotection, 2009Co-Authors: S. Chalupnik, Małgorzata WysockaAbstract:Saline waters from underground coal mines in Poland often contain natural radioactive isotopes, mainly 226 Ra from the Uranium Decay Series and 228 Ra from the thorium Series. More than 70% of the total amount of radium remains underground as radioactive deposits due to spontaneous co-precipitation or water treatment technologies, but several tens of MBq of 226 Ra and even higher activity of 228 Ra are released daily into the rivers along with the other mine effluents from all Polish coal mines. Mine waters can have a severe impact on the natural environment, mainly due to its salinity. Additionally high levels of radium concentration in river waters, bottom sediments and vegetation were also observed. Sometimes radium concentrations in rivers exceeded 0.7 kBq/m3 , which was the permitted level for waste waters under Polish law. The investigations described here were carried out for all coal mines and on this basis the total radium balance in effluents has been calculated. Measurements in the vicinity of mine settling ponds and in rivers have given us an opportunity to study radium behaviour in river waters and to assess the degree of contamination. For removal of radium from saline waters a method of purification has been developed and implemented in full technical scale in two of Polish coal mines. The purification station in Piast Colliery was unique, the first underground installation for the removal of radium isotopes from saline waters. Very good results have been achieved – approximately 6 m3 /min of radium-bearing waters were treated there, more than 100 MBq of 226 Ra and 228 Ra remained underground each day. Purification has been started in 1999, therefore a lot of experiences have been gathered during this period. Since year 2006, a new purification station is working in another colliery, Ziemowit, at the level – 650 meters. Barium chloride is used as a cleaning agent, and amount of water to be purified is reaching 9 m3 /min. Technical measures such as inducing the precipitation of radium in gobs, decreasing the amount of meteoric inflow water into underground workings etc., have been undertaken in several coal mines, and as a result of these measures the total amount of radium released to the surface waters is much has diminished significantly during the last 15 years.
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Changes of radium concentration in discharge waters from coal mines in Poland as a result of mitigation
Uranium Mining and Hydrogeology, 2008Co-Authors: S. Chalupnik, Małgorzata WysockaAbstract:Saline waters from underground coal mines in Poland often contain natural radioactive isotopes, mainly226Ra from the Uranium Decay Series and228Ra from the thorium Series. More than 70% of the total amount of radium remains underground as radioactive deposits due to spontaneous co-precipitation or water treatment technologies, but several tens of MBq of226Ra and even higher activity of228Ra are released daily into the rivers along with the other mine effluents from all Polish coal mines. Different technical measures such as inducing the precipitation of radium in gobs, decreasing the amount of meteoric inflow water into underground workings etc., have been undertaken in several coal mines, and as a result of these measures the total amount of radium released to the surface waters has diminished significantly during the last 15 years.Mine waters can have a severe impact on the natural environment, mainly due to its salinity. Additionally high levels of radium concentration in river waters, bottom sediments and vegetation were also observed. Sometimes radium concentrations in rivers exceeded 0.7 kBq/m3, which was the permitted level for waste waters under Polish law. The investigations described here were carried out for all coal mines and on this basis the total radium balance in effluents has been calculated several times within last 20 years. Measurements in the vicinity of mine settling ponds and in rivers have given us an opportunity to study radium behaviour in river waters and to assess the degree of contamination.
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Contamination of settling ponds and rivers as a result of discharge of radium-bearing waters from Polish coal mines.
Journal of environmental radioactivity, 2001Co-Authors: S. Chalupnik, Małgorzata Wysocka, B. Michalik, K. Skubacz, Antoni MielnikowAbstract:Saline waters from underground coal mines in Poland often contain natural radioactive isotopes, mainly 226Ra from the Uranium Decay Series and 228Ra from the thorium Series. Approximately 40% of the total amount of radium remains underground as radioactive deposits, but 225 MBq of 226Ra and 400 MBq of 228Ra are released daily into the rivers along with the other mine effluents from all Polish coal mines. Technical measures such as inducing the precipitation of radium in gobs, decreasing the amount of meteoric inflow water into underground workings, etc. have been undertaken in several coal mines, and as a result of these measures, the total amount of radium released to the surface waters has diminished by about 60% during the last 5-6 years. Mine water can have a severe impact on the natural environment, mainly due to its salinity. However, associated high levels of radium concentration in river waters, bottom sediments and vegetation have also been observed. Sometimes radium concentrations in rivers exceed 0.7 kBq/m3, which is the permitted level for waste waters under Polish law. The extensive investigations described here were carried out for all coal mines and on this basis the total radium balance in the effluents has been calculated. Measurements in the vicinity of mine settling ponds and in rivers have given us an opportunity to study radium behaviour in river waters and to assess the degree of contamination. Solid waste materials with enhanced natural radioactivity have been produced in huge amounts in the power and coal industries in Poland. As a result of the combustion of coal in power plants, low-radioactive waste materials are produced, with 226Ra concentration seldom exceeding a few hundreds of Bq/kg. A different situation is observed in coal mines, where, as a result of precipitation of radium from radium-bearing waters, highly radioactive deposits are formed. Sometimes the radioactivity of such materials is extremely high; precipitates from coal mines may have radium concentrations of 400,000 Bq/kg--equivalent to 3% Uranium ore. Usually, such deposition takes place underground, but sometimes co-precipitation of radium with barium takes place on the surface, in settling ponds and in rivers. Therefore management of solid waste with technologically enhanced natural radioactivity (TENR) is a very important subject.
