The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform
K. Johan Hogmalm - One of the best experts on this subject based on the ideXlab platform.
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First in situ Re-Os dating of molybdenite by LA-ICP-MS/MS
Mineralium Deposita, 2019Co-Authors: K. Johan Hogmalm, Isabell Dahlgren, Irma Fridolfsson, Thomas ZackAbstract:Conventional dating of molybdenite (^187Re-^187Os) provides one of few options for direct dating of sulfide mineralization. Unfortunately, in situ dating of molybdenite is considered unreliable due to intra-granular decoupling of ^187Re-^187Os. In this study, we developed a new analytical protocol for studies of micron- to grain scale ^187Re-^187Os systematics in molybdenite. Online chemical separation using ICP-MS/MS technology enables in situ dating by β-decay systems (e.g., Rb-Sr and K-Ca in micas) using laser ablation. Here, the methodology is extended to the ^187Re-^187Os system, another β-decay system that cannot be resolved by mass spectrometry. Several reaction gases were evaluated, and production of OsCH_2 by reaction with CH_4 was found to produce strong separation of Os from Re. However, in contrast to the e.g., ^87Rb-^87Sr system, 1–2% of the Parent Isotope Re also reacted to ReCH_2, leaving a significant interference. A mathematical correction of this remaining interference is possible, and ^187Re-^187Os (mass-shifted) can be measured accurately even for fairly extreme ratios. For laser ablation, standards were developed by pressing particulate pellets of conventionally dated molybdenite (Moly Hill and Merlin), because there are no appropriate reference materials available. Six natural molybdenite samples from a range of geological settings, containing > 10 ppm Re, were analyzed by 70 μm laser ablation spots, and ages were calibrated by analysis of molybdenite pellets. Contrary to our expectation, weighted average ages obtained were in agreement (within 1%) with conventional age determinations, with fairly good precision (from ~ 1 to 5% 2 σ depending on Re concentration), suggesting limited or essentially nonexistent decoupling within crystals. Two important implications of this result are that decoupling Re-Os is not universal, and that our new analytical protocol is useful both for dating and for studies of decoupling. The benefit of in situ dating compared to conventional dating is, apart from lower cost and time consumption, the possibility of targeting smaller molybdenite crystals (≥ 100 μm) in thin sections and epoxy mounts. The youngest sample in the study is 920 Ma, but we see potential of dating significantly younger Re-rich molybdenite.
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Laser ablation Rb/Sr dating by online chemical separation of Rb and Sr in an oxygen-filled reaction cell
Chemical Geology, 2016Co-Authors: Thomas Zack, K. Johan HogmalmAbstract:Abstract The Rb-Sr beta-decay dating system is one of the most attractive tools in geochronology, as Rb is sufficiently abundant in common K-bearing minerals like biotite, muscovite and K-feldspar. This allows dating of a wide variety of rocks (e.g., volcanic, magmatic, metamorphic, sedimentary and hydrothermal environments) without the need of preconcentration, as is often required for U-Pb dating of zircon. However, this advantage was to date negatively counteracted by the lack of a suitable in-situ technique, as beta decay systems by nature have isobaric interferences of the daughter Isotope by their respective Parent Isotope. A reaction cell sandwiched between two quadrupoles within an inductively coupled plasma mass spectrometer (ICP-MS) allows exactly this, the online chemical separation of two different elements. Coupled to a laser ablation (LA) system, in-situ Rb-Sr dating is therefore possible if a suitable reaction gas within the reaction cell can be found that separates Sr from Rb. We present here a simple procedure in which Rb-Sr ages can be obtained from a suite of individual phases in regular thin sections. Using the most established reaction gas, oxygen (O 2 ), it is possible to react part of the ablated Sr to SrO + while no RbO + is formed. Measurements of feldspars and micas with a spot size of 80 μm were calibrated against glass standards NIST SRM 610, BCR-2G and biotite from La Posta (California; 91.6 Ma). Results are presented for a variety of magmatic rocks with well-established thermal records: a sample each from the Klokken syenodiorite (Greenland; 1161 Ma), the Ulvo alkaligabbro (Sweden; 1256 Ma) and a pegmatite from the Bohus granite (Sweden; 920 Ma). Obtained in situ Rb-Sr isochron ages are accurate 87 Sr/ 86 Sr ratios are accurate The methodology outlined in this study has significant implications for Rb-Sr studies due to the high spatial resolution: (1) quality of measurements can be better controlled by avoiding alterations and inclusions, (2) large sample numbers can be investigated simply by using regular thin sections, (3) several mineral generations can be targeted that would not be distinguishable in mineral separates, and (4) Isotope zonation within single crystals can be revealed. This will open the Rb-Sr dating system to new fields of study. For example, thermochronologic studies can use 87 Sr/ 86 Sr and 87 Rb/ 86 Sr zonation within crystals to better work out cooling and/or reheating paths. Further applications are in the field of provenance studies and temporal evolution of shear zones.
Tadao Ishii - One of the best experts on this subject based on the ideXlab platform.
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Thermoanalytical study on surface reactivity and characterization of oxide powders at elevated temperatures
Thermochimica Acta, 1992Co-Authors: Tadao IshiiAbstract:Abstract Thermoanalytical studies on the surface reactivity and characterization of oxide powders have been reviewed on the basis of the author's work between 1967 and 1992. Gas-flow DTA apparatus and the emanation thermal analysis method using 226Ra as Parent Isotope were successfully applied for investigating the surface behavior of powders at elevated temperatures.
Minik T. Rosing - One of the best experts on this subject based on the ideXlab platform.
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Early mantle dynamics inferred from 142Nd variations in Archean rocks from southwest Greenland
Earth and Planetary Science Letters, 2013Co-Authors: Hanika Rizo, Maud Boyet, Janne Blichert-toft, Minik T. RosingAbstract:The composition and evolution of the silicate Earth during Hadean/Eoarchean times are widely debated and largely unknown due to the sparse geological record preserved from Earthʼs infancy. The short-lived 146Sm-142Nd chronometer applied to 3.8-3.7 Ga old mantle-derived amphibolites from the Isua Supracrustal Belt (ISB) in southwest Greenland has revealed ubiquitous 142Nd excesses in these rocks compared to modern samples and terrestrial Nd standards. Because the Parent Isotope, 146Sm, was extant only during the first few hundred million years of Solar System history, this implies derivation of the Greenland samples from a source formed in the Hadean. This mantle source is the oldest yet identified on Earth and therefore provides key information about the nature and evolution of early-differentiated reservoirs. In contrast, modern mantle-derived rocks from around the world do not have 142Nd anomalies, suggesting that the primordial heterogeneities detected in Earthʼs early mantle have been erased over time. In order to better constrain the rate at which early mantle heterogeneities have been re-homogenized, we produced new 146Sm-142Nd data for both 3.8 and 3.3 Ga old mafic rocks from different tectonic domains of the ISB, accompanied by their corresponding 147Sm-143Nd and 176Lu-176Hf systematics. The 3.8 Ga suite yields 142Nd excesses comparable to those detected previously in 3.7 Ga old ISB amphibolites, indicating that Eoarchean mafic ISB lavas originated from sources with similar differentiation histories despite being from different juxtaposed tectonic segments. Conversely, 3.3 Ga old amphibolites from the ISB do not show resolvable 142Nd anomalies compared to terrestrial Nd standards. Since Rizo et al. (2012) reported 142Nd anomalies in 3.4 Ga old ISB samples, the present data suggest that the primordial 142Nd heterogeneities in the Isua mantle disappeared between 3.4 and 3.3 Ga. The present data set consists of samples from a unique location where 500 million years of history of the early terrestrial mantle have been preserved, hence offering an exceptional opportunity to gain new insight into the compositional evolution and dynamic workings of Earthʼs primordial mantle.
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Early mantle dynamics inferred from 142Nd variations in Archean rocks from southwest Greenland
Earth and Planetary Science Letters, 2013Co-Authors: Hanika Rizo, Maud Boyet, Janne Blichert-toft, Minik T. RosingAbstract:International audienceThe composition and evolution of the silicate Earth during Hadean/Eoarchean times are widely debated and largely unknown due to the sparse geological record preserved from Earthʼs infancy. The short-lived 146Sm-142Nd chronometer applied to 3.8-3.7 Ga old mantle-derived amphibolites from the Isua Supracrustal Belt (ISB) in southwest Greenland has revealed ubiquitous 142Nd excesses in these rocks compared to modern samples and terrestrial Nd standards. Because the Parent Isotope, 146Sm, was extant only during the first few hundred million years of Solar System history, this implies derivation of the Greenland samples from a source formed in the Hadean. This mantle source is the oldest yet identified on Earth and therefore provides key information about the nature and evolution of early-differentiated reservoirs. In contrast, modern mantle-derived rocks from around the world do not have 142Nd anomalies, suggesting that the primordial heterogeneities detected in Earthʼs early mantle have been erased over time. In order to better constrain the rate at which early mantle heterogeneities have been re-homogenized, we produced new 146Sm-142Nd data for both 3.8 and 3.3 Ga old mafic rocks from different tectonic domains of the ISB, accompanied by their corresponding 147Sm-143Nd and 176Lu-176Hf systematics. The 3.8 Ga suite yields 142Nd excesses comparable to those detected previously in 3.7 Ga old ISB amphibolites, indicating that Eoarchean mafic ISB lavas originated from sources with similar differentiation histories despite being from different juxtaposed tectonic segments. Conversely, 3.3 Ga old amphibolites from the ISB do not show resolvable 142Nd anomalies compared to terrestrial Nd standards. Since Rizo et al. (2012) reported 142Nd anomalies in 3.4 Ga old ISB samples, the present data suggest that the primordial 142Nd heterogeneities in the Isua mantle disappeared between 3.4 and 3.3 Ga. The present data set consists of samples from a unique location where 500 million years of history of the early terrestrial mantle have been preserved, hence offering an exceptional opportunity to gain new insight into the compositional evolution and dynamic workings of Earthʼs primordial mantle
Charlie W. Allen - One of the best experts on this subject based on the ideXlab platform.
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Thermal-Mechanical Response of Non-Uniformly Heated Nominally Flat and Curved LEU Foil Based Target
Volume 7: Fluids and Heat Transfer Parts A B C and D, 2012Co-Authors: Kyler K. Turner, Gary L. Solbrekken, Charlie W. AllenAbstract:Technetium-99m is a radiopharmaceutical currently used in 85% of all diagnostic imaging procedures. The relative long lived Parent Isotope of technetium-99m is molybdenum-99, which is commonly produced by irradiating highly enriched uranium. In accordance with the Department of Energy: National Nuclear Security Administration’s Global Threat Reduction Initiative an effort is underway to develop low enriched uranium based molybdenum-99 production concepts. Achieving comparable molybdenum-99 yields in a low enriched uranium target effectively mandates the use of a high density metal low enriched uranium foil. Using a foil requires a significant modification to the current highly enriched uranium dispersion target designs. One design concept uses a low enriched uranium foil sandwiched between either two flat or curved aluminum plates. The low enriched uranium is enclosed in the sandwiched structure by welding the aluminum plates together about their edges. The plate design is inspired by low enriched uranium fuel plates with the exception that the low enriched uranium is not bonded to the aluminum plates nor is it necessary to clamp the plate edges to prevent lateral translation. The lack of bonding between the low enriched uranium foil and the plates allows easy removal of the foil after irradiation for chemically processing and separation. The un-heated edges of the plate target produce three-dimensional temperature gradients inducing deformations and stress. This paper will review the thermal mechanical response of a low enriched uranium foil based molybdenum-99 production target. This study describes the effect of various curvatures, thermal loads, and heat transfer coefficients on the thermal-induced deflection and stress.Copyright © 2012 by ASME
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Thermal-Mechanical Response of Non-Uniformly Heated LEU Foil Based Target
Volume 10: Heat and Mass Transport Processes Parts A and B, 2011Co-Authors: Kyler K. Turner, Gary L. Solbrekken, Charlie W. AllenAbstract:Technetium-99m is a diagnostic radiopharmaceutical that is currently used in 80% of the global nuclear diagnostic imaging procedures. The Parent Isotope for technetium-99m is molybdenum-99, most commonly obtained through the irradiation of high enriched uranium (HEU) targets. In accordance with the Department of Energy’s Global Threat Reduction Initiative (GTRI) an effort is underway to develop a process to produce molybdenum-99 using low enriched uranium (LEU) targets to maintain production yield relative to HEU targets. Conversion of targets to LEU material effectively mandates that the most efficient process is to cast LEU in the form of a metal foil as opposed to current powder based dispersion designs for HEU. Using a foil requires a significant modification to the current target design. One design concept uses an LEU foil sandwiched between two nominally flat aluminum plates. The LEU is enclosed in the sandwiched structure by welding the aluminum plates together about their edges. The plate design is inspired by high density monolithic LEU fuel plates with the exception that the LEU is not bonded to the aluminum plates nor is it necessary to clamp the plate edges to prevent lateral translation. The lack of bonding between the LEU foil and the plates allows the edges of the plate to be cut off so the foil can be removed after irradiation to be chemically processed. The un-heated edges of the plate target produce 3-D temperature gradients that induce plate deformations. This paper will review thermal mechanical response of an LEU foil based molybdenum-99 plate target geometry. This study describes the effect of various edge holding conditions, thermal loads, and heat transfer coefficients on the thermal-induced deflection and stress in the plates.
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Thermal-Mechanical Analysis of Varying Boundary Conditions on a LEU Foil Based Molybdenum-99 Plate Processing Target
Volume 9: Mechanics of Solids Structures and Fluids, 2010Co-Authors: Kyler K. Turner, Gary L. Solbrekken, Charlie W. AllenAbstract:Technetium-99m is a diagnostic radio-pharmaceutical that is currently used in 85% of the United States diagnostic imaging procedures [1]. All supplies of technetium-99m’s Parent Isotope molybdenum-99 currently originate from the irradiation of high enriched uranium (HEU) in nuclear reactor facilities located outside the United States. In accordance with the Global Threat Reduction Initiative all uranium used in future molybdenum-99 production will use low enriched uranium (LEU). Conversion to LEU material effectively mandates using LEU in the form of a metal foil as opposed to current powder based dispersion designs for HEU. Using a foil requires a significant modification to the current target design. One design approach uses an LEU foil sandwiched between two nominally flat aluminum plates. The LEU is enclosed in the sandwiched structure by welding the aluminum plates together about their edges. The plate design is inspired by LEU fuel plates with the exception that the LEU is not bonded to the aluminum plates nor is it necessary to clamp the plate edges to prevent lateral translation. This paper will review the thermal-mechanical analysis of an LEU based molybdenum-99 target with plate geometry. This study describes the impact of boundary conditions on the thermally-induced stress and strain in the aluminum plates.
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thermal mechanical analysis of annular target design for high volume production of molybdenum 99 using low enriched uranium
ASME 2009 International Mechanical Engineering Congress and Exposition, 2009Co-Authors: Kyler K. Turner, Gary L. Solbrekken, Charlie W. AllenAbstract:Techenetium-99m is a diagnostic radioactive medical Isotope that is currently used 30,000 times a day in the United States. All supplies of techenetium-99m’s Parent Isotope molybdenum-99 currently originate from nuclear reactor facilities located in foreign countries and use highly enriched uranium (HEU). In accordance with the Global Threat Reduction Initiative all uranium used in future molybdenum-99 production will use low enriched uranium (LEU). A design approach to using LEU in a cost-effective manner is to use a target that is based on LEU foil. A potential failure mode for the LEU foil based target is temperature excursion during irradiation due to poor thermal contact between the foil and the target cladding. The purpose of this study is to establish the theoretical basis for experimentally measuring the thermal contact resistance. Replicating in service heating conditions is nearly impossible when testing the thermal contact resistance as part of a study to establish LEU foil warpage tolerances, thus it is necessary to establish an alternate heating configuration that will allow a conservative estimate of the contact resistance. Thermal and mechanical analysis suggests that external heating of an annular target will place the interface into a state that will over-estimate the contact resistance relative to use conditions. Further, the magnitude of the heat load used for testing can be adjusted to control the degree of overestimation.
Thomas Zack - One of the best experts on this subject based on the ideXlab platform.
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First in situ Re-Os dating of molybdenite by LA-ICP-MS/MS
Mineralium Deposita, 2019Co-Authors: K. Johan Hogmalm, Isabell Dahlgren, Irma Fridolfsson, Thomas ZackAbstract:Conventional dating of molybdenite (^187Re-^187Os) provides one of few options for direct dating of sulfide mineralization. Unfortunately, in situ dating of molybdenite is considered unreliable due to intra-granular decoupling of ^187Re-^187Os. In this study, we developed a new analytical protocol for studies of micron- to grain scale ^187Re-^187Os systematics in molybdenite. Online chemical separation using ICP-MS/MS technology enables in situ dating by β-decay systems (e.g., Rb-Sr and K-Ca in micas) using laser ablation. Here, the methodology is extended to the ^187Re-^187Os system, another β-decay system that cannot be resolved by mass spectrometry. Several reaction gases were evaluated, and production of OsCH_2 by reaction with CH_4 was found to produce strong separation of Os from Re. However, in contrast to the e.g., ^87Rb-^87Sr system, 1–2% of the Parent Isotope Re also reacted to ReCH_2, leaving a significant interference. A mathematical correction of this remaining interference is possible, and ^187Re-^187Os (mass-shifted) can be measured accurately even for fairly extreme ratios. For laser ablation, standards were developed by pressing particulate pellets of conventionally dated molybdenite (Moly Hill and Merlin), because there are no appropriate reference materials available. Six natural molybdenite samples from a range of geological settings, containing > 10 ppm Re, were analyzed by 70 μm laser ablation spots, and ages were calibrated by analysis of molybdenite pellets. Contrary to our expectation, weighted average ages obtained were in agreement (within 1%) with conventional age determinations, with fairly good precision (from ~ 1 to 5% 2 σ depending on Re concentration), suggesting limited or essentially nonexistent decoupling within crystals. Two important implications of this result are that decoupling Re-Os is not universal, and that our new analytical protocol is useful both for dating and for studies of decoupling. The benefit of in situ dating compared to conventional dating is, apart from lower cost and time consumption, the possibility of targeting smaller molybdenite crystals (≥ 100 μm) in thin sections and epoxy mounts. The youngest sample in the study is 920 Ma, but we see potential of dating significantly younger Re-rich molybdenite.
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Laser ablation Rb/Sr dating by online chemical separation of Rb and Sr in an oxygen-filled reaction cell
Chemical Geology, 2016Co-Authors: Thomas Zack, K. Johan HogmalmAbstract:Abstract The Rb-Sr beta-decay dating system is one of the most attractive tools in geochronology, as Rb is sufficiently abundant in common K-bearing minerals like biotite, muscovite and K-feldspar. This allows dating of a wide variety of rocks (e.g., volcanic, magmatic, metamorphic, sedimentary and hydrothermal environments) without the need of preconcentration, as is often required for U-Pb dating of zircon. However, this advantage was to date negatively counteracted by the lack of a suitable in-situ technique, as beta decay systems by nature have isobaric interferences of the daughter Isotope by their respective Parent Isotope. A reaction cell sandwiched between two quadrupoles within an inductively coupled plasma mass spectrometer (ICP-MS) allows exactly this, the online chemical separation of two different elements. Coupled to a laser ablation (LA) system, in-situ Rb-Sr dating is therefore possible if a suitable reaction gas within the reaction cell can be found that separates Sr from Rb. We present here a simple procedure in which Rb-Sr ages can be obtained from a suite of individual phases in regular thin sections. Using the most established reaction gas, oxygen (O 2 ), it is possible to react part of the ablated Sr to SrO + while no RbO + is formed. Measurements of feldspars and micas with a spot size of 80 μm were calibrated against glass standards NIST SRM 610, BCR-2G and biotite from La Posta (California; 91.6 Ma). Results are presented for a variety of magmatic rocks with well-established thermal records: a sample each from the Klokken syenodiorite (Greenland; 1161 Ma), the Ulvo alkaligabbro (Sweden; 1256 Ma) and a pegmatite from the Bohus granite (Sweden; 920 Ma). Obtained in situ Rb-Sr isochron ages are accurate 87 Sr/ 86 Sr ratios are accurate The methodology outlined in this study has significant implications for Rb-Sr studies due to the high spatial resolution: (1) quality of measurements can be better controlled by avoiding alterations and inclusions, (2) large sample numbers can be investigated simply by using regular thin sections, (3) several mineral generations can be targeted that would not be distinguishable in mineral separates, and (4) Isotope zonation within single crystals can be revealed. This will open the Rb-Sr dating system to new fields of study. For example, thermochronologic studies can use 87 Sr/ 86 Sr and 87 Rb/ 86 Sr zonation within crystals to better work out cooling and/or reheating paths. Further applications are in the field of provenance studies and temporal evolution of shear zones.
