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Youngouk Lee - One of the best experts on this subject based on the ideXlab platform.
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validation of new neutron production cross sections for Tungsten Isotopes
2009Co-Authors: Do Heon Kim, Hyeong Ill Kim, Choongsup Gil, Youngouk LeeAbstract:New neutron production cross sections of Tungsten Isotopes such as 182 W, 183 W 184 W, and 186 W have been validated through shielding benchmarks and criticality safety benchmarks with the MCNPX-2.5.0 code. The calculation results based on the new evaluations have been compared with those based on ENDF/B-VII.0, JEFF-3.1, JENDL-3.3, and FENDL-2.1 as well as the benchmark experiments. In this paper, some noticeable improvements in calculations of the neutron leakage spectra from Tungsten shields and the k eff 's for critical assemblies with Tungsten are presented.
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evaluation of neutron production cross sections of Tungsten Isotopes for fusion applications
2008Co-Authors: Hyeong Il Kim, Do Heon Kim, Youngouk LeeAbstract:The evaluation of neutron production cross section is presented for Tungsten which is increasingly considered as a prime candidate of plasma facing materials in fusion reactors. The energy and/or angular dependent neutron spectra from existing libraries such as ENDF/B-VII, JEFF-3.1 and JENDL-3.3 failed to reproduce the measured data available for Tungsten Isotopes. Moreover, the integral tests of neutron production from these libraries showed remarkable discrepancies with leakage neutron measurements of OKTAVIAN. In response to these situations, we calculated the neutron production data for four Tungsten Isotopes such as 182,183,184,186W. The calculation was performed by using the nuclear model code EMPIRE-2.19 with a consistent set of input parameters for all Tungsten Isotopes. We could obtain the neutron spectra in good agreements with the measurements by employing the quantum mechanical Multi-Step Direct (MSD) and Multi-Step Compound (MSC) theory for preequilibrium neutron emission. The results have be...
Ghylaine Quitte - One of the best experts on this subject based on the ideXlab platform.
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High-precision measurements of Tungsten stable Isotopes and application to earth sciences
2014Co-Authors: Thomas Breton, Ghylaine QuitteAbstract:Mass-dependent isotope fractionation of Tungsten (W) Isotopes has not received much attention until recently. This is mainly due to the small fractionation expected as Tungsten has a relatively high atomic mass combined with the insufficient precision that could be achieved with the existing techniques. Tungsten is used in the 182Hf182W radio-chronometer. Hence, Tungsten Isotopes are currently mainly used for studying the first stages of the solar system history, as they are well suited to trace metalsilicate equilibration processes. At the same time, evaporation, condensation and diffusion are known to fractionate stable Isotopes. A better understanding of W stable isotope behavior during terrestrial and asteroidal processes will thus potentially shed light on those events. We here present an improved separation procedure based on anion-exchange chromatography that allows achieving quantitative recovery of W. Taking advantage of the last generation of multi-collector inductively coupled plasma mass-spectrometers (MC-ICPMS), we also set up a method to analyze W mass-dependent isotope fractionation with an external reproducibility better than 80 ppm and an internal reproducibility of 30 ppm. This new analytical procedure has been applied to igneous and iron-rich samples, from granites to chondrites and iron meteorites. Isotope variations observed for natural samples are well resolvable and vary from -0.05 to +0.36 per mil per mass unit.
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Tungsten Isotopes in eucrites revisited and the initial 182hf 180hf of the solar system based on iron meteorite data
2004Co-Authors: Ghylaine Quitte, Jean-louis BirckAbstract:Abstract We present a revised chronology for the formation and differentiation of the eucrite parent body based on 182 Hf– 182 W chronometry. A very short ( 182 Hf/ 180 Hf initial ratio of the solar system of (1.60±0.25)×10 −4 . This estimate, deduced from iron meteorite W isotope data, is about 50% higher than recently suggested.
Jean-louis Birck - One of the best experts on this subject based on the ideXlab platform.
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Stony-iron meteorites: History of the metal phase according to Tungsten Isotopes
2005Co-Authors: G Quitte, Jean-louis Birck, Claude J. AllègreAbstract:Abstract The global composition of the early solar system is thought to be roughly chondritic in terms of refractory components, and this means that metal and silicate should be present together in early planetesimals. To fully understand the metal-silicate differentiation process within the eucrite parent body (EPB), it is important to try and identify the metal reservoir that is complementary to the silicate part. The isotope 182 of Tungsten (W), a siderophile element, is partly formed from the decay of 182 Hf, and W Isotopes are useful for examining metal-silicate segregation. The W isotopic composition expected for the metal that is complementary to eucrites falls in the range of iron meteorites. However, mesosiderites seem to be genetically linked to eucrites based on petrologic and oxygen isotopic similarities. Therefore, we undertook the analysis of the metal phase of these stony-irons. Here we present Tungsten isotopic data for mesosiderite and pallasite metal to characterize their parent body (bodies) and to assess possible relationships with eucrites. All stony-iron metals are depleted in radiogenic Tungsten by −1.3 to −4.2 e units, relative to the terrestrial standard, while chondrites, for comparison, are depleted by −1.9 e units. In addition to W isotopic heterogeneity from one stony-iron to another, there is also W isotopic heterogeneity within individual meteorites. A formation model is tentatively proposed, where we show that mesosiderites, pallasites, and eucrites could possibly come from the same parent body. Several hypotheses are discussed to explain the isotopic heterogeneity: the production of cosmogenic Tungsten, the in situ decay of hafnium present in inclusions, and Tungsten diffusion processes after metal-silicate mixing during the cooling of the meteorites. The two latter hypotheses provide the best explanation of our data.
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Tungsten Isotopes in eucrites revisited and the initial 182hf 180hf of the solar system based on iron meteorite data
2004Co-Authors: Ghylaine Quitte, Jean-louis BirckAbstract:Abstract We present a revised chronology for the formation and differentiation of the eucrite parent body based on 182 Hf– 182 W chronometry. A very short ( 182 Hf/ 180 Hf initial ratio of the solar system of (1.60±0.25)×10 −4 . This estimate, deduced from iron meteorite W isotope data, is about 50% higher than recently suggested.
Richard J Walker - One of the best experts on this subject based on the ideXlab platform.
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Tungsten Isotopes in planets
2017Co-Authors: Thorsten Kleine, Richard J WalkerAbstract:The short-lived Hf-W isotope system has a wide range of important applications in cosmochemistry and geochemistry. The siderophile behavior of W, combined with the lithophile nature of Hf, makes the system uniquely useful as a chronometer of planetary accretion and differentiation. Tungsten isotopic data for meteorites show that the parent bodies of some differentiated meteorites accreted within 1 million years after Solar System formation. Melting and differentiation on these bodies took ∼1–3 million years and was fueled by decay of 26Al. The timescale for accretion and core formation increases with planetary mass and is ∼10 million years for Mars and >34 million years for Earth. The nearly identical 182W compositions for the mantles of the Moon and Earth are difficult to explain in current models for the formation of the Moon. Terrestrial samples with ages spanning ∼4 billion years reveal small 182W variations within the silicate Earth, demonstrating that traces of Earth's earliest formative period have...
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section 8 Tungsten Isotopes in the mantle
2016Co-Authors: Richard J WalkerAbstract:Some of the most important discoveries pertaining to the formation and early evolution of the Earth have come about through the measurement of short-lived radiogenic isotope systems. For example, the discovery of isotopic variations in 142Nd (146Sm → 142Nd; t½ = 103 Ma) among early-Earth samples
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Tungsten isotopic evidence for disproportional late accretion to the earth and moon
2015Co-Authors: Mathieu Touboul, Igor S Puchtel, Richard J WalkerAbstract:Examination of three lunar samples reveals that the Moon’s mantle has an excess of the Tungsten isotope 182W of about 20 parts per million relative to the present-day Earth’s mantle; this suggests that the two bodies had identical compositions immediately following the formation of the Moon, and that the compositions then diverged as a result of disproportional late accretion of chondritic material to the Earth and Moon. Two papers published in this issue of Nature present precise measurements of Tungsten isotope composition in lunar rocks that are best explained by the Earth and Moon having had similar composition immediately following formation of the Moon, and then having diverged as a result of disproportional late accretion of material to the two bodies. Mathieu Touboul et al. found small 182W excess of about 21 parts per million relative to the present-day Earth's mantle in metals extracted from two KREEP-rich Apollo 16 impact-melt rocks, while Thomas Kruijer et al. measured Tungsten Isotopes in seven KREEP-rich whole rock samples that span a wide range of cosmic ray exposure ages, and found a 182W excess of about 27 parts per million over the present-day Earth's mantle. Characterization of the hafnium–Tungsten systematics (182Hf decaying to 182W and emitting two electrons with a half-life of 8.9 million years) of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant-impact theory for the formation and evolution of the Moon, and for testing the late-accretion hypothesis. Uniform, terrestrial-mantle-like W isotopic compositions have been reported1,2 among crystallization products of the lunar magma ocean. These observations were interpreted to reflect formation of the Moon and crystallization of the lunar magma ocean after 182Hf was no longer extant—that is, more than about 60 million years after the Solar System formed. Here we present W isotope data for three lunar samples that are more precise by a factor of ≥4 than those previously reported1,2. The new data reveal that the lunar mantle has a well-resolved 182W excess of 20.6 ± 5.1 parts per million (±2 standard deviations), relative to the modern terrestrial mantle. The offset between the mantles of the Moon and the modern Earth is best explained by assuming that the W isotopic compositions of the two bodies were identical immediately following formation of the Moon, and that they then diverged as a result of disproportional late accretion to the Earth and Moon3,4. One implication of this model is that metal from the core of the Moon-forming impactor must have efficiently stripped the Earth’s mantle of highly siderophile elements on its way to merge with the terrestrial core, requiring a substantial, but still poorly defined, level of metal–silicate equilibration.
Thorsten Kleine - One of the best experts on this subject based on the ideXlab platform.
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tracing dehydration and melting of the subducted slab with Tungsten Isotopes in arc lavas
2020Co-Authors: Andreas Stracke, Sarah E Mazza, James B Gill, Junichi Kimura, Thorsten KleineAbstract:Abstract Tungsten is strongly incompatible during magmatic processes and is fluid mobile in subduction zones. Here we show that W isotope fractionation in arc lavas provide a powerful new tool for tracing slab dehydration and melting in subduction zones. Geochemically well characterized, representative arc-lavas from three subduction zones were chosen for this study to evaluate W isotope fractionation under different sub-arc conditions. Arc-lavas from SW Japan are produced by subducting a young, hot slab, and lavas from the volcanic front and rear arc of the Sangihe and Izu arcs are produced during subduction of a cold slab. The heaviest W isotope compositions ( δ 184 W ∼ 0.06 ‰ ) are observed in fluid-rich samples from the volcanic fronts of the Sangihe and Izu arcs. With increasing distance from the volcanic front, more melt-rich samples are characterized by progressively lighter W isotope compositions. Enriched alkali basalts from SW Japan, thought to be the product of mantle melting at a slab tear, and adjacent shoshonites have the lightest W isotope compositions ( δ 184 W ∼ 0 ‰ ). The correlation of W isotope fractionation with various indices of fluid release (e.g., Ce/Pb, Ba/Th) suggests that the heavy W isotope signatures record fluid recycling near the volcanic front due to dehydration of the subducted slab. Upon release of the heavy W, the residual slab preferentially retains isotopically light W, which is released during subsequent melting of drier lithologies in hot subduction zones, such as SW Japan. These data suggest that W Isotopes can be used as a tracer of slab dehydration, potentially helping to determine the onset of cold subduction zone magmatism and hence, modern-style plate tectonics.
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Tungsten Isotopes and the origin of the moon
2017Co-Authors: Thomas S Kruijer, Thorsten KleineAbstract:Abstract The giant impact model of lunar origin predicts that the Moon mainly consists of impactor material. As a result, the Moon is expected to be isotopically distinct from the Earth, but it is not. To account for this unexpected isotopic similarity of the Earth and Moon, several solutions have been proposed, including (i) post-giant impact Earth–Moon equilibration, (ii) alternative models that make the Moon predominantly out of proto-Earth mantle, and (iii) formation of the Earth and Moon from an isotopically homogeneous disk reservoir. Here we use W isotope systematics of lunar samples to distinguish between these scenarios. We report high-precision 182W data for several low-Ti and high-Ti mare basalts, as well as for Mg-suite sample 77215, and lunar meteorite Kalahari 009, which complement data previously obtained for KREEP-rich samples. In addition, we utilize high-precision Hf isotope and Ta/W ratio measurements to empirically quantify the superimposed effects of secondary neutron capture on measured 182W compositions. Our results demonstrate that there are no resolvable radiogenic 182W variations within the Moon, implying that the Moon differentiated later than 70 Ma after Solar System formation. In addition, we find that samples derived from different lunar sources have indistinguishable 182W excesses, confirming that the Moon is characterized by a small, uniform ∼+26 parts-per-million excess in 182W over the present-day bulk silicate Earth. This 182W excess is most likely caused by disproportional late accretion to the Earth and Moon, and after considering this effect, the pre-late veneer bulk silicate Earth and the Moon have indistinguishable 182W compositions. Mixing calculations demonstrate that this Earth–Moon 182W similarity is an unlikely outcome of the giant impact, which regardless of the amount of impactor material incorporated into the Moon should have generated a significant 182W excess in the Moon. Consequently, our results imply that post-giant impact processes might have modified 182W, leading to the similar 182W compositions of the pre-late veneer Earth's mantle and the Moon.
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Tungsten Isotopes in planets
2017Co-Authors: Thorsten Kleine, Richard J WalkerAbstract:The short-lived Hf-W isotope system has a wide range of important applications in cosmochemistry and geochemistry. The siderophile behavior of W, combined with the lithophile nature of Hf, makes the system uniquely useful as a chronometer of planetary accretion and differentiation. Tungsten isotopic data for meteorites show that the parent bodies of some differentiated meteorites accreted within 1 million years after Solar System formation. Melting and differentiation on these bodies took ∼1–3 million years and was fueled by decay of 26Al. The timescale for accretion and core formation increases with planetary mass and is ∼10 million years for Mars and >34 million years for Earth. The nearly identical 182W compositions for the mantles of the Moon and Earth are difficult to explain in current models for the formation of the Moon. Terrestrial samples with ages spanning ∼4 billion years reveal small 182W variations within the silicate Earth, demonstrating that traces of Earth's earliest formative period have...
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lunar Tungsten isotopic evidence for the late veneer
2015Co-Authors: Thomas S Kruijer, Thorsten Kleine, M Fischergodde, Peter SprungAbstract:Precise measurements of the Tungsten isotopic composition of lunar rocks show that the Moon exhibits a well-resolved excess of 182W of about 27 parts per million over the present-day Earth’s mantle: this excess is consistent with the expected 182W difference resulting from a late veneer with a total mass and composition inferred from previously measured highly siderophile elements. Two papers published in this issue of Nature present precise measurements of Tungsten isotope composition in lunar rocks that are best explained by the Earth and Moon having had similar composition immediately following formation of the Moon, and then having diverged as a result of disproportional late accretion of material to the two bodies. Mathieu Touboul et al. found small 182W excess of about 21 parts per million relative to the present-day Earth's mantle in metals extracted from two KREEP-rich Apollo 16 impact-melt rocks, while Thomas Kruijer et al. measured Tungsten Isotopes in seven KREEP-rich whole rock samples that span a wide range of cosmic ray exposure ages, and found a 182W excess of about 27 parts per million over the present-day Earth's mantle. According to the most widely accepted theory of lunar origin, a giant impact on the Earth led to the formation of the Moon, and also initiated the final stage of the formation of the Earth’s core1. Core formation should have removed the highly siderophile elements (HSE) from Earth’s primitive mantle (that is, the bulk silicate Earth), yet HSE abundances are higher than expected2. One explanation for this overabundance is that a ‘late veneer’ of primitive material was added to the bulk silicate Earth after the core formed2. To test this hypothesis, Tungsten Isotopes are useful for two reasons: first, because the late veneer material had a different 182W/184W ratio to that of the bulk silicate Earth, and second, proportionally more material was added to the Earth than to the Moon3. Thus, if a late veneer did occur, the bulk silicate Earth and the Moon must have different 182W/184W ratios. Moreover, the Moon-forming impact would also have created 182W differences because the mantle and core material of the impactor with distinct 182W/184W would have mixed with the proto-Earth during the giant impact. However the 182W/184W of the Moon has not been determined precisely enough to identify signatures of a late veneer or the giant impact. Here, using more-precise measurement techniques, we show that the Moon exhibits a 182W excess of 27 ± 4 parts per million over the present-day bulk silicate Earth. This excess is consistent with the expected 182W difference resulting from a late veneer with a total mass and composition inferred from HSE systematics2. Thus, our data independently show that HSE abundances in the bulk silicate Earth were established after the giant impact and core formation, as predicted by the late veneer hypothesis. But, unexpectedly, we find that before the late veneer, no 182W anomaly existed between the bulk silicate Earth and the Moon, even though one should have arisen through the giant impact. The origin of the homogeneous 182W of the pre-late-veneer bulk silicate Earth and the Moon is enigmatic and constitutes a challenge to current models of lunar origin.
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Tungsten Isotopes in ferroan anorthosites implications for the age of the moon and lifetime of its magma ocean
2009Co-Authors: Mathieu Touboul, H Palme, Bernard Bourdon, Thorsten Kleine, R WielerAbstract:New W isotope data for ferroan anorthosites 60025 and 62255 and low-Ti mare basalt 15555 show that these samples, contrary to previous reports [Lee, D.C., et al., 1997. Science 278, 1098–1103; Lee, D.C., et al., 2002. Earth Planet. Sci. Lett. 198, 267–274], have a W isotope composition that is indistinguishable from KREEP and other mare basalts. This requires crust extraction on the Moon later than ∼60 Myr after CAI formation, consistent with 147Sm–143Nd ages for ferroan anorthosites. The absence of 182Hf-induced 182W variations in the Moon is consistent with formation of the Moon at 62−10+90Myr after CAI formation that has been inferred based on the indistinguishable 182W/184W ratios of the bulk Moon and the bulk silicate Earth. The uncertainties on the age of the Moon and the age of the oldest lunar samples currently hamper a precise determination of the duration of magma ocean solidification and are consistent with both an almost immediate crystallization and a more protracted timescale of ∼100 Myr.
