Behavior Of Isotopes Research Articles

Mechanisms of magnesium isotope fractionation in volcanic soil weathering sequences, Guadeloupe

Magnesium (Mg) stable isotopes are increasingly used as a weathering proxy in soils and rivers, but the impact of the mineralogy of secondary phases on isotope fractionation remains obscure. A better understanding of the behaviour of Mg isotopes during weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone. Here we investigate isotopic variations in δ26Mg in bulk soils and clay fractions relative to their parent andesite in three soil weathering sequences from Guadeloupe formed under contrasting climatic conditions. Soils formed in drier conditions (low precipitation) contain smectite, whereas soils formed under wet conditions (high rainfall) are characterized by halloysite and Fe-oxides or kaolinite.All clay fractions have Mg isotopic compositions (δ26Mg −0.41‰ to −0.10‰) similar to or heavier than their parent andesite (δ26Mg −0.47‰) supporting the preferential incorporation of heavy Mg isotopes in secondary Mg-bearing clay minerals with the first direct measurements on clay fractions. Soils with lighter Mg isotope compositions have greater quantities of exchangeable Mg. The data support a contribution from sea spray to the exchangeable Mg pool correlated to the soil weathering degree. This study highlights for the first time that the soil δ26Mg not only depend on δ26Mg of the parent rock, and on any fractionation that might occur, but also on the Mg retention on the exchange complex, which could in turn be controlled by external inputs such as sea spray.

Lithium, magnesium and silicon isotope behaviour accompanying weathering in a basaltic soil and pore water profile in Iceland

This study presents lithium, magnesium and silicon isotope ratios from pore waters and soils from a well-characterised Histic Andosol in south-west Iceland. The soil δ7Li composition ranges between values slightly lighter than basalt, to those that are much heavier (−1.1‰ to +26.8‰), and are possibly influenced by sea salt. In contrast, precipitation-corrected dissolved (pore water) δ7Li values (1.8–10.0‰) appear to reflect preferential adsorption of 6Li onto secondary minerals, where allophane supersaturation results in high δ7Li values. Conversely low δ7Li together with high [Li] are probably due to destabilisation of allophane at low pH, and thus desorption of Li. When compared to Icelandic river values, it would appear that soil pore waters reflect an intermediate isotope composition between basalts and river waters. Precipitation corrected pore water Mg isotope ratios (δ26Mg) range between −0.46‰ and −0.12‰, and correlate with the amount of heavy Mg adsorbed onto the soil exchange complex. Silicon isotopes in the soils are isotopically lighter (δ30Si=−0.91‰ to −0.53‰) than basalt (−0.29‰), whereas pore waters are heavier (+0.13‰ to +1.03‰). Soil δ30Si values show a clear evolution between unweathered basalt and a hypothetical isotopically light endmember representing secondary minerals. Dissolved Si isotopes also respond to chemical weathering processes, and show that isotopically heavy δ30Si corresponds to high cation fluxes and high secondary mineral formation. However, comparison of all these proposed isotopic weathering tracers suggests that they respond differently to the same chemical weathering conditions. This indicates a differing behaviour during secondary mineral neoformation or adsorption depending on whether the incorporated element is a major or trace constituent. In turn, this behaviour can potentially yield important information on secondary mineral behaviour and destabilisation, and thus on the chemical weathering processes.

Deciphering the Trace Element Characteristics in Kilbourne Hole Peridotite Xenoliths: Melt–Rock Interaction and Metasomatism beneath the Rio Grande Rift, SW USA

Significant differences between bulk-rock lithophile trace element budgets and the sum of the contributions from the constituent minerals are common, if not ubiquitous, in peridotite xenoliths. Notwithstanding the possible contributions from fluid inclusions and grain-boundary glass and micro-phases, it is often difficult to reconcile the bulk-rock incompatible element budgets with those of the silicate phases. In the absence of modal metasomatism this discrepancy is often attributed to the ‘catch-all’yet often vague process of cryptic metasomatism.This study presents comprehensive petrological descriptions, major and trace element and Sr^Nd isotope data for variably metasomatized bulk-rock peridotites, host basalt, and constituent peridotite mineral phases from spinel lherzolite and harzburgite xenoliths from the Kilbourne Hole volcanic maar, New Mexico, USA. Similar measurements were also made on hand-picked interstitial glass from one of the most highly metasomatized samples in an attempt to unravel the sources, effects, and relative timings of multiple metasomatic events. Reaction textures around clinopyroxene grains are evident in the most metasomatized samples. These are accompanied by films of high-SiO2 interstitial glass, which is not in equilibrium with the primary silicate minerals. Trails of glassy melt inclusions terminate in these films against which the margins of the primary minerals appear partially resorbed. Furthermore, different styles of high field strength element fractionation [e.g. (Nb/Ta)N vs (Zr/Hf)N] are evident in the bulk-rocks and the clinopyroxenes that they host. In all of the Kilbourne Hole peridotites analysed, hand-picked, optically clean clinopyroxenes preserve a more unradiogenic Sr isotope signature than the corresponding bulk-rock. Hand-picked interstitial glass from KH03-16 reveals the most radiogenic Sr/Sr of any component recovered from these xenoliths (Sr/Sr1⁄4 0·708043 0·00009; [Sr]1⁄4 81ppm). Similarly, the Nd/Nd of the glass is amongst the most evolved of the peridotite components (Nd/Nd1⁄4 0·512893 0·000012; [Nd]1⁄4 10 ppm). However, the host basalt (Sr/Sr1⁄4 0·703953 0·00012; Nd/Nd1⁄4 0·512873 0·000013), similar in composition to that of the nearby, contemporaneous, Potrillo Volcanic Field basalts, contains nearly an order of magnitude more Sr and more than three times more Nd ([Sr]1⁄4 655 ppm; [Nd]1⁄4 34 ppm) than the interstitial glass. Despite the high Sr and Nd contents of the host basalt the evidence for basalt infiltration is scant, although the effects of melt^rock interaction, both in antiquity and more recently, are preserved in several xenoliths. Mixing between clinopyroxene and the host basalt cannot account for the full range of bulk-rock Sr^Nd isotope ratios; nearly half of the xenoliths require an additional component that could involve varying amounts of interstitial glass. In detail the behaviour of Sr and Nd isotopes has been decoupled,

Modeling radium distribution in coastal aquifers during sea level changes: The Dead Sea case

We present a new approach to studying the behavior of radium isotopes in a coastal aquifer. In order to simulate radium isotope distributions in the dynamic flow field of the Dead Sea aquifer, a multi-species density dependent flow model (SUTRA-MS) was used. Field data show that the activity of 226Ra decreases from 140 to 60dpm/L upon entering the aquifer from the Dead Sea, and then further decreases linearly due to mixing with Ra-poor fresh water. On the other hand, an increase is observed in the activity of the shorter-lived isotopes (up to 52dpm/L 224Ra and 31dpm/L 223Ra), which are relatively low in Dead Sea water (up to 2.5dpm/L 224Ra and 0.5dpm/L 223Ra). The activities of the short lived radium isotopes also decrease with decreasing salinity, which is due to the effect of salinity on the adsorption of radium. The relationship between 224Ra and salinity suggests that the adsorption partition coefficient (K) is linearly related to salinity. Simulations of the steady-state conditions, show that the distance where equilibrium activity is attained for each radium isotope is affected by the isotope half-life, K and the groundwater velocity, resulting in a longer distance for the long-lived radium isotopes. K affects the radium distribution in transient conditions, especially that of the long-lived radium isotopes. The transient conditions in the Dead Sea system, with a 1m/yr lake level drop, together with the radium field data, constrains K to be relatively low (<10). Thus, the sharp decrease in 226Ra cannot be explained by adsorption, and it is better explained by removal via coprecipitation, probably with barite or celestine.

A mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization

The process of coupled assimilation and fractional crystallization (AFC) is one of the most popular petrogenetic concepts that explains magmatic differentiation. Conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced; however, recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period, affecting the whole-rock composition in response to the intra-grain isotopic zoning. This study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization (AIFC) to describe the effects of suspended crystals on the path of magma evolution. The mass balance differential equations for the liquid and suspended crystals are solved simultaneously. The analytical solution of the AIFC equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals, liquid, and magma (crystals plus liquid). The chemical path of the magma differs markedly from that predicted by the conventional AFC model.

Hydrogen and oxygen isotope behaviors during variable degrees of upper mantle melting: Example from the basaltic glasses from Macquarie Island

We present measurements of hydrogen and oxygen isotopes in MORB glasses from Macquarie Island (SW. Pacific Ocean) coupled with determination of bulk H2O content by two independent techniques: total dehydration and FTIR. The incompatible trace elements in these glasses vary by a factor of 12 to 17, with K2O varying from 0.1 to 1.7wt.%; these ranges reflect a variable degree of closed-system mantle melting, estimated from 1 to 15%. Water concentrations determined by the two techniques match well, yielding a range from 0.25 to 1.49wt.% which correlates positively with all of the measured incompatible trace elements, suggesting that water is un-degassed, and behaves conservatively during mantle melting. Also, the agreement between the FTIR-determined and extracted water contents gives us confidence that the measured isotopic values of hydrogen reflect that of the mantle. Comparison of the range of water content with that of other incompatible trace elements allows estimation of the water partition coefficient in lherzolite, 0.0208 (ranging from 0.017 to 0.023), and the water content in the source, 386ppm (ranging from 370 to 440ppm). We observe a fairly narrow range in δD and δ18O values of −75.5±4.5‰ and 5.50±0.05‰ respectively, that can be explained by partial melting of normal lherzolitic mantle. The measured δD and δ18O values of Macquarie Island glasses that range from nepheline- to hypersthene-normative, and from MORB to EMORB in composition, are identical to those in average global MORB. The observed lack of variation of δD and δ18O with 1 to 15% degree of mantle melting is consistent with a bulk melting model of δD and δ18O fractionation, in which water is rapidly scavenged into the first partial melt. The narrow ranges of δD and δ18O in normal mantle are mostly due to the buffering effect of clino- and orthopyroxenes in the residual assemblage; additionally, fast “wet” diffusion of oxygen and hydrogen isotopes through the melting regions may further smooth isotopic differences.

Overview of the US–Japan collaborative investigation on hydrogen isotope retention in neutron-irradiated and ion-damaged tungsten

The effect of neutron-irradiation damage has been mainly simulated using high-energy ion bombardment. A recent MIT report (PSFC/RR-10-4, An assessment of the current data affecting tritium retention and its use to project towards T retention in ITER, Lipschultz et al., 2010) summarizes the observations from high-energy ion bombardment studies and illustrates the saturation trend in deuterium concentration due to damage from ion irradiation in tungsten and molybdenum above 1 displacement per atom (dpa). While this prior database of results is quite valuable for understanding the behavior of hydrogen isotopes in plasma facing components (PFCs), it does not encompass the full range of effects that must be considered in a practical fusion environment due to short penetration depth, damage gradient, high damage rate, and high primary knock-on atom (PKA) energy spectrum of the ion bombardment. In addition, neutrons change the elemental composition via transmutations, and create a high radiation environment inside PFCs, which influences the behavior of hydrogen isotope in PFCs, suggesting the utilization of fission reactors is necessary for neutron-irradiation. Under the framework of the US–Japan TITAN program, tungsten samples (99.99at.% purity from A.L.M.T. Co.) were irradiated by fission neutrons in the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL), at 50 and 300°C to 0.025, 0.3, and 2.4dpa, and the investigation of deuterium retention in neutron-irradiated tungsten was performed in the Tritium Plasma Experiment (TPE), the unique high-flux linear plasma facility that can handle tritium, beryllium and activated materials. This paper reports the recent results from the comparison of ion-damaged tungsten via various ion species (2.8MeV Fe2+, 20MeV W2+, and 700keV H−) with that from neutron-irradiated tungsten to identify the similarities and differences among them.

Sorption and desorption behavior of hydrogen isotopes from tungsten deposits caused by deuterium gas or deuterium plasma exposure

To understand the behavior of hydrogen isotopes in deposits formed on plasma-facing wall is an important issue for development of a fusion reactor. In this study, sorption/desorption behaviors of hydrogen isotopes when tungsten deposits were exposed to deuterium gas or deuterium plasma at 300°C were investigated. Samples of tungsten deposits were produced by the sputtering method using hydrogen plasma. After deuterium gas exposure or deuterium plasma exposure, the desorption behavior of hydrogen isotopes from the deposit was observed by the thermal desorption spectroscopy method. It was found that not a small amount of deuterium is retained in tungsten deposit by not only the plasma exposure but also the gas exposure while the amount of hydrogen incorporated in the deposit during sputter-deposition process is reduced. The amount of deuterium retained in the deposit by the plasma exposure was larger than that by the gas exposure in the experimental conditions in this work. The amount of hydrogen left after deuterium plasma exposure was larger than that after deuterium gas exposure.

The Effect of Electrically Charged Clouds on the Stable Nitrogen Isotope Ratio and the Anion Concentrations in Cloud-based Aerosols

It is very important to determine the stable nitrogen isotope ratio for the nitrogenous substances in aerosols and the geochemistry behavior of stable nitrate ion isotopes in aerosols in order to elucidate the chemical and physical functions of clouds. Hence, aerosol field sampling was conducted in the skies offshore from Malibu Beach and Santa Barbara, California, U.S.A. on 16 and 18 July 2009, using an airplane. The samples were analyzed for nitrate and nitrite ions using ion chromatography (IC) and GC-mass spectrometry (GC-MS). The results indicate a higher stable isotopic ratio of δ (delta) 15N/14N in the aerosols collected at the cloud top of one cloud than the aerosols collected from the cloud base of a second cloud at the same altitude (30.48 meters) on 18 July 2009. NO2 - nitrite ions were present only in the aerosols sampled at the cloud base. At the same altitude, the stable nitrogen isotope ratio in the nitrogenous substances found in the aerosol depended on the aerosol position within the clouds. Furthermore, the altitude effect was small for the isotope ratio. To date, no research has been published that explores the relationship between the electric charge of clouds or the atmosphere and the fate or transformation of aerosols. My investigation indicated that past models describing the fate or transformation of aerosols within clouds are not based on the actual details of the situation. This study showed that the fates of electrically charged aerosols or ionized aerosols were affected by the electrically charged cloud.

High temperature strontium stable isotope behaviour in the early solar system and planetary bodies

This study presents comprehensive strontium stable isotope (88Sr/86Sr) data, measured by multiple-collector inductively-coupled plasma mass spectrometry (MC–ICP-MS), for a suite of carbonaceous chondrites, differentiated meteorites, lunar, martian and terrestrial samples.Carbonaceous chondrites comprise a mixture of refractory inclusions and chondrules that have light δ88Sr values between −0.35 to +0.05‰ and matrix material that possesses a heavy δ88Sr composition of 0.65‰, confirming the results of earlier studies. Consequently, bulk carbonaceous chondrites are relatively heterogeneous in composition ranging from +0.12 to +0.35‰, most likely reflecting clast–matrix variability. The light δ88Sr compositions of the refractory inclusions are consistent with mass dependent fractionation of other refractory elements (Ca and Eu) and are most likely produced by non-equilibrium fractionation (undercooling in the nebula gas) during condensation of hibonite from the solar nebula (Simon and DePaolo, 2010. Stable calcium isotopic composition of meteorites and rocky planets. Earth Planet. Sci. Lett. 289, 457–466).Carbonaceous chondrites, angrites and martian meteorites have indistinguishable compositions at the level of analytical uncertainty of this study. However, statistical analysis indicates that melts derived from the Earth's mantle have heavier δ88Sr values than bulk carbonaceous chondrites and martian meteorites, but compositions indistinguishable from eucrites (δ88Sr=+0.26±0.12‰). Moreover, terrestrial basalts and andesites have restricted δ88Sr values (+0.30±0.07‰), suggesting that mantle melting delivers rather homogenous melts to the Earth's surface with respect to δ88Sr.In contrast, glasses from evolved terrestrial rocks and lunar basalts extend to very light δ88Sr values ~−0.20‰. The Sr stable isotope composition covaries with europium anomaly (Eu/Eu*), as an index of plagioclase fractionation, and δ88Sr can be successfully modelled by the heavy isotopes of Sr being preferentially partitioned into plagioclase with a fractionation factor of ~1.0007 for 88Sr/86Sr. Our results demonstrate that Sr stable isotopes may be significantly fractionated at high temperatures and their measurement can provide insights into planetary evolution and magmatic processes.

Behavior of stable isotopes of dissolved oxygen, dissolved inorganic carbon and nitrate in groundwater at a former wood treatment facility containing hydrocarbon contamination

Abstract The speciation and mobility of a variety of chemical species in groundwater are strongly influenced by redox and pH conditions. Dissolved O2 (DO) and dissolved inorganic C (DIC) concentrations are significant controls of these conditions, respectively. It is not always clear what the major processes are that influence changes in the concentration of DO and DIC across a groundwater flowpath. The combined use of the stable isotope compositions of DO (δ18O–DO) and DIC (δ13C–DIC) has the potential to help investigators discriminate between sources and sinks of DO and DIC in groundwater systems. A total of 31 monitoring wells were sampled to investigate changes in DO, DIC, δ18O–DO and δ13C–DIC in shallow groundwater at the Montana Pole and Treating Plant (MPTP), Butte, Montana, USA. The MPTP site contains significant quantities of petroleum hydrocarbons in soil and groundwater from historical operations as a wood treatment-preservative facility. Dissolved O2 concentrations decreased downgradient across the site (340–6.6 μmol L−1) while DIC concentration increased (3.6–12.8 mmol L−1). A general enrichment in δ18O–DO (16.8–31.6‰) and depletion in δ13C–DIC (−12.7‰ to −18.7‰) along the flowpath is consistent with aerobic microbial respiration. However, the correlation between δ18O–DO and δ13C–DIC was poor which may be caused in part by the remediation treatments being used to mitigate soil and groundwater contamination. The presence of an extensive suboxic zone near the center of the field area suggests that some DIC of unknown isotopic composition could have been added to the groundwater by anaerobic degradation of hydrocarbons. This idea is consistent with a limited amount of NO 3 - isotope data which suggest that denitrification is occurring at the MPTP site.

Process‐evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues: 1. Comparison between models and observations

The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground‐based remote‐sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope‐enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity.

Inference of riverine nitrogen processing from longitudinal and diel variation in dual nitrate isotopes

Longitudinal and diel measurements of dual isotope composition (δ15N and δ18O) in nitrate (NO3‐N) were made in the Ichetucknee River, a large (∼8 m3 s−1), entirely spring‐fed river in North Florida, to determine whether isotopic variation can deconvolve assimilatory and dissimilatory removal. Comparing nitrate concentrations and isotope composition during the day and night we predicted (1) daytime declines in total fractionation due to low assimilatory fractionation and (2) diurnal variation in dual isotope coupling between 1:1 (assimilation) and 2:1 (denitrification). Five daytime longitudinal transects comprising 10 sampling stations showed consistent NO3‐N removal (25–35% of inputs) and modest fractionation (15εtotal between −2 and −6‰, enriching the residual nitrate pool). Lower fractionation (by ∼1‰) during two nighttime transects, suggests higher fractionation due to assimilation than denitrification. Total fractionation was significantly negatively associated with discharge, input [NO3‐N], N mass removal, and fractional water loss. Despite well‐constrained mass balance estimates that denitrification dominated total N removal, isotope coupling was consistently 1:1, both for longitudinal and diel sampling. Hourly samples on two dates at the downstream location showed significant diel variation in concentration ([NO3‐N] amplitude = 60 to 90 μg N L−1) and isotope composition (δ15N amplitude = −0.7‰ to −1.6‰). Total fractionation differed between day and night only on one date but estimated assimilatory fractionation assuming constant denitrification was highly variable and implausibly large (for N, 15ε = −2 to −25‰), suggesting that fractionation and removal due to denitrification is not diurnally constant. Pronounced counterclockwise hysteresis in the relationship between [NO3‐N] andδ15N suggests diel variation in N isotope dynamics. Together, low fractionation, isotope versus concentration hysteresis, and consistent 1:1 isotope coupling suggests that denitrification is controlled by NO3− diffusion into the benthic sediments, the length of which is mediated by riverine oxygen dynamics. While using dual isotope behavior to deconvolve removal pathways was not possible, isotope measurements did yield valuable information about riverine N cycling and transformations.

Stable carbon isotope behaviour of natural seepage of deep underground 13C-rich methane detected along a fault zone and adsorbed in mudstone: Tokyo Bay area, Japan

Abstract Gas was sampled regionally, including by drilling into faults, in the South Kanto gas-field around Tokyo Bay, Japan. Gas samples were collected from cores in a gas sampling container immediately after drilling. A value of δ13C1 = −44.3‰ was obtained for gas in the container and δ13C1 = −36.3‰ for seeping gas in a fault zone. However, typical CH4 in this dissolved-in-water gas-field is mainly depleted in 13C, and δ13C1 values range from −66‰ to −68‰ owing to microbial degradation of organic material. 13C-rich CH4 is so far uncommon in the South Kanto gas-field. Seepages were observed from the surface along the north–south fault zone. The natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m. Gas seepages were not observed below a depth of 40 m. Gas rises along the fault zone dissolved-in-groundwater up to the shallow region and then separates from the groundwater. 13C-rich CH4 (adsorbed CH4) was found to have desorbed from drilled mudstone core samples taken at depths of 1400–1900 m in the main gas-production strata. Similarly, 13C-rich CH4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the Tokyo region. It also appears in the spring-water of spa wells, originating at a depth of 1200–1500 m along a tectonic line. Methane generated by microbial degradation of organic material through CO2 reduction in the South Kanto gas-field mainly originates as biogenic gas mixed with a small amount of 13C-rich CH4, derived from thermogenic gas without oil components in strata. It is assumed that 12C-rich CH4 is easily detached from core or pore water through gas production, whereas 13C-rich CH4 is strongly adsorbed on the surfaces of particles. The 13C-rich CH4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the Kanto region.

First-principles investigation on diffusion and permeation behaviors of hydrogen isotopes in molybdenum

We have investigated diffusion and permeation behaviors of hydrogen (H), deuterium (D), and tritium (T) in bulk molybdenum (Mo) by a first-principles calculations combined with simplified models. The H diffusion energy barrier with quantum correction is shown to be 0.12 eV, in good agreement with the value of 0.11 eV obtained from experiment. According to the diffusion theory presented by Wert and Zener, the diffusion coefficients of H, D and T are estimated, respectively. The H diffusion coefficient is found to be D = 1.27 × 10 - 7 exp ( - 0.12 eV / kT ) m 2 s - 1 , which is also basically consistent with the experiment. Permeability Φ can be approximately evaluated in terms of Φ = SD, where S and D are the solubility and the H diffusion coefficient, respectively. We found that H has the low solubility in bulk Mo, consistent with the results at the temperature from 900 K to 1500 K in the earlier experiment. The permeability of H isotopes are calculated to be one order of magnitude larger than those of the experimental values. Such discrepancy should stem from that the “defect-free” Mo in the present calculations is considered. The permeation flux of H isotopes are finally examined. At the temperature of 1200 K, the fluxes of H, D, and T are calculated to be 1.27 × 10 −6 mol m −2 s −1, 8.95 × 10 −7 mol m −2 s −1, and 7.30 × 10 −7 mol m −2 s −1, respectively.

Deuterium retention in Fe2O3 under low-energy deuterium-plasma exposure

Stainless steel (SUS) is used as the structure material in nuclear fusion devices. Heating and O2 plasma discharge are considered for the removal of tritium. Oxide layer growth is anticipated on heating SUS at a high temperature in low-pressure residual O2 gas. When O2 plasma discharge is performed, oxygen plasma reaches the structure material and iron oxides such as Fe2O3 are formed. Thus, a knowledge of the retention behavior of hydrogen isotopes or deuterium (D) in the oxide layers is important in designing the devices. We investigated D retention in Fe2O3 films and the influence of Fe2O3 crystal structure on D retention and found that D retention in γ-Fe2O3 (cubic-maghemite) is larger than that in α-Fe2O3 (hexagonal-hematite). The results for Fe2O3 are compared with those for SUS and Fe.

Iron isotope evidence for multistage melt–peridotite interactions in the lithospheric mantle of eastern China

Iron isotopic data of the Cenozoic alkaline basalts and peridotite xenoliths entrained in the Cenozoic and Mesozoic basalts, eastern China, are reported to further constrain the Fe isotopic composition of the mantle and investigate the behavior of Fe isotopes during mantle processes. Nine Cenozoic alkaline basalts show limited variation in δ 57Fe that are within the ranges of oceanic basalts, which indicate homogeneous Fe isotope composition of the basalts. The lherzolites from the South China Block also display a limited Fe isotopic variation δ 57Fe of 0.041 to 0.077‰ and an average of 0.060‰ ± 0.029‰ (2 SD). This Fe isotopic composition is similar to that of the bulk silicate Earth, indicating that these samples represent mantle residues that underwent just limited degrees of partial melting. In contrast, both the mantle peridotites and their mineral separates from the North China Craton exhibit an extremely large Fe isotopic variation with δ 57Fe ranging from − 1.002‰ to 0.232‰. This may reflect heterogeneous Fe isotopic compositions of the lithospheric mantle beneath the North China Craton. An average δ 57Fe (− 0.066‰) calculated from all the mantle xenoliths in this study is obviously lower than the average value (0.198‰) of δ 57Fe for the Cenozoic alkaline basalts, consistent with the previous observation that basalts generally have heavier Fe isotopes than mantle peridotites. In individual minerals, δ 57Fe of the olivines (− 0.997 to 0.154‰) are systematically lighter than those of the coexisting pyroxenes (− 0.718 to 0.169‰ for orthopyroxene and − 0.642 to 0.304‰ for clinopyroxene, respectively). Phlogopite of apparently metasomatic origin has the heaviest iron isotopic composition amongst the mineral phases with δ 57Fe of 0.302 to 0.376‰. Extreme Fe isotope variation in these peridotites, in particular for the wehrlites, was probably produced by multistage melt–peridotite interactions, consistent with the petrological observation that some of the xenoliths analyzed such as wehrlites were the products of extensive mantle metasomatism. Positive correlations between δ 57Fe and other major and trace element indicators of metasomatism such as CaO and Rb further support the above suggestion. These characteristics suggest that mantle metasomatism or melt–rock interaction can significantly modify Fe isotopes and play an important role in producing Fe isotopic heterogeneity of the lithospheric mantle. Thus, Fe isotopes can provide important information concerning melt–rock interaction and evolution of the lithospheric mantle.

Gas chromatographic separation of hydrogen isotopes on columns packed with alumina, modified alumina and sol–gel alumina

The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T(2) in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T(2) at 77K temperature with different retention times. The retention times on SiO(2) coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T(2) at 240 K. The peaks were well resolved in less than 5 min on this column.

Development of Monte Carlo Simulation Code to Model Behavior of Hydrogen Isotopes Loaded into Tungsten Containing Vacancies

The behavior of hydrogen isotopes implanted into tungsten containing vacancies was simulated using a Monte Carlo technique. The correlations between the distribution of implanted deuterium and fluence, trap density and trap distribution were evaluated. Throughout the present study, qualitatively understandable results were obtained. In order to improve the precision of the model and obtain quantitatively reliable results, it is necessary to deal with the following subjects: (1) how to balance long-time irradiation processes with a rapid diffusion process, (2) how to prevent unrealistic accumulation of hydrogen, and (3) how to model the release of hydrogen forcibly loaded into a region where hydrogen densely exist already.

Conductance Characteristics of Hydrogen Isotopes between Viscous and Molecular Flow Regions in Spherical Pellet Packed-Beds at 77.4 K

We have been studying the dynamic behavior of hydrogen isotopes flowing between viscous and molecular regions in an adsorbent packed-bed column, for the purpose of developing a pressure swing adsorption (PSA) process system for hydrogen isotope separation. This PSA system consists of adsorption, evacuating desorption and hydrogen replenishing processes. The kinetics in the adsorption process has been becoming to be predictable in theoretical simulation based on experimental results, but it is difficult as yet to simulate the dynamic behaviors in evaluating and replenishing processes because of the complicated geometry of passages in a packed-bed and the change of gas flow patterns between viscous and molecular regions depending on not only the pressure but also the dimension of passages. In the dynamics, the important factor should be known is the mass flow conductance in pellet packed-bed. In this work, we carried out the experiment for examining the dependence of the conductance on the diameter of particles packed in a column, since the geometrical and dimensional conditions of passages are affected by the size of packing pellets. From the experimental result and its analysis, we clarified the pressure and particle-size dependences of the conductance of hydrogen isotopes in spherical pellet packed-beds.