Behavior Of Isotopes Research Articles

Residual oil as a tool in migration and filling history analysis of petroleum reservoirs, Ghazal Field, Saudi Arabia

Stepwise extraction and molecular analysis of non-recoverable oil from intact reservoir core plugs is used to provide constraints on the accumulation history of petroleum in the Permo-Carboniferous Unayzah reservoirs at the Ghazal Field, Saudi Arabia. When integrated with existing tools such as oil geochemistry, gas geochemistry, stable carbon isotopes, fluid inclusions and thermal modeling, the sequential extraction approach helped decode a previously unrecognized component of the hydrocarbon accumulation history. In particular, it indicates that the region received early petroleum charges that were less mature than currently produced light oil and gas condensates, possibly from the prolific Early Silurian Qusaiba shale source rock and other sources. This has significant implications for prospecting for additional oil, particularly in the north/northwest of the Ghazal region where paleo-oil accumulations may have been displaced or spilled. The lower portion of the Unayzah reservoir (Unayzah-C) remained water-wet during early filling of the upper reservoir unit (Unayzah-A) and appears to have been filled only by a late oil charge. Anomalous molecular and carbon isotopic behavior of residual oil extracts from the uppermost segment of the Unayzah reservoir, where the free oil (first of the sequential extracts) is less mature (0.95% Rc) and isotopically lighter (δ 13C−31.15‰) than the adsorbed oil (last sequential extract, 1.05% Rc; δ 13C−29.65‰), suggests a late oil contribution or bitumen contamination from the overlying Khuff Formation.

Towards a metabolic and isotopic steady state in CHO batch cultures for reliable isotope‐based metabolic profiling

Attaining metabolic and isotopic balanced growth is one critical condition for physiological studies using isotope-labeled tracers, but is very difficult to obtain in batch culture due to the extensive metabolite exchange with the surrounding medium and related physiological changes. In the present study, we investigated metabolic and isotopic behavior of CHO cells in differently designed media. We observed that the assumption of balanced cell growth cannot be justified in batch culture of CHO cells directly using conventional, commercially available media. By systematically redesigning media composition and characterizing metabolic steady state based on mass balances and measurement of labeling dynamics, we achieved balanced cell growth for the main cellular substrates in CHO cells. This was done in a step-by-step analysis of growth and primary metabolism of CHO cells with the use of [U-13C]glucose feeding and adjusting concentrations of amino acids in the growth medium. The optimized media obtained at the end of the study provide balanced growth and isotopic steady state or at least asymptotic steady state. As a result, we established a platform to conduct isotope-based physiological studies of mammalian systems more reliably and therefore well suited for later use in metabolic profiling of mammalian systems such as 13C-labeled metabolic flux analysis.

Thermal stress assessment using carbon and oxygen isotopes from Scleractinia, Rocas Atoll, northeastern Brazil

More than 430 C and O isotope analyses were carried out on carbonates from six coral species collected during June 1995, July 1998 and February 1999 at Rocas atoll, offshore northeastern Brazil: Siderastrea stellata Verrill 1868, Porites branneri Rathbum 1887, Porites astreoides Lamarck 1816, Mussismilia hispida Verrill 1902, Madracis decactis Lyman 1859 and Montastrea cavernosa Linnaeus 1886. Samples were collected in pools within the ring of the atoll, at water depths from 1.0 to 7.0 m. Oxygen isotope chemistry demonstrated that the studied species experienced several periods of bleaching; calculated temperature for one species vary, suggesting important changes within the time scale of coral growth. The species P. branneri, P. astreoides, M. cavernosa and the Brazilian endemic species M. hispida registered temperature variations during coral growth more accurately than did S. stellata and M. decactis. Carbon isotope behaviour in coral skeletons of the species examined at this atoll seems to have maintained a close relationship between density and/or zooxanthelar productivity: the greater the algal density, the heavier the δ13C values in skeletons.

Extraction behavior of short-lived isotopes of Mo/W using α-benzoinoxime: A model system for the study of seaborgium

The liquid-liquid extraction behavior of short-lived molybdenum and tungsten isotopes from HCl and HNO 3 as well as HF/HNO 3 acid media was studied using the α-benzoinoxime/chloroform system. The goal of the present experiments was to find an extraction system with a high selectivity for the group 6 elements in the periodic table which is suitable for the study the solution chemistry of seaborgium ( Z =106). It was found that Mo and W are both effectively extracted using α-benzoinoxime as an extractant and the maximum extraction yield is 100% and 94% for Mo and W, respectively. Ions of MO 2 2+ (M=Mo, W) exist in HCl between the concentration range of 0.1−3 M and can be extracted quantitatively into the organic phase. The decrease of extraction yields at lower or higher acid concentration is due to the formation of anionic species MO 4 2- or MO 2 Cl 3 - . The extraction behavior of Mo and W in HNO 3 solution is similar to that in HCl solution. In HNO 3 /HF mixed acid solutions, due to the formation of MO 2 F 3 - a decrease of extraction yield at higher HF concentration, similar to the case of HCl is observed. The extraction equilibrium is reached within 10−30 s, which means the extraction kinetics of α-benzoinoxime/chloroform extraction system is fast enough for the study of the isotope 265 Sg. The extraction behavior of molybdenum and tungsten shows a distinct difference in the range of 0.05 to 0.2 M HF with 1 M HNO 3 . This shows that differences in the complexation with fluoride ion exist in Mo and W. This study focuses on the investigation of the tendency of group 6 element for complexation with fluoride ion.

Chemical behavior of hydrogen isotopes into boronized film in LHD

In D-T fusion experimental devices, it is expected that oxygen and carbon could be contained as impurities in boron film produced by boronization. The chemical behavior of hydrogen isotopes implanted into boron films prepared in LHD at NIFS was studied by comparing the LHD sample with the P-CVD samples prepared at Shizuoka University. The LHD sample formed B–D–B, B–D, B–C–D and B–O–D bonds by D 2 + implantation. B–C–D and B–O–D bonds were mainly formed by the reaction of B–C and B–O bond with implanted D 2 + , and C–C bond and free oxygen were mainly formed the hydrocarbon and water during D 2 + implantation. It was suggested that the total D retention of the LHD sample was slightly larger than that of only the carbon- or oxygen-containing boron sample prepared by P-CVD. This could be largely affected to the amount of C–C bond and free oxygen which formed the hydrocarbon and water.

Stable isotope ( δ18O, δD, δ37Cl) evidence for multiple fluid histories in mid-Atlantic abyssal peridotites (ODP Leg 209)

Serpentinized abyssal peridotites sampled by the Ocean Drilling Program Leg 209 along the mid-Atlantic Ridge near the 15°20′N Fracture Zone have been analyzed for oxygen, hydrogen, and chlorine isotope compositions in order to determine isotopic behavior under a wide range of serpentinization conditions and place constraints on fluid history. Oxygen and hydrogen thermometry suggests peak serpentinization temperatures of 300–500 °C. Serpentine separates have low δD values possibly due to a magmatic fluid component or low-temperature exchange during seafloor weathering. Chlorine geochemistry focused on three holes: 1274A and 1272A (serpentinized peridotites) and 1268A (serpentinite locally altered to talc). Concentrations of both, water-soluble chloride (WSC) and structurally bound chloride (SBC) are significantly lower at Hole 1268A compared to Holes 1274A and 1272A. The δ 37Cl values for WSC and SBC of serpentinites in Holes 1274A and 1272A are slightly positive (avg. WSC = 0.20‰, n = 22 and avg. SBC = 0.35‰, n = 22), representing typical seawater-hydration conditions commonly determined for abyssal peridotite. The SBC of serpentinites from Hole 1268A are also positive (avg. = 0.63‰); whereas, the SBC in talc-dominated samples is negative (avg. = − 1.22‰). The WSC of both talc- and serpentine-dominated samples are also negative (avg. = − 0.15‰). We interpret the chlorine isotope data to preserve a record of multiple fluid events. As seawater hydrated the peridotite, 37Cl was preferentially incorporated into the forming serpentine and water-soluble salts, yielding similar δ 37Cl values on a regional scale as sampled by Holes 1268A, 1274A and 1272A. The resultant pore fluid was left depleted in 37Cl. Locally (Hole 1268A), this evolved fluid was remobilized possibly due to the initiation of hydrothermal circulation in response to emplacement of a mafic magma body. The low δ 37Cl pore fluids attained elevated SiO 2 and sulfur concentrations due to interaction with the gabbroic intrusion and, when ascending through the surrounding serpentinite, caused formation of isotopically negative talc. This secondary fluid also flushed the preserved serpentinite of its previously formed salts, resulting in negative δ 37Cl WSC values. The δ 37Cl SBC values of the serpentinite samples remained unmodified by reaction with the secondary fluid.

Isotopic Evolution of Saline Lakes in the Low-Latitude and Polar Regions

Isotopic fractionations associated with two primary processes (evaporation and freezing of water) are discussed, which are responsible for the formation and evolution of saline lakes in deserts from both low-latitude and the Polar regions. In an evaporative system, atmospheric parameters (humidity and isotopic composition of water vapor) have strong influence on the isotopic behavior of saline lakes, and in a freezing system, salinity build-up largely controls the extent of freezing and associated isotope fractionation. In both systems, salinity has a direct impact on the isotopic evolution of saline lakes. It is proposed that a steady-state “terminal lake” model with short-term hydrologic and environmental perturbations can serve as a useful framework for investigating both evaporative and freezing processes of perennial saline lakes. Through re-assessment of own work and literature data for saline lakes, it was demonstrated that effective uses of the isotope activity compositions of brines and salinity-chemistry data could reveal dynamic changes and evolution in the isotopic compositions of saline lakes in response to hydrologic and environmental changes. The residence time of isotopic water molecules in lakes determines the nature of responses in the isotopic compositions following perturbations in the water and isotope balances (e.g., dilution by inflow, water deficit by increased evaporation, and/or reduction in inflow). The isotopic profiles of some saline lakes from the Polar regions show that they switched the two contrasting modes of operation between evaporative and freezing systems, in response to climate and hydrological changes in the past.

210Pb–226Ra–230Th systematics in very low sedimentation rate sediments from the Mendeleev Ridge (Arctic Ocean)This article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network.GEOTOP Publication 2008-0031.

U-series isotope behaviour in subsurface sediment of the Arctic Ocean is investigated based on high resolution measurements of natural radionuclides (210Pb, 226Ra, 230Th) and a few analyses of anthropogenic 137Cs in cores collected during the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX). Cores from the Mendeleev Ridge, representing distinct bathymetric settings, are analyzed in more detail as a means to assess the dating potential of such radionuclides at sites characterized by very low sedimentation rates (∼3 mm ka–1). The sediment consists of variable proportions of fine-grained carbonates, clays, and ice-rafted debris and shows excesses in 210Pb (210Pbxs) over parent 226Ra content, down to ∼1 cm below core top. This 210Pbxs distribution is due to shallow mixing by benthic organisms and (or) diffusion from the sediment–water interface, as also indicated by 137Cs activities. From ∼1 to 7 cm downcore, 210Pb activities closely follow 226Ra activities. Below 7 cm downcore, 226Ra activities are controlled by variable excesses in parent 230Th (230Thxs) resulting from its scavenging in the overlying water column. 226Ra diffusion is observed towards the water column occuring from the upper ∼7 cm of sediment below the seafloor (with a flux of ∼0.043 disintegrations per minute (dpm) cm–2 a–1) and deeper in the sediment below 230Thxs peaks but with lesser fluxes. Both cores show identical 210Pb profiles despite their 1 km bathymetric difference. This suggests negligible 230Th and 210Pb scavenging below water depths of ∼1.6 km, i.e., the bathymetry of the shallower core. In such settings where sedimentation rates are very low and vertical particle rain is the major sediment source, estimates of the actual 210Pbxs require precise knowledge of the 226Ra-supported fraction, which is controlled by 230Thxs, Ra diffusion, and thus sedimentation rates and porosity.

The influence of weathering processes on riverine magnesium isotopes in a basaltic terrain

This study presents major-, trace-element and Mg isotope data for the dissolved load and suspended particulates of Icelandic rivers draining dominantly basaltic catchments, including both glacier-fed and direct-runoff rivers. These samples provide the opportunity to understand the behaviour of Mg isotopes during chemical weathering, where variations due to lithology are not extant. Given the significant role of Mg in the carbon cycle, such variations may provide important information on the regulation of Earth's climate. Hydrothermal waters, groundwater, precipitation (glacial ice), basalt glass, olivine and representative soils have also been analysed. The dissolved load shows a wide range of δ 26Mg compositions, compared to the parent basaltic glass ( δ 26Mg = − 0.29‰), ranging from − 0.96 to + 0.64‰, while precipitation and hydrothermal waters possess δ 26Mg values of − 0.83‰ and + 0.85‰, respectively, with lower Mg concentrations than the dissolved load. Biomass activity in vegetation and organic material in soils and rivers (colloids) appear to have little effect on the Mg isotope compositions. Rather, the data suggest that Mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions. In some samples seawater, in the form of direct precipitation or glacial runoff, also appears to be an important source of Mg. Glacier-fed rivers, groundwaters, and some direct-runoff rivers, with a high pH, have higher δ 26Mg than basalt, which is most likely due to the incorporation of light Mg isotopes in secondary minerals. In contrast, those direct-runoff rivers which have a relatively low pH, have low δ 26Mg (relative to basalt), consistent with preferential incorporation of heavy Mg isotopes into secondary phases, although it is not possible to rule out some contribution from precipitation. Riverine suspended particulates are depleted in mobile elements, and have δ 26Mg compositions values both higher and lower than unweathered basalt. In the glacier-fed and direct-runoff rivers where the δ 26Mg of the dissolved phase is heavy, due to the formation of secondary phases, the suspended load is light, because it contains more of those phases. The opposite is true for the remainder of the direct-runoff rivers which have low pH. This could be due to dissolution of secondary minerals, enriched in light Mg, which are unstable at low pH, or the formation of new secondary phases.

Monte Carlo Simulation on Permeation of Hydrogen Isotopes Through bcc Fe

A code to model permeation behavior of hydrogen isotopes through bcc Fe was developed by means of a Monte Carlo technique. This code enables correlation of atomic-scale information such as diffusion barrier or adsorption energy with macroscopic quantities such as solubility or permeability. Model parameters were derived from results of ab initio calculations in density function theory. To validate the code, both temperaturedependent permeability and pressure-dependent solubility for hydrogen were evaluated. Simulation results provided reasonable permeability and solubility compared with experimental data, and adequately showed their temperature/pressure dependence.

Breakthrough Curve Analysis of Pressure Swing Adsorption for Hydrogen Isotope Separation

For the purpose of developing an effective system for hydrogen isotope separation, we have been studying the adsorption-desorption dynamic behavior of hydrogen and deuterium in a packed-bed column with synthetic zeolites, aimed at applying the pressure swing adsorption process. The adsorption behavior of molecules in the packed-bed is reflected in the breakthrough curves. To understand the characteristic behaviors of hydrogen isotopes in the packed-bed, we carried out breakthrough experiments in a conventional adsorption process and in a practical process following sequential processes alternating between adsorption and desorption. From the former experiments, the results were obtained that the overall mass transfer was influenced by longitudinal dispersion relating to the superficial velocity and that the process governing the mass transfer within adsorbents was diffusion in the macro-pores of pellets. In the latter experiments, unique profile breakthrough curves were observed. These curves can be described with the numerical simulation assuming the initial distributions in a packed-bed.

Stable carbon and oxygen isotope investigation in historical lime mortar and plaster – Results from field and experimental study

Abstract Lime mortar and plaster were sampled from Roman, medieval and early modern buildings in Styria. The historical lime mortar and plaster consist of calcite formed in the matrix during setting and various aggregates. The stable C and O isotopic composition of the calcite matrix was analyzed to get knowledge about the environmental conditions during calcite formation. The δ 13 C matrix and δ 18 O matrix values range from −31 to 0‰ and −26 to −3‰(VPDB), respectively. Obviously, such a range of isotope values does not represent the local natural limestone assumed to be used for producing the mortar and plaster. In an ideal case, the calcite matrix in lime mortar and plaster is isotopically lighter in the exterior vs. the interior mortar layer according to the relationship δ 18 O matrix = 0.61 · δ 13 C matrix − 3.3 (VPDB). Calcite precipitation by uptake of gaseous CO 2 into alkaline Ca(OH) 2 solutions shows a similar relationship, δ 18 O calcite = 0.67 · δ 13 C calcite − 6.4 (VPDB). Both relationships indicate that the 13 C/ 12 C and 18 O/ 16 O values of the calcite reflect the setting behaviour of the lime mortar and plaster. Initially, CO 2 from the atmosphere is fixed as calcite, which is accompanied by kinetic isotope fractionation mostly due to the hydroxylation of CO 2 ( δ 13 C matrix ≈ −25‰ and δ 18 O matrix ≈ −20‰). As calcite formation continued the remaining gaseous CO 2 is subsequently enriched in 13 C and 18 O causing later formed calcite to be isotopically heavier along the setting path in the matrix. Deviations from such an ideal isotopic behaviour may be due to the evolution of H 2 O, e.g. evaporation, the source of CO 2 , e.g. from biogenic origin, relicts of the natural limestone, and secondary effects, such as recrystallization of calcite. The results of the field and experimental study suggest that isotope values can be used as overall proxies to decipher the origin of carbonate and the formation conditions of calcite in the matrix of ancient and recent lime mortar and plaster. Moreover, these proxies can be used to select calcite matrix from historical lime mortar and plaster for 14 C dating.

Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in 11B relative to 10B (δ 11B = −1.2 to +7.7) and 7Li relative to 6Li (δ 7Li = −1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (δ 11B = −16.6 to −2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle.

Uranium series disequilibria in ground waters from a fractured bedrock aquifer (Morungaba Granitoids—Southern Brazil): Implications to the hydrochemical behavior of dissolved U and Ra

Activity concentrations of dissolved 234U, 238U, 226Ra and 228Ra were determined in ground waters from two deep wells drilled in Morungaba Granitoids (Southern Brazil). Sampling was done monthly for little longer than 1 year. Significant disequilibrium between 238U, 234U and 226Ra were observed in all samples. The variation of 238U and 234U activity concentrations and 234U/ 238U activity ratios is related to seasonal changes. Although the distance between the two wells is short (about 900 m), systematic differences of activity concentrations of U isotopes, as well as of 234U/ 238U, 226Ra/ 234U and 228Ra/ 226Ra activity ratios were noticed, indicating distinct host rock–water interactions. Slightly acidic ground water percolation through heterogeneous host rock, associated with different recharge processes, may explain uranium and radium isotope behavior.

Micro-scale variations of iron isotopes in fossilized microorganisms

AbstractLaser-ablation inductively coupled plasma mass spectroscopy analyses have been performed on carbonaceous filamentous structures that have been interpreted as fossilized microorganisms containing ~10–50 wt% Fe and on non-carbonaceous filamentous structures that have been interpreted to have been formed abiotically containing ~80 wt% Fe. The obtained laser-ablation profiles of the two structural types show a distinct difference in the iron isotopic variations. The centers of the carbonaceous filaments are enriched in 57Fe and 58Fe and depleted in 56Fe. The surficial parts of the filaments display an opposite behavior of the iron isotopes and are thus enriched in 56Fe and depleted in 57Fe and 58Fe. 54Fe usually follows 57Fe and 58Fe but in some cases it follows 56Fe instead. The outer, surficial parts enriched in 56Fe have been interpreted as iron oxides precipitated on the surfaces of the microorganisms as they mediate oxidation of the iron to achieve metabolic energy. The laser-ablation profiles of the abiotically formed non-carbonaceous filamentous structures do not show the same characteristics as the carbonaceous filaments but only irregular elevations of 56Fe. The characteristic profile patterns of the isotope variations in the microfossils suggest that microbially formed iron oxides may be enriched in 56Fe. If that is the case the isotopic profiles could be used to distinguish abiotically formed iron oxides from biologically formed oxides.

Permeation selectivity of gaseous isotopes through dense polymers: Peculiar behavior of the hydrogen isotopes

The small but significant difference in permeation rates of gaseous isotopes through dense polymers has been previously reported in several studies. Most results remain, however, restricted to hydrogen isotopes. In this study, the steady-state permeation selectivity of a series of seven different gaseous isotopes pairs (D/H, 13C/ 12C, 15N/ 14N, 18O/ 16O, 17O/ 16O, and 36Ar/ 40Ar), covering a broad range of molecular weights (H 2, N 2, Ar, O 2, and CO 2), has been investigated through two dense polymeric structures (PDMS and PTFE). It is shown that, with the notable exception of the H 2/HD pair, isotope permeation selectivity can be described for each polymer type through a single expression as a function of the relative molecular weight difference. We show, for the first time, that this behavior is consistent with Frisch and Rogers (1964) model. More interestingly, it suggests that the peculiarities of the H 2/D 2 pair, such as the high-relative mass difference or small size, may explain the inadequacy of the gas in a box quantum approach for this case.

Prospects and problems of using the methods of geochemistry of stable carbon isotopes in soil studies

A review of world investigations into the geochemistry of stable isotopes—a new area for soil science—is presented. Studies of the behavior of stable isotopes in soils are being developed in two major directions: reconstruction of the environmental conditions and indication of the soil processes. Investigations into the reconstruction of the environmental conditions are based on the assumption that the isotopic composition of carbon in the soil humus is inherited from and reflects the isotopic composition of carbon in the corresponding vegetation (the source of soil humus). At the same time, studies into the indication of soil processes are based on the effects of fractionation of carbon isotopes in the course of transformation of carbon compounds. In this case, the isotopic composition of carbon in the soil humus should differ from that in the initial plant material. The analysis of available data suggests that the current state of research does not allow assessing the entire diversity of the effects of isotopic fractionation in soils. New data on the isotopic composition of carbon of soil organic matter and carbonates are being actively accumulated at present. However, it is obvious that the effect of isotopic fractionation should be taken into account in the paleoenvironmental and paleoclimatic reconstructions.

Carbon and hydrogen isotopic fractionation of low molecular weight organic compounds during ultraviolet degradation

Ultraviolet (UV) radiation is a ubiquitous energy source for chemical reactions in nature. In particular, UV radiation provides an important pathway for degradation of organic compounds. Although isotopic change in organic compounds exposed to UV radiation may be an indicator for evaluating the extent of degradation, the isotope behavior has not been yet clarified. In this study, stable carbon and hydrogen isotope fractionations were determined for volatile organic compounds including methanol, acetonitrile, benzene and propionic acid during UV degradation in order to reveal the isotopic behavior with respect to different functional groups. All the studied compounds became enriched in 13C and D with increase in UV exposure time. The isotopic fractionation factor ( α) ranged from 0.9968 to 0.9875 for carbon, and from 0.9890 to 0.9406 for hydrogen. The order of carbon isotopic fractionation was different from that of hydrogen isotopic fractionation, probably due to intra- and inter-molecular reactions with different functional groups. UV degradation is a process potentially able to induce isotope enrichment in organic compounds in natural environments.

Helium Implantation Effects on Retention Behavior of Hydrogen Isotopes in Oxygen-Contained Boron Films

He+ implantation effects on the Retention behavior of hydrogen isotopes implanted into 35% oxygen-contained boron film was studied by means of SEM, AFM, XPS and TDS. It was found that the D retention for only D2+ implanted film was the highest and it decreased for pre-He+ implanted film and post-He+ implanted film. From the SEM and AFM images, the surface morphology of the oxygen-contained boron film was partly cracked, indicating that B2O3 was formed in the film. From the TDS and XPS results, the defective structure and the formation of B-D-B bond, B-D bond and B-O-D bond were observed by He+ and D2+ implantation, respectively. It was suggested that oxygen was trapped as B-O bond. The reaction with implanted D2+ was preceded in different mechanism.

Iron Isotope Fractionation during Pedogenesis in Redoximorphic Soils

Stable Fe isotopes provide a potential new tool for tracing the biogeochemical cycle of Fe in soils. Iron isotope ratios in two redoximorphic soils were measured by multicollector inductively coupled plasma mass spectrometry to study the relationships between pedogenic Fe transformation and redistribution processes, and mass‐dependent fractionation of Fe isotopes. Redoximorphic Fe depletion and enrichment zones were sampled in addition to the bulk soil samples. A three‐step sequential extraction procedure was used to separate different Fe pools, which were examined in addition to total soil digests. Significant enrichments of heavy Fe isotopes of about 0.3‰ in δ57Fe were found in total soil digests of Fe‐depleted zones compared with bulk soil samples and were explained by the preferential removal of light isotopes, presumably during microbially mediated Fe oxide dissolution under anoxic conditions. Accordingly, pedogenic Fe enrichment zones were found to be slightly enriched in light Fe isotopes. Distinct Fe isotope variations of >1‰ in δ57Fe were found between different Fe pools within soil samples, specifically enrichments of light isotopes in pedogenic oxides contrasting with heavy isotope signatures of residual silicate‐bound Fe. Our data demonstrate that pedogenic Fe transformations in redoximorphic soils are linked to isotope fractionation, revealing greater mobility of lighter Fe isotopes compared with heavier isotopes during pedogenesis. No simple quantitative relationship between Fe depletion and isotope fractionation could be inferred, however. Our findings provide new insights into the behavior of Fe isotopes in soils and contribute to the development of Fe isotopes as a tracer for the biogeochemical Fe cycle.