Oxygen Isotope 18O Research Articles

Isotope effect on superconductivity and Raman phonons of Pyrochlore Cd2Re2O7

Cd2Re2O7 is the only α-Pyrochlore exhibiting superconductivity with a transition temperature (Tc) of ∼ 1 K. In this study, we present the effect of oxygen isotope (18O) as well as combined 18O and cadmium isotope (116Cd) substitution on the superconductivity and Raman scattering spectrum of Cd2Re2O7. The change of Tc and the energy gap Δ(T) are reported using various techniques including point contact spectroscopy. The shift in Raman phonon frequencies upon isotope substitution will be compared with measurement of the isotope effect on the superconducting transition temperature.

New CO2 Concentration Predictions and Spectral Estimation Applied to the Vostok Ice Core

The Vostok ice core provides measurements of the CO2 concentration during the last $414\times 10^{3}$ years (yr). Estimations of power spectra show peaks, with the strongest one corresponding to a time period of around $100\times 10^{3}$ yr. In this paper, a new reconstruction method from irregular sampling is used, allowing more accurate estimation of spectral peaks. This method intrinsically decomposes the analyzed signal as a sum of sines, providing amplitudes but also phase measurements of periodic tendencies (due to the nature of the studied phenomena). This decomposition can be conducted with noisy and inaccurate measurements of the sampling instants and the concentrations. The widely used Vostok data were chosen as an example, but the method could also be applied to data from other places (e.g., dome C, Antarctica) or to study other phenomena as nitrogen dioxide NO2, methane CH4, oxygen isotope 18O (closely linked to temperature), deuterium 2H, or dust concentrations.

Applicability of ToF-SIMS and stable oxygen isotopes in KCl-induced corrosion studies at high temperatures

The applicability of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) in combination with the use of stable oxygen isotopes (16O and 18O) in high-temperature corrosion research was addressed in this study. In terms of the corrosion reaction timescale, the focus was on the initiation of KCl-induced high-temperature corrosion and on the behaviour of three commercial alloys under conditions where multiple oxygen sources (air and water vapour) were present.ToF-SIMS proved to be an applicable tool in high-temperature corrosion studies, in this case, providing detailed information about the distribution of the two oxygen isotopes at the sample surfaces. Oxygen from air prefers to form a solid intermediate, potassium chromate (K2CrO4), when reacting with a chromia-forming alloy, whereas oxygen from both sources was found in the oxide formed at the alloy surface. Regardless of the prevailing conditions, the nickel-based austenitic alloy withstood corrosion the best, then the iron-based high alloy austenitic steel, whereas the low alloy ferritic steel had the poorest corrosion resistance ability.

An isotope method to quantify soil evaporation and evaluate water vapor movement under plastic film mulch

Plastic film mulch is a cropping system feature for water saving that is used extensively in arid and semiarid areas. However, research on water flow beneath and through the perforated film mulches is still limited, and the detailed processes of vaporization and transport of evaporation vapor in the soil are not examined thoroughly. Here we used an isotope-based method to quantitatively describe the processes of the soil water and vapor exchange in a maize field under plastic mulch. Micro-lysimeter-based methods and sap flow combined with soil water balance method (E(F-B)) were conducted to compare and verify the results. It shows that heavy oxygen isotope (18O) depleted and enriched alternately along with the processes of condensation and distillation, and enriched again when the second evaporation occurred in condensation water adhered in plastic film. Soil evaporating front was presented in 5–10cm soil layer, and the exchange motions of water vapor occurred in 0–5cm soil layer before it diffused to the outside. During the whole maize growing season, about 4.5% of soil water in the 0–20cm soil layer was evaporated, and 72.6% of the evaporation vapor was condensed and 70.0% of this condensation water was evaporated again. About 2.3% of soil water evaporated through plastic film holes, with the mean evaporation rate of 0.80mm/d. A good agreement was found between the evaporation determined by our isotope-based method (E(Iso)) and (E(F-B)) method. The evaporation rate was relatively high with the ratio of E to ET around 21.2%, although the areas of the holes only taking up 0.5–5.0% of the whole area of the plastic cover. Therefore, the isotope-based method was robust in estimating evaporation under plastic film mulch. These quantitative analyses will improve our understanding of the mechanism of soil water movement and vapor exchange under plastic mulch and provide accurate estimation of evaporation in field.

Project of the borehole neutron generator for the direct determination of oxygen and carbon by activation method

The paper deals with application features of borehole neutron generator (BNG) based on the vacuum accelerating tube (AT) with laser-plasma ion source for determination of oxygen isotope 16O and carbon isotope 12C by direct activation. The project of pulsed BNG for realization of an activation method in the conditions of natural presence of productive hydrocarbons is offered. The diode system with radial acceleration, magnetic electron insulation and laser-plasma source of deuterons at the anode in a sealed-off vacuum accelerating tube is applied. The permanent NdFeB magnet with induction about 0.5 T for produce the insulating magnetic field in the diode gap is proposed. In the experiments on the model of BNG with the accelerating voltage source (≈350 kV), performed by the scheme of Arkadiev-Marx generator, the output of (d, d) neutrons was ∼107 pulse-1.

Mass-independent fractionation of oxygen isotopes during H2O2 formation by gas-phase discharge from water vapour

Hydrogen peroxide is an important atmospheric component involved in various gas-phase and aqueous-phase transformation processes in the Earth’s atmosphere. A study of mass-independent 17O anomalies in H2O2 can provide additional insights into the chemistry of the modern atmosphere and, possibly, of the ancient atmosphere. Here, we report the results of laboratory experiments to study the fractionation of three oxygen isotopes (16O, 17O, and 18O) during H2O2 formation from products of water vapour dissociation. The experiments were carried out by passing an electrical discharge through a gaseous mixture of helium and water at atmospheric pressure. The effect of the presence of O2 in the gas mixture on the isotopic composition of H2O2 was also investigated. All of the experiments showed that H2O2 produced under two different conditions (with or without O2 added in the gas mixtures) was mass-independently fractionated (MIF). We found a positive MIF signal (∼1.4‰) in the no-O2 added experiments, and this signal increased to ∼2.5‰ once O2 was added (1.6% mixing ratio). We suggest that if O2 concentrations are very low, the hydroxyl radical recombination reaction is the dominant pathway for H2O2 formation and is the source of MIF in H2O2. Although H2O2 formation via a hydroxyl radical recombination process is limited in the modern atmosphere, it would be possible in the Archean atmosphere when O2 was a trace constituent, and H2O2 would be mass-independently fractionated. The anomalous 17O excess, which was observed in H2O2 produced by spark discharge experiments, may provide useful information about the radical chemistry of the ancient atmosphere and the role of H2O2 in maintaining and controlling the atmospheric composition.

Study of diffusion processes in the oxide layer of zirconium alloys

Abstract In the active zone of a nuclear reactor where zirconium alloys are used as a coating material, this material is subject to various harmful impacts. During water decomposition reactions, hydrogen and oxygen are evolved that may diffuse through the oxidic layer either through zirconium dioxide (ZrO2) crystals or along ZrO2 grains. The diffusion mechanism can be studied using the Ion Beam Analysis (IBA) method where nuclear reaction 18O(p,α)15N is used. A tube made of zirconium alloy E110 (with 1 wt. % of Nb) was used for making samples that were pre-exposed in UJP PRAHA a.s. and subsequently exposed to isotopically cleansed environment of H2 18O medium in an autoclave. The samples were analysed with gravimetric methods and IBA methods performed at the electrostatic particle accelerator Tandetron 4130 MC in the Nucler Physics Institute of the CAS, Řež. With IBA methods, the overall thicknesses of corrosion layers on the samples, element composition of the alloy and distribution of oxygen isotope 18O in the corrosion layer and its penetration in the alloy were identified. The retrieved data shows at the oxygen diffusion along ZrO2 grains because there are two peaks of 18O isotope concentrations in the corrosion layer. These peaks occur at the environment-oxide and oxide-metal interface. The element analysis identified the presence of undesirable hafnium.

Oxygen-17 anomaly in soil nitrate: A new precipitation proxy for desert landscapes

The nitrogen cycle in desert soil ecosystems is particularly sensitive to changes in precipitation, even of relatively small magnitude and short duration, because it is already under water stress. This suggests that desert soils may have preserved past evidence of small variations in continental precipitation. We have measured nitrate (NO3−) concentrations in soils from the Atacama (Chile), Kumtag (China), Mojave (US), and Thar (India) deserts, and stable nitrogen and oxygen isotope (15N, 17O, and 18O) abundances of the soil NO3−. 17O anomalies (Δ17O), the deviations from the mass-independent isotopic fractionation, were detected in soil NO3− from almost all sites of these four deserts. There was a strong negative correlation between the mean annual precipitation (MAP) and soil NO3− Δ17O values (ΔONO3soil17). This MAP-ΔONO3soil17 correlation advocated ΔONO3soil17 as a new precipitation proxy and was then used to assess precipitation changes in southwestern US at the Pliocene–Pleistocene boundary, in South America during the Miocene, and the Sahara Desert in the past 10 kyr using NO3− Δ17O in paleosols or ancient aquifers. Global and the US maps of surface ΔONO3soil17 were also projected with available MAP datasets based on the MAP-ΔONO3soil17 model.

Cobalt Doping as the Controlling Factor of Oxygen Diffusivity in ZnO by More than Four Orders of Magnitude

Oxygen diffusivity in ZnO ceramics doped with cobalt was investigated using an isotope tracer method. The oxygen isotope (18O) was introduced by 18O/16O exchange annealing in an 18O2 atmosphere, and the depth profile of the 18O concentration was analyzed by secondary ion mass spectrometry. The results show that oxygen diffusivity in ZnO steeply increases with increasing Co concentration. In fact, the bulk oxygen diffusivity in 15 mol% Co-doped ZnO was four orders of magnitude greater than that of nominally non-doped ZnO. Oxygen diffusivity at grain boundaries was also enhanced by Co-doping.

The bound coherent neutron scattering lengths of the oxygen isotopes

The technique of neutron interferometry was used to measure the bound coherent neutron scattering length bcoh of the oxygen isotopes 17O and 18O. From the measured difference in optical path between two water samples, either H217O or H218O versus H2natO, where nat denotes the natural isotopic composition, we obtain bcoh,17O = 5.867(4) fm and bcoh,18O = 6.009(5) fm, based on the accurately known value of bcoh,natO = 5.805(4) fm which is equal to bcoh,16O within the experimental uncertainty. Our results for bcoh,17O and bcoh,18O differ appreciably from the standard tabulated values of 5.6(5) fm and 5.84(7) fm, respectively. In particular, our measured scattering-length contrast of 0.204(3) fm between 18O and natO is nearly a factor of 6 greater than the tabulated value, which renders feasible neutron diffraction experiments using 18O isotope substitution and thereby offers new possibilities for measuring the partial structure factors of oxygen-containing compounds, such as water.

Effect of Partial Oxygen Isotope Substitution on the Phase Diagram of (Pr<sub>1-y</sub>Eu<sub>y</sub>)<sub>0.7</sub>Ca<sub>0.3</sub>CoO<sub>3</sub> Cobaltites

Effect of the partial oxygen isotope substitution on (Pr1-yEuy)0.7Ca0.3CoO3 cobaltites was studied in detail for the crossover region (0.12<у<0.26) of the phase diagram. We prepared a series of the cobaltite samples with the different degrees of enrichment by the heavy oxygen isotope 18O, namely, containing 90%, 67%, 43%, 17%, and 0% of 18O. The Eu doping of the samples was chosen to be near and on the both sides of the crossover doping level ycr. Based on measurements of the ac magnetic susceptibility χ(Т) and electrical resistivity ρ(Т), we were able to analyze the evolution the sample properties with the change Eu and 18O content.

Oxygen isotope exchange in nanosized powders of the Al2O3 oxide

Oxygen isotope exchange (OIE) between nanosized powders of the aluminum oxide Al2O3 and oxygen-containing gases 18O2 and C18O2 has been studied in a temperature range of 100–500°C. The concentration of the oxygen isotope 18O in the powders was determined by nuclear microanalysis technique (NRA). It has been shown that for this oxide the OIE exhibits a significant size effect. It has been established that the OIE of the Al2O3 nanopowder is characterized by a specific time dependence of the concentration of the 18O isotope at the surface of grains and by a low level of the content of 18O in the oxide. A linear dependence of the concentration of 18O in the nanopowders on the specific surface of the nanoparticles has been revealed. The experimental data are discussed in terms of several models of the process of isotope exchange.

Stable isotope composition of subfossil Cerastoderma glaucum shells from the Szczecin Bay brackish deposits and its palaeogeographical implications (South Baltic Coast, Poland)

The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have been reconstructed on the basis of the stable carbon and oxygen isotope (18O and 13C) analysis and radiocarbon dates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core were well preserved in their life positions, representing a geochemical record of past temperature variation over the middle Holocene. Three major periods with different thermal conditions have been distinguished in the interval ~6000–4300calyr BP, when the important Littorina regional transgression took place. During the first period, 6000–5250calyr BP, water temperature decreased by 1.4°C, and then remained constant over the second period (5250–4750calyr BP). In contrast, during the third period (4750–4300calyr BP) both δ-values were highly variable and the mean summer temperature (March–November) increased by about 3.5°C. During first two periods, δ18O and δ13C were significantly correlated, indicating stability of the environmental conditions.

Asymmetric Autocatalysis: Triggered by Chiral Isotopomer Arising from Oxygen Isotope Substitution

Trigger happy: chiral oxygen isotopomers of hydrobenzoin ([(18)O](R)-1 and [(18)O](S)-1) acted as chiral triggers to induce the enantioselective addition of iPr(2)Zn to pyrimidine-5-carbaldehyde. An extremely small chiral influence arising from the presence of the oxygen isotope ((18)O) is amplified through asymmetric autocatalysis to enantioenrich the 5-pyrimidyl alkanol product.

Oxidation and diffusion study on AlCrVN hard coatings using oxygen isotopes 16O and 18O

The present work aims to investigate the oxidation behaviour of AlCrVN hard coatings of equal composition but of different crystal structure. In order to gain more information about the mechanisms that are active during oxidation, a two-stage oxidation procedure has been applied where different isotopes, 16O and 18O, were introduced in each step. The analysis by means of secondary ion mass spectrometry depth profiling with its inherent isotope selectivity provided information on the general oxidation behaviour as well as the oxygen diffusion during the oxidation process. The single-phase coating with its face-centred cubic (fcc) structure presents a higher oxidation resistance as compared to the dual-phase coating containing a wurtzite and an fcc phase. After the annealing treatment the surface of the latter is entirely covered by VO 2 and V 2O 5 as evidenced by Raman spectroscopy. The single-phase coating, on the other hand, reveals unoxidised coating material and AlVO 4 crystals. However, even though exhibiting a significantly different oxidation resistance, the oxygen diffusion is similar. In both cases the peak values of 18O, which was introduced in the second stage, were found near the oxide–nitride interface indicating that O atoms diffused through the already formed oxides. Additional experiments using a gas mixture comprising natural water vapour H 2 16O and 18O 2 revealed that mainly the presence of molecular oxygen causes oxidation as with increasing water vapour partial pressure the oxide layer thickness was significantly reduced.

Differentiation of 18O‐ and 16O‐rich layers in anodic alumina films by glow discharge time‐of‐flight mass spectroscopy

AbstractThe performance of glow discharge time‐of‐flight mass spectrometry in isotopic differentiation is revealed using the distribution of oxygen isotopes 16O and 18O in barrier‐type anodic alumina films as a focus. Anodic alumina films comprising 18O‐rich layers of controlled thickness were formed by the appropriate combination of anodising of superpure aluminium in electrolytes enriched with 18O isotopes and of natural abundance of 18O isotopes. Analysis of the elemental depth profiles of selected ionic species, i.e. 16O18O, allowed determination of the locations of the 18O‐rich layers and the 18O/16O interface. Copyright © 2010 John Wiley & Sons, Ltd.

Molecular and cluster structures in 18O

We have studied the multi-nucleon transfer reaction 12C ( 7Li ,p) at E lab = 44 MeV, populating states in the oxygen isotope 18O . The experiments were performed at the Tandem accelerator of the Maier-Leibniz Laboratory in Munich using the high-resolution Q3D magnetic spectrograph. States were populated up to an excitation energy of 21.2MeV with an overall energy resolution of 45keV, and 30 new states of 18O have been identified. The structure of the rotational bands observed is discussed in terms of cluster bands with the underlying cluster structures: 14C$ \(\displaystyle \otimes\) \(\displaystyle \alpha\)$and 12C ⊗ 2n ⊗ \( \alpha\) . Because of the broken intrinsic reflection symmetry in these structures the corresponding rotational bands appear as parity doublets.

Sahara dust, ocean spray, volcanoes, biomass burning: pathways of nutrients into Andean rainforests

Abstract. Regular rain and fogwater sampling in the Podocarpus National Park, on the humid eastern slopes of the Ecuadorian Andes, along an altitude profile between 1960 and 3180 m, has been carried out since 2002. The samples, accumulated over about 1-week intervals, were analysed for pH, conductivity and major ions (K+, Na+, NH4+, Ca2+, Mg2+, Cl−, SO42−, NO3−, PO43−). About 35% of the weekly samples had very low ion contents, with pH mostly above 5 and conductivity below 10 μS/cm. 10-days back trajectories (FLEXTRA) showed that respective air masses originated in pristine continental areas, with little or no obvious pollution sources. About 65%, however, were significantly loaded with cations and anions, with pH as low as 3.5 to 4.0 and conductivity up to 50 μS/cm. The corresponding back trajectories clearly showed that air masses had passed over areas of intense biomass burning, active volcanoes, and the ocean, with episodic Sahara and/or Namib desert dust interference. Enhanced SO42− and NO3+ were identified, by combining satellite-based fire pixel observations with back trajectories, as predominantly resulting from biomass burning. Analyses of oxygen isotopes 16O, 17O, and 18O in nitrate show that nitrate in the samples is indeed a product of atmospheric conversion of precursors. Some SO42−, about 10% of the total input, could be identified to originate from active volcanoes, whose plumes were encountered by about 10% of all trajectories. Enhanced Na+, K+, and Cl− were found to originate from ocean spray sources. They were associated with winds providing Atlantic air masses to the receptor site within less than 5 days. Episodes of enhanced Ca2+ and Mg2+ were found to be associated with air masses from African deserts. Satellite aerosol data confirm desert sources both on the Northern (Sahara) as on the Southern Hemisphere (Namib), depending on the season. A few significant PO43− peaks are related with air masses originating from North African phosphate mining fields.

On the Mechanism of Cu<sub>2</sub>O Oxidation at High Temperatures

Oxidation mechanism of nonstoichiometric cuprous oxide (Cu2 yO) has been studied as a function of temperature (973-1273 K) and oxygen pressure (1-105 Pa), using microthermogravimetric, marker and two-stage oxidation techniques. The last method consisted in using heavy oxygen isotope 18O in order to confirm the results, obtained with marker technique. It has been found that in early stages of reaction not exceeding 30 hours, CuO formation on the surface Cu2 yO follows approximately cubic rate law. In later stages, during long-term oxidation, lasting hundreds of hours, oxidation process follows strictly parabolic kinetics with the rate, being independent of Cu2 yO pre-treatment. Marker and two-stage oxidation experiments have shown that the growth process of CuO layer proceeds by the outward diffusion of cations, clearly indicating that cation sublattice of CuO is predominantly defected.

Visualization of oxygen transport behavior at metal electrode/oxide electrolyte interface using secondary ion mass spectrometry

The tracks of oxygen transport around platinum or gold electrode/yttria stabilized zirconia (YSZ) electrolyte interface were visualized by oxygen isotope ( 18O) labeling ( T = 773–973 K, p(O 2) = 7 kPa, cathodic polarization E = 0 or − 0.3 V) and multi dimensional imaging using secondary ion mass spectrometry (SIMS). The activation of oxygen exchange reaction was clearly observed as a strong 18O − intensity at metal/YSZ interface treated at T = 973 K indicating that the reaction dominantly occurs at gas/electrode/electrolyte triple phase boundary (TPB). Platinum/YSZ interface exhibited a stronger 18O − intensity than gold/YSZ, however, the intensity distribution was not homogenous. The effect of applying cathodic polarization on the oxygen transport was more clearly observed at gold/YSZ interface than platinum/YSZ. The cause of differences in experimental results is discussed in connection with the different reaction controlling process among the two electrodes materials.