18O Concentration Research Articles

Study of oxygen self-diffusion in oxides by ion beam techniques: comparison between nuclear reaction analysis and SIMS

Oxygen self-diffusion in Fe 1−xO single crystals has been studied by means of the isotope exchange method in H 2/H 2 18O atmospheres. The 18O concentration profiles were determined by using two different techniques based on ion beams: secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA); the latter by means of the narrow nuclear resonance reaction 18 O(p, α) 15 N at 629 keV, Γ = 2.1 keV. The diffusion coefficients obtained from the analysis of the measured profiles are in good agreement with those found in the literature. To compare the depth resolution and sensitivity of both techniques, the 18O profiles of implanted Cr 2O 3 single crystals ( E 18 O =50 keV, fluence=1.6 × 10 16 ions/cm 2 were also measured.

Isotope hydrological study of mean transit times in an alpine basin (Wimbachtal, Germany)

Measurements of tritium and 18O concentrations in precipitation and runoff were used to provide further insight into the groundwater storage properties of the Wimbachtal Valley, a catchment area of 33.4 km 2, extending between 636 and 2713 m a.s.l. in the Berchtesgaden Alps. The catchment includes three aquifer types: a dominant porous aquifer; a fractured dolomite; a karstic limestone aquifer. Employing a simple hydrological model, information about mean transit times of environmental tracers is derived for the groundwater runoff component and several karst springs from the application of the exponential and dispersion flow models to the isotopic input and output data. The mean transit times calculated from a dispersion model with transit times of 4.1 years for 18O and 4.2 years for tritium, which agree well, allow calculation of total (mobile + stagnant) groundwater storage volume, which is equivalent to 6.6 m of water depth. Direct runoff appears negligible as in many other cases.

Environmental tritium and 18O applied in a hydrological study of the Wairau Plain and its contributing mountain catchments, Marlborough, New Zealand

Isotope data (tritium and 18O) for rivers and ground water, acquired since 1968, are combined with geological, hydrological and hydrochemical evidence to determine sources and flow patterns of ground water in gravel aquifers of the Wairau coastal plain and its southern tributary valleys. Determination of the components of groundwater origin depends on a strong west-east gradient of 18O concentration between mountain catchment precipitation feeding rivers flowing to the Plain and rainwater falling directly on the Plain. The main aquifer is postglacial alluvial material deposited by Wairau River, deriving its water from that river; locally infiltrated precipitation contributes at most only a few percent to the flow in the shallowest gravels downstream of the infiltration zone. In the south of the Plain, the unconfined aquifer comprises material deposited during the last glaciation; its ground water has both local precipitation and inflow from southern tributary streams as appreciable sources. The main aquifer is confined near the coast. where it is overlain by up to 60 m of marine sediments deposited during postglacial marine transgression and subsequent coastal progradation. Tritium concentrations show that ground water in the shallowest geological stratum (Rapaura gravels) reaches the confined zone boundary less than 1 year after recharge from the river, with much shallow flow being discharged at the surface just upstream of the boundary; in contrast, ground water in the underlying unit (Speargrass gravels) requires at least 10 years to reach this point. Analysis of tritium concentrations in the confined zone shows a central zone through which the faster-flowing Rapaura component dominates as far as the coast, but also areas to the north and south where ground water in the Rapaura gravels has a dominant older component. The combined evidence reveals that the confined ground water is leaking into the overlying sediments, allowing water to flow from the lower Speargrass gravels into the Rapaura gravels. Because Wairau River is the dominant source of ground water for the main aquifer, its response to bomb-tritium input to its mountain catchments is given detailed consideration. Much of the river water derives promptly from bare catchment areas, but the analysis suggests that about 50% is retained for about 8 years on average before release to the river. Large deposits of scree in higher-lying, formerly glacial catchments appears to be the major factor in the surprisingly large quantity of stored water implied by this result.

Chemical equilibrium and mass balance relationships associated with the Long Valley hydrothermal system, California, U.S.A.

Recent drilling and sampling of hydrothermal fluids from Long Valley permit an accurate characterization of chemical concentrations and equilibrium conditions in the hydrothermal reservoir. Hydrothermal fluids are thermodynamically saturated with secondary quartz, calcite, and pyrite but are in disequilibrium with respect to aqueous sulfide-sulfate speciation. Hydrothermal fluids are enriched in 18O by approximately 1‰ relative to recharge waters. 18O and Cl concentrations in well cuttings and core from high-temperature zones of the reservoir are extensively depleted relative to fresh rhyolitic tuff compositions. Approximately 80% of the Li and 50% of the B are retained in the altered reservoir rock. Cl mass balance and open-system 18O fractionation models produce similar water-rock ratios of between 1.0 and 2.5 kg kg −1. These water-rock ratios coupled with estimates of reservoir porosity and density produce a minimum fluid residence time of 1.3 ka. The low fluid Cl concentrations in Long Valley correlate with corresponding low rock concentrations. Mass balance calculations indicate that leaching of these reservoir rocks accounts for Cl losses during hydrothermal activity over the last 40 ka.

Assessment of nuclear reaction analysis for the measurement of 18O concentration in organic samples

Nuclear reaction analysis (NRA) was assessed as a fast and simple method of determining the natural concentration of 18O in organic samples. Samples investigated included beet sugar, L. aspartic acid, L. glutamic acid, cellulose and sorbic acid. The 18O(p,α) 15N reaction was used and after applying a correction factor to the ratio of alpha particles emitted when the samples were bombarded with 0.73 MeV protons, the 18O concentrations of L. aspartic acid, L. glutamic acid, sorbic acid, and cellulose were determined to be 0.249±0.040, 0.255±0.040, 0.035±0.040, and 0.205±0.040 at%, respectively, using beet sugar that has an 18O concentration of 0.2044±0.0002 at% as a standard. The correction factor accounted for proton energy losses through the target and the resulting variation of cross section with energy. All the organic samples investigated seemed to be very sensitive to heat and unstable under the beam bombardment.

Oxygen rich SIMOX?

18O(200 keV, 2.0*1017 cm-2) has been implanted at 6 K into an 'as implanted' SIMOX wafer (silicon implanted with 16O at 200 keV, 1.8*1018 cm-2 and 500 degrees C). In situ Rutherford backscattering measurements at 6 K, 77 K and room temperature indicate approximately 15% excess oxygen above the stoichiometric value for SiO2 in the buried-oxide layer. Additional room-temperature measurements were carried out off-line by infrared and secondary ion mass spectrometries. A comparison of the original SIMOX material with the sample implanted with 18O at 6 K leads to the conclusion that during warm up the 18O concentration depth profile remains essentially unchanged with the maximum total concentration remaining above the original 16O value. The infrared measurements indicate that all of the oxygen atoms are bound to silicon atoms.

Un cas de diffusion complexe le transport des atomes d'oxygène dans le verre de silice hydratée

The reaction of gaseous H 2 18O on a plane substratum of natural silica glass under given temperature and pressure conditions was re-examined. The reported description of interfacial phenomena led us to renounce the theory that reactive sites are slowly created and destroyed at the same rate. In an analysis of the theory using the same reactivity for all the sites we calculated the theoretical 18O concentration profile, which depends on two experimental parameters only, namely: 1. (i) the 18O isotopic enrichment at the interface; and 2. (ii) the self-diffusion apparent coefficient of hydrogen.

Oxygen diffusion in quartz: Dependence on temperature and water fugacity

Oxygen self-diffusion coefficients ( D) were determined in single crystals of Brazilian quartz by measuring 18O concentration profiles with an ion microprobe. In the α-quartz field at 450–590°C and 100-MPa confining pressure, for diffusion parallel to c, the Arrhenius relation is described by the parameters D 0 = 2.9 · 10 −5 m 2 s −1 and Q = 243 ± 17 kJ (g-at. O) −1. The diffusion rate was also measured in β-quartz from 5- to 350-MPa confining pressure and at 700°C as a function of water, hydrogen and oxygen fugacities as well as for different proton activities. There is a good correlation of D with water fugacity, no correlation with oxygen nor hydrogen fugacities, and no correlation with proton activity over the range for which this parameter could be fixed independent of the water fugacity, The available evidence suggests that the oxygen-bearing species responsible for the rapid transport of oxygen under hydrothermal conditions is molecular water. The rate controlling step for oxygen diffusion may be either the rate of migration of water molecules, or the rate of oxygen exchange between the water molecules and the quartz structure.

A New Intracrystalline Isotope Effect: 18O under the Faces of Amethyst

Abstract The concentration of 18O within well formed crystals of amethyst was found to vary beneath the different growth faces, increasing in the order z→ r→m. The 18O/16O fractionation factor between the faces m and z was measured as 1.0007.

The effect of hydrogen, oxygen, and water fugacity on oxygen diffusion in alkali feldspar

Oxygen self-diffusion in adularia and albite single crystals was studied hydrothermally at 650°C from 5 to 1500 MPa confining pressure using a combination of hydrogen/oxygen buffers, a hydrogen ion buffer, and variable mole fractions of water (dilution with CO 2). Diffusion coefficients (D) were determined from 18O concentration profiles measured with an ion microprobe. There is a good correlation of the D values with water fugacity but not with oxygen fugacity, hydrogen fugacity, hydrogen ion concentration, nor confining pressure over the range for which these parameters could be fixed independent of the water fugacity. Oxygen diffusion must involve the transport of an oxygen-bearing species, and the results of this study suggest that the transport species is molecular water. The rate-limiting step for oxygen diffusion could be either the rate of migration of the molecular water in the crystal or the rate of exchange of its oxygen with the feldspar structure. While protons may play a role in the mechanism of oxygen diffusion in feldspar, above the concentration supplied by pure water additional protons have no measurable effect on diffusion rates.

Hydrology of the Karst aquifer at the experimental site of Guilin in southern China

The experimental site of Guilin is located near the village of Yaji at the border of the Lijiang Plain (Province of Guangxi, southern China). Within upper Devonian limestones and dolomitic limestones, a karst has developed in accordance with intense fracturing resulting from Mesozoic and Tertiary tectonic episodes. Its morphology is characterized by two major types of karst: a cone karst (peak cluster area) bounded by the Lijiang Plain which comprises a tower or mogote karst (peak forest area). Groundwater discharges from a perennial spring (discharge up to 7 m 3 s −1) and three intermittent springs (discharge less than 5 m 3 s −1). Some observation boreholes have been drilled on the peak cluster area dolines and on the Lijiang Plain in front of the spring. Tracing experiments in the dolines showed that the dolines are connected with the springs. The apparent flow velocity ranges between 4 and 180 m h −1. Analyses of storm responses of the perennial spring and the variability in time of 18O concentration, pointed out the important role played by the flows occurring in the subcutaneous zone of the peak cluster area.

Determination of 18O concentrations in musamples of biological fluids

The 18O(p, α) 15N reaction has been developed for the analysis of musamples of biological fluids containing 18O-enriched water. Samples as small as 50 μl have been used. Well characterized Ta 2O 5 targets were prepared from these fluids and irradiated with several hundred nA of protons from the 3 MV Van de Graaff at Lucas Heights. The broad (47 keV) 846 kV resonance in this reaction was used to measure 18O concentrations down to natural backgrounds (0.2 at.%) in a few minutes of accelerator running time. Concentrations of 18O from 0 to 5 at.% were measured in body fluids in small Australian lizards directly after doping with 18O-enriched water and then again after several days of roaming around in their natural desert environments. The changes in these levels were related to the metabolic rates of these animals.

La diffusion reactive de l'eau dans le verre de silice les implications du modele classique

When gaseous H 2 18O reacts on a plane substratum of hydrated silica glass, the elementary composition of which is uniform and constant, 18O concentration profiles are not consistent with an error function complement. We recall the accepted model for the reactive diffusion mechanism of water and we demonstrate a relation allowing the calculation of the apparent self-diffusion coefficient of oxygen atoms from any experimental 18O concentration profile. This coefficient is related to that of hydrogen atoms for the same experiment. Concerning diffusion of gaseous H 2O into silica glass initially free of OH groups, the elementary composition varies at any position, but we can suppose that the hydration equilibrium of silica glass by molecularly dissolved water at this place is reached. Thus we obtain a relation between the apparent diffusion coefficient of hydrogen atoms in these conditions, and that corresponding to the same, but uniform and constant, elementary composition.

Deuterium and oxygen-18 abundance in birds: implications for DLW energetics studies

The doubly labeled water (DLW) technique for measuring energy expenditure may employ one (18O) or two (18O and deuterium) stable isotopes as tracers. These occur naturally in the environment, so when they are used as tracers it is necessary to subtract the background levels. Few studies report data on background concentrations. This work provides such data for a range of avian species. Overall, there was a strong positive correlation (r = 0.63) between the 18O and deuterium concentrations in birds' body water. Variation in the deuterium concentration was less extensive than in the 18O concentration (1:2.7 parts/million). In the European robin, there was a linked, seasonal variation in 18O and deuterium abundance producing high summer and low winter values. Throughout the year, a high individual variability was greater in 18O than in deuterium. A difference between the European robin and the dipper suggests that habitat may also influence background abundance. Investigation of the effect of variation in background abundance on measures of energy expenditure for small passerines (20 g) revealed that employing estimates, instead of direct measurements, had a minor influence over an experimental period of 1 day but could potentially introduce errors as large as 54% over a 2-day period.

Measurement of the activation energy of the low temperature oxidation of coal using secondary ion mass spectrometry

Accurate determination of the activation energy of the low temperature oxidation of coal provides insights into the mechanism of the reaction. In this paper, secondary ion mass spectrometry (SIMS) has been used to measure the relative surface concentrations of 18O on coal surfaces oxidized in 18O 2 at 23, 70 and 90 °C respectively. These results have been used with the Arrhenius equation to estimate the activation energy for the deposition of 18O at the coal surface, i.e. 47.1 and 82.0 kJmol −1 in the ranges 23–70 °C and 70–90 °C, respectively.

Sources and flow of north Canterbury plains groundwater, New Zealand

Geological, hydrological, isotope (tritium and 18O) and chemical (mainly nitrate and chloride concentrations) evidence is interpreted to give a mutually consistent picture of the recharge sources and flow patterns of the important groundwater resource in the deep glacial and interglacial deposits of the sector of the Canterbury Plains between the Selwyn River and Ashley River. Particular attention is paid to the confined gravel aquifers which presently provide about 300,000 m 3 daily of mainly very high-quality water for the needs of Christchurch city. The study period for tritium measurements extends over 27 years, encompassing the peak and decline of thermonuclear tritium fallout in this region. Major rivers emerging from the hill and mountain catchments to the west of the Plains are depleted in 18O relative to average low-level precipitation. Most of the groundwater is river-recharged, but some areas of significant local precipitation recharge contribution are clearly identified by 18O and chemical concentrations. The pressure distribution, tritium and chemical data reveal that the artesian ground-water underlying Christchurch ascends from deeper aquifers into the shallowest aquifer via gaps in the confining layers; much of this flow is induced by withdrawal, and the data reveal nothing about possible offshore discharge through the seaward extension of the shallowest aquifer, which is known to outcrop 40 km beyond the coast. The Christchurch aquifers are recharged by infiltration from Waimakariri River in its central Plains reaches, and the resulting flow regime is east- and southeast-directed; satisfactory water quality of the deeper Christchurch aquifers appears to be guaranteed for the future provided the river can be maintained in its present condition. Shallow groundwater, and water recharged to depth by other rivers, irrigation and local precipitation on the unconfined western areas of the Plains, are more susceptible to agricultural and other pollutants; none of this water is encountered in the deeper aquifers under Christchurch, but only in shallow aquifers and surface discharges, or else flowing to the southeast, well away from the city area.

Dilution kinetics of chemicals used for estimation of water content of body compartments in perinatal medicine.

Dilution kinetics of markers commonly used for estimation of body water content and distribution in perinatal medicine (p-aminohippurate, inulin, antipyrine, H218O, bromide, and T1824) were studied in pregnant and neonatal baboons. Amniotic fluid concentrations of p-aminohippurate and inulin decreased exponentially after intraamniotic injection of these markers; from 2-24 h after injection, concentrations decreased linearly on semilogarithmic plot (r = 0.96-1.00). Plasma concentrations of antipyrine decreased exponentially during the first 60 min after intravenous injection, then linearly from 1-5 h (r = 0.92-0.90). Plasma concentrations of 18O decreased linearly from 1-6 h after injection in three or four cases (r = 0.94-0.99). Plasma concentrations of bromide decreased during the first 2 h after injection, then stabilized for at least 3 h. Plasma concentrations of T1824 decreased linearly from 10-60 min after intravenous injection (r = 0.97-1.00). Then the decline became exponential until 5 h. These data allow us to make specific recommendations regarding the optimal time and method of amniotic fluid and blood sampling during body water studies.

Assessment of 18O enriched water as a marker of total body water

The water content of biological systems was measured using a nuclear reaction technique. The method, which can be used to determine the total body water (TBW) in humans, has been tested on rabbits and mice. A measured amount of 18O enriched water was administered and the 18O concentration of the system was essayed using the 18O(p, α) 15N reaction. The rate of the distribution of 18O injected into a rabbit was measured and the 18O exchange between intracellular and extracellular water volume was determined. The targets for the nuclear reaction analysis were prepared by anodic oxidation of the tantalum at constant voltage directly from serum and plasma without the addition of a buffer. The anodic constant of tantalum for plasma, serum, and urine was measured. The Ta 2O 5 targets were exposed to a proton beam with an energy of 0.73 MeV and the resulting reaction alpha particles were recorded.

Measurement of oil reservoir dispersivity by nuclear reaction analysis

The dispersion of water in a consolidated porous medium was measured using the 18O(p, α) 15N nuclear reaction. Reservoir rock core was saturated with water enriched to 0.56 at.% of 18O. During a miscible displacement of the resident 18O enriched water by a brine solution with natural 18O abundance, effluent mixtures of the fluids were collected as a function of time and pore volume injected. The targets used for the nuclear reaction analysis were prepared by anodic oxidation of tantalum at constant voltage. The Ta 2O 5 film was bombarded with 0.73 MeV protons and the resulting reaction alpha particles were recorded. The number of the reaction alpha particles being proportional to the 18O concentration in the effluent mixture was used as the concentration index for the determination of water dispersion profile and rock dispersivity.

Origin and movement of groundwater and major ions in a thick deposit of Champlain Sea clay near Montréal

At a site near Montréal, piezometers and core samples were used to assess the origin, age, and rate of groundwater movement in a 28 m thick deposit of Champlain Sea clay. 3H occurs only within the upper 3–4 m, which indicates that groundwater below this surficial weathered zone originated prior to 1952. Concentrations of 18O, Na+, and Cl− in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33% seawater and 67% freshwater. Profiles of several major ions show a gradual increase in concentration with depth. Mathematical simulations of vertical migration of Ca2+, Mg2+, K+, Na+, and Cl− provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a. When the downward advection rate of 0.13 cm ∙ a−1 obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model, the simulated major-ion profiles deviate markedly from the field profiles. This suggests that the hydraulic gradient in the clay is less than the threshold gradient necessary to cause Darcian flow. This study suggests that, in areas where clayey Champlain Sea deposits are thick, opportunities exist for locating waste disposal facilities that would have no significant potential for causing contamination of groundwater resources beneath the clay. Key words: groundwater, permeability, diffusion, environmental isotopes, threshold gradient, geochemistry, subsurface waste disposal.