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1.
Cosmic-ray-produced53Mn (t½ = 3.7 × 106years) has been determined by neutron activation analysis in twenty-two chondrites including three Antarctic meteorites: Yamato-7301 (j), -7305 (k) and -7304 (m).53Mn was also measured in four mesosiderites, three iron meteorites, Bencubbin (unique) and Udei Station (iron with silicate inclusions). In addition, preliminary results for10Be (1.6 × 106 years) were obtained in the Yamato meteorites using a low-background needle GM counter. Based on published values of rare gas ages, corrections were made for undersaturation; the average specific saturation activities of53Mn were found in the range 450 ± 90dpm53Mn/kg Fe in most of the chondrites and 490 ± 75dpm53Mn/kg Fe in the mesosiderites. Two meteorites had extremely low contents of53Mn: 102 ± 6 in Yamato-7301 and 48 ± 3dpm53Mn/kg Fe in Bondoc. The Bondoc mesosiderite was already known to have a low concentration of cosmogenic radionuclides due to its large pre-atmospheric size. Several possible mechanisms are discussed to explain the low53Mn activity in Yamato-7301: (1) long terrestrial age of about 7 m.y.; (2) low production rate of53Mn due to heavy pre-atmospheric shielding (>70cm); (3) multi-stage irradiation history resulting in an undersaturation of53Mn; and (4) a mechanism in which two or three of the above factors are combined. The ratio of53Mn production rate in Ni to that in Fe has been estimated to be 1/3, based on the measurements of53Mn in the metallic and silicate phases of St. Séverin meteorite, as well as on published results of some high-energy bombardment experiments.  相似文献   

2.
The reasons why53Mn (a cosmogenic radionuclide with a half-life of 3.7 × 106 y) appears as one of the best indicators of the presence of interplanetary dust are summarized. This paper reports the detection of53Mn in pre-1952 snow samples collected on the Eastern Antarctic Plateau in the vicinity of Plateau Station. The measurements were carried out by neutron activation and X-ray spectrometry on three samples weighing a few hundred kg and covering each the time interval 1935–1950. The specific activity of53Mn was found to be (0.82 ± 0.17) disint.min?1/103 tons of snow, corresponding to a deposition rate at Plateau Station of (2.2 ± 0.5) × 10?5 disint. min?1 m?2 y?1. The mean global deposition rate would be three times higher if53Mn were assumed to behave in the same way as stratospheric90Sr. By comparing this figure with existing data on the meteorite flux reaching the earth and with the galactic and solar production rates of53Mn, it is concluded that the bulk of the53Mn found at Plateau Station is associated with interplanetary dust in which it had been produced by the action of solar protons on iron. The deposition rate of extra-terrestrial dust-borne iron must be between 1.3 × 10?5 and 1.3 × 10?4 g m?2 y?1 at Plateau Station. These results support jointly with other studies the concept of an interplanetary zodiacal cloud of dust with a chemical composition and density not essentially different from chondritic meteorites, with a relatively ‘flat’ grain size distribution and a mass influx to the earth of the order of 105 tons/y.  相似文献   

3.
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been determined by neutron activation in nine Allan Hills-77 meteorites. Additionally,36Cl (1/2 = 3.0 × 105years) has been measured in seven of these objects using tandem accelerator mass spectrometry. These results, along with14C (t1/2 = 5740years) and26Al (7.2 × 105 years) concentrations determined elsewhere, yield terrestrial ages ranging from 0.1 × 105 to 7 × 105 years. Weathering was not found to result in53Mn loss.  相似文献   

4.
The effect of resuspension on benthic fluxes of oxygen (O2), ammonium (NH4+), nitrate (NO3?), phosphate (PO43?), silicate (Si(OH)4), dissolved inorganic carbon (DIC), total dissolved iron (Fe) and total dissolved manganese (Mn) was studied at three different stations in the Gulf of Finland (GoF), Baltic Sea during three cruises in June–July 2003, September 2004 and May 2005. The stations were situated on different bottom types in the western, central and eastern part, respectively, of the open GoF. The fluxes were measured in-situ using the autonomous Göteborg benthic lander. To simulate resuspension events, the stirring speed was increased in two of the four chambers of the lander after approximately half of the incubation time. The other two chambers were used as control chambers. Clear effects of resuspension were observed on the oxygen fluxes where an increase of the consumption was observed in 88% of the cases and on average with 59% (stdev=53). The NH4+ fluxes were affected in 50% of the cases (4 out of 8 incubations) at stations with low bottom water oxygen concentrations, but in no cases where the bottom water was oxygenated (0 out of 9 incubations). The NH4+ fluxes decreased by 26±27% in 2005 and by 114±19% in 2003. There was no clear effect of resuspension on the fluxes of any of the other solutes in this study. Thus, resuspension events did not play a significant role in release/uptake of NO3?, PO43?, Si(OH)4, DIC, Fe and Mn in GoF sediments. However, increased oxygen consumption as a result of resuspension may lead to spreading of anoxic/suboxic bottom water conditions, and thus indirectly to increased benthic release of phosphate, ammonium and iron.  相似文献   

5.
Results of a detailed petromagnetic study of sediments of the Koshak section, including the Mesozoic/Cenozoic (K/T) boundary, are presented. The rocks are shown to have a very low magnetization. A relatively high magnetization is characteristic of two thin clayey beds, one at the K/T boundary and the other 0.6 m above it: x up to 2.5 × 10?9 m3/kg, M s up to 0.6 × 10?3 A m2/kg, and M rs up to 0.4 × 10?3 A m2/kg. This is related to relatively high concentrations of hemoilmenite (up to 0.2%), magnetite (up to 0.01%), and goethite (up to 0.24%) in these beds. It is evident that the distribution of these magnetic minerals is lithologically controlled (the predominant occurrence in clayey beds), which is expressed, in particular, in the relation between the paramagnetic (clayey) and diamagnetic (carbonate) contributions to the magnetization of the sediments. Thus, clayey interbeds are sharply distinguished by the value of the paramagnetic magnetization (M p = (83–86) × 10?5 A m2/kg) as compared with purely diamagnetic chalk (M d = ?(26–35) × 10?5 A m2/kg). Minor concentrations of metallic iron (up to ～0.002%) discovered in the sediments have a lithologically uncontrolled distribution (metallic iron is more often observed near the K/T boundary rather than in clayey beds). Most probably, magnetite, hemoilmenite, and goethite were accumulated mostly with clay and other terrigenous material, while fine particles of iron are likely to have been dispersed by air. The whole set of the data of this work suggests that the K/T boundary is not distinguished by characteristic magnetomineralogical and magnetolithologic features.  相似文献   

6.
Production rates of22Na (T1/2 = 2.6years) from aluminium by the action of cosmic rays are measured at the Mont Blanc (altitude 4600 m), the Aiguille du Midi (3840 m), and the Col du Lautaret (2070 m). They are2.3 ± 0.5,1.8 ± 0.3,and0.77 ± 0.18 atoms min?1 kg?1, respectively, in good agreement with the calculated production rates, 2.4, 1.7 and 0.6 atoms min?1 kg?1, respectively, at the three stations.Production rates of24Na (T1/2 = 15hours) from aluminium and magnesium are also measured at the Aiguille du Midi; the observed rates of3.4 ± 0.4and6.0 ± 1.7 atoms min?1 kg?1, respectively, agree well with the theoretically expected rates of 3.7 and 5.6 atoms min?1 kg?1.The production rates of3H,7Be,10Be,14C,22Na,26Al,36Cl,37Ar,39Ar,53Mn,54Mn, and55Fe in terrestrial rocks by the action of cosmic rays are calculated in order to show the possibility of applying the measurements of these cosmogenic radionuclides to the earth science.  相似文献   

7.
We have measured by accelerator mass spectrometry the26Al contents of 20 and the10Be contents of 14 iron meteorites. The26Al contents are typically 30% or more lower than values obtained by counting techniques; the10Be contents are 10–15% lower. The production rates (P) of these nuclides decrease by more than a factor of two as the4He/21Ne ratio increases with increasing shielding from 200 to 400. For the lighter shielding conditions expected in stony meteorites we estimateP26(Fe) as 3–4 dpm/kg andP10(Fe) as 4–5 dpm/kg. The average P/10P26 activity ratio is close to 1.5. Exposure ages calculated from21Ne/26Al ratios cannot be calibrated so as to agree with both40KK/ ages and ages based on the shorter-lived nuclides39Ar and36Cl. If agreement with the latter is forced, then the disagreement with40KK/ ages may signal a 35% increase in the cosmic-ray intensity during the last 107 a.  相似文献   

8.
The combination of magnetic and geochemical methods was used to determine the mineralogy, grain size and domain structure of magnetic particles in indoor dust collected in 195 sites in Warsaw, Poland. Data show an asymmetric distribution of magnetic susceptibility (χ) in the wide range of 20–1514 × 10?8 m3 kg?1. Comparison of magnetic parameters shows that the internal dust contains outside pollution characteristic for air and soil. More than 90% of indoor dust samples were characterized by roughly uniform magnetic mineralogy, typical for fine grained magnetite (diameter of 0.2–5 μm), and grain size between pseudo-single-domain and small multi-domain with small contribution of superpara-magnetic particles (～10%). Samples with χ larger than 220 × 10?8 m3 kg?1 contain mainly magnetite and an anthropogenic metallic Fe with T C > 700°C. The indoor dust contains, characteristic for the urban areas, spherical magnetic particles originated from fossil fuel combustion processes and mixture of irregular angular iron-oxides grains containing other elements, including Na, Ca, Al, Si, K, S, Mn, Cl, and Mg.  相似文献   

9.
The thermal expansion of stishovite has been determined by an X-ray camera technique in a temperature range of 18 – 600°C at an atmospheric pressure. The thermal-expansion coefficients along the crystallographic a- and c-axes at 300 K are αa = (6.0 ± 0.6) · 10?6K?1 and αc = (1.4 ± 0.5) · 10?6K?1, respectively. The volume coefficient at 300 K is αν = (13.5 ± 0.6) · 10?6K?1.  相似文献   

10.
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been measured in twenty Antarctic meteorites by neutron activation analysis.36Cl (t1/2 = 3.0 × 105years) has been measured in fourteen of these objects by tandem accelerator mass spectrometry. Cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases.14C (t1/2 = 5740years) and26Al (t1/2 = 7.2 × 105years) data. The terrestrial ages range from 3 × 104 to 5 × 105 years. Many of the L3 Allan Hills chrondrites seem to be a single fall based on these results. In addition,10Be (t1/2 = 1.6 × 106years) and36Cl have been measured in six Antarctic ice samples. The first measurements of10Be/36Cl ratios in the ice core samples demonstrate a new dating method for ice.  相似文献   

11.
Dissolved and particulate Mn and Fe in the nearshore waters were determined at 27 stations along the west coast of Taiwan during 19-23 November 2004. The latitudinal distributions of Mn and Fe were very similar; however, the concentration in the dissolved phase was lower, whereas that in the particulate phase was higher in the northern regime. The higher percentage of Fe than Mn that was associated with particles resulted in a two-order of magnitude higher particle-water partition coefficient for Fe, Kd(Fe), than that for Mn, Kd(Mn). The removal fluxes of Mn and Fe could be estimated by multiplying the particulate 234Th removal flux with the Mn/234Th and Fe/234Th ratios in suspended particles, which ranged from 0.1 to 3.8 mmol m−2 d−1 for Mn, and from 3.4 to 194.5 mmol m−2 d−1 for Fe. Residence times ranged from 1 to 20 days for Mn and Fe were estimated in the nearshore.  相似文献   

12.
Solute concentrations and fluxes in rainfall, throughfall and stemflow in two forest types, and stream flow in a 90 ha catchment in southern Chile (39°44′S, 73°10′W) were measured. Bulk precipitation pH was 6·1 and conductivity was low. Cation concentrations in rainfall were low (0·58 mg Ca2+ l?1, 0·13 mg K+ l?1, 0·11 mg Mg2+ l?1 and <0·08 mg NH4–N l?1), except for sodium (1·10 mg l?1). Unexpected high levels of nitrate deposition in rainfall (mean concentration 0·38 mg NO3–N l?1, total flux 6·3 kg NO3–N ha?1) were measured. Concentrations of soluble phosphorous in bulk precipitation and stream flow were below detection limits (<0·09 mg l?1) for all events. Stream‐flow pH was 6·3 and conductivity was 28·3 μs. Stream‐water chemistry was also dominated by sodium (2·70 mg l?1) followed by Ca, Mg and K (1·31, 0·70 and 0·36 mg l?1). The solute budget indicated a net loss of 3·8 kg Na+ ha?1 year?1, 5·4 kg Mg2+ ha?1 year?1, 1·5 kg Ca2+ ha?1 year?1 and 0·9 kg K+ ha?1 year?1, while 4·9 kg NO3–N ha?1 year?1 was retained by the ecosystem. Stream water is not suitable for domestic use owing to high manganese and, especially, iron concentrations. Throughfall and stemflow chemistry at a pine stand (Pinus radiata D. Don) and a native forest site (Siempreverde type), both located within the catchment, were compared. Nitrate fluxes within both forest sites were similar (1·3 kg NO3–N ha?1 year?1 as throughfall). Cation fluxes in net rainfall (throughfall plus stemflow) at the pine stand generally were higher (34·8 kg Na+ ha?1 year?1, 21·5 kg K+ ha?1 year?1, 5·1 kg Mg2+ ha?1 year?1) compared with the secondary native forest site (24·7 kg Na+ ha?1 year?1, 18·9 kg K+ ha?1 year?1 and 4·4 kg Mg2+ ha?1 year?1). However, calcium deposition beneath the native forest stand was higher (15·9 kg Ca2+ ha?1 year?1) compared with the pine stand (12·6 kg Ca2+ ha?1 year?1). Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

13.
Various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west-central Minnesota. There is a marked change in magnetic properties as a function of depth in the core. X-ray analysis and Curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil. The intensity of anhysteretic remanent magnetization (ARM) decreases sharply as the depth increases. In contrast, the stability of ARM was found to be higher for the subsoil. The surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization (VRM). The VRM acquisition coefficient (Sa) of the subsoil (Sa= 3.18 × 10?6emu g?1, 3.18 × 10?6A m2 kg?1) was about ten times weaker than that of the top soil sample (Sa = 3.868 × 10?7emu g?1, 3.868 × 10?7A m2 kg?1). The magnetic domain state indicator, the ratio of coercivity of remanence to coercive force, Hcr/Hc, was 1.5 and 3.85 for the top soil and subsoil, respectively. It appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size. We conclude that the magnetic grains in surface soil samples were more single-domain (SD) like whereas the magnetite grains in the subsoil samples were more likely in pseudo-single-domain (PSD) or small multidomain (MD) range. The observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs.  相似文献   

14.
Water samples collected at the 21°N hydrothermal site on the East Pacific Rise crest, including Deep-Tow and hydrocast samples collected in 1977 and three hot vent water samples collected recently with the submersible “Alvin”, contain significant additions of3He,4He, and Mn. Although the vent water collections were at least 50-fold diluted with ambient seawater, they are up to 53 times enriched in3He and 7.4 times enriched in4He relative to saturated seawater, with concentrations of total dissolvable manganese (TDM) up to 310 μg/kg.3He and4He covary in the vent samples, with3He/4He about 8 times the atmospheric ratio, reflecting a mantle helium source. In contrast to the helium isotopes the Mn/3He ratio in the vent samples is variable, ranging from 4.3 × 104 up to 1.0 × 105 g/cm3. Profiles of3He/4He and TDM in the water column at 21°N show a sharp maximum ofδ(3He) = 47%and TDM= 0.69 μg/kg, much higher than the average values of 34% and 0.2 μg/kg for the deep water in this region. This spike in3He and Mn occurs at 2400 m depth, 200 m above the level of the 21°N vents, and 100 m higher than any local bathymetry, evidence for upward transport of the hydrothermal discharge via rising plumes of hot vent water. Two of the 21°N Deep-Tow samples associated with small (?0.010°C) temperature anomalies hadδ(3He) = 38%and TDM= 0.28 and 0.58 μg/kg, also slightly elevated relative to background. The Deep-Tow and hydrocast samples have lower Mn/3He ratios than average vent samples due to Mn removal by scavenging. Comparison of vent samples and water column measurements at 21°N indicate that the pure vent water could be detected using3He and Mn even when diluted ～105 times with seawater, confirming that these two tracers are extremely sensitive indicators of submarine hydrothermal activity.  相似文献   

15.
Early diagenetic manganese nodules from the northeast Pacific nodule belt and from the southeast Pacific (Peru Basin) show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10-Åmanganate (A1 substance) and amorphous material which is composed of an intimate mixture of ferric hydroxide, silicate, and δ-MnO2 (A2 substance). The formation of rhythmic sequences of A1 and A2 microlayers is explained by physico-chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface: (a) upward diffusion of Mn2+ in the interstitial water as a result of decay of organic matter and Mn mobilization; (b) oxidation of Mn2+ and formation of 10-Åmanganate in the upper part of the peneliquid sediment layer, leading to pH depression in the microenvironment of the nodule surface which decreases the mobility of silicate, resulting in formation of A2 layers; (c) restoration of pH and renewed precipitation of 10-Åmanganate.Based on data of 171 bulk analyses and on electron microprobe investigations, interelement relationships between Co, Mn, and Fe are pointed out. Fe and Co show a significant positive correlation (r = 0.84), while Mn and Co are poorly negatively correlated (r = ?0.21), assuming linear regression. The enrichment of Co within the amorphous A2 phase is attributed to specific surface adsorption and subsequent oxidation of Co2+ to Co3+ in the strong electric field of Si4+. Robust complexes of Co(III) and ≡ FeH2SiO4? prevent most of the Co from being available for the 10-Åmanganate precipitation. Concerning the relation between Mn and Fe and Co respectively, the highest correlation coefficients are obtained using an inverse logarithmic regression. Under early diagenetic conditions, the concentration and precipitation of Mn2+ in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter. The Nernst equation describes the relationship as a reciprocal logarithmic function. However, the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential. These different characteristics in the precipitation of Mn and the Fe- and Si-rich colloidal phase may cause the significantly negative logarithmic correlation of Mn versus Fe and Co, respectively.  相似文献   

16.
A second-order hydrostatic theory is developed on the assumption that the trace of the Earth's inertia tensor, its mass and mean radius are invariant under any process causing deviations from the hydrostatic state.The hydrostatic flattening and the zonal coefficients of the hydrostatic gravitational field are obtained as ??1 = 299.638, J2 = 1072.618 × 10?6 and J4 = ?2.992 × 10?6, respectively.The internal theory using the preliminary reference earth model (PREM) of Dziewonski and Anderson (1981) yields ??1 = 299.627, J2 = 1072.701 × 10?6 and J4 = ?2.992 × 10?6. The agreement between these and the hydrostatic values indicate that PREM is suitable as a reference model as it represents the spheroidal density distribution in a state of zero non-hydrostatic stress while satisfying the fundamental geodetic observations of the invariant quantities.The small discrepancy between the hydrostatic flattening and the value deduced from PREM suggests that the density is underestimated at large depths and/or it is slightly overestimated in shallow regions of the Earth.The discrepancies between the hydrostatic and observed quantities persist after the removal of the accountable effects of isostatically compensated topography, permanent tidal deformation and the present mass anomalies associated with the Late-Pleistocene deglaciation. These ‘corrected’ discrepancies point to a triaxial non-hydrostatic figure which cannot be explained by the delayed response of the Earth to tidal deceleration.  相似文献   

17.
The hyporheic zone of riverbed sediments has the potential to attenuate nitrate from upwelling, polluted groundwater. However, the coarse‐scale (5–10 cm) measurement of nitrogen biogeochemistry in the hyporheic zone can often mask fine‐scale (<1 cm) biogeochemical patterns, especially in near‐surface sediments, leading to incomplete or inaccurate representation of the capacity of the hyporheic zone to transform upwelling NO3?. In this study, we utilised diffusive equilibrium in thin‐films samplers to capture high resolution (cm‐scale) vertical concentration profiles of NO3?, SO42?, Fe and Mn in the upper 15 cm of armoured and permeable riverbed sediments. The goal was to test whether nitrate attenuation was occurring in a sub‐reach characterised by strong vertical (upwelling) water fluxes. The vertical concentration profiles obtained from diffusive equilibrium in thin‐films samplers indicate considerable cm‐scale variability in NO3? (4.4 ± 2.9 mg N/L), SO42? (9.9 ± 3.1 mg/l) and dissolved Fe (1.6 ± 2.1 mg/l) and Mn (0.2 ± 0.2 mg/l). However, the overall trend suggests the absence of substantial net chemical transformations and surface‐subsurface water mixing in the shallow sediments of our sub‐reach under baseflow conditions. The significance of this is that upwelling NO3?‐rich groundwater does not appear to be attenuated in the riverbed sediments at <15 cm depth as might occur where hyporheic exchange flows deliver organic matter to the sediments for metabolic processes. It would appear that the chemical patterns observed in the shallow sediments of our sub‐reach are not controlled exclusively by redox processes and/or hyporheic exchange flows. Deeper‐seated groundwater fluxes and hydro‐stratigraphy may be additional important drivers of chemical patterns in the shallow sediments of our study sub‐reach. © 2015 The Authors. Hydrological Processes Published by John Wiley & Sons Ltd.  相似文献   

18.
The pressure-temperature conditions in the primordial nebula which could produce the observed Ni, Ga and Ge abundances in the major iron meteorite groups have been calculated assuming equilibrium condensation. Included in these calculations are the effect on the metal composition of Fe oxidation and sulphide formation during accretion, GeS and GaCl in the nebula gases and pressure variations in the nebula. It was found that the IIAB irons had their abundances of these elements fixed at the low-pressure extreme of the range which gives the IAB irons, but at 50 ± 10K higher temperatures. IIIAB and IVA formed over the same temperature range as IAB (600–670?40+60 K) in regions where the pressure was lower by a factor of 20 and 104 respectively. Group IVB accreted soon after condensation of the metal and at pressures of less than 10?3 atmosphere. The distribution of sulphur and carbon are consistent with this. The abundance of carbon in group IAB suggests that this and group IIAB accreted at about 10?4 atmosphere, so that IIIAB and IVA accreted where the pressure was 5 × 10?6 and 10?8 atmosphere, respectively.  相似文献   

19.
We present the distribution of226Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface226Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the226Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of226Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary226Ra can be traced up to at least 1–1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic226Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2–4 km)226Ra data give the following set of best fits: upwelling velocity(Vz) = 3.5m/yr, vertical eddy diffusivity(Kz) = 0.6cm2/s, horizontal (north-south) eddy diffusivity(Ky) = 1 × 107cm2/s, and water-column regeneration flux of226Ra(J) = 3.3 × 10?5dpmkg?1yr?1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of226Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constantVz and Kz. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities.  相似文献   

20.
Absolute18O content of standard mean ocean water   总被引：1，自引：0，他引：1  
The absolute values of the18O/16O ratio (Rs) and the relative18O content (Xs) in SMOW have been determined by comparing SMOW mass spectrometrically with well-defined synthetic mixtures of pure D218O and H216O. The results are:RS = (2005.20 ± 0.45) × 10?6, XS = (2000.45 ± 0.45) × 10?6  相似文献   

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