Excesses Of Isotopes Research Articles

Nuclear mass measurements map the structure of atomic nuclei and accreting neutron stars

We present mass excesses (ME) of neutron-rich isotopes of Ar through Fe, obtained via TOF-$B\rho$ mass spectrometry at the National Superconducting Cyclotron Laboratory. Our new results have significantly reduced systematic uncertainties relative to a prior analysis, enabling the first determination of ME for $^{58,59}{\rm Ti}$, $^{62}{\rm V}$, $^{65}{\rm Cr}$, $^{67,68}{\rm Mn}$, and $^{69,70}{\rm Fe}$. Our results show the $N=34$ subshell weaken at Sc and vanish at Ti, along with the absence of an $N=40$ subshell at Mn. This leads to a cooler accreted neutron star crust, highlighting the connection between the structure of nuclei and neutron stars.

Uniform 182W isotope compositions in Eoarchean rocks from the Isua region, SW Greenland: The role of early silicate differentiation and missing late veneer

Abstract Eoarchean rocks from the Isua region in southern West Greenland are known to exhibit isotope anomalies of 182W and 142Nd. The excess 182W in many rocks from the Isua region have been explained by two endmember models: (1) missing late veneer or (2) silicate differentiation shortly after Earth’s formation. Furthermore, it has been proposed that pristine W isotope systematics in rocks from the Isua region (herein the Isua supracrustal belt and adjacent area) have been obscured by metamorphic disturbance. To address these issues, we present a comprehensive dataset, combining high precision 182W isotope data with trace element data, including high precision elemental W-Th-U-Ta abundance data. We present an improved analytical protocol that allows processing gram-sized samples with W abundances in the lower ng/g range. This protocol also results in markedly improved ion exchange column yields and cleaner W fractions, thereby minimizing nuclear volume effects on 183W. To compare with previous studies, our dataset includes some samples from previously investigated units in the Isua region (Isua Supracrustal Belt (ISB) mafic–ultramafic assemblages and Ameralik dikes). In addition, several Eoarchean key units in the Isukasia terrane (Isua region) and the Faeringehavn terrane (Nuuk region) have been examined for their W isotope composition in this study for the first time. These newly investigated units include recently recognized mantle-like peridotites from both terranes that display PGE abundances and patterns similar to modern depleted mantle peridotites, felsic lithologies from the ISB, as well as key amphibolite and TTG localities from low-strain domains south of the ISB. Virtually all rocks from the Isua region show significant W enrichment with W/Th of up to 160 in mafic to ultramafic samples. None of the samples from SW Greenland that were object of 182W isotope analysis in this study and virtually all previous studies appear to have preserved near canonical W/Th ratios (i.e., between 0.09 and 0.24). Independent of W enrichment, however, it can now be shown that there is a uniform 182W isotope excess in the different rock types from the Itsaq Gneiss Complex (IGC) (average 12.8 ppm ± 1 ppm, 95% confidence interval). Importantly, none of the rock suites investigated exhibit modern mantle-like 182W isotope signatures of µ182W = 0. By combining 182W signatures in the different lithologies with elemental W systematics, we therefore can infer that the 182W excess in Eoarchean rocks from the Isua region is widespread, and independent of W enrichment. Hence, we regard the 182W excess as an intrinsic feature of the Eoarchean assemblages in the Isua region. Notably, mantle-like peridotites from both the Isukasia and Faeringehavn terranes display the same 182W excess, as all other units, although they have been shown to display the full inventory of Highly Siderophile Elements (HSE) found in Phanerozoic mantle peridotites. Evidently, the W isotope budget in these rocks is clearly decoupled from HSE systematics, which hampers a straightforward explanation for 182W isotope excesses in terms of the missing late veneer model. As Platinum Group Element (PGE) patterns in mantle-like Eoarchean peridotites from the Isua region are similar to those in Phanerozoic rocks, we rather propose that to a large extent the 182W excesses are a vestige of early silicate differentiation processes, in line with positive 142Nd anomalies found in rocks from the Isua region, suggesting initial silicate differentiation prior to 4.50 Ga.

Cropping systems sustainability: Inoculation and fertilisation effect on sulla performances in a new cultivation area

To assess the feasibility of the sulla [Sulla coronaria (L.) Medik] forage legume in a new agroecosystem, its host-specific symbiotic interaction needs to be taken into account. This study aimed to investigate the effects of inoculation and nitrogen (N) fertiliser on productive performances and N-fixation ability of sulla established in a new habitat within a Mediterranean agropastoral area. Sulla plants, previously inoculated (with peat-based, liquid inoculants, and using soil from an existing sulla field) and unfertilised or N fertilised were evaluated in Sardinia (Italy). During 2013-2014, sulla plants were sampled at four growing stages, from vegetative stage to seed set, and shoot length, shoot dry matter (DM) yield and N content were monitored. Moreover, atom% 15N isotopic excess, proportion of N derived from the atmosphere and fixed N of sulla shoots were quantified. Inoculation and N fertilisation both affected growth, DM and N yields, and N-fixation of sulla. Compared to the best inoculated treatment, the DM yield and fixed N of the control only represented 10 to 22% and 2 to 11%, respectively. Nitrogen fertilisation caused temporary decreases in the N fixing ability of sulla. Results pointed out that rhizobial inoculation is essential for the exploitation of sulla outside its traditional cropping area.

A model for 12CH2D2 and 13CH3D as complementary tracers for the budget of atmospheric CH4

AbstractWe present a theoretical model to investigate the potential of 13CH3D and 12CH2D2, the doubly substituted mass‐18 isotopologues of methane, as tools for tracking atmospheric methane sources and sinks. We use electronic structure methods to estimate kinetic isotope fractionations associated with the major sink reactions of methane in air (reactions with OH and Cl radicals) and combine literature data with reconnaissance measurements of the relative abundances of 13CH3D and 12CH2D2 to estimate the compositions of the largest atmospheric sources. This model atmospheric budget is investigated with a simplified box model in which we explore both steady state and dynamical (nonsteady state) conditions triggered by changes in emission or sink fluxes. The steady state model predicts that sink reactions will generate a marked (>100‰) clumped isotope excess in atmospheric Δ12CH2D2 relative to the net source composition. 12CH2D2 measurements may thus be useful for tracing both atmospheric source and sink fluxes. The effect of sinks on Δ13CH3D is much less pronounced, indicating that 13CH3D in air will give a more focused picture of the source composition.

In situ isotopic studies of the U-depleted Allende CAI Curious Marie: Pre-accretionary alteration and the co-existence of 26Al and 36Cl in the early solar nebula

The isotopic composition of oxygen as well as 26Al-26Mg and 36Cl-36S systematics were studied in Curious Marie, an aqueously altered Allende CAI characterized by a Group II REE pattern and a large 235U excess produced by the decay of short-lived 247Cm. Oxygen isotopic compositions in the secondary minerals of Curious Marie follow a mass-dependent fractionation line with a relatively homogenous depletion in 16O (Δ17O of −8‰) compared to unaltered minerals of CAI components. Both Mg and S show large excesses of radiogenic isotopes (26Mg∗ and 36S∗) that are uniformly distributed within the CAI, independent of parent/daughter ratio. A model initial 26Al/27Al ratio [(6.2±0.9)×10−5], calculated using the bulk Al/Mg ratio and the uniform δ26Mg∗∼+43‰, is similar to the canonical initial solar system value within error. The exceptionally high bulk Al/Mg ratio of this CAI (∼95) compared to other inclusions is presumably due to Mg mobilization by fluids. Therefore, the model initial 26Al/27Al ratio of this CAI implies not only the early condensation of the CAI precursor but also that aqueous alteration occurred early, when 26Al was still at or near the canonical value. This alteration event is most likely responsible for the U depletion in Curious Marie and occurred at most 50kyr after CAI formation, leading to a revised estimate of the early solar system 247Cm/235U ratio of (5.6±0.3)×10−5. The Mg isotopic composition in Curious Marie was subsequently homogenized by closed-system thermal processing without contamination by chondritic Mg. The large, homogeneous 36S excesses (Δ36S∗∼+97‰) detected in the secondary phases of Curious Marie are attributed to 36Cl decay (t1/2=0.3Myr) that was introduced by Cl-rich fluids during the aqueous alteration event that led to sodalite formation. A model 36Cl/35Cl ratio of (2.3±0.6)×10−5 is calculated at the time of aqueous alteration, translating into an initial 36Cl/35Cl ratio of ∼1.7–3×10−5 at solar system birth. The Mg and S radiogenic excesses suggest that 26Al and 36Cl co-existed in the early solar nebula, raising the possibility that, in addition to an irradiation origin, 36Cl could have also been derived from a stellar source.

ISOTOPIC EXCESSES OF PROTON-RICH NUCLEI RELATED TO SPACE WEATHERING OBSERVED IN A GAS-RICH METEORITE KAPOETA

The idea that solar system materials were irradiated by solar cosmic rays from the early Sun has long been suggested, but is still questionable. In this study, Sr, Ba, Ce, Nd, Sm, and Gd isotopic compositions of sequential acid leachates from the Kapoeta meteorite (howardite) were determined to find systematic and correlated variations in their isotopic abundances of proton-rich nuclei, leading to an understanding of the irradiation condition by cosmic rays. Significantly large excesses of proton-rich isotopes (p-isotopes), 84Sr, 130Ba, 132Ba, 136Ce, 138Ce, and 144Sm, were observed, particularly in the first chemical separate, which possibly leached out of the very shallow layer within a few ?m from the surface of regolith grains in the sample. The results reveal the production of p-isotopes through the interaction of solar cosmic rays with the superficial region of the regolith grains before the formation of the Kapoeta meteorite parent body, suggesting strong activity in the early Sun.

Software LS-MIDA for efficient mass isotopomer distribution analysis in metabolic modelling.

BackgroundThe knowledge of metabolic pathways and fluxes is important to understand the adaptation of organisms to their biotic and abiotic environment. The specific distribution of stable isotope labelled precursors into metabolic products can be taken as fingerprints of the metabolic events and dynamics through the metabolic networks. An open-source software is required that easily and rapidly calculates from mass spectra of labelled metabolites, derivatives and their fragments global isotope excess and isotopomer distribution.ResultsThe open-source software “Least Square Mass Isotopomer Analyzer” (LS-MIDA) is presented that processes experimental mass spectrometry (MS) data on the basis of metabolite information such as the number of atoms in the compound, mass to charge ratio (m/e or m/z) values of the compounds and fragments under study, and the experimental relative MS intensities reflecting the enrichments of isotopomers in 13C- or 15 N-labelled compounds, in comparison to the natural abundances in the unlabelled molecules. The software uses Brauman’s least square method of linear regression. As a result, global isotope enrichments of the metabolite or fragment under study and the molar abundances of each isotopomer are obtained and displayed.ConclusionsThe new software provides an open-source platform that easily and rapidly converts experimental MS patterns of labelled metabolites into isotopomer enrichments that are the basis for subsequent observation-driven analysis of pathways and fluxes, as well as for model-driven metabolic flux calculations.

Radioactive Cs capture in the early solar system

Barium isotopic compositions of primitive materials in the solar system are generally affected by s- and r-process nucleosynthetic components that hide the contribution of the isotopic excess of 135Ba formed by decay of radioactive 135Cs. However, the Ba isotopic composition of the chemical separates from chondrules in the Sayama CM2 chondrite shows an excess of 135Ba isotopic abundance up to (0.33 ± 0.06)%, which is independent of the isotopic components from s- and r-process nucleosyntheses. The isotopic excesses of 135Ba correlate with the elemental abundance of Ba relative to Cs, providing chemical and isotopic evidence for the existence of the presently extinct radionuclide 135Cs (t1/2 = 2.3 million years) in the early solar system. The estimated abundance of 135Cs/133Cs = (6.8 ± 1.9) × 10−4 is more than double that expected from the uniform production model of the short-lived radioisotopes, suggesting remobilization of Cs including 135Cs in the chondrules of the meteorite parent body.

Evolution of isotopic composition and deuterium excess of brines in the Sichuan Basin, China

The isotopic composition and parameters for deuterium excess of brines, which were sampled in the Sichuan Basin, show obvious regularities of distribution. The brine isotopic composition shows distinct two systems of marine and terrestrial deposits, with the Middle Triassic strata as the boundary. Brine hydrogen isotopic composition of marine deposits is lower while oxygen isotopic composition is higher than that of the SMOW, respectively, indicating that the brines were derived from seawater with different evaporating degrees at different times. From the Sinian strata, up to the Cambrian, Permian Maokou Formation and the Triassic Jialingjiang Formation, the δD values of brines tend to become relatively positive with the strata becoming younger. Brines of terrestrial deposits are considered to have been derived from precipitation and their isotopic composition is close to the globe meteoric water line (GMWL). Brines of transitional deposits between marine and terrestrial ones (the Upper Triassic Xujiahe Formation) have δD and δ18O values falling between the two end members of marine deposit brines and precipitation, indicating that the brines are a mixture of precipitation and vaporing seawater. Water samples from the brine-bearing strata of different ages show various deuterium excesses (d) with an evident decreasing trend as the age of strata gets older and older. Brine-bearing strata of the Triassic Leikoupo-Jialingjiang Formation, the Permian Maokou Formation, the Cambrian and Sinian strata are all carbonate rocks which have experienced intensive water/rock reaction and the deuterium excess essentially changes with time. All brine-bearing-strata surrounding the basin or faults, as well as those brine wells exploited for resources, have been obviously influenced by the precipitation supply. Therefore, the deuterium excesses of their brines have increased to different extents, depending on the amount of involvement of meteoric water. The variation and distribution of d values of the brines from different Triassic strata are related to the embedded depth of the strata. The deuterium excesses of brines become lower with increasing burial depth of the strata.

Recalculation of data for short‐lived radionuclide systems using less‐biased ratio estimation

Abstract–Ratios determined from counting a subset of atoms in a sample are positively biased relative to the true ratio in the sample (Ogliore et al. 2011). The relative magnitude of the bias is approximately equal to the inverse of the counts in the denominator of the ratio. SIMS studies of short‐lived radionuclides are particularly subject to the problem of ratio bias because the abundance of the daughter element is low, resulting in low count rates. In this paper, we discuss how ratio bias propagates through mass‐fractionation corrections into an isochron diagram, thereby affecting the inferred initial ratio of short‐lived radionuclides. The slope of the biased isochron can be either too high or too low, depending on how it is calculated. We then reanalyze a variety of previously published data sets and discuss the extent to which they were affected by ratio bias. New, more accurate, results are presented for each study. In some cases, such as for 53Mn‐53Cr in pallasite olivines and 60Fe‐60Ni in chondrite sulfides, the apparent excesses of radiogenic isotopes originally reported disappear completely. Many of the reported initial 60Fe/56Fe ratios for chondrules from ordinary chondrites are no longer resolved from zero, though not all of them. Data for 10Be‐10B in CAIs were only slightly affected by bias because of how they were reduced. Most of the data sets were recalculated using the ratio of the total counts, which increases the number of counts in the denominator isotope and reduces the bias. However, if the sum of counts is too low, the ratio may still be biased and a less‐biased estimator, such as Beale’s estimator, must be used. Ratio bias must be considered in designing the measurement protocol and reducing the data. One can still collect data in cycles to permit editing of the data and to monitor and correct for changes in ion‐beam intensity, even if total counts are used to calculate the final ratio. The cycle data also provide a more robust estimate of the uncertainties from temporal variations in the secondary ion signal.

Sulfur isotope evidence of little or no stratospheric impact by the 1783 Laki volcanic eruption

Historic records and research have suggested that the 1783–1784 eruption of the Laki fissure volcano in Iceland impacted Northern Hemisphere climate significantly, probably as a result of the direct injection of volcanic materials into the stratosphere where the volcanic aerosols would linger for years to cause surface cooling across the Northern Hemisphere. However, recent modeling work indicates the Laki climatic impact was limited to the Northern Hemisphere and only in the second half of 1783. We measured sulfur‐33 isotope excess (Δ33S) in volcanic sulfate of historical eruptions including Laki found in Summit, Greenland ice cores. No Δ33S excess is found in sulfate of apparently tropospheric eruptions, while sulfate of stratospheric eruptions is characterized by significant Δ33S excess and a positive‐to‐negative change in Δ33S during its gradual removal from the atmosphere. Because the same characteristics have been previously found in volcanic sulfate in Antarctica snow, the results from Greenland indicate similar global processes of stratospheric chemical conversion of SO2 to sulfate. The isotopic composition of Laki sulfate is essentially normal and shows no characteristics of sulfate produced by stratospheric photochemical reactions. This clearly indicates that the Laki plume did not reach altitudes of the stratospheric ozone layer. Further, the short aerosol residence time (<6 months) suggests that the bulk of the Laki plume and subsequent aerosols were probably confined to the middle and upper troposphere. These conclusions support the hypothesis of D'Arrigo and colleagues that the unusually cold winter of 1783–1784 was not caused by Laki.

ChemInform Abstract: Biosynthesis of Hyoscyamine Involves an Intramolecular Rearrangement of Littorine.

The direct biosynthesis of hyoscyamine 3 from littorine 1 has been demonstrated by feeding (RS)-phenyi[1,3-13C2]lactoyl[methyl-2H3]tropine (littorine 13) to transformed root cultures of Datura stramonium. In tropane alkaloids isolated 7 days later and examined by GC–MS, the labelling patterns of hyoscyamine 3 and apoatropine 4 indicated that the quintuply labelled precursor had been incorporated intact. Incorporations into the M + 5 peaks of hyoscyamine 16 and apoatropine 4 of 4.4 and 3.8% isotopic excess were found respectively. The % isotopic excesses in the M + 2 and M + 3 ions of these alkaloids indicate that a biosynthetic route involving the hydrolysis of the ester followed by re-esterification could only account for 0.2% isotopic excess in the observed M + 5 incorporation into hyoscyamine 16. Furthermore, the incorporation of (RS)-phenyl[1,3-13C2]lactoyl[methyl-2H3]tropine 13 into hyoscyamine 16 and apoatropine was not diminished in the presence of added tropine 6 or (RS)-phenyllactic acid. The retention of a high isotopic excess within hyoscyamine 16, coupled to the inability of either added tropine 6 or phenyllactic acid to dilute the extent of labelling, shows that hyoscyamine 3 is derived directly by the rearrangement of littorine 1. That this rearrangement is Intramolecular is shown by the high level of 13C spin-spin coupling observed in the 13C NMR spectrum of the derived hyoscyamine 16.

Transport and selective uptake of radium into natural clay minerals

Understanding of the environmental behavior of Ra is important from the viewpoint of the long-termed repository safety of radioactive waste, but investigation of Ra behavior in natural environment is difficult to detect. We found isotopic evidence of Ra transportation and its selective uptake into clay minerals from Pb isotopic analyses. Illite grains found in calcite veins included in sandstone near the Oklo uranium deposit, Republic of Gabon, show extremely low 207Pb/ 206Pb (∼ 0.0158) isotopic ratios. Although the Pb isotopic ratios of calcite and quartz coexisting with illite indicate the formation age of each component, those of illite do not. In addition, illite grains having low 207Pb/ 206Pb isotopic ratios contain a strongly large amount of Ba (1230 to 6010 ppm) in contrast with low contents of Ba in calcite and quartz (< 0.26 ppm). Considering the chemical similarity between Ba and Ra, the 207Pb/ 206Pb isotopic data suggest an excess of 206Pb due to selective adsorption of 226Ra (and also Ba) into illite grains. This is a very rare example to show evidence of the selective adsorption behavior of Ra from the isotopic excesses of 206Pb, although the adsorption ability of Ra itself in nature was largely reported.

Isotopologue distributions of peptide product ions by tandem mass spectrometry: Quantitation of low levels of deuterium incorporation

Protonated molecular peptide ions and their product ions generated by tandem mass spectrometry appear as isotopologue clusters due to the natural isotopic variations of carbon, hydrogen, nitrogen, oxygen, and sulfur. Quantitation of the isotopic composition of peptides can be employed in experiments involving isotope effects, isotope exchange, and isotopic labeling by chemical reactions and in studies of metabolism by stable isotope incorporation. Both ion trap and quadrupole-time of flight mass spectrometry are shown to be capable of determining the isotopic composition of peptide product ions obtained by tandem mass spectrometry with both precision and accuracy. Tandem mass spectra of clusters of isotopologue ions obtained in profile mode are fit by nonlinear least squares to a series of Gaussian peaks which quantify the M n/M 0 values which define the isotopologue distribution (ID). To determine the isotopic composition of product ions from their ID, a new algorithm that predicts the M n/M 0 ratios and obviates the need to determine the intensity of all of the ions of an ID is developed. Consequently a precise and accurate determination of the isotopic composition of a product ion may be obtained from only the initial values of the ID, however, the entire isotopologue cluster must be isolated prior to fragmentation. Following optimization of the molecular ion isolation width, fragmentation energy, and detector sensitivity, the presence of isotopic excess ( 2H, 13C, 15N, 18O) is readily determined within 1%. The ability to determine the isotopic composition of sequential product ions permits the isotopic composition of individual amino acid residues in the precursor ion to be determined.

Measurement of the 13C/12C ratio of soil-plant individual sugars by gas chromatography/combustion/isotope-ratio mass spectrometry of silylated derivatives.

Carbohydrate is an important pool in the terrestrial carbon cycle. The potential offered by natural and artificial 13C-labelling techniques should therefore be applied to the investigation of the dynamics of individual sugars in soils. For this reason, we evaluated the method of 13C sugar analysis by gas chromatography/combustion/isotope-ratio mass spectrometry (GC/C/IRMS) after hydrolysis and direct trimethylsilylation. Trimethylsilylation involved the addition of several carbon atoms per sugar. These atoms have to be taken into account in the estimation of the carbon isotope ratio. The analysis of standard and natural pentoses and hexoses of known 13C enrichments revealed that the number of analysed added carbon atoms was less than expected from stoichiometry. This was attributed to incomplete derivatization and/or incomplete oxidation of methylsilyl carbon before IRMS. Using a calibration of the number of analysed added carbon atoms, the isotope excess of enriched samples could be determined with a relative error close to 5%. Concerning the determination of natural abundances by GC/C/IRMS, we could measure the delta 13C of standard C3- and C4-derived sugars with an accuracy of +/-1.5 per thousand using the previous calibration. We were able to apply this technique to plant-soil systems labelled by pulse-chase of 13CO2, revealing the nature and dynamics of sugars in the plant rhizosphere.

Solar wind and other gases in the regoliths of the Pesyanoe parent object and the moon

We report new data from Pesyanoe‐90,1 (dark lithology) on the isotopic signature of solar wind (SW) Xe as recorded in this enstatite achondrite which represents a soil‐breccia of an asteroidal regolith. The low temperature (≤800°C) steps define the Pesyanoe‐S xenon component, which is isotopically consistent with SW Xe reported for the lunar regolith. This implies that the SW Xe isotopic signature was the same at two distinct solar system locations and, importantly, also at different times of solar irradiation. Further, we compare the calculated average solar wind “SW‐Xe” signature to Chass‐S Xe, the indigenous Xe observed in SNC (Mars) meteorites. Again, a close agreement between these compositions is observed, which implies that a mass‐dependent differential fractionation of Xe between SW‐Xe and Chass‐S Xe is &gt;1.5%o per amu. We also observe fractionated (Pesyanoe‐F) Xe and Ar components in higher temperature steps and we document a fission component due to extinct 244Pu. Interestingly, the Pesyanoe‐F Xe component is revealed only at the highest temperatures (&gt;1200°C). The Pesyanoe‐F gas reveals Xe isotopic signatures that are consistent with lunar solar energetic particles (SEP) data and may indicate a distinct solar energetic particle radiation as was inferred for the moon. However, we cannot rule out fractionation processes due to parent body processes. We note that ratios 36Ar/38Ar≤5 are also consistent with SEP data. Calculated abundances of the fission component correlate well with radiogenic 40Ar concentrations, revealing rather constant 244Pu/K ratios in Pesyanoe, and separates thereof, and indicate that both components were retained. We identify a nitrogen component (δ15N = 44%o) of non‐solar origin with an isotopic signature distinct from indigenous N (δ15N = −33%o). While large excesses at 128Xe and 129Xe are observed in the lunar regolith samples, these excesses in Pesyanoe are small. On the other hand, significant 126Xe isotopic excesses, comparable to relative excesses observed in lunar soils and breccias, are prominent in the intermediate temperature steps of Pesyanoe‐90,1.

A new hypothesis for the existence of superheavy elements in the earth"s crust

In a new hypothesis the existence of superheavy elements (SHE) in the earth"s crust that decays by spontaneous fission into two unequal fragments around 50 and 230 is postulated. Several phenomena such as excesses of stable and unstable isotopes and radioactive daughter isotopes in natural decay series are interpreted as fission fragments of spontaneously splitting long-lived SHE. These phenomena are only indirect indications, not a proof of the existence of SHE.

Isotopic search for live 135Cs in the early solar system and possibility of 135Cs– 135Ba chronometer

Here we report the isotopic excess of 135Ba studied from Ba isotopic measurements of acid leachates of Allende calcium–aluminum rich inclusions (CAIs) and two primitive chondrites, Beardsley (H5) and Zag (H6 clasts). From the excess 135Ba abundances of CAIs, after subtraction of the r-process nucleosynthetic component in a model-dependent manner, a value for 135Cs/ 133Cs=(4.8±0.8)×10 −4 is proposed as the initial ratio in the early solar system. A correlation between excess 135Ba abundances and Cs/Ba ratios observed in the Beardsley and the Zag meteorites reveals the possible existence of primordial 135Cs in the two meteorite parent bodies. On the assumption of two cases for 135Cs/ 133Cs initial in the early solar system, the 135Cs– 135Ba isochron suggests that primitive (aqueous) alteration in the Beardsley and Zag meteorite bodies occurred at 8.2∼11.9 Ma and 13.9∼17.6 Ma after CAI formation, respectively. Our results are apparently consistent with previously reported data from Pb–Pb model age determinations, and 53Mn– 53Cr chronometry for chondrites. This is the first report of isotopic excess of 135Ba in meteorites, which may relate to live 135Cs in the early solar system and the 135Cs– 135Ba chronological application.

A new method to determine the 17O isotopic abundance in CO2 using oxygen isotope exchange with a solid oxide.

This paper discusses a simple method to determine 17O isotope excess or deficiency ('mass-independent isotopic composition') in CO2 gas. When applying conventional mass spectrometry of CO2 (m/z 44, 45 and 46) to determine the 17O/16O ratio, the 13C/12C ratio has to be established separately. This can be achieved by analysing an aliquot of sample CO2 before and after subjecting it to oxygen isotope exchange with a pool of oxygen with 'normal' 17O/16O ratio, i.e. with Delta17O approximately equal to delta17O-0.516 x delta18O = 0. Cerium oxide has been shown to be practically well suited for the exchange of CO2 oxygen; the reagent is safe and does not produce any contamination. The CO2-CeO2 exchange reaction has 99.8 +/- 0.7% recovery yield. At 650 degrees C this reaction reaches equilibrium in 30 min and, as tested, results in complete oxygen replacement. Delta17O determinations depend on accuracy of CO2 delta measurements: the repeatability of +/-0.015 per thousand (1sigma) in delta(45)R and delta(46)R determination relative to the working reference results in an error of Delta17O as small as +/-0.33 per thousand. Such a precision is sufficient for Delta17O determination in stratospheric CO2. The calculated Delta17O value systematically depends on absolute 17R and 13R ratios in isotopic reference materials, which are presently not yet known with certainty (the 17R value is most important), and may be inadequate for 17O-correction with a = 0.516. Within the present uncertainty, Delta17O determined in 17O-enriched CO2 agrees with the value directly measured in the enriched O2 from which this CO2 was produced. Besides Delta17O determination, investigated CO2-CeO2 equilibration may have several other implications. Fast, complete isotopic exchange of CO2 by reaction with CeO2 may also be employed to get reproducible 17O-correction and, hence, to better monitor small delta13C shifts and to isotopically equilibrate mixtures of CO2 gases.

Application of the 15N technique to determine the contributions of nitrification and denitrification to the flux of nitrous oxide from aerated pig slurry

In order to elucidate and quantify nitrogen transformations occurring during aerobic treatment of pig slurry, two laboratory experiments were carried out with contrasting levels of aeration, high level (experiment 1) and low level (experiment 2) of aeration. During these experiments, after reaching steady-state conditions, a single pulse of NO 3 −- 15N tracer was added directly to the reactor. When nitrification conditions were prevailing (experiment 1), no transformation of added NO 3 −- 15N occurred (98.7% 15N-recovery as nitrates in the liquid slurry). Moreover, the unlabelled nitrous oxide (N 2O) measured (7.4% of the total nitrogen content of the raw slurry) strongly demonstrated that the source of N 2O emitted was nitrification. During simultaneous nitrification and denitrification conditions (experiment 2), the added NO 3 −- 15N was found in gaseous nitrogen forms (N 2O- 15N : 27%; N 2- 15N : 18%) and in the liquid (TN- 15N : 54%). From this result, it was evident that N 2O was mainly emitted by denitrification process. Using the decrease of the isotopic excess of the NO 3 −- 15N we calculated that 92% of NO 2 −-N was directly denitrified (as gaseous forms) without any previous oxidation to nitrate.