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Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been analysed at sub-annual resolution in three sections from a110 m ice core dated to the 18th and 20th centuries, as well as snow pit samples dated to 2004/2005, recovered from the East Rongbuk Glacier in the high-altitude Himalayas. Ice core sections indicate that atmospheric chemistry prior to ~1,953 was controlled by mineral dust inputs, with no discernible volcanic or anthropogenic contributions. Eighteenth century monsoon ice core chemistry is indicative of dominant contributions from local Himalayan sources; non-monsoon ice core chemistry is linked to contributions from local (Himalayan), regional (Indian/Thar Desert) and long-range (North Africa, Central Asia) sources. Twentieth century monsoon and non-monsoon ice core data demonstrate similar seasonal sources of mineral dust, however with a transition to less-radiogenic isotopic signatures that suggests local and regional climate/environmental change. The snow pit record demonstrates natural and anthropogenic contributions during both seasons, with increased anthropogenic influence during non-monsoon times. Monsoon anthropogenic inputs are most likely sourced to South/South-East Asia and/or India, whereas non-monsoon anthropogenic inputs are most likely sourced to India and Central Asia.

A joint IUPAC/IUPAP Working Party (JWP) has confirmed the discovery of the elements with atomic numbers 114 and 116. In accordance with IUPAC procedures, the discoverers proposed names as follows: flerovium with the symbol Fl for the element with Z = 114 and livermorium with the symbol Lv for the element with Z = 116. The IUPAC Inorganic Chemistry Division recommended these proposals for acceptance, and they were adopted on 23 May 2012 by the IUPAC Bureau as delegated to act by the IUPAC Council meeting on 3–4 August 2011.

The aim of this work was to develop thermal ionization mass spectrometry (TIMS) isotopic procedures to measure Zn isotope fractionation (δZn) in natural materials. This work represents the most recent development of Zn isotope measurements and the first δZn identification in terrestrial materials using TIMS and a double spike technique. The developed procedures evaluate and solve several critical analytical issues involved in TIMS Zn isotope analysis. For example, no more than 1 μg Zn was used for isotopic analyses which, considering the high ionization potential and low thermal ionization of Zn, represents a useful breakthrough in Zn isotope TIMS analysis. The effect of the ion exchange process on δZn was assessed and found equal to +0.07 ± 0.02‰ amu −1 per column. The ionization efficiency of Zn was enhanced to 0.22 ± 0.07%, which is four times more than what was achieved previously. The magnitude of δZn accompanied by the 95% confidence associated uncertainties were calculated relative to the IRMM 3702, using a Monte Carlo approach for each individual analysis, while the calculated average of δZn for number of analysis was accompanied by a 95% confidence calculated using GUM Workbench software. δZn values where always calculated using two different sets of isotopes which always agreed within uncertainty. These developments enabled sub-per mil δZn to be revealed relative to δZn zero for natural materials. Most of the samples measured are Standard Reference Materials SRMs, where, except for BCR-1 and BIR-1, this is the first time Zn isotopic fractionation has been measured in these samples. No previously published results for Zn isotopic fractionation have been published on these samples using double spiking. Consistent δZn of ∼+ 0.3‰ amu −1 was found in 5 sediments from a range of localities. δZn in two metamorphic samples is similar to that found in igneous rocks but different to that found in sedimentary rocks, which is consistent with our understanding that high temperature and pressure processes do not fractionate the composition of chalcophile elements. The isotope fractionation of Zn in a clay sample is within uncertainties the same as the sediments. The isotope fractionation of Zn of −0.088 ± 0.070‰ amu −1 was also measured in a standard rice sample. δZn in Antarctic Krill of +0.21 ± 0.11‰ amu −1 was found to be similar to the average δZn of +0.281 ± 0.083‰ amu −1 for marine sediments. River water was fractionated by −1.09 ± 0.70 ‰ amu −1 , while restrained tap water yielded the maximum isotope fractionation of −6.39 ± 0.62‰ amu −1 . δZn in high pure Zn standard materials ranged from −5.11 ± 0.36‰ amu −1 for AE 10760 to +0.12 ± 0.16‰ amu −1 for Zn IRMM 10440 with some evidence for a relationship between Zn isotope fractionation and its purity. All of the measured isotope fractionation yields an atomic weight within the IUPAC atomic weight of Zn.

– The isotope fractionation of Zn in meteorites has been measured for the first time using thermal ionization mass spectrometry and a double spiking technique. The magnitude of δZn ranged from −0.29 to +0.38‰ amu−1 for five stone meteorites whereas the iron meteorite Canyon Diablo displays δZn of 1.11 ± 0.11‰ amu−1. The results for chondrites in this work can be divided into positive and negative δZn, supporting a previous proposal that chondrites are a mixture of materials from two different temperature sources. The Zn isotope fractionation present in meteorites may represent a primordial heterogeneity formed in the early solar system. An anomalous isotopic composition of Zn obtained for the Redfields iron meteorite suggests large-scale inherited isotope heterogeneity of the protosolar nebula, or the presence of a parent body that has formed within its own isotopically anomalous reservoir. These anomalies are in the same direction but smaller than nuclear field shift effects observed in chemical exchange reactions. The isotope dilution mass spectrometry (IDMS) technique was used to measure Zn concentration, yielding a range from 20.1 μg g−1 to 302 μg g−1 in five stone meteorites and from 0.019 to 26 μg g−1 in seven iron meteorites. The IDMS-measured abundance of Zn in Orgueil is 302 ± 14 μg g−1 and should be considered for future compilations of the abundance of Zn in the solar system.

Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been determined at monthly resolution in five Law Dome (coastal Eastern Antarctica) ice core sections dated from ∼1757 AD to ∼1898 AD. ‘Natural’ background Pb concentrations in ∼1757 AD average ∼0.2 pg g−1 and can be attributed to mineral dust and volcanic emissions, with 206Pb/207Pb ratios reaching up to 1.266 ± 0.002. From ∼1887 AD to ∼1898 AD, Pb concentrations reached ∼5 pg g−1 and 206Pb/207Pb ratios decreased to 1.058 ± 0.001 as a result of additional inputs of Pb from anthropogenic sources. Seasonal variability in the late 1880s has been investigated by decoupling volcanic Pb from the total measured Pb concentrations, revealing spring and autumn maxima, and consistent winter minima, in anthropogenic Pb and mineral dust (Ba) concentrations. We link this variability to the annual cycle in the position and strength of the Antarctic Circumpolar Trough and, the Southern Ocean westerly winds to the north of the trough region. During the autumn and spring seasons, these systems increase in strength, transporting more impurity laden air from the Southern Hemisphere continental regions to Eastern Antarctica and Law Dome. As this Pb is isotopically identical to that emitted from south-eastern Australia (Broken Hill, Port Pirie) this implies a relatively direct air trajectory pathway from southern Australia to Law Dome (Eastern Antarctica).

A thermal ionisation mass spectrometric technique enabled the abundance of Zn in geological and biological reference materials and water samples to be measured by double spiking isotope dilution mass spectrometry enriched in the 67Zn and 70Zn isotopes. In the past, thermal ionisation mass spectrometry proved to be difficult for low-level zinc isotopic measurements. The size of Zn samples used for isotopic determination, in particular the biological RMs, represents an important breakthrough. These results represent the most accurate and precise concentrations measured for Zn in these samples. The maximum fractional uncertainty was that for TILL-3 (2%), while the minimum fractional uncertainty was 0.7% for both BCR-1 and W-2. The inhomogeneity of Zn in HISS-1 was revealed while other reference materials appeared homogeneous at the 95% confidence uncertainty. The certified concentration of Zn in HISS-1 and IMEP-19 by their producers are 28% and 3.8% higher than the values measured in this work. These are the first Zn concentration measurements in these materials by the isotope dilution-TIMS technique, except for BCR-1, NIES No 9 and IMEP-19. Reducing the blank enabled accurate measurement in water at the ng g-1 level demonstrating the applicability of the technique for low-level Zn samples. Une technique de spectrometrie de masse a ionisation thermique a permis de mesurer l’abondance en Zn dans des materiaux de reference geologiques et biologiques et des echantillons d’eau en utilisant une methode de dilution par double « spike » enrichi en isotopes 67Zn et 70Zn. Par le passe, les mesures isotopiques a faible teneur de zinc se sont averees difficiles par spectrometrie de masse a ionisation thermique. Les tailles des echantillons de Zn utilises pour les determinations isotopiques, en particulier les materiaux de reference biologiques (RMs), representent une important percee. Ces resultats representent les concentrations en Zn les plus exactes et precises mesurees dans ces echantillons. L’incertitude fractionnaire maximale est celle de TILL-3 (2%), tandis que l’incertitude fractionnaire minimum est de 0.7% pour BCR-1 et W-2. L’heterogeneite en Zn de HISS-1 a ete revelee alors que d’autres RMs semblent homogenes dans l’intervalle de confiance de 95%. Les concentrations de Zn certifiees par les fournisseurs de HISS-1 et IMEP-19 sont respectivement de 28% et de 3.8% plus elevees que les valeurs mesurees dans ce travail. Ce sont les premieres mesures de concentration du Zn dans ces materiaux par la technique de « dilution isotopique/TIMS », sauf pour BCR-1, NIES n° 9 et IMEP-19. La reduction du niveau du « blanc » a permis une mesure precise du Zn dans l’eau a un niveau de concentration de l’ordre du ng g-1, demontrant l’applicabilite des techniques pour des echantillons a faible teneur en Zn.

The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) of the International Union of Pure and Applied Chemistry (iupac.org) has revised the Table of Isotopic Compositions of the Elements (TICE). The update involved a critical evaluation of the recent published literature. The new TICE 2013 includes evaluated data from the “best measurement” of the isotopic abundances in a single sample, along with a set of representative isotopic abundances and uncertainties that accommodate known variations in normal terrestrial materials.

The biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of 19 elements. The standard atomic weights of four elements have been revised based on recent determinations of isotopic abundances in natural terrestrial materials: cadmium to 112.414(4) from 112.411(8), molybdenum to 95.95(1) from 95.96(2), selenium to 78.971(8) from 78.96(3), and thorium to 232.0377(4) from 232.038 06(2). The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) also revised the standard atomic weights of fifteen elements based on the 2012 Atomic Mass Evaluation: aluminium (aluminum) to 26.981 5385(7) from 26.981 5386(8), arsenic to 74.921 595(6) from 74.921 60(2), beryllium to 9.012 1831(5) from 9.012 182(3), caesium (cesium) to 132.905 451 96(6) from 132.905 4519(2), cobalt to 58.933 194(4) from 58.933 195(5), fluorine to 18.998 403 163(6) from 18.998 4032(5), gold to 196.966 569(5) from 196.966 569(4), holmium to 164.930 33(2) from 164.930 32(2), manganese to 54.938 044(3) from 54.938 045(5), niobium to 92.906 37(2) from 92.906 38(2), phosphorus to 30.973 761 998(5) from 30.973 762(2), praseodymium to 140.907 66(2) from 140.907 65(2), scandium to 44.955 908(5) from 44.955 912(6), thulium to 168.934 22(2) from 168.934 21(2), and yttrium to 88.905 84(2) from 88.905 85(2). The Commission also recommends the standard value for the natural terrestrial uranium isotope ratio, N(238U)/N(235U)=137.8(1).

Southern Ocean aerosols were collected at the Cape Grim Baseline Air Pollution Station from onshore air under baseline conditions between February 1999 and April 2000. Thermal ionization techniques (TIMS) and isotope dilution mass spectrometry (IDMS) were used to measure the isotopic composition and concentration of lead in the air giving concentrations as low as 0.6 ± 0.1 pg · m−3. Air collected under baseline conditions for 12 months (May 1999–April 2000) yielded an overall lead concentration of 11.0 ± 0.2 pg · m−3 and isotopic composition of 206Pb/207Pb = 1.154, 208Pb/207Pb = 2.387 and 206Pb/204Pb = 17.93. The range in isotopic ratios was consistent with the mixing of lead from major population centers in the Southern Hemisphere in the mid to high latitudes, except for the presence of highly radiogenic lead in some samples. Contributions from radiogenic lead of up to ∼0.8% were observed. Three periods with the highest percentage contribution of radiogenic lead (>0.5%) were investigated in more detail, and 4-d back-trajectories and radon concentrations were used to help identify the sources. The sources are probably associated with the mining and processing of uranium rich ores in southern Africa and possibly South Australia.

The biennial review of atomic-weight, Ar(E), determinations and other cognate data have resulted in changes for the standard atomic weights of the following elements: FromToZinc65.39 ± 0.0265.409 ± 0.004Krypton83.80 ± 0.0183.798 ± 0.002Molybdenum95.94 ± 0.01 95.94 ± 0.02Dysprosium162.50 ± 0.03162.500 ± 0.001 Presented are updated tables of the standard atomic weights and their uncertainties estimated by combining experimental uncertainties and terrestrial variabilities. In addition, this report again contains an updated table of relative atomicmass values and half-lives of selected radioisotopes. Changes in the evaluated isotope abundance values from those published in 1997 are relatively minor and will be published in a major review of each element in 2003. Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on parent nuclides that might affect isotope abundances or atomic-weight values are included in this report for the information of the interested scientific community.

— -The elemental and isotopic abundances of Te and Pd have been measured by thermal ionization mass spectrometry in a purified sample of interstellar nanodiamonds from the Allende meteorite, after combustion of the diamonds in an oxygen plasma. Small positive anomalies were found in 128Te (4.0 ± 1.5 %0) and 130Te (9.3 ± 2.8 %0) from three analyses of the Allende nanodiamond sample EB, and in 110Pd (9.4 ± 5.7 %0) from two analyses of the same sample. No other anomalies of a significant nature were found in either Te or Pd. These results are consistent with the neutron burst model (Meyer et al., 2000), and the r-process based rapid separation model of Ott (1996) in that 128, 130Te and 110Pd are enhanced relative to their solar abundances. However, in the framework of the neutron burst model, some separation between stable products and radioactive precursors may be required in order to be consistent with the full data set of Te isotopes. In the framework of the rapid separation scenario, our data suggests a separation time of approximately 4000 s, based on the magnitudes of the precursor life-times for 128Te and 130Te. The elemental abundance ratio Te-H/Xe-H agrees with the prediction of the rapid separation model, provided little fractionation occurred during trapping of the exotic components by the diamonds, but differs significantly from expectations based on the neutron burst model. Differences in the inferred 128Te/130Te ratio between our work and that of Richter et al. (1998) point to the need for further investigations.

The biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of five elements. The atomic weight of bromine has changed from 79.904(1) to the interval [79.901, 79.907], germanium from 72.63(1) to 72.630(8), indium from 114.818(3) to 114.818(1), magnesium from 24.3050(6) to the interval [24.304, 24.307], and mercury from 200.59(2) to 200.592(3). For bromine and magnesium, assignment of intervals for the new standard atomic weights reflects the common occurrence of variations in the atomic weights of those elements in normal terrestrial materials.

The isotopic and elemental abundances of Zn, Pd, Ag, Cd, Sn, and Te have been measured in three acid-resistant residues extracted from the Allende meteorite. High-efficiency, low-contamination ion-exchange procedures were developed to separate and purify the nanogram amounts of these elements present. Elemental-abundance determinations performed by Mass Spectrometric Isotope Dilution agree with previously published work for similarly derived residues. No isotope anomalies similar to those found for Xe (Xe-HL) in these samples were detected for any of these elements, which is consistent with the residues not being derived directly from the Xe-HL carriers. The lack of major Te-isotope anomalies does not support earlier reports of {sup 126}Te and {sup 130}Te excesses which were measured by neutron activation in similar samples. Small excesses were detected in the minor isotopes of Sn and Te, but these may be due to measurement problems associated with the small ion currents obtained for these samples. Two of the residue solutions contain Cd with up to several percent excesses for {sup 106}Cd and {sup 108}Cd. Interpretations of these results are limited by the unknown nature of the carrier minerals in the residues but may indicate the presence of a p-process component in Allende residues.

The isotopic composition of Te has been measured in a purified sample of interstellar microdiamonds from the Allende meteorite. Small positive anomalies were only found in 128Te (4.0 ± 0.3‰) and 130Te (9.3 ± 2.0‰) from three analyses of the Allende microdiamond sample EB#2. The magnitude of the anomalies are smaller than in the heavy noble gases, although the absolute amount of anomalous Te is greater than that of anomalous Xe in the same sample. The anomalies in Te can be interpreted in terms of standard r-process nucleosynthesis followed by rapid separation of the stable isotopes from their radioactive precursors.

Procedures are described which permit mass spectrometric isotope-dilution analysis to be used to determine Ag, Te and Pd in rock samples at the ng g level. The concentrations ( ng g ) of Ag, Te and Pd were found to be 25.7 ± 0.7, 1.2 ± 0.6 and 0.08 ± 0.05 respectively in BCR-1 and 3.5 ± 0.2, 4.2 ± 0.7 and 2.9 ± 1.7 respectively in PCC-1.

Devillers et al. recently measured the isotopic composition of tin in order to establish its absolute isotope abundance and the atomic weight. However, because of interferences, particularly at 115, and possibly at 114, accurate abundances could not be assigned to these very low abundance isotopes. The astrophysical and cosmochemical significance of the minor tin isotopes has prompted us to remeasure the isotopic composition of tin. A silica/alumina/ boric acid activator was developed which permitted submicrogram samples of tin to be analysed free of 115 and 114 interferences. The abundance of 115 Sn was found to be 5.5% lower and that of 114 Sn to be 1.1% higher than the corresponding values reported by Devillers et al. The abundances of the other isotopes are in excellent agreement with their values and the accurate isotopic data now available provides a sound basis for a study of isotopic anomalies to be undertaken in meteorites.

Seventeen geochemical reference samples have been analysed for Ag, Te, Pd using mass spectrometric isotope dilution analysis. For most samples, analytical data on these elements were lacking. The concentration range encountered was generally in the nanogram levels.

Thermal ionisation mass spectrometry has been used to measure the isotopic and elemental abundances of Mo, Ru, Pd, Ag, Cd, Sn and Te in a number of sandstones and shales in the immediate vicinity of Reactor Zone 9 at the Oklo mine site. The mass spectrometric isotope dilution technique was used to measure the elemental abundances of these elements. The data show that considerable amounts of the fissiogenic Mo, Ru, Pd, Ag and Te which escaped from the reactor zone, have been retained in the peripheral rocks, although Cd and Sn were not contained to any significant extent in these samples. Some information on the retention of Sb and Tc was also obtained. Evidence of element fractionation has also been demonstrated in that 99 Tc and Sn were fractionated from Ru and Te, respectively within 1 Ma of the end of reactor criticality. The presence of excess 125 Te in some of the peripheral rock samples indicates that Sb was mobilised from Reactor Zone 9 within tens of years of the completion of reactor criticality. The implications of these results to the storage of radioactive wastes in natural geological repositories is discussed.

The isotopic analysis of nanogram quantities of high ionization potential elements by thermal ionization mass spectrometry using an ionization activator is affected by the presence of impurities which can suppress the ion beam and introduce spectral interferences. Microelectrodeposition of the sample directly on to the mass spectrometer filament prior to the addition of the silica gel-phosphoric acid activator is an effective means of purifying the sample, yet it adds minimal blank. Such procedures have been developed for nanogram samples of Pd, Ag, Cd, Te and Pb.

The isotopic composition of Pd, Ag, Cd and Te has been measured by solid source mass spectrometry for four samples from reactor zones 2, 3–4, 5–6 and 7, and from four host rock samples external to the reactor zones from the Oklo mine site. The concentrations of these elements have also been determined in the eight samples using the stable isotope dilution technique. Cumulative fission yields have been derived from the reactor zone samples after correcting where necessary for the terrestrial component of the element concerned. It has been shown that fission-produced Pd and Te are retained almost in their entirety in the uraninite reactor zone samples, whereas a significant fraction of fission-produced Ag and Cd have migrated from the reactor zones. Fission product Cd is observed in the host rock samples, whereas no strong evidence of fission-produced Ag could be found. Thus the fission-produced Ag which has migrated from the reactor zones has not been retained in the four host rock samples analysed, although the presence of fission product Ag may be masked by the presence of natural Ag. It is possible that the fission product Ag has been retained in the Oklo mine-site, and further host rock samples will be studied to evaluate this possibility. The implications of these results to the storage of radioactive wastes in natural geological repositories is discussed.

The isotopic composition of molybdenum, ruthenium, palladium, silver, cadmium, tin, tellurium, neodymium and uranium have been measured by solid source mass spectrometry in eight uraninite samples from Reactor Zone 9 at the Oklo natural reactors. Cumulative fission yields have been derived for most of these elements, after correcting where necessary for the primordial component of the element concerned. Neutron capture reactions on a number of nuclides with significant thermal cross sections, and fission chains in which one of the precursor nuclides has a lengthy half-life, have also been examined to provide information on the relative mobilities of the elements involved. The Pd fission yields have been utilised to calculate the proportions of235U,238U and239Pu fission to be approximately 88%, 8% and 4% respectively in Reactor Zone 9. It has also been shown that nearly 50% of the fissioning235U nuclides were produced from the α-decay of239Pu. The integrated neutron flux in this zone was calculated to be approximately 3.6 × 1020 n cm−2. Estimates of the spectral index show that approximately two-thirds of the neutrons in Zone 9 were thermalised. Although it is unlikely that the Oklo reactors operated continuously, this study has shown that the duration of criticality in Zone 9 was approximately 2.2 × 105 years. During this period the average fission density was 0.92 × 1020 fissions cm−3, which represent a total energy output of 4 × 108 J g−1 of sample with an average power output of 8.1 × 10−5 W g−1 of sample. The accurate analysis of the isotopic abundances of nine elements, has enabled the nuclear characteristics of Reactor Zone 9 to be established, thus providing a base for estimating the nuclear inventory of the various fission products. This will allow a comparison to be made with the present-day elemental abundances and hence an evaluation of the mobility of these elements in the geological environment at Oklo.

Eight samples from a planar cross section of one of the natural fission reactor zones at the Oklo U mine were analyzed to determine the abundances and isotopic composition of U, Mo, Ru, Pd, Ag, Cd, Sn, Te and Nd. Fission product concentrations were calculated from the isotopic compositions. The relative abundances of these fission products are different from those produced by fission i.e. portions have been lost or gained from all the samples. The proportions of Te, Ru, 99Ru, Pd and Mo in the eight samples are invariant. We attribute this regularity to retention at the site of production—primary retention. Based upon this interpretation, we suggest that fixed proportions of Ru, Tc, Pd and Mo have been removed from the reactor zone. In contrast, Nd and Sn have been depleted in some regions of the zone and enriched in others. Portions of Ag and virtually all the fissiogenic Cd have been removed from the reactor zone. By analogy with anthropogenic spent fuel, we suggest that the degree of primary retention was controlled by phase assemblages formed in the Oklo natural reactor fuel in response to microscale conditions of pressure, temperature and composition produced by the nuclear reactions. The ability of these putative minerals to retain nuclear products was a function of their stability under physiochemical conditions established by the geological environment over the last 2 Ga. An integrated study of the natural reactors would test our hypothesis and provide valuable information for evaluating the long-term effectiveness of anthropogenic spent fuel as a container of nuclear waste in the geochemical environment.

The mass spectrometric isotope dilution technique was used to measure the elemental abundances of Pd, Ag, Cd and Te in Orgueil (C1), Ivuna (C1), Murray (C2) and Allende (C3) chondrites. The Pd abundance of 554 ppb for the C1 chondrites is almost identical to the recommended value of Anders and Ebihara (1982); that for Cd (712 ppb) is approximately 5% higher, whereas that for Ag (198 ppb) is approximately 10% lower than the recommended values. A smooth distribution for the abundances of the odd- A nuclides between65 ≦ A ≦ 209 have been observed except for small irregularities in the Pd-Ag-Cd and the Sm-Eu mass regions (ANDERS and Ebihara, 1982). The results from the present work have the effect of smoothing out the dip in the Pd-Ag-Cd region and indicate that there is no systematic fractionation of cosmochemical element groups in this mass region. A Te abundance of 2.25 ppm has been determined for the C1 chondrites Orgueil and Ivuna in agreement 2+with the value of Smith et al. (1977). This value is some 30% lower than the value of Krahenbuhl et al . (1973) but is in good agreement with the more recent measurements from Chicago. The Krahenbuhl et al . value causes 128 Te and 130 Te to lie approximately 30% above the r -process peak at A = 130 (Kappeler el al. , 1982), whereas the new value fits smoothly into the general trend.

A long known way of anchoring isotope ratio values to the SI system is by means of gravimetrically prepared isotopic mixtures. Thermal ionization mass spectrometry (TIMS) is the traditionally associated measurement technique, but multi-collector double focusing inductively coupled plasma (MC-ICP)-MS now appears to be an attractive alternative. This absolute calibration strategy necessitates that mass discrimination effects remain invariant in time and across the range of isotope ratios measured. It is not the case with MC-ICPMS and the present work illustrates, in the case of Zn isotopic measurements carried out using locally produced synthetic Zn isotope mixtures (IRMM-007 series), how this calibration strategy must be adjusted. First, variation in mass discrimination effects across the measurement sequence is propagated as an uncertainty component. Second, linear proportionality during each individual measurement between normalized mass discrimination and the average mass of the isotope ratios is used to evaluate mass discrimination for the ratios involving low abundance isotopes. Third, linear proportionality between mass discrimination and the logarithm of the isotope ratio values for n(67Zn)/n(64Zn) and n(68Zn)/n(64Zn) in the mixtures is used iteratively to evaluate mass discrimination for the same ratios in the isotopically enriched materials. Fourth, ratios in natural-like materials (including IRMM-3702 and IRMM-651) are calibrated by external bracketing using the isotopic mixtures. The relative expanded uncertainty (k = 2) estimated for n(68Zn)/n(64Zn) and n(67Zn)/n(64Zn) ratio values in the synthetic isotopic mixtures and the natural-like zinc samples was in the range of 0.034 to 0.048%. The uncertainty on the weighing (0.01%, k = 1) was the largest contributor to these budgets. The agreement between these results and those obtained with a single detector TIMS and with another MC-ICPMS further validated this work. The absolute isotope ratio values found for IRMM-3702-material also proposed as "delta 0" for delta-scale isotopic measurements-are n(66Zn)/n(64Zn) = 0.56397 (30), n(67Zn)/n(64Zn) = 0.082166 (35), n(68Zn)/n(64Zn) = 0.37519 (16), and n(70Zn)/n(64Zn) = 0.012418 (23). The derived Zn atomic weight value Ar(Zn) = 65.37777 (22) differs significantly from the current IUPAC value by Chang et al. [1]. Remeasurement, with isotopic mixtures from the IRMM-007 series, of the Zn isotope ratios in the same Chang et al. [1] material have revealed large systematic differences (1.35 (27)% per atomic mass unit) that suggest unrecognized measurement biases in their results.

The elemental abundance of tin has been determined by the mass spectrometric isotope dilution technique for four carbonaceous chondrites, including the Cl chondrites Orgueil and Ivuna. A solar system abundance of 3.98 (normalized to Si = 10 6 atoms) can be derived from these data, which is in excellent agreement with the presently accepted value. Recently, a theoretical value of 2.82 ± 0.21 (Si = 10 6 atoms) has been proposed for the abundance of tin based on an s -process nucleosynthesis model. This value is 26% lower than the presently accepted solar system abundance. The present data confirm the higher value for tin and indicate that a reexamination of the assumptions on which the nucleosynthetic value is based is required.

A unique example of the utility of isotope geochemistry may be found in studies of the isotopic abundances of elements in samples from the Oklo uranium mine in the African Republic of Gabon. These studies demonstrate that two billion years ago, in a span of a few hundred thousand years, nuclear fission and associated processes profoundly changed the isotopic and chemical composition of discrete lenses of highly uraniferous rock within the mine (1,2). These changes can be quantified by characterizing operating parameters of the natural nuclear fission reactors and interpreting them in the context of the systematics of the nuclear reactions. Comparisons between the present, measured, composition of the natural reactor remnants and their calculated nuclear-reaction induced composition provides a quantitative characterization of compositional changes in the rocks during the last two billion years.