Determination Of Lead Isotopes Research Articles

Rapid determination of lead isotopes in water by coupling DGT passive samplers and MC-ICP-MS laser ablation

We have developed a method for measuring Pb-isotope compositions in natural water, based on coupling a commercially available chelex-100 DGT passive sampler with direct laser-ablation MC-ICP-MS on DGT resin.

Determination of isotopic distribution of lead by a matrix assisted laser desorption/ionization versus a laser desorption/ionization time of flight mass spectrometry

In this work it has been shown that both the laser desorption/ionization mass spectrometry (LDI MS) and the matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) are the simple and quick methods for determination of relative natural isotopic distribution of lead. The analysis of metal salts with these approaches does not require any time-consuming preparation of samples: a single run can take only a minute, and numerous information can be obtained. Results obtained in this work show that chosen matrix has no negative effect on quantitative determination of lead isotopes and support once more the applicability of MALDI TOF MS for lead isotope distribution determination in the sample, and accuracy of data obtained. Additionally, the generation of PbnOn and PbnOn-1 (n: 2 - 6) clusters have been successfully achieved in the positive mode, using the both LDI and MALDI methods. All stoichiometries were confirmed using isotopic pattern modelling.

Determination of lead isotopes in a new Greenland deep ice core at the sub-picogram per gram level by thermal ionization mass spectrometry using an improved decontamination method

An improved decontamination method and ultraclean analytical procedures have been developed to minimize Pb contamination of processed glacial ice cores and to achieve reliable determination of Pb isotopes in North Greenland Eemian Ice Drilling (NEEM) deep ice core sections with concentrations at the sub-picogram per gram level. A PL-7 (Fuso Chemical) silica-gel activator has replaced the previously used colloidal silica activator produced by Merck and has been shown to provide sufficiently enhanced ion beam intensity for Pb isotope analysis for a few tens of picograms of Pb. Considering the quantities of Pb contained in the NEEM Greenland ice core and a sample weight of 10g used for the analysis, the blank contribution from the sample treatment was observed to be negligible. The decontamination and analysis of the artificial ice cores and selected NEEM Greenland ice core sections confirmed the cleanliness and effectiveness of the overall analytical process.

Diffusion studies with radioactive ions

An overview of themodified radiotracer based diffusion studies carried out at IGISOL is provided. The experimental procedures are briefly described followed by examples involving IGISOL as the key facility. In this respect the studies related to silicon-germanium (Si1-xGex) alloys and on the related diffusion systematics are summarized. Another group of examples is related to mobility determination of lead isotopes in glass for verifying retrospective radon measurements. Finally an outlook to future possibilities related to employing radiotracers in solid state research is provided.

Lead isotopes in groundwater as an indicator of water–rock interaction (Masheshwaram catchment, Andhra Pradesh, India)

This study reports on the lead geochemistry and Pb-isotope ratios of ground waters along a small (53 km 2) endoreic granitic catchment in India (Masheshwaram, Andhra Pradesh). The main focus is on granitic parent rock composition, water chemistry and isotope tracing, through the determination of lead isotopes in water by Multi-Collector ICP-MS using an improved new procedure. This method is efficient to give reliable Pb-isotope ratios with uncertainties (i.e. lower than 0.3% on each 206Pb, 207Pb, 208Pb ratios normalized to 204Pb) low enough to allow the different types of groundwater to be discriminated. Lead concentrations span over one or two orders of magnitude up to approximately 20 µg L − 1 . Pb isotopes fluctuate largely as exemplified by the 206Pb/ 204Pb ratio, ranging from 17.01 up to 25.35. Most of the lead in the ground waters is of geogenic origin, and through the lead isotopic signature in groundwater, we have traced and fingerprinted the processes of water–rock interaction considering the granite matrix. Combining a weathering model and field observations, we were able to define a two step weathering process that includes a control on the Pb-isotope ratios by accessory phases and by the main mineral from the granite in a second step of weathering.

Mobility determination of lead isotopes in glass for retrospective radon measurements

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.

Routine lead isotope determinations using a lead-207–lead-204 double spike: a long-term assessment of analytical precision and accuracy

Lead-isotope data obtained on a multicollector mass spectrometer over a four year period using a 207Pb–204Pb double spike to correct for the effects of mass discrimination, are reported. Considerable improvements in both precision and accuracy over conventional correction procedures were noted, without recourse to rigorous loading or run conditions. An external precision in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios ±0.003, 0.003 and 0.01 (2 × standard deviation), respectively, is routinely obtainable independent of minor variations in loading and run parameters.

Comparison between lead isotopes 234U/ 238U activity ratio and saturation index in hydrogeochemical exploration for concealed uranium deposits

At several sites where uranium mineralization was known — West Morvan test area and Lodève basin (France), and Cigar Lake (Saskatchewan, Canada) — we have applied both isotopic and conventional geochemical methods based on major and trace elements concentrations for the detection of concealed uranium deposits. Isotopic methods comprise: (1) the analysis of lead isotopes in groundwater, in order to find any contribution of radiogenic lead from the supposed surrounding or overlying mineralizations: (2) the measurement of 234U/ 238U activity ratios, variations of which have been proven to be correlated with the presence of uranium accumulatiions. The conventional geochemical methods consist simply in looking for uranium or accompanying elements in groundwaters. A more elaborate method uses the notion of saturation indices of uranium-bearing minerals, thus requiring accurate and complete determinations of major ions and other parameters of groundwaters. The data show that determination of lead isotopes is efficient in many contexts, and gives results that are rather independent of the geochemical characteristics (i.e., reducing or oxidizing) of the waters. The information is global and expresses the presence of uraiium accumulation in the vicinity of the sampling point. No information about grades and distance to the mineralization can be obtained. The anomalous lead can be transported either in solution or on particles, as lead is readily adsorbed on many substrates such as clays or oxides. The analysis of 234/ 238U activity ratios in groundwaters provide information which is more difficult to decipher. In general, oxidized waters encountering uranium accumulations show high uranium concentrations and low 234U/ 238U activity ratios, but groundwaters which are more reducing or close to uraninite saturation will produce either high 234U/ 238U activity ratios if the exchange surface between uranium-bearing phases and groundwater is large enough to promote preferential 234U enrichment in the fluid phase (selective leaching or alpha recoil) or low 234U/ 238U activity ratios if the exchange surface is smaller. High 234U/ 238U are observed above dispersed uranium accumulations, frequently situated in the vicinity of massive uranium deposits. This pattern is observed at all studies sites, where contrasting signatures between massive ore zones and surrounding secondary mineralizations are found. In this case, the 234U/ 238U activity ratio may give information on the succession of the relative ore grades. The use of uranium concentration anomalies has often been questioned, because: (1) non-significant anomalies may appear in oxidizing waters; (2) reduced waters may not be able to record significant U anomalies. The concept of saturation indices of uranium minerals generally allows a more accurate detection of the mineralized areas, but it requires a careful determination of redox potentials, in some cases by in situ measurements, but more generally by calculating the redox potential from dissolved iron, assuming equilibrium with iron oxides. Waters flowing through mineralized areas are generally saturated with respect to uranium minerals, without any clear U concentration peak (this is the case around the Cigar Lake U deposit). If they are not saturated, they are generally strongly oxidized and thus show very high uranium concentrations (this is the case of the Nord-Tréviels part of the Lodève uraniferous basin). If no uranium accumulation is present, saturation indices are generally strongly negative, but in strongly reducing waters, even far from any uranium deposit, one can obtain uraninite saturation. This is the case in Lodève sulphide-bearing waters, or in alkaline geothermal waters from the Pyrénées. If we analyze both U concentration and U saturation index, we can see that waters flowing through mineralized zones have either high U concentrations or are very close to U saturation. One can say that, with little doubt, any water that does not possess one of these two characteristics is of no interest for uranium detection.

Inductively coupled plasma mass spectrometric determination of lead isotopes

Inductively coupled plasma mass spectrometry (ICP-MS) offers the opportunity to measure stable isotopes of the elements. When the isotope proportions differ sufficiently among source materials, isotope ratio analysis provides a means to distinguish the origin of pollutants such as lead. Relative standard deviations of 1.1%, 0.76%, and 0.86% were obtained for an 8-h period using a 5-min measurement interval for the m/z 4/z 208:206, and 204:206 lead ratios, respectively. By use of 95% tolerance limits, significant differences in lead isotope ratios were observed for lead ores from Idaho, Missouri, and Yugoslavia, as well as for commercial lead standards. Lead isotope ratios for Missouri ore differed as much as 19% from values for National Bureau of Standards Common Lead Isotopic Standard (SRM 981). Lead isotope data obtained by ICP-MS are consistent with paint as the source of lead in blood for one case study but not for another. An isotopic detection limit of 2 pptr (parts per American trillion) was both calculated and measured for lead.

Determination of Lead Isotope Ratios in Archeological Products by Ion Microanalyzer

Determination of lead isotopes of the standard and archeological samples using ion microanalyzer has been conducted and compared with the results obtained by other mass spectrometric method. The measurement for the metallic samples, NBS SRM981 and ancient bronze coin, was made at the mass resolution of 2500, using O2+ ion with net energy 12.3keV and ion current 0.3-2μA as a primary ion beam, while for other non-metallic samples a primary ion beam of O- ion, net energy 9.8keV and ion current 40-250nA, was used to eliminate surface charging. Isotope ratios 204Pb/206Pb, 207Pb/206Pb, 208Pb/206Pb were determined with precisions 0.1-0.5%. Upon the measuring conditions examined, ten ancient glasses and glazes of faience excavated in Japan and in Iraq were analyzed. From the data obtained as well as those reported, it has been inferred that the glass sample found in Mikumo, Kyushu, was imported in Yayoi period from the north of China presumably as a Zenkankyo (Mirror of the Earlier Han), while four glass samples found in Heiankyo, Kyoto, were imported in Heian period from the south of China as Gokankyo (Mirror of the Later Han). Glazes of faience excavated in Iraq showed different lead isotope ratios from either of the glass samples excavated in Japan.

Some new lead isotope determinations from the proterozoic sulfide ores of central Sweden

Lead isotope determinations were made on galenas from three strata-bound sulfide ores in the early Proterozoic (Svecokarelian) Bergslagen district of central Sweden and four epigenetic deposits in the Alvdalen and Vansbro districts in the early to middle Proterozoic post-Svecokarelian belt. The leads from the strata-bound Bergslagen deposits show exceptional isotopic homogeneity over large areas. Their isotopic composition suggests the existence of a pre-Svecokarelian crust in the district and is consistent with exhalative-sedimentary ore formation in an active continental margin environment. The Vansbro and Alvdalen leads display constant compositions within each district, but marked divergence between the districts. Their compositions preclude derivation exclusively from recycled Svecokarelian lead and suggest a substantial lead contribution from a mantle-like source. The difference between model ages and geologic ages for many of the deposits, with a small but significant excess of radiogenic lead, suggests a significant deviation of the Fennoscandian Shield from conventional global lead evolution models.

Interpretation of lead-uranium ages of pitchblende deposits in the central Front Range, Colorado

Published lead-uranium ages of 11 pitchblende ores from deposits of classes 2 and 3, as defined by Sims and Sheridan, in the central Front Range, vary from a low of 35 m.y. to a high of 113 m.y. These age determinations are re-evaluated in the light of the following real or potential sources of error: (1) precision of the lead analyses; (2) precision of the lead isotope determinations; (3) uncertainties in the common lead correction arising from inappropriate choice of isotopic composition, excessive amounts of common lead, and postdepositional uranogenic enrichment; (4) leaching of uranium relative to lead; (5) radon loss; (6) sample size; and (7) loss of lead relative to uranium. It is concluded that the largest Sample to sample age differences stem from factors 1, 4, and 6 and that the largest discordancies in the measured Pb206/U238 and Pb207/U235 ages within single samples can be related to factors 2 and 3. The ages previously published were recalculated using improved common lead corrections and newer decay constants and were ranked in accordance with criteria 1 through 7. In 4 of the 11 samples dated, the use of the improved common lead correction reversed the age sequence Pb206/U238 < Pb207/U235 < Pb207/Pb206 commonly attributed to radon loss. Samples ranked the highest for dating purposes on the basis of criteria 1 through 7 yielded concordant Pb206/U238-Pb207/U235 ages. Two such samples from class 2 deposits yielded Pb206/U238 ages of 56.6 and 58.9 m.y.; the rounded average, 58 m.y., is considered to be a best estimate of the true age of the class 2 deposits. One sample from class 3 deposits was judged to be markedly superior to the other three on the basis of criteria 1 through 7, and, in addition, yielded the most concordant Pb-U ages of any samples from the Front Range. Its Pb206/U238 age, 72.5 m.y., is considered to be a best estimate of the true age of the class 3 deposits. The preferred ages of the class 2 and class 3 deposits are in harmony with the published K-Ar ages obtained on separate members of the Cretaceous-Tertiary intrusive sequences to which, it is inferred, class 2 deposits are directly and class 3 deposits are indirectly related.

Minor elements in sphalerite and galena from Binnatal

The trace element contents of 23 sphalerites and galenas from Binnatal, Switzerland, have been determined. Most of these samples have been previously studied in respect to lead and sulphur isotope abundances. Coloration of sphalerites — varying from yellow to black for nearly identical iron contents — seems to be strongly influenced by the manganese content. A linear relationship between sulphur isotope composition and copper content in sphalerites was found. Trace elements in galenas show a significant inverse relationship between silver and copper. With the determination of the bismuth content, it is possible to distinguish several galena types; a similar grouping has been found by lead isotope determinations. The results of the trace analyses are discussed in connection with the occurrence of a large number of very rare and special Pb-As-sulphosalt minerals in the Binnatal dolomites.