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Volume 52 (2004)
- Issue 6 Pages 307-
- Issue 5 Pages 263-
- Issue 4 Pages 159-
- Issue 3 Pages 93-
- Issue 2 Pages 57-
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Volume 52, Issue 4
Displaying 1-10 of 10 articles from this issue
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REVIEW
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Nobuo TAKAOKA2004 Volume 52 Issue 4 Pages 159-170
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSHistory of the geochemical research of 130Te double beta decay and the process coming to an idea of primitive Xe are described on the basis mainly of the author's personal experiences. The geochemical research of 130Te-ββ-decay at Osaka University started in 1961, when the author entered the Graduate School of Science of Osaka University, under the supervision of Prof. Kore-ichi Ogata who had designed and installed an ultrahigh-vacuum, high-sensitivity mass-spectrometer at his noble gas laboratory in 1960. The first report that the half-life of 130Te-ββ-decay is 8.2×1020 years was published in 1966. This lifetime was supported by research groups of University of Missouri and confirmed by our new result of 7.9×1020 years, while other research groups of MPI für Physik and Washington University reported the half-lives of 130Te-ββ-decay that are longer by a factor of ∼3. With the excellent noble-gas machine, the author worked well long till 1990 for noble gas researches on meteoritic and terrestrial samples as well as the geochemical research of 128Te- and 130Te-ββ-decays. In the course of a research on meteorite Xe, in 1972, the author had the idea of primitive Xe with which one might be able to understand a mystery in isotope compositions of xenon found among terrestrial atmosphere, solar wind and meteorites. How to work with meteorites is suggested to identify the primitive Xe component in meteorites.View full abstractDownload PDF (367K)
REGULAR PAPER
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Takafumi HIRATA2004 Volume 52 Issue 4 Pages 171-176
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSA new technique for the removal of isobaric interferences on Ba has been developed for ICP-mass spectrometer. Mass spectrometric interferences on Ba by 138La+, 136Ce+, or 138Ce+ isobaric signals were effectively eliminated by a selective production of oxide ions. The La+ and Ce+ ions could be quantitatively converted to oxide ions (LaO+ and CeO+) by the ICP ion source under the low-power operation. Production efficiency of oxide signals for La and Ce was remarkably enhanced, i.e., >2,000,000 times the level obtained by the conventional ICP power (1.35 kW). Residual signal intensity of La+ signal was almost the same level as the instrumental background. The overall contribution of isobaric 138La and 138Ce to 138Ba signals were 0.02% and 0.1%, respectively, even with the presence of × 10,000 times higher concentration of La and Ce. The data obtained here demonstrate that the level of the isobaric interferences by 138La, 136Ce, and 138Ce signals produced by the low-power ionisation was negligible within the analytical precision achieved in this study (∼1%). It should be noted that the analytical sensitivity for Ba obtained by the low-power ICP remains almost 85% of the level achieved by the conventional ICP power. This is very promising because the present technique can be applied to the laser ablation sampling technique which requires high sensitivity without chemical separation or purification procedures.View full abstractDownload PDF (206K) -
Masaharu TANIMIZU, Takamasa HAYASHI, Tsuyoshi TANAKA2004 Volume 52 Issue 4 Pages 177-181
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSPrecise and accurate Ce isotope analysis technique was developed with one order of magnitude smaller ion beam intensity compared with previous studies to apply 138La-138Ce decay system to smaller samples. 138Ce/142Ce and 136Ce/142Ce isotope ratios were accurately determined by canceling not only the fluctuation of ion beam intensities but also the Faraday cup efficiencies and amplifier gains with the dynamic multicollector technique. In situ 18O/16O determination for Ce18O correction and 140Ce/142Ce normalization for mass fractionation were applied to the accurate analysis. A repeated analysis of 138Ce/142Ce and 136Ce/142Ce ratios of a Ce isotopic reference, JMC304, were 0.0225889±0.0000013 and 0.0168810±0.0000030. This technique has almost the same precision and reproducibility in comparison with previous Ce isotope studies, and will be suitable for samples with limited amount like extra-terrestrial materials, including detection of p-process nuclide anomalies of 138Ce and 136Ce.View full abstractDownload PDF (169K) -
Yumiko INOUE, Yukiyasu TSUTSUMI, Kentaro TERADA, Yuji SANO2004 Volume 52 Issue 4 Pages 182-188
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSWe report here in situ measurements of Rb and Sr isotopes in K-rich minerals (muscovite, phlogopite, and K-feldspar) using Sensitive High-Resolution Ion MicroProbe (SHRIMP). Several grains of the K-rich minerals were extracted from eight granitic rocks with various formation ages and mounted on epoxy-resin disks. Chemical compositions were measured by an electron probe microanalyzer (EPMA). Then they were set in the source chamber of SHRIMP. A 4-5 nA mass filtered O2- primary beam was used to sputter a 30-μm-diameter flat-bottomed crater and secondary positive ions were extracted by a 10 kV accelerating voltage for mass analysis. A mass resolution of 8900-9300 at 1% peak height was attained to reduce isobaric hydride interferences such as 87RbH+ on 88Sr+. The magnet was cyclically peak-stepped from mass 84 (84Sr and 28Si56Fe) to mass 88 (88Sr and 30Si58Fe), including the background, mass 85 for 85Rb and 29Si56Fe, mass 86 for 86Sr and 30Si56Fe, and mass 87 for 87Rb, 87Sr, and 29Si58Fe, respectively. No SiFe compounds of any mass number contributed significantly for the samples analyzed. Observed 87A/85A ratios (where A is an arbitrary element) were plotted against 88A/85A ratios for each sample. A least-square fitting was made in the diagram. The gradient and Y-intercept correspond to initial 87Sr/88Sr and initial 87Rb/85Rb ratios or present (87Rb/85Rb)+(87Sr*/85Rb) ratios, respectively, where “ * ” denotes radiogenic. The initial 87Sr/88Sr ratios are mostly consistent with the upper mantle 87Sr/88Sr ratios of various ages within experimental error. There is a positive correlation between the initial 87Rb/85Rb ratios and formation ages of the granitic rock samples, as it is expected from 87Rb decay. Further evaluation of the instrumental isotopic mass fractionation and relative sensitivities for Rb and Sr are required before the in situ 87Rb-87Sr measurement is routinely applied as a dating method.View full abstractDownload PDF (229K) -
Otohiko SHIMIZU, Tsuyoshi TANAKA, Ryoko SENDA2004 Volume 52 Issue 4 Pages 189-195
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSA negative thermal ionization technique using a small and cost-efficient quadrupole mass spectrometer is presented. Intense ion beams of negatively charged oxides of Re, Os, Ir, and Ru were observed, and the principal molecular species formed in this technique are ReO4-, OsO3-, IrO2-, and RuO3-, respectively. The production of these ion species in the distinct mass ranges allows the isotopic analyses without any chemical separation of these elements each other. For 5 ng Os, all Os isotopic ratios were determined with the precision of better than ±0.5% except 184Os/192Os because of very low isotopic abundance of 184Os. For 30 ng Re, 10 ng Ir, and 30 ng Ru, isotopic measurements were also made with the precision of better than ±0.5%. The precision of the isotopic ratio measurements for Re, Os, Ir, and Ru is sufficient for the isotope dilution technique to determine the concentration of these elements in geological samples easily and cost-efficiently. In addition, an iridosmine from Hokkaido was analyzed for Os and Ir by direct loading technique, and 187Os/188Os ratio of 0.1229±0.0029 was obtained.View full abstractDownload PDF (267K)
TECHNICAL REPORT
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Takayuki FUJIMOTO, Chikako NISHIMURA, Hidehiro OMORI, Jun-ichi MATSUDA2004 Volume 52 Issue 4 Pages 196-204
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSWe measured carbon abundances and isotopic ratios of inorganic carbon (natural graphite, fullerene, shock-produced diamond) and calcite of sedimentary rocks using ANCA-SL (Automated Nitrogen Carbon Analysis for Solids and Liquids, PDZ Europa Ltd.), which was developed for the routine analyses for the stable isotope study of metabolic cycles. The main problem for the use of this equipment to the inorganic samples is whether the sample is fully combusted or not. We found that graphite was not fully combusted although fullerene and fine diamond were completely combusted. It is likely that the incomplete combustion of the graphite is due to their large grain size used in this study. We also found that there is a variation of isotopic ratios in samples with different weights. The usual precision of δ13C was <0.3‰, but we could reach the precision of <0.1‰ when we used the similar weights for the samples and the standard. The carbon isotopic ratios in calcite from sedimentary rocks have been also measured. The samples were from the mass extinction boundaries, but there was no systematic variation of carbon isotopic ratios across the boundaries.View full abstractDownload PDF (290K) -
Minoru KUSAKABE, Seiji MARUYAMA, Tomoki NAKAMURA, Toru YADA2004 Volume 52 Issue 4 Pages 205-212
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSTechnical details of an on-line CO2 laser-BrF5 fluorination system, installed at Institute for Study of the Earth's Interior, Okayama University, were described. The system allows us precise determination of oxygen three isotope composition (δ17O and δ18O) of rocks and minerals. The δ17O and δ18O values of some international and laboratory reference materials such as UWG2 garnet, NBS-28 quartz, NBS-30 biotite, San Carlos olivine, forsterite, fayalite, enstatite, augite, magnetite, zircon, and basalt glass from Juan de Fuca Ridge were determined with the precision of less than 0.1‰. The data plot well on the terrestrial fractionation line defined as δ17O=0.52×δ18O. The analytical system can be used for analysis of meteoritic materials. The results for international reference materials show generally good agreement with literature values. There exists, however, a small interlaboratory difference in δ18O values of reference materials that reflects how standardization was made at each laboratory. A common standardization, such as comparison of reference materials with O2 directly converted from VSMOW, is required to obtain better agreement within the international community.View full abstractDownload PDF (294K) -
Gen SHIMODA2004 Volume 52 Issue 4 Pages 213-218
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSA separation scheme for lead and uranium is described. Before the separation of lead, uranium was collected using columns with a conventional method, namely, the separation and collection of uranium were conducted using 6 M and 0.5 M hydrochloric acid, respectively. This process separated lead from iron, thallium, and probably bismuth, which would suppress lead ionization in a thermal ionization mass spectrometer (TIMS). For lead separation, columns with a low ratio of height over inner diameter (H 10 mm, i.d. 4 mm) were employed to strip lead quickly from the resin (AG1-X2 and AG1-X8). Furthermore, 7 M nitric acid was adopted as the eluent instead of the commonly used 6 M hydrochloric acid to achieve a quantitative recovery of lead. These improvements enable us to collect lead with only 0.35 mL of 7 M nitric acid for both types of resin. Recoveries using this method obtained by the measurement of GSJ standard rock samples JA-2 and JA-3 were 96.4% and 99.7%, respectively. Total procedure blanks in two separate runs were 13 pg and 15 pg, respectively. It is therefore suggested that this method is suitable for separation and purification of lead for quantitative and isotopic analyses of geological materials.View full abstractDownload PDF (220K) -
Noriko EBISAWA, Hirochika SUMINO, Ryuji OKAZAKI, Yutaka TAKIGAMI, Naot ...2004 Volume 52 Issue 4 Pages 219-229
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSImprovements in ion collectors of the VG3600 mass spectrometer used for 40Ar-39Ar dating in the Radioisotope Center, University of Tokyo, have been performed. We also constructed a new compact vacuum line for extraction and purification of noble gases, and connected it to the mass spectrometer. The new noble gas mass spectrometry system enables us to measure all noble gases (He, Ne, Ar, Kr, and Xe) at low detection limits corresponding to 2×10-15 cm3 STP or 5×103 atoms of Kr and Xe. A newly designed W-coil furnace effectively heats small samples (1-100 mg) in a Mo-crucible with condition of low blank levels (10-10 and 10-15 cm3 STP for Ar and Xe). Smaller sample sizes required for 40Ar-39Ar dating have reduced activity levels. The system was preliminarily applied to I-Xe dating of neutron irradiated meteorites, Bjurböle, Allende and Yamato-74191, and discovered a late formation age of Yamato-74191 (26 Ma after Bjurböle) compared with the Allende meteorite.View full abstractDownload PDF (407K)
NOTE
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Takahito OSAWA2004 Volume 52 Issue 4 Pages 230-232
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSTo determine the Ne isotopic compositions for small samples with extremely small contents of Ne, mass interferences due to double charge 40Ar and carbon dioxide have to be corrected. Since mass interference due to 40Ar++ significantly affects 20Ne/22Ne ratios, the accurate estimation for the contribution of 40Ar++ is required in Ne analysis. Accurate 40Ar++/40Ar+ ratio (α) is determined from two experiments. First, the peak heights of mass 20 and 40 are measured alternately in a static condition. Second, the same experiment is performed while a trap made of sintered stainless steel is cooled at liquid nitrogen temperature. Since peak heights are proportional to time, four increase rates of peak heights are obtained and α can be calculated from the rates.View full abstractDownload PDF (126K)
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