Lead and Strontium Stable Isotope Measurements by Using a High Lateral Resolution Secondary Ion Mass Spectrometer(NanoSIMS)

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  • SANO Yuji
    Center for Advanced Marine Research, Ocean Research Institute, The University of Tokyo

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Other Title
  • 二次元高分解能二次イオン質量分析計（ＮａｎｏＳＩＭＳ）を用いた鉛とストロンチウム同位体測定
  • 安定同位体利用技術 二次元高分解能二次イオン質量分析計(NanoSIMS)を用いた鉛とストロンチウム同位体測定
  • アンテイ ドウイタイ リヨウ ギジュツ 2ジゲン コウブンカイノウ 2ジ イオン シツリョウ ブンセキケイ NanoSIMS オ モチイタ ナマリ ト ストロンチウム ドウイタイ ソクテイ
Published
2008
DOI
  • 10.3769/radioisotopes.57.579
Publisher
Japan Radioisotope Association

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Description

The method of Pb and Sr isotope measurements at about 5μm resolution was developed by using a high lateral resolution secondary ion mass spectrometer(NanoSIMS NS50). Since the both elements have radiogenic nuclides such as 206Pb, 207Pb, and 87Sr, natural variations of isotopic ratios are large. It is possible to detect a meaningful variation in a terrestrial sample, even though the experimental error is relatively large. In the case of monazite U-Pb dating, a 4 nA O− primary beam was used to sputter the sample and secondary positive ions were extracted for mass analysis using a Mattauch-Herzog geometry. The multi-collector system was modified to detect 140Ce+, 204Pb+, 206Pb+, 238U16O+, and 238U16O2+ ions simultaneously. Based on the monazite standard from North-Central Madagascar, we have determined the 206Pb/238U ratios of samples. 207Pb/206Pb ratios were measured by a magnet scanning with a single collector mode. 44 monazite grains extracted from a sedimentary rock in Taiwan were analyzed. Observed ages were consistent with the U-Th-Pb chemical ages by EPMA. Then NanoSIMS has been used to measure 87Sr/86Sr ratios in natural calcium carbonate samples. Multi-collector system was adjusted to detect 43Ca+, 80Ca2+, 86Sr+, and 87Sr+ ions at the same time. Magnetic field was scanning for the EM#4 counter to detect 85Rb+, 86Sr+ and 87Sr+, while the EM#4b can measure 86Sr+, 87Sr+, and 88Sr+, respectively. Repeated analyses of a coral skeleton standard(JCp-1) show that 87Sr/86Sr ratio agrees well with the seawater signature, after the series of corrections such as Ca dimer, 87Rb, and a mass bias estimated by 88Sr/86Sr ratio. The method is applied to an otolith from ayu (Plecoglossus altivelis altivelis) collected from the Yodo river, Japan. The spatial variation of 87Sr/86Sr ratios was consistent with amphidromous migration of the fish, namely, born in the lake and grown in the coastal sea and finally collected in a river.

Journal

  • RADIOISOTOPES

    RADIOISOTOPES 57 (9), 579-591, 2008

    Japan Radioisotope Association

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