3:45 PM - 4:00 PM
[MTT44-03] A current status of high precision in situ isotopic analysis by SIMS in JAMSTEC and perspectives for future researches
Keywords:high precision in situ isotopic analysis, ion microprobe, SIMS, oxygen isotope, lead isotope
While SIMS is a destructive technique, required amount of sample with SIMS analyses is very small (e.g., for oxygen two-isotope analysis, less than 1ng with a pit of ~10 micrometer in size and ~1 micrometer in depth) [e.g. 1,2]. SIMS analysis with a smaller beam and improvement of efficiency of analysis are highly required for multilateral analyses of the same sample.
A large geometry and ultra-high sensitivity magnetic sector SIMS with multiple detectors (CAMECA IMS 1280-HR) was installed in the Kochi Institute for Core Sample Research, JAMSTEC in early 2014. The Kochi's latest generation IMS 1280-HR has a capability to perform in-situ stable isotope analyses with sub-permil (down to +/-0.2 permil, 2SD) precision and accuracy for samples of a few to tens micrometer in size [1,3].
Here, we will present preliminary results of oxygen two-isotope (18O/16O) measurements in selected minerals using two Faraday cup detectors in multi-detection, and the Pb three-isotope (206Pb/207Pb/208Pb) measurements in several standard materials using an axial electron multiplier detector with mono-collection. The achieved spot-to-spot reproducibility for 18O/16O is ~+/-0.3 permil (2 SD) with a ~10 micrometer spot for silicates and carbonates. The achieved precision and spatial resolution are promising to explore seasonal variations of precipitation recorded in speleothems [e.g., 4]. The spot-to-spot reproducibility for Pb three-isotopes is ~+/-7 permil with a ~20 micrometer spot for USGS BCR-2G standard glass ([Pb]=11ppm). Developed Pb isotopic measurements can be applied to researches for glass inclusions entrapped in minerals, which elucidate heterogeneity of the Earth's mantle [e.g., 5]. In the future work, we will use multiple electron multipliers to detect three Pb isotope signals simultaneously. This may provide better precision with a smaller spatial scale (~10 micrometer).
In addition to the development of high precision and high spatial resolution analysis with SIMS, we are planning to build a coordinated analytical system which provides information of microstructure and elemental/isotopic distributions for smaller-scale samples, such as a piece of asteroid which will be returned by the JAXA Hayabusa-2 mission in 2020 and samples of the ultra-deep drilling by Chikyu.
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