Precise analysis of 234U/238U ratio using UO2+ ion with thermal ionization mass spectrometry for natural samples

Tetsuya Yokoyama, Akio Makishima, Eizo Nakamura

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39 Citations (Scopus)


We have developed a new, highly precise method for U isotopic analysis using a thermal ionization mass spectrometry (TIMS) by measuring UO+2 ions emitted from a very small amount (100- 10 ng) of U. A new ionization activator, a silicic acid-diluted phosphoric acid solution, was found to be effective not only for producing a strong and stable UO+2 ion beam, but also for keeping the mass fractionation during measurement small and constant. U isotope analysis was carried out by a "dynamic multi collection" method using three Faraday cup collectors and a secondary electron multiplier in ion counting mode with RPQ (RPQ-SEM). For precise isotope analysis, baselines of the Faraday cups and a conversion factor between Faraday cups and the RPQ-SEM were precisely determined simultaneously with U isotope collection. Analytical precision and reproducibility of 234U/238U ratio ranged from 0.10% to 0.38% (2σmean) and from 0.13% to 0.31% (2σ), respectively, for 100-10 ng of U extracted from a natural rhyolitic obsidian. The precision and reproducibility were improved compared with previous studies, and thus, our method is especially useful for samples with very low abundance of U.

Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalChemical Geology
Issue number1-4
Publication statusPublished - Nov 21 2001


  • Precise analysis
  • Thermal ionization mass spectrometry
  • U/U ratio

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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