Charge neutralization and oxygen isotopic analysis of insulators with the ion microprobe

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The Cameca IMS 3f ion microprobe at Arizona State University has been modified to allow the analysis of 18O/16O ratios on 10- to 20-micrometer spots in insulating minerals in thin section. A primary beam of K+ or Cs+ is used, and charge is neutralized by an electron flood gun operating at -7.5 kilovolts. Negative secondary ions are accelerated to -4.5 kiloelectronvolts into the mass spectrometer, where 18O- is detected on the electron multiplier by pulse counting, and 16O- is detected on the electron multiplier or directly measured by an electrometer. In either configuration, internal precisions of 1.2 to 1.7 per mil (1 standard error of the mean) in 18O/16O ratios can be achieved. Preliminary analyses, showing quartz to be 10 to 15 per mil lighter than hydrothermally altered plagioclase, suggest that matrix effects are important. -Authors

Original languageEnglish (US)
Pages (from-to)137-143
Number of pages7
JournalUS Geological Survey Bulletin
StatePublished - Jan 1 1989


ASJC Scopus subject areas

  • Geology

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