Negative thermal ion mass spectrometry of osmium, rhenium, and iridium

Journal Article · Tue Jan 01 04:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(91)90427-7· OSTI ID:5835772

Creaser, R A; Papanastassiou, D A; Wasserburg, G J ^[1]

---

1. California Institute of Technology, Pasadena (USA)

The authors report on a technique for obtaining intense ion beams of negatively charged oxides of Os, Re, and Ir by thermal ionization, in a conventional surface ionization mass spectrometer. It was found that the principal ion species of Os, Re, and Ir produced are OsO{sub 3}{sup {minus}}, ReO{sub 4}{sup {minus}}, and IrO{sub 2}{sup {minus}}. The sharp distinction in the masses of the dominant molecular species produced by this technique permits the measurement of isotopic compositions of each element from mixtures of platinum-group elements without significant isobaric interferences. For {sup 187}Re-{sup 187}Os isotope studies, this technique offers the advantage of isotopic analyses without prior chemical separation of Re from Os, as no isobaric interference between the oxides of {sup 187}Os and {sup 187}Re exists under these conditions. For 4 ng Os, stable ion currents of 3 {times} 10{sup {minus}12} A can be maintained for over one hour, which allows determination of isotopic ratios with a Faraday collector to a precision of better than {plus minus}2{per thousand} (2 {sigma}{sub m}). For 70 pg Os, isotopic ratios can be measured with a precision of better than {plus minus}5{per thousand} using a secondary electron multiplier. The detection limit for Os is estimated to be below 10{sup {minus}14} g. Osmium isotopic ratios have also been determined by direct loading of natural iridosmine with a precision of {plus minus}0.5{per thousand} or better. They have obtained ionization efficiencies of 2-6% for Os and >20% for Re; these are superior to those reported for other techniques available to data, and demonstrate that negative thermal ion mass spectrometry will have widespread application to {sup 187}Re-{sup 187}Os chronometry and to studies of the geochemistry and environmental chemistry of the platinum-group elements.

• OSTI ID: 5835772
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Journal Issue: 1 Vol. 55:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
BEAMS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
COSMOCHEMISTRY
EVEN-ODD NUCLEI
GEOCHEMISTRY
HEAVY NUCLEI
ION BEAMS
IRIDIUM COMPOUNDS
IRIDIUM OXIDES
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
MASS SPECTROSCOPY
NUCLEI
ODD-EVEN NUCLEI
OSMIUM 187
OSMIUM COMPOUNDS
OSMIUM ISOTOPES
OSMIUM OXIDES
OXIDES
OXYGEN COMPOUNDS
RADIOISOTOPES
REFRACTORY METAL COMPOUNDS
RHENIUM 187
RHENIUM COMPOUNDS
RHENIUM ISOTOPES
RHENIUM OXIDES
SPECTROSCOPY
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
YEARS LIVING RADIOISOTOPES