Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry

Uranium and thorium isotopic and concentration measurements by magnetic sector inductively... We have developed techniques by sector-field inductively coupled plasma mass spectrometry (ICP-MS) for measuring the isotopic composition and concentration of uranium and thorium, focusing on the rare isotopes, 230 Th and 234 U. These isotopes have been widely used as tracers in earth sciences, e.g., chronology, paleoclimatology, archeology, hydrology, geochemistry, and oceanography. Measurements made on reference materials demonstrate that the analytical precision approximates counting statistics and that the accuracy of the measurement is within error of accepted values. Routine measurement times are 20 min for U and 10 min for Th. The sensitivities (ions counted/atoms introduced) are 2–3‰ for U and 1.5–2‰ for Th. Samples of 10–40 ng of 238 U (0.5–2.0 pg of 234 U) give measurement precisions of 1–2‰ (2 σ ) for δ 234 U and U concentration ((U)). Only 0.4 pg of 230 Th are needed to achieve ( 230 Th) and 230 Th/ 232 Th data with errors less than 5‰ even for cases where 230 Th/ 232 Th is 10 −5 or less. Our ICP-MS data, including uranium standards, thorium standards, 238 U– 234 U– 230 Th– 232 Th dating of speleothems and 230 Th– 232 Th in oceanic particulates, replicates measurements made by thermal ionization mass spectrometry (TIMS). Compared to TIMS, the ICP-MS method allows smaller sample size and higher sample throughput due to higher sensitivity, fewer sample preparation steps and shorter measurement times. However, mass biases, intensity biases, spectral interferences and instrumental blanks are significant and must be addressed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Chemical Geology Elsevier

Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry

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Publisher
Elsevier
Copyright
Copyright © 2002 Elsevier Science B.V.
ISSN
0009-2541
eISSN
1872-6836
D.O.I.
10.1016/S0009-2541(01)00404-1
Publisher site
See Article on Publisher Site

Abstract

We have developed techniques by sector-field inductively coupled plasma mass spectrometry (ICP-MS) for measuring the isotopic composition and concentration of uranium and thorium, focusing on the rare isotopes, 230 Th and 234 U. These isotopes have been widely used as tracers in earth sciences, e.g., chronology, paleoclimatology, archeology, hydrology, geochemistry, and oceanography. Measurements made on reference materials demonstrate that the analytical precision approximates counting statistics and that the accuracy of the measurement is within error of accepted values. Routine measurement times are 20 min for U and 10 min for Th. The sensitivities (ions counted/atoms introduced) are 2–3‰ for U and 1.5–2‰ for Th. Samples of 10–40 ng of 238 U (0.5–2.0 pg of 234 U) give measurement precisions of 1–2‰ (2 σ ) for δ 234 U and U concentration ((U)). Only 0.4 pg of 230 Th are needed to achieve ( 230 Th) and 230 Th/ 232 Th data with errors less than 5‰ even for cases where 230 Th/ 232 Th is 10 −5 or less. Our ICP-MS data, including uranium standards, thorium standards, 238 U– 234 U– 230 Th– 232 Th dating of speleothems and 230 Th– 232 Th in oceanic particulates, replicates measurements made by thermal ionization mass spectrometry (TIMS). Compared to TIMS, the ICP-MS method allows smaller sample size and higher sample throughput due to higher sensitivity, fewer sample preparation steps and shorter measurement times. However, mass biases, intensity biases, spectral interferences and instrumental blanks are significant and must be addressed.

Journal

Chemical GeologyElsevier

Published: May 1, 2002

References

  • 238 U, 234 U and 232 Th in sea water
    Chen, J.H; Edwards, R.L; Wasserburg, G.J
  • The half-lives of uranium-234 and thorium-230
    Cheng, H; Edwards, R.L; Hoff, J; Gallup, C.D; Richards, D.A; Asmerom, Y
  • Distribution of 230 Th in the Labrador Sea in relation to ventilation
    Moran, S.B; Charette, M.A; Hoff, J.A; Edwards, R.L; Landing, W.M
  • Observations of 231 Pa/ 235 U disequilibrium in volcanic rocks
    Pickett, D.A; Murrell, M.T
  • Absolute age determination of archaeological sites by uranium series dating of travertines
    Schwarcz, H.P

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