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GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 11, 1592, doi:10.1029/2003GL017242, 2003

Laser spectroscopic measurement of helium isotope ratios

L.-B. Wang

Physics Division, Argonne National Laboratory, Argonne, Illinois, USA
Physics Department, Univ. of Illinois at Urbana-Champaign, Urbana, USA


P. Mueller

Physics Division, Argonne National Laboratory, Argonne, Illinois, USA


R. J. Holt

Physics Division, Argonne National Laboratory, Argonne, Illinois, USA


Z.-T. Lu

Physics Division, Argonne National Laboratory, Argonne, Illinois, USA


T. P. O'Connor

Physics Division, Argonne National Laboratory, Argonne, Illinois, USA


Y. Sano

Ocean Research Institute, The Univ. of Tokyo, Nakanoku, Japan


N. C. Sturchio

Dept. of Earth and Environmental Sciences, Univ. of Illinois at Chicago, Chicago, USA


Abstract

A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of 3He/4He = 10−7 − 10−5. The resonant absorption of 1083 nm laser light by the metastable 3He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of 4He was measured by a direct absorption technique. The results on three different samples extracted from the atmosphere and commercial helium gas were in good agreement with values obtained with mass spectrometry. The achieved 3σ detection limit of 3He in helium is 4 × 10−9. This demonstration required a 200 μL STP sample of He. The sensitivity can be further improved, and the required sample size reduced, by several orders of magnitude with the addition of cavity enhanced spectroscopy.

Received 3 March 2003; accepted 6 May 2003; published 13 June 2003.

Index Terms: 9820 General or Miscellaneous: Techniques applicable in three or more fields; 1040 Geochemistry: Isotopic composition/chemistry; 1094 Geochemistry: Instruments and techniques; 0394 Atmospheric Composition and Structure: Instruments and techniques; 1894 Hydrology: Instruments and techniques.

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Citation: Wang, L.-B., P. Mueller, R. J. Holt, Z.-T. Lu, T. P. O'Connor, Y. Sano, and N. C. Sturchio (2003), Laser spectroscopic measurement of helium isotope ratios, Geophys. Res. Lett., 30(11), 1592, doi:10.1029/2003GL017242.