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Laser spectroscopic measurement of helium isotope ratios
Author(s) -
Wang L.B.,
Mueller P.,
Holt R. J.,
Lu Z.T.,
O'Connor T. P.,
Sano Y.,
Sturchio N. C.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2003gl017242
Subject(s) - helium , spectroscopy , mass spectrometry , materials science , analytical chemistry (journal) , laser , isotope , isotopes of helium , metastability , detection limit , absorption spectroscopy , absorption (acoustics) , helium 3 , saturation (graph theory) , atomic physics , optics , chemistry , physics , nuclear physics , organic chemistry , quantum mechanics , chromatography , composite material , mathematics , combinatorics
A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of 3 He/ 4 He = 10 −7 − 10 −5 . The resonant absorption of 1083 nm laser light by the metastable 3 He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of 4 He 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 3 He 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.