JMSSJ On-line

JMSSJ On-line, Vol. 44 (1996) No. 1, pp. 39-61

Ar Isotope Analysis for K-Ar Dating Using Two Modified-VG5400 Mass Spectrometers-I: Isotope Dilution Method		>> Full Text PDF >> References
*Keisuke NAGAO,^a) Atsumi OGATA,^a) Yayoi N. MIURA,^{a), b)} and Kenji YAMAGUCHI^a)** ^a) Institute for Study of the Earth’s Interior, Okayama University (Misasa, Tottori 682-01, Japan)* ^b) Present address: Earthquake Research Institute, University of Tokyo (Bunkyo-ku, Tokyo 113, Japan)

Two noble gas mass spectrometry systems (MS-I and MS-II) have been installed in 1989, one of which was designed in our laboratory for Ar isotope analysis to measure K-Ar age by isotope dilution method using ³⁸Ar-spike. The whole system was modified and improved to obtain high quality Ar data. The improved system composed of an Ar extraction and purification line and a Modified-VG5400 mass spectrometer enables us to determine precise Ar isotope composition easily and speedily irrespective to operator’s skillfulness. Formulas calculating radiogenic ⁴⁰Ar abundance, which takes account of correction for Ar isotopes of both spike and blank, are presented. For samples with young K-Ar age, formulas to estimate the radiogenic ⁴⁰Ar abundance based on ⁴⁰Ar/³⁶Ar ratio are also proposed. Replicate analyses on many K-Ar standard samples show that the system can be applicable to samples with ages ranging 0.01 to 1500 Ma without any systematic analytical errors.

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