Measurement on He and Ar Isotopic Compositions in Solid Samples by Mass Spectrometry

Sun Mingliang; Ye Xianren

An analytical technique for the simultaneous determination of He and Ar contents and isotopic tom-positions in rocks by static mass spectrometer has heen developed. The gases in rocks are extracted bymelting at 1 600℃.The purification of noble gases、an be made out by。titanium sponge Better at600℃，two Zr-Al Betters, and a Ti subliming Better. Heavier noble gases, such as argon, krypton andxenon are absorbed in a charcoal trap held at liquid nitrogen temperature. The purified helium and neonfractions are admitted to the mass spectrometer for helium measurement. After that, pumping out the Heand Ne, the charcoal trap is heated, and then the released(Ar₊ Kr₊Xe)fractionis admitted to the massspectrometer for argon measurement. The air with constant isotopic compositions of noble gases is con-sidered as a standard sample. The average sensitivities of⁴He，²⁰Ne and ³⁶ Ar are(9. 00 +0.35）×10^-10，(1. 4 01+0. 03 2）×10^-9 and(1. 76+0. 21）×10^-10 cm³ STP,respectively. The blank levels of the sys-tem fo r⁴He and ³⁶Ar are 1. 3860 ×10⁹ and 4. 08×10^-11cm³STP, respectively. Measured He and Ar con-tents and isotopic compositionsinedogites are given in this paper. Itis the first report on He and Arisotopic compositions in rocks in China.

Measurement on He and Ar Isotopic Compositions in Solid Samples by Mass Spectrometry

Lanzhou Institute of Geology Chinese Academy of Sciences Lanzhou 730000

Received Date: 1996-01-12

Publish Date: 1997-03-10

Key words:

Abstract: An analytical technique for the simultaneous determination of He and Ar contents and isotopic tom-positions in rocks by static mass spectrometer has heen developed. The gases in rocks are extracted bymelting at 1 600℃.The purification of noble gases、an be made out by。titanium sponge Better at600℃，two Zr-Al Betters, and a Ti subliming Better. Heavier noble gases, such as argon, krypton andxenon are absorbed in a charcoal trap held at liquid nitrogen temperature. The purified helium and neonfractions are admitted to the mass spectrometer for helium measurement. After that, pumping out the Heand Ne, the charcoal trap is heated, and then the released(Ar₊ Kr₊Xe)fractionis admitted to the massspectrometer for argon measurement. The air with constant isotopic compositions of noble gases is con-sidered as a standard sample. The average sensitivities of⁴He，²⁰Ne and ³⁶ Ar are(9. 00 +0.35）×10^-10，(1. 4 01+0. 03 2）×10^-9 and(1. 76+0. 21）×10^-10 cm³ STP,respectively. The blank levels of the sys-tem fo r⁴He and ³⁶Ar are 1. 3860 ×10⁹ and 4. 08×10^-11cm³STP, respectively. Measured He and Ar con-tents and isotopic compositionsinedogites are given in this paper. Itis the first report on He and Arisotopic compositions in rocks in China.

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Measurement on He and Ar Isotopic Compositions in Solid Samples by Mass Spectrometry

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