Accurate Measurement of Argon Isotope Composition of Air by Argus Multi-collector Noble Gas Mass Spectrometer

Abstract

Accurate measurement of Argon isotopes is the premise of Ar-Ar dating with high precision. Two main kinds of instruments for Ar isotope measurement are Single-collector and Multi-collector Mass Spectrometers, among which the Multi-collector Noble Gas Mass Spectrometer can produce data with better accuracy and reproducibility. Some main factors affecting the accuracy and reproducibility of the results during the measurement of the Ar isotopes by the Argus Multi-collector Noble Gas Mass Spectrometer are discussed in this paper. Results show that the background of the whole system in static mode is very low and has little effect on the measurement of Ar isotope composition. The efficiency of the multiplier of the instrument is better than 99.67%, which can improve the measurement precision of low Ar samples. When the signal of 40Ar is less than 0.5 V, the standard error is only 0.11% for the 40Ar/36Ar ratios measured by the CDD, while the standard error is 0.53% when the ratios are measured using a Faraday cup. The mass discrimination effect of the instrument could be calibrated with the logarithmic law through the repeated measurement of argon isotopes in air and the relative standard error of the mass discrimination is only 0.0434%. Using the example of the determination of argon isotopes in air, it can be demonstrated that the efficiency of the measurement by Argus Multi-collector Mass Spectrometer is higher than that of the Single-collector Mass Spectrometer with higher precision and accuracy. Therefore, the Multi-collector Mass Spectrometer is highly suitable for the high-precision Ar-Ar dating of young and potasium-poor samples.

Keywords

• noble gas mass spectrometer
• multi-collecting
• jump collecting
• ar-ar dating
• efficiency of cdd
• mass discrimination effect