Performance of the NGX High-Resolution Multiple Collector Noble Gas Mass Spectrometer

This paper describes the design, setup, and performance of a new analytical system installed at Lancaster University, UK, to determine noble gas isotopes in gas samples using an NGX high-resolution multiple collector noble gas mass spectrometer. The fixed position Faraday cups are configured to simultaneously measure all nine Xe isotopes whilst permitting all other noble gases, such as He, to be analyzed in peak jumping mode. The stability, sensitivity, and reproducibility of the measurements using this new noble gas analytical system were examined by repeating runs of atmospheric air. Reproducibility of the measurements obtained from 90 and 73 air standard runs are 4.2% and 0.4% for He-3/He-4 and Ne-21/Ne-20, respectively. There is no significant difference in the Ar-40/Ar-36 ratio measurements with various Ar-40 abundances, suggesting good sensitivity and pressure linearity of the NGX instrument. The standard errors for Xe-124/Xe-130, Xe-126/Xe-130, Xe-128/Xe-130, Xe-129/Xe-130, Xe-131/Xe-130, Xe-132/Xe-130, Xe-134/Xe-130 and Xe-136/Xe-130 in 46 air measurements are 0.782%, 0.804%, 0.053%, 0.029%, 0.029%, 0.029%, 0.030%, and 0.031%, respectively. In contrast, the corresponding reference values from Basford et al. (1973) are 0.342%, 0.505%, 0.148%, 0.139%, 0.153%, 0.076%, 0.156%, and 0.138%, respectively. This suggests that multicollection measurements of Xe isotopes on Faraday cups using the NGX have higher precision than the previous results except for Xe-124 and Xe-126, where low abundances affect the measurement precision. Compared to traditional peak jumping single-collector mass spectrometers, the NGX has significantly decreased analytical time in Xe analysis by allowing simultaneous measurements of all isotopes. As a consequence, high analytical precision can be achieved.