Mass Spectrometer Systems for Isotope Geochemistry(1). High Sensitivity Mass Spectrometry of Rare Gases by a System with a Getter Ion Pump

Abstract

A 20 cm, 90° direction focussing mass spectrometer was constructed for laboratory use in isotope geochemistry. The mass spectrometer is of conventional design but has a greater flexibility for future modifications. For obtaining high vacuum of better quality and for its easy maintenance, a 40 l/s getter ion pump was employed in the main pumping system together with a chemisorption pump. Without using an oil diffusion pump, vacuum of better than 10^-8mm Hg was easily obtained, although argon background was always high as expected. The absolute amount of the residual argon in the analyzer tube was found to range from 1 to 10 × 10^-7ml STP.
The mass spectrometer was used for the high sensitivity mass spectrometry of rare gases using a six-stage secondary electron multiplier. It was demonstrated that the system has a enough sensitivity to measure 10^-9ml STP xenon. The residual gases in the analyzer up to xenon mass regions were also analyzed.