A simple high-sensitivity technique for purity analysis of xenon gas

We report on the development and performance of a high-sensitivity purity-analysis technique for gaseous xenon. The gas is sampled at macroscopic pressure from the system of interest using a UHV leak valve. The xenon present in the sample is removed with a liquid-nitrogen cold trap, and the remaining impurities are observed with a standard vacuum mass-spectroscopy device. Using calibrated samples of xenon gas spiked with known levels of impurities, we find that the minimum detectable levels of N2, O2, and methane are 1×10−9, 160×10−12, and 60 ×10−12 g/g, respectively. This represents an improvement of about a factor of 10 000 compared to measurements performed without a cold trap.