Method of determining noble gases in trace meteorite specimens using a laser microprobe

Noble gas analysis of meterorite based on traditional high temperature furnace method requires large sample amount due to high blank contribution. Hence, in order to extract rare gases in trace meteorite specimens, laser microprobe is an efficient tool where only a few milligrams of meteorite specimens in the micrometer scale are sufficient. Consequently, some problems such as large specimens' size and uneven distribution of rare gases as in the traditional furnace method can be resolved. However, due to small specimens' size and small gas amount in microanalysis, an extraction system of rare gas with an extremely low background is very much necessary. At present, the Chinese noble gas laboratories have not yet demonstrated sound analytical technology to determine rare gases in trace meteorite specimens using a laser microprobe. In this study, we have obtained ultra-high vacuum system with extremely low background laser microprobe with a sample tray (diamond window), a purification system, and a Noblesse noble gas mass spectrometer from Nu instruments. The measured gas amount of each noble gas isotope was corrected for the corresponding background, element disturbance, air intake proportion, mass discrimination, and sensitivity, to obtain absolute isotopic abundance. These gas amounts were corrected for trapped gases to obtain the cosmogenic gas amounts. Thus the determined average values of cosmic-ray exposure ages of the standard meteorite Millbillillie are consistent with the ages obtained by whole rock melting using high temperature furnace method. The establishment of the microanalysis will enable extracting noble gases from precious or rare meteorite samples where available sample amount will be limited and provide a promising tool for use in the quickly developing comparative planetology and deep-space exploration.