Abstract
The isotopic ratios of lithium, 7Li/6Li, have been measured by a modified type surface ionization mass spectrometer whose ion source was newly designed. It needs no chemical preparation prior to the ionization, and makes an analysis of small portions of sample possible. We mainly analyzed the Murchison meteorite and compared with terrestrial laboratory standard samples, spodumene and lepidolite. Many kinds of isotope anomalies for Murchison have been reported, and these anomalies are considered to be originated from presolar events. Spallation reactions are thought to be one of the processes that produced lithium isotopes, and to synthesize 7Li and 6Li isotopes as almost the same quantities. If lithium isotopes produced by such reactions in the presolar stage have been maintained in meteorites, there may be an isotopic anomaly of lithium whose ratio, 7Li/6Li, is extremely lower than that for terrestrial standards. The mean isotopic ratio, 7Li/6Li, for one laboratory standard, spodumene, is 10.519±0.0004, and that for another one, lepidolite, is 11.329±0.0009. The discrepancy between these lithium isotopic ratios is estimated to be due to the different fractionation processes of these minerals. The isotopic ratios for Murchison are within a range from 10.056 to 11.356. This range of the scattering for Murchison is within those for previous works. The lithium isotopic ratios for Murchison analyzed so far gave no significant difference from those for terrestrial standards.
