Isotopic Ratio of Lithium in Chondrite Measured by an Ion Probe Mass Spectrometer

Abstract

Isotopic abundance ratios of lithium, 7Li/6Li, for four stony meteorites and for a terrestrial granite sample, G-1, are measured by an ion probe mass spectrometer. The measured ratios for the meteorites are about 13 percent lower than the ratio for G-1. The results are inconsistent with those obtained by conventional mass spectrometers with surface ionization ion sources at other laboratories. The mass discrimination effects and the systematic errors, which may lower the measured ratios preferentially for the meteorites, are thoroughly investigated in connection with the characteristics of the ion probe mass spectrometer. The origin of the instrumental bias, however, is not found. Although further experimental work with both types of mass spectrometer should be required to reach the final conclusion, the difference is likely existent from the results.