Absolute Isotopic Abundance Ratio And Atomic Weight Of a Reference Sample of Gallium.

An absolute value has been obtained for the isotopic abundance ratio of a reference sample of gallium (Standard Reference Material 994), using thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated gallium isotopes, were used to calibrate the mass spectrometers. The resulting absolute 69Ga/71Ga ratio is 1.50676±0.00039, which yields atom percents of 69Ga=60.1079±0.0062 and 71Ga=39.8921±0.0062. The atomic weight calculated from this isotopic composition is 69.72307±0.00013. The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error.