Absolute isotopic abundance ratio and atomic weight of terrestrial rubidium

Abstract

An absolute value hsas been obtained for the isotopic abundance ratio of terrestrial rubidium, using solid-sample thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated rubidium isotopes, were used to calibrate the mass spectrometers. The resulting absolute 85Rb/87Rb ratio is 2.59265 ± 0.00170 which yields atom percents of: 85Rb = 72.1654 ± 0.0132 and 87Rb = 27.8346 ± 0.0132. The atomic weight calculated from this isotopic composition is 85.46776 ± 0.00026. The indicated uncertainties are overall limits of error based on 95 percent confidence limits for the mean and allowances for the effects of known sources of possible systematic error.