Absolute Isotopic Abundance Ratios and Atomic Weight of Magnesium.

Absolute values have been obtained for the isotopic abundance ratios of magnesium, using surface emission mass spectrometry. Samples of known isotopic composition, prepared from nearly pure separated magnesium isotopes, were used to calibrate the mass spectrometers. The resulting absolute values are 25Mg/24Mg = 0.12663 ±0.00013 and 26Mg/24Mg = 0.13932 ± 0.00026, yielding an atomic weight (12C = 12) of 24.30497 ±0.00044. The indicated uncertainties are overall limits of error based on 95 percent confidence limits for the mean and allowances for effects of known sources of possible systematic error.