ABSOLUTE ISOTOPIC ABUNDANCE RATIO AND ATOMIC WEIGHT OF A REFERENCE SAMPLE OF RHENIUM.

Abstract

An absolute value has been obtained for the isotropic abundance ratio of a reference sample of rhenium, using surface emission mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated rhenium isotopes, were used to calibrate the mass spectrometers. The resulting absolute **1**8**5Re/**1**8**7Re ratio is 0. 59738 plus or minus 0. 00039, which yields atom percents of **1**8**5Re equals 37. 398 plus or minus 0. 016 and **1**8**7Re equals 62. 602 plus or minus 0. 016. The atomic weight calculated from this isotopic composition is 186. 20679 plus or minus 0. 00031.