|Isotope||Atomic mass (Da)||Isotopic abundance (amount fraction)|
|85Rb||84.911 789 74(3)||0.7217(2)|
|87Rb||86.909 180 53(5)||0.2783(2)|
In its 1961 report, the Commission recommended Ar(Rb) = 85.47 based on the average of Ar(Rb) = 85.473 for the chemical determinations and mass-spectrometric determination of Nier, who reported Ar(Rb) = 85.4678(2). In 1969, the Commission recommended the current value of Ar(Rb) = 85.4678(3) based on new isotope-abundance measurements.
87Rb is β– active with a half-life of 48.8(5) Ga, which leaves Ar(Rb) unaffected at the currently given precision of about 3 parts per million in up to 106 a. In contrast, accumulation of the 87Sr product of 87Rb decay causes anomalous atomic-weight values of strontium in many Rb-bearing materials.
© IUPAC 2003