Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 63 Eu 151 150.9198578(18) 0.4781(6) 151.964(1) g 153 152.9212380(18) 0.5219(6) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page