Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 58 Ce 136 135.90712921(41) 0.00185(2) 140.116(1) g 138 137.905991(11) 0.00251(2) 140 139.9054431(23) 0.88450(51) 142 141.9092504(29) 0.11114(51) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page